Page:Popular Science Monthly Volume 62.djvu/144

138 elements. Like Coleridge's Mariner, floating on the sea, surrounded by the sea, and yet perishing for lack of water, so plants growing on the bottom of the aerial ocean, with four fifths of its bulk consisting of nitrogen, and that to a depth of 200 miles or more, would yet starve for lack of nitrogen if there were not means in nature's workshop to combine that very inert gas. Now, soils of average fertility contain rather more than .1 per cent of nitrogen; in other words, the soil taken to a depth of one foot contains 3,500 pounds of nitrogen to the acre. The quantity is not constant, because of the various factors that lead either to the increase or decrease of that treasure hoard which it had taken ages to accumulate. In the processes of decay and fermentation, due to the activity of molds and bacteria, much of the combined nitrogen is set free and is returned to the atmosphere; in all processes of burning and explosion great quantities of nitrogen are again liberated. This latter fact led Bunge to say that every shot fired kills whether it hits anything or not, for it takes away that much life-giving substance from living things. Then again, as the insoluble proteid molecules are broken down and changed into simple salts, the nitrogen that thus becomes soluble, if not taken up by the crop, is leached out of the soil, and ultimately finds its way to the ocean. Enormous quantities of nitrates are thus carried by the streams to the sea, there to feed its denizens, to return, perhaps, in very slight measure to the land, though changed into other forms. Thus the great swarms of coarse fish caught for fertilizer purposes return in their bodies the nitrogen that had once traveled to the sea; thus, also, the still extensive nitrate beds of arid South America are a fractional return of what the sea had taken to itself. That the dissolved nitrates poured into the sea year after year by streams great and small do not remain there as such is clearly evidenced by the analysis of sea-water which shows but traces of nitrates. And so it appears that the soluble nitrogen salt, greedily taken up by plants in the field, is also quickly consumed in the sea. Of course, the nitrate deposits of South America were not deposited from the ocean as such, but resulted from the decay of great masses of seaweed.

Then there are opposite tendencies. There are agencies which lead to the increase of the nitrogen stock in the soil. It was Cavendish who first showed that when electric sparks are passed through air confined over a solution of caustic potash, small quantities of oxidized nitrogen are formed. In a similar manner, the electric discharges in the atmosphere cause the formation of small quantities of combined nitrogen, and Berthelot had shown that silent electric discharges also cause the combination of gaseous nitrogen. Similarly it has been claimed that in the burning of gas, coal, wax, etc., slight amounts of nitrogen become combined. All these factors, and others not mentioned, are, however, of