EXPEEIMENTS ON SOLID AND GASEOUS EXPLOSIVES. 



373 



smaller, or, thirdly, when very fine cord is used, a more satisfactory ignition is 

 obtained. This point in itself would be well worth more careful investigation, but as 

 the present research refers principally to the properties inherent to cordite itself, it was 

 desirable to be independent of such disturbing factors. The ideal conditions would be 

 realised if a method could be found of igniting every particle of the explosive at the 

 same instant over its entire surface. These conditions are approached by the process 

 used. 



After the required quantity of cordite had been filled in and the explosion chamber 

 closed, the air therein contained was displaced by a mixture of oxygen and hydrogen 

 at, or near, atmospheric pressure, and this was fired off in the usual way by an electric 

 current. The velocity of the explosion of this mixture is such that the effect of the 

 gaseous combustion is practically over before the pressure of the burning cordite 

 begins to make itself felt, and each cord, being entirely surrounded by the flaming 

 gases, cannot fail to ignite over its entire surface. On the records the impact of this 

 preliminary explosion is marked by a slight tremor occurring just before the actual 

 rise of pressure occurs. The pressure due to the gaseous explosion is about 

 10 atmospheres which, when compared with the 1000 or 2000 atmospheres resulting 

 from the explosion of the cordite, does not form a serious correction. 



General Shape of the Curves. 



All the records exhibit certain general characteristics. The typical curve of rise of 

 pressure is illustrated in fig. 1 0. It consists of three parts : (a) beginning nearly 



- Time in seconds. 

 Fig. 10. Typical time pressure curve resulting from the explosion of cordite in closed vessel. 



asymptotical to the time axis and, gradually rising more rapidly, corresponds to the 

 first stage of the combustion ; (b) referring to the full blast of the explosion, shows a 

 much faster and almost constant rate of rise ; while at (c) the rapid decrease in the 

 surface of the explosive can no longer be counterbalanced by the accelerating effect of 

 the higher pressure. At c, therefore, the curve turns round sharply and merges into 

 the cooling curve. So much for the general shape of the records. As we shall see 



