PROEEDINGS OF THE POLYTECHNIC ASSOCIATION. 507 



ON THE EXPLOSIVE FORCE OF GUNPOWDER. 



Autliorities very widely differ as to the degree of strain to which heavy guns 

 are sxibjected in experimental or in service firing; and still more widely in 

 their estimates of the expansive force which gunpowder would be capable 

 of elerting could it be exploded in a space incapable of enlargement, which 

 it exactly fills. The magnitude of the differences may be illustrated by 

 the following examples: 



In the work published in 1*142 by Benjamin Robins, entitled "New 

 Principles of Gunnery," the absolute expansive force of gunpowder 

 exploded within its own bulk, is set down at one thousand atmospheres. 

 This estimate was founded on certain experiments which may briefly be 

 described as follows: First, by actually' collecting the gases generated by 

 the combustion of a given weight of powder, Mr, Robins inferred that 

 these gases, reduced to the actual temperature previous to explosion, 

 exceed, under the ordinary atmospheric pressure, the bulk of the powder 

 by which they are produced, in the ratio of 244 to 1. In order to ascertain 

 the effect upon elasticity prodnc(!d by the heat of combustion, he drew out 

 a portion of a musket barrel into a conical form, leaving an orifice at that 

 end of only one-eighth of an inch. The other end being closed, he subjected 

 the apparatus to the highest heat of a furnace, and then immersed the 

 conical end, which he first stopped with an iron plug, in water. After the 

 tube had sufficiently cooled, he removed the plug and allowed the water to 

 enter. The amount of the fluid found in the tube after the complete resto- 

 ration of the original temperature, compared with the entire capacity of 

 the tube itself, furnished the data for computing the expansion which the 

 air had undergone in the furnace. The relative volumes of the air in. the 

 tube before and after expansion, when reduced to a common temperature, 

 were determined, by a series of experiments of this kind, to be as 796 to 

 194|. Combining the data, Mr. Robins computed the maximum possible 

 elasticity of the gases generated in the firing- of gunpowder, at 999| 

 atmospheres; or, in round numbers, at 1000. It is here assumed that the 

 heat of burning gunpowder is no greater than that of an ordinary furnace. 



At a later period, this subject was investigated by Gay Lussac. Accord- 

 ing to his determination, the bulk of the gases generated in the combustion 

 exceeds the original bulk of the powder, in the ratio of 450 to 1. He esti- 

 mates the temperature of combustion at 1000" C; and computes the result- 

 ing elastic pressure at more than 2100 atmospheres. Dr. Hutton, relying 

 upon the approximate correctness of a formula which he had constructed 

 for computing the velocities of projectiles fired from a gun, and taken as 

 data the velocities actually observed, as ascertained by Robins' pendulum, 

 concladed the maximum pressure to be somewhere between HOO and 2300; 

 thus substantially agreeing with Gay Lussac. The results of Dr. Gregory 

 are not materially different from this, the maximum pressure being put by 

 him at 2250. 



In the year 1791, Count Rumford communicated to the Royal Society of 

 London the results of an elaborate series of experiments upon the force of 

 gunpowder, in which the estimates of pressure had been deduced, among 

 other methods, from the observed effect of small charges of powder in lift- 

 ing heavy weights. He puts the greatest force actually observed at about 



