202 CHEMICAL DISCOVERY AND INVENTION 



is as yet uncertain, but the continual increase in the demand for 

 ammonia, not only for agricultural but for manufacturing 

 purposes, coupled with the idea of utilising this compound as a 

 step toward the production of nitric acid and nitrates, shows 

 that this possibility is not to be lightly ignored. 



A very pretty and interesting experiment sometimes exhibited 

 in the lecture room consists in bubbling oxygen through a little 

 moderately strong solution of ammonia contained in a flask, in 

 which is suspended a coil of clean platinum wire. White fumes 

 of ammonium nitrate and nitrite appear in the neighbourhood 

 of the coil, and if the supply of oxygen is rapid the flask will 

 become filled with orange coloured peroxide of nitrogen, and the 

 bubbles of gas, containing as they do an explosive mixture of 

 oxygen and ammonia, often burn as they escape from the 

 surface of the liquid and are ignited by the now red-hot metal. 

 In this experiment air may be substituted for oxygen with 

 similar though more moderate effects. 



It is perhaps remarkable that these phenomena should have 

 remained unnoticed by the industrial chemist till quite recent 

 times. Early in the present century, however, the conditions 

 of the reaction between ammonia and air in the presence of 

 platinum were investigated by Professor W. Ostwald of Leipzig, 

 and it was found that the yield of nitric acid amounted to 

 something like 85 per cent of the theoretical. The ammonia 

 mixed with a relatively large volume of air is passed through a 

 layer of platinum coated with the spongy metal, or other less 

 expensive catalysts such as one of several metallic oxides, and 

 maintained at a temperature of 300 C. or somewhat higher. 



It appears that in this process the purity of the ammonia is 

 not a matter of much importance, and even the gas from crude 

 gas liquor may be used. Of course ammonia from any source 

 may be employed, and this method of producing nitric acid has 

 latterly been associated with the process of Frank and Caro in 

 which synthetical calcium cyanamide is decomposed by steam : 



CaCN 2 +3H 2 =CaC0 3 +2NH 3 . 



The catalytic processes which have become most familiar are 

 those in which the addition of oxygen is the object in view, and 

 the idea of adding hydrogen to nitrogen as a practical means of 

 obtaining ammonia is still in the early stages of development. 



But the researches of Professor Sabatier of Toulouse on com- 



