26 MODERN SCIENCE READER 



larger cordite is cut off in suitable lengths, the drums and 

 cut material being dried at 100 F., thus driving off the 

 remainder of the acetone. 



Cordite varies from yellow to dark brown in color ac- 

 cording to its thickness. When ignited it burns with a 

 strong flame, which may be extinguished by a vigorous 

 puff of air. Macnab and Ristori give the yield of per- 

 manent gases from English cordite as 647 c.c., containing 

 a much higher per cent, of carbon monoxide than the gases 

 evolved from the old form of powder. Sir Andrew Noble 

 failed in attempts to detonate the substance, and a rifle 

 bullet fired into the mass only caused it to burn quietly. 



Lyddite is probably the explosive which has received 

 most notice during the past few months. In 1873, Spren- 

 gel, in a paper read before the Chemical Society, stated 

 that "picric acid alone contains a sufficient amount of 

 oxygen to render it, without the help of foreign oxidizers, 

 a powerful explosive when fired with a detonator. Its 

 explosion is almost unaccompanied by smoke." 



Picric acid was first prepared by Woulfe in 1771, by 

 treating indigo with nitric acid. It may be made by the 

 direct nitration of phenol (carbolic acid), but a better 

 result is obtained by first dissolving the phenol in sulphuric 

 acid, forming phenol sulphonic acid, which is dissolved in 

 water, and nitrating this compound with nitric acid (14). 

 On cooling, the picric acid separates out, and is purified 

 by recrystallization from hot water, the yellow crystalline 

 product being dried at a temperature not exceeding 

 100 C. 



Picric acid containing as much as 17 per cent, of water 

 can be detonated by a charge of dry picric powder; a thin 

 layer may also be exploded by a blow between metal sur- 

 faces, its sensitiveness to shock being greatly increased by 

 warming, for at a temperature just below its melting point 

 a pound weight falling from a height of 14 inches will 

 explode it. 



The sensitiveness of picric acid can be reduced by con- 



