86 M. E. Wiedemann on the Specific Heats of Gases. 



from the heating- vessel. When 10 litres of gas were passing 

 through the apparatus per minute the thermometer remained 

 constant at 100°. 



Another method for determining that the gases are 

 thoroughly warmed has been proposed by Regnault. He 

 placed a thermometer in the anterior part of the spiral of the 

 heating-vessel. This method is open to the objection that 

 the thermometer is exposed to the influence of the heat radi- 

 ated from the sides of the apparatus. A gas which has only 

 cooled slightly will therefore produce an extremely small 

 effect on the indication of the thermometer. 



In order to ascertain whether the heated gas entirely parted 

 with its heat in the calorimeter, experiments were carried out 

 with a similarly constructed instrument, in which the three 

 tubes filled with silver were replaced by two tubes filled with 

 copper ; the numbers representing the specific heats were 

 identical within the limits of experimental error. It was also 

 determined that the heat was entirely given up during the 

 passage of the gas through the first tube ; when one of the 

 tubes only was filled with copper gauze and a thermometer 

 surrounded with gauze was placed in the second tube, the 

 temperature indicated by the thermometer was almost iden- 

 tical with that of the surrounding liquid. By using three 

 tubes no doubt could arise as to whether the heat was entirely 

 given up in the calorimeter. 



Even if the gas did not enter and leave the calorimeter at 

 the exact temperature indicated by the thermometer in the 

 heating-vessel and in the calorimeter respectively, the result 

 of the experiments would be but very slightly affected thereby, 

 inasmuch as the total cooling of the gas is represented by the 

 difference between these two temperatures, and this difference 

 always amounts to at least 75° C. 



Method of Observation. 



In carrying out the measurements the following was the 

 method of procedure : — 



The balloon Q, after having been entirely emptied, was 

 filled with the gas to be examined, the gas being pure and 

 dry. - 



For this purpose the balloons B and C were disconnected, 

 and the stopcocks T and V were opened. In order that the 

 gas should enter Q at a fixed temperature, it was caused to 

 traverse a cylinder filled with copper gauze and surrounded 

 with water, which was maintained at the temperature of the 

 air of the room. 



The thermometer (F) was arranged so as to indicate the 



