1893.] On the Densities of the Pri?icipal Gases. 



Fig. 2. 



ia9 



n 



XZ7 



the tap of tlie globe. The lower chamber of the manometer was now 

 in connexion with the globe, and through a regulating tap (not 

 shown) with the gas-generating apparatus. By means of the Toppler 

 the vacuum in the manometer could be carried to any desired point. 

 But with respect to this a remark must be made. It is a feature of 

 the method employed* that the exhaustions of the globe are carried 

 to such a point that the weight of the residual gas may be neglected, 

 thus eliminating errors due to a second manometer reading. There 

 is no difficulty in attaining this result, but the delicacy of the 

 Toppler employed as a gauge is so great that the residual gas still 

 admits of tolerably accurate measurement. Now in exhausting the 

 head of the manometer it would be easy to carry the process to a 

 point much in excess of what is necessary in the case of the globe, 

 but there is evidently no advantage in so doing. The best results 

 will be obtained by carrying both exhaustions to the same degree of 

 perfection. 



At the close of the filling the pressure has to be adjusted to an 

 exact value, and it might appear that the double adjustment required 

 (of pressure and of mercury) would be troublesome. Such was not 



* Due to von Jolly. 



