THE SOAP-BOILER.

1. The business of the soap-boiler consists in manufacturing soap, by the combination of certain oily and alkaline substances.

2. The earliest notice of this useful article occurs in the works of Pliny, in which it is stated, that soap was composed of tallow and ashes; that the mode of combining them was discovered by the Gauls; but that the German soap was the best.

3. For many ages before the invention of soap, saponaceous plants, and several kinds of earth, together with animal matters and the ley from ashes, were employed for the purpose of cleansing the skin, and articles of clothing. The idea of combining some of these substances, with the view of forming soap, probably originated in accident.

4. The vegetable oils and animal fats, capable of saponification, are very numerous; but those most commonly employed in the manufacture of the soaps of commerce, are olive-oil, whale-oil, tallow, lard, palm-oil, and rosin; and the alkalies with which these are most frequently combined, are soda, the ley of ashes, or its residuum, potash.

5. Soda is sometimes called the mineral alkali; because it is found, in some parts of the world, in the earth. It was known to the ancients, at a very early period, under the denomination of natron. It received this appellation from the lakes of Natron, in Egypt, from the waters of which it was produced by evaporation, during the summer season.

6. The soda of commerce is now chiefly obtained from the salsola, a genus of plants which grows on the sea-shore. In Spain, the plant from which soda is obtained is denominated barilla; hence, the substance produced from it by incineration has received the same appellation. The ashes of a sea-weed which grows on the coasts of Scotland and Ireland, is called kelp. In Europe, barilla and kelp are more extensively employed in the manufacture of soap than any other alkaline substances; but, in this country, where wood is so much used for fuel, common ashes are generally preferred.

7. The process of making the ordinary brown or yellow soap, from wood-ashes, is conducted in the following manner. The alkali is first obtained in a state of solution in water, by leeching the ashes as described in [page 26], and then poured, in a weak state, into a copper or iron caldron, having a large wooden tub carefully affixed to the top of it.

8. When the ley has been properly heated, the tallow, either in a tried state or in the suet, is gradually added. More ley, of greater concentration, is poured in; and the ingredients are moderately boiled for several hours; while a person, as represented in the preceding cut, aids their chemical union by agitating them with a wooden spatula.

9. After a quantity of rosin has been added, and properly incorporated with the other materials, the fire is withdrawn until the next morning, when it is again raised; then, with the view of forming the paste into hard soap, a quantity of muriate of soda (common salt) is added. The muriatic acid of this substance, uniting with the potash, forms with it muriate of potash, which dissolves in the water, while the soda combines with the tallow and rosin. Hard soap, therefore, contains no potash; although this alkali is generally employed during the early part of the process of making it.

10. After the addition of the muriate of soda, the boiling and stirring are continued two or three hours, when the fire is withdrawn, and the contents of the caldron are suffered to be at rest. When the soap has completely separated from the watery part and extraneous matters, it is laded into another caldron, again diluted with strong ley, and heated. The paste having been brought to a proper consistence, more common salt is added as before, and for the same purposes.

11. The chemical part of the process having been thus completed, the soap is laded into single wooden boxes, or into one or more composed of several distinct frames, which can be removed separately from the soap, after it has become solid enough to stand without such support. The soap is cut into bars, of nearly a uniform size, by means of a small brass wire.

12. Manufacturers of soap have contrived various methods of adulterating this article, or of adding ingredients which increase its weight, without adding to its value. The most common means employed for this purpose is water, which may be added, in some cases, in considerable quantities, without greatly diminishing the consistence of the soap.

13. This fraud may be detected by letting the soap lie for some time exposed to the atmosphere. The water will thus be evaporated, and its quantity can be known by weighing the soap, after its loss of the superfluous liquid. To prevent evaporation, while the soap remains on hand, it is said, that some dealers keep it in saturated solutions of common salt. Another method of adulteration is found in the use of pulverized lime, gypsum, or pipe-clay. These substances, however, can be easily detected by means of a solution in alcohol, which precipitates them.

14. The process of manufacturing soft soap, differs but little in its details from that described in the preceding paragraphs. The chief difference consists in omitting the use of salt. Soft soap, therefore, is composed of a greater proportion of water, and more alkali than is necessary to saturate the unctuous matters. Soft soap is made by almost every family in the country, from ashes, grease, and oily matters, reserved for the purpose.

15. The celebrated Marseilles white soap, is composed of

Soda,6.
Olive-oil,60.
Water,34.

Castile soap, of

Soda,9.
Olive-oil,76.5.
Water, with a little coloring matter,14.5.

Fine toilet-soaps are made with oil of almonds, nut-oil, palm-oil, suet, or butter, combined with soda or potash, according to their preparation in a solid or pasty state.

16. In the manufacture of white soap, the tallow is more carefully purified, and no rosin is used. In other particulars, the process differs but little from that employed in the production of the common kind. Two tons of tallow should yield three tons of white soap. In making the same quantity of common brown or yellow soap, twelve hundred weight less is required, on account of the substitution of that amount of yellow rosin.

17. The mottled appearance of some soaps is caused by dispersing the ley through it, towards the close of the operation, or by adding a quantity of sulphate of iron, indigo, or the oxide of manganese. Castile soap, now manufactured in the greatest perfection at Marseilles, in France, receives its beautifully marbled appearance from the sulphate of iron.