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



facts. One of the fundamental propositions of the theory was 

 that the calcination of a metal is the expulsion of its phlogiston, 

 and that the calx can only be reduced in the presence of a body 

 which can communicate to it the lost phlogiston. Yet it was 

 well known that mercury becomes a calx when heated to a cer- 

 tain temperature, and that the calx is revived by increasing the 

 temperature. But the phlogistians generally omitted the expla- 

 nation of this from their handbooks. Becher states that the 

 calx is formed by the absorption of a " certain mercurial sul- 

 phur," viz. a certain volatile combustible body. Stahl states 

 that the calx of mercury does not weigh more than the mercury 

 which produced it; yet before he was born Boyle had employed 

 balances which turned with one thirty-second of a grain for che- 

 mical operations. That thorough and ardent phlogistian Mac- 

 quer sacrificed the fact to the theory ; he would not allow that 

 red oxide of mercury was a calx, consequently he heads the sec- 

 tion which gives an account of its preparation as follows: — 

 "Donner au mercure par Faction dufeu V apparence d'une chaux 

 metallique"*. The fact that it can be reduced to the metallic 

 form without the presence of a body containing phlogiston proves, 

 he asserts, "that during that long calcinationf it lost none of 

 its phlogiston." Another objection to the theory was the fact 

 that calces weigh more than the metals which produce them, or, 

 otherwise stated, that the loss of phlogiston is synonymous with 

 gain of weight ; but this received an explanation which was 

 somewhat plausible at first sight. Ancient writers frequently 

 assert that all fire and heat have a tendency upwards J; some at- 

 tributed this to the attraction of the pure fire above. According 

 to Descartes, flame is pointed and tends upwards because it con- 

 tains a good deal of materia ccelestis, which is much lighter than 

 air, and confers lightness upon bodies. So also said the phlo- 

 gistians : — phlogiston confers negative weight; it is a principle 

 of levity, and when associated with matter it lessens its weight, 

 just as inflated bladders lessen the weight of a swimmer. It 

 will be remembered also that Cardanus gave a very similar ex- 

 planation of the increase of weight of calces more than a century 

 before the birth of Stahl [vide p. 19) . Macquer, after remarking 

 that 100 lbs. of lead produce 110 lbs. of minium, frankly owns 

 that not one of the many hypotheses proposed to account for 

 the gain of weight during the process of calcination is satis- 

 factory. 



* Vide his Elemens de Chimie-pratique, 1751. 



t " Mercurius precipitatus per se," as it was called, was prepared by 

 gently heating mercury in matrasses with long necks for a length of time, 

 generally for about three months, but sometimes for as many as fifteen. 



X Thus Aristotle, " eVei Kara cpvariv ye to Beppbv civco necfivKc cpepeaOai 

 nav." — MeTeoopoXoyiKaiv lib. i. cap. 4. 



