Thermodynamic Properties of Air, 297 



The apparatus having been filled repeatedly with pure and 

 dry air, I bring the movable manometric tubes Mx and M 3 to 

 such levels as to fill both eudiometers Ej and E 2 with mercury; 

 the meniscs are then brought as near as possible to the zero 

 marks of the eudiometer-divisions. (The stopcocks P, N x , 

 N 2 , Rj, R 2 are opened for this purpose.) The small volumes 

 in the eudiometer-tubes left between the meniscs of mercury 

 and the zero marks will be denoted here by iv 1 and iv 2 . 



As soon as equality of pressure in the interior of the appa- 

 ratus and in the atmosphere ( = b) has been established, I close 

 the discharging-valves R t and R 2 , as well as P, and charge 

 the apparatus with compressed air at that particular pressure 

 for which the expansion is to be measured. During the 

 charging both bulbs s x and s 2 remain in connexion with the 

 large store of air contained in the reservoirs Z, S', S". This 

 connexion ensures great constancy of pressure in case there 

 should be a small leakage of air somewhere. 



During the charging of the bulbs I determine their tempera- 

 tures (t and 0), as well as the temperature ( = r) of the sur- 

 rounding air. Next, I shut the charging-valves Nj and N 2 

 both at the same instant, and immediately after that I open 

 the discharging-valves R : , R 2 . The interval of time during 

 which the charge remains imprisoned in the bulbs is less than 

 one second. 



The air flows now from the bulbs into the eudiometers. 

 During this I lower the manometric tubes M ± and M 2 , so as 

 to reduce the gas (which fills now several bulbs in each eudio- 

 meter) as nearly as possible to atmospheric pressure. The 

 temperatures of the water-baths surrounding the eudiometers 

 having been equalized by air-currents blown in through p' 

 and p" , I proceed to determine, with the aid of the telescope 

 of the cathetometer, — 



(1) The temperatures $ x and S 2 of the gas in both eudio- 

 meters ; 



(2) The volumes u x and u 2 of air in both eudiometers, 

 reckoned from the zero marks; 



(3) The differences of level of mercury in the eudiometers 

 E and in the corresponding manometric tubes M 2 and M 2 . 



Taking into account the corrections mentioned in § 4, as 

 well as the barometric pressure, it is easy to find the pressures 

 of air in the eudiometers E, and in the bulbs s, which are 

 now in communication with E. I shall denote these pressures 

 by B x and B 2 . 



During these determinations the temperatures of the bulbs 

 are again measured ( = £' and 6 1 ). 



In this manner every single determination of the coefficient 



