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and because no vegetables exift without them; and by way of diftinction from other fubftances which are ef fential to the conftitution of fome particular vegetables, but not to all.

Of these three principles, two of them, namely HYDROGEN and OXYGEN, have a great tendency to unite with CALORIC, or matter of heat, and it takes in confequence an elaftic form, or gas;-while the CARBON, on the contrary, is a fixed principle, and has very little affinity or defire to combine with the matter of heat.

On the other fide, the OXYGEN, which tends to unite with nearly equal forces either to the HYDROGEN or the CARBON in the ordinary temperature, has on the contrary greater affinity with the CARBON at a red heat: the oxyGEN confequently quits at this degree of heat the HYDROGEN, and unites with the CARBON, and forms FIXED

AIR.

Although we be far from knowing the degree of these forces of affinities, and from being enabled to exprefs them by numbers, at least we are certain, from what paffes daily before us, that however variable they may be with regard to the degree of temperature, they are all nearly in equilibrium, or, what is the fame thing (from 3D 2

the

*

the digestive and excreting + living powers), the equi

librium is always kept up at the temperature in which they exift; thus vegetables do not contain either OIL, or WATER, OF FIXED AIR, but they contain THE ELEMENTS of all thefe fubftances. The HYDROGEN is not combined, either with OXYGEN or with CARBON reciprocally; although in the living ftate the principles of thefe three fubftances form a triple combination, whence EQUILIBRIUM or reft result.

A very flight change in the temperature is fufficient to overturn all this entanglement of combinations.

If the temperature to which the vegetable is expofed does not much exceed that of boiling water,

1. The HYDROGEN and OXYGEN reunite, and form WATER, which paffes in the diftillation;

2. A portion of HYDROGEN and of CARBON unite together, and form a VOLATILE OIL;

3. Another portion of CARBON becomes free, and being the most fixed principle, remains in the re

tort.

*The powers in the body which repair.

†Those powers which throw off fuperfluities.

Monf. LAVOISIER does not mean to deny the existence of orLs altogether in vegetables; for fome OILS may be expressed; and essential OILS evaporate fpontaneously and by the heat of the air; and their existence is therefore evident. But the OILS of which he denies the previous exiftence are thofe only which are obtained by diftillation.

But

But if, instead of a heat nearly equal to boiling water, a red heat be applied to vegetable substances, then WATER is no longer formed (or rather that WATER which may be formed by the first effect of heat is decompofed).

1. The OXYGEN unites to the CARBON, to which it has a greater affinity at this degree of heat, and FIXED AIR is formed;

2. The HYDROGEN now becoming difengaged, escapes in the form of GAS, while it unites with THE

MATTER OF HEAT.

At this degree of heat no OIL is formed, or if it were formed, it would be decompofed.

We fee then that the decompofition of vegetable matters is effected, at this degree of heat, by means of double and treble affinities, and that while,

1. The CARBON attracts the OXYGEN in order to

form FIXED AIR;

2. The MATTER OF HEAT attracts the Hydrogen, and they together form INFLAMMABLE GAS *.

The

* That vegetables are compofed of HYDROGEN, OXYGEN, and CARBON, may be alfo proved by SYNTHESIS. If you put a pea into a bottle it will at a given temperature fhoot out and branch itself into foliage. This cannot arife from the extenfion of parts; for though a guinea may be beat

out

The diftillation of moft vegetable fubftances furnishes a proof of this theory, if we are to give that name to the fimple declaration of a fact.

The play of affinities is ftill more complicated in those plants which contain AZOTIC AIR, as the cruciform plants, and in those which contain PHOSPHORUS; but as these substances enter into combination only in a small quantity, they do not produce great changes, at least apparently, in the phænomena of distillation.

It appears, in the first place, that the PHOSPHORUS remains combined to the CHARCOAL, which renders it

out to cover a small room, yet will it have no increase of weight. Here it evidently has acquired fomething, and the question then naturally prefents itself, "Whence this addition ?"

It is exposed to nothing but WATER, HEAT, and AIR. It without doubt procures,

1. HYDROGEN from the water.

2. OXYGEN from the fame, and likewife from the decompofition of 3, CARBONIC ACID AIR, which it imbibes. Vide page 29, note *. The moisture of the atmosphere may also supply fome portion of WATER, to be decomposed and adjusted to the other principles.

As large quarries of marble, and whole mountains, are formed from the exuviæ or shells of marine animals, so here do we fee that the most folid oaks, &c. arife from the WATER of the earth and atmosfphere, and the FIXED AIR thrown off from the combuftion of the body, and other organized substances. These truths, equally new as they are fimple, recal us to the FIRST CAUSE, who, by differently combining a few fimple bodies, has infinitely diversified the nature and appearance of things. Some years back, and this doctrine would have been looked upon as the dream of a vifionist, fo oppofed is true philofophy often to the ordinary conceptions of mankind!

8

fixed.

fixed. As to the AZOTIC AIR, it unites with the HYDROGEN, and forms VOLATILE ALKALI*.

Animal matters being compounded nearly of the fame principles as the cruciform plants, give nearly the fame results in diftillation; but as they contain more HYDROGEN, and more AZOTIC AIR, they furnish larger quantities of OIL and VOLATILE ALKALI.

In vegetables and animals poffeffing life, there is an express organization of parts, which evidently appears to have been defigned by the SUPREME INTELLIGENCE for the purpose of uniting the powers of mechanism to those of chemistry. In this point of view, we may confider the folid and confiftent parts of vegetables and animals as compofing an apparatus for performing a number of CHEMICAL PROCESSES with the fluids that circulate through themt. It is true, indeed, that this whole feries of operations is, for the most part, performed with fuch a minute fet of veffels; at the fame time that the principles applied to each other, to exercise their respective chemical attractions, seem in general to be so powerfully

*Vide Part I. p. 27.

That the living organized machinery accomplishes all these miracles, as they seem to us, we have a beautiful example in the process of ENGRAFTING,

where

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