208 DETERMINATION OF ALKALIES IN MINERALS. 



25. The manner of proceeding is as follows: to the filtrate 

 and washings concentrated in the way mentioned (22), and 

 still remaining in the flask, pure nitric acid is added — about 

 three grammes of it to every gramme of sal ammoniac sup- 

 posed to exist in the liquid. A little habit will suffice to guide 

 one in adding the nitric acid, as even a large excess has no 

 effect on the accuracy of the analysis. 



26. The flask is now warmed very gently, and before it 

 reaches the boiling-point of water a gaseous decomposition 

 will take place with great rapidity. This is caused by the 

 decomposition of the sal ammoniac in the manner described 

 in the note. It is no advantage to push the decomposition 

 with too great rapidity. A moderately warm place on the 

 sand-bath is best adapted for this purpose. With proper pre- 

 cautions the heat can be continued and the contents of the 

 flask evaporated to dryness in that vessel; but it is more judi- 

 cious to pour the contents of the flask, after the liquid has 

 been reduced to half an ounce, into a porcelain capsule (always 



the whole process if concentrated nitric be used. If, however, it be diluted, 

 little or none is formed, and the gas is readily given off at about 212° Pah. 



In all my experiments the protoxide of nitrogen constituted from seven 

 eighths to twenty -four twenty -fifths of the gaseous products, and when 

 washed from its chlorine by a little lime-water or soda possessed all the 

 properties of pure protoxide of nitrogen; and I would recommend it as a 

 convenient way of forming this gas, especially when not required for 

 respiration. 



The character of the decomposition which takes place is somewhat curious 

 and unexpected. At first I supposed that the decomposition resulted in the 

 formation of equal volumes of NO, CI, and 1ST; but it appears that such is 

 not the case, and that all but a very small portion of the ammonia, with its 

 equivalent of nitric acid, is converted into NO, the liberated hydrochloric 

 acid mixing with the excess of nitric acid. A little of the sal ammoniac 

 and nitric acid does undergo the decomposition first supposed, and in this 

 way only can the small amounts of chlorine and nitrogen be accounted for. 

 At the time this method was first tried I also tried the decomposing effects 

 of nitrate of ammonia on sal ammoniac, that has been shown by Maumene 

 (Comptes Eendus, October 15, 1851) to result in the formation of chlorine 

 and nitrogen; but the difficulty of controlling the decomposition once com- 

 menced, the pufling-up of the mixture, and the necessity of having the salts 

 dry to begin with, render this method (which was proposed by the author 

 for forming chlorine) useless in processes for removing the sal ammoniac in 

 analysis. 



