134 THE POPULAR SCIENCE MONTHLY 



THE ORIGIN" OF NTTEATE DEPOSITS 



By WILLIAM H. ROSS, Ph.D. 



BDEEAD OF SOILS, U. S. DEPARTMENT OF AGRICULTURE 



THE origin of all nitrate deposits was at one time accounted for by 

 oxidation. The theory was held that the production of nascent 

 nitrogen through the decomposition of organic matter caused a union to 

 take place between the oxygen of the air and the nitrogen of the organic 

 matter. Since then it has been shown that nitrates may be produced in 

 various ways, and new theories are still being advanced from time to 

 time to explain the origin of the nitrate deposits which occur in various 

 parts of the world. The fact that different views have often been ad- 

 vanced to explain the origin of the same deposit has given rise to a great 

 deal of discussion, and there still exists a wide difference of opinion as 

 to the source from which the nitrogen may have been derived. By the 

 source in this case is usually meant the preceding form in which the 

 nitrogen appeared rather than the ultimate source of the nitrogen since 

 this is generally admitted to be the atmosphere. The object of the pres- 

 ent writing is to give a review of the various theories which have been 

 advanced in this connection. 



The fixation of nitrogen, that is, the transformation of elementary 

 nitrogen into a combined state, may be brought about in the laboratory 

 in a great many ways. Some of these processes have been shown to be 

 profitable commercially and large quantities of nitrates and other com- 

 pounds of nitrogen are now being manufactured in Europe and likewise 

 in Canada, at Niagara Falls, but up to the present no commercial plant 

 for the manufacture of " atmospheric nitrogen " products has yet been 

 established in this country. These various processes of fixing nitrogen 

 artificially may be grouped into four classes according as there is pro- 

 duced (1) nitrates or nitrites, (2) ammonia, (3) nitrides, or (4) cyana- 

 mid and its related compounds. 



The fixation of nitrogen in nature also takes place in a number of 

 different ways, but, unlike the technical operations just referred to, this 

 is brought about principally by organic processes. Small amounts, how- 

 ever, are also fixed in nature by inorganic processes in a way analogous 

 to some of the artificial methods, and in this way there are formed 

 nitrates or nitrites, ammonia and nitrides. 



The best known case of the inorganic fixation of nitrogen in nature 

 occurs when nitric acid is formed in the air by lightning discharges at 

 the time of thunder storms. The quantity of nitrogen which is combined 



