82 DR MATTHEW HAY ON THE 



But why the whole of the nascent nitrous acid should not thus be decomposed 

 by the sulphuretted hydrogen I do not, in the meantime, attempt to explain, 

 beyond suggesting that the nascent nitrous acid may in part combine with 

 the alkali ; and, once so united, it is incapable of being acted on by the 

 sulphuretted hydrogen. 



But the sulphuretted hydrogen does not play an altogether passive part in 

 the actual decomposition of the nitroglycerine itself, for when an aqueous 

 solution of an alkaline sulphide, such as potassium sulphide or ammonium 

 sulphide, is poured over pure undissolved nitroglycerine, and the mixture 

 vigorously shaken, the solution gradually becomes reddish, and the tempera- 

 ture rises, and apparently, when the temperature has risen sufficiently, the 

 whole or nearly the whole of the nitroglycerine suddenly decomposes with a 

 copious formation of sulphur. In fact, the nitroglycerine seems to become 

 suddenly converted into a mass of sulphur. It will be remembered that when 

 potash alone is allowed to act on nitroglycerine under similar circumstances, 

 the decomposition proceeds very slowly. The presence, therefore, of 

 sulphuretted hydrogen very greatly promotes the decomposition of nitro- 

 glycerine ; but in what particular manner I have not endeavoured to ascertain. 



Action of Water. — In order to ascertain to what extent water when boiled 

 with nitroglycerine is capable of deconvposing it, a given quantity of a saturated 

 aqueous, and, owing to the insolubility of nitroglycerine in water, a necessarily 

 weak, solution of nitroglycerine was heated over the water-bath. After ten 

 minutes 1 active heating, the fluid exhibited no signs of decomposition, and con- 

 tained no trace of nitrous acid. It was then continuously heated for three 

 hours. It still remained colourless, and on the addition of starch and iodide of 

 potassium gave no blue ; but when these reagents were added along with 

 dilute sulphuric acid, a distinct blue was obtained. The nitrous acid present 

 was evidently combined with some other decomposition product of the nitro- 

 glycerine ; it was estimated and found to amount to 17 per cent, of the whole 

 nitroglycerine employed. A given portion of the fluid was heated with potash, 

 in order to learn how much of the nitroglycerine remained undecomposed, and 

 a quantity of nitrous acid (nitrous anhydride) was obtained, equivalent to 8*88 

 per cent, of the whole nitroglycerine ; from which it is to be concluded that 

 73 '48 per cent, of the nitroglycerine had been decomposed by heating with 

 water for three hours. It is to be considered that a portion of this may have 

 been lost by simple evaporation, although this was to a certain extent avoided 

 by heating in a long-necked Florence flask. 



Action of Alcohol. — A one per cent, solution of nitroglycerine in absolute 

 alcohol was heated over the water-bath for one hour, the alcohol being renewed 

 from time to time. There was no change in colour, and nitrous acid could not 

 be detected, even when sulphuric acid was added along with the usual reagents. 

 A portion of the fluid was decomposed with potash, and the nitrous anhydride 



