HISTORY OF PROPELLANTS 35 



explosives I have examined as varying between 4,000 and 

 5,000 C. I need not say that at less densities they are 

 very much lower. 



I have mentioned that the percentages of the several 

 gases generated by the explosion vary greatly, dependent 

 upon the pressure under which the explosion takes place, 

 and I shall exhibit to you three diagrams, in two of which 

 there are, with increase of density, large increases in 

 volume, and in the third a considerable decrease. 



All of the new propellants develop on explosion a very 

 much higher temperature than did the old gunpowders, 

 and the introduction of armored vessels has necessitated 

 the employment of guns fifteen or sixteen times heavier 

 than the guns in use fifty years ago, and capable of giving 

 to their projectiles energies nearly fifty times as great. 



Now, as regards the serious question of erosion, in the 

 case of the very large guns it is important to remember 

 that while the surface of the bore subject to the more 

 violent erosion increases approximately as the caliber or 

 a little more, the charge of the propellant required to give 

 to similar projectiles the same maximum velocity increases 

 as the cube of the caliber ; and, consequently, unless special 

 arrangements as to the projectile are made, or other means 

 adopted, the life of the largest guns before re-lining, must 

 be short when compared with that of smaller guns. 



It, therefore, becomes a matter of great importance that 

 attention should be given to the best method of reducing 

 erosion when very large charges are used, either by lower- 

 ing the temperature of explosion of the propellant, or 

 possibly by introducing with the charge some cooling 

 agent. 



As regards the first of these points some very consider- 

 able advance has been made, but I venture to think that the 

 question of erosion has, at least in this country, hardly 

 received sufficient attention, and that, in some respects, 

 mistaken notions as to the amount of erosion with reduced 

 charges are entertained. 



