186 THE EARL OF BERKELEY, MR. E. G. J. HARTLEY AND DR. C. V. BURTON: 



c 



c 



Fig. 3. 



Pure Air. 



It was now noticed that although the air passing through the train of vessels was 

 filtered, yet a certain amount of reaction had taken place in the 1st sulphuric acid 

 vessel (vessel D of original paper), for the acid had turned brown during the course 

 of the experiments. This was completely remedied by drawing the air from outside 

 the laboratory and by avoiding rubber tubing on the entry side. This latter 

 modification was obtained by means of a mercury cup placed outside the bath, but in 

 the axis of oscillation of the platform. 



An experiment with four sulphuric acid vessels in series was then made, with the 

 air current running for 92 hours, the temperature of the bath being constant at about 

 30 C. The 1st vessel gained 0'0021 gr., 2nd O'OOIO gr., 3rd 0'0012 gr., and 4th 

 O'OOIS gr. It was now thought that possibly these changes in weight were due to the 

 absorption of mercury vapour by the sulphuric acid. An attempt to test this was 

 made by furnishing two out of the four vessels with gold sleeves suspended in the 

 entry tubes. A run of 92 hours at 30 C. gave O'OOIS gr., 0'0013 gr., 0'0004 gr., and 

 O'OOIO gr. respectively, and the gold sleeves were not found to have altered in weight. 



Hitherto the vessels, while on the balance, had not been closed ; in view of the fact 

 that the errors now seemed to be considerably less than heretofore, it was thought 

 better to have vessels made with their entry and exit tubes fitted with ground- 

 glass stoppers. These vessels were then tested as before. 



