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which it communicates a milky appearance, but without any drops of oil floating on the surface. When the soap has not these qualities, the combination has not been well made, or the quantity of salt or of oil is too great, which faults must be corrected. In soft or liquid soaps, green or black soaps, cheaper oils are employed, as oil of nuts, of hemp, of fish, &c. These soaps, excepting in consistence, are not essentially different from white soap. Fixed alkalies are much disposed to unite with oils that are not volatile, both vegetable and animal, for this union can be made even without heat. The compound resulting from it partakes at the same time of the properties of oil and of alkali; but these properties are modified and tempered by each other, according to the general rule of combinations. Alkali formed into soap has not nearly the same acrimony as when pure; it is even deprived of almost all its causticity, and its other saline alkaline properties are almost entirely abolished, The oil contained in soap is less combustible than when pure, from its union with the alkali, which is an uninflammable body. It is miscible, or even soluble in water to a considerable degree, by means of the alkali. Soap is entirely soluble in spirit of wine; and still better in aqua-vitæ sharpened by a little alkaline salt, according to Mr. Geoffroy. The manufacture of soap in London first began in 1524; before which time the city was served with white soap from foreign countries, and with gray soap speckled with white from Bristol, which was sold for a penny a pound; and also with black soap; which sold for a halfpenny the pound. The principal soaps of our own manufacture are the soft, the hard, and the ball soap. The soft soap is either white or green. When oil unites with alkali, in the formation of soap, it is little altered in the connexion of its principles; for it may be separated from the alkali by decomposing soap with any acid, and may be obtained nearly in its original

state.

An acid soap is formed by the addition of concentrated acids to the expressed oils. Thus the oil is rendered partially soluble in water; but the union is not sufficiently complete to answer any valuable purpose.

The ball soap, commonly used in the north, is made with leys from ashes and tallow. The leys are put into the copper, and boiled till the watery part is quite gone, and there remains nothing in the copper but a sort of saline matter (the very strength or essence of the ley); to this the tallow is put, and the copper is kept boiling and stirring for above half an hour, in which time the soap is made; and then it is put out of the copper into tubs or baskets with sheets in them, and immediately (whilst soft) made into balls. It requires nearly twenty-four hours in this process to boil away the watery part of the ley.

The chief ingredients in green soft soup used in making this are leys drawn from potash and lime, boiled with tallow and oil. First, the ley of a proper degree of strength (which must be estimated by the weight of the liquor) and tallow, are put into the copper together, and as soon as they boil up, the oil is added; the fire is then damped or stopped up, while the ingredients re

main in the copper to unite; when they are united, the copper is again made to boil, being filled with leys as it boils, till there be a sufficient quantity put into it; then it is boiled off and put into casks. When the soap is first made it appears uniform; but in about a week the tallow separates from the oil into those white grains which we see in the common soap. Soap thus made would appear yellow, but by a mixture of indigo, added at the end of the boiling, it is rendered green.

Hard soap is made with leys from ashes and tallow, and is most commonly boiled twice; the first, called the half-boil, has the same operation as the first half-boil of soft white soap. Then the copper is charged with fresh leys again, and the first half-boil put into it, where it is kept boiling, and fed with leys as it boils, till it grains or is boiled enough; then the ley is discharged from it, and the soap put into a frame to cool and harden. Common salt is made use of for the purpose of graining the soap; for when the oil or tallow has been united with the ley, after a little boiling, a quantity of salt is thrown into the mass, which dissolving readily in water, but not in the oil or tallow, draws out the water in a considerable degree, so that the oil or tallow united with the salt of the ley swims on the top. When the ley is of a proper strength, less salt is necessary to raise the curd when it is too weak. There is no certain time for bringing off a boiling of any of these sorts of soap; it frequently takes up part of two days.

Alkaline soaps are very useful in many arts and trades, and also in chemistry and medicine. Their principal utility consists in a detersive quality that they receive from their alkali, which is capable of acting upon oily matters, and of rendering them saponaceous and miscible with water. Hence soap is very useful to cleanse any substances from all fat matters with which they are soiled. Soap is therefore daily used for washing linen and woollen cloths from oil, and for whitening silk, and freeing it from the resinous varnish with which it is covered. Pure alkaline lixiviums might be employed for the same purposes; but when their activity is not miti gated by the oil, as it is in soap, they are capable of altering, and even of destroying entirely by their causticity, most substances, especially animal matters, as silk, wool, &c., whereas soap cleanses from oil almost as effectually as pure alkali, without altering or destroying the stuff.

Soap was imperfectly known to the ancients. It is mentioned by Pliny as made of fat and ashes, and as an invention of the Gauls. Aretaus says that the Greeks obtained their knowledge of its medical use from the Romans. Its virtues, according to Bergius, are detergent, resolvent, and aperient, and its use recommended in jaundice, gout, calculous complaints, and in obstructions of the viscera. The efficacy of soap in jaundice was experienced by Sylvius, and recommended by various authors; and it was thought of use in supplying the place of bile in the primæ viæ. But it has lost much of its reputation in jaundice, since it is now known that gall stones have been found in many after death, who had been daily taking soap for months and

even years. Of its good effects, in urinary calculous affections, we have the testimony of several, especially when dissolved in lime water, by which its efficacy is considerably increased for it thus becomes a powerful solvent of mucus, which an ingenious modern author supposes to be the chief agent in the formation of calculi; it is, however, only in the incipient state of the disease that these remedies promise effectual benefit; though they generally abate the more violent symptoms where they cannot remove the cause. With Boerhaave soap was a general medicine; for, as he attributed most complaints to viscidity of the fluids, he, and most of the Boerhaavian school, prescribed it, in conjune tion with different resinous and other substances, in gout, rheumatism, and various visceral complaints. Soap is also externally employed as a resolvent, and gives name to several officinal preparations. From its properties soap must be a very effectual and convenient anti-acid. It absorbs acids as powerfully as pure alkalies and absorbent earths, without naving the causticity of the former, and without oppressing the stomach by its weight like the latter. Soap must also be one of the best of all antidotes to stop quickly, and with the least inconvenience, the bad effects of acid corrosive poisons, as aquafortis, corrosive sublimate, &c.

Concerning the chemical constitution of soaps and saponification, no exact ideas were entertained prior to M. Chevreul's researches.

Fats are compounds of a solid and a liquid substance; the former called stearine, the latter resembling vegetable oil, and therefore called elaïne. When fat is treated with a hot ley of potash, or soda, the constituents react on one another, so as to generate the solid pearly matter margaric acid, and the fluid matter oleic acid, both of which enter into a species of saline combination with the alkali; while the third matter that is produced, the sweet principle, remains free. We must therefore regard our common soap as a mixture of an alkaline margarate and oleate, in proportions determined by the relative proportions of the two acids producible from the pecu.iar species of fat. It is probable, on the other nand, that the soap formed from vegetable oil is chiefly an oleate. No chemical researches have hitherto been made known, on the compounds of resin with alkalies, though these constitute the brown soaps so extensively manufactured in this country. All oils or fats do not possess in an equal degree the property of saponification. Those which saponify best, according to D'Arcet senior, Lelievre, and Pelletier, are, 1. Oil of olives, and of sweet almonds. 2. Animal oils; as hog's-lard, tallow, butter, and horse-oil. 3. Oil of colza, or rape-seed oil. 4. Oil of beechmast and poppy-seed, when mixed with oliveoil or tallow. 5. The several fish-oils, mingled like the preceding. 6. Hempseed-oil. 7. Nutvil and linseed-oil. 8. Palm-oil. 9. Resin. In general, the only soaps employed in commerce are those of olive-oil, tallow, lard, palmoil, and resin. A species of soap can also be formed by the union of bees'-wax with alkali; but this has no detergent application, being used only for painting in encausto.

I shall first describe, says Dr. Ure in his valuable Chemical Dictionary, the fabrication of oliveoil soap: To this oil there is usually added onefifth of that of rape-seed; without which addition the section of the soap would not be sufficiently smooth and uniform, but clotty, and unprofitable to the retailer. 100 parts of olive-oil consist, according to Chevreul, of seventy-two parts of elaïne, and twenty-eight of stearine; while 100 parts of rape-seed oil consist of fifty-four elaïne, and forty-six of stearine. Since, however, the prime equivalents of the margaric and oleic acids, which result from the above two principles, are nearly the same, that of the former being about thirty-four and of the latter thirty-six, it does not seem necessary to consider, in a chemical point of view, the proportions of the two oils. Besides the oils, the matters employed in the manufacture of this soap are, first, the soda (barilla) of commerce, of good quality, that is, containing from thirty to thirty-six per cent. of dry carbonate; secondly, quicklime; thirdly, water. 100 parts of oil require about fifty-four parts of the best barilla for saponification; and three parts of the barilla require one of quicklime. After bruising the soda, and slaking the lime, they are mingled, and a certain quantity of cold water is poured upon the mixture. At the end of twelve hours, the liquor is allowed to run off. It is called the first ley, and marks from 20° to 25° on the hydrometer of Baumé (specific gravity 116 to 1.21). On treating the residuum twice with fresh water, to exhaust it, two other leys are obtained: the one from 10° to 15° (spe→ cific gravity 1.072 to 1.114); the other from 4° to 5° (specific gravity 1027 to 1.036). When the manufacturer has laid in a stock of leys, of different densities, he engages in the soap-boiling. For this purpose he employs boilers (caldrons) which vary much in their construction, and which may contain from 5000 lbs, to 2500 lbs. of soap. In all cases, they have at their bottom a pipe two inches and two-thirds in diameter, called the thorn (epine).

They begin by putting weak ley into the boiler; they then pour in gradually the oil, and boil the mixture. The combination is soon effected, forming a species of emulsion: they temper the fire, and add successively weak ley and oil, taking care to maintain the mass in a homogeneous pasty state, without ley at the bottom or oil on the surface, in order to accelerate the combination. When they have thus put into the boiler all the oil which they wish to saponify, they add to it slowly some strong ley, which completes the saturation of the oil, converting the emulsion, with an oily excess, into a perfect soap, which separates from the ley, and which collects upon the surface.

Whenever this phenomenon occurs, the ley, although very abundant, is no longer fit for saponification; there is now present in it only some neutral salts, carbonate of soda, and a little caustic soda, unabsorbed. For this reason, when the fire has been allowed to fall, they withdraw the ley by the pipe, so as to leave the soap nearly dry. Fresh leys are now added, which are caustic and concentrated; and the fire is rekindled. Thus there is poured into the boiler

more caustic ley than is required to saturate the
oil; the mixture is then boiled, to leave no doubt
of the saturation of the oil with alkali; and the
ebullition is stopped when the ley has attained
a specific gravity of 1.15 or 1.2. This ley, over
which the soap floats, is next withdrawn, like
the preceding, and the soap is left dry at the
bottom of the boiler. In this state, the soap is
of a deep blue color, bordering on black, and
contains only sixteen per cent. of water. This
color proceeds from a combination of the oil,
alumina, and hydrosulphuret of iron, which is
formed during the pasty process, and which dis-
solves in the soap. The alumina is derived
from the furnaces in which the soda is fabricated,
and gets dissolved in it during the lixiviation.
The sulphureted hydrogen comes from the hy-
drosulphuret of soda contained in the ley, and is
set at liberty the moment that the paste or glue
is made. As to the oxide of iron, it proceeds
from the materials employed, or from the hearth
of the furnace, or from the plant itself, when na-
tive barilla is employed. This oxide of iron is
held in solution by the hydrosulphuret of soda.
When the leys do not contain enough of oxide
of iron to color the aluminous soap into a fine
blue, they add to the boiling a sufficient quan-
tity of iron, which is done by sprinkling in a so-
lution of copperas, after the pasty operation. At
any rate, it appears that the oil unites almost
immediately with the alumina and the oxide of
iron; that there thence results a yellowish alu-
mino-ferruginous soap, and that it is only by the
heat of ebullition that this soap acquires the blue
color. The soap made by the above process
may be converted either into white or marbled
soap. To convert it into white soap, we must
mingle it gradually with dilute leys, with a gen-
tle heat, and allow deposition to take place, with
a covered boiler. The blackish alumino-ferru-
ginous soap, not being soluble in the soda-soap
at this temperature, separates from it, and falls
to the bottom of the boiler. The soap-paste,
which has become perfectly white, is now taken
out, and run into the wooden frames, where it
becomes hard on cooling. From these it is fi-
nally removed, and cut into bars.

This soap is known in France under the name of soap in tables (savon en table). According to M. Thenard, it consists of,

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'According to M. D'Arcet's analysis, as reported to me by M. Clement, Marseilles white soap s composed of,

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edulcorated with very weak leys, and purified by subsidence and decantation, it contains no excess of alkali, nor any foreign body. It is hence much smoother and milder than the marbled soap, of which we are now to treat.

"When the soap-boiling is finished, and when the ley over which it swims has acquired a specific gravity of from 1.15 to 1-20, the soap is of a blackish-blue color, as we have said above. In this state, if, instead of wishing to make tablesoap, we desire to make the marbled kind, we pursue the following plan :

"We have seen that the soap contains then but sixteen per cent. of water, and that the entire mass has a dark color. We must add water to supply the deficiency, in order that the coloring matters be separated from the white paste, and that it may unite into veins of greater or less size, so as to form a species of blue marbling, in a white basis. The separation of this body may be compared to a species of crystallisation. For its proper production, the soap must be suitably diluted, and it must not be allowed to cool either too slowly or too quickly. If it be too much diluted, and if it cool too slowly, we obtain only a white soap, the whole marbling falling to the bottom. In the opposite case, it is entirely in little grains, like a mass of granite.

'This process is founded, we perceive, on the smaller solubility of the alumino-ferruginous soap at a low temperature; and on the property which the solution possesses of not being able to retain it, and of separating from it at a certain density.

At all events, whenever there is added to the boiling a suitable quantity of weak ley, to bring it to the desired point, this soap is run into the frames in the same way as the white soap, and is taken out after cooling to be cut into bars. The frames or boxes, for cooling the soap, are either wooden boxes with moveable sides fixed by wedges, or are stone troughs jointed with ce ment. The platform on which they rest must be so constructed, as to allow the ley to run off into a reservoir. This mottled soap is always harder and more uniform in its proportions than the white table-soap. In fact, the production of the marbling does not permit the manufacturer to vary the quantity of the water; for this depends on the marbling. White table soap, on the contrary, may receive as much water as the manufacturer shall desire, and it is even the whiter the more water it contains. It thence appears that the marbled soap deserves a preference.

'Some years ago, continues our author, I analyzed the foreign Castile soap, as also an imita

tion of it made in London. The first had a

specific gravity of 1.0705. It consisted of,

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"I have since examined several of the common white soaps. The average of soda per cent. is about five, from which their detergent quality may be inferred to be considerably inferior to the preceding soaps, which were all carefully manufactured. The soap lately imported from sndia, when freed from the soda powder on its urface, yields less than five per cent. of combined soda, and is hence not so powerful a detergent as many of the common soaps of this country. It is, moreover, highly charged with muriate of soda. The composition of a good soft, or potash soap, made by a respectable manufacturer in Glasgow, was as follows:Potash 9 Fat Water

43.7

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47.3

100.0

Here the equivalent proportions are no longer observed. As we may estimate the mean atomic weight of the oleic and margaric acids at 35, or ten times that of lime (oxygen being 1), we see that 9 of potash should take 52-5 of fat, instead of 437: 6 of soda (equivalent to nine of potash) in a hard soap, will indicate in like manner 52.5 of fat. I consider this proportion to be that of good soap, such as the best Marseilles; but we shall generally find, I believe, somewhat less than 5 in 100 parts of our soaps of commerce, sometimes only 4-5; and hence such soaps may be estimated at

Soda Fat

Water and muriate of soda

43.75

that contain far less of the real saponified compound than the above. It is the practice of some persons to keep the soap in strong brine, after it has been charged with a large dose of common salt. Such adulterations should be detect

ed, and their authors exposed. My alkalimeter, noticed in the introduction, will enable any person, however little skilled in chemistry, to ascertain in a few minutes the detergent or washing quality of any soap.

The specific gravity of soap is in general greater than that of water. Its taste is faintly alkaline. When subjected to heat, it speedily fuses, swells up, and is then decomposed. Exposed to the air, in thin slices, it soon becomes dry; but the whole combined water does not leave it, even by careful desiccation on a sand bath. Thus 100 parts of Berry's cake soap, analyzed above, loses only twelve per cent.; and 100 of the best Glasgow white soap, only twenty-one. If we suppose good hard soap to consist of 1 prime soda, 1 prime saponified fat, and 20 primes water, we shall have its theoretic composition to be

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This is probably the true constitution, whicn
of a little suboleate or submargarate, and a slight
may be occasionally modified by the formation
variation in the quantity of water, either from
evaporation, or the presence of a little in excess,
desiccated, if it still retains ten atoms of inti-
not chemically combined. When such soap is
mately combined water, the proportion of this
with the last of the above results.
per cent. will be twenty-two, nearly coinciding

water. This solution is instantly disturbed by
Soap is much more soluble in hot than in cold
the greater number of acids, which, seizing the
alkali, either separate the fatty principles, or
unite with them into an acido-soapy emulsion.
The solution is likewise decomposed by almost
all the earthy and metallic salts, which give birth
to insoluble compounds of the oleic and marga-
ric acids with the salifiable bases.

Soap is soluble in alcohol; and in large quantity by the aid of heat. When boiling alcohol is saturated with soap, the liquid, on cooling, forms a consistent transparent mass of a yellow color. When this mass is dried, it still retains its transparency, provided the soap be a compound of tallow and soda; and in this state it is sold by the perfumers in this country.

Good soap possesses the property of removing from linen and cloth the greater part of fatty substances which may have been applied to them.

With regard to marbled soaps, Chaptal, in his Chimie Appliquée, says, that it is not till after 5.00 or 4-5 two days' boiling, that the process of variegation 394 is begun. With this view th part of the sul. 51.25 56.1 phate of iron, relatively to the oil intended for saponification, is diluted, and decomposed with a weak lixivium. This solution (mixture) is then poured into the caldron, which is kept in a state of ebullition till the paste becomes black;

100.00 100.0

There are debased soaps, however, of which the pretended snow-soap is the most remarkable,

after which the fire is extinguished, and the lixivium which remains unincorporated is drawn off. When this is done, they rekindle the fire, and supply the paste with ley during twenty-four hours; after which, the fire being put out, the matter is left to settle, and the lixivium drawn off as before. This process is repeated for eight or nine days, at the end of which the fire is removed, and the lixivium evacuated. As soon as the mass has settled, about twelve pounds avoirdupois of Spanish-brown diffused through water are added to it. When this is done, two workmen, stationed on boards set over the caldron, and furnished with long poles, to the extremity of each of which is attached a board about ten inches square, raise up the paste, and agitate it in different directions, while others pour lixivium in at intervals, till the paste be rendered fluid. After this operation the soap is removed into the moulds. The description of the marbling process previously given is taken from Thenard, and seems the more correct, though the above manipulations are no doubt worthy of attention. We ascertain that soap has attained a due degree of consistence, 1. By allowing a small portion of it to fall and coagulate on a slate. 2. If on shaking a spatula, which has been dipped into the paste, briskly in the air, the soap be detached in the form of ribands, without adhering to the wood. 3. By the peculiar odor of soap, and by handling it between the fingers. At the stage of saponification, when the paste is becoming stiff, and beginning to separate from the aqueous liquor, Messrs. Pelletier, D'Arcet, and Lelievre, advise us, at this period, to throw into the caldron a few pounds of sea-salt, in order to produce a more complete separation; the paste then assumes a grained form, somewhat resembling spoiled cream; the ebullition is maintained during two hours, after which the fire is withdrawn, and the agitation discontinued. When a few hours have elapsed, the liquor which has subsided to the bottom of the caldron, is drawn off by means of the pipe; the fire is rekindled, the soap is dissolved by the aid of a little water poured into the caldron, the mixture is agitated, and when it is completely liquefied, and in a boiling state, the remainder of the first ley (about 1.14 specific gravity) is gradually added to it. In some manufactures, says M. Chaptal, the strongest lixivium (the first) is employed at the commencement of the ebullition; by which method the paste becomes quickly thickened to a considerable degree, and requires to be managed by persons skilled in such operations. It is judged necessary to pour in fresh ley when the paste sinks down, and remains at rest. They continue to employ the strong ley till it be nearly exhausted. Then the boiling subsides, that is, it sinks down, and appears as if stationary. It boils in this quiet manner during three or four hours; after which it is moistened by pouring into it the second lixivium (1.072 to 1.089 specific gravity), while care is at the same time taken progressively to augment the heat. It very rarely happens, when the strongest lixivium has been used at the beginning, that the third ley (1027 to 1.04 specific gravity) is necessary. This is employed only when the paste does not

boil, because then the object is to dilute it. As soon as the boiling is finished, the fire is withdrawn; the lixivium is then drawn off; after which the paste is left to cool, and taken up before it be fully coagulated, by means of copper or wooden buckets, to be transferred into moulds, into the bottoms of which a portion of pulverised lime has been previously introduced, to prevent the soap from adhering to them. At the end of two or three days, when the soap has become sufficiently hard, they remove it from the mould, and divide it into wedges of different sizes by means of a brass wire. They place these wedges on a floor edgeways, where they are allowed to remain till they become perfectly firm and dry.

The fair trader, adds M. Chaptal, lays his account with procuring five pounds of soap from three pounds of oil. The soap is not marketable till it ceases to receive any impression from the fingers.

It must not be supposed that the lixivium employed at the commencement of the process should be constantly continued. The great art of soap-making consists in knowing to deter mine, from the appearance of the paste and other circumstances, what kind of lixivium should be employed during each step of the operation. The overseers regulate their conduct in this respect by observation and experience. The form and size of the bubbles, the color of the paste, the volume of that which is thrown out on the edges of the vessel, the consistence of the matter and its disposition to swell, as well as the appearance of the steam, all furnish them with criteria by which to regulate their conduct. It sometimes happens that the paste, though apparently very firm, yet when set in the cold air to concrete, throws out much water, and is resolved into small grains possessing little consistency. In this case it is evident that the ley is in excess, and must be dissipated by heat, or precipitated (separated) by means of marine salt. Frequently, also, the paste becomes greasy, and the oil appears to separate from the soda. As this in general proceeds from the paste not being imbued with sufficient water to keep it in combination, it is necessary to add to it a portion of water, or very weak lixivium, to remedy this defect.

The adulterations most commonly practised on soap are the following:-When the soap is made, they add to it much water, which renders it white. Frequently pulverised lime, gypsum, or pipeclay, are incorporated with it. The former of these frauds is readily discovered by the rapid loss of weight which the soap suffers on exposure to a dry air; the second can be easily detected by solution in alcohol, when the earthy matters fall down.

Hard soap is made in Scotland chiefly with kelp and tallow. That crude alkali rarely contains more than from one to five per cent. of free soda, mixed with some sulphate and hydrosulphite, and nearly thirty-three per cent. of muriate of soda. To every ton of kelp, broken into small fragments, about one-sixth of new slaked lime is added. The whole, after mixture, are put into a large tub called a cave, having a perforation at the bottom, shut with a wooden plug.

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