50 FRUIT TREES AND THEIR ENEMIES 



not so perfect as in other cases. Paraffin cannot be 

 emulsified with sulphur. 



Those who are interested in the nature and 

 behaviour of emulsions, will find some investigations 

 on the subject described in the Eighth Report of the 

 Woburn Experimental Fruit Farm. 



17. Soap. — Ordinary soap is a "salt" of one of the 

 alkali metals with a non-volatile fatty acid, generally 

 oleic, palmitic or stearic acid, according to the sub- 

 stances from which the soap has been made — cocoa- 

 nut oil, palm-kernel oil, olive oil, tallow, cottonseed 

 oil, fish-oil, resin, etc. The sodium salts constitute 

 the hard, or curd soaps, the potassium salts, the soft 

 soaps. Both contain considerable percentages of 

 water, and the latter may also contain a certain 

 amount of glycerin, and a little free alkali. Soft 

 soaps vary considerably in colour, ranging from 

 amber-yellow to brown ; those made from fish-oil 

 are greenish, and possess an offensive smell, but 

 other soaps are sometimes coloured green artificially. 

 American fish-oil soaps are known as whale-oil soap, 

 although they are not, as a rule, made from whale 

 blubber. 



Soft soaps are freely soluble in water, whereas hard 

 soaps are comparatively insoluble ; the result is that 

 when any compound containing sodium, such as 

 caustic soda or common salt, is added to a solution ot 

 soft, or potash, soap, this is converted into hard, 

 or soda, soap, which is thrown out of solution, or 

 "salted out," as it is termed, forming a flocculent 

 mass which rises to the surface. If paraffin has 

 been emulsified with the soft soap, it also becomes 



