330 Sir Andrciv Noble [March 23, 



to the gravimetric density is not nearly so much affected as might be 

 expected from the considerable alteration in the above factors. 



3. The work that gunpowder is capable of performing in expand- 

 ing in the bore of a gun was determined both by actual measurement 

 and by calculation, and the results were found to accord very closely. 



4. The total potential energy of exploded gunpowder supposed 

 to be fired at the density of unity was found to be about 332,000 

 gramme units per gramme, or 486 foot-tons per lb. of powder. 



I must confess that when I gave the lecture I have referred to, 

 seeing the many centuries during which gunpowder had held its own 

 as practically the sole propelling agent for artillery purposes, seeing 

 also that gunpowder differs in certain important points from the 

 explosives to which I shall presently call your attention, I had 

 serious doubts as to whether it would be possible so far to modify 

 these latter as to permit of their being used in large charges and 

 under the varied conditions required in the Naval and Military 

 Services. 



Gunpowder is not like guncotton, cordite, nitro-glycerine, lyddite, 

 and other similar explosives, a definite chemical combination in a 

 state of unstable equilibrium, but is merely an intimate mixture of 

 nitre, sulphur and charcoal, in proportions which can be varied to 

 a very considerable extent without striking differences in results. 

 These constituents do not, during the manufacture of the powder, 

 sutler any chemical change, and being a mixture it cannot be said 

 under any condition truly to detonate. It deflagrates or burns with 

 great rapidity, varying very largely with the pressure and other cir- 

 cumstances under which the explosion is taking place; a train like 

 that to which I set fire taking as you see an appreciable time to 

 burn, while in the bore of the gun a similar length of charge would 

 be consumed in less than the hundredth part of a second. 



You will further have observed the heavy cloud of smoke which 

 has attended the deflagration you have seen. Nearly six-tenths of 

 the weight of the powder after explosion remains as a finely divided 

 solid, giving rise to the so-called smoke familiar to many of you, 

 and of which a good illustration is shown in this instantaneous 

 photograph. By way of comparison I burn similar lengths of gun- 

 cotton in the form (1) of cotton, (2) of strand, (3) of rope ; and you 

 will observe the different rates at which these varied forms of the 

 same material are consumed, the rate depending in this case upon 

 the greater aggregation and higher density, consequently higher 

 pressure, of the successive samples. 



Although the names of cordite and ballistite are probably familiar 

 to all of you, the appearance may not be so familiar, and I have here 

 on the table samples of the somewhat Protean forms which these 

 explosives, or explosives of the same nature, are made to assume. 



Here, for instance, are forms of cordite, the explosive of the 

 Service, for which we are indebted to the labours of Sir F. Abel and 

 Prof. Dewar. This, which is in the form of fine threads, is used in 



