The Fixation of Nitrogen.

Progress, Volume I, Issue 10, 1 August 1906, Page 263

The Fixation of Nitrogen.

The romantic deportment of the nitrogen atom is fascinatingly interesting to the student of chemistry. Wherever he looks he sees that the living, moving, doing thing m the world is nitrogen ; it is at once the most restless and the most powerful of the elements. When nitrogen enters into a collocation of atoms we invariably expect the collocation to do something active, whether good or ill ; for the nitrogen compounds have properties and qualities they are never inert

So it is that, entering into combination with a few other atoms, it will yield us the most delicate and delicious of perfumes, while it is equally ready to join forces with, others to produce substances whose smell of utter vileness has the psychological effect of causing the experimenter to " wish he was dead." In the aniline dyes it enhances our clothing with a thousand beautiful colours, and in still another thousand forms it enters the chambers of the sick in the healing guise of all the synthetic medicines. It lurks m prussic acid, the ptomaines, and a host of deadliest poisons ; it drives our bullets in the form of gunpowder ; it explodes our mines as dynamite and guncotton ; it dissolves our metals as nitric acid ; it extracts our gold as cyanide ; and in an infinity of ways it menaces or ministers to mankind. Nitrogencontainmg substances, then, are active substances, and their activity seems to be due to a certain " temperamental nervousness " of the nitrogen atom which sends it flying on the slightest pretext from one atomic community to another. On this account we call nitrogen a " labile " element. But it is only when we consider nitrogen in its relation to life that we see how truly momentous is this fact of its lability. We have been accustomed in the past to ascribe to carbon the role

of life element paramount, but the more the 'juestion is studied, the more does it appear evident that the carbon constituent of the body is the mere brick and mortar of it, good enough to constitute its physical substratum, and good enough, too, to burn as fats and carbohydrates to maintain its fires, but that the working, building, " vital " thing, the thing that is the moving-spring of protoplasm and that brings about the continuous adjustment of internal to external conditions that we call life, is the versatile, restless nitrogen. It looks as though the living being constituted a vast unstable plasma in which the nitrogen atom, with oxygen on the one hand and carbon or hydrogen on the other, very much as it is in mtro-glycenne, swings the atoms of the living body through all the multiplex atomic relations of growth and decay. The lability of living substance is the lability of the nitrogen atom, and we may say, with much more propriety than " Ohne Phosphor kern Gedanke," " Ohne Stickstoff kern Leben " — no life without nitiogen.

And yet — and this is a most interesting thing — this nitrogen, which when combined with elements of another kind is so energetic and so useful, is, in its care-free, solitary condition, a stubborn lazy, inert gas. In this the elemental conditions it is one of the most abundant and pervading bodies on the face of the earth. It constitutes four-fifths of the air that blows in our faces, and so much of it there is that every square yard of earth's surface has pressing down upon it nearly seven tons of atmospheric nitrogen. Chemically speaking, it is all but unalterable, though the " all but " is vastly important to us. One or two metals, such as calcium and magnesium and a few compounds of metals, may be made to unite with it. We find, too, that certain organisms, bacteria — " nitrifying microbes " they are called — have within their little bodies laboratories for attaching nitrogen to other elements, though the mechanism of this action no man understands. Still, again, we find that the lightning flash will cause the nitrogen and oxygen of the air to combine in the path of its streak to form nitrous acid, or that it will cause the nitrogen and water vapour to react to form ammonia. Outside, however, of the minute quantities which are extracted from the air m these various ways, the whole great ocean of atmospheric nitrogen under which we live and move maintains, in a chemical sense, a listless, useless lethargy. Now, nitrogen which is united with other elements (it matters very little which) and which is so temperamentally nervous and active and useful we call " fixed " nitrogen, while the nitrogen which exists in the elemental lethargic condition of the nitrogen of the air we call " free " nitrogen, and the object of this paper is to present the various modern attempts to solve the problem of transforming

in large quantities the free and useless nitrogen into the fixed and useful kind. This problem is of immense importance to the whole world — to every race, to every human being — for as a matter of hard, cruel fact we either must solve this problem or starve. This statement is a most unlikeable one, for it is sensational and alarmist, but how true, it is easy to show. The invaluable " fixed " nitrogen which we have within us, and which we are continuously using up, we must continually restore. In order to do this we eat it. We eat it in the form of animal food or of certain plant products, such as wheaten bread. But plants and animals, too, depend upon the soil for every trace of the nitrogen they contain, and the soil in its turn has won it from the reluctant air through the slow accumulations of the washing rain, from the lightnings of a million storms, or through slow transformations by billions of nitrifying organisms through what, so far as we are concerned, is infinite time. Not only so, but the valuable nitrogen-containmg substances we employ m our civilisation are m the same parlous position of depending upon the soil. Every cannon-shot disperses in an instant the fixed nitrogen which it required millions of microbes centuries to accum-

ulate. We filch this nitrogen from the soil immensely faster than it is restored by natural processes, and the land grows sick and barren and refuses to grow our crops. Everybody knows what we must do to cure the land ; we must use manure or fertiliser. In other words, we must mix with the soil substances containing fixed nitrogen which the plant may utilise in building up what we must and will haye — bread and meat, to say nothing of other substances such as gunpowder and dyes and medicines. In the olden time natural manure was sufficient to meet the demands of sparse populations accustomed to poor food and little of it ; but m these days of rapidly multiplying civilised man, who requires more food and better food, particularly wheaten bread, the natural manure of the world is a mere drop in the bucket of his wants ; and this would be true even if he could utilise the fixed nitrogen of the sewage and drainage of his towns, which, it is horrifying to learn, England alone hurries down her watercourses to the sea to the value of a year.

As a matter of fact we were long ago forced to the employment of three other fertilisers. The first of these was Peruvian guano. This substance was produced from the excrements and remains of sea-birds deposited m a very and region It contained fixed nitrogen in the form of about twenty per cent, of ammonia. We say the first " was " guano, for while in 1856 the year's sale amounted to 50,000 tons, to-day it is practically nothing at all. We have eaten it up. The second fertiliser is ammonium sulphate. This is obtained as a by-product in the distillation of coal-tar in the manufacture of coke. In 1900 the world's production of ammonium sulphate was 500,000 tons, worth some But this amount is a fixed quantity ; we may have so much and no more from our coal-tar distilleries, and large as the amount seems, it is inadequate to supply the one-hundredth of the imperious and increasing demands of our Mother Earth. There is actually but one substance, the third, possible of being used on a world-wide scale as a nitrogenous manure. This is nitrate of soda, or, as it is called Chili saltpetre. It occurs native over a narrow band of land between the Andes and the coast hills, a rainless district, where for countless ages the continuous fixation of atmos-

pheric nitrogen by the soil, its conversion into nitrate by nitrifying organisms, its combination with soda, and the crystallisation of the nitrate have been steadily proceeding against the time when, as now, earth's increasing family would insistently demand it for bread. In order to drive home to the reader the validity of the statement we are about to make, let us examine the pay roll of the years. The Chili saltpetre beds yielded in iB6O, 68,500 tons ; m 1870, 182,000 tons , in ISBO, 225 000 tons ; in 1890, 1,025,000 tons ; m 1900, 1,453,000 tons ; and since 1900 every year has added 50,000 tons to the demand of the year before. The amount yielded m 1900 — 1,453,000 tons — was sold for one-quarter of it passing into the thousands of nitrogen compounds used in our civilisation, and the other three-quarters into food through its fertilising action in agriculture. 1 European and American agriculture and a hundred varied kinds of industry are thus wholly and implicitly dependent upon a fmy little strip

of land in a South American republic, and upon the grace of the " Nitre Kings " who own it ; and were the little republic to close her gates of export, hungry months and insurrections would follow as infallibly as the night the day. This is, of course, embarrassing and highly significant of the interdepending conditions of our civilisation ; but when we begin to estimate the amount of nitre taken out and the amount still remaining in the beds, and compare this amount with the crescendo ratio of the world's demand, we are more than philosophically interested — we are practically frightened. We see that what has happened to guano will inevitably happen to saltpetre. It is a matter of plain, hard cold-drawn fact, as everybody now knows who knows anything about the Chili saltpetre beds and the needs of agriculture, that these saltpetre beds will not last longer than twenty years, if present conditions continue. About the year 1925, then, there will be no more nitre ; and a year or two after that, or before it, famine will stalk on the lands of civilised men. This is acknowledgedly true if present conditions continue. But the phrase, " if present conditions continue'", contains the crux of the whole matter. Why should they continue ? We have "lnjthejenveloping

air an immense and inexhaustible supply of nitrogen — 33,880 tons of it upon every acre of land. This is " free " nitrogen and the world demands it " fixed." If man must fix the wandering air into his own bodily substance and into substances that are the implements of his advancement, he will so fix it, and withm the quarter of a century which is his margin. Let us see how far we have progressed. In attacking this problem, man of necessity and convenience imitated nature. If the cosmic processes were too slow, it was for man to hasten them. If there exist certain little organisms capable of fixing atmospheric nitrogen, why not favour them, breed them, multiply them to our needs ? It was discovered by Hellnegel that certain leguminous plants, such as clover, beans, and peas, have near the base of their stalks little nodosities, little pimples, which turned out to be veritable colonies or cities of nitrifying microbes. These interesting microbes on every pea plant, for mere board wages, work full time m turning over the useless atmospheric nitrogen to the plant in a

fixed and useful form. Furthermore, it was discovered that soil inoculated with such microbes would grow these plants even when innocent of any trace of manunal nitrogen. The deduction is obvious. Why should we not blossom the desert with clover or peas, and thereafter plough the plants into the ground to afford manure for a succeeding crop of wheat. In 1896 Nobbe and Hiltner produced this microbe in a commercial portable form under the name of " Nitragin." The experiment failed, as nearly all first experiments fail The bacteria died, and, as it subsequently appeared, probably for want of suitable food, and possibly, too, from injuries suffered by secretions from the seed itself in the early stages of germination. But to know the cause of failure was to succeed They now supply this necessary nourishment in in the form of grape sugar and peptones added to* the water in which they are distributed for spreading upon the soil. Their measure of success has been so great that we find to-day several manufacturers perfecting the method

and establishing their processes for the wholesale production of nitrifying microbes. Another method has been ascribed to Professor G. Moore, of the United States Department of Agriculture He has sent out to the farmers of the country the dried germs packed in cotton. With them go two packages containing the food upon which they are to multiply when placed in water — one containing granulated sugar, potassium phosphate, and magnesium sulphate, and the other ammonium phosphate The microbes when placed in the solution of these substances multiply with prodigious rapidity and serve to inoculate either the seed or the soil. But there are many other nitrifying microbes besides those concerned with legpmmous plants — dozens of tribes and hundreds of species, and investigation is to-day feverishly busy with them. We have every reason to believe that by multiplying nitrifying organisms alone, we should be able, in some measure at least, to restore to the soil the fertilising nitrogen which m the past we have wilfully and extravagantly wasted.

We have said that the lightning bolt burns the air in its path into oxides of nitrogen which, when washed b} the ram into the soil, quicklybecome fixed into nitrates. We have learned to harness the lightning and why should we not, therefore, imitate nature in this respect as well, and utilise the combining efficiency of the electric spark, and burn the air to make our daily bread ? Over a hundred years ago the masterly Cavendish showed that with the tiny electric sparks at his command this could actually be accomplished, and afterwards, by this very method, Lord Rayleigh burned the air to obtain the interesting argon hidden within it. In the powerful heat of the electric arc there is a combustible gas, and the only reason that this gas, when once ignited, has not spread through the surrounding atmosphere and deluged the world in a sea of nitric acid is the peculiar fact that its ignition point is above the temperature of its flame It is not hot enough to set fire to the adjacent mixture. ( To be continued. )