Every one has noticed the peculiar fresh smell of the air which follows a thunderstorm; the same pungent odour appears in the vicinity of a frictional electric machine when in operation. This smell has been attributed to ozone, but it is now thought that it may be due to oxides of nitrogen; in other words, the electric discharges of lightning or of the frictional machine have burned the air--that is, combined the nitrogen and oxygen of the air, forming oxides of nitrogen. [Illustration: Mr. Charles S. Bradley.] [Illustration: Mr. D. R. Lovejoy.] The fact that an electric spark will thus form an oxide of nitrogen has long been known, but it remained for two American inventors, Mr. Charles S. Bradley and Mr. D. R. Lovejoy, of Niagara Falls, N. Y., to work out a way by inventive genius for applying this scientific fact to a practical purpose, thereby originating a great new industry. I shall not attempt here to describe the long process of experimentation which led up to the success of their enterprise. Here was their raw material all around them in the air; their problem was to produce a large number of very hot electric flames in a confined space or box so that air could be passed through, rapidly burned, and converted into oxides of nitrogen (nitric oxides and peroxides), which could afterward be collected. They took the power supplied by the great turbine wheels at Niagara Falls and produced a current of 10,000 volts, a pressure far above anything ever used before for practical purposes in this country. This was led into a box or chamber of metal six feet high and three feet in diameter--the box having openings to admit the air. By means of a revolving cylinder the electric current is made to produce a rapid continuance of very brilliant arcs, exactly like the glaring white arc of the arc-lamp, only much more intense, a great deal hotter. The air driven in through and around these hot arcs is at once burned, combining the oxygen and nitrogen of which it is composed and producing the desired oxides of nitrogen. These are led along to a chamber where they are combined with water, producing nitric or nitrous acid; or if the gases are brought into contact with caustic potash, saltpetre is the result; if with caustic soda, nitrate of soda is the product--a very valuable fertiliser. And the inventors have been able to produce these various results at an expense so low that they can sell their output at a profit in competition with nitrates from other sources, thus giving the world a new source of fertiliser at a moderate price. [Illustration: Eight-Inch 10,000-Volt Arcs Burning the Air for Fixing Nitrogen.] [Illustration: Machine for Burning the Air with Electric Arcs so as to Produce Nitrates.]