Political and commercial geology and the world's mineral resources

by Unknown

—Being indisposed to participate in chemical combinations, nitrogen in the course of world evolution was left largely to itself; and since in the free state it is normally gaseous, it established its home in the atmosphere. Thus it comes about that the atmosphere today is approximately four-fifths nitrogen gas, and after all is said and done the atmosphere is bound to constitute the great source to which we must turn for our supplies. With a source so boundlessly ever-present, the question of supply at first glance looks simple enough. But atmospheric nitrogen, it must be remembered, is nitrogen uncombined, and the demand is not for nitrogen itself but for nitrogen-bearing compounds. Once in a state of combination, it may remain so indefinitely, and the form of combination may be changed more or less readily to suit the demand. Before it can be put to use, however, it must be induced to surrender its gaseous freedom and affix itself in some such state of combination. The free nitrogen must become fixed nitrogen—hence the terms fixed nitrogen, nitrogen fixation, and the like in common use. Toward this end it must be induced to do what it has not seen fit to do of its own accord, and the very trait of aloofness responsible for the inexhaustible resources of atmospheric nitrogen stands as an obstacle opposing their utilization. The obstacle has not proven insuperable, as will appear later; but it is sufficiently a source of trouble even to this day, so that the fixed-nitrogen situation may with peculiar appropriateness be characterized as distinctly in the air.

Nitrate Ore Deposits.

—The disposition on the part of nitrogen to take up its abode in the atmosphere has an obvious result in minimizing the development of mineral nitrates. Atmospheric nitrogen is not entirely stagnant, however. Natural processes are constantly at work effecting substantial fixation. The processes are not obtrusively energetic, as in the case of atmospheric oxygen, whose fixation processes constitute the ever-present phenomena of oxidation. Still, in various ways, the most prominent among which is undoubtedly a form of bacterial action, nitrification and the building up of nitrate minerals everywhere in the soil goes quietly forward, and their concentration in ore deposits of more or less plentiful occurrence is thus to be looked for in the natural course of geologic events. In attempting to trace their further course, however, we are confronted at the outset by the principle of solubility. The nitrate minerals are in the nature of soluble salts. They leach from the immediate environment in which they form, just as do the soluble minerals in general. Mostly these latter are carried in solution to the ocean, adding themselves to its salinity; but under exceptional conditions of topography, where the drainage feeds into land-locked basins, the water finds itself entrapped with no avenue of escape except through evaporation. Here the salts accumulate, become concentrated, and finally give rise to deposits.

This, in outline, is the course set for the soluble mineral salts as a class, and it is along this course that we must expect to trace the development of nitrate ore deposits. But the ocean, with its 3¹⁄₂ per cent. of salinity, has only traces of nitrate minerals; and the same is true for the waters of land-locked basins, in all the various stages of concentration. Their solubility is such that they can not have escaped in substantial form along the way. There is only one inference to be drawn. Evidently the inherent trait of aloofness is not lost to nitrogen when it does combine. The compounds do not survive for any length of time, but undergo dissociation, releasing their nitrogen and returning it to the atmosphere even as other processes are slowly withdrawing it from the atmosphere.

With this the eternal cycle is closed for nitrogen, and closed without apparent provision for any considerable side-tracking, such as would be required in the building up of ore deposits. So much for the rule; now as to the exceptions: Mostly they are of minor consequence. Pockety enrichments in the soil are common. Accumulations tend to build up in caves, and may even grow to be of consequence in a small way, as during the Civil War, when they helped materially toward relieving the nitrogen troubles of the blockaded Confederacy. In arid country, too, they not infrequently assume sufficient prominence to be of interest, especially at the hands of the promoter. Finally, there are the Chilean nitrate fields, which far from being of minor consequence, go to the other extreme in catering to the needs of the entire world.

These occurrences, especially the last named, have served to keep alive the hope that others of economic importance await discovery. The Chilean deposits alone among them all deserve more than passing notice. The origin of these deposits is veiled in uncertainty. Just why or how the natural forces, which elsewhere as a matter of universal observation have been seen to oppose both the formation of nitrogen salts and the accumulation of such as do manage to form, should have failed in this particular instance remains wholly conjectural. A conclusive explanation would be of the utmost value in determining the likelihood of similar occurrences elsewhere. But none has been forthcoming, and nothing is to be gained to the present purpose from stopping to inquire into the plausibility of the various attempts that have been made. Confronting us on the one hand are the evidences of a nitrogen cycle established, seemingly, without affording any visible loophole of opportunity for the accumulation of extensive deposits; on the other hand stands the bare fact of enormous deposition. This fact of existence unquestionably carries with it the possibility of duplication elsewhere. However, the fact of occurrence merely suggests the possibility, but does not determine the chances of recurrence. These are recorded in the prevalence of the conditions requisite to extensive deposition. In the case of nitrogen they are unique beyond comprehension, and the prospect of recurrence is to precisely the same degree unlikely. Accordingly, to all practical purposes, a review of the world’s nitrate ore deposits, both real and potential, resolves itself down to a review of the Chilean occurrence.

The Chilean nitrate fields lie in the arid valley basin to the east of the lofty coast range and just south of the present Peruvian boundary line. They do not occur as a single expansive area of deposition, but as deposits scattered here and there along the desert land at the bases of the mountain slopes. The formation consists of a conglomerate or breccia of rock material from the adjacent slopes, cemented with a mixture of soluble salts in which sodium chloride, common salt, is the dominant member, with sodium nitrate ranking second. The formation is called caliche. It lies for the most part just below the surface of the ground and varies from a few feet to many feet in thickness. Only in scattered patches is the caliche high enough in content of sodium nitrate to warrant treatment. These patches are sought out and excavated, and the picked ore is loaded in carts, which haul it to the extraction plant for treatment. Here the soluble salts as a whole are extracted in solution, and the nitrate in turn is segregated from the other salts by crystallization. Aside from haulage, hand labor is used throughout.

The caliche regarded as worth treating contains not less than 10 per cent. nitrate and ranges up to 25 per cent. and over, with an average of around 18 per cent. The product marketed is of two general grades—the ordinary, listed as 95 per cent. nitrate, and the refined, a guaranteed 96 per cent. nitrate, low in sodium chloride. The deposits have been worked more or less consistently, and with steadily increasing output, since about 1830. Their importance in the scheme of nitrogen supply may be gathered from [Figures 16] to [18].

Organic Nitrogen.

—Another source of fixed nitrogen grows out of its relationship to life processes, and is consequent on the very requirements of organized society which earlier it is called upon to assist in meeting. In other words, fixed nitrogen participates in the material cycle of life. It enters into the material demands of life for food, and it is yielded up among the material discards available to absorption. All manner of residuum, animal and vegetable alike, affords at least a potential source of fixed-nitrogen supply. Some of these are in service; others for one reason or another are not. Prominent among those in the former class are animal excreta, the so-called tankage from animal rendering plants, slaughter-house refuse, fish scrap, and vegetable-product refinery refuse. Most prominent among those still largely potential are sewage and garbage disposal.