EXPLOSIVES : MANUFACTURE AND USE. 251 



pedoes and submarines — would be quite useless in shrapnel 

 shells. These examples give one a slight idea of the all-em- 

 bracing nature of this branch of our subject, but from the 

 apparent chaos a few underlying principles may be evolved. 

 For instance, practically all blasting explosives are exploded 

 by detonators, which give the initial shock. All sporting and 

 military small-arm cartridges are exploded by caps — the idea 

 benig to make the initial shock less violent. The same applies 

 in a modified form to cartridges for large guns, and then, last 

 of all, we have that wonderful development of the explosive 

 force of uninflammable mixture of gases — in the motor car — in- 

 ternal combustion engines. All of these have meant, as you 

 know, years of patient scientific research. 



The velocity of projectiles can now be determined with the 

 nicest exactitude by a whole host of methods. Not only so, 

 but, thanks to the modern developments of photography, the 

 bullet of the shell, or even the pellet, can be photographed on 

 its path, and the very air pressure waves registered. Some of 

 you may remember the old rough and ready methods of test- 

 ing the penetration of shot-gun pellets. You took up your 

 stand about 40 yards away from a parafiin tin and fired, exam- 

 ining the effect; or else you got pads of brown paper, and 

 noticed to what depth the pellets penetrated. All that has now 

 given place to scientific determination of velocity, and the 

 underlying" principles are really very simple. Velocities are 

 now measured by an instrument called the chronograph. 



It is occasionally necessary to make a complete examination 

 of the possibilities of an explosive under all conditions, as, for 

 instance, the number of calories and gas volume which unit 

 weights evolve. I have, however, not time to go into those 

 matters. 



In the early days of smokeless powder, as no doubt many 

 of my audience will recollect, the erosion of guns was very bad. 

 This was caused partly by the high velocities obtained, but 

 mainly by the very high temperatures produced by the powders. 

 Now this difficulty has been overcome, mainly by a new system 

 of rifling, but with the Maxim and other quick-firing guns it 

 was a long time before all the difficulties were overcome. In 

 the initial trials the calorimeter was in constant use. 



Before I conclude this very cursory review, I should like to 

 refer to some experimental work which has been done in the 

 Transvaal — work which has been the result of years of patient 

 observation and research. The results will have a profound 

 influence on mining operations as carried on in the Witwaters- 

 rand and other centres of mining activity where the conditions 

 are similar, and they will, I trust, greatly improve the working 

 conditions of those who labour in the bowels of the earth. 

 Incidentally, I may mention that in a few years' time some of 

 the Transvaal mines will just about reach sea level. One can 

 readily realise therefore how difficult becomes the question of 

 ventilation the lower one goes down. Within the past few 

 years a great amount of attention has been directed to a solu- 

 tion of this problem, and I am pleased to say that it has been 



