cubic feet of air, and a total of 1180 cal.
5. Air at 0° C. and heated to 25° C. requires 63 cubic meters or 2230
cubic feet, and a total of 1075 cal.
6. Air at -15° C. (5° F.) requires 4·5 cal. per cubic meter to raise it
to 0° C., and acquires a capacity for drying of about 2 grm. per meter.
We will apply these figures to a drying room arranged with a screw-fan
with a central division, or two floors, so that the air can be either
circulated or replaced with fresh air from the outside at will (see Fig.
94, p. 435). Such a room with 100 feet of length clear of space required
for fans, air passages, and heating pipes, and 20 feet × 8 feet in
section, should hang about 800 medium butts, weighing say 12¹⁄₂ kilo (27
lb.) each, and when wet from the yard, containing the same weight of
water. A 48-inch Blackman fan, under these conditions would probably
move say 20,000 cubic feet (565 cubic meters) of air per minute, at the
cost of 2 or 2¹⁄₂ horse-power. This, in a room of the section named,
would give an average velocity of 125 feet per minute or rather under
1¹⁄₂ miles an hour; not at all too much to keep the air freely
circulating among closely hung leather. If we assume that these butts
are to be dried in a week (practically 10,000 minutes) under the
conditions of No. 2, the 10,000 kilos of water they contain will require
1,700,000 cubic meters of air, or about 170 cubic meters per minute, or
about ³⁄₁₀ of the air must be fresh every time it passes through the
fan. 1 kilo of water requiring 1110 cal. must be evaporated per minute.
Under the conditions of No. 4, only 97 cubic meters of air per minute
would be required, or about ⁵⁄₆ might be circulated without change, but
the total heat required would be about the same, 1180 cal. Under the
conditions of Nos. 4 and 6 some 1620 cal. per minute would be employed.
It is hardly necessary to provide for the full amount of heat required
by No. 6, since in this country such conditions occur but seldom, and
never for more than a few days at a time, and during such a period, much
less heat would suffice to carry on the drying at a slower rate, and
keep out the frost.
Beside the heat required for actual drying, it is necessary to provide
for that lost by the building during cold weather, and this is much more
difficult to calculate. If, by arranging the outlet for moist air on the
pressure side of the fan, the internal pressure of the building be kept
a little lower than the outside, there can be no loss by escape of hot
air, any leakage being inwards, and supplying a part of the change of
air which, we have seen, is necessary. In a brick building with glass
windows, the loss of heat is far less than in the old-fashioned wooden
louvre-boarded structure, and where fan-drying is in constant use, the
brick structure is much to be preferred. Frequent windows, with
casements horizontally pivoted at the centre, will supply enough air for
favourable conditions of air-drying, and when the weather is bad, resort
is had to the fan. Most modern drying rooms in the Leeds district are
built upon this plan. Where louvre-boarded structures must be used for
fan-drying, the sides should be made as tight as possible in winter by
sheets of canvas or sail-cloth nailed on, for which purpose old sails
can be bought in seaport towns at reasonable rates, a few louvre-boards
only being kept open for the admission of air in suitable positions.
Box, in his ‘Practical Treatise on Heat’[183] puts the loss through
walls in brick buildings for a difference of 30° F. (16·6° C.) between
inside and outside temperatures, at the approximate amounts shown in the
following table.
[183] E. & F. N. Spon, Ltd., London.
LOSS OF HEAT THROUGH WALLS.
----------+------------+----------------------------------------------
Thickness| K.-calories| --
of Wall |per Sq. Foot|
in Inches.| per Hour. |
----------+------------+----------------------------------------------
4·5 | 1·76 |Stone walls must be about one-half thicker, to
9 | 1·44 |afford equal warmth with brick ones.
14 | 1·20 |The loss from glass windows amounts to 3 or 4
18 | 1·06 |k.-calories per square foot per hour.
----------+------------+----------------------------------------------
If the building is of several stories, the loss to the roof in the
intermediate ones need hardly be taken into account, but if the ceiling
is not tight, and open to the roof, the loss may be great, but difficult
to estimate. If we consider the drying room already described, the total
area of the walls and ceiling is about 4000 feet, and to maintain its
temperature 30° F. above the atmosphere at 1·2 cal. per sq. foot would
require 4800 cal. per hour or 80 cal. per minute, a very small amount
compared to that consumed in drying.
The following table calculated from data given by Box will give some
idea of the amount of steam or hot-water piping required for heating.
The sizes given are for the internal diameter of the pipe, allowance
being made for the increased heating surface of pipes of ordinary
thickness. Small pipes are considerably more effective in proportion to
their surface than large ones, and for high-pressure heating 1¹⁄₂ or
2-inch wrought-iron pipes are to be recommended as in many ways
preferable to cast iron. The gilled or ribbed pipes now often used are
also advantageous as giving a greatly increased heating surface.
HEAT GIVEN BY STEAM-PIPES.
------+---------+-----------+-----------------+------
| Steam |Temperature| K.-calories per |
|Pressure,| of |hour per foot run|
| lb. per | Pipe. | of Pipe. |
| sq. in. | | |
------+---------+-----------+-----+-----+-----+------
| | °F. |2 in.|3 in.|4 in.|
| 52 | 300 | 102 | 137 | 169 |
| 35 | 280 | 92 | 121 | 148 |
| 21 | 260 | 81 | 106 | 130 |
| 10 | 240 | 68 | 92 | 113 |
| 2·5 | 220 | 59 | 81 | 97 |
| | 210 | 54 | 72 | 89 |
| | 200 | 49 | 66 | 81 |
| | 190 | 45 | 60 | 74 |
| | 180 | 40 | 54 | 67 |
| | 170 | 36 | 49 | 60 |
------+---------+-----------+-----+-----+-----+------
The temperature of the air to be heated is understood to be 60° F.; at
lower temperatures the quantity of heat given off by the pipes would be
greater, and at higher temperatures less; the amount being approximately
proportional to the difference of temperature between the air and the
hot pipes. It is also important to note that the table refers to
steam-pipes in still air, and that if placed in a powerful draught, (as
immediately before or behind the fan), their heating effect may be at
least doubled. This has not been considered in the following
calculations.
Applying these figures to the estimate of 1110 calories per minute
required for drying in our building, and assuming 80 calories per minute
for the loss of heat through the walls, we have a total of about 71,400
calories per hour, and to obtain this would require 736 feet of 4-inch
pipe at 220° F. (heated by exhaust steam) or 700 feet of 2-inch pipe
heated to 300° F. by steam at 52 lb. pressure.
If we adopt the estimate of 1620 calories of No. 5 and 6, we shall
require 1050 and 1000 feet of the two pipes respectively, and this
covers approximately the worst conditions. We must, however, remember
that these estimates are made for continuous drying during the
twenty-four hours, and that if the fan and steam are only applied during
a portion of this time, the supply both of air and steam must be
proportionately increased, or the time of drying correspondingly
lengthened.
It is very desirable, however, that the fan should be driven by a small
separate engine, the steam for which will only form a small proportion
of that required for heating, and of which the whole of the heat will be
recovered, since even that utilised in driving the fan will again be
converted into heat by the friction of the air, and will therefore cost
nothing. This arrangement will enable the drying to proceed so long as
the necessary steam is maintained, which in bad weather can easily be
done by the night watchman. It may also be pointed out that, during a
great part of the year, the goods can be dried to a “sammied” condition
without heat, or in the open air, or in the case of dressing leather, a
considerable part of the water can be removed by pressing or squeezing,
effecting a further economy.
[Illustration: FIG. 93.--Blackman Fan.]
It must be left to the reader to apply the same calculation to other
sorts of leather than sole, but it may be pointed out that the essential
point, as regards heating and ventilation, is the weight of water to be
evaporated in a given time, and that the actual size and shape of the
drying room is unimportant, so long as adequate heating and circulation
of the air between the leather is secured; and these remarks also apply
to the particular form of fan or other ventilation employed, and to the
means of heating. As the quantity of heat consumed is very considerable,
it is well to look out for sources of waste heat which can be employed,
or for means by which the heat of the fuel can be more directly and
completely utilised than it is in raising steam. Thus a large amount of
heat can sometimes be obtained by passing air through pipes or
“economisers” fitted in a chimney-flue;[184] or gilled stoves or
“calorifers” may be used in a separate chamber to directly heat the air
which is drawn in by the fan.
[184] These pipes should be provided with scrapers to remove soot as
in Green’s economiser, or their efficiency will be much diminished.
[Illustration: FIG. 94.--Section of Drying Rooms with Fan.]
Figs. 93 and 94, furnished by the James Keith and Blackman Co., Ltd.,
give a good idea of the construction of screw fans, and the general
principle of arrangement of fan drying rooms, the air in this case being
circulated in opposite directions on two floors, and the amount of
change being regulated by the shutters at A, etc. The grouping of pipes
at the ends of the two floors which it shows is in general a good
arrangement, but the length between them should not be too great, or the
drying will be unequal in different parts of the room. Sometimes this is
convenient; thus if most of the heat be supplied to the air coming fresh
from the inlet on the upper floor, the damper and colder air of the
lower room can be continuously used for drying wet goods from the yard,
and the upper reserved for drying off the finished leather. A
disadvantage of this plan is that open air drying can seldom be utilised
except in an elevated building; and even when it is adopted, means
should be provided for heating the lower room in cold weather. In place
of two floors, it is obvious that a single floor may be divided into two
compartments by a longitudinal partition. Whatever pipes are grouped at
the ends of the building, it is advisable to arrange sufficient to
prevent frost, against the walls, or in the old-fashioned way on the
floors beneath the leather, but not too close to it, and protected by a
wooden lattice on which the workmen can stand, which removes the risk of
accident from wet leather falling on the hot pipes. The latticed space
should be open at the end facing the air current, so as to receive a
portion of the draught, which will become heated and ascend, its place
being taken by damp and cold air from the leather, to be re-warmed.
Water-vapour in itself is lighter than air, but the contraction produced
by the cooling of evaporation more than compensates this, and the damp
air is therefore heavier than the dry. The arrangement of hot pipes near
the ceiling of a drying room, which has been borrowed from some American
tanneries, is wrong in principle, unless the air is forced in at the
upper part of the room, or the upper floor is latticed, and only acts in
other cases when the air is thoroughly mixed and circulated by
mechanical ventilators; while pipes near the floor will continue to
produce a certain amount of circulation of the air, even when the fan is
not running. In protecting pipes by lattices care should be taken not to
confine them too closely, or their heating effect will be seriously
diminished. In fan-drying, leather should be hung edgeways to the
current of air, so as to allow of its free and uniform passage between.
In the case of sole leather the butts or bends are conveniently
suspended by S-hooks of brass or iron wire, to hooks or nails fixed in
the joists. If gangways between the leather must be left in the
direction of the draught, they should be closed at intervals in the
length of the room by curtains or shutters, so as to deflect the
air-current into the leather.
Screw fans like the Blackman can be used either to suck or to blow the
air, though the former is preferable where it can be arranged, because
it produces a more uniform current in the room. On the blowing side the
air issues with considerable velocity in a sort of cone, but little
coming through the centre of the fan, while that near the edges spreads
rapidly from its centrifugal motion. This is rather advantageous where
the fan blows into an open room, but involves waste of power where it
discharges into narrow and square air-ways. The ends of the vanes of the
Blackman are turned in at the rim of the fan to prevent this tangential
discharge, but it is probable that where a fan is to _blow_ into a room,
it would be more advantageous to put it on the inner side of the wall,
and without curved ends to the vanes, so as to distribute the air as
widely as possible. A somewhat similar result would be attained with a
Blackman, by placing it in a position the reverse of that for which it
is intended, and running it also the reverse way; but its “efficiency”
might possibly be lessened.
Screw-fans are good for moving large volumes of air at comparatively low
velocities, and against little or no resistance, but they are quite
unsuitable for forcing air against high resistance, or through narrow
channels, and for this purpose centrifugal fans like the Capel (Fig. 95)
are much more suitable, and mechanically more efficient. In any case
there is much loss of power in forcing air through narrow airways, and
if a screw fan must be employed for the purpose, the channel should be
as large in section as the area of the fan, and all sharp angles in its
course should be avoided. There is great loss of power where a current
of air or water has to pass suddenly either from a wider to a narrower
channel, or the reverse, and in both cases the resistance is diminished
by making the enlargement or contraction gradual or “bell-mouthed.” Thus
a pipe conveying water at a given head into or out of a cistern will
discharge a much larger quantity, if the ends are bell-mouthed, than if
it terminates abruptly. For the same reasons, air suffers considerable
resistance if it has to pass suddenly into, or out of a larger space,
such as a drying room; and unnecessary partitions, and other abrupt
changes of dimension in the current should be avoided. Curves should
also take the place of angles as much as possible.
[Illustration: FIG. 95.--Capel Centrifugal Fan.]
Systems in which air is drawn or forced over systems of heating pipes by
a centrifugal fan, and then distributed through comparatively small
airways among the leather which is to be dried are in some cases
convenient and advantageous. Among these may be mentioned the Sturtevant
and the Seagrave-Bevington. There can be no valid patent on the general
principle of heating by distributing air in this way, but only on the
particular arrangement or appliances used in the special case.
Centrifugal fans should be considerably larger in diameter than in axial
length, those with long vanes of small radius being wasteful in power
from the insufficient supply of air to the centre. There is also no
reason why, in some cases, centrifugal fans should not be substituted
for screw-fans in drying on the system which I first described,
especially in cases where the air has to encounter considerable
resistance, as for instance in traversing a filter to remove dust. One
of the best filters for this purpose is a table of wire-gauze covered to
a depth of 3 or 4 inches with loose wool. Hair or cheaper fibrous
materials may be substituted for the wool, but are less efficient. The
air must of course be sucked downwards through the gauze. When the wool
becomes dirty, it may be washed, if possible in a wool- or hair-washing
machine, and again spread on the table in a damp condition, as it will
quickly be dried by the current of air. Flannel is also useful where the
wool-filter is impracticable, but requires frequent washing.
Apart from wind, natural ventilation is seldom to be relied on for
drying on any considerable scale. Heated air is, of course, lighter than
cold, and this is the cause of chimney-draught, but to get a good
circulation in this way, a high shaft, and high temperature is required.
Nevertheless, in one of its best forms, the method has been a good deal
used in America, in the so-called “turret-dryer,” a building of seven or
eight stories in height, constructed of wood with latticed floors, and
heated by steam-piping at the bottom, where the air is admitted. The
method is not likely to be much used in this country, as apart from the
questions of cost of building, fire-risk, and trouble of raising and
lowering the leather, a good draught will only be obtained when the
outer temperature is low in comparison to that inside, and in our milder
and moister climate the conditions are not nearly so favourable as in
the United States. As the air is rendered heavier by the cooling of
evaporation to a larger extent than it is lightened by the water vapour,
there is a tendency in drying by upward ventilation for the warm air to
form local upward currents, while the cold and damp air falls back; and
from this irregularity of flow, it is difficult to saturate the air
equally. This may be avoided by downward ventilation, in which the warm
air is admitted at the top of the drying room and the cold and damp air
allowed to escape at the bottom. This fact suggests that in using
systems of drying such as the Sturtevant, it would be better to place
the distributing pipes at the top rather than the bottom of the room,
but in this case care would have to be taken that there were no openings
left by which the air could escape at the top of the room without
descending through the leather. If this be avoided, the warm air will
float on the top of the colder and damper, and press it uniformly down
and out. I believe the merit of first having applied the principle of
downward ventilation to leather-drying is due to Edward Wilson of
Exeter. It is necessary that the hot air should be _forced_ in at the
top, or the cold air _sucked out_ from the bottom; and the mere placing
of hot pipes near the top of the room (p. 436) will not cause the
required circulation. Wilson placed his heating pipes in a partitioned
space at the side of the room, at the bottom of which cold air was
admitted from the outside, which escaped into the room at the top. As
the temperature of this side chamber was high and the air consequently
light, an upward current was produced in it, though probably somewhat
inefficiently, as the height of the column of heated air could only be
small. Assisted by a fan, and circulating a part of the air, the method
should give good results, especially over two (latticed) floors. As the
air could not be satisfactorily heated in its downward course, the
method would not be suited for more than about two floors, and the
drying in the lower room would be cool and gentle.
One or two points in the practical arrangement of steam-pipes may be
mentioned, as they are often overlooked even by professional engineers.
The steam must _always_ be admitted at the highest point in the system,
and there must be a steady descent, without hollow places where
condensed water can accumulate, to the steam-trap by which it is
removed. In horizontal pipes, about 1 inch descent in 100 is sufficient.
If water accumulates, there is not merely serious danger in case of
frost, but during use, by the sudden condensation of the steam, a vacuum
is frequently formed, into which the water is shot like the liquid in a
“water hammer,” producing violent and noisy concussions, and in some
cases even fracture of the pipes, or loosening of their joints. If
high-pressure steam is used, a very small supply-pipe will feed a
considerable system of heating pipes or radiators, but with exhaust
steam, great pains should be taken to have pipes of ample size, to avoid
back-pressure on the engines. In both cases it is often convenient to
arrange the pipes, not as a continuous line, in which drainage is
generally difficult, but in parallels like the bars of a gridiron. With
high-pressure steam, there need be no fear, if the pipes are kept clear
of air by allowing a little escape through small air-taps, of the steam
failing to find its way to all parts of the pipe, as a vacuum is
produced by condensation in proportion to the heat given off. With
exhaust-steam, no steam-trap is desirable, but any steam not condensed
should escape freely into the open air or a chimney (after separating
condensed water), and it is well to render the resistance in all the
pipes of a gridiron approximately equal, which may be done by admitting
steam at one corner, and allowing it to escape at the opposite
(diagonal) one. In the arrangement of steam-pipes in parallels, the
practicability of repair to one pipe or joint without interfering with
the others must always be considered. If screwed wrought-iron pipes are
used, each parallel must be provided with a bolted flange, or “running
socket,” to permit of unscrewing. The difficulty of accurately adjusting
the lengths of the several parallels must be considered, especially with
flanged metal pipes, and also their motion by expansion when hot, which
amounts to 1 or 2 parts per 1000 of length according to the temperatures
of steam and air. Expansion-joints with stuffing boxes are costly and
troublesome, and apt to leak, and may in many cases be avoided by
suitable arrangement of the pipes. Thus instead of having the pipes
rigidly fixed at both ends, one end of the system may be left free to
move, each pipe being separately returned to an exit pipe at the same
end but lower in level than the supply; or a single exit pipe may be
thus returned, its expansion and contraction being practically the same
as that of the heating pipes. In moderate lengths of wrought-iron pipe,
sufficient relief may often be obtained from the flexure of the pipe, if
in some part of its course it is carried at right angles to its general
direction, which is often necessary for other reasons. If pipes are laid
in long lengths, the loose end should be supported on rollers or short
pieces of pipe, so as to avoid moving the supports or straining the pipe
in expansion.
It is useless to attempt to regulate the temperature of low pressure
steam-pipes by turning down the steam, since, so long as the pipe is
supplied with sufficient steam to fill it, its temperature cannot be
less than 100°, and even with high-pressure pipes, the power of
regulation by altering the steam-pressure is very limited. It is far
better to arrange the pipes or radiators in groups, from some of which
the steam can be turned off entirely when less heat is needed. It must
not be forgotten that if these discharge into a common steam-trap, it
will be necessary to turn off their exits as well as their steam supply,
or steam will come back into them from the other pipes, and probably
prevent the escape of condensed water. In some cases it is more
convenient to give the several sections independent exits or
steam-traps.
Many good steam-traps are now on the market, depending either on the
expansion and contraction of metals, or on floats in a closed box, which
open a valve as the water accumulates. Traps of the latter class with
closed copper balls are to be avoided, as the ball is sure eventually to
become filled with water. Several traps have been devised in which an
open vessel is used as a float, which is always kept empty by the
discharge of the water through a pipe dipping into it.
The condensed water from steam-pipes is rarely suitable for use in the
tannery, from the dissolved and suspended iron-oxide which it contains,
from which it can only be freed by boiling and filtering, or treatment
with precipitants (p. 95). Its most appropriate use is generally return
to the boiler. Systems were formerly in vogue by which it was allowed to
run back to the boiler as it condensed, but these could only answer when
the pressure in the pipes was equal to that in the boiler, which is
rarely the case. It must generally be forced in by the feed-pump or
injector.
Hot water has often been advocated in preference to steam for heating,
but is more costly, as it requires a separate boiler, and much larger
pipe-surface for the same effect. Its only important advantage is that
the pipes maintain their heat for some time, even when the fire has gone
down, while steam-pipes cool at once if steam is allowed to go down in
the boiler. In any considerable tannery, however, this will seldom or
never be the case, since if a good pressure of steam is up at night,
when the fires are banked up, the boiler will in itself contain a large
reserve of heat, and, of course, working pressure will be required
before the engines can start in the morning. Hot water systems require
careful planning to obtain reliable and uniform circulation.
CHAPTER XXVII.
_CONSTRUCTION AND MAINTENANCE OF TANNERIES._
As few architects have specially studied the construction of tanneries,
and in most cases much of the arrangement depends on the knowledge of
the tanner himself, a short chapter on the subject will not be out of
place.
In the selection of a site, a clay or loamy soil is to be preferred to a
gravelly or sandy one, as lessening the liability to leakage, and waste
of liquor. Perhaps, however, the first consideration of all is the
possibility of drainage and disposal of effluent waste liquors and
washing waters, since it is now rarely possible to run these, without
previous treatment, into a river or stream. Some information is given in
Chapter XXVIII. on the methods of partial purification which are
available to the tanner, but these are always costly and troublesome,
and the possibility of running direct into a sewerage system, or a tidal
river is of great advantage. Under the Public Health Act, authorities
are bound to receive manufacturing effluents into their sewers if the
latter are of sufficient capacity, and the effluents not such as either
to damage the sewers, or interfere with the processes of purification
adopted by the authority. This act is in many districts practically
superseded by special legislation, but tanners’ effluents are generally
received into sewers if freed from solid matter. When mixed with other
sewage, they do not interfere with irrigation or bacterial treatment. In
selecting a site within a sewered district, regard must be had to the
possibility of causing a nuisance to the neighbourhood by foul smells.
Really injurious smells should not be caused by a properly conducted
tannery, but it is difficult to avoid odour, and a single badly disposed
neighbour may cause infinite trouble and expense.
Another important consideration is the water supply, since for the large
quantities used in a tannery, town water is generally very expensive.
With regard to quality and impurities of water information may be found
in Chapter X.; but, as a general rule, the softer and purer the supply
the better. It is also of great advantage when the source is at such a
level that the water can flow into the tan-yard, or at least into the
beam-house, without pumping. Filtration too, when needed, is much
facilitated by a sufficient head of water.
Commercial facilities, such as nearness to markets and sources of supply
of raw materials, and the availability of rail and water carriage are of
an importance at least equal to the points already considered, but
hardly come within the scope of this work.
The site chosen, the next question is the arrangement of the buildings.
It is very doubtful, where ground is not inordinately expensive, whether
it is wise to erect drying-sheds over the pits. In case of fire, very
serious damage is done to liquor and leather by the heat and burning
timber. If the turret form of drier be decided on, strong foundations
are required, and the ground-floor or basement is occupied with heating
apparatus; if fan-drying, no lofty buildings are needed, and the drying
rooms are conveniently placed over the finishing and currying shops;
and, on the other hand, the tan-house may be easily and cheaply covered
with slated roofs, with nearly vertical sections of glass, to the north
if possible, like a weaving-shed, through which sufficient light for
convenient work and cleanliness is admitted. The direct rays of the sun
should be avoided, but in the writer’s opinion the balance of advantage
is largely in favour of a liberal supply of light. Iron roofs are
unsuitable, since the moisture condenses on, and rusts them; and
particles of oxide fall into the liquors, and cause iron-stains.
Good ventilation along the ridge of the roof should be provided,
wherever there is any steam or hot liquor used; or the condensed
moisture soon leads to decay.
In arranging the general plan of the buildings, much depends on local
circumstances; but as far as possible, they must be so arranged that the
hides and leather work straight forward from one department to another
with as little wheeling or carrying as possible; that the buildings
where power is used be near to the engine so as to avoid long
transmissions, which are very wasteful of power; and that the different
buildings be so isolated as to diminish the risk of the whole being
destroyed in case of fire.
A chapter on the construction and maintenance of tanneries and leather
works would be incomplete if it did not refer to the very important
question of Fire Insurance.[185] To an extent this may be regarded as a
fixed charge against any business, very much in the same way as local
and imperial rates. It is not, however, to be lost sight of, that to
some considerable extent the amount of insurance premium is regulated by
the insured himself. If a man conducts his business in unsuitable and
badly constructed buildings; if attention is not paid to some of the
elementary hazards connected with a fire outbreak; he must not blame the
insurance companies for the demand of what he considers an excessive
premium. If this faulty construction and imperfect equipment of
buildings pertain to any considerable extent throughout a given trade
where the process is more or less hazardous, it is futile to appeal to
insurance companies, which, after all, are merely commercial and not
charitable institutions, for a reduction in the rates. The only standard
to guide the company is the loss-ratio, and given a high loss-ratio,
there must be a corresponding premium paid.
[185] With regard to fire insurance, I am much indebted to Mr. A. W.
Bain, of Leeds for valuable information.
There is, however--thanks to modern science--a method available whereby
the great bulk of fires may be checked in their inception; an appliance,
automatic in its operation, and of proved efficiency. This appliance is
known as the sprinkler. A system of water-pipes is fixed under the
ceilings of the building to be protected, to which are attached
sprinkling jets at suitable intervals, each of which is closed by a
valve held in place by a joint of fusible metal, which gives way if the
temperature rises beyond a given point. There are two or three
recognised patterns approved by the Fire Offices Committee after patient
investigation and practical test. These appliances have now been at work
for something like fifteen years in this country. One of the first
trades to recognise their utility was that of the cotton-spinner. At one
time serious fires in the cotton trade were of frequent occurrence.
Now--owing to the efficient fire appliances--while fires may be as
frequent in their inception as formerly, they are stopped at such a
stage as to prevent any considerable loss. The consequence has been that
the cotton-spinner, at one time the owner of a highly-rated risk, and
one which few companies cared to insure, is now in the position of
having his business eagerly sought after, and large discounts offered
him off the charges he was once called upon to pay.
More important still is the consideration to him that his business is
not so liable to be interfered with or stopped as the result of fire.
There are, it is estimated, at the present moment, no less a proportion
than 90 per cent of the cotton-spinners whose premises are protected by
sprinkler installations.
Other hazardous risks such as corn-millers’, woollen and worsted
manufacturers’, saw-millers’, engineers’, are adopting these appliances
freely, and it is a matter of surprise that so very few tanneries or
currying shops--so far as I have been able to learn, not more than
twelve--have done the same. The consequence is that the loss-ratio in
tannery risks still retains its unenviable notoriety: the rates for fire
insurance have risen considerably, and as a result the tanners’ profits
are correspondingly less. Considering the extent and importance of many
of the tannery risks throughout Great Britain, one can only express
surprise that these appliances have been so little adopted.
The construction of a new tannery demands serious attention from an
insurance standpoint. The boiler-house should be a detached building;
the grinding of bark and myrobalans should be conducted in buildings
isolated from the general works; in fact no better advice could be given
to a tanner, either in the construction of new premises, or the
rearrangement and remodelling of old, than to consult an experienced
insurance man, whether official or broker, as to the best means of
constructing and arranging to secure the most favourable terms.
Another point which should be provided for, and which is often
overlooked, is the feasibility of future extension without serious
changes of arrangement. It may be taken as a probability of the future,
even if it be not already a fact, that small tanneries cannot be made to
pay, and that if a business succeeds, its extension will prove
desirable; and in an ill-planned yard this may involve either entire
reconstruction of a very expensive and inconvenient sort, or the
separation of new departments, so as to involve serious increase of
carrying. A good arrangement is that of a long front building serving to
connect the whole, behind which the various departments are erected at
right angles leaving room for extension backwards as required.
As regards the first of these conditions, if the various soaks, limes,
bates, and handlers are well arranged, it is hardly necessary to do more
than draw the goods from one pit into the next throughout the whole of
the process. To, and from the layers, the goods must generally be
carried or wheeled. In the sheds, if it be a sole-leather tannery, the
butts should first come into turrets or open sheds for the rough drying;
then into a room sheltered from draughts to temper for striking. The
striking machines or beams should be in an adjoining room, or
immediately below; then a small shed-space for drying before rolling;
next the roller room; and then the warm stove for drying off. If two of
the latter can be provided to be used alternately, it will allow the
goods to be aired off without taking down, and they may then be
immediately handed or lowered into the warehouse, without fear of
over-drying, which is sometimes difficult to avoid where leather must be
taken direct out of the hot drying-room. The same principles are easily
applied in yards for lighter leathers.
To lessen loss of power in transmission, the engine should be near the
centre of the main range of buildings, with perhaps the grinding
machinery on one side, and the leather finishing on the other; but this
would be rather liable to increase the fire-risk. A very good plan would
be to have the engine-house in the centre as suggested, but separated
from the buildings on each side by brick gables; and with the
boiler-house behind it, and under a separate roof, say of corrugated
iron. If it be impossible to have the engine near its work, it is in
most cases better to employ a separate high-pressure engine, which may
be within a glass partition, and will work all day with scarcely any
attention. The loss of power in carrying steam for moderate distances
through sufficiently large and well-clothed pipes is much smaller than
that of long lines of shafting. The writer has known cases where fully
half the indicated power of the engine was consumed in friction of the
engine, shafting and belts. High-pressure engines are as a rule to be
preferred to condensing for tannery use, since the waste steam can
generally be employed for heating, and both the first cost and that of
maintenance are smaller. Where much fuel is used, it is quite worth
while to have the cylinders indicated occasionally, both running light,
and driving the machinery; much information is gained in this way as to
the power spent on the various machines, and very frequently large
economy is effected by proper adjustment of the valves. To work
economically, an engine should be of ample power for all it has to do;
and adjusted to its work, not by lowering the pressure of steam, or by
checking it at the throttle-valve, but by setting the slide-valves to
cut off as early in the stroke as may be. As to how early this is
possible, an indicator-diagram will at once give information. If the
whole of the waste steam can be used profitably for heating purposes,
economy in the working of the engine is of little consequence, but,
otherwise, it is very injudicious, for the sake of a little saving in
first cost, to put in an old or inferior engine, which has to be dearly
paid for in waste of fuel. In the choice of an engine, the advice of an
expert engineer is desirable, since many engines which are mechanically
well made, are uneconomical through the faults of a rule-of-thumb
design. In this respect the English engine-builder is frequently
inferior to his better trained continental competitor.
In place of using small steam engines to distribute power, electric
driving deserves consideration. For long drives the loss of power is
much less than that of shafting, and by concentrating the whole
production of the power in one large and well-constructed engine, the
cost per horse-power can be much reduced. While large and
well-constructed engines may develop 1 horse-power at a cost in coal of
1¹⁄₂ lb. per hour, it is not uncommon to use 12 lb. for the same output.
In tanneries, however, the power used bears a much less proportion to
total expenses than it does in the textile and many other trades. The
first cost of electric driving is somewhat high. Motors of the
“armoured” or iron-cased type must be used in all positions where they
are subject to wet or dust. It must be borne in mind that an electric
motor will not start against a heavy load, as it only develops its full
power at a high speed, and if it receive the full pressure of the
current before this is attained, its coils will probably be burnt out,
unless saved by the melting of its safety-fuse. A similar danger is
incurred, if the motor is brought up by overloading while the current is
on. It is therefore generally necessary to connect a motor with its work
by a belt which is only brought on to the working pulley when its full
speed is attained.
In some cases the use of gas-engines is convenient and economical; for
though gas from town-supplies is an expensive fuel, the best gas engines
give a higher mechanical efficiency than steam-engines, and they work
with very little attention.
In arranging shafting, moderate speeds, say 100-150 revolutions per
minute, should be chosen for main lines, and when higher speeds are
necessary, they should be got by light and well balanced counter-shafts,
with wrought iron or wooden pulleys. (Cp. p. 452.) In calculating
speeds, it must be remembered that they vary inversely as the size of
the pulleys. Thus a 3-feet pulley running at 100 revolutions will drive
a 2-foot pulley at 150 revolutions, and a 12-inch one at 300. Of course
the higher its speed, the more power any shaft will transmit, but
increased friction and wear and tear soon limit this advantage. The
velocity of a belt in feet per minute is obtained by multiplying the
number of revolutions per minute by the girth of the pulley in feet or
by its diameter multiplied by 3¹⁄₇, or more accurately, 3·1416.
Pulleys should always be of ample breadth for the power they have to
transmit; and it is more economical, both in power and cost, to use
broad single belting than the same strength in double. If the pulley
will not take a belt broad enough for the work it has to do, a second
belt may be made to run on the top of the first, as suggested by Mr. J.
Tullis, and will do its share of the work. Belts should be washed
occasionally with soap and tepid water, and oiled with castor or
neatsfoot oil; but if of sufficient breadth, should not require the use
of rosin, or adhesive materials, to make them grip the pulley.
Chrome-leather belts should be kept thoroughly oiled. They have a much
greater adhesion than vegetable tannages, and this is increased by
oiling. Good chrome belting is much stronger than bark-tanned; and is
unaffected by damp or steam, but generally stretches somewhat more.
Makers of machines often err in constructing their driving pulleys too
small both in breadth and diameter.
The horse-power which a belt is capable of transmitting obviously varies
extremely with circumstances, but may be approximately calculated by the
formula
_a_ . _v_
---------,
66000
where _a_ is the area of contact of the belt with the smallest pulley,
and _v_ its velocity in feet per minute. Another rule is, that at a
velocity of 1000 feet per minute, each inch of breadth of belt should
transmit 2¹⁄₂ horse-power on metal pulleys, or 5 on wooden ones, on
which the adhesion is greater. Adhesion may also be increased by
covering the pulleys with leather or indiarubber. Both rules assume that
the belt is of ample strength. One horse-power would be transmitted by a
belt running 1000 feet per minute with a pull of 33 lb. A good single
belt should not break with a much less stress than 1000 lb. per inch of
breadth, and should stand about ¹⁄₁₀ as much as a working stress.
The following table gives the experimental breaking stresses and
extensions of some leathers. It may be noted that 1 square inch
sectional area is equal to a belt 4 inches wide × ¹⁄₄ inch thick; and
that _kilos per cm²_ × 14·22 = lb. per inch².
BREAKING STRESSES OF LEATHER.[186]
-----------------------------+------------+---------+---------
-- |Kilo per sq.| Lb. per | Stretch
| centimetre.|sq. inch.|per cent.
-----------------------------+------------+---------+---------
Belting leather, layer system| 283 | 4,030 | 25·4
„ „ Durio system| 298 | 4,240 | 21
Well-tanned chrome leather | 740 | 10,500 | 32·5
Over-tanned chrome leather | 234 | 3,330 | 23
Stuffed alumed leather | 835 | 11,900 | 38·3
Alumed “rawhide” | 921 | 13,100 | 31·4
-----------------------------+------------+---------+---------
[186] ‘Gerber,’ 1900, p. 73.
Good English tanned belting leather breaks at from 4500 to 5500 lb. per
sq. inch sectional area.
Over-tanned leathers are less tough, whether of vegetable or mineral
tannage, than those somewhat lightly tanned, and the tensile strength of
leather varies considerably with the part of the hide from which it is
taken, that from approximately over the kidneys being the strongest.
Even thick and tough leather is easily torn if a cut or nick is once
started, and all holes used in jointing belts should be carefully
rounded. Glucose, and the use of acid in bleaching both lessen the
toughness of belts, and they may also be rendered tender by the heat
evolved in slipping on a pulley.
Countershafting and high-speed machinery, such as disintegrators,
striking machines of the Priestman type, etc., should run without
material jar or vibration. If this occurs, it is generally a sign that
the running part is not equally balanced. In this case the shaft or
spindle must be taken out of its bearings, and supported on two exactly
horizontal straight-edges, on which it will roll till the heaviest part
is downwards; and weight must then be taken off or added till it will
lie in any position. In this way the writer has had to add fully 2 lb.
of iron to balance the drum of a striking machine before equilibrium was
secured, and a most troublesome vibration prevented. Of course all
machinery should be supported as solidly as possible; and if
circumstances permit, most machines are better on a ground floor. In
placing bark mills, however, it is frequently convenient to fix them at
a higher level, so that the ground material may be sent down shoots by
its own weight to the required places. An alternative plan is to set the
mill on the ground over a pit, and to raise the ground material with a
bucket-elevator. This may be done successfully by letting the material
fall directly from the mill into the buckets; but otherwise it must be
thrown in with a shovel, as buckets will not pick up ground bark, even
from a hopper; and in any case such elevators are apt to be troublesome.
In a grinding plant designed by the writer, the unground material was
filled on the basement floor into an iron barrow, which was wheeled into
an iron sling working between upright guide-rails like a hoist. On
pulling a brake line, the barrow was raised to the top of the building,
and its contents were tipped into a large hopper, after which the barrow
righted itself, and descended for another load. In the bottom of the
hopper was a sliding shover, which forced the material on to vibrating
screens, by which it was guided either into a disintegrator, or
crusher-rolls, at pleasure. Both these discharged through iron spouts
into large hoppers on the outside of a brick gable, from which powdery
materials like myrobalans and valonia could be run direct into barrows
or trucks. It is very desirable that such hoppers should be separated
from the main building by a fireproof partition. Fires may occur from
hard substances getting into disintegrators along with the bark, etc.
and if this occur with a dry and dusty tanning material, it is not
unlikely that it may result in an explosion such as sometimes happens in
flour mills, in which the fire is rapidly conveyed along spouts, and
into chambers filled with dusty air. Insurance companies generally
charge an extra rate for disintegrators, and it is very desirable to
keep the mill-house structurally apart from other buildings, either by
actual separation or by the introduction of brick gables dividing the
roofs. On the whole, however, mills of the coffee-mill type are probably
quite as dangerous as disintegrators; since if they become partially
choked, the heat caused by friction is very great.
In America, the fire-risk from mills is often lessened or prevented by
the introduction of a jet of steam into the chamber or spout by which
the mill discharges, but this is only permissible if the tanning
material is conveyed at once to the leaches or yard.
The use of chain-conveyors for handling tanning material both wet and
dry is practically universal in America, though comparatively rare in
England. Various forms are used, the most common consisting of a chain
of square links of malleable cast iron which hook into each other, so
that a broken link can be immediately replaced (see p. 325). At
intervals special links are inserted, which can be had of various
patterns, for the attachment of scrapers or buckets. The endless chain
runs in a trough of rectangular or V-shaped section, and is driven by a
toothed wheel, over which it runs like a belt. In some cases the
returning half of the chain can be utilised to bring back the spent tan
on its way to the boiler house. For dry materials, cotton or leather
belts with short wooden cross-laths attached, may often be used
satisfactorily in place of the chain.
For lubricating purposes, mineral oils of high density are not more
dangerous than animal or vegetable, but rather the reverse; as, though
they are possibly more inflammable, and make more smoke, their mixture
with cotton-waste and other porous materials is not spontaneously
combustible, as those of vegetable and animal oils occasionally are. The
danger of spontaneous combustion is very considerable when heaps of
leather shavings or cuttings containing fish-oils are allowed to
accumulate in warm workshops, and, especially near steam-pipes. Heavy
mineral oils should always be used as cylinder-oils in high-pressure
engines, in preference to other oils or tallow, since they are not
decomposed by steam, and do no harm if blown into the feed-water, but
serve to loosen and prevent scale and deposit. Ordinary oils and tallow,
on the other hand, when submitted to the action of high-pressure steam,
are separated into glycerin and fatty acids (see p. 351), and the
latter corrode the valve faces and seatings, and are liable with
“temporary hard” waters to form a very dangerous porous deposit in the
boilers, which often leads to overheating of the tubes.
Next to the machinery, the pits demand special consideration. The
chapter on the subject in the late Mr. Jackson Schultz’s book on
‘Leather Manufacture,’ is well worth attentive study as giving American
practice on the subject.
The old-fashioned method of sinking pits is to make them of wood, and
carefully puddle them round with clay, which should be well worked up
before use. It is of no use to throw it in in lumps and attempt to
puddle it between the pits, which will not be made tight, but probably
displaced by the pressure. Such pits, if made of good pine and kept in
constant use, are very durable, some of the original pits at Lowlights
Tannery, constructed in 1765, having been in use till 1889. Loam mixed
with water to the consistence of thin mortar may also be employed, the
pits being filled up with water, to keep them steady, at the same rate
as the loam is run in. Probably the best materials for pit-sides are the
large Yorkshire flagstones. Where these are not attainable, very durable
pits may be made of brick, either built with Lias lime, and pointed with
Portland cement, or built entirely with the latter. Common lime cannot
be used, as it spoils both liquors and leather; and even cements with
too large a percentage of lime are unsatisfactory. Brick and common
mortar are, however, suitable for lime-pits, and for these Mr. C. E.
Parker’s plan of constructing the bottom of cement, the ends and sloping
hearth of brick, and the sides of 3-inch planks bolted together is also
very satisfactory (Fig. 96).
The writer has constructed wooden pits in two ways. In the one case,
after making the excavation, beams were laid in a well-puddled bed of
clay; on these a floor of strong tongued and grooved deals was laid, and
on this the pits were constructed of similar wood to the floor, and
puddled round with clay. In the second case the pits were built like
large boxes above ground, and when finished, lowered on to a bed of clay
prepared for them, and then puddled both around and between. It may have
been due to defective workmanship in the first case, but those made on
the last-named plan, which is that adopted from very early times,
certainly proved the tightest and most satisfactory. Mr. Schultz
describes a plan as the Buffalo method, in which a floor is laid as just
described, and grooves cut with a plane for the reception of the sides,
which are formed of perpendicular planks, each end and side being
finally tightened up by the insertion of a “wedge plank.” Owing to the
perpendicular position of the side-planks such pits would be difficult
to repair in the common case of decay at the top.
[Illustration: FIG. 96.--Mr. C. E. Parker’s construction of Lime-Pits.]
If bricks be used, great care must be taken that the cement is not
merely laid so as to fill the joints towards the two surfaces of the
wall, as is the habit of modern bricklayers, but actually floated into
all the joints so as to make the wall a solid mass; or leaks can hardly
be avoided. Hard pressed bricks are best, and should be tested as to
whether they discolour liquor. Cement-pits are very good, and, though
not particularly cheap in material, which must be of the best, are
readily made by intelligent labourers under good supervision. The first
step is to lay a level floor of good concrete, in which glazed pipes for
emptying the pits may be embedded; care being also taken that all joints
in these are thoroughly tight, since future repairs are impossible. The
next step is to make frames, the exact length and breadth of the pits
required, and perhaps 15 inches deep. These are arranged on the floor
where the pits are to be, and the intervening spaces are filled with
concrete of perhaps 1 of cement to 3 or 4 of crushed stone or brick.
Rough stones and bricks may also be bedded in the concrete as the work
goes on, to help to fill up. After the first layer has set, the frames
may be raised and a second added, and so on. The work is generally
finished by floating over it, while still damp, a little pure cement, to
give a smooth surface. Before using, the cement should be tried on a
small scale, to be sure that it does not discolour leather or liquors,
and the pits should always be seasoned with old or cheap liquor before
actual use.
[Illustration: FIG. 97.--Cleaning Rod Joint.]
If possible, both leaches and handler-pits should be provided with plugs
and underground pipes, communicating with a liquor-well some feet below
their levels. Glazed fire-clay is very suitable both for pipes and
plug-holes, which should be in the pit corners. If fire-clay blocks for
plug-holes cannot be obtained, they may be cast in good cement, the
wooden mould being soaked with hot paraffin wax to prevent adhesion.
Means must be provided for the ready clearing of the pipes when choked
with tanning materials. A good plan is to let each line of pipes end in
a liquor-well large enough for a man to go down. As it is almost
impossible to make plugs fit without occasional leakage, it is not well
to run pits with very different strengths of liquors to one well, but
the layers, handlers, and different sets of leaches should each have
their own, so as to avoid mixture. A good means of clearing pipes
consists in a series of iron rods 3-4 feet long, connected by hooks
fitting into double eyes, as shown in Fig. 97. It is obvious that in a
narrow pipe or drain, these cannot become disconnected. Pipes may often
be forced out by fitting a strong delivery-hose of a steam-pump into one
of the plug-holes.
It is, as Schultz points out, of questionable advantage to lay wooden
troughs under the alleys for supplying liquor to each pit, since it is
almost impossible to preserve them from decay; but the same objection
would not apply to glazed pipes, jointed with pitch or cemented. A good
and cheap plan in practice, is to let the liquor-pump, or a raised
liquor-cistern, discharge into a large and quite horizontal trough
raised 6 or 7 feet above the level of the yard, and provided with
plug-holes at intervals, from which the liquor can be run into the
various pits by short spouts or sailcloth hose. In place of plugs in the
raised trough, a simple and convenient valve devised by the writer may
be advantageously employed. A lead weight is made by casting in a
hemispherical tin basin of about 5 inches diameter and 2 inches deep in
the centre, a loop of strong brass wire with turned up lower ends, being
suspended in the middle, so as to become fixed in the lead. To prevent
adhesion, the tin must be previously burned off, and the basin well
blackleaded. This weight forms the valve, which rests in use on a 6-inch
washer of good indiarubber with a 4-inch hole, which is held by a wood
block against the bottom of the trough, through which a 5-inch hole is
cut. The valve is raised by a lever or cord, and is absolutely
water-tight in use. It is shown in section in Fig. 79, p. 333.
It is very advantageous in practice, instead of pumping direct into the
pits, to have one or more tanks, into which liquor can be delivered by
the pump, and which are sufficiently raised to allow it to be run from
them into the horizontal distributing troughs which have been mentioned.
This is specially important with regard to liquors for leaches and
suspenders which are worked on a circulating system, since they do not
run very quickly, and much time is lost in pumping out pits, if the
speed of the pump has to be regulated by the rate at which the liquor
will circulate. It also enables liquors to be run through suspender- and
rocker-pits during the night or at meal-times while the machinery is
standing; and it is often useful on beginning work in the morning, to
have an empty tank into which the first liquor can be pumped.
Direct-acting steam-pumps without fly-wheels are very unsatisfactory for
tan-yards, since they are usually uncertain in their action, difficult
to run slowly, and apt to “hammer”; and they are also costly in steam,
which cannot be used expansively. Steam-pumps with fly-wheels, operating
the steam-valve by an eccentric, are free from these defects, and though
more costly at the outset, soon save the difference in lessened repairs
and consumption of steam. Pumps with a capacity of 8000 gallons per hour
are very suitable, and can be used with a 3-inch hose pipe; smaller
sizes are decidedly more liable to choke with tanning material. Rubber
mitre-valves work satisfactorily, and do not choke frequently, but are
costly, and easily damaged by hot liquors. On the whole brass
clack-valves are the most satisfactory, but the hinge-pins, instead of
fitting neatly in circular sockets, should be held in slots, allowing
the back of the valve to rise half an inch, when it will clear itself of
small hard myrobalan stones and suchlike things, which getting under a
more tight-fitting hinge would prevent the valve closing, and so stop
the pump. Whatever valves are employed, means should be provided for
easy access without unscrewing too many bolts. If the several
valve-chambers of the pump are closed by a single cover with an
indiarubber washer, the spaces between them which make the joint should
be faced with brass or gun-metal, as, if the least leakage takes place
over an iron surface, the friction and solvent power of the liquors soon
eat away the metal and render a good joint impossible. Where colour is
of first importance, it is well to have the whole pump of gun-metal, but
in any case the working cylinder should be brass-lined, and the piston
and rod, and the valves and seatings should be of brass or gun-metal.
Spring-rings are far better than pump-leather and are unaffected by hot
liquors; chrome leather, however, will stand a good deal of heat.
Double-acting force-pumps have practically superseded the older
single-acting double or triple pumps. Instead of direct driving with a
steam cylinder, it is sometimes advantageous to drive by belt, but at
least one steam pump should be provided, so that pumping can be done
when the main engine is not running, and the speed of the pump can be
regulated to the work, which is impossible in a belt-driven pump. Steam
pumps are sometimes very useful as fire engines.
Centrifugal pumps are very suitable for tannery work, where the liquor
is drawn from a well, but are not well adapted for use with
suction-pipes. If the form with vertical spindle is adopted, which is
sunk below the liquor in the well, the pump fills itself, and needs no
foot-valve, but unless the well is very large, or some convenient means
is devised of withdrawing the pump, repair or cleaning is difficult. If
the horizontal pattern is used, which is above the ground, repair,
cleaning, and driving is much easier, but a foot-valve is necessary,
which may itself give trouble, and some convenient means, such as a pipe
from a raised tank, should be provided for filling the pump with liquor,
as, unlike suction pumps, centrifugals will not start unless full,
although they raise very large quantities when running, and from their
steady flow, will deliver much more through a given pipe than an
ordinary reciprocating pump with the same power. In selecting the pump,
care should be taken that the pattern allows ready access, not only to
the foot-valve, but to the body of the pump.
It is seldom satisfactory to use windbores or strainers to prevent
tanning material getting into a pump, as they speedily become choked;
and it will be found better, after taking such precautions as are
possible, to have the pump and valve of ample size and suitable
construction to pass what comes with the liquor. The writer has known a
mop-head pumped and delivered through a 3-inch hose without stoppage, by
a Tangye fly-wheel steam-pump with brass clack-valves such as have been
alluded to.
Pulsometers have not, in the experience of the writer, proved
satisfactory in tanneries, warming and diluting the liquor, consuming
much more steam than a pump of the same power, and becoming easily
choked. For the same reasons, steam-jet water-raisers are not to be
recommended except where raising is to be combined with heating, as in
some leaching devices (p. 334).
CHAPTER XXVIII.
_WASTE PRODUCTS AND THEIR DISPOSAL._
The products which are of no direct value to the tanner and currier in
the manufacture of leather, and which are nevertheless obtained in
fairly large quantities, are of very varying characters. In the present
chapter, the most important of them will be described, and some of their
uses mentioned.
_Hair_ is removed from the skin of the animal in the process of
depilation (p. 143) in the form of a wet sodden mass, containing a
considerable amount of lime when the skin has been through the
lime-pits.
As white hair is the more valuable, care should be taken in the
unhairing to keep it separate from the coloured. It is washed first in
plain water to get rid of as much of the lime as possible, and then in
water containing a little acid. Hydrochloric acid is often used for this
purpose, but sulphurous acid (p. 25) is preferable as it has a slight
bleaching action on the hair. The acid neutralises and renders soluble
the lime which still remains in the hair, so that it can be easily
removed by washing with water. In many tanneries, hair-washing machines
are used. The washed hair is dried by laying it out on frames; or
preferably, the greater part of the water is first removed by a
centrifugal drier, or by pressing, and the drying is completed in a
drying room, the temperature of which is a few degrees higher than that
of the outside air, and which is provided with a fan or some other
appliance for mechanical ventilation. Tables of wire gauze on which the
hair is spread, and through which the warm air of the room is drawn by a
centrifugal fan, are the most effective.
Coloured hair is sometimes washed and treated like the white hair, but
is usually sold direct to plasterers, in which case there is no
necessity to remove all the lime and other impurities which the hair
contains. A considerable amount of hair is also sold to iron founders,
who use it in preparing cores and in loam-casting. The loose lime may be
effectively beaten from dried hair by passing it through a disintegrator
with one of the grates removed.
_Fleshings and Glue-stuff._--The various scraps of fat and flesh, more
or less free from actual hide substance, are usually worked up for glue,
though if they cannot be sold for a fair price it will pay to boil them
in order to recover the fat they contain. If this is to be done, the
fatty portions may be thrown out at the beam and not mixed with the
fleshings as in the ordinary way. Before boiling, the fat is treated
with sulphurous, sulphuric or hydrochloric acid, sufficient to
neutralise the lime present. The boiling should be carried on very
gently, so as to allow the fat to rise without emulsifying with the
gelatinous matter. For boiling, open steam may be used, but in this case
the size formed will have little value; on the other hand, if sulphurous
acid has been used and a wooden vat with a copper steam-coil be
employed, really good glue may be obtained, and the slight trace of
bisulphite which it may contain will prevent its putrefaction. Except
under special conditions it will not pay to make glue on a small scale
in England, as its value depends much on its appearance, and the
necessary plant is somewhat expensive. In some places, however, size can
be sold to advantage. Fig. 98 shows a glue-boiling plant.
After separation of the fat by skimming, the clear size is run off from
the residual matter into wooden cooling troughs about 5 feet long by 9
inches deep and 15 inches wide, in which it is allowed to set (Fig. 92,
p. 425). Great care is required that both size and coolers are quite
sweet and free from putrefaction, the coolers being frequently washed
with sulphurous acid solution or fresh milk of lime. The jelly is cut
out in blocks, and sliced into cakes of appropriate thickness by means
of a series of frames like slate-frames which fit over the block of
glue, and between which a wire or thin blade stretched on a saw-frame is
inserted to cut the glue into sheets. In some factories a machine is
used, with a series of parallel blades against which the glue-block is
pushed. The sheets are afterwards separated by girls and laid to dry on
nets, on which they are frequently turned. When dry, the cakes may be
washed with warm water to remove any adhering dirt, but this causes
some loss of weight, and in many cases it pays better to dry in a stove
until quite hard, then grind in a disintegrator and sell as
“size-powder,” in which appearance counts for little if the colour and
strength of the size are good.
[Illustration: FIG. 98.--Glue Boiling.]
_Fat._--The fat, whether obtained in the manufacture of glue, or by
boiling the fleshings and shavings for its recovery alone, is skimmed
from the surface of the heated liquor, and should afterwards be freed
from gelatinous matter by washing it with hot water in a tub and running
off the upper layer after allowing the water to settle out. The fat thus
obtained is a light-coloured grease of buttery consistence.
There are various other sources of waste fats which may be considered
here. If glue is made from dried glue-stuff without previous treatment
with acid, the fat skimmed off the pans, though dark in colour, will be
neutral or alkaline, and a considerable additional quantity of fat and
free fatty acids may be obtained by reboiling the “scutch” or refuse
with open steam in lead pans with the addition of water and enough
sulphuric acid to render the contents of the pan distinctly acid. This
grease will be dark and of unpleasant smell from volatile fatty acids,
but its odour may be to a considerable extent improved by blowing air
and steam through it, and washing with water, or by heating to a
temperature somewhat above the boiling-point of water for a considerable
time. The same sort of treatment may be applied to the fat pressed out
of sheepskins, and to that obtained by boiling currier’s shavings with
water and a little acid.
Recovered fats may be separated into a tolerably firm grease suitable
for use instead of tallow in currying, and an oil not unlike neatsfoot
oil, by melting, allowing to cool slowly to a soupy consistency to
promote the crystallisation of the harder fats, and forcing the mixture
through flannel cloths in a filter press. The temperature at which the
filtration should take place is generally 20-25° C. The oil is, of
course, “tender,” or liable to solidify in cold weather; and the more so
the higher the temperature at which filtration takes place. The tallow
is obtained in cakes. If from fresh fleshings, it will be white and with
little odour, but that from dried glue-stuff is usually brown and of
unpleasant smell, while recovered grease from curriers’ shavings or
“moisings” is always dark in colour.
If the fleshings are to be sold wet, they should be preserved in a sweet
lime liquor; if to be dried, they are washed carefully in a fresh lime,
spread on frames, and frequently turned over so that they may dry evenly
and rapidly. Heat, if employed at all, is in most cases only used at the
end of the drying operation, but some tanners dry from the first in a
room the temperature of which is a few degrees higher than the normal,
and which is provided with good ventilation. For the purposes of the
glue manufacturer, the roundings and larger pieces are more valuable
than the fleshings, and should be treated with correspondingly greater
care by the beamsman and his assistants.
_Bate-Shavings_ are very valuable as sizing materials. They should be
well washed in water, or with a very dilute solution of sulphurous acid,
and are then laid out in thin layers to dry. They may also be partially
dried by pressing between latticed boards in a screw or hydraulic press,
and are then best finished as cakes. On the manufacture of sulphurous
acid compare p. 25.
_Horns_ are usually kept until the “slough,” “pith,” or internal bone
can be knocked out, having become loosened through drying and
putrefaction. If kept dry, practically no longer time is required, and
the smell and other annoyances incidental to storing in a damp place are
avoided. The sloughs may be removed by steaming, but the horns are
somewhat damaged by this treatment. The sloughs are principally ground
for “bone-meal,” but some are boiled for glue, either without
preparation, or after decalcifying with dilute hydrochloric acid.
The actual horn itself, which is quite incapable of making glue, is used
chiefly in the manufacture of combs, buttons, and similar articles. The
value of horns is to a considerable extent dependent on their size,
small horns being unprofitable to work up for the articles above
mentioned.
_Spent Tan._--The tan as it is obtained from the leaches after
extraction has, naturally, no value for the tanner except as a fuel.
Spent tan cannot be profitably sold as manure, as its worth in this
respect is extremely small. In those places where white lead is still
made by the Dutch process, oak-bark is used to cover up the earthen
pots, and commands a good price. It is, however, essential that oak-bark
only should be used, as many other tanning materials give off products
which injure the colour of the white lead. The quantities of tan used
for hot-beds, and for deadening the noise of traffic in the streets, are
so small that they are of no practical account in the disposal of this
product. Spent tan is not nearly so good as wood for the manufacture of
paper, and an attempt to distil it and thereby obtain pyroligneous acid
and wood-spirit did not result in any commercial success. On the
Continent, fine-ground tan is usually pressed into briquettes for use as
domestic fuel, but it would be hard to obtain a market for these in
England.
On the whole, in spite of its low heating value, spent tan is best
utilised as a fuel. For this purpose specially constructed furnaces are
necessary on account of the dampness of the tan, and its low calorific
value, which varies, however, with the particular materials: thus while
oak-bark and valonia are only poor fuels, hemlock and myrobalans are
much better on account of the resin and lignine they contain.
The first successful furnaces for raising steam with wet tan were
introduced in the United States, and consisted of large arched
combustion chamber with abundant grate-area, and with four or six
feed-holes in the fire-brick top which formed a floor on which the spent
tan was laid, and where to some extent it was dried by the waste heat.
The flames and furnace gases were conducted under the boilers, the flue
being very large and deep so as to collect the light ash which was drawn
in great quantities from the furnace, and the gases then returned
through the tubes of the boiler, afterwards passing down the sides and
going to the chimney. The wet fuel was fed in through the firing holes
alternately, so that only a part of the grate-space was covered at once
with wet fuel; which was speedily ignited by the heat from other parts
of the furnace, and especially from the vaulted arch.[187] The large
grate-area was a necessity not only on this account, but because of the
light weight of the fuel and its low calorific power, which involved the
need of burning a large volume. Fig. 99 represents a furnace of similar
principle constructed by Messrs. Huxham and Browns. Furnaces of this
type are, the author believes, still largely in use in the United
States, but in Germany “step-grates” sloping from the furnace-doors
towards the back, are now preferred. In these the combustible material
rests upon the flat surfaces of the grate, while the air enters by the
spaces between the steps without the fuel being able to fall through.
Fig. 100 represents the furnace on this principle constructed by the
Moenus Co. of Frankfort.
[187] Detailed drawings and particulars are given in Jackson Schultz’s
‘Leather Manufacture in the United States,’ New York, 1876.
[Illustration: FIG. 99.--Huxham and Browns’ Furnace.]
The essential conditions which are to be observed in the proper burning
of the tan are a sufficiently large grate-area, a correct and sufficient
supply of air, and a combustion-chamber of very high temperature. It is
consequently not possible to burn tan very successfully in an ordinary
Lancashire or Cornish boiler, since not only the grate-space is too
limited, but the water of the boiler prevents the upper part of the
furnace from attaining a high temperature; and it is therefore difficult
to get the damp tan rapidly into vigorous combustion. The difficulty may
to some extent be overcome by mixing the tan with a proportion of coal,
and by closing the ash-pit and employing a forced draught unless the
chimney is a very powerful one. In this way large quantities of tan may
be burnt, but without effecting any great saving of coal. The heating
power of the tan is improved by the partial removal of its water by
pressing, and this is almost essential where a special furnace is not
employed.
[Illustration: FIG. 100.--Moenus Step-grate Furnace.]
The answer to the question as to whether tan should be used as fuel in
the wet state in which it is obtained from the leaches, or whether it
should be previously pressed, depends upon the nature and quantity of
the tan. Where abundant quantities of a fairly good material such as
hemlock bark are to be disposed of, the cost of pressing is an
unnecessary expenditure; but if it is desirable to obtain the highest
value from the fuel, or if the furnaces are not well constructed for
burning very wet fuels, it will be profitable to press the tan.
Hydraulic presses have been used for this purpose, but those now
commonly employed consist of powerful rollers arranged in the same way
as those of the valonia-crusher (p. 322). The pressure is given by
levers loaded with weights or fitted with powerful springs. The liquid
which runs from these presses is of little value, as it contains such
large quantities of finely divided material that it is almost impossible
to filter it, and if run upon the leaches it chokes them and prevents
their proper circulation. Much of the cost of pressing is caused by the
labour of feeding it to the press, and this may be greatly reduced by
the use of mechanical conveyors (p. 325) from the leaches. A tan press
is shown in Fig. 101.
[Illustration: FIG. 101.--Tan Press.]
_Sewage and other Waste Liquids._--The waste liquors from the different
liming, bateing, puering, tanning, washing and other soaking processes
are, without any doubt, the most troublesome of any of the side-products
which are obtained in the manufacture of leather. In former times they
were simply run into the nearest stream, but nowaday the various
sanitary authorities and other similar bodies will only permit
comparatively pure waters to be turned into a public stream or
watercourse.
Various methods of effecting the necessary purification of the waste
liquors from tanneries have been proposed at different times, and have
been used with varying degrees of success. These methods may be divided
into three heads: precipitation, followed by filtration or sedimentation
land-treatment; and bacterial purification.
The first of these depends on the power of certain substances, such as
alumina and oxide of iron, to carry down organic matter with them if
precipitated in solutions containing it. The method usually consists in
adding a sufficient quantity of lime to render the waste liquid slightly
alkaline, and then treating it with some crude salt of aluminium or of
iron. By this means a precipitate of aluminium or iron hydrate is
formed, which encloses within itself a considerable proportion of the
organic matter of the liquid, and after settling to the bottom of the
precipitation-tank is drawn off as “sludge.” Various chemicals are sold
under fancy names, such as “alumino-ferric,” “ferrozone,” etc., and have
a composition not very dissimilar to that of crude sulphate of iron or
alumina. In some cases by-products, such as the acid liquors used in
preparing iron articles for “galvanizing,” can be used with advantage.
In the case of the waste liquors from a tannery, the use of these
chemicals may often be avoided if sufficient care be taken in regulating
the proportion of the various liquids which are to be mixed together and
run into the settling tank. As tanning matter combines with lime and
dissolved hide-substance to form a heavy brown insoluble precipitate, it
is clear that if care be taken to have rather more waste lime-liquor
mixed with the waste tan-liquors than is necessary to throw all the tan
out of solution, a very considerable amount of purification of the
effluent will have taken place without any cost whatever to the tanner.
Hence, if the proportion of waste lime is small in comparison to that of
the tanning liquors, an extra addition of lime may be necessary in order
to precipitate the tannin.
The precipitation- or settling-tanks are usually square or rectangular
vessels or pits, the size of which varies with the quantity of liquid to
be treated, but the depth of which rarely exceeds six feet. They may be
divided into two classes--the “intermittent,” and the “continuous.” In
the former class the tank is filled with the mixed waste liquids, taking
care that such a sufficiency of lime is present that the mixture is
faintly alkaline to phenolphthalein paper, and is then allowed to rest
until the suspended matter has settled down to the bottom of the tank,
when the clear, or almost clear upper liquid is drawn off, the remainder
being the “sludge”; some means must also be employed to prevent the
passage of scum and floating matters. In the case of the intermittent
process it is advisable to have two tanks, one of which is being filled
while the other one is settling or being emptied. With the continuous
process the liquids are run into the tank in the proportions calculated
to give a maximum amount of purification, as described above, but as
they enter very slowly the undissolved matter soon settles, and
consequently the liquid may be continuously run out at the further end
of the tank. This plan, though it does not yield such good results in
the hands of unskilled workmen, is yet useful in many cases, as only one
tank is absolutely necessary. It is desirable that in running off the
tanks, the effluent should be taken as near the surface as possible, by
means of a hinged pipe attached to a float, or some equivalent device;
and care is required, as the tank gets low, to avoid the escape of any
of the sludge.
For continuous settling the tanks are usually long and somewhat shallow
rectangular ponds, into which the previously well-mixed precipitating
liquid flows through a wooden trough fixed across one end and as long as
the breadth of the tank, and perforated with holes to allow the uniform
and quiet influx of the liquid, which finally escapes by a similar
trough crossing the opposite end of the tank. In front of the
exit-trough a “scum board” must be placed, which is a simple plank
dipping slightly below the surface of the liquid, so as to prevent any
oil, scum or other floating matter from passing out of the tank along
with the clear effluent. Whether the intermittent or continuous system
is employed, the effluent should in most cases be afterwards passed
through a bacterial filter-bed, or treated by land filtration before it
is allowed to flow into a stream or river. Tannery effluents are usually
received into sewers without further treatment than mixing and settling
to remove solid matter, and many authorities are satisfied with the
removal of merely such coarse suspended matters as might choke the
sewers. Where continuous precipitation-tanks are used, they must be
emptied at frequent intervals, and the sludge run on to cinder-filters,
to part with most of its water. These filters are conveniently placed at
a lower level than the settling tanks, and it is generally necessary to
return the effluent from them for further precipitation and settling.
Several types of continuous settling tank with upward flow have been
devised by Mr. Candy and others, which are very suitable for use where
space is limited; but otherwise less costly constructions are often
sufficient. Apart from the question of obtaining an effluent
sufficiently good to satisfy the sanitary authority, the treatment of
the sludge is one of the greatest difficulties in the purification of
effluents. It is usually very bulky, easily putrescible, and therefore
difficult to dry; it is of little value for manure; and if allowed to
remain long wet, its smell is very offensive.
It has been mentioned that in most cases the liquid, and in every case
the sludge, must be freed from solid undissolved matter by filtration.
This may take place through open filters or through filter-presses. The
open filters generally consist of a pit with an exit at the bottom for
the filtered liquid. This pit is filled with either stones and sand,
with clinker, ashes or coke. Most tanners use clinker and ashes, as they
do not cost anything; and the material should be so arranged that while
the lowest layers are very coarse, the surface of the filter-bed should
be of the finest material. As soon as this has become covered with so
thick a layer of solid matter that the filtration proceeds too slowly,
the top surface of the filter may be removed with a rake (taking care to
remove as little of the ashes or sand as possible), and burnt, or dried
and used as manure. In some cases, filter-presses are used which are
composed of grooved or perforated plates with cloths between them
through which the liquid is forced by pressure. The solid matter remains
behind in the form of a comparatively dry “cake.” The filter-cake, dried
if desired, is sold as manure, for which it is in many ways very
suitable. Although they work much more rapidly than do the open filters,
the cloths so soon become rotten and have to be replaced, that the open
ash-filter is on the whole the most convenient for the tanner’s use. It
will be readily understood that apparatus of this kind, though very
efficient on a small scale, is quite out of the question when many
thousand gallons of liquid have to be filtered daily, and so can only
be effectively applied to “sludge.”
No system of chemical precipitation has as yet proved entirely
satisfactory. Undoubtedly a great deal of purification is effected by
this means, but in most cases the “purified” liquid is still too impure
to be turned into a stream, though for various reasons this is often
permitted by the authorities.
A great advance was made in the purification of effluents when
manufacturers were compelled by law to allow the effluent from the
precipitation-tank to filter through land set apart for that purpose. In
this case certain hardy cereals were sown on the land, which was watered
as often as possible with the effluent. This latter, after soaking
through the land, was drained off into the nearest stream. Although in
many ways this treatment was satisfactory, it had the disadvantage of
being very expensive, especially in the neighbourhood of large towns
where the price of land is high, and, in addition to this, the
conditions necessary for success were far from being correctly
understood, so that the land often became “sewage-sick” or waterlogged,
and ceased to purify the effluent. It was not until the researches of
bacteriologists proved that the purification by land-filtration was
mainly due to the bacteria in the soil, that any really satisfactory
solution of the problem could be found, but the question has now been to
a considerable extent simplified by the introduction of “bacterial
treatment.”
Bacteria, considered from the point of view of their action on organic
matter, are often classified as “anaerobic” and “aerobic,” though many
species are capable of existing under both conditions (Cp. L.I.L.B.,
Section XXIV.). The anaerobic bacteria thrive only in the absence of
air, and their chemical action consists in breaking down the organic
matter on which they feed into simpler, and generally more soluble
forms, by processes which do not involve oxidation. The aerobic
bacteria, on the other hand, require air or oxygen for their existence,
and produce changes which are generally of a less complex character, but
result in the complete oxidation and conversion of the organic matter to
simple compounds, such as nitrates and carbonic acid, which are
perfectly harmless and inoffensive. The two classes therefore are to a
large extent complementary to each other, the anaerobic bacteria
converting the animal or vegetable substances into more soluble and
simple compounds which are adapted to the needs of the aerobic, which
complete the destruction of the organic matter.
In harmony with what has just been said, bacterial treatment of sewage
is of two kinds, each of which may be used alone, or in conjunction with
a preliminary precipitation-process, but which are generally best used
successively. The oldest form of bacterial purification depends mainly
on the action of anaerobic bacteria, and is known as the “septic tank.”
This originally consisted of a tank sometimes filled with small pieces
of coke, but generally containing the liquid only, and which was tightly
closed to prevent access of air and escape of foul gases. It has,
however, been found that if deep tanks (6 to 10 feet) are employed, they
soon become in continuous use so covered with scum and floating matter
as effectually to prevent access of air and light, or any serious escape
of smell. The liquid to be purified is allowed to flow very slowly
through a tank or series of tanks of this description, entering about a
foot below the surface through a distributing trough at one end, and
flowing out similarly at the other, at such a rate as to change the
contents of the tank about once in twenty-four hours; and when the tank
is in working order, the liquid is much purified by the process, and
most of the solid organic matter has become liquefied and disappears. It
not unfrequently happens, especially where the septic tank treatment is
not very prolonged, that the liquid which escapes has a stronger and
more offensive odour than it had on entering the tank. It is
nevertheless really purer than before, the increased smell being due to
the volatile products of the partially decomposed organic matter; and,
by passing the liquid through an open coke-filter, the smell will be
effectually removed. In all cases it must be borne in mind that as
septic tanks and bacterial filters depend for their efficiency on the
organisms they contain, time must be allowed for these to develop and
accumulate before good results are obtained; and for this about six
weeks’ use is generally necessary, after which they will continue to act
for an indefinite period until they become choked by sand and inorganic
matter.
It must not be supposed that the action in the septic tank is wholly
anaerobic; and with weak sewage, most of the organic matter may under
favourable circumstances be converted into nitrates and carbonic acid
by this means only; but generally a much more complete purification is
effected by the subsequent use of “bacterial filters.” These in their
simplest form consist of tanks of about 4 feet deep, filled with coke,
broken bricks, or clinkers, and fitted with drain pipes at the bottom,
by which they can be easily emptied. These tanks, often known as
“contact-beds,” are filled with the sewage or septic tank effluent,
which is allowed to remain on them two hours, and the tank is then
emptied, and allowed a rest of six hours for oxidation and aeration. In
most cases the sewage requires two such treatments, the last often
through a bed with finer coke, in order to be completely freed from
putrescible matter. In place of the intermittent process, as applied on
the contact-beds, continuous aerobic filtration is often employed, the
bed being so constructed as to allow of free admission of air at the
bottom and sides, and the liquid to be purified being distributed on the
surface by a sprinkler, or some similar device, and allowed to trickle
through the bed. The continuous process seems likely to supersede the
intermittent one, as the beds are not only capable of treating a much
larger quantity of sewage in proportion to their area, but are also less
liable to choke. About six weeks is required, with either contact-beds
or continuous filters, before the material they contain becomes coated
with the necessary bacterial layer and they get into full working order.
The results as regards the effluent are perfectly satisfactory, and the
great difficulty and cost consists in the slow but inevitable choking of
the beds, which involves the replacement of the porous material. This is
considerably delayed by the use of a settled or precipitated sewage, and
in this respect, beside its bacteriological function, the septic tank
serves a useful purpose in settling insoluble matter, which is much more
cheaply removed from it than from the filter-beds. It will be obvious
that ordinary settling-tanks, if deep, fulfil many of the functions of
the septic-tank, and both lead to the production of a much more uniform
liquid from the different effluents which the tanner produces, which is
important in the subsequent bacterial purification. A good deal of
interesting information on these subjects will be found in a paper by
Mr. W. H. Harrison on the ‘Bacteriological Treatment of Sewage.’[188]
[188] Journ. Soc. Chem. Ind., 1900, p. 511.
There are a good many patents in connection with the various methods of
sewage purification, and some caution is necessary to avoid their
infringement, though of course the general principles of settling and
filtration, and the destruction of organic matter by bacterial action,
are open to all.
As a general rule the waste-liquors from a tan-yard or leather dye-works
are exceedingly impure. They contain the organic matter (in a state of
great putrefaction) from the soaks, bates and puers; other organic
matter, also more or less putrefied, from the tan-pits; the lime
liquors, with their large proportion of lime and of dissolved
hide-substance, and in addition the various dyes and other chemicals
which may have been used in the conversion of the raw hide into the
finished leather; and hence their efficient purification has presented
difficulties which do not occur in most other trades.
The different waste liquids are best run into a capacious tank, and,
after being thoroughly mixed up together, are allowed to settle for some
hours. By this means the greater part of the tanning matter will combine
with the lime also present to form a heavy, brown insoluble substance;
some of the dye and other organic matter will become entangled in this,
and thus be removed from the liquid. The clear liquid is next run off
into a bacterial filter (preferably a septic tank, followed by an open
coke filter), and then into the nearest stream. If the tannery is near
to a town, and the corporation sewers can be utilised, it is probable
that a filter made of spent tan may be substituted, as this material
will not only remove all excess of lime from the liquid but will also
fix much of the colouring matter as well (Koenig). The tan, after being
used for this purpose, contains so much lime in its pores that it is
said to be useful as manure.
In tanneries where large quantities of disinfectants such as mercuric
chloride, carbolic acid, etc., are used, it is necessary that the mixed
liquids shall contain so much lime as to make them distinctly alkaline.
In this way most of the disinfectants will be either precipitated or
rendered inactive. Where arsenic is used in the limes it may be
advisable to add a little ferrous sulphate (green vitriol or copperas),
in order that the arsenic may form an insoluble compound with the iron,
and so be removed along with the sludge. The ink produced by the action
of the iron salt on the tan liquors will be completely removed by the
bacterial filter.
APPENDICES.
APPENDIX A.
METHOD OF THE INTERNATIONAL ASSOCIATION OF LEATHER TRADES CHEMISTS FOR
THE ANALYSIS OF TANNING MATERIALS. INCLUDING ALTERATIONS ADOPTED AT THE
LEEDS CONFERENCE IN 1902.
SECTION I.--SAMPLING FROM BULK.[189]
[189] See London Report, pp. 22-29 and 124.
1. _Liquid Extracts._--In drawing samples, at least 5 per cent. of the
casks must be taken, the numbers being selected as far apart as
possible. The heads must be removed, and the contents mixed thoroughly
by means of a suitable plunger, care being taken that any sediment
adhering to sides or bottom shall be thoroughly stirred in. All samples
must be drawn in the presence of a responsible person.
2. _Gambier and Pasty Extracts._--Gambier and pasty extracts should be
sampled from not less than 5 per cent. of blocks, by a tubular sampling
tool, which shall be passed completely through the block in seven
places. Solid extracts shall be broken, and a sufficient number of
portions drawn both from the inner and outer parts of the blocks to
fairly represent the bulk. In both cases samples shall be rapidly mixed
and enclosed at once in an air-tight bottle or box, sealed and labelled.
3. _Valonia, Algarobilla, Divi-divi, and General Tanning Materials._
Valonia, algarobilla, and all other tanning materials containing dust or
fibre, shall be sampled, if possible, by spreading at least 5 per cent.
of the bags in layers one above another on a smooth floor, and taking
several samples vertically down to the floor. Where this cannot be done,
the samples must be drawn from the centre of a sufficient number of
bags. While valonia and most materials may be sent to the chemist
ground, it is preferable that divi-divi, algarobilla, and other fibrous
materials shall be unground. Bark in long rind, and other materials in
bundles, shall be sampled by cutting a small section from the middle of
3 per cent. of the bundles with a saw.
4. _Samples for more than one Chemist._--Samples to be submitted to more
than one chemist must be drawn as one sample, and well mixed; then
divided into the requisite number of portions, not less than three, and
at once enclosed in suitable packages, sealed and labelled.
SECTION II.--PREPARATION FOR ANALYSIS.[190]
[190] See London Report, p. 40 _et seq._
1. _Liquid Extracts._--Liquid extracts shall be thoroughly stirred and
mixed immediately before weighing, which shall be rapidly done to avoid
loss of moisture. Thick extracts, which cannot be otherwise mixed, may
be heated to 50° C., then stirred and rapidly cooled before weighing,
but the fact that this has been done must be noted in the Report.
2. _Solid Extracts._--Solid extracts shall be coarsely powdered and well
mixed. Pasty extracts shall be rapidly mixed in a mortar, and the
requisite quantity weighed out with as little exposure as possible, to
avoid loss of moisture. Where extracts are partly dry and partly pasty,
so that neither of these methods is applicable, the entire sample shall
be weighed and allowed to dry at the ordinary temperature sufficiently
to be pulverised, and shall then be weighed, and the loss of weight
taken into calculation as moisture.
In such cases as gambier, in which it is not possible to grind, or by
other mechanical means to thoroughly mix the constituents of the sample,
it is permissible to dissolve the whole, or a large portion of the
sample, in a small quantity of hot water, and immediately after thorough
mixing to weigh out a portion of the strong solution for analysis.
3. _Barks, and other Solid Tanning Materials._--The whole sample, or not
less than 250 grms., shall be ground in a mill until it will pass
through a sieve of 5 wires per centimetre. Where materials such as barks
and divi-divi contain fibrous materials which cannot be ground to
powder, the ground sample shall be sieved, and the respective parts
which do and do not pass through the sieve shall be weighed separately,
and the sample for analysis shall be weighed so as to contain like
proportions.
SECTION III.--PREPARATION OF INFUSION.
1. _Strength of Solution._--The tannin solution employed shall contain
from 0·35 to 0·45 grms. per 100 c.c. of tanning matters absorbed by
hide. (Paris 1900.)
2. _Solution of Liquid Extracts._--A sufficient quantity shall be
weighed into a covered basin or beaker, from which it shall be washed
into a liter flask with boiling water and well shaken, and the flask
shall be filled to the mark with boiling water. The neck being covered
with a small beaker, the flask shall be placed under a cold water tap or
otherwise rapidly cooled to a temperature between 15° and 20° C., and
made up accurately to the mark, after which it shall be thoroughly
mixed, and the filtration at once proceeded with.
_Note._--Tannin infusions may be kept from fermenting by the addition of
3 to 5 drops of essential oil of mustard per liter. (F. Kathreiner.)
3. _Filtration._--The filtration of the solution for analysis may take
place through any paper which may be considered most suitable for the
particular case, and with or without the use of kaolin, absorption of
tanning matter, if any, being corrected for by an amount determined by a
similar filtration of a clear solution. Perfectly clear solutions need
not be filtered.
To determine the correction, about 500 c.c. of the tanning solution of
the strength prescribed for analysis is obtained perfectly clear,
preferably by the method of filtration which is to be corrected for.
After thorough mixing, 50 c.c. is evaporated to determine “total soluble
No. 1.” A portion of the remainder is then filtered in the manner for
which correction is to be made, and 50 c.c. of the filtrate is
evaporated for “total soluble No. 2.” Deducting No. 2 from No. 1 the
difference is the correction required, which must be added to the total
soluble found by analysis. It is generally advisable, both in analysis
and in the second filtration for correction, to filter first 150 c.c.
(which in analysis may be used for the determination of non-tannins),
and then to employ the next 50 c.c. for evaporation, keeping the filter
full during the operation; but whatever procedure is adopted must be
rigidly adhered to in all analyses to which the correction is applied.
Where kaolin is employed, a constant weighed quantity (1 or 2 grm.) must
be used, which is first washed with 75 c.c. of the liquor by
decantation, and then washed on to the filter with a further quantity of
liquor, of which 200 c.c. is filtered as above.[191]
[191] It is obvious that in the first instance it will be necessary to
determine the correction for each particular material employed, but it
will soon be found that the correction is practically constant for
large groups of tanning materials, so long as the same method of
filtration is rigidly adhered to.
4. _Solid Extracts._--Solid extracts shall be dissolved by stirring in a
beaker with boiling water, the undissolved portions being allowed to
settle, and treated with further quantities of boiling water, and the
solution poured into a liter flask. After the whole of the soluble
matter is dissolved, the solution is treated similarly to that of a
liquid extract.
5. _Extraction of Solid Materials._--Such quantities shall be weighed as
will give an infusion of the strength already prescribed. (_Preparation
of Infusion_, Resolution 1.) Not less than 500 c.c. of the infusion
shall be extracted at a temperature not exceeding 50° C., after which
the temperature shall be gradually raised to 100° C.,[192] and the
extraction continued till the percolate is free from tannin and the
whole made up to one liter, the weaker portions of the solution being
first concentrated if necessary by evaporation in a flask, in the neck
of which a funnel is placed.
[192] In substances which, like canaigre, contain a large quantity of
starch, the extraction should be completed at a temperature of 50°
C.--H. R. P.
SECTION IV.--DETERMINATION OF TANNING MATTERS AND NON-TANNINS; ETC.
1. _Total Soluble Matter._--100 c.c.[193] of the clear filtered tanning
solution, or a smaller quantity if the balance employed is of sufficient
delicacy, shall be evaporated in an open weighed basin of platinum, hard
glass, porcelain, or nickel, on the water-bath, and the basin shall
afterwards be dried till constant in an air-oven, at a temperature of
100° to 105° C., or at a temperature not exceeding 100° C. _in vacuo_
till constant, care being taken that no loss occurs by splintering of
the residue. The use of the vacuum-oven for drying the residues is
recommended when possible.
[193] 50 c.c. is sufficient, and is the quantity now generally
employed.
2. _Determination of Non-Tannins._--That the filter method shall remain
the official method until the next Conference, but that members be
permitted to employ the chromed hide-powder method of the American
Association of Official Agricultural Chemists of 1901 (Appendix C) where
it is desired, the fact being clearly stated on the report that the
A.O.A.C. method has been employed, and not that of the I.A.L.T.C.
(Leeds, 1902, see note, p. 480.)
That the “bell form”[194] of filter, as described by Professor Procter,
shall be employed; not less than 5 grms. of hide-powder be used; the
hide-powder should be so packed in the tube that the detannised liquor
shall come over at a rate of about one drop in two seconds; and the
filtrate be rejected so long as it gives a turbidity with a clear
tanning solution. The filtrate may be used for the determination of
non-tannin so long as it gives no reaction with salted gelatine
solution.[195] The first 30 to 35 c.c. should be thrown away, and the
next 50 c.c. of detannised solution, or an aliquot part of it,
evaporated in a weighed basin on a water bath, and then dried till
constant in an air-oven at a temperature of 100° to 105° C., or, _in
vacuo_, not exceeding 100° C.
[194] It is obvious that the exact form and dimensions of the filter
must be adapted to the character of the hide-powder available, as
considerable differences exist in the absorptive power of different
samples.
[195] 8 to 9 grams of good gelatine are dissolved in 500 c.c. of hot
water, 100 grams of salt added, and the whole cooled and filtered.
3. _Hide-Powder._--That the hide-powder must be sufficiently absorbent
for use in the filter, and that in a blank experiment conducted with
distilled water in the same way as an analysis, the residue from the
evaporation of 50 c.c. should not exceed 5 milligrams.
The Freiberg Hide-Powder, made by Mehner and Stransky, containing
between 10 and 20 per cent. of cellulose (as suggested by Cerych), is
recommended by the Conference (Liège, 1901) and is very suitable for the
filter method; but the powder, when analysed by the Kjeldahl method and
calculated to 18 per cent. of moisture, must not contain less than 11·5
per cent. of nitrogen (Leeds, 1902).
4. _Determination of Moisture and “Total Dry Matter.”_--That the
moisture in the sample be determined by drying a small portion at the
temperature adopted in the determination of the “total soluble.” In
extracts yielding turbid solutions which can be thoroughly mixed, it is
generally preferable after mixing the solution and before filtration, to
measure off and evaporate 50 c.c. for the determination of total dry
matter (and moisture) in the same manner as the “total soluble.”
5. _Statement of Results._--It is recommended, when full analysis is
given, that the Statement should be made in the following manner:--
(1) _Tanning Matters Absorbed by Hide._--Obtained by deducting the
“soluble non-tanning matters” found by evaporating the hide-powder
filtrate from the “total soluble.”
(2) _Soluble Non-Tanning Matters._--Found by evaporation of filtrate
from hide-powder filter.
(3) _Insoluble._--By deducting “total soluble matter” from the “total
dry matter.”
(4) _Moisture._--Determined by drying a portion at the temperature
adopted in the determination of “total soluble.”
If other determinations are given they shall form a separate additional
statement.
_Density._--The statement of densities of extracts, etc., should be
given as specific gravity in preference to arbitrary degrees, such as
Baumé, Twaddell, etc.
SECTION V.--COLOUR MEASUREMENT.
_Colour Measurement._--It is recommended that the method used by English
chemists, namely, measuring with Lovibond’s Tintometer (as described by
Professor Procter and Dr. Parker, Journ. Soc. Chem. Ind., 1895, 125),
shall be used, and the results stated in units of red, yellow and
black. The measurement may be made on the solution used for analysis,
but must be calculated to one containing 0·5 per cent. of tanning
matter, in a centimetre cell.
ANALYSIS OF USED LIQUORS.
It was decided at Liège, 1901, and Leeds, 1902,[196] that the “Shake
Method” with chromed hide-powder, of the American Association of
Official Agricultural Chemists, 1901 (A.O.A.C.), should be employed in
the detannisation of used tanning liquors, as with these the filter
method is apt to give too high results owing to the amount of
non-volatile acids which they contain. The method of the A.O.A.C. is
given in Appendix C.
[196] Procter and Blockey quoted experiments at the Leeds Conference,
proving that gallic acid and some other non-tanning substances were
largely absorbed by the hide-powder filter, though probably not
permanently retained by leather; while the error, though still
considerable, was much less when the chromed hide-power shake method
was employed. Where only gallotannic and gallic acids are present, as
in the case of sumach and commercial gallotannic acids, the most
accurate quantitative estimation is probably that by the Löwenthal
method carried out as described L.I.L.B., p. 123, but considerable
skill is required in its execution.
ANALYSIS OF SPENT TANS.
It was decided at Leeds, 1902, that spent tans must be analysed like
fresh tanning materials; but where the prescribed strength of solution
cannot otherwise be obtained it is permissible to concentrate the entire
solution by evaporation. It is advisable, where suitable apparatus is
available, to concentrate _in vacuo_; but failing this, an ordinary
flask may be used, in the neck of which a funnel is placed.
APPENDIX B.--THE DECIMAL SYSTEM.
The metrical system of weights and measures, and the Centigrade
thermometer scale have been generally used throughout the book, as more
international and scientific than the complicated systems still
unfortunately in use in this country. They have been fully explained in
the Author’s ‘Laboratory Book,’ p. 2; but as this is not always at hand,
a short sketch may be permitted here.
The basis of the metrical system is the “meter,” which is approximately
¹⁄₁₀,₀₀₀,₀₀₀ of the distance from the earth’s pole to the equator, and
is equal to 39·3708 English inches, and for many practical purposes may
be roughly reckoned as 40 inches. The meter is divided into 10 parts or
“decimeters,” 100 parts or “centimeters,” and 1000 parts or
“millimeters.” The standard of capacity is a cube of 1 decimeter, or
about 4 inches, and consequently contains 1000 cubic centimeters, and is
denominated a “liter.” The standard of weight is 1 cubic centimeter of
water (at 4° C.), which is called a “gram.” Hence 1 liter of water
weighs 1 “kilogram,” or 1000 grams. 1 cubic meter of water contains 1000
liters, and weighs 1000 kilograms, or 1 metrical ton (2200 lb. English).
For purposes of reduction, the following figures may be given:--
1 gram = 15·431 grains. 1 lb. av. = 453·6 grams.
1 liter = 0·22 gallon. 1 gallon = 4·543 litres.
Actual reduction is, however, generally unnecessary if the question be
treated as one of proportion. Thus a solution of 1 gram per liter is of
the same strength as one of 1 lb. per 100 gallons (1000 lb.), and very
approximately, as one of 1 oz. avoirdupois per cubic foot. In the case
of pits, it is often simplest to measure them directly with a meter
rule; length, breadth and depth, measured in decimeters and multiplied
together, giving the contents in liters, and, in the case of water, the
weight in kilograms.
The Centigrade or Celsius thermometer divides the difference between the
freezing and the boiling points of water into 100°. The following table
gives the points at which its scale agrees without fractions with that
of Fahrenheit:
COMPARISON OF CENTIGRADE AND FAHRENHEIT DEGREES.
°C. °F.
-20 -4
-15 +5
-10 14
-5 23
0 32
5 41
10 50
15 59
20 68
25 77
30 86
35 95
40 104
45 113
50 122
55 131
60 140
65 149
70 158
75 167
80 176
85 185
90 194
95 203
100 212
105 221
110 230
115 239
APPENDIX C.
OFFICIAL METHOD FOR ANALYSIS OF TANNING MATERIALS, ADOPTED AT THE
EIGHTEENTH CONVENTION OF THE AMERICAN ASSOCIATION OF OFFICIAL
AGRICULTURAL CHEMISTS, 1901.
I. PREPARATION OF SAMPLE.
Barks, woods, leaves, dry extracts, and similar tanning materials should
be ground to such a degree of fineness that they can be thoroughly
extracted. Fluid extracts must be heated to 50° C., well shaken, and
allowed to cool to room-temperature.
II. QUANTITY OF MATERIAL.
In the case of bark and similar material, use such quantity as will give
about 0·35 to 0·45 gram tannins per 100 c.c. of solution, extract in
Soxhlet or similar apparatus at steam-heat for non-starchy materials.
For canaigre and substances containing like amounts of starch use
temperature of 50° to 55° C., until near complete extraction, finishing
the operation at steam-heat. In case of extract, weigh such quantity as
will give 0·35 to 0·45 gram tannins per 100 c.c. of solution, dissolve
in 900 c.c. of water at 80° C., let stand twelve hours, and make up to
1000 c.c.
III. MOISTURE.
(_a_) Place 2 grams, if it be an extract, in a flat-bottom dish, not
less than 6 cm. in diameter, add 25 c.c. of water, warm slowly till
dissolved, continue evaporation and dry.
(_b_) All dryings called for, after evaporation to dryness on
water-bath, or others, shall be done by one of the following methods,
the soluble solids and non-tannins being dried under similar, and so far
as possible identical conditions:
1. For eight hours at the temperature of boiling water in a steam bath.
2. For six hours at 100° C., in an air bath.
3. To constant weight _in vacuo_ at 70° C.
IV. TOTAL SOLIDS.
Shake the solution, and without filtering immediately measure out 100
c.c. with a pipette, evaporate in a weighed dish, and dry to constant
weight, at the temperature of boiling water. Dishes should be
flat-bottomed, and not less than 6 cm. in diameter.
V. SOLUBLE SOLIDS.
Double-pleated filter paper (S. and S., No. 590, 15 cm.) shall be used.
To 2 grams of kaolin add 75 c.c. of the tanning solution, stir, let
stand fifteen minutes, and decant as much as possible. Add 75 c.c. more
of the solution, pour on filter, keep filter full, reject the first 150
c.c. of filtrate, evaporate the next 100 c.c. and dry. Evaporation
during filtration must be guarded against.
VI. NON-TANNINS.
Prepare 20 grams of hide-powder by digesting twenty-four hours with 500
c.c. of water, and adding 0·6 gram chrome alum in solution, this
solution to be added as follows. One-half at the beginning and the other
half at least six hours before the end of the digestion. Wash by
squeezing through linen, continue the washing until the wash-water does
not give a precipitate with barium chloride. Squeeze thoroughly by hand,
and remove as much water as possible by means of a press, weigh the
pressed hide, and take approximately one-fourth of it for moisture
determination. Weigh this fourth carefully and dry to constant weight.
Weigh the remaining three-fourths carefully and add them to 200 c.c. of
the original solution; shake ten minutes, throw on funnel with cotton
plug in stem, return until clear, evaporate 100 c.c. and dry. The weight
of this residue must be corrected for the dilution caused by the water
contained in the pressed hide-powder.[197] The shaking must be done in
some form of mechanical shaker. The simple machine used by druggists,
and known as the milk-shake, is recommended.
[197] For method of correction, see p. 313.
PROVISIONAL METHOD.--To 14 grams of dry chromed hide-powder in a shaker
glass add 200 c.c. of the tannin solution, let stand two hours, stirring
frequently, shake fifteen minutes, throw on funnel with a cotton plug in
the stem, let drain, tamp down the hide-powder in the funnel, return the
filtrate until clear and evaporate 100 c.c.
VII. TANNINS.
The amount of these is shown by the difference between the soluble
solids and the corrected non-tannins.
VIII. TESTING HIDE-POWDER.
(_a_) Shake 10 grms. of hide-powder with 250 c.c. of water for five
minutes, strain through linen, squeeze the magma thoroughly by hand;
repeat this operation three times, pass the last filtrate through paper
(S. and S. No. 590, 15 cm.) till clear, evaporate 100 c.c. and dry. If
this residue amounts to more than 10 mg. the hide must be rejected.
(_b_) Prepare a solution of pure gallo-tannin by dissolving 6 grams in
1000 c.c. of water. Determine the total solids by evaporating 100 c.c.
of this solution and drying to constant weight. Treat 200 c.c. of the
solution with hide-powder exactly as described in paragraph 6. The
hide-powder must absorb at least 95 per cent. of the total solids
present. The gallo-tannin used must be completely soluble in water,
alcohol, acetone and acetic ether, and should not contain more than 1
per cent. of substances not removed by digesting with excess of yellow
mercuric oxide on steam-bath for two hours.
IX. TESTING NON-TANNIN FILTRATE.
(_a_) _For Tannin._--Test a small portion of the clear non-tannin
filtrate with a few drops of a 1 per cent. solution of Nelson’s gelatin.
A cloudiness indicates the presence of tannin, in which case repeat the
process described under VI., using 35 instead of 20 grams of
hide-powder.
(_b_) _For Soluble Hide._--To a small portion of the clear non-tannin
filtrate add a few drops of the filtered tannin solution. A cloudiness
indicates the presence of soluble hide, in which case repeat the process
described under VI., giving the hide-powder a more thorough washing.
The temperature of solutions shall be between 16° and 20° when measured
or filtered. All dryings should be made in flat-bottomed dishes of at
least 6 cm. diameter, S. and S. No. 590, 15 cm. filter paper should be
used in all filtrations.
APPENDIX D.
The following Lists of Colours have been furnished by Mr. M. C. Lamb,
Director of the Leather Dyeing Department of Herold’s Institute, London,
who has devoted much time to testing the various dyes with regard to
their permanence and suitability for leather. Many of the colours have
also been tested and found satisfactory in the Leather Department of the
Yorkshire College. The following abbreviations of makers’ names are used
in the lists:--
B. BASLER CHEMISCHE FABRIK, A. G. Basle, Switzerland.
B.A.S.F. BADISCHE ANILIN UND SODA FABRIK. Ludwigshafen a. Rhine,
Germany.
Ber. BERLIN ANILINE CO. Berlin S.O., Germany.
B.S. Spl. BROOKE, SIMPSON & SPILLER. Atlas Dye Works, Hackney Wick,
London, N.E.
By. FARBEN-FABRIKEN, late BAYER & CO. Elberfeld, Germany.
C. L. CASSELLA & CO. Frankfort a. Main, Germany.
C.A. FRENCH ANILINE COLOUR WORKS. Vieux-Conde (Norde), France.
C. & R. CLAUS & RÉE. Clayton, near Manchester.
D. DAHL & CO. Barmen, Germany.
D. & H. DURAND, HUGUENIN & CO. Basle, Switzerland.
G. R. GEIGY & CO. Basle, Switzerland.
Ger. GERBER & CO. Basle, Switzerland.
K. KALLE & CO. Bierbrich a. Rhine, Germany.
Leon. A. LEONHARDT & CO. Muhlheim a. Main, Germany.
Leitch J. W. LEITCH. Milnsbridge Chemical Works, Huddersfield.
Lev. LEVINSTEIN LTD. 21 Minshull Street, Manchester.
M.L.B. MEISTER, LUCIUS & BRUNING. Hoechst a. Main, Germany.
Mo. GILLIARD, P. MONNET & GARTIER. Lyons, France.
N. NOETZEL, ISTEL & CO. Griesheim a. Main, Germany.
O. K. OEHLER & CO. Offenbach a. Main, Germany.
P. ST. DENIS DYESTUFF CO., late POURIER. St. Denis, near
Paris.
R. SOCIÉTE CHIMIQUE DES USINES DU RHONE. Lyons, France.
R. H. & S. READ, HOLLIDAY & SONS. Huddersfield.
S.C.Ind. SOCIETY OF CHEMICAL INDUSTRY. Basle, Switzerland.
Uer. CHEMISCHE FABRIKEN. Uerdingen a. Rhein, Germany.
W. Bros. WILLIAMS BROS. & CO. Hounslow, Middlesex.
STAINING.
SINGLE ACID DYES SUITABLE FOR STAINING VEGETABLE TANNED LEATHER.
_Browns._
Solid brown. (M.L.B.)
Acid brown. (W. Bros.)
Brown A2. (B.S. Spl.)
Brown A1. (B.S. Spl.)
Mikado brown B. (Leon.)
New acid brown. (B.S. Spl.)
Bronze acid brown. (By.)
Golden brown Y. (C.), (By.)
Acid anthracene brown R. (By.)
Fast brown N. (B.A.S.F.)
Nut brown A. (C.)
Fast brown. (By.)
Fast brown G. (Ber.)
Resorcin brown. (Ber.)
Resorcin brown. (D.)
Acid brown. (Ber.)
Dark nut brown. (W. Bros.)
Acid brown R. (C.)
Acid brown R. (Uer.)
Acid brown R. (R. H. & S.)
New golden brown A1. (C.)
Dark brown. (C.)
Acid brown L. (B.A.S.F.)
Acid brown D. (C.)
_Yellows._
Azo yellow. (Uer.)
Phosphine subst. (B.S. Spl.)
Chrysoine. (W. Bros.)
Azo-acid-yellow. (Ber.)
New phosphine G. (C.)
Cuba yellow 2072. (S.C. Ind.)
Cuba yellow (W. Bros.)
Azo-flavine RS. (C.) and (B.A.S.F.)
Azo-flavine 3R. (B.A.S.F.)
Indian yellow R. (By.)
Turmeric yellow. (G.)
Solid yellow G. (Leon.)
Solid yellow B. (Leon.)
Indian yellow R. (C.)
Cuba yellow. (C.)
Napthol yellow S. (By.), (C.), (B.A.S.F.)
Turmeric yellow. (C.), (G.)
Fast acid yellow. (C.A.)
_Reds and Oranges._
Scarlet R. (By.)
Crocein scarlet 3BN. (By.)
Orange 2. (M.L.B.), (S.C. Ind.), (C.) and (B.A.S.F.)
Orange 2B. (By.)
Mandarin G extra. (Ber.)
Brill. crocein M.O.O. (C.)
Bordeaux G. (By.)
Atlas orange. (B.S. Spl.)
Bordeaux cov. (Ber.)
Fast red 21528. (By.)
Fast red A. (Leon.), (By.), (Ber.), and (B.A.S.F.)
Bordeaux B. (M.L.B.)
_Greens._
Acid green extra conc. (C.)
Guinea green B. (Ber.)
Guinea green G. (Ber.)
Acid green GG. (By.)
Acid green BB. (By.)
Acid green B. (By.)
Acid green G. (By.)
Acid green 000. (Leon.)
Acid green extra. (By.)
Acid green (Uer.)
Acid green (R. H. & S.)
Light green SF. (B.A.S.F.)
Erioglaucine. (G.)
_Violets._
Acid violet 4RS. (Ber.)
Acid violet 7B. (Ber.)
Acid violet 6B. (By.)
Formyl violet S4B. (C.)
_Blues._
Bavarian blue D.B. (Ber.)
Marine blue o. (K.)
Solid blue. (M.L.B.)
Blue 1. (Lev.)
Blue 2. (Lev.)
Blue 3. (Lev.)
SINGLE BASIC DYES SUITABLE FOR STAINING VEGETABLE TANNED LEATHER.
_Browns._
Bismark brown GG. (C.)
Chrysoidine AG. (O.)
Bismark brown 2B. (K.)
Bismark brown (By.)
Bismark brown R.C.E. (Lev.)
Bismark brown M. (By.)
Vesuvine conc. (M.L.B.)
Vesuvine conc. (B.A.S.F.)
Bismark brown C extra. (Leon.)
Bismark brown RS. (B.S. Spl.)
Bismark brown 3762. (W. Bros.)
Rheonine A. (B.A.S.F.)
Rheonine N. (B.A.S.F.)
Brown R. (G.)
Brown G. (G.)
Manchester brown. (C.)
_Yellows._