CHEMISTRY OF NITROGLYCERINE. 83 



obtained was found to be equivalent to 33 45 per cent, of the whole nitro- 

 glycerine, proving that the nitroglycerine had not been apparently decomposed 

 by heating with alcohol. 



From this it is evident that the alcohol used as a menstruum in ascertaining 

 the action of other substances on nitroglycerine did not of itself aid in the 

 decomposition of the nitroglycerine. 



Preparation of Nitroglycerine. — After I had observed that nitroglycerine 

 yielded, when decomposed with an alkali, a large amount of nitrous acid, and being 

 fully sensible of the insufficiency of existing analyses to determine the elementary 

 composition of nitroglycerine, doubts arose in my mind, as I have already 

 stated, as to whether nitroglycerine was actually a tri-nitrate of glyceryl. I 

 have already given some important reasons in connection with its alkaline 

 decomposition products for regarding it as the tri-nitrate, and not as any form 

 of a nitrite. But I have thought it advisable to supply what additional proof 

 could be obtained of its composition from a consideration of the yield of nitro- 

 glycerine from a given weight of glycerine. For this purpose I prepared nitro- 

 glycerine with various proportions of glycerine and acids, in order to ascertain 

 the highest possible yield of nitroglycerine. Another important object which I 

 had at the same time in view was to learn how far such variations in the method 

 of the preparation of nitroglycerine might affect its composition. The latter 

 object was very desirable, owing to the very discrepant statements which have 

 been made by previous investigators as to nitroglycerine consisting entirely of 

 tri-nitrate of glyceryl, or of a mixture of the tri-nitrate with the di-nitrate and 

 mono-nitrate. 



In the preparation of the nitroglycerine, Price's pure glycerine, dried for 

 six hours in the air-bath at a temperature of 120°C, was always employed ; the 

 specific gravity, after drying, was 1260 at 14°C. The acids were each of two 

 strengths — nitric acid, of a specific gravity of 1*422 (referred to as strong nitric 

 in what follows), and 1/494 (referred to as fuming nitric acid) : sulphuric acid, 

 of a specific gravity of 1-844 (referred to as strong sulphuric acid), and 1*984 

 (referred to as fuming sulphuric acid) ; all at 15*5°C. In every instance the 

 nitric and sulphuric acids were first mixed and placed in a vessel containing 

 salt and ice, and cooled to below 0°C. In certain cases where urea was also 

 used, it was added to the nitric acid previous to mixture with the sulphuric 

 acid. Into the cooled mixture of the acids the glycerine was slowly dropped 

 and well mixed by constant stirring, the temperature, as ascertained by a ther- 

 mometer, never being permitted to rise above 10°C. After standing for a 

 variable time, the mixture was poured into a large and measured quantity of 

 cold water, when the nitroglycerine was precipitated. It was now very care- 

 fully collected, after thorough stirring with the water, and was in this slightly 

 impure state dried in the air-bath at 70°C. It dried quickly, but assumed a 

 yellowish tint, and had a pungent acid odour. The weight of the dried nitro-, 



VOL. XXXII. PART I. O 



