CHAPTER XII 



THE FIRST BEGINNINGS OF MODERN CHEMISTRY AND ITS 

 INFLUENCE UPON THE DEVELOPMENT OF BIOLOGY 



The phlogiston theory 



So LONG AS chemical processes had their explanation in the phlogiston 

 theory, it was certainly possible to offer a provisional explanation of 

 a number of phenomena in the sphere of combustion and oxidization, 

 but any deeper insight into the material changes which both animate and 

 inanimate nature daily undergo was of course out of the question. In par- 

 ticular the qualitative side of the chemical process was, as far as this theory 

 went, inexplicable. In spite of this, the theory was stubbornly maintained 

 during the greater part of the eighteenth century, doubtless because so many 

 discoveries had been made under the assumption of its correctness, which 

 the chemists hesitated to interpret anew. For the rest a more accurate knowl- 

 edge of the process of combustion presupposed a knowledge of the types 

 of gas that play a part therein, and this knowledge was not acquired until 

 the latter half of the eighteenth century. The progress made in this field of 

 inquiry is primarily bound up with three names: the Englishmen Priestley 

 and Cavendish, and the Swede Scheele. Priestley deserves still further mention 

 as a discoverer in the biological sphere; Cavendish (173 1-1810) is best known 

 as the discoverer of hydrogen, and Scheele (i74z-86), one of the most bril- 

 liant experimental scientists of all time, succeeded in making, in spite of his 

 short life, a large number of chemical discoveries, his treatise On Air and Fire 

 becoming especially famous. 



Joseph Priestley was born in 1733 of a Free Church family of the artisan 

 class living in the north of England. After studying in his sect's theological 

 training-college he was eventually ordained a minister and served in several 

 parishes, partly in Birmingham. An extreme radical, both in religion and 

 politics, he was a supporter of the French Revolution, which resulted in his 

 being subjected to personal persecution; the mob attacked him in his home, 

 which they pillaged, and he himself escaped with his life and fled to London. 

 As he found no peace there either, he emigrated to America and died there 

 in 1804. Priestley had begun to carry out chemical experiments independ- 

 ently; throughout his life he worked quite unsystematically, heating up 

 and treating with reagents everything that fell into his hands, but as he 

 possessed a great gift for arranging and observing his experiments, he did 



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