146 



NA TURE 



[July 29, 190Q 



The finally purified pulp is passed to a moulding 

 machine, where it is lightly compressed to remove the 

 bulk of the water, and converted into a form in which 

 it can be easily handled. If intended for use in mines or 

 torpedoes, or for demolition purposes, the lightly com- 

 pressed shapes are submitted to heavy hydraulic pressure, 

 converting them into dense hard blocks. 



The other high explosive of which I am to speak, viz. 

 nitroglycerine, enters into the composition of many modern 

 propellants. Nitroglycerine was discovered by Sobrero in 

 1847, but it remained for a long time a chemical curiosity 

 only. 



Alfred Nobel commenced its manufacture as a blasting 

 agent about 1868, for which purpose he absorbed nitro- 

 glycerine with an infusorial earth known as kieselguhr, 

 and gave the compound the name of dynamite ; but, prior 

 to this, nitroglycerine had been made on a large scale in 

 America, where it was frozen after manufacture for pur- 

 poses of transport, and used for blasting. » 



Nitroglycerine is a liquid, and is a much more violent 

 explosive than guncotton, and whereas the manufacture 

 of guncotton is absolutely safe throughout, that of nitro- 

 glycerine is dangerous. The risks attendant on the manu- 

 facture of nitroglycerine are due to the facts that the 

 temperature resulting from the chemical reaction is not 

 so easily controlled, and that nitroglycerine, being a liquid 

 insoluble in water, the processes after nitration have to be 

 carried out with a substance not rendered inert, as gun- 

 cotton is, by admixture with water. For these reasons the 

 nitration of glycerine in the early days of the production 

 of nitroglycerine on a manufacturing scale was carried out 

 in very small quantities. 



With the introduction of dynamite, the small pots used 

 for the nitration of glycerine', standing in vessels full of 

 ice water, were replaced by lead tanks, in which consider- 

 able quantities of glycerine, amounting to several hundred 

 pounds, were nitrated at one operation. In these vessels 

 the temperature was controlled bv means of cold water 

 circulating through lead coils fixed in the tank, and the 

 whole contents of the tank were kept in agitation during 

 the nitration by means of mechanical stirrers or bv com- 

 pressed air escaping through small holes in lead pipes 

 situated at the bottom of the nitrating vessel. On com- 

 pletion of the nitration it was the practice in the early 

 days to drown the whole of the charge of nitroglvcerine 

 and waste acid in a large bulk of water, from vvhich the 

 nitroglycerine separated out and was removed for sub- 

 sequent purification by washing with alkaline solutions 

 in lead tanks. This system entailed the loss of the waste 

 acid, and was superseded by a process in which the nitro- 

 glycerine and waste acid were run from the nitrating 

 vessel into another vessel termed a separator, and allowed 

 to separate in it. The nitroglvcerine, being lighter than 

 the waste acid, came to the top, and was run off into a 

 third tank for preliminary purification, consisting of 

 several water washings. 



This preliminary purification removes most of the free 

 acid adhering to and dissolved in the nitroglvcerine, but 

 in order to obtain a stable product a further and' pro- 

 longed purification is necessary, as in the case of gun- 

 cotton. This is effected in lead tanks bv repeated wash- 

 ings 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 verv thorough agitation the 

 nitroglycerine, even after the removal bv skimming of as 

 much as possible of the washing liquid, still contains a 

 small proportion of water suspended in it in a verv fine 

 state of division. It also contains small quantities of 

 fiocciilent imnurities and mineral matter derived from the 

 glycerine and acids. To get rid of these bodies filtration 

 is resorted to ; coarse crystalline salt is very usually 

 emplovcd as a medium, but at Waltham Abbev it has 

 been found that a filter in the form of a mat of sponges 

 NO. 2074, '^'Of-- 81] 



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 so long as it con- 

 tained 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 modifica- 

 tions 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, probably, a separating house, on artificial 

 mounds, has to be resorted to, entailing a very consider- 

 able expense. 



In the next place, owing to the corrosive nature of the 

 mixture of nitroglvcerine and waste acid, and to the acid 

 nature of the nitroglycerine even when separated from 

 the waste acid, the only material which can be used for 

 the cocks necessary to allow the nitroglycerine and acid 

 to run from, vessel to vessel is earthenware. The use of 

 earthenware cocks is attended with considerable risk, 

 owing to the fact that there is friction in them between 

 the key and the body of the cock, and there is always 

 the risk in moderately cold weather of the nitroglycerine 

 freezing and fixing the key ; force, if used in these circum- 

 stances, would be very liable to cause accident. .'Xgain, 

 the necessity of storing the waste acid under observation 

 for long periods is a costly one, both as regards labour 

 and plant required. 



It was to overcome these disadvantages that the whole 

 system in current use for the manufacture of nitroglycerine 

 received very careful consideration at the Royal Gu:. powder 

 Factorv some years ago. 



The first step that was taken to improve matters was 

 to abolish the use of earthenware cocks in the preliminary 

 and final washing tanks. As the nitroglycerine when it 

 was ready to leave these tanks was thoroughly free from 

 acid, it was possible to get rid of the cocks on these 

 tanks, and to replace them by rubber tubes. During the 

 washing operations this tube is secured to a nozzle fixed 

 to the outside of the tank at a point above the level of 

 the liquid. To run off the nitroglycerine it is only neces- 

 sarv to slip the rubber tube off the nozzle and direct it 

 into another vessel or into a lead gutter used to convey 

 the nitroglycerine to the next operation. 



Rubber, however, could not be used in the case of the 

 separator or the nitrator, where either acid nitroglycerine 

 or a mixture of nitroglycerine and acid had to be drawn 

 off. To overcome the difficultv in this case an entirely 

 new system was invented at Waltham Abbey. Instead of 

 running the nitroglycerine and waste acid on completion 

 of the nitration process into the separator, the separation 

 is allowed to take place in the nitrating vessel itself. 

 Nitroglycerine as it seoarates from the waste acid comes 

 to the top, it being the lighter of the two liquids, and 

 to remove it from the nitrator all that is necessarv is to 

 raise the liquid contents of the vessel graduallv until the 

 nitroglycerine reaches the top of the nitrator, where a pipe 

 or Efutter is fixed to lead the nitroglvcerine away into the 

 preliminary washing tank. This raising of the charge is 

 effected bv introducing into the bottom of the nitrator, 

 throuch the same pipe by which the nitrating acid is 

 admitted, the waste acid from a previous charge. The 

 rate of inflow of the waste acid is regulated, so that the 

 nitroglvcerine displaced is as free as possible from acid in 

 suspension. 



