I9I2.] BOGERT— CARBON COMPOUNDS. 257 



formed. These ideas were successfully combated by Boyle, who 

 had shown, as early as 1661, in his " Sceptical Chymist," that the 

 application of heat leads to quite different results depending upon 

 whether air is present or not, and that the various residues thus 

 obtained are unlike. 



Many organic substances were discovered during this phlogiston 

 period, but their real composition (even qualitative) remained 

 unrecognized. For example, it was assumed that the ultimate con- 

 stituents of alcohol were oil and water, or a combustible and a 

 mercurial principle. By far the greater number of the investiga- 

 tions recorded were still in the inorganic field, probably for reasons 

 already given, and also because it had not as yet been possible to 

 prepare organic compounds synthetically. While, as has been said, 

 many authors adopted Lemery's method of separating mineral, 

 vegetable and animal substances, .others still adhered to the old 

 system of grouping together all acids (sulfuric with lactic, tartaric, 

 etc.), all salts, etc. 



Boyle's influence was soon efifective in directing a closer scrutiny 

 of the composition of compounds, and gradually the true elements 

 were isolated and studied. 



The discovery of the composition of carbonic acid gas by La- 

 voisier in 1775, and that of water by Cavendish, showed the pres- 

 ence of carbon and hydrogen in alcohol (1784). Lavoisier, having 

 established the true principle upon which combustion depends, ana- 

 lyzed various organic substances and came to the conclusion that 

 vegetable substances were composed generally of carbon, hydrogen 

 and oxygen, while animal substances contained also nitrogen and 

 occasionally phosphorus. He did not distinguish organic chemistry 

 as a special branch of the science, or define it as " the chemistry of 

 the compound radicals." He discussed all acids together, subdivid- 

 ing them into mineral, vegetable and animal. 



Macquer, who was professor of medicine in the University of 

 Paris, and a contemporary of Lavoisier, in his " Elements of the 

 Theory and Practise of Chymistry " (English translation of 1775) 

 discusses mineral, vegetable and animal oils together, and in the 

 separate sections of his work devoted to vegetable and animal 



