944 
DR. J. JOLY ON THE SPECIFIC HEATS 
those described in Part 1. Some modifications in the structure of the calorimeter, &c., 
must, however, be noticed. 
The differential form of the steam calorimeter was used throughout ; the mode of 
experiment being to compare the calorific capacity of a strong spherical copper vessel, 
firstly when containing but one atmosphere of the gas, and secondly when charged 
with the requisite mass of the gas, with that of an idle vessel of closely similar mass 
and volume. Each of these comparative observations embraced a series of from three 
to ten experiments, according to the mass of gas operated upon ; a larger number 
being requisite when the mass was small. The identical calorimeter, described in 
Part I., was used in the present experiments up to the completion of the experiments 
of Table IX. An improved differential calorimeter was then completed for the 
re(]uirements of the experiments upon the temperature variation of the specific heat. 
It was accordingly taken into use, and with it the experiments were completed. As 
its peculiarities of construction are mainly to render it suitable for the experiments 
described in Part III., its description is deferred to that paper. 
To carry out experiments at the high pressures contemplated, new copper spheres 
of greater strength than the former ones had to be provided. The dimensions were 
also reduced, and, what was most important, the brazed equatorial joint entirely 
dispensed with. This was effected by spinning the entire sphere out of the one piece 
of copper till the vessel was closed down to an orifice of about 2 centims. in diameter. 
Into this opening an accurately turned piece of gun-metal was brazed. Still further 
to diminish the number of joints, this piece of brass was so formed that it constituted 
the valve seat receiving the steel screw-valve, and carried the connecting nozzle used 
in filling it.* Several of these vessels were made, designed to have a capacity of about 
80 cub. centims., and to be 2 millims. thick in the walls. Assuming the tensile 
strength of copper to be 2 X 10® grammes per square centimetre, these vessels would 
possess a bursting strength of some 300 atmospheres. The safe limit would be about 
100 atmospheres, which pressure was somewhat exceeded on one occasion. One of 
these vessels having been chosen for use, its internal and external volume were 
measured. The external volume was found to be 9 8‘752 cub. centims. ; the internal, 
83T68. Its mass was 137'00 grammes. The external volume of the idle sphere was 
found to be 9 9 ’810 at 13° C. ; and the mass, 135‘55 grams. 
The active sphere was now tested by putting into it some 12 grammes of carbon 
dioxide, and heating it in a current of steam for 1 5 or 20 minutes. It became visibly 
more truly spherical by this treatment, and a re-determination of its external volume 
afforded 101‘737 cub. centims. at 16° C., showing a stretch of 2*985 cub. centims., 
]3robably due principally to a more perfect sphericity. The experiments on the gas 
were now begun, using a mass of 10*5 grammes. Later on, after the experiments of 
Table IX., tbe volumes were again determined. The external gave 101*738 cub. 
centims. at 16°*7 C., which may be considered identical with the previous result; the 
* See Part I. {loc. cit.), p. 78. 
