148 



Scientific Proceedings, Royal Dublin Society. 



particularly the humidity of the atmosphere. In order to verify this point 

 a further experiment was made. 



The effect of the humidity of the air in contact with the water on the 

 rate of solution is shown by the following experiment : — 



Four tubes, each 320 mm. long and 40 mm. diameter, were placed in a 

 thermostat after being filled with de-aerated water. Three of these tubes, 

 after 50 ce. water had been withdrawn from each, were then connected by 

 means of rubber corks and glass tubing, so that a current of air could be 

 drawn through the series. The fourth tube was left open to the atmo- 

 sphere. 



Unfiltered air was drawn through the air-space of tube 1, and then 

 through two Z7-tubes containing calcium chloride, from which the dried air 

 passed into the air-space of tube 2, whence it passed directly into the air- 

 space of tube 3. Thus the air in tube 2 was much drier than that in the 

 atmosphere; and that in tube 3 was more moist, and probably nearly 

 saturated with aqueous vapour. 



The results are given in the following table : — 



Table III. 



Experiment with air of different degrees of humidity. 



Temperature of Experiment, 15" 0. 



It should be noted that tube 4 was exposed in the middle of the thermo- 

 stat at a time when the humidity of the air was considerable. Hence the 

 value/ is rather low. 



On examining these results it will be noticed that the tube through 

 which the dried air was drawn shows the largest proportion of dissolved air, 

 although the time of exposure was practically the same in each case. In 

 fact, the figures show that the water in this tube absorbed more than twice 

 as much air as that in the tube through which the moist air was drawn. 



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