CHEMISTRY 197 



formulas of hydrochloric acid, water, and 

 methane, as follows : — 



H-Cl, H-O-H, ^>C<^ 



Accordingly, oxygen appears to possess two 

 valences and carbon four. These conclu- 

 sions are justified by an almost inconceivable 

 wealth of experience; they are the means of 

 constructing the elaborate constitutional for- 

 mulas which are so necessary a part of organic 

 chemistry ; and there can be no doubt that 

 in almost all the compounds with which we 

 shall be concerned hydrogen is invariably 

 univalent, oxygen bivalent, and carbon quad- 

 rivalent. On this basis the construction of 

 possible formulas of organic compounds is 

 merely an exercise in a somewhat peculiar 

 department of mathematics. 



B 



HYDROCARBONS 



The compounds of carbon and hydrogen 

 may first be considered. With but a single 

 atom of carbon in the molecule one only is 

 possible : — 



H 



I 



H-C-H 



I 



H 



f 



