296 INDUSTRIAL PLANTS 
poppy-oil, from the seeds of the opium poppy (Fig. 172), and 
nut-oil, from the kernels of the English walnut (Fig. 27). 
These being comparatively expensive are reserved for fine 
painting. 
Linseed-oil is invaluable also as a solvent for copal and 
other resins, with which it unites at a high temperature to 
form the highest class of varnishes. Entirely by itself it is 
used extensively to give an attractive “‘oil finish” to wood- 
work. In certain varnishes the volatile oil or spirits of tur- 
pentine, known commonly to the trade as “turps,” is the 
solvent used, and is likewise indispensable to painters as a 
means of thinning their colors. 
Any of the fixed oils combined with an alkali makes soap. 
When potash (or lye from wood ashes) is used soft soap is 
formed; hard soap being made with soda. Chemically the 
fixed oils are mixtures, in various proportions, of compounds 
called glycerides. A glyceride is so called because it consists 
of glycerin (the familiar sweetish substance soluble in water) 
combined with an acid. Linoleic, oleic, and palmatic acids 
are among the most important in vegetable oils. The gly- 
ceride of linoleic acid, called linolein, forms 80% of linseed- 
oil, and gives to this and to other drying oils their peculiar 
power of hardening by oxidation. Olein, the glyceride of 
oleic acid, is the main constituent of olive-oil. It is liquid 
at ordinary temperatures and becomes rancid by oxidation. 
Palmatic acid forms a glyceride, palmatin, which is not liquid 
at ordinary temperatures. It is the main solid constituent 
of coconut and other palm-oils. When any fixed oil is mixed 
with an alkali, the glycerides present are decomposed each 
into its peculiar acid and glycerin, and the acids unite with 
the alkali to form soap, leaving the glycerin free. 
Inferior grades of linseed oil and other cheap oils are used 
for soft-soap. Oil from the olive (Fig. 113) is used extensively 
for castile, and other fine toilet soaps. Other hard soaps of 
various grades are made from “‘ cocoa-butter ”’ (see section 39), 
and oils from coconut (Fig. 36), cotton-seed (Fig. 215), peanut 
(Fig. 32), and almond (Fig. 31). 
To give an agreeable odor to soap a large variety of volatile 
oils are introduced during the process of preparing the product 
