» ROPERTIES OF CARBON. 23 



of more than four, of tix elementary bodies. These four are carbon, 

 oxygen, hydrogen, and nitrogen. With the exception of the matter ii' 

 destructible by tire (the ash), chemical analysis* has hitherto failed to detect 

 the presence, in any notable quantity, of more than these four substances. 

 The same remarks apply with almost equal truth to animal substances. 

 The destructible part of these also consists of tlie same four elements. 



To the agriculturist, therefore, an acquaintance with these four con- 

 stituent parts of all that lives and grows on the face of the globe is 

 indispensable. It is impossible for him to comprehend the laws by 

 which the operations of nature in the vegetable kingdom are conducted, 

 nor the reason of the processes he himself adopts in order to facilitate or to 

 modify these operations, without this previous knowledge of the nature 

 of the elements — the raw materials as it were — out of which all the 

 products of vegetable growth are elaborated. 



I shall first, therefore, exhibit to you briefly the properties of these 

 organic constituents of plants, in order that w^e may be prepared for the 

 further inquiries — by what means or in what form they enter into the cir- 

 culation of plants — and how, when they have so entered, they are con- 

 verted into those substances of which the skeleton of the plant consists 

 or which are produced in its several organs. 



§ 2. Carbon — its properties and relations to vegetable life. 



Carbon is the name given by chemists to the substance of wood char- 

 coal in its purest form. When wood is distilled in close vessels, or 

 burned in heaps covered over, so as to prevent the free access of air, 

 wood charcoal is left behind. When this process is well performed, the 

 charcoal consists of carbon with a slight admixture only of earthy and 

 saline matters, which remain behind on burning the charcoal in the air. 



Heated in the air, charcoal burns with little flame, and, with the ex- 

 ception of the ash which is left, entirely disappears. It is converted into 

 a kind of air known among chemists by the name of carbonic acid, which 

 ascends as it is formed and mingles with the atmosphere. 



Charcoal is light and porous, and floats upon water, but plumbago or 

 black lead and the diamond, which are only other forms of carbon, are 

 heavy and dense. The former is 2i, and the latter 3|, times heavier 

 than water. The diamond is the purest form of carbon, and at a high 

 temperature it burns in the air or in oxygen gas, and, like charcoal, dis- 

 appears in the state of carbonic acid gas. 



Of this carbon all vegetable substances contain a very large portion. 

 It forms from 40 to 50 per cent., by weight, of all the parts of plants 

 which are cultivated for the food of animals or of man, [that is, of these 

 plants in their dried state.] In the economy of nature, therefore, it per- 

 forms a most important part. 



The light porous charcoals obtained from wood [especially from the 

 willow, the pine, and the box], and from animal substances, possess 

 several interesting properties, which are of practical application in the 

 ar^f culture. 1°. They have the power of absorbing in large quanti- 

 ty into their pores, the gaseous substances and vapours which exist in 



• Under the general name of chemical analysis are comprehended the various processes 

 by which, aa above explained, natural forms of matter may be resolved or separated into 

 the several elentenis or simple substances of which they consist. 



