86 HOW CROPS GROW. 
is found in the juices of plants that grow on the sea-shore 
Oxalate of ammonia is employed as a test for lime. 
Exp. 36.—Dissolve 5 giims of oxalic acid in 50 ¢. c. of hot water, add 
solutior of ammonia or solid carbonate of ammonia until the odor of the 
latter slightly prevails, and allow the liquid to cool slowly. Long, needle 
like erystals of a salt of oxalic acid and ammonia—the oxalate of ammonia 
separate on cooling, the compound being sparingly soluble in cold wa- 
ver. Preserve for future use. 
Exp. 37.—Add to any solution of lime, as lime-water, (see note, p. 36,) 
cr hard well water, a few drops of oxalate of ammonia solution. Oxalate 
of lime immediately appears as a white powdery precipitate, which, from 
its extreme insolubility, serves to indicate the presence of the minutest 
quantities of lime. Addafew drops of chlorhydric or nitric acid to the 
oxalate of lime; it disappears. Hence oxalate of ammonia is a test fo 
lime only in solutions containing no free mineral acid. (Acetic anG 
oxalic acids, however, have little effect upon the test.) 
Definition of Acids, Buses, and Salts.—In the popular 
sense, an weid is any body having a sour taste. It is, in 
fact, true that all sour substances are acids, but all acids 
are not sour, some being tasteless, others bitter, and some 
sweet. A better characteristic of an acid is its capability 
of combining chemically with dases. Thestrongest acids, 
z. e. those bodies whose acid characters are most strongly 
developed, if soluble, so as to have any effect on the nerves 
of taste, are sour, viz., sulphuric acid, phosphoric acid, 
nitric acid, ete. 
Bases are the opposite of acids. The strongest bases, 
when soluble, are bitter and biting to the taste, and cor- 
rode the skin. Potash, soda, ammonia, and lime, are ex- 
amples. Magnesia, oxide of iron, and many other com- 
pounds of metals with oxygen, are insoluble bases, and 
hence destitute of taste. Potash, soda, and ammonia, are 
termed alkalies ; lime and magnesia, alkali-earths. 
Salts are compounds of acids and bases, or at least re- 
sult from their chemical union. Thus, in Exp. 20, the salt, 
phosphate of lime, was produced by bringing together 
phosphoric acid, and the base, lime. In Exp. 37, oxalate 
of lime was made in a similar manner. Common salt—in 
