Manchester Memoirs, Vol. Ivii. (191 3), No. 19. 35 



From a letter written in 1782 to Joseph Banks, the 

 famous president of the Royal Society, I give below an 

 extract showing how much Priestley still adhered to the 

 Phlogiston theory, on which Lavoisier had already made 

 ■vigorous attacks."'' 



Birmingham, 



28th Dec, 1782. 

 Dear Sir, 



I think myself much honoured by your sending 

 me the Derbyshire mineral,^^ and shall endeavour, in 

 due time, to give you the best account that I can of it. 

 At present I have made only one experiment upon it, 

 but this seems to afford sufficient data for explaining 

 the phenomenon you mention. 



It yields, I find, a considerable quantity of very 

 pure or dephlogisticated air^* by heat. Supposing, 

 therefore, that the air incorporates with it, and thereby 

 loses its fluidity, heat will be generated, as when water 

 incorporates with lime, and the pure air, which that 

 heat expels from it, will contribute to promote the 

 escape of its phlogiston, and so produce a proper 

 ascension,^'' as is the case with substances that contain 

 nitre, or anything else that yields pure air with heat. 

 I should think it is very possible to make artificial 



^-^ The theory was for the first time clearly set out in these two papers : 

 '' Sur la Combustion des Chandles dans I'air atniospherique, et dans I'air 

 eminement respirable,' and ' Sur la Combustion en general,' both read in 

 1777 and printed in 1780. 



»■' This was undoubtedly pyrolousite. See 'The Examination of 

 Manganese in Experiments,' 2nd ed., vol. iii., p. 154. 



"^^ This is oxygen in the terminology of the phlogiston theory. 

 ^'^ Ascension means distillation in the terminology of the time, the 

 word still lingering from the alchemistic period. Example : 

 ' For two of our inferior works are at fixation, 

 'A third is in ascension . . . .' 

 ' The Alchemist,' by Ben Johnson. It has nothing to do with decrease of 

 weight caused by the introduction of phlogiston, as Bolton, I.e., p. 46, 

 suggests. 



