296 INDUSTRIAL PLANTS 



poppy-oil, from the seeds of the opium poppy (Fig. 172), and 

 nut-oil, from the kernels of the EngUsh wahiut (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 ^nade with soda. Chemically th(> 

 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 arc introduced during the process of preparing the product 



