FREEZING OF WATER. 39 



the procefs of freezing nine times, without changing the 

 water, and the laft portion of air that I procured in this 

 manner was as great as any of the preceding; fo that 

 there remained no reafonable doubt, but that air might 

 be produced from the fame water in this manner ad libitum. 

 Having got near two inches of air in the glafs tube, 

 I put an end to the experiment ; and examining the air, 

 found it to be wholly phhgi/iicated, not being affeded 

 by nitrous air, and having nothing inflammable in it. 



During the procefs of freezing the air in the tube was 

 generally comprelTed into about one- fifth of its ufual 

 bulk ; but, when 1 began to thaw the ice, which I did 

 by means of hot water in the place of the freezing mix- 

 ture, it foon expanded to its former dimenfions, and no 

 feniible portion of it was abforbed during the whole pro- 

 cefs, which was about a week. Sometimes the violence 

 of the preffure, occafioned by the expanfion of the water 

 in freezing, would force a little water out of the veflel 

 between the cork and the glafs tube, or the iron veflel, 

 which prefently became ice. This 1 always carefully re- 

 moved, and applied frefh cement to the place, to prevent 

 the introdudlon of any air from without before 1 began 

 to melt the ice. And that no external air had entered, 

 was evident both from the manner in which the air was 

 produced as the water recovered its fluidity, and from 

 the quality of it when examined after the procefs. 



In the courfe of the experiments with the glafs veflels 

 a phenomenon occurred that was wholly unexpeded by 

 me, and which was very amufmg. Having left the 

 veflTels filled partly with water and partly with mercury 

 in the evening, I generally found them in the morning 

 feemingly quite full of mercury, every part of the ice 

 within the vefl^el being covered with it. This muft have 

 been occafioned by a vacuum having been formed be- 

 tween the glafs and the ice, and into this the mercury 



had 



