154 W. E. Woodbridge on the Pressure of Fired Gunpowder, 



force of fired gunpowder he deduced from that estimated suffi- 

 cient for the rupture of his eprouvette, which, was burst by a 

 charge rilling its cavity, and concluded it to be not less than 

 54750 atmospheres. Although his conclusions have not always 

 been received as rigorously correct, and some must be considered 

 to be very erroneous, the experiments have ever since been re- 

 garded as furnishing important data, and have been made the 

 subject of careful analysis, especially by Piobert, with reference 

 to the circumstances of practice. 



The principles on which to estimate the strength of hollow 

 cylinders were not well understood at the time of Count Rum- 

 ford's experiments ; and the strength of his eprouvette was not 

 more than one-tenth of that which he assigned to it. It does not, 

 however, necessarily follow that the estimated bursting pressure 

 must be reduced in the same ratio, since the relations of succes- 

 sive rupture to time are but imperfectly known. 



The following experiment seems to show that the extreme 

 force of gunpowder fired in small quantities does not exceed 

 6200 atmospheres. I enclosed in a hollow cylinder of cast-steel 

 If inch in exterior diameter and \ inch in diameter interiorly, 

 20 grains of Hazzard's Kentucky rifle powder, which filled, 

 loosely, the cavity. This was fired by a flash of powder pene- 

 trating through the aperture of a valve (of steel) opening inward, 

 but designed to prevent the escape of gas outward. The cylin- 

 der was not ruptured, and being put under water, no gas was 

 found to escape. (The weight of the instrument was too great 

 to test the loss of gas by my scales.) On pressing in the valve 

 by means of a screw, an abundance of gas escaped, carrying 

 with it the odor of sulphuretted hydrogen. The seat of the valve 

 was found to remain perfect, a fact which when compared with, 

 a former trial in which the gases escaped in consequence of a 

 slight defect of the valve, is presumptive proof of its immediate 

 action. The residuum was found to weigh 1045 grains. The 

 calculated strength of the cylinder would be equal to an internal 

 pressure of about 98000 lbs. per square inch, or 6200 atmos- 

 pheres of 15 lbs. 



In the experiments above mentioned, the quantities of powder 

 employed were small and the circumstances under which it was 

 exploded were very different from those attending the firing of 

 it in practice. Desirous of ascertaining the actual pressures sus- 

 tained by fire-arms of different calibres, when fired with charges 

 variously modified, by a method more exact than the deductions 

 from these experiments afforded, I was led to devise the plan 

 which, will now be presented, together with some account of such 

 experiments as have already been made in accordance with it. 



I proposed to ascertain the pressure of the gases evolved by 

 the combustion of gunpowder, by including in the cavity within 



