Determining the Absolute Density of a Gas. 385 



Volume of vessel in which the gas is weighed : — 

 For Regnault's method 1800 cub. centim. 

 „ new „ 160 „ 



Weight of vessel in which the gas is weighed : — 



For Regnault's method 200 grams. 

 „ new „ 41 „ 



Error of buoyancy on the weight of gas : — 



For Regnault's method 1 in 280. 

 „ new „ 1 in 560. 



Ratio of weight of gas to weight of vessel in which it is 

 weighed : — 



For Regnault's method 1 to 1261. 

 ,, new „ 1 to 258. 



Regarding the last numbers I may observe that the case 

 assumed is unfavourable to the new method. The compression 

 of 1800 cub. centim. (at 760 millim.) in the sphere raises the 

 pressure to 12*5 atmospheres, but it may safely be filled to 17, 

 or, it will carry some 36 per cent, more gas than is assumed 

 above. 



The volumenometer which I am about to take into use in 

 estimating the density of the samples of gas used in my 

 experiments on the specific heats of gases has only lately been 

 constructed. A first and hasty experiment on the density of 

 dry air may, however, indicate the magnitudes dealt with, and 

 the accuracy obtainable when restricted to the use of water in 

 the volumenometer. The interior volume of the volumeno- 

 meter determined by weighing it filled with water at 15°* 6 7, and 

 again filled with air, but wet on the walls, was found to be 

 1751*0 cub. centim. This is with great probability correct to 

 unity, the first place of decimals being perhaps open to small 

 error. 



The data in the experiment on air density are as follows : — 

 Weight of air inserted =2*1092 less 0*0001 for error of 

 buoyancy = 2* 1091. Temp, of water jacket =15°* 70. Bar. 

 760*32 reduced to 0° C. Head of water 0*388 inches (=A) 

 + 0*120 inches correction for capillarity (by subsequent 

 experiment). Total press. 760*32 + 0*95 millim. = 761*27. 

 Max. vapour tension of water at 15*7 = 13*3 millim.; hence 

 the pressure, finally, is 747*97 millim. The volume for the 

 experiment may be taken as 1751 cub. centim., neglecting 

 the temperature effect of 0°*03. 



