( H ) 



No. II. 



Experiments relating to the change of Place in differenl 

 kinds of Air iJjrough feveral inter pofing Subfances. By 

 Dr. Joseph Priestley. 



O' 



^NE of the moft extraordinary circumftances 

 that ever occurred in the courfe of my 

 experiments is that of the vapour of vpater, or of mer- 

 cury, changing places with any kind of air, in veflels 

 through which air could not be made to pafs without 

 great force, fo that for moft purpofes they might be 

 confidered as air-tight. Of this remarkable faft, and of 

 all the circumrtances that led to the complete afcertain- 

 ing of it, 1 have given an account in my former pub- 

 lications. I had alfo obferved that different kinds of 

 air capable of forming a chemical union would do it 

 through a bladder that was perfeftly air-tight, that in 

 this manner pure air was imbibed by the blood through 

 the membrane of the lungs, v^rhile phlcgifton was tranf- 

 mitted into the air within them. Since that time I have 

 extended and diverfified the experiments, and have ob- 

 ferved that what was done by air and water, will be done 

 by any two kinds of air, and whether they have an af- 

 finity to one another or not, that this takes place in cir- 

 cumftances of which I was not at all apprized befoi"e, 

 and fuch as experimenters ought to be acquainted with, 

 in order to prevent miftakes of confiderable confequence. 

 Having procured earthen velTels of a \trj clcfe tex- 

 ture, fo as to be apparently inipervious to air, contain- 

 ing about an ounce meafure, 1 could fill them with 

 any particular kind of air, and then place them inverted 

 in a large glafs jar containing a different kind of air. I 

 then heated the fmall earthen veflels through the glafs jar 

 by means of a burning lens, and I never failed to lind 



after 



