II 



THE BEGINNINGS OF MODERN CHEMISTRY 



THE " PNEUMATIC" CHEMISTS 



MODERN chemistry may be said to have its be- 

 ginning with the work of Stephen Hales (1677- 

 1761), who early in the eighteenth century began his 

 important study of the elasticity of air. Departing 

 from the point of view of most of the scientists of the 

 time, he considered air to be " a fine elastic fluid, with 

 particles of very different nature floating in it" ; and he 

 showed that these " particles " could be separated. He 

 pointed out, also, that various gases, or " airs, " as he 

 called them, were contained in many solid substances. 

 The importance of his work, however, lies in the fact 

 that his general studies were along lines leading away 

 from the accepted doctrines of the time, and that they 

 gave the impetus to the investigation of the properties 

 of gases by such chemists as Black, Priestley, Caven- 

 dish, and Lavoisier, whose specific discoveries are the 

 foundation-stones of modern chemistry. 



JOSEPH BLACK 



The careful studies of Hales were continued by his 

 younger confrere, Dr. Joseph Black (1728-1799), whose 

 experiments in the weights of gases and other chem- 

 icals were first steps in quantitative chemistry. But 



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