1907.] on Fifty Years of Explosives. 463 



Commencing with the old gunpowders, Sir F. Abel and I differed 

 from the opinion of our distinguished predecessors, Bunsen and 

 Schischkoff, in placing the temperature of explosion of gunpowder 

 much lower than their estimate. Dependent on the nature of the 

 powder, I satisfied myself that the temperature of explosion of the 

 various powders I examined ranged from 1800^ C. to about 2200° C, 

 the latter temperature being apparently reached by the Spanish Pellet,, 

 with which powder Iridio-platinum wire was fully melted, while the 

 Mining powder just melted platinum. 



Pellet gun-cotton gave a much higher temperature, the platinum 

 wire being apparently volatilised. 



I may mention that, in these early experiments, I made the 

 determination of heat for only one density for each explosive ; but 

 finding in modern explosives that the transformation varied so greatly 

 with the density of charge, determinations were made for every 

 density, the results being the curves I have just shown you. 



To obtain the temperature of explosion I used two methods ; the 

 first was that followed by Bunsen and Schischkoff, who determined 

 the temperature by dividing the units of heat by the specific heat. 



The second was, knowing the pressure at the moment of 

 explosion, and also at 0^ C, it w^as possible, the co-efficient of 

 expansion with temperature being known, to calculate w^hat tempera- 

 ture was necessary to raise the pressure of the volume of gas at 0° C. 

 and 760 mm. to the pressure at the moment of explosion. 



With respect to the first of these two methods, for any degree of 

 accuracy it is essential that the specific heats should be as accurately 

 determined as possible. Carbonic anhydride, as I have already 

 pointed out, on account of its great preponderance of weight, is, as 

 regards specific heat, by far the most important product, and 

 fortunately there has been recently published by Holborn and Austin 

 a very careful determination of specific heat for CO2 and some other 

 gases. The formula they give connecting the specific heat and the 

 temperature has been proved by them up to 800° C, and their 

 determinations up to the same temperature have been confirmed by 

 Langen. 



At the lower temperatures the increments to the specific heat 

 with increase of temperature is very considerable, but these incre- 

 ments rapidly decrease, and vanish altogether when 1400° C. is 

 reached, at which temperature CO2 is partially dissociated. 



The other principal gases, carbonic oxide, hydrogen and nitrogen, 

 although no gas rigorously follows Marriotte's Law, are among those 

 which follow it most closely, the specific heat increasing but slightly 

 between 0° C. and 800° C"., and the increments as with CO2 being 

 smaller as the temperature is increased. I have treated all these 

 gases at the temperature with which we are concerned as perfect 

 es. 



Now the two formulae I have referred to srive, for five of the 



