298 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1910. 



fers in amount with the temperature differences, with the rate at 

 which the heat is set free in the reaction, with the materials of which 

 the chambers are composed and the extent of the exposed surface in 

 the chambers. Using chambers made of the same material it becomes 

 possible, by varying the areas of these exposed surfaces in the differ- 

 ent experiments to a known extent, to measure the heat-absorbing 

 effect of surfaces of known area, and by combining this data with 

 that recorded for the pressure, to ascertain the total dynamic effect 

 of the charge of the explosive tested. This apparatus moreover af- 

 fords a means by which the gaseous, liquid, and solid products of the 

 reactions attending explosion may be collected for chemical analysis 

 and physical inspection and study. 



In plate 7 are shown two of these gauges, one of which is open and 

 ready to load while the other is closed for firing. It will be observed 

 that they are in principle like the bombs used by Noble and Abel 

 in their Researches on Fired Gunpowder, but they are markedly de- 

 veloped in details of construction and in the addition of accessories. 

 One of these cylinders has a chamber capacity of 15 liters, the other 

 of 20 liters, but the volume of the latter may be reduced at will by 

 inserting steel disks of known volume and area. The surface is 

 thereby changed so that while the cooling surface of the small cham- 

 ber is 3,911 square centimeters, that of the large cylinder, when one 

 large steel disk is inclosed, is 6,555, and when three of the smaller 

 disks are inclosed, 7,621 square centimeters. 



These cylinders are made of steel 12.5 centimeters in thickness and 

 the removable heads are secured in place by 12 heavy stud bolts, 

 packed with lead washers, and an iron yoke. A system of sheaves 

 and suspended counterweights is provided to aid in detaching the 

 heavy heads from the cylinders and mounting them upon the spe- 

 cially designed wagons, so as to give ready access to the interiors of 

 the cylinders. 



Before the charge is fired the cylinders are exhausted to 10 milli- 

 meters of mercury. To permit of this being done a well-glanded tube 

 is inserted in a perforation in an upper segment of each cylinder 

 near one end, and this is provided with a valve by which to isolate 

 the air pump after the vacuum has. been attained. On the opposite 

 upper segment of the cylinder from the exhaust a second opening is 

 provided in which a glanded housing is inserted, which affords a 

 means for introducing the electric detonator and so packing its legs 

 as to prevent air entering about them while the cylinder is exhausted 

 or gases escaping about them after the explosive has been fired and 

 while a considerable pressure obtains within the cylinder. 



A third perforation in the top of the segment carries a properly 

 glanded tube provided with a piston 0.3937 centimeter in diameter, 

 which can move up and down within this tube. This piston is held 



