426 



FARMERS' REGISTER 



[No. 7 



throughout each other. This process is repeated 

 aCTaiii antl again, and thus tlie clover increases in 

 size. But whence is this gas obtained'? From 

 many sources; li-om the breath ofanimals, for wiiilst 

 animals inhale oxygen they exhale carbonic acid 

 liom the burnmg of most combustible bodies, but 

 principally from decaying vegetiibles sucli as are 

 Ibund in the woods and along the It^nce sides. 

 The quantity of the several elemenis wiiich enter 

 into the composition of our globe is fixed ; it is 

 impossible lor man either to increase or diminish 

 this quantity; and it is also impossible lor him to 

 convert one of these elements into another. All 

 he can do is to make an economical use of that 

 which already exists, to gather up those portions 

 which subserve no valuable end and apply them 

 to use. This is what the farmer does in sowing 

 his land with clover. He impresses ihe very 

 wind into his service, for every wind which sweeps 

 over a field of clover, laden as that wind is with the 

 materials of which vegetables are Ibrmed, is made 

 to contribute to its growth. After a large portion of 

 vegetable matter has in this way been collected 

 upon the once barren spot, it is ploughed under, 

 and secured for future use. 



It is a fact well ascertained, that animals, whilst 

 they inhale a large portion of oxygen, exhale a 

 large portion of carbonic acid. From the long 

 continuation of this process we would suppose that 

 the composition of our atmosphere would in the 

 course of time eufl'er a material change ; that it 

 would become so surcharged with carbonic acid as 

 to be unfit for the support of animal life. And yet 

 so far as we can ascertain, the composition of our 

 atmosphere is very much the same now that it 

 was a thousand years ago. In what way is this 

 uniformity of composition preserved ? If we call 

 to mind the nature of the food of plants, the matter 

 admits of a very simple explanation. Plants take 

 in carbonic acid, and retaining the carbon fixed in 

 their tissues, return the oxygen to the atmosphere; 

 a process just the reverse of that performed by ani- 

 mals. In this, we see one of those beaut ii'ul 

 compensating arrangements with which creation 

 abounds. 



Chapter XVII. 



ELABORATION OF THE SAP. NATURE OP 

 PROXIiMATE PRINCIPLES. INFLUENCE OF 

 LIGHT. INFLUENCE OF HEAT. 



By the elaboration of the sap, is meant, its con- 

 version, from crude sap, into the several proximate 

 principles of which vegetables consist, such as 

 sugar, gum, resin, tannin, &c. In order to under- 

 stand this subject, and also, how it is that such 

 substances as compose the food of plants, are ca- 

 pable of being connected into the various proxi- 

 mate principles which Ihe vegetable kingdom pre- 

 sents, it will be necessary, in the first place, to at- 

 tend to a lew fieneral fleets respecting the compo- 

 sition of these proximate principles. Among the 

 most important of these facts are^ 



1st. That they are all composed of pretty much 

 the same elements, and li-etiuently contain those 

 elements in the same proportions. 



2nd. That they are all decomposed with facility, 

 and frequently are mutually convertible into each 

 other. 



3rd. That in general they cannot be formed 

 by art. 



We will examine each of there general state- 

 menis, somewhat in detail. 



1st. The proximate [jrinciples of vegetables are 

 all composed of pretty much the same elen)ents; 

 and frequently contain these elements in the same 

 proportions. "^Fhis will be evident from an inspec- 

 tion of the following table, prepared from a state- 

 ment of their compositions as given in Turner's 

 Chemistry. The numbers opposite the names ol 

 the substances refer to their e(iuivalcnts ; if it is de- 

 sired to find their composition in grains, the num- 

 bers for oxygen must be nmltiplied by 8, lor carbon 

 by 6.12, lor nitrogen by 14.15, and for hydrogen 

 byl. 



From an inspection of the composition of the 

 substances mentioned in the above table, it will 

 be seen that several of them consist, not only of 

 the same elements, but contain those elements in 

 the same proportions, or, in the language of che- 

 mistry, are isomeric. This is explained, by sup- 

 posing that whilst the difl'erent substances contain 

 the same elements, that yet those elements are 

 dilfercntly united with each other. An example 

 will make this plain. Suppose that we have one 

 equivalent of sulphur, four of oxygen, and one of 

 copper, to combine ; these may readily be so united 

 as to form two entirely distinct compounds ; tvvo 

 equivalents of the oxygen may unite with the one 

 of sulphur and form sulphurous acid ; and the re- 

 maining two with the one ol copper, forming bi- 

 noxide of copper ; these two binary compounds 

 then uniting would form the sulphite of the binox- 

 ide of copper ; or three equivalents of oxygen inay 

 unite with the one of sulphur, forming sulphuric 

 aciii, and the remaining one with Ihe one of cop- 

 per, forming protoxide ol'copper; these two binary 

 compounds then uniting would form the sulphate 

 of the protoxide ol copper, a compound entirely 

 different from the former. Or expressing it in 

 chemical symbols, we might have 



(S + 2 ox.) (Cu -f 2 ox.)=S -f Cu -f 4 ox. 

 Or (S -f 3 ox.) (Cu + ox.) =8 -f Cu -f 4 ox. 

 It is in this way that the difference between the 

 different isomeric subptances with which we meet 

 in the vegetable kingdom, is supposed to be pro- 

 duced. 



2nd. The proximate principles of vegetables, all 

 readily undergo decomposition, and are frequently 

 convertible into each other. Most vegetable sub- 



