110 THE CULTURE OF FARM CROPS. 



and sulphuric acid in notable amounts. Hence the favor- 

 able result of its use as a fertilizer for these crops. 



NITRATE OF POTASH or saltpeter is a well known sub- 

 stance and consists of potash and nitric acid, and can be 

 formed by dissolving pearl ash (carbonate of potash) in 

 nitric acid and evaporating. It exists in large beds in 

 South America and is generally diffused in the soil in small 

 quantities, being produced wherever potash and decaying 

 vegetable matter happen to be in conjunction in the soil, 

 by the action of the nitrifying organism which exists in the 

 soil and is supposed to aid in the production of nitric acid. 

 This salt exerts a most remarkable effect upon plants ; con- 

 taining as it does two of the most important elements of 

 plant growth and being extremely soluble. As little as 50 

 Jbs. per acre, applied when the soil was damp has exerted 

 a marked effect upon the vegetation in the course of a sin- 

 gle night. 



OXALATE OF POTASH. Oxalic acid has not been men- 

 tioned heretofore, but it deserves a passing notice here be- 

 cause it exists in many plants which are known by their 

 ^agreeable acidity. Sorrel, and the common garden rhu- 

 barb, owe their sourness to this acid ; it is also found in the 

 chick pea ; several varieties of the rumex family (to which 

 rhubarb belongs) as the docks; also in tormentilla; bistort; 

 gentian ; saponaria ; and many others. Lichens and va- 

 rious mosses also contain this acid in combination with lime 

 and soda. It is also noteworthy because it is closely akin 

 to carbonic acid, being a derivative from the element car- 

 bon, consisting of two parts of carbon and three of oxygen, 

 and can be easily formed in a plant by the addition of one 

 equivalent of carbonic oxide (C. O.) to one of carbonic ac- 

 id (C. Oo); forming t?ogether(Co Os) oxalic acid. This acid 

 is very readily changed to carbonic acid by heat: thus 

 when oxalate of potash is heated in a capsule over a lamp, 

 it is decomposed and carbonic acid is left. It has been 

 supposed that this salt of potash exists freely in plants and 

 trees, and that this change occurs in their combustion, and 

 the formation of the ashes. It may therefore perform an 



