| It has already been mentioned that uranium, in a very finely divided condition, takes fire on exposure to air. The black powder obtained by reduction of the oxide by means of magnesium exhibits this property. Chesneau observed that the sparks detached from uranium by friction with hard steel would ignite mixtures of methane and air, as well as such inflammable liquids as alcohol and benzene, and he concluded that their temperature could not be below 1000° C. The product obtained by Feree by heating uranium amalgam in vacuo burned spontaneously in the air. Alloys of uranium and iron containing more than 20 per cent, of uranium are pyrophoric, the activity increasing with increase in uranium content. |