proved by feeding the roots of the plant with additional nitrogen compounds. On all but the richest soils, the suitable application of ammonia or nitrates causes a notable increase in the quantity of food-plants, and also causes an increased proportion of the nitrogenous constituents of plants. If nitrogen compounds could be laid down cheaply enough, it would augment the supplies of food and raiment, and the comfort of man, in no small degree.
Right here it comes to mind that uncombined nitrogen forms over three-fourths of the weight of the air—a provision of about eleven pounds on every horizontal square inch—and a question rises, "Why cannot the vital forces take hold on the pure element and use freely from its most lavish supply?" Well, because the universe exists. The stomach does not digest the carbon of charcoal; nor do the lungs take oxygen from water. To propose any alteration in the character of one of the sixty-three elements is to undertake the reconstruction of the universe. It is the character of nitrogen to refuse chemical combinations. Uncombined nitrogen is nowhere available for vital uses, to any appreciable extent. Filling perfectly its humble service in Nature as a diluent in the air, its qualification is to be inert and to remain changeless. Among the resources of life and in the marts of subsistence where its compounds rank high in value, nitrogen as a simple has no place at all.
This barrier between nitrogen and its compounds seems to hold firm from age to age. Out of the ocean of atmospheric nitrogen the plant selects the scattering molecules of nitrogen compounds and elaborates therefrom many nitrogenous substances. The animal elaborates some of these into other compounds. But in the final decay of products and tissues, and food not assimilated, the nitrogen of all returns again to ammonia—again in the aerial ocean, and again the resource of plants. If ammonia is oxidized in the air to nitric acid, the latter is deoxidized in the soil to nitrous acid and then to ammonia. All these compounds are very frail, and change most constantly, but together they hold the little stock of united nitrogen, losing little of it and gaining little for it, from epoch to epoch.
There are leakages, to and fro through this remarkable barrier, it is true, but they are so small that little is known of them, except that they show the strength of the barrier that limits them. On the one side, there is a little loss, by the liberation of traces of nitrogen in certain organic decompositions. Also, the explosive agents used by man in warfare and the arts result in the liberation of nitrogen—an expenditure of life-resources. On the other side, by the electrical disturbances of the atmosphere, traces of nitrogen are brought into union. The roll of thunder indicates the restoration of a modicum of that good material which was wasted for the roll of artillery. Again, it is believed that in organic decay under restricted conditions some measure of nitrogen is brought into union with nascent hydrogen.
