PRIESTLEY. 413 



His apparatus, however, and his contrivances for col- 

 lecting, keeping, transferring gaseous bodies, and for 

 exposing substances to their action, were simple and 

 effectual, and they continue to be still used by chemical 

 philosophers without any material improvement. It 

 was fortunate in this respect that he began his pneu- 

 matic inquiries with seeking for the means of im- 

 pregnating water with carbonic acid ; this inquiry 

 naturally turned his attention to the contrivance of 

 apparatus and generally of manipulations, serviceable in 

 the examination of bodies whose invisible form and 

 elastic state renders inapplicable to them the machi- 

 nery of the old laboratory, calculated only for solids 

 and liquids. 



The pertinacity with which Priestley clung to the 

 phlogistic theory is marvellous. It might have bee^, 

 expected, that the fact of a combustion leaving the 

 residue, whether of two gases, or of a gas and an in- 

 flammable body, exactly equal in weight to the sum of 

 the weights of the bodies burnt and which had disap- 

 peared in the process, would have been accepted as a 

 proof that these two bodies had entered into an union, 

 giving out the latent heat which had previously held 

 the gaseous body or bodies in a state of aeriform 

 fluidity. It might, in like manner, have been ex- 

 pected, that when a metal, by absorbing oxygen gas, 

 becomes calcined, and gains in weight precisely the 

 weight of the gas which has disappeared, the calcination 

 should be ascribed to the gas, and that the reproduction 

 of the gas by heat, or by its abstraction by electric 

 affinity for some other body, should be allowed to 

 restore the metallic state by simply severing that 



