Other Materials.
Water.—Water intended for use in soap-making should be as soft as possible. If the water supply is hard, it should be treated chemically; the softening agents may be lime and soda ash together, soda ash alone, or caustic soda. There are many excellent plants in vogue for water softening, which are based on similar principles and merely vary in mechanical arrangement. The advantages accruing from the softening of hard water intended for steam-raising are sufficiently established and need not be detailed here.
Salt (sodium chloride or common salt, NaCl) is a very important material to the soap-maker, and is obtainable in a very pure state.
Brine, or a saturated solution of salt, is very convenient in soap-making, and, if the salt used is pure, will contain 26.4 per cent. sodium chloride and have a density of 41.6° Tw. (24.8° B.).
The presence of sulphates alters the density, and of course the sodium chloride content.
Salt produced during the recovery of glycerine from the spent lyes often contains sulphates, and the density of the brine made from this salt ranges higher than 42° Tw. (25° B.).
Soapstock.—This substance is largely imported from America, where it is produced from the dark-coloured residue, termed mucilage, obtained from the refining of crude cotton-seed oil. Mucilage consists of cotton-seed oil soap, together with the colouring and resinous principles separated during the treatment of the crude oil. The colouring matter is removed by boiling the mucilage with water and graining well with salt; this treatment is repeated several times until the product is free from excess of colour, when it is converted into soap and a nigre settled out from it.
Soapstock is sold on a fatty acid basis; the colour is variable.
FOOTNOTES:
[1] Calculated by us from saponification value.