452 



GUN-COTTON AND NITBO-CELLULOSES. 



P. 



I". 



But these results should be interpreted in accordance with 

 their new researches on the calibration of " crushers " (p. 23). 



The latter gave for - = 0'20, a maximum pressure of 1985 



n 



F F 



kgm. ; which would make = 9825 kgm. The limit , that 



n n 



is, the specific pressure, relating to gun-cotton would therefore 

 seem to need to be reduced to about 10,000 kgm., in round 

 numbers, for high densities of charge. The theoretical pressure 

 calculated from our formula would, on the contrary, be 

 applicable to low densities. To obtain the maximum effect of 

 gun-cotton, theory, in accordance with the latest experiments, 

 shows that this powder must be compressed and reduced to the 

 smallest possible volume. For the initial pressures are thereby 

 increased. 



20. Let us now compare gun-cotton with other explosive 

 substances. It is especially distinguished by the magnitude 

 of the initial pressures. Thus, according to theory, the initial 

 pressure will be more than treble that of ordinary powder, 

 which is, in fact, the empirical ratio given by Piobert. 1 This 

 theoretical pressure, calculated from the reactions of the final 

 state, will, moreover, be diminished in practice, as in the case of 

 ordinary powder, owing to the incomplete state of combination 

 of the elements and the complexity of the compounds which 

 tend to be formed. Hence results a less sudden and more 

 regular expansion, following upon a combination which has 

 become more complete during cooling. 



On the contrary, pure nitroglycerin, weight for weight, 

 realises a work greater by half than gun-cotton, the initial 

 pressure being nearly the same. It is not surprising, there- 

 fore, that, nitroglycerin should have been found preferable for 

 industrial purposes, at least in the form of dynamite ; the more 

 so as the latter needs no previous compression, is easier to divide, 

 and, above all, more economical. But it is easier to distribute 

 non-compressed gun-cotton in a uniform manner over a con- 

 siderable space, which offers certain advantages in practice. 



1 " Trait^ de I'Artillerie," 2' Edition, p. 496. 



