On the transposition of AIRS. 15 



after the experiment, that the air within the earthen 

 veflel was the fame with that which had been on the out- 

 fide of it, while that within it was mixed with that on 

 the outfide ; but in fome cafes the mixture was. a che- 

 mical one, forming a kind of air different from either of 

 them, while at other times they were only difFufed 

 through one another. It will be necelfary therefore to 

 recite the circumllances as I obferved them, that future 

 experimenters may give more attention to them, and 

 endeavour to afcertain the caufe of this difference, which 

 I have not been able to do. 



I put one meafure of dephlogifticated aif into the 

 fmall earthen veffel in a large glafs jar containing in- 

 flammable air, and after heating it about half an hour, 

 found the quantity of inflammable air confiderably di- 

 miniihed, and the air within the earthen vefl"el wholly 

 inflammable, and increafed in quantity one half. 



I repeated the procefs with inflammable air in the 

 earthen vefl~el, and dephlogifl;icated air in the jar, and 

 then found the dephlogifl:icated air fomething diminifli- 

 ed, and the quality of it inferior to what it had been 

 before. The air in the earthen vefl^el was wholly de- 

 phlogiflicated, hardly difliinguifhable from that in the 

 glafs veflel. There was no fixed air in either of them. 



In both thefe cafes the mixture of the two kinds of air 

 in the glafs jar was evidently a chemical one, the quan- 

 tity being diminiflied ; but the air that had been tranf- 

 mitted through the earthen veflel in the contrary direc- 

 tion had undergone no change, being the very fame with 

 that in the glafs jar. Of the reafon of this difference I 

 cannot form any probable conjedlure. 



"When the two kinds of air were feparated by a blad- 

 der, and no heat was applied, I fometimes found that 

 the tranfmiffion had been made both ways, without any 

 chemical union, 



Having 



