ELEMENTS OF SOILS. 223 



great proportion of liquids. The physical constitution of the atmosphere heing determined, 

 life, its functions, and its apparatus, are adjusted to those conditions. 



Carbon is a solid. The diamond is always referred to as an example of pure carbon, 

 because, when burned, (lie residue is carbon in union with oxygen. The common form, 

 charcoal, differs but slightly from the diamond in composition, but the physical properties 

 are quite different, although the difference is not greater than that of pure alumina and 

 the sapphire. So it is not improbable that, like the instance here cited, the difference is 

 due to crystallization. Carbon forms the solid parts of organic bodies, except those which 

 are formed of the compounds of lime. In the vegetable kingdom, especially, carbon is 

 the element which gives solidity and strength to the individual. It also enters largely 

 into the composition of fluids, or it may be said that this state is preparatory to a conver- 

 sion into the solid form. Carbon is always black when uncrystallized. Chalk and lime, 

 magnesia, together with a great number of other bodies of the mineral kingdom, are com- 

 pounds of carbon, or rather triple compounds of oxygen, carbon, and lime or some other 

 base. Carbon is widely distributed in both the organic and inorganic worlds. It is asso- 

 ciated with the oldest products of the latter, and is brought up from the lowest depths of 

 the earth, and hence is as ancient and consequential as any of the elements except oxygen. 



Soil without carbon, very r rarely, if ever, produces perfect vegetables. The experiments 

 which go to prove the contrary are suspicious. Soil which has been heated to redness 

 does not part with its carbon ; the acids do not destroy it ; and hence those instances where 

 it has been attempted to destroy organic matter, or the carbon in soil, may be set off against 

 the difficulty of destroying it under circumstances more favorable. Crenic or apocrenic 

 acids are scarcely destroyed by a red heat, when the quantity is very small ; so the organic 

 matter of soils is very rarely consumed, when brought to a bright redness preparatory for 

 analysis. 



Principal compoitnds of the four preceding elements. 



The compounds which oxygen, hydrogen, nitrogen and carbon, form among themselves, 

 are water, air, and carbonic acid. These will be fully treated in this place, as they are 

 agents of the highest importance in the economy of life. 



Water. Few substances are anhydrous ; although it is necessary to premise that w T e do 

 not here mean to employ the term in its usual sense. Some substances retain water me- 

 chanically, and, if dried, are truly anhydrous, or without water in their constitution. We 

 mean, by the term anhydrous, to specify that condition of substances in which they neither 

 contain water mechanically by absorption, nor chemically by combination. We use the 

 word with a wider than the usual latitude ; and for this reason, that so far as the welfare 

 of either kingdom of nature is involved, the mechanical combination is as important as the 

 chemical. 



Nearly four-fifths of the matter of animals is liquid, all of which is lost simply by drying 

 in the atmosphere at its natural temperature. Vegetable matter contains less. Wood 



