CHAPTEE XX. 



CARBON COMPOUNDS [contbmed)— OILS AND FATS— SOAPS— HARD SOAP 

 —SOFT SOAP— WHALE OIL SOAP— FISH OIL SOAP. 



123. Natural Fats. — Preparation. — Oils and fats are chemical 

 compounds of glyceiiue and fatty acids. They are found, in nature, 

 both in plants and in animals. They are extracted either by hot 

 or cold pressure between plates, or heated millstones, or by an 

 appropriate solvent — ^ether, carbon disulphide, chloroform, benzine, 

 petroleum spirit, etc. 



Properties. — Oils are insoluble in water ; they oxidize in the air, 

 resinifying in so doing. 



Colza oil, extracted from seeds of Brassica camjiestrls — D. = 0-913 

 at 15° C, solidifies at 6-2° C. 



Pojypy oil, extracted from seedsof Papaver somniferiim — -D. = 0*925, 

 congeals at 19° C. 



Olive oil, obtained by hot crushing of ripe olives — D. = 0'919 at 

 12° C, congeals above 0^ C. 



Linseed oil, extracted from the seeds of Linum usitatissivium, has a 

 density of 0-939 at 12= C. 



Whale oil, extracted from certain organs of the whale — D. = 0-927, 

 concretes at 0^ C. 



Action on Plants. — Vegetable respiration being carried on in the 

 leaves, these organs should remain in contact with the air so that they 

 may fulfil their physiological functions. The application of oil on the 

 leaves is therefore injurious to the plant. The pure oils themselves, 

 applied uniformly on the trunk of a tree, have an injurious effect 

 on the health of the plant. Mouillefert found, in fact, that young 

 vines are killed if the greater part of their roots are covered with 

 oil. 



Action on Insects. — Although the action of oil on insects is 

 mechanical, they are as efiicient as poisonous insecticides. The oil 

 penetrates everywhere, and by invading the respiratory organs 

 asphyxiates the insects. Eggs covered with a layer of oil also die, 

 because the exchange of gases through the membrane of the egg can 

 no longer be carried on. 



Use. — Oils are used in the pure state or as emulsions with pure 

 or soapy water. The emulsions are prepax'ed like emulsions of 

 petroleum with water. 



Silpha opaca (beet carrion beetle). — Brocchi overcomes the 

 ravages of this inseci in the North by an emulsion of soft soap 1 lb., 

 rape oil or poppy oil 15 lb., water 84 lb. Fouquier d'Herouel describes 

 (325) 



