by the Proof-house before a gunmaker sells them, and 

 the charge used by the Proof-house gives a much higher 

 pressure than a standard cartridge, so we see that if a 

 gun retains its pressure-resisting qualities, there is practi- 

 cally no chance of a factory-loaded cartridge giving a 

 pressure that could cause a burst. Nevertheless, bursts 

 are frequent. 



To understand the causes of these bursts, it is necessary 

 to know a good deal about the nature of steel. Much has 

 been found out on this question in late years, the lines of 

 research having been extended to the closer study of 

 chemical analysis and micro-photography. It is sufficient 

 here to say that it is now realised that steel, in common 

 with many other metals, suffers from "fatigue" unless it 

 is, from the nature of its mixture and the temperature and 

 time of annealing it has undergone, left in its finished state 

 in a condition of comparative repose, i.e., the different 

 molecules must not be unduly striving to break apart. 



Unless, therefore, the gunmaker anneals his material so 

 as to leave the molecules in a state of rest, they are 

 striving all the time to break apart. Probably if left long 

 enough, the gun would crack spontaneously without ever 

 having a cartridge fired in it, but the continual jar of firing 

 quickens the disruption of the molecules. According to 

 the nearness to the state of equilibrium of the molecules 

 the final breaking apart takes a shorter or longer time, 

 but, sooner or later, the break must occur, and then, of 

 course, without this knowledge and an examination of 

 the crystals of the ^eel, it would appear as though there 

 could be no reason for the accident except a high pressure 

 given by the cartridge. 



89 



