Commercial Nitrates 175 



Early use of nitrates. The natives of India recog- 

 nized long ago the stimulating action of nitrate in 

 plant growth. It is stated that the natives of certain 

 districts in Bengal, " particularly a caste called Quirees 

 (hereditary gardeners), who cultivate the best lands 

 and produce the best crops, are in the habit of irrigating 

 their fields with water from wells so strongly impreg- 

 nated with saltpeter and other salts as to be brackish. 

 They consider onions, turnips, and peas to be most 

 benefited by this irrigation." Saltpeter is also believed 

 to have been used as a manure by the peasants of Mantua, 

 and is known to have been employed by Digby in Eng- 

 land in the reign of Charles I. It was likewise recom- 

 mended as a top-dressing by Evelyn in the reign of 

 Charles II. Early in the nineteenth century, the use of 

 saltpeter was slight, but not uncommon, in England, and 

 a few decades later the application of Chile saltpeter 

 was resorted to by many farmers to supplement the 

 natural production of nitrates in the soil. 



Conditions influencing the formation of nitrates. The 

 rapidity with which nitrates are formed from the soil- 

 humus is determined largely by soil and climatic con- 

 ditions. The nitrifying bacteria must have sufficient 

 moisture and a favorable temperature for their develop- 

 ment. They must have the proper supply of humus 

 as the source of nitrogen; they will not develop in the 

 absence of lime or magnesia, which serve, in the average 

 soil, to neutralize the nitric acid formed by the bacteria. 

 The presence of lime and magnesia, or of other basic 

 substances, as they are called, is of extreme importance. 

 They combine with the nitric acid produced by the bac- 



