82 M. E. Wiedemann on the Specific Heats of Gases, 



mercurv (at 0° C.) were frequently employed ; 9000 millims. 

 was an attainable pressure. The gases could easily be sent 

 through the warming-apparatus and calorimeter in sufficient 

 quantity and with the necessary velocity. As the volume of 

 the copper containing-vessel was known, the quantity of gas 

 used could be calculated from the pressure existing before and 

 after the experiment. That part of the apparatus in which 

 the gases were warmed consisted of an oil-bath containing a 

 tube of brass or platinum 8 millims. in width and 10 metres 

 in length, through which the gas was allowed to flow. The 

 calorimeter consisted of a similarly shaped spiral of thin sheet- 

 tin surrounded with water. In taking an observation a known 

 quantity of the gas under examination was allowed to flow 

 through the warming-apparatus, which was heated to a deter- 

 minate temperature ; the heat thus absorbed was again given 

 up to the water in the calorimeter ; and from a determination 

 of this quantity of heat the specific heat of the gas could be 

 readily calculated. 



In order to ensure correct determinations, it was especially 

 necessary that the gas should be completely heated to the 

 temperature of the warming-apparatus, and that it should also 

 entirely give up its heat in the calorimeter. The spiral 

 through which the gas flowed was therefore required to pre- 

 sent a considerable surface to the gas and thus to be of con- 

 siderable length. This was the more requisite, inasmuch as 

 the gas passed through the apparatus with a very considerable 

 velocity, as much as 24 litres per minute. The length of the 

 spiral necessitated that the vessel containing it should be of 

 somewhat large dimensions. In the greater number of Reg- 

 nault's researches the mass of water used amounted to 

 660 grms., calculated to the water-value of the spiral, the 

 outer vessel, and the stirrer. In order to bring about a suf- 

 ficient elevation of temperature in this mass of liquid, a large 

 quantity of heated gas was necessarily employed. 



The first problem to be solved appeared then to be how to 

 diminish the size of the calorimeter and at the same time to 

 allow the gas to give up all its heat — in other words, how to 

 bring the heated gas into contact with the largest possible sur- 

 face in the smallest possible space. For this purpose a method 

 first made use of by Ericson in the construction of his air- 

 machine was employed. It consisted in passing the gas over 

 copper gauze, which exposed a large surface for carrying away 

 the heat. 



Description of the Apparatus (Plate I.). 



The heating-vessel consists of a copper box (hard-soldered), 

 M, 20 centims. in height, 18 centims, in breadth, and 21 cen- 



