258 BOGERT— CARBON COMPOUNDS. [April 20. 



chemistry divides the subject according to the method of treatment 

 employed to obtain the substance rather than according to the char- 

 acter of the substance itself. Thus we have as the main headings,. 

 " Operations on unfermented vegetables," " Operations on fermented 

 vegetable substances," and " Operations on animal substances." 



Fourcroy (about 1790), however, in his well-known text-book, 

 makes a clean-cut division, placing the vegetable acids in the section 

 dealing with the vegetable kingdom, and the animal products all 

 under the animal kingdom. 



It should be noted that at this time carbon was supposed to exist 

 as such in plants and animals. So Chaptal, in 1791, says: 



" Carbone exists ready formed in vegetables. It may be cleared of all the 

 volatile and oily principles by distillation, and, by subsequent washing in pure 

 water, it may be deprived of all the salts which are mixed and confounded 

 with it." 



In Thomson's ''System of Chemistry"' (third edition, 1807), 

 marsh gas and olefiant gas are discussed with the element carbon, 

 but the other carbon compounds are scattered vmder various head- 

 ings where they are mixed in with inorganic substances. 



In the text-books and treatises on chemistry at this period it was 

 customary to combine mineralogy and geology with the mineral 

 part, botany with the vegetable section, and physiology with the 

 portion dealing with animal chemistry, while occasionally physics 

 received as much space as chemistry in the introductory chapters. 



The setherin theory of Dumas and Boullay, propounded by 

 them in 181 5, and later adopted by Berzelius, was an adaptation of 

 the early theories concerning the composition of organic compounds 

 (by which they were supposed to consist of an aqueous and a com- 

 bustible principle) to new conditions. In their theory, many deriva- 

 tives of alcohol were regarded as compounds of CoH^ (to which 

 Berzelius had given the name "setherin"), in the same way that 

 ammonium salts are derived from NH3 : 



QH,-HC1 = NH3-HC1, 



QH, • H^O ( alcohol ) = NH3 • H,0, 



CoH4-H2S04 = NH3H,SO„ 



(QHJoHoO (ether) = (NH3),H30( ?). 



