4o6 Colonel Sir Frederic L. Nathan [Jan. 29, 



the nitroglycerine and waste acid were rnn from the nitrating vessel 

 into another vessel termed a separator, and allowed to separate in it. 

 The nitroglycerine, being lighter than the waste acid, came to the top 

 and was run off into a third tank for preliminary purification con- 

 sisting of several water washings. 



This preliminary purification removes most of the free acid 

 adhering to and dissolved in ^the nitroglycerine, but in order to 

 obtain a stable product a further and prolonged purification is neces- 

 sary, as in the case of guncotton. This is effected in lead tanks, by 

 repeated washings with warm dilute sodium carbonate solution. The 

 alkali remaining in the nitroglycerine after this treatment is thoroughly 

 removed by washing with purified warm water. As nitroglycerine is 

 a somewhat viscous liquid, special care has to be taken that the 

 washing solutions are brought into very intimate contact with every 

 portion of the charge of nitroglycerine. For this purpose, the method 

 universally employed is to agitate the contents of the washing tanks 

 by means of the escape of air under compression through small holes 

 in the bottom of the tank. As a result of this very thorough agita- 

 tion, the nitroglycerine, even after the removal, by skimming, of as 

 much as possible of the washing liquid, still contains a small pro- 

 portion of water suspended in it in a very fine state of division. It 

 also contains small quantities of flocculent impurities and mineral 

 matter derived from the glycerine and acids. To get rid of these 

 bodies, filtration is resorted to ; coarse crystaUine salt is very usually 

 employed as a medium, but at Waltham Abbey it has been found that 

 a filter in the form of a mat of sponges is more efficacious and free 

 from the objections salt filters possess. 



After the removal of the nitroglycerine from the waste acid, which 

 takes place in a comparatively short space of time, the waste acid was 

 run out of the separator into large lead vessels, where it remained for 

 days, in order to allow of the formation and removal of the last traces 

 of nitroglycerine. This process is known as after-separation, and 

 was necessary to enable the waste acid to be dealt with without risk, 

 because as long as it contained any traces of nitroglycerine, it could 

 not be stored or handled, without risk of violent decompositions, or 

 even of explosions, taking place.. 



This system of manufacture, comprising nitration, separation, 

 preliminary washing, final washing and after-separation, all carried 

 out in different vessels and in different houses, was the one which, 

 with slight modifications in detail, was followed almost universally, 

 and is still in use in many of the older factories in this country and 

 abroad. Its disadvantages are several. In the first place, owing to 

 the fact that it is unsafe to transport or to carry liquid nitroglycerine 

 about, factories are always designed so that it may flow from process 

 to process by gravity. The result, obviously, is that nitroglycerine 

 houses must" be built on the side of a hill, or, as this is not always 

 possible, the alternative of building a nitrating house and also, prob- 



