24 HISTORY OF CHEMISTRY. [LECTURE II. 



of the glass. Another person might perhaps have concluded 

 from this that there had been a production of matter ; Lavoisier, 

 however, explains it as an error of experiment. Although this 

 is a bold view for the period, yet it shows that he is guided by 

 profound ideas, and understands how to criticise his own experi- 

 ments. All later investigations have confirmed the accuracy of 

 his explanation. 



Scheele, 18 on his part, was occupied about the same time, with 

 similar investigations, and arrived at the same results ; but the 

 mode in which the Swedish chemist conducts the experiment is 

 very different. He analyses the earth and finds that it consists of 

 the same substances as the glass in which the water was heated. 



A later paper of Lavoisier's treats of the increase in weight 

 on combustion. As early as 1772, he hands in to the French 

 Academy a sealed paper, in which he shows that the products 

 of the combustion of phosphorus and sulphur are heavier than 

 the substance burned. This he attributes to an absorption of 

 air (of air, because oxygen had not then been discovered). 19 In 

 an investigation on the calcination of tin, 20 he causes this ope- 

 ration to take place in closed vessels ; these he weighs before 

 and after, without observing any difference ; whence he con- 

 cludes that no fire material is taken up. He shows, further, 

 that the metal has increased in weight by just as much as the 

 air has lost. 



Oxygen is discovered shortly afterwards, whereupon Lavoi- 

 sier repeats the experiments of Priestley and of Scheele : but 

 his conclusions are totally different from those of the two other 

 chemists. He is already prepared for this discovery, and, with 

 him, it becomes the foundation of a new theory. Oxygen he 

 at once recognises as that part of the air which unites with the 

 combustible substance during its combustion ; and he calls it 

 " air eminemment respirable" In the same paper he shows that 

 fixed air is a compound of carbon with this air, and that the 

 latter is also contained in nitre. 21 



18 Dumas, Le9ons. 129. 19 Lavoisier, Oeuvres. 2, 103. 20 Ibid. 



2, 105. a Ibid. 2, 128. 



