208 COMMON SUBSTANCES 



243. Alcohol. Common alcohol (C 2 H 5 OH) is formed 

 when dextrose or grape sugar ferments ( 267). Hence 

 it often appears when fruit juices are allowed to stand 

 for some time. As a solvent, alcohol is much used in 

 making varnishes, 'tinctures, perfumes, and drugs. It 

 is useful in medicine because it stimulates the action 

 of certain parts of the body; but a continual use of 

 alcohol in any quantity is injurious. It burns with 

 a hot, smokeless flame, being thus useful in several 

 of the arts. 



244. Fats and Oils. Fats and oils are salts formed 

 by the union of glycerin with different acids. Fats are 

 solid substances, and occur usually in animal matter. 

 Oils are liquids ; they occur in both plant and animal 

 matter. The acids that may unite with glycerin to form 

 fats or oils are called fatty acids. 



245. Soap. A soap is an alkali salt of a fatty acid. 

 Soap may be made by boiling fats together with an 

 alkali (NaOH or KOH). The fats break up into their 

 acids and glyceryl, the metal of the alkali uniting with 

 the acid to form soap, and glycerin being given off. 

 Thus soap is a salt of the metal Na or K with an acid 

 obtained from a fat. 



Soap acts upon the oily matter that is mixed with 

 dirt on the skin or on fabrics ; the oil is broken up into 

 tiny particles that may be washed away by water, carry- 

 ing the dirt with them. Water alone could not do this, 

 because fats and oils do not dissolve in it. Many kinds 

 of soap contain much free alkali ; this renders them effect- 

 ive for cleansing, but often injurious to certain fabrics. 



