The chemical catechism, with notes, illustrations, and experiments / By Samuel Parkes.

  • Parkes, Samuel, 1759-1825.
Date:
1810
Catalogue details

Licence: Public Domain Mark

Credit: The chemical catechism, with notes, illustrations, and experiments / By Samuel Parkes. Source: Wellcome Collection.

    178/588 (page 156)
    IVhy are the alkalies employed in making soap ? An alkali is an essential ingredient in soap, as it is the only article capable of converting tallow or oil into a saponaceous substance, and enabling it to combine with water*. Jl'hy are thejixed alkalies employed in making colours ? Many colours are now manufactured in this country which cannot be made without an alkali: thus, animal matters are always incinerated with * To make soap, it is necessary to employ a fixed alkali in a caustic state. In this country the business is usually conducted in the following manner: Spanish barilla or Scotch kelp is broken in pieces, or coarsely ground by a horse mill; and, when mixed with a sufficient quantity- of quick-lime to absorb the carbonic acid, the whole is thrown into large wooden or iron vats, and covered with water. In large works, these vats are generally of cast iron, and sufficiently capacious to hold 3 or 4 tons of alkaline ashes. At a proper time, the water, impreg- nated with the caustic alkali, is let off into iron receivers be- low, and the vats are covered again with water, which, after standing a sufficient time, is let off' as before. This liquor is called soap-boilers’ ley. When a sufficient quantity of this is prepared, Russian or English tallow is put into a large iron boiler, and melted with a portion of the above-mentioned alkaline ley. At first the tallow appears liquid like oil, but during its boiling it acquires by degrees consistence as it saponifies. When the alkali is uniformly combined with the tallow, the weak liquor is pumped from beneath the soap, and fresh leys are added in their stead. These are boiled as before, till the soap exhibits certain appearances well known to the manufacturer : it is then cooled down, and poured into deep wooden frames 15 inches wide and 45 inches long ; where it remains till it has acquired a sufficient degree of solidity to be cut up for sale. It is the alkali which gives soap its detergent quality, and which renders it soluble in water. The tallow serves to moderate the sharp- ness of the alkali, and to prevent its injuring the hands of those who use it. In making yellow soap, resin is used in the proportion of about 1 part to 3 or 4 parts of tallow. The resin makes the soap more detersive, -and enables the manufacturer to sell it