30 Froceedings of the Royal Physical Society. 



In order fully to prove the truth of his speculations in this 

 matter, he performed an experiment, the converse of these in 

 which sulphur and phosphorus were burned. In this experi- 

 ment he heated some lead oxide with carbon, the result of 

 which was quite satisfactory, as showing that the oxide con- 

 tained air, which was in union with the lead, and which was 

 given off during the heating operation, leaving the pure lead 

 behind. The phlogistians would, of course, have explained 

 this action by saying that the calx of lead, as they called lead 

 oxide, was changed into the metallic state in consequence of 

 having absorbed phlogiston from the charcoal. These ex- 

 periments of Lavoisier, and the conclusions he drew from 

 them, although not quite correct, were certainly a most 

 decided step in advance. Lavoisier's next work had 

 reference to respiration, combustion, and fermentation, and 

 he showed, as Black had done some twenty years before, 

 the production of fixed air, as carbonic acid was then called. 

 Following these researches, he made some very important 

 experiments, in which he heated different metals in closed 

 glass globes, and thereby was enabled to prove that the 

 heated metal not only absorbed air from without, but that it 

 only absorbed a certain part of the air, and that the part 

 which was left had properties quite different from those 

 possessed either by common or fixed air. Lavoisier, there- 

 fore, it is clear, held the opinion at this time (1774) that the 

 air was composed of at least two substances. He had not, 

 however, yet heard of Priestley's discovery of oxygen, and he 

 does not seem at that time to have possessed nearly so much 

 information on this point as he showed himself to be pos- 

 sessed of some time afterwards, by reading a paper in the 

 following year, and after he had heard of Priestley's great 

 discovery. In this paper, which was on the nature of the 

 principle which combines with metals during their calcina- 

 tion, he shows that at last the theory of combustion is fully 

 understood. In this paper he calls oxygen vital air, and 

 three years afterwards he called it oxygen, the name it has 

 since borne. This name is certainly a little unfortunate, as 

 whatever Lavoisier's opinion on the point may have been, 

 acids exist which do not contain any oxygen. 



