540 Scientific Proceedings, Royal Dublin Society. 



Volume of vessel in which the gas is weighed : — 



For Rcgnault's method 1800 c.cs. 



„ 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 c.cs. (at 760 mms.) 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 experi- 

 ments on the specific heats of gases has only lately been con- 

 structed. 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 volumenometer 

 determined by weighing it filled with water at 15°*67, and again 

 filled with air, but wet on the walls, was found to be 1751*0 c.cs. 

 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. 7760*32 reduced 

 to 0°O. Head of water 0*388 inches (= h) + 0*120 inches correction 

 for capillarity (by subsequent experiment). Total press. 76*032 + 

 0*70 mms. = 761*05. Max. vapour tension of water at 15*7 = 

 13*3 mms. ; hence the pressure, finally, is 747*75 mms. The 

 volume for the experiment may be taken as 1751 c.cs., neglecting 

 the temperature effect of 0°*03. 



