102 ANNUAL OF SCIENTIFIC DISCOVERY. 



be made as light as possible, that the upward force of an explosion 

 should not be checked and deflected laterally. Tiie terribly de- 

 structive effects of several recent explosions show the desirability 

 of constructing powder magazines of light materials, of raising 

 them several feet above the ground, and of placing them, when 

 possible, in isolated situations as free as possible from surrounding 

 buildings. Mecli. Mag. 



GUN-COTTON. 



One great objection to the use of gun-cotton in fire-arms is its 

 liability to attract moisture. The Messrs. Prentice prevent this 

 by enclosing the charge in an excessively thin film of India- 

 rubber, blown in the shape of a bubble. The charge is placed in 

 a sort of barrel, and before this is placed a small disc of very thin 

 India-rubber sheeting, which is securely pressed against the muz- 

 zle of the barrel; air is then forced in behind, and the bubble of 

 rubber is blown ; as soon as this is done, the charge is pushed into 

 the bubble, the neck of which is immediately secured by a pair of 

 forceps and tied ; the quantity left on the charge is very minute, 

 and does not interfere in the least with the ignition of the charge. 



The Messrs. Prentice also prepare a very condensed charge, 

 1 inch of which will be found equal to 6 ounces of powder ; of 

 14 inches in diameter 5 inches in length are equivalent to one pound 

 of powder, costing 4^ pence. By its use in hard granite rock a 

 large saving in boring is effected ; the charges slip readily into 

 the holes, leave no residue on the side, and require the fuze to 

 be connected only with the uppermost piece. The smoke, though 

 invisible, in the atmosphere of a close mine, may be very injuri- 

 ous to the workmen resuming work too soon after a blast has 

 been fired. 



Mr. W. A. Dixon retards the explosion of gun-cotton by modi- 

 fying the form in which it is used, by manufacturing it into cloth, 

 and by incorporating it with a non-explosive material. It is 

 coiled with a spiral piece of paper, the centre of the charge alone 

 being pure gun-cotton. The result is that the first portion burns 

 freely so as to overcome the vis inertias of the shot or bullet, 

 while the remainder of the charge is so adapted that it shall all 

 have spent its whole force just as the empty case leaves the muz- 

 zle. Thus the sudden ignition of the whole charge, and the 

 danger attending it, are wholly obviated. 



Mr. Prentice afterward improved gun-cotton by interweaving 

 other cotton of suitable fibrous material in an inert state with it, to 

 retard and modify the rapidity of its explosion for special pur- 

 poses. He has ascertained in practice that it is desirable to 

 employ as little inert cotton or other fibrous material as possible, 

 in order to obtain the desired degree of retardation in the burning 

 of the pyroxyline, especially for fire-arms, in order not to foul the 

 barrels. He has further ascertained that the points of contact and 

 intersection of the converted with the unconverted fibre should be 

 as numerous as possible ; and that the more minutely the fibres 

 are divided, and the more intimately they are interspersed 



