PROGRESS IN EXPLOSIVES GUTTMANN. 273 



and nitric acid of 91 per cent only).'^ This corresponds to about 255 

 parts of nitric acid monohydrate and 436.4 parts of sulphuric acid 

 monohydrate, or a total of 691.4 parts of acid monohydrate with 35.8 

 parts of HoO (4.9 per cent) to each 100 parts of glycerin. 



It is now customary to add sulphuric acid cntaining 20 per cent 

 of anhydride (oleum) to the original mixture, but it is still found 

 impracticable to add it to the waste acid. It will be seen from the 

 paper of Sir Frederic Nathan and Mr. Rintoul on " Nitroglycerin and 

 its manufacture " that the use of anhydride has reduced the quantity 

 of sulphuric acid required. Five years ago already I found in the 

 Pozsony factory of Nobel's the use of mixed acid consisting of 37.2 

 per cent HNO3, 60 per cent H0SO4, and 2.8 per cent H^O, and made 

 with anhj^dride. Although no artificial refrigeration was used, the 

 yield of nitroglycerin amounted to 220 for 100 glycerin, and a ratio 

 6.318 of acid to 1 of glycerin. Factories using Nathan, Thomson, 

 and Rintoul's process now employ a mixture of 41 per cent HNO3, 

 57.5 per cent HoSO^, and 1.5 per cent HoO, corresponding to 250 

 pounds IINO3, 350 pounds HoSO^, and 9 pounds HoO for each 100 

 pounds of glycerin, which gives a ratio of 6.09 of acid to 1 of 

 glycerin, as against 6.91 to 1 formerly required. It is thus seen that 

 this process requires about the same quantity of nitric acid per 100 

 glycerin as the old process, but about 86 pounds, or roughly 20 per 

 cent, less sulphuric acid. It will therefore simply depend upon the 

 price of the sulphuric anhydride whether it is advantageous to use it. 



With the present prices of £3 per ton of 96 per cent sulphuric acid 

 and £3 15s. Od. per ton of sulphuric monohydrate, containing 20 per 

 cent of anhydride, the difference between the cost of materials with 

 the former yield of 220 and the present one of 229 nitroglycerin is, 

 per ton, £3 Os. 2d, or approximately 5.6 per cent. 



This apparent saving is quite counterbalanced by the fact that in 

 the new j^rocess 1.9 tons less of waste acid are obtained. 



In making this comparison it must, however, be remembered that 

 with the new process the same apparatus will hold 18 per cent larger 

 charges. 



After nitration the mixture is allowed to stand, when the nitro- 

 gylcerin separates from the waste acid and floats on the top of it. 

 The separation is sometimes considerably delayed by the formation 

 of a silicious colloid, which agglomerates with particles of cell sub- 

 stance and other impurities, forming fern-like growths. The Dyna- 

 mit Actiengesellschaft in Hamburg ^ found a very efficient means of 

 promoting separation in the addition of high-boiling paraffins in 



o Journal of the Society of Chemical Industry, March 16, 1908. Compare also 

 Guttmann, Manufacture of Explosives, Vol. II, p. 93. 

 6 British patent No, 13562, of 1904. 



