ning 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.

[2] Calculated by us from saponification value.

[3] Calculated by us from saponification value.

[4] Calculated by us from saponification value.

[5] Calculated by us from saponification value.

[6] Calculated by us from saponification value.

[7] Calculated by us from saponification value.

[8] Calculated by us from saponification value.

[9] Calculated by us from saponification value.

[10] Calculated by us from saponification value.

[11] Calculated by us from saponification value.

[12] Calculated by us from saponification value.

CHAPTER IV.

BLEACHING AND TREATMENT OF RAW MATERIALS INTENDED FOR SOAP-MAKING.

_Palm Oil--Cotton-seed Oil--Cotton-seed "Foots"--Vegetable
Oils--Animal Fats--Bone Fat--Rosin._

Having described the most important and interesting oils and fats used
or suggested for use in the manufacture of soap, let us now consider
briefly the methods of bleaching and treating the raw materials, prior
to their transference to the soap-pan.

_Crude Palm Oil._--Of the various methods suggested for bleaching palm
oil, the bichromate process originated by Watts is undoubtedly the best.
The reaction may be expressed by the following equation, though in
practice it is necessary to use twice the amount of acid required by
theory:--

K_{2}Cr_{2}O_{7} + 14HCl = 2KCl + Cr_{2}Cl_{6} + 7H_{2}O + 6Cl.

6Cl + 3H_{2}O = 6HCl + 3O.

The palm oil, freed from solid impurities by melting and subsidence, is
placed in the bleaching tank, and washed with water containing a little
hydrochloric acid. Having allowed it to rest, and drawn off the liquor
and sediment (chiefly sand), the palm oil is ready for treatment with
the bleaching reagent, which consists of potassium bichromate and
commercial muriatic acid. For every ton of oil, 22 to 28 lb. potassium
bichromate and 45 to 60 lb. acid will be found sufficient to produce a
good bleached oil.

The best procedure is to act upon the colouring matter of the oil three
successive times, using in the first two treatments one-third of the
average of the figures just given, and in the final treatment an
appropriate quantity which can