224 



ORIGIN OF THE NITRATES. 



Take, first, the action of the spark. It is well known that 

 ammonia is decomposed by a series of sparks into its elements, 

 the volume of the gas being practically doubled after a rather 

 short period of time. Nevertheless, there remains a trace of 

 ammonia, not capable of measurement, though capable of being 

 manifested, as will be presently shown. Now, nitrogen and 

 hydrogen undergo reciprocally a commencement of combination, 

 by the action of a series of electric sparks. However, the pro- 

 portion of ammonia formed is so slight as not to be shown by a 

 change in volume. But it is sufficient to introduce into the 

 gases a bubble of hydrochloric acid gas to produce abundant 

 fumes. (In order that the experiment may be reliable, it is 

 necessary to operate with gases thoroughly dried before the 

 experiment and over dry mercury, the least trace of water 

 vapour being indicated in the same way by hydrochloric acid 

 gas.) This reaction is so delicate that it reveals the thousandth 

 part of a mgrm. in a small volume of gas. 



To accumulate the effects of this reaction, it is sufficient to 

 operate in presence of dilute sulphuric acid, so as to gradually 

 absorb the ammonia. It is then easy to collect a considerable 

 quantity of it at the end of a sufficient time. The author has 

 not been able to discover the inventor of this experiment, but 

 it appears as already classic in the first edition 

 of Kegnault's "Traite de Chimie," printed in 

 1846, and dates from still further back. 



10. The action of the silent discharge is far 

 more efficacious than that of the spark in 

 causing the union of nitrogen with hydrogen. 



The silent discharge has also the double 

 property of decomposing ammonia into its 

 elements and of combining elementary nitrogen 

 and hydrogen. These two gases being mixed 

 in the ratio of three volumes of hydrogen to 

 one volume of nitrogen, if the silent discharge 

 be made to act upon the mixture, after a few 

 hours as much as three per cent, of the mixture 

 will be found to have been transformed into 

 ammonia. The latter may then be measured 

 by volume, and manifested by all its reactions. 



11. The apparatus which was most commonly 

 employed for making the silent discharge act upon 

 the gases is formed of two distinct glass tubes 



(1) A very thin stoppered tube, enlarged at the lower part, 

 and forming a test-tube, so arranged as to permit of the intro- 

 duction, the extraction, and the rigorously exact measurement 

 of the gases over mercury, all as clearly and easily as with 

 ordinary gas test-tubes. 



This tube is surrounded by a thin strip of platinum, arranged 



Fig. 34. Silent 

 discharge test- 

 tube. 



