CHEMISTRY AND ITS DEVELOPMENT 215 



came, not from the water, but from the glass of the vessel. 

 In 1772 he turned the same quantitative method of experi- 

 menting and reasoning to the conversion of metals into 

 calces, and in 1774 published the following observation: 

 ' ' When metallic tin is heated in a sealed retort full of air, 

 it becomes transformed into its calx; the weight of the 

 sealed retort with its contents is exactly the same after the 

 reaction as before; if the retort is now opened, air rushes 

 into it and the weight is increased; the increase is equal 

 to the difference in weight between the calx formed and 

 the mass of metallic tin employed." From this Lavoisier 

 concluded that the transformation of tin into its calx in- 

 volved the absorption of air, and that phlogiston had noth- 

 ing to do with the phenomenon. It also became evident to 

 him that the balance of precision could serve the chemist 

 no less than the telescope served the astronomer, and that 

 the principle of indestructibility, which could and should 

 be established experimentally, ought to be at the basis of 

 all chemical reasoning. When Priestley and Scheele dis- 

 covered oxygen, they thought that it was this constituent 

 of air that was capable of absorbing phlogiston from metals ; 

 Lavoisier demonstrated that it was this constituent of air 

 that combined with metals to form calces. He recognized 

 that the same gas combined with sulphur, phosphorus, char- 

 coal and other combustible substances and as he regarded 

 the resulting compounds as acids, he gave to the gas the 

 name oxygen (from the Greek oxys, acid, and genes, pro- 

 ducing), and adopted the view that it was an indispensable 

 constituent of all acids (this view was discarded half a 

 century later). Carbonic acid he recognized as a com- 

 pound of carbon and oxygen, and when Cavendish found 

 that the sole product of the combustion of hydrogen in 

 oxygen was water, Lavoisier understood that water was not 

 an element, but a compound of hydrogen and oxygen, and 

 had no difficulty in determining its quantitative composi- 

 tion. Carbonic acid and water he also showed to be the 

 products of the combustion of organic substances, and soon 



