520 



NATURE 



[June 23, 192 1 



and the time taken by the wave to traverse the 

 length of the time-piece. This momentum is 

 measured by catching the time-piece in a ballistic 

 pendulum, and, the velocity of the propagation of 

 the wave through steel being known, the mean 

 pressure exerted during an extremely small time 

 interval can be calculated. 



(One of the instruments for determining the 

 pressure developed by a detonator was shown, 

 and a detonator fired, the mark drawn by the 

 swing of the pendulum which caught the time- 

 piece being shown on the screen.) 



The application of this apparatus not only 

 gave important information as to the limiting 

 quantity of fulminate necessary to bring about 

 complete detonation of the tetryl and as to the 

 effect of the thickness of the wall of the gaine, 

 but it also emphasised the necessity for 

 avoiding gaps in the train of detonation on 

 account of the very rapid falling off in violence 

 of the blow when even a small air-gap is intro- 

 duced. 



Main Filling. — It was early recognised that the 

 supply of picric acid and T.N.T. by itself would 

 be quite insufficient. It was at this point that the 

 late Lord Moulton took steps to secure supplies of 

 essential explosives and their ingredients, with 

 such success that the supply of explosives in no 

 Ipng time came to be ahead of the demand. But 

 H0ven when a method for the production of T.N.T. 

 had been worked out, and its supply on a fairly 

 large scale was in prospect, it was apparent that 

 the demand for high explosive was such that it 

 could not be met by the supplies of nitro-com- 

 pounds in sight. 



Experiments were then made to test the capa- 

 bilities of mixtures of ammonium nitrate and tri- 

 nitrotoluene for shell filling, and these gave much 

 promise from the start. They were found to 

 •possess the requisite degree of inertness and in- 

 ' sensitiveness to enable them to withstand set- 

 -back on firing from a gun, to have a high rate of 

 detonation, and when detonated in a shell, as was 

 'done first in March, 1915, to give evidence of 

 the required violence necessary to fragment the 

 shell. 



The first mixture (later termed amatol 40/60, 

 these being the proportions of ammonium nitrate 

 to T.N.T.) was capable of being poured as a 

 thick porridge into shell, and so presented few 

 difficulties for large-scale production. This was 

 iat once followed up by similar experiments with 

 a still greater proportion of ammonium nitrate, 

 up to that which is practically the theoretical one 

 for complete combustion of all the carbon of the 

 trinitrotoluene to carbon dioxide, and of all the 

 hydrogen in both substances to water. This 

 explosive, amatol 80/20, was fired in a shell 

 in April, 1915, and gave excellent results. Its 

 explosive properties, as regards insensitiveness, 

 stability, and tests for power, were satisfactory, 

 and it was almost immediately approved as a Ser- 

 vice explosive. 



: . NO. 2695, VOL. 107] 



Amatol 80/20. — ^The development of amatol 

 80/20 was slower. Prepared originally on the 

 large scale by bringing together the finely pow- 

 dered ingredients in a mixing machine, or by 

 grinding them under edge-runners, 80/20 amatol 

 was ultimately most readily produced by taking 

 advantage of the plasticity of the heated mixture 

 due to the trinitrotoluene melting. Hydraulic 

 presses were used for introducing the powdered or 

 ground explosive into shell; for the plastic 80/20, 

 a worm feed was found expeditious and rapid. 



In the course of the manufacture of the enor- 

 mous quantities of these substances many points 

 of interest and of difficulty arose, which were 

 solved by the assistance of more and more scien- 

 tific investigators. 



The following tables give some data on the 

 explosive properties of the amatols in comparison 

 with some other explosives : — 



Heat of Detonation and Gases Evolved. 



It will be seen that the addition of 40 per cent, 

 of ammonium nitrate to T.N.T. does not markedly 

 reduce its heat value, rate of detonation, or pres- 

 sure developed, and that amatol 80/20 has a high 

 content of heat energy, but a rate of detonation 

 and pressure lower than T.N.T. itself. It is, 

 however, still sufficiently violent to fragment shell 

 satisfactorily, and the somewhat slower develop- 

 ment of the pressure, together with the high 

 calorific value of the explosive, may be of 

 advantage in enabling the fragments to acquire a 



