M. V. Regnault on the Expansion of Gases. 



137 



The apparatus being arranged and the 3tirring having been 

 continued for a quarter of an hour, I make observations during 

 the first five minutes, during which the calorimeter is only sub- 

 ject to external disturbing causes ; an assistant tben suddenly 

 opens the stopcock of Thilorier's reservoir. The gaseous car- 

 bonic acid bursts into the worm of the vessel, where it produces 

 the pressure of the reservoir, then passes through the capillary 

 worm of silver, where it expands, and enters the superposed 

 boxes of the calorimeter with a slight excess of pressure over the 

 external air. 



A water manometer, communicating by a tubulure with the 

 upper gas-box of the calorimeter, only indicates an excess of pres- 

 sure of 50 millims., which corresponds to 3*7 millims. of mer- 

 cury. Thus the gas only retains a very slight excess of pressure 

 on emerging from the calorimeter. 



The flow is permitted to last four minutes ; this time is suffi- 

 cient for the passage of about 120 litres of carbonic acid. The 

 stopcock of the reservoir is then suddenly closed, the observation 

 of the thermometers continued minute by minute until the tenth 

 minute. Finally, the variations of the thermometer of the ca- 

 lorimeter are followed during the last five minutes, when it is no 

 longer subjected to any but external disturbing causes. 



The greatest care must be devoted to the construction and 

 preservation of the apparatus ; for it must keep a gas under a 

 pressure of about fifty-five atmospheres without the least loss. 



The elastic force of the carbonic acid which reaches the calo- 

 rimeter is calculated from the temperature t of the water sur- 

 rounding the Thilorier reservoir, and by the aid of the formula 

 which I have given (Memoires de VAcademie, vol. xxxi. p. 130). 

 I assume that this elastic force is maintained from the reservoir 

 until the arrival of the gas at the entrance of the silver capillary 

 worm. It is probable that it is really somewhat less; but the 

 difference must be very small, for the section of the silver ca- 

 pillary is but a tenth that of the large worm of the vessel. 



The volume of the carbonic acid used in each experiment is 

 indicated by the gas-meter. 



Combining the results thus obtained for carbonic acid under 

 high pressure with those I previously obtained under lower pres- 

 sures, I have constructed the following Table : — 



Excess of pressure 



producing the 



outflow. 



Cooling experienced 

 by the gas. 



Value of y r 



millims. 

 3354 

 7764 



38591 



- 5°-434 

 -12-731 



-81-960 



-1-619 



-1-6396 



-21238 



