CHEMISTRY OF NITROGLYCERINE. 75 



treated with moderate excess of dilute sulphuric acid, and heated for a few 

 minutes. Red fumes were evolved with brisk effervescence ; and a dark 

 reddish-brown precipitate was formed, which evidently constituted the colouring 

 matter of the decomposition products of nitroglycerine, although the colour 

 was not wholly removed by the addition of the acid. The precipitate was 

 collected on a filter, and washed with dilute acid and dried ; it weighed 0040 

 gram. It was insoluble in acid solutions, but freely soluble in dilute solu- 

 tions of alkalies or alkaline carbonates, and was of a resinoid character, and is 

 probably similar in nature to aldehyde-resin, or even to caramel. 



As regards the peculiar alcohol-gelatinising body which I have mentioned 

 as existing amongst the products of the alkaline decomposition pi nitro- 

 glycerine, it was met with in the course of an examination of the decomposed 

 products of 15 grms. of nitroglycerine, obtained in the usual way. The 

 supernatant alcoholic fluid was treated with excess of dilute alcoholic sulphuric 

 acid, in order to precipitate all the potash, both free and combined. The filtrate 

 was afterwards neutralised, and the sulphuric acid precipitated by means of 

 pure carbonate of barium. The evaporated filtrate yielded a residue which 

 crystallised on cooling, and contained no glycerine, and which was very freely 

 soluble in water without gelatinisation. It was also freely soluble in hot 

 absolute alcohol ; but on allowing the solution to cool, even if the proportion of 

 the residue to the alcohol was 1 to 20 or 30, the solution became a firm, partly 

 crystalline-looking jelly, which could not be poured out of the test-tube in which 

 it formed. This body, whatever be its exact constitution, is certainly a very 

 exceptional organic substance, and deserves further examination. 



No gases are generated when potash acts on nitroglycerine in alcoholic 

 solution. This was ascertained by placing the solution of nitroglycerine in a 

 retort connected with a tube inverted over mercury, and boiling to drive out 

 all the air. Alcoholic potash was then added, precautions being taken to 

 prevent the simultaneous admission of air, and the boiling was continued for 

 some time without any gas being formed. 



These are the products formed when alcohol is the medium through which 

 the potash attacks the nitroglycerine. Similar products are obtained when 

 water is employed, and the only apparent difference is that, on account of the 

 very sparing solubility of nitroglycerine in water, the decomposition proceeds 

 with great slowness, fully two hours' boiling over the water-bath being required 

 to effect the decomposition of one gram, of nitroglycerine in a strong solu- 

 tion of pure potash. Less red colouring matter is formed than when alcohol is 

 employed, and much more oxalic acid seems to be produced ; but the amount 

 of nitrous acid is the same. 



From this detailed account of the decomposition of nitroglycerine by caustic 

 potash, it will be seen that the usual equation is very, far from representing 



VOL. XXXII. PART I. . N 



