W. E. Woodbridge on the Pressure of Fired Gunpowder. 157 



due to the elevation of temperature mentioned, than that pro- 

 duced by the same force slowly applied. The actual amount of 

 this difference has not been ascertained, but data which lack the 

 precision necessary to exact results, indicate that the correction 

 due to this cause, which increases with both depression of tem- 

 perature, and increase of pressure, is not unimportant. No 

 attempt has been made however, to introduce this correction into 

 the results subsequently presented of the experiments with the 

 piezometer. The subject has been reserved in hope of future 

 experiments, for which apparatus has been partially prepared. 



In the fall of 1852 a piezometer was constructed on the plan 

 which has been described, and was used, to test its working, for 

 a few firings, in a 4 pdr. gun at Perth Amboy, N. J. In Feb., 

 1853, assistance was granted me from the U. S. Ordnance De- 

 partment for testing my plan, and the subject was referred to 

 Major Alfred Mordecai, with whom I had the pleasure and 

 honor to be associated in making the experiments thus author- 

 ized, which, however, on account of various hindrances, were 

 not undertaken until the winter of 1854-5. 



Two six-pounder guns, one of iron and the other of brass, 

 were used in the experiments. The diameter of the bore of 

 each was, at the seat of the shot, 3*69 in., very nearly. The 

 powder used was Dupont's cannon-powder, made in 1837. The 

 shot were strapped to sabots of poplar (whitewood) of the full 

 size of the bore unless otherwise specified. The tiring was per- 

 formed at Washington Arsenal, D. C. The oil used in the pie- 

 zometer in all these experiments was of the same kind as that 

 used in the experiments on compression, (unbleached winter- 

 strained sperm oil,) being portions of the same mass. 



In the first trials, the piezometer, covered with a case of paper 

 to protect it from the heat attending the explosion, was attached 

 by screwing to the bottom of the bore of the gun, occupying a 

 place in the centre of the charge, but the screw was twice bro- 

 ken off, and this mode of using the instrument, which was orig- 

 inally adopted to avoid injuring the gun so as to render it un- 

 serviceable, was exchanged for the following. 



The new piezometer was enclosed in a hollow plug of steel 

 screwed into the side of the gun so that the cavity of the plug 

 communicated with the bore of the gun. A leather case sur- 

 rounded the instrument to protect it against injury from the 

 shock of firing, and the remaining space within the cavity of 

 the plug was filled with oil, which was retained by a disc of 

 cork or leather loosely closing the communication with the bore. 

 This arrangement was used in all the subsequent firing with 

 cannon, and was entirely satisfactory. The length of the pie- 

 zometer was 2*5 inches, its diameter 0*7 inch, and the diameter 

 of its piston 0*252 in. The adjustment of the quantity of oil in 



