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 grams of oxalic acid in 50 c. c. of hot water, add 

 solution 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 crystals of a salt of oxalic acid and ammonia the oxalate of ammonia 

 separate on cooling, the compound being sparingly soluble in cold wa- 

 ter. Preserve for future use. 



EXP. 37. Add to any solution of lime, as lime-water, (see note, p. 36,) 

 or 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. Add a few drops of chlorhydric or nitric acid to the 

 oxalate of lime; it disappears. Hence oxalate of ammonia is a test for 

 lime only in solutions containing no free mineral acid. (Acetic and 

 oxalic acids, however, have little effect upon the test.) 



Definition of Acids, Bases, and Salts. In the popular 

 sense, an acid 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 bases. The strongest acids, 

 i. 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, etc. 



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 



