220 THE POPULAR SCIENCE MONTHLY. 



differences are observed in the tension developed by small charges and 

 by very much larger charges of gunpowder having the same density 

 (i. e., occupying the same volume relatively to the entire space in which 

 they are exploded), the reverse is the case with respect to gun-cotton. 

 Under similar conditions in regard to density of charge, 100 grammes 

 of gun-cotton gave a measured tension of about 20 tons on the square 

 inch, 1,500 grammes gave a tension of about 29 tons (in several very 

 concordant observations), while a charge of 2*5 kilos gave a pressure 

 of about 45 tons, this being the maximum measured tension obtained 

 with a charge of gunpowder of five times the density of the above. 



The extreme violence of the explosion of gun-cotton as compared 

 with gunpowder when fired in a closed space was a feature attended 

 with formidable difficulties. In whatever way the charge was arranged 

 in the firing-cylinder, if it had free access to the inclosed crusher- 

 gauge, the pressures recorded by the latter were always much greater 

 than when means were taken to prevent the wave of matter suddenly 

 set in motion from acting directly upon the gauge. The abnormal or 

 wave-pressures recorded at the same time that the general tension in 

 the cylinder was measured amounted in the experiment to 42'3 tons, 

 when the general tension was recorded at 20 tons ; and in another, 

 when the pressure was measured at 29 tons, the wave-pressure recorded 

 was 44 tons. Measurements of the temperature of explosion of gun- 

 cotton showed it to be about double that of the explosion of gunpow- 

 der. One of the effects observed to be produced by this sudden enor- 

 mous development of heat was the covering of the inner surfaces of 

 the steel explosion-vessel with a net-work of cracks, small portions of 

 the surface being sometimes actually fractured. The explosion of 

 charges of gun-cotton up to 2'5 kilos in perfectly closed chambers, 

 with development of pressures approaching to 50 tons on the square 

 inch, constitutes alone a perfectly novel feat in investigations of this 

 class. 



Messrs. Noble and Abel are also continuing their researches upon 

 fired gunpowder, being at present occupied with an inquiry into the 

 influence exerted upon the chemical metamorphosis and ballistic effects 

 of fired gunpowder by variation in its composition, their attention be- 

 ing directed especially to the discovery of the cause of the more or less 

 considerable erosion of the interior surface of guns produced by the 

 exploding charge an effect which, notwithstanding the application 

 of devices in the building up of the charge specially directed to the 

 preservation of the gun's bore, has become so serious that, with the 

 enormous charges now used in our heavy guus, the erosive action on 

 the surface of the bore produced by a single round is distinctly per- 

 ceptible. As there appeared to be prima facie reasons why the ero- 

 sive action of powder upon the surface of the bore at the high temper- 

 atures developed should be at any rate in part due to its one compo- 

 nent sulphur, Noble and Abel have made comparative experiments 



