ents the
English degrees and corresponds to 99 per cent. sodium carbonate
(Na_{2}CO_{3}).

_Soda ash_, 48 deg., sometimes called "caustic soda ash," often contains
besides carbonate of soda, 4 per cent. caustic soda (sodium hydrate),
and 10 per cent. salt (sodium chloride), together with water and
impurities.

The 48 degrees refers to the amount of alkali present in terms of sodium
oxide (Na_{2}O), but expressed as English degrees.

_Caustic potash_ (potassium hydrate) is offered as a liquid of 50-52 deg. B.
(98-103 deg. Tw.) strength, and also in solid form as 75-80 deg. and 88-92 deg. The
degrees in the latter case refer to the percentage of potassium hydrate
(KHO) actually present.

_Carbonate of Potash._--The standard for refined carbonate of potash is
90-92 per cent. of actual potassium carbonate (K_{2}CO_{3}) present,
although it can be obtained testing 95-98 per cent.

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 deg. Tw. (24.8 deg. 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 deg. Tw. (25 deg. 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
grai