242 THE POPULAR SCIENCE MONTHLY 



instead of forming in larger proportion as the temperature is raised, 

 it forms in smaller proportion; thus, if a mixture of nitrogen and 

 hydrogen be heated for a long time to 800° centigrade, only one hun- 

 dredth of one per cent, of ammonia forms, while it can be calculated 

 that at 400° one half of one per cent, of ammonia must finally result. 

 We ought therefore to work at as low a temperature as possible; but 

 we then meet the difficulty that the rate of combination becomes 

 extremely slow. Thus, owing to the extreme inertness of nitrogen, no 

 detectable quantity of ammonia is produced, even when nitrogen and 

 hydrogen are heated together for several hours at 400°. When, how- 

 ever, it is known that a chemical change tends to take place in a certain 

 direction and when the only difficulty is that it is going on too slowly, 

 there is always a reasonable hope of overcoming this difficulty; for we 

 know that chemical changes are often greatly accelerated by mere con- 

 tact with suitable solid substances. Such substances are called catalyz- 

 ers, and Professor Wilhelm Ostwald, one of Germany's distinguished 

 scientists, predicted a dozen years ago that the great advances in the 

 chemical industries within the next few decades would be made through 

 the more extensive employment of catalytic processes. This prediction 

 has found one of its many fulfilments in the commercial development 

 of the method for the production of ammonia here under considera- 

 tion. For after many years' investigation, certain metals have been 

 found which cause a rapid combination of nitrogen and hydrogen even 

 at comparatively low temperatures. The first metal that was found to 

 have this power in a marked degree was osmium, a metal similar to 

 platinum. As the total quantity of this element in our possession is 

 estimated to be 200 pounds, and as it is valued at about $1,000 a 

 pound, this discovery was hardly a practical one. Later it was found, 

 however, that under special conditions some of the commoner metals, 

 such as uranium, manganese, and even iron, when extremely pure, can 

 be made to serve the purpose. Without entering into further details, 

 it may be stated that a satisfactory yield of ammonia can be attained 

 by carefully purifying the hydrogen and nitrogen gases, by highly 

 compressing them (up to 50 or 100 atmospheres) and then passing the 

 compressed gases slowly over one of these metals at 500-600° ; and 

 that a large factory for the manufacture of ammonia by this process 

 is now being erected in Germany. 



Certain other chemical processes for the fixation of atmospheric 

 nitrogen, less direct than those already described, but nevertheless 

 commercially practicable, have also been developed and put into opera- 

 tion within the past ten years. There is therefore little doubt that 

 from these sources a large additional supply of nitrogen-compounds 

 will soon be available and that their cost will be gradually lowered. 

 To the vital problem of feeding the human race the chemist is there- 

 fore making an important contribution. 



