LECTURE I.] HISTORY OF CHEMISTRY. 1 3 



dish and Kirwan, was, however, easily disposed of. It ex- 

 plained the conversion of the metals into their calces by 

 means of acids a matter which had begun to present diffi- 

 culties to the older phlogiston theory, but it no longer took 

 cognisance of the real phenomena of combustion. In the 

 calcination of a metal, where did the phlogiston (the hydrogen) 

 go to ? A previous assertion made by Scheele 15 that during 

 the combustion of sulphur in air, the air takes up phlogiston 

 and unites with it, whereby its volume is diminished, was easily 

 refuted now when the properties of phlogiston (i.e. of hydrogen) 

 were known; and the phlogiston theory thus became, in its 

 j new form, no longer applicable to that class of phenomena 

 which it was advanced in the first instance to explain. 



The facts which contributed to the fall of this theory in- 

 creased from year to year. In 1774, a few months before the 

 discovery of oxygen, Bayen found that mercuric oxide was 

 converted into mercury on heating. Whence came the phlo- 

 giston which was required to bring about this change ? Bayen 

 perceived the importance of his discovery, and regarded mer- 

 curic oxide as different from the metallic calces proper. He 

 found at the same time that the loss of weight in the reduction 

 of the mercuric oxide was equal to the weight of the air 

 obtained. How little attention was, in general, bestowed upon 

 a fact so important, is proved by the views of Macquer who -. 

 assumed that there must be a loss of weight in connection 

 with the oxidation and the subsequent reduction of a metal. 

 When Lavoisier came forward at a still later date, in opposition 

 to the phlogiston theory, Macquer stated that the news that 

 important facts had been discovered, adverse to the phlogiston 

 theory, caused him some concern, but that he was quite com- 

 posed again when he ascertained that it was merely a question 

 of relations by weight. 16 



Others, however, thought differently; and Tillet, after having 

 again confirmed the increase of weight during the formation of 

 litharge from metallic lead, drew attention, in a report to the 



13 Kopp, Geschichte. 3, 201. 10 Dumas, Lemons. 133. 



