THE SOAP-BOILER.

The Soap-boiler makes the article called Soap, which is composed of an oil and an alkaline salt, for the purpose of washing linen, the hands, and other domestic and manufacturing operations.

The combination of an oil with an alkali uniformly produces a compound, soluble in water, and in which the characteristic properties of oils and alkalies are destroyed or changed. But as combinations of soda and potash are only employed in this business, we shall, of course, confine ourselves to a particular consideration of them.

It is probable that ages must hare elapsed before mankind arrived at a knowledge of the composition of soap. Saponaceous plants,
argils, marls, fuller's earth, a species of argil, extensively, and in an early period, known, and magnesia, appear all to have been employed in cleansing linen and other cloths, long before the discovery of soap. We even see that some animal matters were employed, with advantage, for the same purpose. It is equally certain, that the use of ash-leys preceded the discovery of soap. But the capability of combining oil with alkali, so as to form a solid compound, soluble in water, and can dissolve spots of grease without changing the colour of the stuffs, on which they are found, is a discovery of inestimable value in the arts. This discovery, successively
improved, constitutes what is now termed the art of soap-making.

There is scarcely any substance manufactured by the art of man, more useful than that of soap : at first sight it may seem strange, that the article which is used to clean and whiten other substances, should itself be formed of grease, or oil, and that the coarsest fat may be made into soap.

Soap is either hard or soft ; it is variously named, according to its colour: we have white, mottled, yellow soap, &c. But all the kinds
are made with fat or oil, combined with either potash or soda ; but principally with soda, unless a soft-soap is wanted, as potash liquifies upon exposure to atmospheric air, whereas soda effloresces, or, in other words, parts with the water which it contains, and, therefore, is the most proper for hard-soaps.

Potash is an alkaline salt, obtained from vegetables in the following manner; vegetable substances of any kind, burnt in the open air,
and reduced to ashes, contain a certain proportion of salt, which is to be obtahied from the ashes by mixing them with water : when
the water is filtered, it is to be evaporated by heat, and the saline'substance the potash, or if it be very fine and white, the pearl-ash, is left at the bottom of the vessel.

Soda is generally obtained in this country from an article imported from Spain, called barilla which consists of the ashes of a plant named soda, which grows plentifully in some parts of that country, particularly on the shores of the Mediterranean. Both potash and soda are called fixed alkalies, because they are not commonley dissipated by heat ; the former is also sometimes denominated vegetable alkali; the latter mineral alkali ; distinctions which are neither correct, nor of any real use in science.

These alkalis, as they are usually found, cannot be employed in the manufacture of soap till they are deprived of their carbonic acid, and the earthy matter which they contain. This process is conducted in the following manner : into a vessel about eight feet square, and one foot deep, is introduced quicklime, in the proportion of one-fifth of the weight of oil intended to be converted into soaps:. water is slightly sprinkled over the quicklime, which then grows hot, cracks, smokes, and falls down into powder ; after which the soda, or barilla, previously pounded, must be carefully mixed with it, by means of a shovel.in order to favour the operation, a little water is occasionally added. As soon as the mixture is accomplished, it is transferred into tubs. In small establishments the vessels are made of white wood; but in those which are on a larger scale, they are composed of stones, lined with bricks, formed on the spot, and aunk into a mortar made of puzzolana, or similar earths. These cisterns are usually about five feet by four, and one and a half in depth. They are perforated at the lower part of the side, next the workhouse, with two holes, which are closed by stop-cocks, or pegs of wood. Under each of these vessels are reservoirs, constructed with the same card, und intended for the reception and preservation of the leys, when the lime and soda is transferred to the tub, or to these cisterns, a quantity of water is poured on the mixture, sufficient to cover it to the height of a foot and a half. After leaving the water in this state for several hours, it is drawn off into one of the reservoirs. This ley marks from fifteen to twenty degrees of concentration and is called the first ley; Water is to be again put upon the mixture, and to stand and afterwards to be drawn off as before : this is termed the second ley: and the operation is repeated as long as ley of any power comes from the mixture.

In large manufactories, the ley is made no stronger than to be able to sustain a new-laid egg; The oil, or tallow, is first boiled with a part of the ley, which may be diluted with water, till the whole is formed into a soapy compound. The stronger ley is then to be added, and kept slowly boiling, while a person assists the union by constant agitation. When it is sufficiently boiled, a separation will appear to be taking place; the soap being at top and the fluid below : to effect this separation completely, a quantity of common -salt is added. The materials are usually boiled three or four hours, when the fire is withdrawn. The soap is found to unite at the top of the liquor; which is now called the waste ley, and being of no further use, it is drawn off.

The soap is now melted with another ley and when a little boiled it is cast into wooden frames. These frames are moveable, and range exactly one upon the other, and the soap is filled in from the bottom to the top. When it is perfectly set and cold, the workman takes off the upper frame, and with a piece of copper wire he cuts off the soap which that frame contained. He then takes off another frame, and, so on till he comes to within five or six of the bottom, and there he finds the ley has drained from the soap into the middle of the substance; of course, from this height to the bottom., the cakes of soap have an oval hole left in them. This ley he takes carefully out with an iron ladle, and puts into the bucket which stands before him. By a like process he cuts the soap into narrow slices, as it is usually sold in the shops.

The tallow for making soap is reckoned very good if 13cwt of it with alkali yield a ton weight of soap.

White soap is made of olive oil and soda. Yellow soap is made with tallow and yellow rosin, in the proportion of ten parts of tallow
and three and a half of rosin; these, if good, will, with alkali, yield twenty of soap.

Mottled soap obtains its. speckled appeance by dispersing the ley through the soap towards the end of the operation, or by adding a quantity of sulphate of iron, which, by its decomposition, deposits its oxide through the soap, and gives it the appearance of streaked marble. Some manufacturers use oxide of manganese for the same purpose. We believe, however, that the colouring ingredient, in the mottled soap of London, is indigo. Certain it is, that the soap known in commerce by the name of Castile soap, (the best, however, ot this sort is brought from Marseilles,) is an oil soap, united with a considerable quantity of the sulphate of iron, in the decomposition of which the beautiful marbling of that soap is effected.

In France, a cheap soap is made by using woollen rags, old woollen cloths, and even the horns, &c. of animals, instead of oil. These
substances are soluble in caustic ley, and by proper boiling form soap ; but it has a very disagreeable smell.

Soap is easily and completely dissolved in water ; but in hard water it curdles, or is only imperfectly dissolved ; on this account, a
solution of soap in spirits of wine is used to discover whether the water of any spring or pond be hard or soft ; for if the water be soft, the solution will unite with it ; but if it be hard, the soap will separate in flakes.

The soap-manufacturer is subject to the excise laws ; and he pays a heavy duty for every pound of soap which he makes. His coppers, and even his furnace-doors, are furnished with locks and keys, and he dares not open them but in the presence of an excise officer, and he must give notice of twenty-four hours, or more, in writing, to the officers before he begins making. His house is no longer an Englishman's castle, into which none may come but by his leave ; the excise officers are required to enter it at all times, by day or by night; who may, between the hours of five in the morning ana eleven at night, unlock and examine every copper, and every part of the dwelling-house, none daring to obstruct them, without incurring very heavy penalties. To similar restrictions the tallow-chandler and other trades under the exciserfews are subject. The soap-manufacturer must also take out an annual license from the excise-office, besides being subject to these fiscal regulations.