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.