These waste gases were chemically investigated, and it was discovered that approximately one-fifth of the total volume thrown off consisted of carbon monoxide gas which has a very high heating value. Thereupon the Germans set to work to recover this gas, to clean it and to convert it into a fuel for driving suitably designed gas engines. Years of labour and study were devoted to the problem, which was discovered to be exceedingly abstruse. But the obstacles were overcome and the blast-furnace gas engine made its appearance. The perfection of this means of utilizing a waste product has revolutionized a certain phase of industry throughout the world. One of the first firms to adopt the new idea was the Krupp establishment, where the gas collected from eight blast-furnaces which hitherto had been allowed to escape into and mingle with the atmosphere was harnessed to drive fifteen big engines. The perfection of this achievement in waste utilization speedily became reflected throughout the country and was subsequently introduced into this country where vast strides in connection with its use have been made. Much has been related concerning the development of the airship in Germany, but this has been due in no small measure to the fact that it afforded a profitable outlet for the utilization of a waste product--one absolutely vital to the airship. I refer to hydrogen. This gas is produced in enormous quantities at many German works, and, for a considerable period, had to be ignored because no industrial use for it was apparent. A certain quantity was absorbed in the synthetic production of precious stones--topaz, rubies, and sapphires--but this consumption was trifling. Its fellow, oxygen, remained a drug on the market for many years until the coming of the oxy-acetylene and oxy-hydrogen method of welding and cutting metals came into popular favour. Then the demand for oxygen expanded so rapidly as to compel the laying down of plants for the production of oxygen from water by electrolysis. But the increased output of oxygen released still larger quantities of hydrogen for which practically no market obtained. Consequently the endeavours of Zeppelin and his contemporaries received every encouragement. With the conquest of the air by the dirigible all anxiety concerning the profitable use of hydrogen disappeared. At one large factory, producing this gas in huge volumes, a special plant capable of filling the largest Zeppelin craft was laid down. The low figure at which hydrogen was obtainable was responsible in no small measure for the popularity of ballooning in Germany in days previous to the coming of the airship. The use of coal-gas for this purpose was discouraged: it was far more valuable for fuel applications, whereas the hydrogen was not only a superior lifting agent but deserved employment because it offered a remunerative outlet for a waste, and would assist in the expansion of other industries depending upon supplies of cheap oxygen.