32 PRACTICAL FARM CHEMISTRY. 



Another simple compound of importance to the 

 farmer is the following : 



Chlorine ) forming chloride of sodium or common 

 Sodium ) salt. 



Compounds between simple substances, as we 

 have seen, are readily formed. These simple com- 

 pounds, acids as well as alkalies, also have a strong 

 desire to enter into more complicated chemical com- 

 binations; but, while neither of them can combine 

 with a simple substance (or element), each acid seeks 

 the union with an alkali, and each alkali the union 

 with an acid. It is only the same old story. The 

 male or positive|principle in nature seeks the female 

 or negative principle, and the female or negative 

 principle cannot find its rest and satisfaction except 

 in union with the opposite principle. We will also 

 find that these simple compounds have their prefer- 

 ences — Miss Alkali accepting one Mr. Acid and 

 refusing another when a choice is given. Some of 

 the acids (called " strong acids, " sulphuric acid for 

 instance) seem to be veritable "Don Juans," step- 

 ping in between unions already formed, we might 

 say, forcing a divorce by driving off the weaker 

 acid and taking the bride. Carbonic acid is one of 

 the "weak" ones, and often has to take a back seat. 

 It happens that the weak party is content with 

 taking up the alkali that the strong acid has cast 

 aside for a more congenial union. The two parties 

 then exchange partners — by a sort of double divorce 

 and cross- marriage. A case of this kind is that of 

 gypsum and ammonia. 



It is not unusual to see married life modify or 

 change prominent characteristics in both parties; to 

 neutralize each other's vices, harshnesses, or mischiv- 

 ous inclinations. A chemical union also, and 



