ij90 Transactions of the American Institute. 



inch, and is very greatly different from the pressure exerted by the 

 most of the solid and liquid explosive substances we are acquainted 

 with ; a result the very opposite to that which was supposed to be 

 the case by most people until now. In order to obtain a pressure 

 more nearly like that exerted by solid and liquid explosive substances, 

 it would be required to compress the bulk of the explosive gaseous 

 mixtures until their density was nearly that of the explosive solids 

 and liquids. Leaving out of the question for the moment the diffi- 

 culty of this operation, the result would be liquefaction of most of 

 the hydrocarbonated gases while the oxygen remained in a gaseous 

 state, and the destruction of the homogeneity ojf the explosive mix- 

 tures, and accordingly, also, the possibility of obtaining its instanta- 

 neous explosion by a spark. 



Dr. Yan der Weyde — In rating the effect of explosive mixtures, the 

 velocity is often overlooked. Gunpowder is weak, because it burns 

 so slowly. White gunpowder, made with chlorate of potash, burns 

 six times faster ; and for that reason does not answer the purpose of 

 gunpowder. In making gunpowder for large guns, it is necessary to 

 make it in large grains, to make the combustion slower ; but in blast- 

 ing we want sudden expansion. The fulminates do not produce more 

 gas than gunpowder ; but the enormous velocity of the production of 

 the gases makes the difference. A mixture of hydrogen and oxygen 

 will explode in the open air, but gunpowder in the open air only 

 burns rapidly. For projectiles we want the combustion to be so regu- 

 lated that the last grain of gunpowder shall be burned at the moment 

 the ball leaves the musket. 



Prof. John Phin — If you lay two trains, one of gunpowder, and 

 another, crossing it, of fulminate of mercury, the gunpowder will 

 burn to the point where the other crosses it, and no farther. The 

 fulminate will scatter the gunpowder without igniting it, and the rest 

 of the train of gunpowder will be left unconfirmed. But if you con- 

 fine the gunpowder so that the fulminating mercury shall give it a 

 hard blow and explode it at the same time, it increases the force of 

 the explosion. 



Dr. Yan der "Weyde — That is the reason that gunpowder is more 

 effective with percussion caps than with flint. 



Prof. Phin — Fulminating murcury must be mixed with something 

 else in order to fire gunpowder. Mix together a quantity of iron 

 filings and of fine hard-grained powder, and throw them through an 

 alcohol flame, and the iron filings will burn, and the gunpowder will 

 not. 



