20 Mr. G. F. Rodwell on the Theory of Phlogiston. 



as I have elsewhere stated*, appears to have been his mode of 

 reasoning : — Air possesses weight ; it may be produced by heat- 

 ing water, which during distillation separates into a heavier and 

 a lighter part ; hence as air approximates to a liquid nature, it 

 may be supposed to be separated into a heavier and a lighter 

 part by the action of heat ; now the heavier part (the " dregs ") of 

 air is more nearly allied to a liquid than air, for it has assumed 

 a "viscid grossness;" and this part attaches itself to calces during 

 the process of calcination, and causes such of them as possess 

 much ash to be heavier than before calcination. If we calcine 

 a vegetable or animal substance, there is no gain of weight, be- 

 cause the assimilated thickened air weighs less than the volatile 

 matter expelled by heat ; but in the case of a metal the assimir 

 lated air weighs more than the volatile matter expelled, hence 

 there is gain of weight. Thus he imagined that all calces, from 

 a vegetable ash to a metallic calx, attract this thickened air. 



Glauber some years later suggested that the gain may arise 

 from the coagulation of heat by the metal during calcination. 

 Boyle, in a treatise entitled " Fire and Flame weighed in a Ba- 

 lance," published in 1672, details some experiments which he 

 made in order to determine the amount gained by various metals 

 during calcination. From the fact that lead and tin were found 

 to undergo partial calcination when fused in sealed vessels, he 

 inferred that ( ' glass is pervious to the ponderous parts of flame," 

 and that the gain of weight is due to the assimilation of " extin- 

 guished flame," or as he otherwise expresses it, of " igneous par- 

 ticles/ 3 by the calx. He further gives it as his opinion that the 

 calx of a metal is not its " terra damnata," but the metal plus 

 something assimilated during calcination. Lemery also main- 

 tained that the gain arises from the absorption of " corpuscules de 

 feu." 



V. Of Becher and Stahl, and of the rise and development of the 

 theory of Phlogiston. 

 Let us now consider the rise of the theory of phlogiston as 

 indicated in the writings of its originator Becher; and while 

 we do so let us keep in yiew the four relevant phases of prior 

 ideas which I have endeavoured to elucidate in the preceding 

 pages, viz. (a) ideas regarding the (t subtilis ignis" (/3) ideas 

 regarding the three chemical principles, (7) ideas regarding 

 the process of calcination, and (8) ideas regarding the nature 

 of fire. 



John Joachim Becher was born at Spiers in 1625 : little 

 * " On the supposed Nature of Air prior to the discovery of Oxygen, 

 Chemical News, vol. x. p. 209. 



