﻿612 New Form of Sulphuric- Acid Drying- Vessel. 



In a run at 30° C. nearly 7 grammes of water was passed 

 over 23 c.c. of acid (4 c.c. in the first branch) at the rate of 

 •11 gramme per hour without any loss ; the spent acid in the 

 first (inlet) branch was then replaced by 4 c.c. of fresh acid 

 and the run continued at a rate of '075 gramme per hour 

 until another 7 grammes had passed — again there was no loss. 



The ^advantages of the new form over the Winkler seem 

 therefore to be as follows : — 



(1) There is no constriction in the air-current. 



(2) There is no danger from sulphuric-acid spray. 



(3) Even after a somewhat prolonged use the drying- 

 agent is still effective; with the Winkler, however, the water 

 absorbed dilutes the whole of the acid, and the issuing air is 

 saturated up to the vapour pressure of the solution. 



(4) As by far the greater quantity of water is taken up 

 in the inlet branch, it is only necessary to renew the acid in 

 this branch for the vessel to be again efficient. 



(5) For any prolonged run it is easily seen that less acid 

 is required in the new form than in the Winkler. 



In view of Mr. Manley's observations that sulphuric acid 

 itself has an appreciable vapour pressure *, being, for example,, 

 found condensed on the lids of desiccators, experiments 

 were made to ascertain the magnitude of any error that 

 might be introduced by neglecting this effect. 



Air at the laboratory temperature was passed over sulphuric 

 acid in a vessel very similar to that already described and 

 then over water. At the end of six days the water was 

 tested with a drop of barium chloride solution, which, after 

 standing some few minutes, gave a slight turbidity. By 

 comparison with the turbidity produced by known amounts 

 of sulphuric acid, the water was estimated to have contained 

 *0001 gramme of acid. The same experiment was repeated 

 with the train of vessels immersed in a bath at 30° C., the 

 air being passed for three days ; again the amount of acid 

 carried over into the water was found to be about 

 •0001 gramme. 



It may be mentioned that during the operation of weighing,, 

 air, dried by passing over sulphuric acid, is circulated through 

 the balance-case. So far there are no signs of any harm 

 having been done to the balance, But an alternative method 

 for drying the air seems to be to pass it over stick potash, 

 as the following experiment shows : — 



Air derived from outside the laboratory, during very 



* Loc. cit. 



