126 ANNUAL OP SCIENTIFIC DISCOVERY. 



per cent, of water, according to their composition. The mass is 

 now suKjectod to a pressure of from 600 to 1,000 hundred weight 

 per square inch, according to the velocity of combustion to be 

 im])arted to the ]i()\V(ier. The cake obtained is then granuhited, 

 polisht'd, and dricnl in the ordinary manner. The process remains 

 the same for all kinds. 



Gunpowder cannot well bear over 20 per cent, ofpicrateof 

 potassa, while for cannon powder it should not exceed 15 per 

 cent. For tiie latter from 8 to 15 per cent, are taken, according 

 to the desired velocity of combustion. Designolle prepares also 

 colored tire-work compositions by means of picmtes, of which the 

 following are recipes: Gold rain — 50 parts of picrate of am- 

 monia, and 50 parts of picrate of iron ; (ireen lire — 48 parts of 

 j)icrnte of :unm«>nia, and 52 parts of nitrate of l)aryta; Red lire — 

 5-4 parts of picrate of ammonia, and 46 parts of nitrate ofstrontia. 

 Until recently, the picrate of potassa has been very expensive, 

 but improvements made in its mode of preparation enable the 

 manulacturer to sell it at a price sufliciently low to ensure its ap- 

 plication for all practical purposes. 



NEW PROPERTY OF GUN-COTTON. 



According to the "Chemical News," it is possible to burn gun-cot- 

 ton in the i)alm of the hand without the least danger; a delicate 

 balance in the pan on which gun-cot*ton is exploded does not 

 swing from its poise. The same quantity of gun-cotton, if it be 

 pressed into a cavity, explodes with a force equal to that of nitro- 

 glycerine, and 10 times greater than that of gunpowder, provided 

 it be ignited by percussion in the same way as nitro-glyccrine. 

 This discovery may enable us to employ gun-cotton as a substi- 

 tute for nitro-glycerine, and as the danger of freezing or of pre- 

 mature explosion is avoided, it may prove to have many advan- 

 tages over other explosive agents. 



Some recent experiments made at the Woolwich Arsenal, near 

 London, encourage tiie hope that gun-cotton can be successfully 

 used as a most destructive agent. A palisade was built of oak 

 timljers a foot thick, firmly fixed in the ground, and supported in 

 the rear by strong trusses. Discs of gun-cotton weje placed 

 along the face of the palisade about a foot above the ground, and 

 were fired by a battery in the usual way. The effect may be de- 

 scribed as wonderful. The palisixde was literally blown away 

 amid a deafening report, as if the massive timbers olYered no 

 more resistance on one side of the gun-cotton than the atmos- 

 phere on the other. The discs require no fixing; merely lay- 

 ing them on is suilicient. Solid blocks of iron and stone can be 

 shivered into fragments by firing a disc laid on the top. In fu- 

 ture sieges, if some desperate fellow can but get to the gate or a 

 thin part of the walls, and hang on a few discs of gun-cotton, a 

 breach can be made by firing with a galvanic current from along 

 distance, 



