32 R. A. F. PENROSE, JR. 



association with bat guano. In some cases, where these caves are 

 in limestone, the nitrate occurs in the form of calcium nitrate, which 

 was probably produced by the oxidation of the nitrogenous materials 

 of the bat guano and the subsequent action of these oxidized products 

 on the limestone. As caves in limestone are very common, the occur- 

 rence of calcium nitrate is frequently observed. In the old days 

 nitrate was also made artificially from organic refuse in what were 

 known as niter heaps. These produced mostly calcium nitrate, 

 which was then converted to potassium nitrate. The nitrates in the 

 soils of India and in the niter heaps were derived from nitrogenous 

 animal matter, just as the cave nitrates were derived from guano, 

 and the process in all these cases was made possible by the agency of 

 certain bacteria already described in this paper (see p. i8). 



In California, nitrate deposits occur in the arid region of the 

 southeastern part of the state, in San Bernardino and Inyo counties, 

 and elsewhere. The conditions there are not unlike those of northern 

 Chile, the region consisting of high arid basins bordered by mountain 

 ranges. The nitrate is mostly in the form of sodium nitrate, though 

 some potassium nitrate occurs, and is associated with common salt 

 (sodium chloride) and other saline materials, very much as in Chile. 

 As yet these deposits have not become of much commercial value. 



In recent years efforts have been made to obtain nitrogen from the 

 air and to convert it to nitrates or other nitrogen compounds available 

 for commercial purposes. The atmosphere contains nitrogen in the 

 proportion of approximately 79 parts to the 100. This nitrogen, as 

 has long been known, can be oxidized by electrical and other methods 

 and converted to nitrates and other salts of nitrogen. Numerous 

 methods for this operation have been devised, but their discussion is 

 beyond the scope of the present paper, and the reader is referred to 

 the readily accessible literature on the subject for further information. 



