8 ORGANIC AGRICULTURAL CHEMISTRY 



Properties. — By analysis the composition of methane has 

 been shown to be 12 parts by mass of carbon to 4 parts by 

 mass of hydrogen. Its molecular mass equals 16. It is repre- 

 sented, therefore, by the chemical formula CII4, or one atom 

 of carbon to four atoms of hydrogen. It is a colorless gas 

 lighter than air. It burns in the air with a yellow flame which 

 deposits carbon on a cold surface. Mixed with air or with 

 oxygen in the proportion of one volume of methane to two 

 volumes of oxygen it explodes on ignition. Such an explosive 

 mixture in coal mines is known as fire damp and is the cause 

 of mine explosions. 



Constitution. — It will not be necessary to consider in each 

 case the proofs or reasons for conceptions which we shall bring 

 forth, but merely state them, assuming that the proofs not here 

 given have been fully developed. 



In considering methane as a chemical compound three facts 

 are at the foundation of our conceptions in regard to it, and 

 these conceptions will lead to an understanding of the definite 

 relationship between all of the organic compounds which we 

 shall study. These three facts are as follows : 



Methane, CH4, is (i) A saturated compound. 



(2) A symmetrical compound, in which all 

 four of the hydrogen atoms stand in exactly the same relation 

 to the carbon atom. 



(3) The carbon atom in methane and in 

 practically all organic compounds is tetravalent, i.e. it has the 

 power of holding four and only four hydrogen atoms, or any 

 other univalent element, or group of elements, in combination. 



Structural Formula. — The result of these facts is expressed 

 in what is termed the structural or constitutional formula for 

 methane, i.e. a formula which indicates the way in which the 

 compound is built up or constituted. The geometrical figure 

 which can represent perfect symmetry of one body joined to 

 four others is the regular tetrahedron, and in all space relation 

 formulas carbon is considered as being at the center of such a 



