360 



Lord Kayleigh. On the relative 



[Feb. 9, 



what rapidly is thoroughly dry, having been in good contact with 

 the phosphoric anhydride. In this way the pressure on the dry side 

 is reduced to about 2 inches of mercury, but this residue is sufficient 

 to allow the damp side of the apparatus to be exhausted to a still 

 lower pressure before the tap between the two sides of the apparatus 

 is reopened. When this is done, the first movement of the gas is 

 retrograde ; and there is no danger at any stage of imperfect purifica- 

 tion. The generator is then re-started until the gas (after from two of 

 five hours) begins to blow off again. 



In closing the globe some precaution is required to secure that 

 the pressure therein shall really be that measured by the barometer. 

 The mercury seal is at some distance from, and at a lower level than, 

 the rest of the apparatus. After removal of the mercury the flow of 

 gas is continued for about one minute, and then the tap between the 

 dry and damp sides is closed. From three to five minutes more were 

 usually allowed for the complete establishment of equilibrium before 

 the tap of the globe was turned off. Experiments on oxygen appeared 

 to show that two minutes was sufficient. For measuring the atmo- 

 spheric pressure two standard mercury barometers were employed. 



The evacuations were effected by the Toppler to at least 

 so that the residual gas (at any rate after one filling with hydrogen) 

 could be neglected. 



I will now give some examples of actual results. Those in the 

 following tables relate to gas prepared from sulphuric acid, with sub- 

 sequent purification, as already described : — 



Grlobe (14), empty. 



Date. 



Left. 



-t). , , j Balance 

 El S ht - reading. 



18S7. 



Oct. 27— Nov. 5 



a i4 + -394 





22- 66 

 22 -89 



23- 00 

 21-72 



Nov. 7— Nov. 8 



Nov. 9— Nov. 10 



Nov. 11— Nov. 12 





Globe (14), full. 



Date. 



Left. 



Eight. 



Balance 

 reading. 



Barometer. 



Temperature. 



1887. 









in. 



C. 



Nov. 5—7.. 



a u + -2400 



<*« 



20'52 



29 -416 



14-7° 



Nov. 8— 9.. 



G- 14 + 0-2364 



<*„ 



19-77 



29-830 



12-3 



Nov. 10—11.. 



G-. 4 +0-2360 





19-18 



22 -807 



11-2 



Nov. 12—14.. 



G 14 + 0-2340 





19-51 



30-135 



10'3 



