The bleaching of goods, which are never laid down on the green, and
which are not dried between two operations, may be completed in a couple
of days. They answer as well for the printer as the others, and they are
as white. Cotton fibres or yarns suffer no diminution of their strength,
when the cloth has been properly treated in the above described
processes.
Accurate experiments have demonstrated that their strength is not
impaired by being boiled in milk of lime for two hours at the ordinary
pressure, provided they be constantly kept covered with liquid during
the whole ebullition, and that they be well washed immediately
afterwards; or, by being boiled in pure water under the pressure of ten
atmospheres of steam; or by being boiled under the same pressure in a
caustic soda ley, marking 3° of Tweedale, or specific gravity 1·015,
though it has increased to double the density in the course of the boil,
by the escape of the steam; or by being boiled under the atmospheric
pressure at 14° of Tweedale, or specific gravity 1·070; or by being
immersed for eight hours in chloride of lime, capable of decolouring
three times its bulk, of test solution of indigo (see CHLORINE); and by
being afterwards dipped in sulphuric acid of specific gravity 1·067,
Tweedale 14°; or by being steeped for eighteen hours in sulphuric or
muriatic acid of specific gravity 1·035, 7° Tweedale.
In other well-conducted bleach-works the following is the train of
operations:-- 1. Cleansing out the weaver’s dressing by steeping the
cloth for twelve hours in cold water, and then washing it at the stocks
or the dash-wheel. 2. Boiling in milk of lime, of a strength suited to
the quality of the goods, but for a shorter time than with the soda ley;
two short operations with the lime, with intermediate washing, being
preferable to one of greater duration. 3 and 4. Two consecutive leys of
ten or twelve hours’ boiling, with about two pounds of soda crystals for
1 cwt. of cloth. 5. Exposure to the air for six or eight days, or the
application of the chloride of lime and the sulphuric acid. 6. A ley of
caustic soda, like the former, sometimes with less alkali. 7. Exposure
to the air for six or eight days, or chlorine and the sour, as above. 8.
Caustic soda ley, as before. 9. Chlorine and the sour. 10. Rinsing in
hot water, or scouring at the dash-wheel.
If the number of vessels to be heated exceeds four or five, there is an
economy in using steam as the medium of heat; but under this number
there is an advantage in the direct application of fire to a boiling or
bucking apparatus; since when only two vessels are in activity, there is
a waste of fuel by the extra steam power. It deserves to be remarked
also, that the increase of the bulk of the liquid by the condensation of
the steam, does not permit the spent white ley to be turned to use for
the green goods, on account of its excessive dilution. With the milk of
lime boil, however, this dilution would be rather an advantage.
It has been found that the introduction of bran into the fermenting
steep (when this is used) endangers the texture of the goods, by causing
a putrefactive fermentation in some places.
When in the milk of lime boil there is too much of this caustic earth,
or when it is poured in on the top of the goods, they are apt to suffer
damage. The milk of lime should be introduced from beneath into the
under compartment of the bucking apparatus. For the same reason, after
the caustic soda lye, the vessel should be filled up with water, if the
goods be not immediately transferred to the dash-wheel. When they are
allowed to become partially dry on the top, they are easily injured. The
copper of the bucking apparatus ought to be of a size proportioned to
that of the surmounting crib or vat; for when it is too small, the
liquid is too long of being brought into proper circulation, and the
goods may be meanwhile injured. In a bucking apparatus, which requires
five or six hours to be brought into full play, those goods are very apt
to be injured, which lie immediately under the overflow pipe.
When the chloride of lime steep is too strong, sometimes small round
holes are made in the calico, just as if they had been cut out by a
punch, especially in the borders or thicker parts of the goods. This
accident is owing to the presence of bubbles of chlorine. From the
saturated state of the liquid, they remain gaseous a sufficient length
of time for corroding the parts of the cloth with which they are in
contact. These will be obviously the denser parts, for they confine the
gas most completely, or prevent its diffusion through the mass. This
evil is prevented by diluting the chloride steep to the proper degree,
and moving the goods through it.
The greasy spots, described above, show themselves in the maddering by
attracting the dye-stuff more copiously than the pure parts of the
cloth, so as to mottle it; they are also recognised in the white goods
by being somewhat repulsive of moisture. When the combination of fatty
matters with chlorine takes place at the surface of cotton goods, it is
of a nature to resist the action of alkalies. It is the stearine, or the
principle of suet, particularly, which, by this means, acquires such a
strong affinity for cottons; the elaine, or the principle of oils, has
no such remarkable affinity. Lime, in some circumstances, seems to act
as a mordant to greasy matters, and to fix them fast. Hence the weaver
should be prohibited, in all cases, from allowing candle-grease to touch
his web. Goods soiled with it should never be allowed to lie by in the
warehouse, but be immediately cleansed before the air has fixed the
stearine by converting it into margaric acid. Lime should, in these
cases, be prudently employed; chlorine should never be used till the
greasy stains are thoroughly removed; and the bleacher should never
warrant his pieces for the printer till he has verified some of them by
the water test.
I shall conclude this general analysis of the principles of bleaching by
a few precepts. Avoid lime, at the first ley, for goods which contain
greasy spots; but use it freely after one or two soda leys, and apply
two soda leys after it. Do not apply chlorine between these leys, but
reserve it for the final operation. By this plan the goods will be well
bleached, and very little worn. Use the souring steeps freely, giving
them after each ley, whether of lime or soda, since the calcareous base,
with which the greasy spots get charged merely from hard water, is an
obstacle to the further action of the leys.
I shall now give some practical instructions concerning the several
steps of the bleaching process, as applied to cotton, linen, silk, and
wool.
The first thing which the cotton bleacher does, is to mark the pieces
with the initials of the owner, by means of a stamp imbued with coal
tar. The linen bleacher marks with nitrate of silver, a far more
expensive substance, but one which resists better the severer treatment
which his goods are destined to undergo.
The cotton goods are generally singed before they are sent to the
bleacher, and this is done either by passing them rapidly over a red-hot
semi-cylinder of iron, or over a row of gas flames, by Mr. Hall’s
ingenious contrivance. (See SINGEING.) Each piece is next creased
together lengthwise like a rope, folded into a bundle, and fixed by a
noose at the end. In this open state it is easily penetrated by the
water of the soaking cistern into which it is thrown. It is then scoured
by the dash or wash-wheel. It is now ready for the bucking or steaming
apparatus, where it is treated with milk of lime. The steam chamber
resembles the bucking vessel, without its bottom copper; that is to say,
a few inches below the grated bottom of the bucking tub, there is a
close iron sole, through the centre of which the steam is admitted by
several small apertures, for the purpose of diffusing it throughout the
goods, and causing a liquid circulation by its pressure, as the steam
does in the proper bucking boiler. One pound of lime previously made
into a cream consistenced mixture, and passed through a sieve, is used
for every thirty or forty pounds of cloth, according to its colour and
texture; and this cream mixed with more water is interstratified with
the pieces, as they are laid regularly in the vessel. Whenever this is
stocked with goods, all their interstices are filled up with water.
After the lime bucking, the cloth is transferred to the dash-wheel.
A pound of cloth requires for its whitening about half a pound of good
average chloride of lime or bleaching powder, as it is commonly called,
and this ought to be dissolved in about three gallons of water. Mr. Crum
of Thorniebank, near Glasgow, an extensive and excellent bleacher, has
so modified Dr. Dalton’s ingenious plan of testing the power of
bleaching liquors by green sulphate of iron, as to give it much greater
precision for the bleacher’s use, than the discolouration of indigo
originally proposed by Berthollet. Mr. Crum dissolves four ounces of
fresh green vitriol in hot water, and then adds the solution of
bleaching powder by small quantities at a time, till the iron becomes
wholly peroxidised, when the smell of chlorine will become perceptible.
When the bleacher has once found by trial the proper blanching power
which his chlorine steep ought to have, he can verify its standard, by
seeing how much of it must be added to an ounce, or any given weight of
fresh copperas, dissolved in hot water, to cause the peroxidisement and
the exhalation of the peculiar odour. M. Gay Lussac’s new method by
arsenious acid will be described under chlorine. From the experiments
which I made some years ago[9], upon indigo, it will be seen that this
dye stuff is so variable in its quantity of colouring matter, that no
two chemists operating with it independently, as a test for chloride of
lime, could arrive at the same result. They must provide themselves with
absolute indigo, by an expensive and troublesome process, not suited to
the busy bleacher. The vitriolage, as the French term it, or the souring
of the English bleacher, consists in immersing the goods for four hours
in dilute sulphuric acid, containing one gallon of oil of vitriol to
from 25 to 30 of water, thoroughly intermixed by stirring; for the
density of the acid is an obstacle to its equal distribution through the
water. This dilute acid will have a density of from 1·047 to 1·040, and
will contain from 7 to 6-1/2 per cent. by weight of the oil of vitriol.
[9] Quarterly Journal of Science, Literature, and the Arts, vol. vii.
p. 160.
The goods are now washed, and then boiled for eight or nine hours in an
alkaline ley, containing about two pounds of crystals of soda, or their
equivalent in soda ash or pearl-ash, for every 100 lbs. of cloth. The
ley must be made previously caustic by quick lime. A washing in the
wheel follows this boil; and then a chlorine steep for five hours in a
liquor two thirds of the strength of the former. It is next soured in
the dilute sulphuric acid, for two, three, or four hours, according to
the colour and quality of the cotton, and then thoroughly washed.
The cloth is now bleached white, but cannot be presented in the market
till it undergoes certain finishing processes. The piece is elongated
from the folds which it contracts during the rotation of the dash-wheel,
by being thrown into a stream of water in a cistern, terminated by the
squeezing rollers, which take in the end of the piece, and run it
through between them, with the effect of making it nearly dry. Two
pieces of cloth pass simultaneously through the rollers, and are
disentangled spontaneously, so to speak, without the help of hands.
[Illustration: 117 118]
The squeezing rollers or squeezers, for discharging the greater part of
the water from the yarns and goods in the process of bleaching, are
represented in _figs._ 117, 118., the former being a side-view, to show
how the roller gudgeons lie in the slots of the frame, and how the shaft
of the upper roller is pressed downward by a weighted lever, through a
vertical junction road, jointed at the bottom to a nearly horizontal
bar, on whose end the proper weight is hung. In _fig._ 118. these
rollers of birch-wood are shown in face; the under one receiving motion
through the toothed wheel on its shaft, from any suitable power of water
or steam. Upon the shaft of the latter, between the toothed wheel and
the roller, the lever and pulley for putting the machine into and out of
geer is visible. The under roller makes about 25 revolutions in the
minute, in which time three pieces of goods, stitched endwise, measuring
28 yards each, may be run through the machine, from a water trough on
one side, to a wooden grating upon the other.
When the goods are run through, they are carried off upon a grated
wheelbarrow, in a nearly dry state, and transferred to the spreading
machine, called at Manchester a _candroy_. In many bleach-works,
however, the creased pieces are pulled straight by the hands of women,
and are then strongly beat against a wooden stock to smooth out the
edges. This being done, a number of pieces are stitched endwise
together, preparatory to being mangled.
[Illustration: 119 120 121]
_Calender._--_Fig._ 120. is a cross section of this machine, and _figs._
119. 121. are front views broken off. The goods are first rolled upon
the wooden cylinder _a_, near the ground; by the tension roller _b_,
upon the same cylinder, the goods receive a proper degree of stretching
in the winding off. They then pass over the spreading bars _c c c_, by
which they are still more distended; next round the hollow iron cylinder
_d_, 16 inches diameter, and the paper cylinder _e_, of like dimensions;
thence they proceed under the second massive iron cylinder _f_, of 8
inches diameter, to be finally wound about the projecting wooden roller
_g_. This is set in motion by the pulleys _h_, _fig._ 121., and _i_,
_fig._ 120., and receives its proper tension from the hanging roller
_k_; _l_ is a press cylinder, of 14 inches diameter, made of plane-tree
wood. By its means we can at all times secure an equal degree of
pressure, which would be hardly possible did the weighted lever press
immediately upon two points of the calender rollers. The compression
exercised by the cylinders may be increased at pleasure by the bent
lever _m_, weights being applied to it at _n_. The upper branch of the
lever _o_ is made fast by screws and bolts at _p_, to the upper
press-cylinder. The junction leg _q_ is attached to the intermediate
piece _r_, by left and right-handed screws, so that according as that
piece is turned round to the right or the left, the pressure of the
weighted roller will be either increased or diminished. By turning it
still more, the piece will get detached, the whole pressure will be
removed, and the press-roller may be taken off; which is a main object
of this mechanism.
The unequable movement of the cylinders is produced by the wheels _s t
u_, of which the undermost has 69, the uppermost has 20, and the
carrier-wheel _t_, either 33, 32, or 20 teeth, according to the
difference of speed required. The carrier-wheel is bolted on at _v_, and
adjusted in its proper place by means of a slot. To the undermost iron
cylinder, the first motion is communicated by any power, for which
purpose either a rigger (driving pulley) is applied to its shaft at _u_,
or a crank motion. If it be desired to operate with a heated calender,
the undermost hollow cylinder may be filled with hot steam, admitted
through a stuffing box at one end, and discharged through a stuffing box
at the other, or by a red-hot iron roller.
Pure starch would be too expensive a dressing for common calico
shirtings, and therefore an extemporaneous starch is made by mixing one
pound of flour with one gallon of water, and allowing the mixture to
ferment in a warm place for twenty-four hours. In this way, a portion of
_lactic_ acid is formed, which dissolves the gluten, or separates it
from the starch; so that when the whole is thrown upon a sieve, a liquid
paste passes through, which, being boiled, answers well for stiffening
the goods, without giving them a gray tinge. The paste is thinned with
water to the desired degree, and faintly tinged with solution of indigo.
The starch, which is sometimes thickened with porcelain clay, Paris
plaster, or Spanish white, is put into a trough, and is evenly imparted
to the cloth as this is drawn down through it, by the traction of
rollers. There is a roller near the bottom of the trough, round which
the cloth is made to run, to secure its full impregnation; while the
upper rollers serve to expel its excess of the starch, and throw it back
into the cistern. See STARCHING APPARATUS.
The goods are next dried in an apartment heated by two, three, or more
flues, running along the floor, and covered usually with fire-tiles. At
first the heat is moderate, but it is gradually raised to upwards of
110° F.
The goods must now be passed again through the calender, in order to
receive their final smoothness and lustre. They are in the first place
damped with a peculiar machine, furnished with a circular brush, whose
points revolve in contact with water in a trough placed beneath them,
and sprinkle drops of water upon the goods as they are drawn forwards by
a pair of cylinders. They are then subjected to the powerful pressure of
the calender rollers.
The calendered pieces are neatly folded into compact parcels, and
stamped with the marks of each particular manufacturer, or various
devices to suit the markets for which they are designed. They are
finally piled on the sole of an hydraulic press, with a sheet of
pasteboard between each piece; but with occasional plates of iron to
secure uniformity of pressure throughout. When sufficiently condensed by
the press, they are taken out, and despatched to their respective
manufacturers in a state ready for sale.
There are no less than 25 steps in the bleaching of calicoes, many of
them effected with expensive machinery; yet the whole do not produce to
the bleacher more than 10 pence per piece, of 24 yards.
The following system was pursued a few years back, by a skilful bleacher
of muslins near Glasgow:--
“In fermenting muslin goods, we surround them with our spent leys, from
the temperature of 100° to 150° F., according to the weather, and allow
them to ferment for 36 hours. In boiling 112 lbs. = 112 pieces of
yard-wide muslin, we use 6 or 7 lbs. of pearl-ashes, and 2 lbs. of soft
soap, with 360 gallons of water, and allow them to boil for 6 hours;
then wash them, and boil them again with 5 lbs. of pearl-ashes, and 2
lbs. of soft soap, and allow them to boil 3 hours; then wash them with
water, and immerse them into the solution of oxymuriate of lime, at 5 on
the test-tube, and allow them to remain from 6 to 12 hours; next wash
them, and immerse them into dilute sulphuric acid at the specific
gravity of 3-1/2 on Tweedale’s hydrometer = 1·0175, and allow them to
remain an hour. They are now well washed, and boiled with 2-1/2 lbs. of
pearl-ashes, and 2 lbs. of soft soap for half an hour; afterwards washed
and immersed into the oxymuriate of lime as before, at the strength of 3
on the test-tube, which is stronger than the former, and allowed to
remain for 6 hours. They are again washed, and immersed in diluted
sulphuric acid at the specific gravity of 3 on Tweedale’s hydrometer =
1·015. If the goods be strong, they will require another boil, steep,
and sour. At any rate, the sulphuric acid must be well washed out before
they receive the finishing operation with starch.
“With regard to the lime, which some use instead of alkali immediately
after fermenting, the same weight of it is employed as of pearl-ashes.
The goods are allowed to boil in it for 15 minutes, but not longer,
otherwise the lime will injure the fabric.”
More recently the plan adopted is as follows; by which the purest whites
are produced for the London market.
“Lime is seldom used for our finer muslin goods, as it is found to
injure their fabric, and the colours do not keep for any length of time.
“An alkaline ley is made by boiling equal weights of lime and soda
together for an hour: this alkali is used for boiling goods the same as
potash, but without soap.
“In finishing jacounets or muslins, after washing them from the sour,
they are run through spring-water containing a little fine smalts, which
give them a clear shade; if of a coarse fabric, a little well-boiled
starch is added to the water. From this they are wrung or pressed, and
taken up by the selvage for the breadthing frame, and are run off it
upon a tin cylinder heated by steam, by which the piece is completely
dried in 15 minutes: it is then stripped from the cylinder, neatly
folded and pressed, which finishes the piece for the market. From 6_d._
to 9_d._ per piece of 12 yards is obtained for the bleaching and
finishing of those goods.
“Book muslins, after being washed from the sour, are wrung or pressed;
then they are hung up to dry in a heated stove, previous to being put
into starch, prepared by boiling 3 lbs. of it to every 5 gallons of
water, with 20 ounces of smalts: they are wrung out of this starch, and
taken to a room heated to 110° F.; the starch is wrought into the piece
till clear, then taken into a cold room, and the selvages dressed or
set, before being put on the breadthing frame in the heated stove, where
the piece is stretched to its length, while three or four persons at
each selvage keep the piece to its breadth. If a stiff finish is wanted,
they keep exactly opposite each other; but in breadthing the piece of
elastic, they cross the piece in breadthing, which gives it a springy
elastic finish. From 9_d._ to 15_d._ per piece of 12 yards is obtained
for the bleaching and finishing of these goods.
“Sewed trimmings, flounces, and dresses are run through spring water
containing fine smalts with a little well-boiled starch. They are then
taken to the drying stove, where they are stented till dry, which
finishes the piece for the market. From 6_d._ to 8_d._ per piece is
obtained for trimmings and flounces, and from 9_d._ to 1_s._ for
dresses, bleaching and finishing.”
In the bleaching of cotton cloth, where fixed colours are previously
dyed in the yarn before it is woven into cloth, such as the Turkey or
Adrianople red, and its compounds of lilac or purple, by the addition of
iron bases, various shades of blue from indigo, together with buff and
gold colour, tinged with the oxides of iron, great care is necessary.
The common process of bleaching pulicates, into which permanent colours
are woven, is, to wash the dressing or starch well out in cold water; to
boil them gently in soap, and, after again washing, to immerse them in a
moderately strong solution of the oxymuriate of potash; and this process
is followed until the white is good: they are then soured in dilute
sulphuric acid. If the goods are attended to in a proper manner, the
colours, in place of being impaired, will be found greatly improved, and
to have acquired a delicacy of tint which no other process can impart to
them.
Pulicates, or ginghams, which have been woven along with yarn which has
been previously bleached, are first freed by washing from the starch or
dressing: they are then washed, or slightly boiled with soap. After
which, they are completely rinsed in pure spring water, and then soured.
Besides these common processes for bleaching, another was some time ago
introduced, which consisted in immersing the cotton or linen goods in
pretty strong solution of caustic alkali, and afterwards exposing them
to the action of steam in a close vessel. It is now generally abandoned.
The cotton or linen goods having been previously cleaned by steeping and
washing, were, after being well drained, steeped in a solution of
caustic alkali of the specific gravity of 1020. After the superfluous
alkaline ley had been drained from them, they were arranged on a grating
in a receiver. The cover was then placed on the vessel, and firmly
screwed down; and the steam was admitted by turning the stop-cock of the
pipe which communicated with a steam boiler of the common construction.
The stains which come out upon maddered goods, in consequence of
defective bleaching, are called in this country _spangs_. Their origin
is such as I have described above, as the following statement of facts
will show. The weaver of calicoes receives frequently a fine warp so
tender from bad spinning or bad staple in the cotton, that it will not
bear the ordinary strain of the heddles, or friction of the shuttle and
reed, and he is obliged to throw in as much weft as will compensate for
the weakness or thinness of the warp, and make a good marketable cloth.
He of course tries to gain his end at the least expense of time and
labour. Hence when his paste dressing becomes dry and stiff, he has
recourse to such greasy lubricants as he can most cheaply procure; which
are commonly either tallow or butter in a rancid state, but the former
being the lowest priced is preferred. Accordingly, the weaver, having
heated a lump of iron, applies it to a piece of tallow held over the
warp in the loom, and causes the melted fat to drop in patches upon the
yarns, which he afterwards spreads more evenly by his brush. It is
obvious, however, that the grease must be very irregularly applied in
this way, and be particularly thick on certain spots. This irregularity
seldom fails to appear when the goods are bleached or dyed by the common
routine of work. Printed calicoes examined by a skilful eye, will be
often seen to be stained with large blotches evidently occasioned by
this vile practice of the weaver. The ordinary workmen call these
_copper_ stains, believing them to be communicated in the dyeing copper.
Such stains on the cloth are extremely injurious in dyeing with the
indigo vat. The following plan is adopted by some Scotch bleachers with
the effect, it is said, of effectually counteracting spangs from grease.
The goods having been singed and steeped in pure water, as is customary
in common bleaching, they are passed through a pair of rollers to press
out the impurities which have been loosened by the steeping. It must
here, however, be observed, that where the expense of one extra drying
can be afforded, the process might be very much improved by steeping the
brown calicoes for thirty or forty hours before singeing, because this
would separate much of that impurity which usually becomes fixed in the
stuff on its being passed over the hot cylinders. When the pieces have
been thus singed, steeped, and pressed, they are boiled four times, ten
or twelve hours at each time, in a solution of caustic potash, of the
specific gravity of from 1·0127 to 1·0156, washing them carefully and
thoroughly in pure water between each of these boilings. They are then
immersed in a solution of the chloride of potash, originally of the
strength of 1·0625, and afterwards reduced with twenty-four times its
measure with water.
When the preparation is good, these proportions will whiten cotton goods
completely in eight hours. In this steep they are, however, generally
suffered to remain twelve hours. It has been supposed that the common
bleaching liquor (chloride of lime) cannot, without injury, be
substituted for chloride of potash, but I believe this to be a mistake.
Some printers take the pieces from this solution, and, while wet, lay
them upon the grass, and there expose them to the sun and weather for
two or three days. They are thence removed to the sours, made of the
specific gravity of about 1·0254 at the temperature of 110° of
Fahrenheit. In bleaching common goods, and such as are not designed for
the best printing, the specific gravity of the sours is varied from that
of 1·0146 to that of 1·0238, if weighed when they become of the
temperature of the atmosphere. In these they are suffered to lie for
five or six hours, after which they are taken to the dash-wheel and
washed thoroughly. When this operation is finished, they are submitted
to four more boilings as before, with a solution of caustic potash;
taking care to wash well between each of these boilings. Sometimes
pearl-ash, made caustic, is used for the last of these boilings, lest
the sulphur, which always exists in the potashes of commerce, should
impair the whites. They are next immersed in the diluted chloride of
potash, of the strength before mentioned; after which they are well
washed in pure water, and then winched for half an hour in common sours.
The last process is that of careful washing in plenty of clean water,
after which they are not put into the stove, but are immediately hung up
in the airing sheds to dry gradually. The water must be good, and
abundant.
The number of operations, as here described, is great; but I know of no
other mode of procedure by which perfect bleaching is so likely to be
effected at all times and in all seasons, without disappointment. It
must here be remarked, that, for the best purposes of printing, it would
not be sufficient to take goods which have been bleached in the common
way and finish these by the better process; because the sulphate of lime
deposited in the cloth by that operation will be apt to spoil them for
madder colours; at least, a printer who is curious in his business would
hesitate to work up such cloth.
_Bucking or Bowking._--This is one of the most important operations in
the bleaching of both cotton and linen goods. There are several methods
whereby this process is carried on; but of these we shall select only
two, distinguishing them as the old and new method of bucking. In the
former way, the cloths have been steeped in the alkaline lye, as before
described, and afterwards well washed, are regularly arranged in a large
wooden vat, or kieve; a boiler of sufficient capacity is then filled
with caustic alkaline lye, which is heated to the temperature of blood.
The boiler is then emptied by a stop-cock upon the linens in the kieve,
until they are covered with the liquor. After having remained on the
cloth for some time, it is run off by a stop-cock, at the bottom of the
kieve, into an iron boiler sunk in the ground, from whence it is raised
into the boiler by a pump. The heat is now elevated to a higher
temperature, and the lye again run upon the goods in the kieve; from
whence it is returned into the boiler, as before described: and these
operations are continued, always increasing the heat, until the alkaline
lye is completely saturated with the colouring matter taken from the
cloth, which is known by its having acquired a completely offensive
smell, and losing its causticity.
When we consider the effect which heated liquids have upon coloured
vegetable matter, we shall see the propriety of the temperature of the
alkaline lye being gradually increased. Thus, when vegetable substances
are hastily plunged into boiling liquids, the colouring matter, in place
of being extracted, is, by this higher temperature, fixed into them. It
is on this principle that a cook acts in the culinary art, when the
green colour of vegetables is intended to be preserved: in place of
putting them into water when cold, they are kept back until the water is
boiling; because it is well known that, in the former case, the green
colour would be entirely extracted, whereas, when the vegetables are not
infused until the water is boiling, the colour is completely preserved
or fixed. On the same principle, when the temperature of the alkaline
lye is gradually raised, the extractive and colouring matter is more
effectually taken from the cloth; and the case is reversed when the lye
is applied at the boiling temperature: so much so, that linen which has
been so unfortunate as to meet with this treatment, can never be brought
to a good white.
When the alkaline lye is saturated with colouring matter, it is run off
as unfit for further use in this operation; but, were the goods to be
instantly taken out of the kieve, and carried to be washed in the
dash-wheel while hot, a certain portion of the colouring matter would be
again fixed into them, which is extremely difficult to eradicate. In
order to prevent this, the most approved bleachers run warm water upon
the cloth as soon as the impure lye is run off: this combines with and
carries off part of the remaining impurities. A stream of water is then
allowed to run upon the cloth in the kieve, until it comes off almost
transparent. The goods are now to be taken to the wash-stocks, or to the
dash-wheel, to be further cleaned, with the greatest efficacy.
The improved mode of bowking was the invention of Mr. John Laurie, a
native of Glasgow. It is now practised by many bleachers in Lancashire,
some on more perfect plans than others; but we shall give the
description of the kind of apparatus approved of by those whose
experience and skill have rendered them the most competent judges.
[Illustration: 122]
In _fig._ 122., A B C D is the wooden kieve, or kier, containing the
cloth; C E F D represents the cast-iron boiler; G G, the pump; _g_ K,
the pipe of communication between the kieve and the boiler. This pipe
has a valve on each of its extremities: that on the upper extremity,
when shut, prevents the lye from running into the boiler, and is
regulated by the attendant by means of the rod and handle _g_ B. The
valve at K admits the lye; but, opening inwards, it prevents the steam
from escaping through the pipe _g_ K. The boiler has a steam-tight iron
cover, _g_ L; and at C D, in the kieve, is a wooden grating, a small
distance above the cover of the boiler.
At M O is a broad plate of metal, in order to spread the lye over the
cloth. It is hardly necessary to say that the boiler has a furnace, as
usual, for similar purposes.
While the lye is at a low temperature, the pump is worked by the mill or
steam-engine. When it is sufficiently heated, the elasticity of the
steam forces it up through the valves of the pump, in which case it is
disjoined from the moving power.
N P is a copper spout, which is removed at the time of taking the cloth
out of the kieve.
[Illustration: 123]
The boilers A, _fig._ 123., used in bleaching, are of the common form,
having a stopcock, H G, at bottom, for running off the waste lye. They
are commonly made of cast iron, and are capable of containing from 300
to 600 gallons of water, according to the extent of the business done.
In order that the capacity of the boilers may be enlarged, they are
formed so as to admit of a crib of wood, strongly hooped, or, what is
preferable, of cast iron, to be fixed to the upper rim or edge of it. To
keep the goods from the bottom, where the heat acts most forcibly, a
strong iron ring, covered with netting made of stout rope, C, is allowed
to rest six or eight inches above the bottom of the boiler. Four double
ropes are attached to the ring E, for withdrawing the goods when
sufficiently boiled, which have each an eye for admitting hooks from the
running tackle of a crane. Where more boilers than one are employed, the
crane is so placed, that, in the range of its sweep, it may withdraw the
goods from any of them. For this purpose, the crane turns on pivots at
top and bottom; and the goods are raised or lowered at pleasure, with
double pulleys and sheaves, by means of a cylinder moved by cast-iron
wheels. The lid is secured by the screw bolts D D, and rings B B. F is a
safety valve.
The efficacy of Laurie’s bowking apparatus is remarkable. While the heat
is gradually rising, a current of fresh lye is constantly presented to
the different surfaces for saturating the goods, so as to increase its
detersive powers. Besides, the manner in which the apparatus is worked,
first by the water-wheel or steam-engine, and then by its intrinsic
operation, puts it completely out of the power of servants to slight the
work; not to speak of the great saving of alkali, which, in many cases,
has been found to amount to 25 per cent.
[Illustration: 124 125 126]
A simple modification of the bowking apparatus is shown in _figs._ 124,
125, 126.; the first being a vertical section, the second, a horizontal
section in the line _x_ of the first. It consists of two parts: the
upper wide part, _a a_, serves for the reception of the goods, and the
lower or pot, _b_, for holding the lye; _c c_ is an iron grating, shown
apart in _fig._ 126. The grating has numerous square apertures in the
middle of the disc, to which the rising pipe _d_ is screwed fast. The
upper cylinder is formed of cast iron, or of sheet iron well rivetted at
the edges; or sometimes of wood, this being secured at its under edge
into a groove in the top edge of the lye-pot. The mouth of the cylinder
is constructed usually of sheet iron. _e e_ is the fire-grate, whose
upper surface is shown in _fig._ 125.: it is made of cast iron, in three
pieces. The flame is parted at _f_, and passes through the two apertures
_g g_, into the flues _h h_, so as to play round the pot, as is visible
in _fig._ 125.; and escapes by two outlets into the chimney. The
apertures _i i_ serve for occasionally cleaning out the flues _h h_, and
are, at other times, shut with an iron plate. In the partition _f_,
which separates the two openings _g g_, and the flues _h h_, running
round the pot, there is a circular space at the point marked with _k_,
_fig._ 125., in which the large pipe for discharging the waste lye is
lodged. The upper large cylinder should be encased in wood, with an
intermediate space filled with sawdust, to confine the heat. The action
of this apparatus is exactly the same as of that already explained.
Besides the boiling, bucking, and other apparatus above described, the
machinery and utensils used in bleaching are various, according to the
business done by the bleacher. When linen or heavy cotton cloths are
whitened, and the business is carried on to a considerable extent, the
machines are both complicated and expensive. They consist chiefly of a
water-wheel, sufficiently powerful for giving motion to the wash-stocks,
dash-wheels, squeezers, &c., with any other operations where power is
required.
[Illustration: 127 128]
_Figs._ 127, 128. represent a pair of wash-stocks. A A are called the
stocks, or feet. They are suspended on iron pivots at B, and receive
their motion from wipers on the revolving-shaft C. The cloth is laid in
at D, and, by the alternate strokes of the feet, and the curved form of
the turnhead E, the cloth is washed and gradually turned. At the same
time, an abundant stream of water rushes on the cloth throughout holes
in the upper part of the turnhead. Wash-stocks are much used in Scotland
and in Ireland. In the latter country, they are often made with double
feet, suspended above and below two turnheads, and wrought with cranks
instead of wipers. Wash-stocks, properly constructed, make from 24 to 30
strokes per minute.
This mode of washing is now entirely given up in Lancashire, where a
preference is given to what are called dash-wheels and squeezers. The
dash are small water-wheels, the inside of which is divided into four
compartments, and closed up, leaving only a hole in each compartment for
putting in the cloth.
There are, besides, smaller openings for the free admission and egress
of the water employed in cleansing. The cloth, by the motion of the
wheel, is raised up in one part of the revolution of the wheel; while,
by its own weight, it falls in another. This kind of motion is very
effectual in washing the cloth, while, at the same time, it does not
injure its strength. The plan, however, where economy of water is of any
importance, is very objectionable; because the wheel must move at by far
too great a velocity to act to advantage as a water-wheel.
[Illustration: 129 130]
The wash or dash-wheel, now driven by power in all good bleach and
print-works, is represented in _fig._ 129., upon the left side in a back
view, and upon the right side in a front view (the sketch being halved).
_Fig._ 130. is a ground plan.
_a a_ is the washing-wheel; _b b_ its shaft-ends; _c c_ their brass
bearings or plummer-blocks, supported upon the iron pillars _d d_. The
frame is made of strong beams of wood, _e e_, bound together by cross
bars with mortises. _f f_, two of the circular apertures, each leading
to a quadrantal compartment within the dash-wheel. In the back view (the
left-hand half of the figure) the brass grating _g g_, of a curvilinear
form, is seen, through which the jets of water are admitted into the
cavity of the wheel; _h h_, are the round orifices, through which the
foul water runs off, as each quadrant passes the lower part of its
revolution; _i_, a water-pipe, with a stop-cock for regulating the
washing-jets; _k k_, the lever for throwing the driving-crab _l_, or
coupling-box, into or out of geer with the shaft of the wheel. This
machine is so constructed, that the water-cock is opened or shut by the
same leverage which throws the wheel into or out of geer. _m_, a wheel,
fixed upon the round extremity of the shaft of the dash-wheel, which
works into the toothed pinion connected with the prime mover. When the
end of the lever _k_, whose fork embraces the coupling-box upon the
square part of the shaft, is pushed forwards or backwards, it shifts the
clutch into or out of geer with the toothed wheel _m_. In the latter
case, this wheel turns with its pinion without affecting the dash-wheel.
_n n_, holdfasts fixed upon the wooden frame, to which the boards _o o_
are attached, for preventing the water from being thrown about by the
centrifugal force.
The dash-wheel is generally from 6 to 7 feet in diameter, about 30
inches wide, and requires the power of about two horses to drive it.
From one to two pieces of calico may be done at once in each quadrantal
compartment, in the course of 8 or 10 minutes; hence, in a day of 13
hours, with two such wheels 1200 pieces of yard-wide goods may be
washed.
After the process of washing by the dash-wheel, the water is expressed
from the cloth by means of the squeezers already described.
_Bleaching of Linen._--Linen contains much more colouring matter than
cotton. The former loses nearly a third of its weight, while the latter
loses not more than a twentieth. The fibres of flax possess, in the
natural condition, a light gray, yellow, or blond colour. By the
operation of rotting, or, as it is commonly called, water-retting, which
is employed to enable the textile filaments to be separated from the
boon, or woody matter, the colour becomes darker, and, in consequence
probably of the putrefaction of the green matter of the bark, the
colouring substance appears. Hence, flax prepared without rotting is
much paler, and its colouring matter may be in a great measure removed
by washing with soap, leaving the filaments nearly white. Mr. James Lee
obtained a patent in 1812, as having discovered that the process of
steeping and dew-retting is unnecessary, and that flax and hemp will not
only dress, but will produce an equal if not greater quantity of more
durable fibre, when cleaned in the dry way. Mr. Lee stated that, when
hemp or flax plants are ripe, the farmer has nothing more to do than to
pull, spread, and dry them in the sun, and then to break them by proper
machinery. This promising improvement has apparently come to nought,
having been many years abandoned by the patentee himself, though he was
favoured with a special act of parliament, which permitted the
specification of his patent to remain sealed up for seven years,
contrary to the general practice in such cases.
The substance which gives steeped flax its peculiar tint is insoluble in
boiling water, in acids, and in alkalies; but it possesses the property
of dissolving in caustic or carbonated alkaline lyes, when it has
possessed the means of dehydrogenation by previous exposure to oxygen.
Hemp is, in this respect, analogous to flax. The bleaching of both
depends upon this action of oxygen, and upon the removal of the
acidified dye, by means of an alkali. This process is effected generally
by the influence of air in combination with light and moisture acting on
the linen cloth laid upon the grass: but chlorine will effect the same
object more expeditiously. In no case, however, is it possible to
acidify the colour completely at once, but there must be many alternate
exposures to oxygen or chlorine, and alkali, before the flax becomes
white. It is this circumstance alone which renders the bleaching of
linen an apparently complicated business.
Having made these preliminary observations with regard to the method of
applying the alkaline lyes used in bleaching linen cloth, I shall now
bring the whole into one point of view, by detailing the connection of
these processes, as carried on at a bleach-field, which has uniformly
been successful in returning the cloth of a good white, and has
otherwise given satisfaction to its employers; and I shall only remark,
that I by no means hold it up as the best process which may be employed,
as every experienced bleacher knows that processes must be varied, not
only according to existing circumstances, but also according to the
nature of the linens operated upon.
In order to avoid repetition, where washing is mentioned, it must always
be understood that the linen is taken to the wash-stocks or dash-wheel,
and washed well in them for some hours. This part of the work can never
be overdone; and on its being properly executed between every part of
the bucking, boiling, steeping in the chloride of lime solution, and
souring, not a little of the success of bleaching depends. By exposure
is meant, that the linen cloth is taken and spread upon the bleach-green
for four, six, or eight days, according as the routine of business calls
for the return of the cloth, in order to undergo further operations.
A parcel of goods consists of 360 pieces of those linens which are
called Britannias. Each piece is 35 yards long; and they weigh, on an
average, 10 lbs. each; the weight of the parcel is, in consequence,
about 3600 lbs. avoirdupois weight. The linens are first washed, and
then steeped in waste alkaline lye, as formerly described under these
processes; they then undergo the following operations:--
1st, Bucked with 60 lbs. pearl-ashes, washed, exposed on the field.
2d, Ditto 80 ditto ditto ditto ditto.
3d, Ditto 90 potashes ditto ditto ditto.
4th, Ditto 80 ditto ditto ditto ditto.
5th, Ditto 80 pearl-ashes, ditto ditto ditto.
6th, Ditto 50 ditto ditto ditto ditto.
7th, Ditto 70 ditto ditto ditto ditto.
8th, Ditto 70 ditto ditto ditto ditto.
9th, Soured one night in dilute sulphuric acid, washed.
10th, Bucked with 50 lbs. pearl-ashes, washed, exposed on the field.
11th, Immersed in the chloride of potash or lime 12 hours.
12th, Boiled with 30 lbs. pearl ashes, washed, exposed on the field.
13th, Ditto 30 ditto ditto ditto ditto.
14th, Soured, washed.
The linens are then taken to the rubbing-board, and well rubbed with a
strong lather of black soap, after which they are well washed in pure
spring water. At this period they are carefully examined, and those
which are fully bleached are laid aside to be blued, and made up for the
market; while those which are not fully white are returned to be boiled,
and steeped in the chloride of lime or potash; then soured, until they
are fully white.
By the above process, 690 lbs. weight of alkali is taken to bleach 360
pieces of linen, each piece consisting of 35 yards in length; so that
the expenditure of alkali would be somewhat less than 2 lbs. for each
piece, were it not that some parts of the linens are not fully whitened,
as above noted. Two pounds of alkali may therefore be stated as the
average quantity employed for bleaching each piece of goods.
The method of bleaching linens in Ireland is similar to the foregoing;
any alteration in the process depending upon the judgment of the
bleacher in increasing or diminishing the quantity of alkali used. But
it is common, at most bleach-fields, to steep the linens in the chloride
of lime or potash at an early stage of the process, or after the goods
have undergone the fifth or sixth operation of bucking. By this means
those parts of the flax which are most difficult to bleach are more
easily acted upon by the alkali; and, as before noticed, souring early
in very dilute sulphuric acid, assists greatly in forwarding the
whitening of the linens. Mr. Grimshaw, calico-printer, near Belfast, was
the first who recommended early souring, which has since been very
generally adopted.
_The bleaching of Silk._--Silk in its raw state, as spun by the worm, is
either white or yellow of various shades, and is covered with a varnish,
which gives it stiffness and a degree of elasticity. For the greater
number of purposes to which silk is applied, it must be deprived of this
native covering, which was long considered to be a sort of gum. The
operation by which this colouring matter is removed is called scouring,
cleansing, or boiling. A great many different processes have been
proposed for freeing the silk fibres from all foreign impurities, and
for giving it the utmost whiteness, lustre, and pliancy; but none of the
new plans has superseded, with any advantage, the one practised of old,
which consists essentially in steeping the silk in a warm solution of
soap; a circumstance placed beyond all doubt by the interesting
experiments of M. Roard. The alkalies, or alkaline salts, act in a
marked manner upon the varnish of silk, and effect its complete
solution; the prolonged agency of boiling water, alone answers the same
purpose; but nothing agrees so well with the nature of silk, and
preserves its brilliancy and suppleness so perfectly, as a rapid boil
with soap-water. It would appear, however, that the Chinese do not
employ this method, but something that is preferable. Probably the
superior beauty of their white silk may be owing to the superiority of
the raw material.
The most ancient method of scouring silk consists of three operations.
For the first, or the _ungumming_, thirty per cent. of soap is first of
all dissolved in clean river water by a boiling heat; then the
temperature is lowered by the addition of a little cold water, by
withdrawing the fire, or at least by damping it. The hanks of silk
suspended upon horizontal poles over the boiler, are now plunged into
the soapy solution, kept at a heat somewhat under ebullition, which is
an essential point; for if hotter, the soap would attack the substance
of the silk, and not only dissolve a portion of it, but deprive the
whole of its lustre. The portions of the hanks plunged in the bath get
scoured by degrees; the varnish and the colouring matter come away, and
the silk assumes its proper whiteness and pliancy. Whenever this point
is attained, the hanks are turned round upon the poles, so that the
portion formerly in the air may be also subjected to the bath. As soon
as the whole is completely ungummed, they are taken out, wrung by the
peg, and shaken out; after which, the next step, called the _boil_, is
commenced. Into bags of coarse canvass, called _pockets_, about 25 lbs.
or 35 lbs. of ungummed silk are enclosed, and put into a similar bath
with the preceding, but with a smaller proportion of soap, which may
therefore be raised to the boiling point without any danger of
destroying the silk. The ebullition is to be kept up for an hour and a
half, during which time the bags must be frequently stirred, lest those
near the bottom should suffer an undue degree of heat. The silk
experiences in these two operations a loss of about 25 per cent. of its
weight.
The third and last scouring operation is intended to give the silk a
slight tinge, which renders the white more agreeable, and better
adapted to its various uses in trade. In this way we distinguish the
China white, which has a faint cast of red, the silver white, the azure
white, and the thread white. To produce these different shades, we begin
by preparing a soap-water so strong as to lather by agitation; we then
add to it, for the China white, a little annotto, mixing it carefully
in; and then passing the silk properly through it, till it has acquired
the wished for tint. As to the other shades, we need only azure them
more or less with a fine indigo, which has been previously washed
several times in hot water, and reduced to powder in a mortar. It is
then diffused through boiling water, allowed to settle for a few
minutes, and the supernatant liquid, which contains only the finer
particles, is added to the soap bath, in such proportion as may be
requisite. The silk, on being taken out of this bath, must be wrung
well, and stretched upon perches to dry; after which it is introduced
into the sulphuring chamber, if it is to be made use of in the white
state. At Lyons, however, no soap is employed at the third operation:
after the boil, the silk is washed, sulphured, and azured, by passing
through very clear river water properly blued.
The silks intended for the manufacture of blonds and gauzes are not
subjected to the ordinary scouring process, because it is essential, in
these cases, for them to preserve their natural stiffness. We must
therefore select the raw silk of China, or the whitest raw silks of
other countries; steep them, rince them in a bath of pure water, or in
one containing a little soap; wring them, expose them to the vapour of
sulphur, and then pass them through the azure water. Sometimes this
process is repeated.
Before the memoir of M. Roard appeared, extremely vague ideas were
entertained about the composition of the native varnish of silk. He has
shown that this substance, so far from being of a gummy nature, as had
been believed, may be rather compared to bees’ wax, with a species of
oil, and a colouring matter, which exists only in raw silks. It is
contained in them to the amount of from 23 to 24 per cent., and forms
the portion of weight which is lost in the _ungumming_. It possesses,
however, some of the properties of vegetable gums, though it differs
essentially as to others. In a dry mass, it is friable and has a
vitreous fracture; it is soluble in water, and affords a solution which
lathers like soap; but when thrown upon burning coals, it does not
soften like gum, but burns with the exhalation of a fetid odour. Its
solution, when left exposed to the open air, at first of a golden
yellow, becomes soon greenish, and ere long putrefies, as a solution of
animal matter would do in similar circumstances. M. Roard assures us
that the city of Lyons alone could furnish several thousand quintals of
this substance _per annum_, were it applicable to any useful purpose.
The yellow varnish is of a resinous nature, altogether insoluble in
water, very soluble in alcohol, and contains a little volatile oil,
which gives it a rank smell. The colour of this resin is easily
dissipated, either by exposure to the sun or by the action of chlorine:
it forms about one fifty-fifth of its weight.
Bees’ wax exists also in all the sorts of silk, even in that of China;
but the whiter the filaments, the less wax do they contain.
M. Roard has observed that, if the silk be exposed to the soap baths for
some time after it has been stripped of its foreign matters, it begins
to lose body, and has its valuable qualities impaired. It becomes dull,
stiff, and coloured in consequence of the solution more or less
considerable of its substance; a solution which takes place in all
liquids, and even in boiling water. It is for this reason that silks
cannot be alumed with heat; and that they lose some of their lustre in
being dyed brown, a colour which requires a boiling hot bath. The best
mode, therefore, of avoiding these inconveniences, is to boil the silks
in the soap-bath no longer than is absolutely necessary for the scouring
process, and to expose them in the various dyeing operations to as
moderate temperature as may be requisite to communicate the colour. When
silks are to be dyed, much less soap should be used in the cleansing,
and very little for the dark colours. According to M. Roard, raw silks,
white or yellow, may be completely scoured, in one hour, with 15 lbs. of
water for one of silk, and a suitable proportion of soap. The soap and
the silk should be put into the bath half an hour before its ebullition,
and the latter should be turned about frequently. The dull silks, in
which the varnish has already undergone some alteration, never acquire a
fine white until they are exposed to sulphureous acid gas. Exposure to
light has also a very good effect in whitening silks, and is had
recourse to, it is said, with advantage by the Chinese.
Carbonate of soda has been proposed to be used instead of soap in
scouring silk, but it has never come into use. The Abbé Collomb, in
1785, scoured silk by eight hours’ boiling in simple water, and he found
the silks bleached in this way to be stronger than by soap, but they are
not nearly so white. A patent has been taken out in England for
bleaching them by steam, of which an account will be found under the
article SILK.
It appears that the Chinese do not use soap in producing those fine
white silks which are imported into Europe. Michel de Grubbens who
resided long at Canton, saw and practised himself the operation there,
which he published in the Memoirs of the Academy of Stockholm in 1803.
It consists in preparing the silk with a species of white beans, smaller
than the Turkey beans, with some wheat flour, common salt, and water.
The proportions are 5 parts of beans, 5 of salt, 6 of flour, and 25 of
water, to form this vegetable bath. The beans must be previously washed.
It is difficult to discover what chemical action can occur between that
decoction and the varnish of raw silk; possibly some acid may be
developed, which may soften the gummy matter, and facilitate its
separation.
Baumé contrived a process which does not appear to have received the
sanction of experience, but which may put us in the right way. He
macerates the yellow raw silk in a mixture of alcohol at 36° (sp. gr.
0·837) and one thirty-second part of pure muriatic acid. At the end of
forty-eight hours, it is as white as possible, and the more so, the
better the quality of the silk. The loss which it suffers in this
menstruum is only one fortieth; showing that nothing but the colouring
matter is abstracted. The expense of this menstruum is the great
obstacle to Baumé’s process. The alcohol, however, might be in a very
great measure recovered, by saturating the acid with chalk, and
redistillation.
_Bleaching of Wool._--Wool, like the preceding fibrous matter, is
covered with a peculiar varnish, which impairs its qualities, and
prevents it from being employed in the raw state for the purposes to
which it is well adapted when it is scoured. The English give the name
_yolk_, and the French _suint_, to that native coat: it is a fatty
unctuous matter, of a strong smell, which apparently has its chief
origin in the cutaneous perspiration of the sheep; but which, by the
agency of external bodies, may have undergone some changes which modify
its constitution. It results from the experiments of M. Vauquelin, that
the _yolk_ is composed of several substances; namely, 1. a soap with
basis of potash, which constitutes the greater part of it; 2. of a
notable quantity of acetate of potash; 3. of a small quantity of
carbonate, and a trace of muriate, of potash; 4. of a little lime in an
unknown state of combination; 5. of a species of sebaceous matter, and
an animal substance to which the odour is due. There are several other
accidental matters present on sheep’s wool.
The proportion of yolk is variable in different kinds of wool, but in
general it is more abundant the finer the staple; the loss by scouring
being 45 per cent. for the finest wools, and 35 per cent. for the
coarse.
The yolk, on account of its soapy nature, dissolves readily in water,
with the exception of a little free fatty matter, which easily separates
from the filaments, and remains floating in the liquor. It would thence
appear sufficient to expose the wools to simple washing in a stream of
water; yet experience shows that this method never answers so well as
that usually adopted, which consists in steeping the wool for some time
in simple warm water, or in warm water mixed with a fourth of stale
urine. From 15 to 20 minutes of contact are sufficient in this case, if
we heat the bath as warm as the hand can bear it, and stir it well with
a rod. At the end of this time the wool may be taken out, set to drain,
then placed in large baskets, in order to be completely rinsed in a
stream of water.
It is generally supposed that putrid urine acts on the wool by the
ammonia which it contains, and that this serves to saponify the
remainder of the fatty matter not combined with the potash. M. Vauquelin
is not of this opinion, because he found that wool steeped in water,
with sal ammoniac and quick lime, is not better scoured than an equal
quantity of wool treated with mere water. He was hence led to conclude
that the good effects of putrefied urine might be ascribed to any thing
else besides the ammonia, and probably to the urea. Fresh urine contains
a free acid, which, by decomposing the potash soap of the yolk,
counteracts the scouring operation.
If wools are better scoured in a small quantity of water than in a great
stream, we can conceive that this circumstance must depend upon the
nature of the yolk which, in a concentrated solution, acts like a
saponaceous compound, and thus contributes to remove the free fatty
particles which adhere to the filaments. It should also be observed that
too long a continuance of the wool in the yolk water, hurts its quality
very much, by weakening its cohesion, causing the filaments to swell,
and even to split. It is said then to have lost its _nerve_. Another
circumstance in the scouring of wool, that should always be attended to,
is never to work the filaments together to such a degree as to occasion
their felting; but in agitating we must merely push them slowly round in
the vessel, or press them gently under the feet. Were it at all felted,
it would neither card nor spin well.
As the heat of boiling water is apt to decompose woollen fibres, we
should be careful never to raise the temperature of the scouring bath to
near this point, nor, in fact, to exceed 140° F. Some authors recommend
the use of alkaline or soapy baths for scouring wool, but practical
people do not deviate from the method above described.
When the washing is completed, all the wool which is to be sent white
into the market, must be exposed to the action of sulphurous acid,
either in a liquid or a gaseous state. In the latter case, sulphur is
burned in a close chamber, in which the wools are hung up or spread out;
in the former, the wools are plunged into water, moderately impregnated
with the acid. (See SULPHURING.) Exposure on the grass may also
contribute to the bleaching of wool. Some fraudulent dealers are accused
of dipping wools in butter-milk, or chalk and water, in order to whiten
them and increase their weight.
Wool is sometimes whitened in the fleece, and sometimes in the state of
yarn; the latter affording the best means of operating. It has been
observed that the wool cut from certain parts of the sheep, especially
from the groins, never bleaches well.
After sulphuring, the wool has a harsh crispy feel, which may be removed
by a weak soap bath. To this also the wool comber has recourse when he
wishes to cleanse and whiten his wools to the utmost. He generally uses
a soft or potash soap, and after the wool is well soaked in the warm
soap bath, with gentle pressure he wrings it well with the help of a
hook, fixed at the end of his washing tub, and hangs it up to dry.
_Bleaching of rags, and paste for paper making._--After the rags are
reduced to what is called half stuff, they should have the greater part
of the floating water run off, leaving just enough to form a stir-about
mass. Into this a clear solution of chloride of lime should be poured,
of such a strength as is suited to the colour of the rags, which should
have been previously sorted; and the engine is kept going so as to churn
the rags with the bleaching agent. After an hour, the water may be
returned upon the engine, and the washing of the paper resumed. From two
to four pounds of good chloride of lime are reckoned sufficient to
bleach one hundred weight of rags.
When the rags consist of dyed or printed cottons, after being well
washed and reduced to half stuff, they should be put into a large cask
or butt, supported horizontally by iron axles upon cradle bearings, so
that it may be made to revolve like a barrel-churn. For each hundred
weight of the coloured rags, take a solution containing from four to
eight pounds of chloride of lime; add it to the liquid mixture in the
butt along with half a pound of sulphuric acid for every pound of the
chloride; and after inserting the bung, or rather the square valve, set
the vessel in slow revolution backwards and forwards. In a short time
the rags will be colourless. The rags and paper paste ought to be very
well washed, to expel all the chlorine, and perhaps a little muriatic
acid might be used with advantage to dissolve out all the calcareous
matter, a portion of which is apt to remain in the paper, and to operate
injuriously upon both the pens and the ink. Some of the French paper
manufacturers bleach the paste with chlorine gas. Paper prepared from
such paste, well washed, is not apt to give a brown tint to maps, as
that carelessly bleached with chloride of lime is known to do.
BLENDE. (_Fr. and Germ._) Sulphuret of zinc, so named from the German
_blenden_ to dazzle, on account of its glistening aspect. It is called
black jack from its usual colour. Its lustre is pearly adamantine. Spec.
gravity from 3·7 to 4·2. It contains frequently iron, copper, arsenic,
cadmium and silver, all associated with sulphur. It is worked up partly
into metallic zinc, and partly into the sulphate of zinc, or white
vitriol. It consists of 66·72 zinc, and 33·28 sulphur; being nearly by
weight as two to one. See ZINC.
BLOCK MANUFACTURE. Though the making of ships’ blocks belongs rather to
a dictionary of engineering than of manufactures, it may be expected
that I should give some account of the automatic machinery for making
blocks, so admirably devised and mounted by M. I. Brunel, Esq. for the
British navy, in the dock-yard of Portsmouth.