THE FORMATION OF OILS IN PLANTS 145 



butter, and can be used for edible purposes. It is removed 

 from the mowha kernels in the same way as most forms of 

 oil. The cake left after crushing the oil contains much 

 saponin, a poisonous glucoside. The cake has been fed to 

 cattle without actually killing them, but the feeding results 

 have been very unsatisfactory. Efforts have been made to 

 extract the saponin by a commercial method, but, up to the 

 present, no particular success has resulted. Mowha cake, 

 as well as the true soap nut, has been used for exterminating 

 worms from lawns, and for several other horticultural 

 purposes. As the mowha cake has some manurial value, 

 and is relatively rather rich in potash, after the saponin has 

 done its work of destroying insect life, it serves as a manure, 

 the nitrogen amounting to 2 J per cent, and the potash to 

 I J per cent. 



Hemp Seed Oil. — Hemp has been referred to for its 

 fibre (see p. 127), but the seed can also be pressed for its 

 oil. When fresh drawn, the oil is of a pale colour, but soon 

 becomes darker on keeping. It is used for illuminating 

 purposes, for soap, and also in varnishes. 



The Essential Oils. — ^The greater number of these oils 

 are used as scents, requiring a special trade, but of the 

 common materials under this class, oil of turpentine is 

 the most important. Many species of pine trees serve as 

 sources for this material. Under the best systems, after 

 carefully removing the bark, vertical incisions are made in 

 the tree. Sticky resinous matter oozes out, and is received 

 by a cup, which is placed immediately under the slits. These 

 slits are gradually extended in an upward direction, and the 

 cups follow them. When the crude exudation of the trees 

 is distilled with water, oil of turpentine distils over, and the 

 remaining material is known as colophony or rosin. 



REFERENCES TO SECTION III 



Souchida, " Notes on Some Fatty Oils," Joum. Soc. Chem. Ind., 1916, 

 p. 1089. 



Imperial Institute Monograph, " Oil Seeds and Feeding Cakes." 

 (Murray.) 



Leathes, " The Fats. Monograph on Bio-chemistry." (Longmans.) 



D. 10 



