274 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1908. 



quantities of 0.5 to 2 per cent of the weight of glycerin, while Dr. 

 L. F. Reese, of Wilmington," adds as little sodium fluoride as 0.002 

 per cent (1 in 50,000) of the glycerin employed to the nitrating 

 mixture with excellent results. Both methods are now used in very 

 large factories. For more than thirty years some factories had been 

 in the habit of employing one vessel only for both nitrating and 

 separating, and withdrew the nitroglycerin from three earthenware 

 cocks, placed at short intervals at the separating line. This enabled 

 them to gain considerably in levels and to carry out the manufacture 

 right up to the final washing on practically the same level. 



The waste acid was always sent to after-separation houses, which 

 were frequently called by the German name of " Nachscheiclung." 

 Since the waste acid sometimes had to be kept in these after-separation 

 houses for a week, in order to get rid of all the drops of nitroglycerin 

 which separated out, decomposition occasionally set in. A plan was 

 thereupon introduced in France and elsewhere which consisted in 

 gradually diluting the waste acid by the addition of from 2 to 3 per 

 cent of water, thereby stopping the further formation and separa- 

 tion of nitroglycerin. 



At the government factory at Waltham Abbey these methods have 

 been improved upon. A so-called " nitrator separator " is used, in 

 which the nitroglycerin has time to separate from the acids, and waste 

 acid is then added from below, thereby bringing the level of the 

 nitroglycerin to a point where it will run out through a gutter into 

 the preliminary washing tank. In this way the use of cocks is 

 avoided. A^^ien all the nitroglycerin has been displaced about 2 

 per cent of water is introduced gradually. 



The result of this combination of a number of useful processes, 

 namely, the employment of anhydrous sulj)huric acid to produce a 

 mixed acid containing little water, the use of refrigerated water to 

 cool the acids, the displacement of the nitroglycerin by means of 

 waste acid, which obviated the remixing of acid and nitroglycerin 

 on emptying the nitrator, and the addition of water to stop the 

 separation of further quantities of nitroglycerin, was that they 

 together contributed to yield much better results. As a matter of 

 fact in well-conducted works the yield of nitroglycerin with the 

 proportions of 6.91 to 1 mentioned above was between 217 and 220; 

 at Waltham Abbey it was possible to obtain by the " displacement 

 process " a yield of 229 parts nitroglycerin for 100 parts glycerin, 

 instead of the former 220 parts. According to Mr. de Mosenthal the 

 Nobel works obtained similar good results. This yield has to the 

 author's knowledge been only once exceeded in a Belgian factory, 

 when a charge of nitroglycerin had to be drowned on a cold winter's 



a British patent No. 20310, of 1D05. 



