4. The _warming_, to such a degree merely as, when it touches water, it
may make a slight hissing sound; in which state it is dipped in the very
weak aquafortis, whereby it acquires minute insensible asperities,
sufficient to retain the silver leaves that are to be applied.
5. The _hatching_. When these small asperities are inadequate for giving
due solidity to the silvering, the plane surfaces must be hatched all
over with a graving tool; but the chased surfaces need not be touched.
6. The _bluing_, consists in heating the piece till its copper or brass
colour changes to blue. In heating, they are placed in hot tools made of
iron, called _mandrins_ in France.
7. The _charging_, the workman’s term for silvering. This operation
consists in placing the silver leaves on the heated piece, and fixing
them to its surface by burnishers of steel, of various forms. The
workman begins by applying the leaves double. Should any part darken in
the heating, it must be cleared up by the scratch-brush.
The silverer always works two pieces at once; so that he may heat the
one, while burnishing the other. After applying two silver leaves, he
must heat up the piece to the same degree as at first, and he then fixes
on with the burnisher four additional leaves of silver; and he goes on
_charging_ in the same way, 4 or 6 leaves at a time, till he has
applied, one over another, 30, 40, 50, or 60 leaves, according to the
desired solidity of the silvering. He then burnishes down with great
pressure and address, till he has given the surface a uniform silvery
aspect.
_Silvering by the precipitated chloride of silver._--The white curd
obtained by adding a solution of common salt to one of nitrate of
silver, is to be well washed and dried. One part of this powder is to be
mixed with 3 parts of good pearlash, one of washed whiting, and one and
a half of sea salt. After clearing the surface of the brass, it is to be
rubbed with a bit of soft leather, or cork moistened with water, and
dipped in the above powder. After the silvering, it should be thoroughly
washed with water, dried, and immediately varnished. Some use a mixture
of 1 part of the silver precipitate, with 10 of cream of tartar, and
this mixture also answers very well.
Others give a coating of silver by applying with friction, in the
moistened state, a mixture of 1 part of silver-powder precipitated by
copper, 2 parts of cream of tartar, and as much common salt. The piece
must be immediately washed in tepid water very faintly alkalized, then
in slightly warm pure water, and finally wiped dry before the fire. See
PLATED MANUFACTURE.
The inferior kinds of plated buttons get their silver coating in the
following way:--
2 ounces of chloride of silver are mixed up with 1 ounce of corrosive
sublimate, 3 pounds of common salt, and 3 pounds of sulphate of zinc,
with water, into a paste. The buttons being cleaned, are smeared over
with that mixture, and exposed to a moderate degree of heat, which is
eventually raised nearly to redness, so as to expel the mercury from the
amalgam, formed by the reaction of the horn silver and the corrosive
sublimate. The copper button thus acquires a silvery surface, which is
brightened by clearing and burnishing.
Leather is silvered by applying a coat of parchment size, or spirit
varnish, to the surface, and then the silver leaf, with pressure.
SIMILOR, is a golden-coloured variety of brass.
[Illustration: 1030 1031]
SINGEING OF WEBS. The old furnace for singeing cotton goods is
represented in longitudinal section, _fig._ 1030., and in a transverse
one in _fig._ 1031. _a_ is the fire-door; _b_, the grate; _c_, the
ash-pit; _d_, a flue, 6 inches broad, and 2-1/2 high, over which a
hollow semi-cylindrical mass of cast iron _e_, is laid, one inch thick
at the sides, and 2-1/2 thick at the top curvature. The flame passes
along the fire-flue _d_, into a side opening _f_, in the chimney. The
goods are swept swiftly over this ignited piece of iron, with
considerable friction, by means of a wooden roller, and a swing frame
for raising them at any moment out of contact.
In some shops, semi-cylinders of copper, three quarters of an inch
thick, have been substituted for those of iron, in singeing goods prior
to bleaching them. The former last three months, and do 1500 pieces with
one ton of coal; while the latter, which are an inch and a half thick,
wear out in a week, and do no more than from 500 to 600 pieces with the
same weight of fuel.
In the early part of the year 1818, Mr. Samuel Hall enrolled the
specification of a patent for removing the downy fibres of the cotton
thread from the interstices of bobbin-net lace, or muslins, which he
effected by singeing the lace with the flame of a gas-burner. The second
patent granted to Mr. Hall, in April, 1823, is for an improvement in the
above process; viz., causing a strong current of air to draw the flame
of the gas through the interstices of the lace, as it passes over the
burner, by means of an aperture in a tube placed immediately above the
row of gas-jets, which tube communicates with an air-pump or exhauster.
[Illustration: 1032]
_Fig._ 1032. shows the construction of the apparatus complete, and
manner in which it operates; _a_, _a_, is a gas-pipe, supplied by an
ordinary gasometer; from this pipe, several small ones extend upwards to
the long burner _b_, _b_. This burner is a horizontal tube, perforated
with many small holes on the upper side, through which, as jets, the gas
passes; and when it is ignited, the bobbin-net lace, or other material
intended to be singed, is extended and drawn rapidly over the flame, by
means of rollers, which are not shown in the figure.
The simple burning of the gas, even with a draught chimney, as in the
former specification, is found not to be at all times efficacious; the
patentee, therefore, now introduces a hollow tube _c_, _c_, with a slit
or opening, immediately over the row of burners; and this tube, by means
of the pipes _d_, _d_, _d_, communicates with the pipe _e_, _e_, _e_,
which leads to the exhausting apparatus.
This exhausting apparatus consists of two tanks, _f_ and _g_, nearly
filled with water, and two inverted boxes or vessels, _h_ and _i_, which
are suspended by rods to the vibrating beam _k_; each of the boxes is
furnished with a valve opening upwards; _l_, _l_, are pipes extending
from the horizontal part of the pipe _e_, up into the boxes or vessels
_h_ and _i_, which pipes have valves at their tops, also opening upward.
When the vessel _h_ descends, the water in the tank forces out the air
contained within the vessel at the valve _m_; but when that vessel rises
again, the valve _m_ being closed, the air is drawn from the pipe _e_,
through the pipe _l_. The same takes place in the vessel _i_, from which
the air in its descent is expelled through the valve _n_, and, in its
ascent, draws the air through the pipe _l_, from the pipe _e_. By these
means, a partial exhaustion is effected in the pipe _e_, _e_, and the
tube _c_, _c_; to supply which, the air rushes with considerable force
through the long opening of the tube _c_, _c_, and carries with it the
flame of the gas-burners. The bobbin-net lace, or other goods, being now
drawn over the flame between the burner _b_, _b_, and the exhausted tube
_c_, _c_, by means of rollers, as above said, the flame of the gas is
forced through the interstices of the fabric, and all the fine filaments
and loose fibres of the thread are burnt off, without damaging the
substance of the goods.
To adjust the draught from the gas-burners, there are stopcocks
introduced into several of the pipes _d_; and to regulate the action of
the exhausting apparatus, an air vessel _o_, is suspended by a cord or
chain passing over pulleys, and balanced by a weight _p_. There is also
a scraper introduced into the tube _c_, which is made, by any convenient
contrivance, to revolve and slide backwards and forwards, for the
purpose of removing any light matter that may arise from the goods
singed, and which would otherwise obstruct the air passage. Two of these
draught tubes _c_, may be adapted and united to the exhausting
apparatus, when a double row of burners is employed, and the inclination
of the flame may be directed upwards, downwards, or sideways, according
to the position of the slit in the draft tube, by which means any
description of goods may, if required, be singed on both sides at one
operation.
The greater part of the bobbin-net lace made in England, is sent to Mr.
Hall’s works, at Basford, near Nottingham, to be singed; and at a
reduction of price truly wonderful. He receives now only one farthing
for what he originally was paid one shilling.
SKIN (_Peau_, Fr.; _Haut_, Germ.); the external membrane of animal
bodies, consists of three layers: 1. the epidermis, scarf-skin,
(_Oberhaut_, Germ.); 2. the vascular organ, or papillary body, which
performs the secretions; and 3. the true skin, (_Lederhaut_, Germ.), of
which leather is made. The skin proper, or dermoid substance, is a
tissue of innumerable very delicate fibres, crossing each other in every
possible direction, with small orifices between them, which are larger
on its internal than on its external surface. The conical channels thus
produced, are not straight, but oblique, and filled with cellular
membrane; they receive vessels and nerves which pass out through the
skin (_cutis vera_), and are distributed upon the secretory organ. The
fibrous texture of the skin is composed of the same animal matter as the
serous membranes, the cartilages, and the cellular tissue; the whole
possessing the property of dissolving in boiling water, and being,
thereby, converted into glue. See GLUE, LEATHER, and TAN.
SLAG (_Laitier_, Fr.; _Schlacke_, Germ.); is the vitreous mass which
covers the fused metals in the smelting-hearths. In the iron-works it is
commonly called _cinder_. Slags consist, in general, of bi-silicates of
lime and magnesia, along with the oxides of iron and other metals; being
analogous in composition, and having the same crystalline form as the
mineral, _pyroxene_. See COPPER and IRON.
SLATES (_Ardoises_, Fr.: _Schiefern_, Germ.) The substances belonging to
this class may be distributed into the following species:--
1. Mica-slate, occasionally used for covering houses.
2. Clay-slate, the proper roofing-slate.
3. Whet-slate.
4. Polishing-slate.
5. Drawing-slate, or black chalk.
6. Adhesive slate.
7. Bituminous shale.
8. Slate-clay.
1. _Mica-slate._--This is a mountain rock of vast continuity and extent,
of a schistose texture, composed of the minerals mica and quartz, the
mica being generally predominant.
2. _Clay-slate._--This substance is closely connected with mica; so that
uninterrupted transitions may be found between these two rocks in many
mountain chains. It is a simple schistose mass, of a bluish-gray or
grayish-black colour, of various shades, and a shining, somewhat pearly
internal lustre on the faces, but of a dead colour in the cross
fracture.
Clay-slate is extensively distributed in Great Britain. It skirts the
Highlands of Scotland, from Lochlomond by Callender, Comrie, and
Dunkeld; resting on, and gradually passing into mica-slate throughout
the whole of that territory. Roofing-slate occurs, on the western side
of England, in the counties of Cornwall and Devon; in various parts of
North Wales and Anglesea; in the north-east parts of Yorkshire, near
Ingleton, and in Swaledale; as also in the counties of Cumberland and
Westmorland. It is likewise met with in the county of Wicklow and other
mountainous districts of Ireland.
All the best beds of roofing-slate improve in quality as they lie deeper
under the surface; near to which, indeed, they have little value.
A good roofing-slate should split readily into thin even laminæ; it
should not be absorbent of water either on its face or endwise, a
property evinced by its not increasing perceptibly in weight after
immersion in water; and it should be sound, compact, and not apt to
disintegrate in the air. The slate raised at Eisdale, on the west coast
of Argyllshire, is very durable.
_Cleaving and dressing of the slates._--The splitter begins by dividing
the block, cut lengthwise, to a proper size, which he rests on end, and
steadies between his knees. He uses a mallet and a chisel, which he
introduces into the stone in a direction parallel to the _folia_. By
this means he reduces it into several manageable pieces, and he gives to
each the requisite length, by cutting cross grooves on the flat face,
and then striking the slab with the chisel. It is afterwards split into
thinner sections, by finer chisels dexterously applied to the edges. The
slate is then dressed to the proper shape, by being laid on a block of
wood, and having its projecting parts at the ends and sides cut off with
a species of hatchet or chopping-knife. It deserves to be noticed, that
blocks of slate may lose their property of divisibility into thin
laminæ. This happens from long exposure to the air, after they have been
quarried. The workmen say, then, that they have lost their waters. For
this reason, the number of splitters ought to be always proportioned to
the number of block-hewers. Frost renders the blocks more fissile; but a
supervening thaw renders them quite refractory. A new frost restores the
faculty of splitting, though not to the same degree; and the workmen
therefore avail themselves of it without delay. A succession of frosts
and thaws renders the quarried blocks quite intractable.
3. _Whet-slate, or Turkey hone_, is a slaty rock, containing a great
proportion of quartz, in which the component particles, the same as in
clay-slate and mica-slate, but in different proportions, are so very
small as to be indiscernible.
4. _Polishing slate._ Colour, cream-yellow, in alternate stripes;
massive; composition impalpable; principal fracture, slaty, thin, and
straight; cross fracture, fine earthy; feels fine, but meagre; adheres
little, if at all, to the tongue; is very soft, passing into friable;
specific gravity in the dry state, 0·6; when imbued with moisture, 1·9.
It is supposed to have been formed from the ashes of burnt coal. It is
found at Planitz, near Zwickau, and at Kutschlin near Bilin in Bohemia.
5. _Drawing-slate, or black chalk_; has a grayish-black colour; is very
soft, sectile, easily broken, and adheres slightly to the tongue; spec.
grav. 2·11. The streak is glistening. It occurs in beds in primitive and
transition clay-slate; also in secondary formations, as in the
coal-measures of most countries. It is used in crayon drawing. Its trace
upon paper is regular and black. The best kinds are found in Spain,
Italy, and France. Some good black chalk occurs also in Caernarvonshire
and in the island of Islay.
6. _Adhesive slate_, has a light greenish-gray colour, is easily broken
or exfoliated, has a shining streak, adheres strongly to the tongue, and
absorbs water rapidly, with the emission of air-bubbles and a crackling
sound.
7. _Bituminous shale_, is a species of soft, sectile slate-clay, much
impregnated with bitumen, which occurs in the coal-measures.
8. _Slate-clay_, has a gray or grayish-yellow colour; is massive, with a
dull glimmering lustre from spangles of mica interspersed. Its slaty
fracture approaches at times to earthy; fragments, tabular; soft,
sectile, and very frangible; specific gravity, 2·6. It adheres to the
tongue, and crumbles down when immersed for some time in water. It is
found as an alternating bed in the coal-measures. (See the sections of
the strata under PITCOAL.) When breathed upon, it emits a strong
argillaceous odour. When free from lime and iron, it forms an excellent
material for making refractory fire-bricks, being an infusible compound
of alumina and silica; one of the best examples of which is the schist
known by the name of Stourbridge clay.
SMALL WARES, is the name given in this country to textile articles of
the tape kind, narrow bindings of cotton, linen, silk, or woollen
fabric; plaited sash cord, braid, &c. Tapes are woven upon a loom like
that for weaving ribbons, which is now generally driven by mechanical
power. Messrs. Worthington and Mulliner obtained a patent, in June,
1825, for improvements in such a loom, which have answered the purposes
of their large factory in Manchester very well; and in May, 1831, Mr.
Whitehead, of the same town, patented certain improvements in the
manufacture of small wares. The objects of the latter patent are, the
regular taking up of the tape or cloth, as it is woven, a greater
facility of varying the vibration of the lay, together with the saving
of room required for a range of looms to stand in.[55] See BRAIDING
MACHINE.
[55] Newton’s London Journal, vol. xiii. p. 192; and vol. i. combined
series, p. 212.
SMALT, see AZURE and COBALT.
Imported for home consumption in 1834, 162,232 lbs.; in 1835, 96,649; in
1836, 79,531; duty, 4_d._ per lb.
SMELTING, is the operation by which the ores of iron, copper, lead, &c.,
are reduced to the metallic state. See METALLURGY, ORES, and the
respective metals.
SOAP (_Savon_, Fr.; _Seife_, Germ.); is a chemical compound, of
saponified fats or oils with potash or soda, prepared for the purposes
of washing linen, &c. Fatty matters, when subjected to the action of
alkaline lyes, undergo a remarkable change, being converted into three
different acids, called stearic, margaric, and oleic; and it is these
acids, in fact, which combine with the bases, in definite proportions,
to form compounds analogous to the neutro-saline. Some chemical writers
describe under the title soap, every compound which may result from the
union of fats with the various earths and metallic oxides--a latitude of
nomenclature which common language cannot recognise, and which would
perplex the manufacturer.
Soaps are distinguished into two great classes, according to their
consistence; the hard and the soft; the former being produced by the
action of soda upon fats, the latter by that of potash. The nature of
the fats contributes also somewhat to the consistence of soaps; thus
tallow, which contains much stearine and margarine, forms with potash a
more consistent soap than liquid oils will do, which consist chiefly of
oleine. The drying oils, such as those of linseed and poppy, produce the
softest soaps.
1. _Of the manufacture of hard soap._--The fat of this soap, in the
northern countries of Europe, is usually tallow, and in the southern,
coarse olive oil. Different species of grease are saponified by soda,
with different degrees of facility; among oils, the olive, sweet almond,
rapeseed, and castor oil; and among solid fats, tallow, bone grease, and
butter, are most easily saponified. According to the practice of the
United Kingdom, six or seven days are required to complete the formation
of a pan of hard soap, and a day or two more for settling the
impurities, if it contains rosin. From 12 to 13 cwt. of tallow are
estimated to produce one ton of good soap. Some years ago, in many
manufactories the tallow used to be saponified with potash lyes, and the
resulting soft soap was converted, in the course of the process, into
hard soap, by the introduction of muriate of soda, or weak kelp lyes, in
sufficient quantity to furnish the proper quantity of soda by the
reaction of the potash upon the neutral salts. But the high price of
potash, and the diminished price as well improved quality of the crude
sodas, have led to their general adoption in soap-works. The soda-ash
used by the soap-boiler, contains in general about 36 per cent. of real
soda, in the state of dry carbonate, mixed with muriate of soda, and
more or less undecomposed sulphate. I have met lately with soda-ash,
made from sulphate of soda, in which the materials had been so ill
worked, and so imperfectly decomposed, as to contain 16 per cent. of
sulphate, a circumstance equally disgraceful, as it was ruinous to the
soda manufacturer. The barillas from Spain and Teneriffe contain from 18
to 24 per cent. of real soda. The alkali in both states is employed in
England; barilla being supposed by many to yield a finer white or curd
soap, on account of its freedom from sulphur.
The crude soda of either kind being ground, is to be stratified with
lime in cylindrical cast-iron vats, from 6 to 7 feet wide, and from 4 to
5 feet deep; the lowest layer consisting, of course, of unslaked or
shell quicklime. The vats have a false bottom, perforated with holes,
and a lateral tubulure under it, closed commonly with a wooden plug,
similar to the _épine_ of the French soap pans, by which the lyes
trickle off clear and caustic, after infiltration through the beds of
lime. The quantity of lime must be proportional to the carbonic acid in
the soda.
Upon 1 ton of tallow put into the soap pan, about 200 gallons of soda
lye, of specific gravity 1·040, being poured, heat is applied, and after
a very gentle ebullition of about 4 hours, the fat will be found to be
completely saponified, by the test of the spatula, trowel, or pallet
knife; for the fluid lye will be seen to separate at once upon the steel
blade, from the soapy paste. Such lyes, if composed of pure caustic
soda, would contain 4 per cent. of alkali; but from the presence of
neutro-saline matter, they seldom contain so much as 2 per cent.; in
fact, a gallon may be estimated to contain not more than 2 ounces; so
that 200 gallons contain 25 pounds of real soda. The fire being
withdrawn from the soap pan, the mass is allowed to cool during one
hour, or a little more, after which the spent lyes, which are not at all
alkaline, are run off by a spigot below, or pumped off above, by a pump
set into the pan. A second similar charge of lye is now introduced into
the pan, and a similar boiling process is renewed. Three such boils may
be given in the course of one day’s work, by an active soap-maker. Next
day the same routine is resumed with somewhat stronger lyes, and so
progressively, till, towards the sixth day, the lye may have the density
of 1·160, and will be found to contain 6 per cent. of real soda.[56]
Were the lye a solution of pure caustic soda, it would contain at this
density no less than 14-3/4 per cent. of alkali. The neutro-saline
matter present in the spent lye is essential to the proper granulation
and separation of the saponaceous compound; for otherwise the watery
menstruum would dilute and even liquefy the soap. Supposing 12-1/2 cwt.
of tallow to yield upon an average 20 cwt. of hard soap, then 20 cwt. of
tallow will produce 32 cwt.; and as its average contents in soda are 6
per cent., these 32 cwt. should require 1·52 cwt. of real soda for their
production. If barilla at 20 per cent. be the alkali employed, then 7·6
cwt. of barilla must be consumed in the said process. If the alkali be
soda-ash of 40 per cent., half the weight will of course suffice. I have
reason to believe that there is great waste of alkali incurred in many
soap-works, as 6 cwt. of soda-ash, of at least 30 per cent., is often
expended in making 1 ton of soap, being 50 per cent. more than really
enters into the composition of the soap.
[56] According to my own experiments upon the soda lye used in the
London soap-works.
The barillas always contain a small proportion of potash, to which their
peculiar value, in making a less brittle or more plastic hard soap than
the factitious sodas, may with great probability be ascribed. Chemistry
affords many analogies, especially in mineral waters, where salts,
apparently incompatible, co-exist in dilute solutions. We may thus
conceive how a small quantity of stearate or oleate of potash may resist
the decomposing action of the soda salts. The same modification of the
consistence of hard soap may, however, be always more conveniently
produced by a proper admixture of oleine with stearine.
Soda which contains sulphurets is preferred for making the mottled or
marbled soap, whereas the desulphuretted soda makes the best white curd
soap. Mottling is usually given in the London soap-works, by introducing
into the nearly finished soap in the pan a certain quantity of the
strong lye of crude soda, through the rose spout of a watering-can. The
dense sulphuretted liquor, in descending through the pasty mass, causes
the marbled appearance. In France a small quantity of solution of
sulphate of iron is added during the boiling of the soap, or rather with
the first service of the lyes. The alkali seizes the acid of the
sulphate, and sets the protoxide of iron free, to mingle with the paste,
to absorb more or less oxygen, and to produce thereby a variety of
tints. A portion of oxide combines also with the stearine to form a
metallic soap. When the oxide passes into the red state, it gives the
tint called _manteau Isabelle_. As soon as the _mottler_ has broken the
paste, and made it pervious in all directions, he ceases to push his
rake from right to left, but only plunges it perpendicularly, till he
reaches the lye; then he raises it suddenly in a vertical line, making
it act like the stroke of a piston in a pump, whereby he lifts some of
the lye, and spreads it over the surface of the paste. In its subsequent
descent through the numerous fissures and channels, on its way to the
bottom of the pan, the coloured lye impregnates the soapy particles in
various forms and degrees, whence a varied marbling results.
Three pounds of olive oil afford five pounds of marbled Marseilles soap
of good quality, and only four pounds four ounces of white soap; showing
that more water is retained by the former than the latter. Oil of
grains, as linseed and rapeseed, do not afford so solid a soda soap as
oil of olives; but tallow affords a still harder soap with soda. Some of
the best Windsor soap made in London contains one part of olive oil
(gallipoli) for every nine parts of tallow. Much of the English hard
soap is made with kitchen and bone fat, of a very coarse quality; the
washing of the numerous successive lyes, however, purifies the foul
fats, and deprives them of their offensive smell in a great degree. It
is common now at Marseilles to mix ten per cent. of the oil of grains
with olive oil; for which purpose a large proportion of the oils
extracted from seeds in the mills of the _Department du Nord_ is sent to
Marseilles; but five per cent. of poppy-seed oil, mixed with tallow,
renders the soap made with the mixture stringy and unfit for washing;
because the two species of fat refuse to amalgamate.
The affinity between the stearine of tallow and the alkali, is so great
that a soap may be speedily made from them in the cold. If we melt
tallow at the lowest possible temperature, and let it cool to the fixing
point, then add to it half its weight of caustic lye, at 36° B.,
agitating meanwhile incessantly with a pallet knife, we shall perceive,
at the end of some hours of contact, the mixture suddenly acquire a very
solid consistence, and at the same moment assume a marked elevation of
temperature, proving the phenomenon to be due to chemical attraction. In
some trials of this kind, the thermometer has risen from 54° to 140° F.
According to recent experiments made in Marseilles, 100 pounds of olive
oil take, for their conversion into soap, 54 pounds of crude soda, of 36
per cent. alkaline strength. One part of lime is employed for rendering
three parts of the soda caustic. The richer the oil is in stearine, the
more dilute should be the lye used in the saponification; and _vice
versâ_ when it abounds in oleine. For oil of the former kind, the first
lyes added have a density of from 8° to 9° B.; but for the latter kind,
the density is from 10° to 11°. When four parts of olive oil are mixed
with one part of poppy, rape, or linseed oil, as is now the general
practice at Marseilles, then for such a mixture the first lyes have
usually a specific gravity of from 20° to 25°, the second from 10° to
15°, and the third from 4° to 5°, constituting a great difference from
the practice in Great Britain, where the weaker lyes are generally
employed at the commencement. The chief reason for this practice is,
however, to be found in the more complete causticity of the weak than of
the strong lyes, according to the slovenly way in which most of our
soap-boilers prepare them. Indeed, one very extensive manufacturer of
soap in London assured me that the lyes should not be caustic; an
extraordinary assertion, upon which no comment need be made. In common
cases, I would recommend the first combination of the ingredients to be
made with somewhat weak, but perfectly caustic lye, and when the
saponification is fairly established, to introduce the stronger lye.
In a Marseilles soap-house, there are four lye-vats in each set: No. 1.
is the _fresh vat_, into which the fresh alkali and lime are introduced;
No. 2. is called the _avançaire_, being one step in advance; No. 3. is
the small _avançaire_, being two steps in advance, and therefore
containing _weaker_ liquor; No. 4. is called the _water_ vat, because it
receives the water directly.
Into No. 3. the moderately exhausted or somewhat spent lyes are thrown.
From No. 3. the lye is run or pumped into No. 2., to be strengthened;
and in like manner from No. 3. into No. 1. Upon the lime paste in No.
4., which has been taken from No. 3., water is poured; the lye thus
obtained is poured upon the paste of No. 3., which has been taken from
No. 2. No. 3. is twice lixiviated; and No. 2., once. The receiver under
No. 1. has four compartments; into No. 1. of which the first and
strongest lye is run; into No. 2. the second lye; into No. 3. the third
lye; and into No. 4. the fourth lye, which is so weak as to be used for
lixiviation, instead of water; (_pour d’avances_).
The lime of vat No. 4., when exhausted, is emptied out of the window
near to which it stands; in which case the water is poured upon the
contents of No. 3.; and upon No. 2. the somewhat spent lyes.
No. 1. is now the _avançaire_ of No. 4; because this has become, in its
turn, the _fresh_ vat, into which the fresh soda and quicklime are put.
The lye discharged from No. 3. comes, in this case, upon No. 2.; and
after being run through it, is thrown upon No. 1.
144 pounds of oil yield at Marseilles, upon an average, not more than
from 240 to 244 pounds of soap; or 100 pounds yield about 168; so that
in making 100 pounds of soap, at this rate nearly 60 pounds of oil are
consumed.