214 MODERN SCIENCE READER 



near Paris. In the course of the period many substances 

 were introduced a therapeutic agents, and Scheele dis- 

 covered a number of important compounds of carbon. 



If, after we have become accustomed to think of modern 

 chemistry as founded in the latter part of the eighteenth 

 century, we take up the writings of phlogistic chemists prior 

 to that time, we may be greatly surprised to find that our 

 general principles were not at all unknown to them. They 

 certainly believed in the indestructibility of matter, and 

 some of them described molecules and atoms in much the 

 same way as we describe them at the present day. And 

 yet their knowledge cannot be rightly considered as consti- 

 tuting a science. Their abstract speculations were very 

 keen; their knowledge of chemical facts was quite ex- 

 tensive; but that mathematical correspondence between 

 abstract principles and concrete phenomena which alone 

 constitutes science did not exist. And so, even when the 

 properties of gases were no longer unknown, all chemical 

 knowledge remained in a state of confusion, and elements 

 continued to be considered as compounds, compounds as 

 elements, combinations as decompositions, and decomposi- 

 tions as combinations, until the work of establishing the 

 scientific correspondence was begun by Lavoisier. 



Endowed by nature with a keenly critical mind, Lavoisier 

 acquired the habit of quantitative thinking by early train- 

 ing in mathematics and physics, and by subsequent associa- 

 tion with some of the most brilliant mathematicians and 

 physicists of his time. As early as 1770 we find him solv- 

 ing a problem of chemistry by a purely quantitative 

 method. It was known, namely, that when water is kept 

 boiling for some time in a glass vessel, there is formed in 

 it an earthy deposit; it was therefore believed that water 

 could be converted into "earth". Lavoisier heated water 

 in a glass vessel, weighed the vessel before and after the 

 operation, and found that the vessel plus the deposit after 

 the operation weighed exactly as much as the vessel alone 

 weighed before. He thus proved that the earthy deposit 



