70 DR MATTHEW HAY ON THE 



same quantity as in the case of the nitroglycerine solution. The purity of the 

 nitrite of sodium was previously ascertained by titration with a standard 

 solution of permanganate of potash ; and the strengths employed of the 

 standard solutions of the nitrite were 1 in 500,000, and 1 in 1,000,000. The 

 solution of decomposed nitroglycerine was diluted with distilled water until, 

 on the addition of the starch reagent, a depth of blue was obtained precisely 

 similar to that given by the strongest of the standard solutions of the nitrite. 

 The solution was then diluted with an equal bulk of water, and, for the 

 purpose of control, compared with the weaker standard solution. From the 

 amount of dilution needed it was easy to estimate the quantity of nitrous acid 

 present in the solution of the decomposed nitroglycerine. This method is 

 only approximately correct, but it is the only method available. Any error 

 was as far as possible eliminated by making the dilutions and comparisons with 

 extreme care, and by occasionally repeating the estimation of the nitrous acid. 

 The following were the results obtained. (The letters following the various 

 specimens of nitroglycerine are for the purpose of identifying each specimen 

 with its mode of preparation, which will be afterwards stated.) 



I. Nitroglycerine, A. — 11533 grms. dissolved in about 5 c.c. of alcohol, 

 and treated with fully 1*5 grms. of caustic potash dissolved in about 

 12 c.c. of alcohol. Boiled over water-bath for half an hour, water 

 being added to replace the evaporated alcohol, and heating 

 continued until the whole of the alcohol was driven off. Fluid 

 diluted to 30 c.c. 1 c.c. of this was further diluted, and employed 

 for the estimation of the nitrous acid. A dilution corresponding to 

 1 of the original nitroglycerine in 620,000 of water was found to 

 contain the same proportion of nitrous acid as the 1 in 1,000,000 

 standard solution of nitrite of sodium. The nitroglycerine had, 



therefore, produced a quantity of nitrous anhydride - — \~- corre- 



— ■ 



sponding to 62 per cent, of the anhydride in Na.O.NO, or 34143 per 

 cent, of the weight of the nitroglycerine. 



A second estimation of the nitrous acid in the same solution 

 of decomposed nitroglycerine gave 35*244 per cent, of N 2 3 . 



II. Nitroglycerine, A. — 1 c.c. of a 10 per cent, solution heated to the 

 boiling point with a small excess of alcoholic solution of potash ; 

 diluted with two volumes of water and again heated to the boiling 

 point, and the nitrous acid then estimated. 



N O 

 The nitroglycerine yielded 3524 per cent, of 1 8 . 



III. Nitroglycerine, A. — Same in all respects as IT. 



The yield of nitrous anhydride was 35'24 per cent. 



