570 Professor George Lunge [March 15, 



of coal are consumed than for the latter, since coke is indispensable 

 for the smelting of iron and for other metallurgical purposes. Up 

 to about twenty years ago all the volatile by-products in the manu- 

 facture of coke \Yere lost— that is to say, tar, gas, and ammonia. The 

 recovery of these by-products was first carried through in one or 

 two French coke-works, about 1861, but nowhere else for a number 

 of years, although in 1879 the late Dr. R. Angus Smith had 

 earnestly recommended to the English coke-works the adoption of 

 that system. Even now, both in France and England as well as 

 in America, the recovery coke-ovens have found only a very limited 

 adoption ; in England perhaps 5 per cent, of the coke is made in this 

 way, against upwards of 50 per cent, in Germany. In consequence 

 of this, whilst twenty years ago Germany imported nearly all ammonium 

 sulphate required for its agriculture from this country, she now 

 imports none, and has, on the contrary, become a large exporter of 

 that commodity. The reasons for this wonderful change are various. 

 One of them is undoul)tedly the revival of that spirit of push and 

 enterprise which, after lying dormant for centuries in consequence 

 of the ravages of the Thirty Years' War, caught up the German 

 people, and enlivened German industry in all directions. Without 

 going into details on this matter, we may take it that a considerable 

 reserve of ammoniacal nitrogen exists in the quarter indicated, and 

 that the present production of about half a million tons of ammonium 

 sulphate might be greatly increased in that manner. 



But that reserve is, after all, nothing like sufficient to cover the 

 requirements of agriculture in the future ; and it is quite likely that 

 in the long run all the really available nitrogen of the coal would not 

 suffice foi" the wants of man. And what about the time when coal 

 itself will be exhausted ? Well, there is an eternal and inexhaustible 

 source of nitrogen to which we must turn, and that is the atmo- 

 spheric air. Four-fifths of this consists of nitrogen, calculated to 

 amount to 4000 billions of tons, mixed with a quarter of that weight 

 of oxygen. More than 100 years ago, in 1785, Cavendish discovered 

 the fundamental fact that, by the action of the electric arc, the 

 nitrogen of the air combines with oxygen to form nitric acid. The 

 formation of ammonia from atmospheric nitrogen has also been 

 effected, Ijoth by electricity and (which is more important) in other 

 ways as well, as we shall see anon. But until a very few years ago 

 these facts had never been put to any practical use, and the problem 

 of turning tlie atmospheric nitrogen into annnonia, or nitric acid, 

 although frequently approached in a ])urely scientific or, experimentally, 

 in a technical way* had not been solved. Our days have seen the 

 realisation of that most important task. 



Let us first speak of annnonia. We are led up to this ])y what is, 

 verily, a long and circuitous path. We nnist start from the discovery 

 of calcium carbide (announced in 1802 by the celebrated Woehler), 

 the technical preparation of which substance was first effected by 



