On air heated 



No. vr. 



Experiments on Air expofed to Heat in metallic Tubes. By 

 Dr. Joseph Priestley. 



Read Aug. T " T AVING lately fcnt to the fociety an ac- 

 15. 1800. JTJL count of fome pretty remarkable experi- 

 ments upon air heated in eart/jen tubes, 1 now take the 

 liberty to communicate the refult of fome that I have 

 made on air heated in metallic tubes. They are not lefs 

 remarkable than the others ; and being unable to explain 

 feveral of them on any known theory, I Ihall be glad 

 of the afliftance of the members of the fociety in the in- 

 vefligations to which they may lead. 



I. Of a mixture of dcphlogijlicated and inflammable air 

 not exploding in a red heat. 



One remarkable circumflance attending the heating 

 of air in earthen tubes, and alfo in thofe of metal, is that 

 no mixture of dephlogifticated and inflammable air will 

 explode in them, though it always does in tubes of glafs 

 in which there is no metallic ingredient. With refpedl 

 to earthen tubes, the fa£t may perhaps be explained by 

 the eafy tranfmiffion of air through tlie heated tube, and 

 even before the tube is red hot. The air in the infide 

 changing places with that on the outfide. In metallic 

 tubes, this is not always the cafe, and when it is, it takes 

 place much more flowly ; fo that an explofion might 

 be expe£ted notwithflanding this property. 



Since, however, this mixture of dephlogifticated and 

 inflammable air will not explode in tubes of flint glafs, 

 in which there is the calx of lead, and they become black 

 in this procefs, as they do when inflammable air only is 

 heated in them, this air muft be feparated from the de- 

 phlogifticated, and unite with the calx of lead. It is 



therefore 



