PROCEEDINGS OF THE POLYTECHNIC ASSOCIATION. 509 



the inferior limit of the pressure per square inch clue to tlie combustion of 

 gunpowder in its own volume, at, in round numbers, 200,000 pounds." 



On the other hand, Mr. Norman Wiard, of New York city, a practical 

 gun-founder of large experience, who has given a great deal of attention to 

 the subject experimentally, in a recently published essay, expresses very 

 strong conviction that all the estimates of the maximum possible pressure 

 of gunpowder heretofore made are greatly in excess; and that this maxi- 

 mum pressure cannot exceed 743 atmospheres, or about eleven thousand 

 pounds to the square inch. 



These examples are cited, not with any intention to exhaust the list of 

 authorities, but simply fur the purpose of illustrating the wide differences 

 between them. None of the results presented can be said to rest u\yun en- 

 tirely unexceptionable data; and among those which most largely differ, 

 are some which seem to possess almost equal claims to acceptance. In the 

 year 1857, however, there was published in Poggendorf 's Annalen, for 

 November, a paper by Messrs. Bunsen and Schischkuff, of Heidelberg, en- 

 titled " Chemische Theorie des Schiesspulver," in which this subject is in- 

 vestigated with a thoroughness never before attempted, and the data are 

 presented for determining the maximum force of gun-powder in a form 

 which seems to leave nothing to desire. This force is computed by them 

 to be equal to 4373.6 atmospheres. The objects successively aimed at by 

 these investigators were to ascertain, first, by the most rigorous methods 

 of analj'sis, the nature of the several products resulting from the combus- 

 tion of powder, and their relative quantities; secondly', the volume of the 

 gaseous products reduced to 0* C, as compared with the original volume 

 of the powder; thirdly, the volume of the fixed products, both at the tem- 

 perature of experiment and that of combustion; and finally, the absolute 

 amount of heat evolved in the combustion, and (considering the capacities 

 for heat of the several substances present and their respective weights) the 

 actual temperature of the whole mass in the instant of combustion. 



As it appears, in this investigation, that the fixed products occupy no 

 inconsiderable portion of the space which the powder originally filled, it 

 follows tiiat the conclusions of Robins and Gay Lussac, had they been in 

 other respects exact, would have materially underrated the maximum theo- 

 retic pressure; since these gaseous products, in an absolutely closed space, 

 are by so much the more compressed as the cavity is practically diminished 

 by the presence of the portions which are not gaseous. 



It is impossible to read the article of Messrs. Bunsen and Schischkoff, 

 without being strongly inclined to believe that their conclusion is as near 

 the truth as it is possible, in an inquiry of so difficult a nature, to arrive. 

 At the same time, one cannot fail to observe, in reading it, that they have 

 furnished the means of testing the correctness of their result, by taking 

 the velocities wliich projectiles of given weight, fired from guns of given 

 length and calibre, are observed to have acquired at the moment of leaving 

 the gun; and computing, according to recognized principles of physics, the 

 initial pressures which would be necessary to produce such velocities. 



In making such a computation, one assumption must be made, (at least 

 in the first instance) which is not true; and which in s6 far as it is not 

 true, will have the effect to make the computed maximum less than the real 



