INDUSTRIAL USES 31 



beech-nut oil, cotton-seed, sesame and croton oils, and the 

 lesser-known oils of the apple, pear, orange, barley, and rye 

 seeds. 



2. The rape oil group comprising garden cress, hedge 

 mustard, wild radish, black mustard seed, white mustard 

 seed, radish seed, and rape or colza oil. 



The oils of the latter sub-group have a lower saponification 

 value (p. 21) than any other vegetable oils, and arachidic 

 acid seems to be a normal constituent of them all. 



To determine whether an oil is a drying one or not, a drop 

 is spread on a glass plate, such as a microscope slip, and left 

 for several days at atmospheric temperature. Non-drying oils 

 such as olive and castor oils are unaltered after about eighteen 

 days ; semi-drying oils such as cotton-seed, sesame, and rape 

 oil are more or less dry, but still sticky in from seven to 

 eight days, whereas real drying oils, like poppy and especially 

 linseed, are quite dry in from three to six days. 



The mechanism of the process of drying is very imperfectly 

 understood ; it would appear to be in part a chemical change 

 involving oxidation, with the resulting formation of a substance 

 known as Linoxyn,* and partly a physical change. f 



INDUSTRIAL USES OF VEGETABLE FATS AND OILS. 



Economically, fats are of considerable value, being used for 

 food, illumination, lubrication, soap manufacture, and for a 

 variety of other purposes. 



The following is a brief consideration of some of the more 

 important industrial uses of the commoner fats and oils of 

 vegetable origin. 



Olive Oil is extracted from the fleshy pericarp of the fruit 

 of the olive, Olea europcsa, by pressure. The best quality oil, 

 which is expressed without the application of heat, is used for 

 food ; lower grade oils, obtained by extracting the residues 

 from the presses with fat solvents, such as carbon disulphide 

 or light petroleum, arc used in the manufacture of soap (see 



P- 33)- 



* Holden : " J. Soc. Dyers and Col.," 1927, 43, 157. 

 t Wolff : " Chem. Zeit.," 1924, 48, 897. 



