256 BOGERT— CARBON COMPOUNDS. [April 20 



longer regarded as the only causes of varieties in substances; the difference in 

 chemical properties receives more attention, the existence of elements, the 

 producers of such properties is assumed; and thus the path is prepared which 

 leads to the idea of chemical composition. Then we see the Aristotelian 

 theory gradually becoming indistinct, whilst the idea of the importance of the 

 chemical deportment and composition of bodies assumes prominence, and at 

 last we see clearly that the differences between the substances which nature 

 presents to us in such overpowering numbers, or which we have ourselves 

 formed artificially, depend upon differences in their chemical composition. 

 The idea of chemical composition, which makes its first appearance in- 

 distinctly in the history of the chemistry of the Middle Ages, now forms the 

 foundation of the science." 



The most important and interesting problem at this time, and the 

 one upon which most attention was focused, was the chemistry of 

 combustion. Attempts to explain the phenomena of combustion 

 finally led to the phlogiston theory of Stahl, which dominated the 

 science from the end of the seventeenth through the eighteenth 

 century. 



In 1675, Nicolas Lemery published his " Cours de Chimie," 

 which soon became one of the most popular textbooks of the time 

 and passed through thirteen editions during its author's lifetime. 

 In it he divided all natural substances into mineral, vegetable, and 

 animal; including in the second group plants, resins, gums, fungi, 

 fruits, acids, juices, flowers, mosses, manna and honey; and under 

 the third heading describing the various parts of animal bodies. 

 This classification was quite generally adopted, and thus arose a 

 distinct separation of mineral chemistry from the chemistry of 

 substances occurring in plants and animals. The phlogistonists had 

 previously opposed any such subdivision, contending that the differ- 

 ences observed depended upon a variation in the composition of 

 the bodies classed under the three heads. So Becher, in 1669, 

 argued that the same elements occur in the three natural kingdoms, 

 but that they are combined in a simpler manner in mineral sub- 

 stances than in vegetable or animal. Stahl, in 1702, asserted that 

 in vegetable as well as in animal substances the watery and com- 

 bustible principles predominated, and that these ultimate constitu- 

 ents made their appearance when the organic compound was heated 

 out of contact with air, water and combustible charcoal being 



