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 advanced 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 present 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 compounds 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 produced (1) nitrates or nitrites, (2) ammonia, (3) nitrides, or (4) cyanamid 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, however, 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