48 Biological Chemistry. 



bitter and personal in character, and in which several of 

 the most distinguished chemists of the nineteenth century 

 took a very prominent part. 



Part I. The Chemistry of the Hydrocarbons. 



The simplest type, perhaps, of any organic compound 

 is the gas known as methane, or marsh gas, which is found, 

 as the name indicates, in marshes and other places where 

 decay of vegetable matter is taking place. It is also an 

 important constituent of the gases which issue from 

 petroleum wells. It can be readily prepared also in the 

 laboratory by heating together sodium or potassium acetate 

 with (four times the weight of) soda-lime. The composi- 

 tion of the gas and its vapour density correspond with the 

 formula CH 4 . 



Now one of the fundamental conceptions upon which 

 the principles of the chemistry of the carbon compounds 

 have been built up is, that carbon is a tetrad or quadrivalent 

 element that is to say, it is an element which combines 

 normally with four univalent elements, or two bivalent 

 elements, or one bivalent element and two univalent 

 elements, or with one trivalent and one univalent 

 element, etc. If hydrogen is taken as a type of a uni- 

 valent element, the conception of the valencies of elements 

 may be illustrated by the formula of the following typical 

 compounds : 



HC1 H 2 O H 2 N H 4 C 



Hydrochloric acid. Water. Ammonia. Marsh gas. 



In these formulae one, two, three, and four atoms respect- 

 ively of hydrogen are combined with one atom of other 

 elements ; these are typical uni-, bi-, ter- and quadri-valent 

 elements. If these valencies are accepted as correct, it 

 should be possible to form various carbon compounds con- 



