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from the air, and under the influence of the light which the sun, its inexhaustible source, pours in unceasing floods upon the surface of the globe.

And as if in these great phenomena all must be connected with causes which appear the most distant from them, we must, moreover, remark how the oxide of ammonium, the nitric acid, from which plants borrow a part of their azote, are themselves almost always derived from the action of the great electric sparks which flash forth in stormy clouds, and which (furrowing the air through a vast extent) produce there the nitrate of ammonia which analysis detects in it.

Thus, from the craters of those volcanoes whose convulsions so often agitate the crust of the globe, continually escapes carbonic acid, the principal nutriment of plants; from the atmosphere flashing with lightnings, and from the midst of the tempest itself, there descends upon the earth the other and no less indispensable nutriment of plants, that whence they derive almost all their azote, the nitrate of ammonia contained in storm showers. Might not this be called, as it were, an idea of that chaos of which the Bible speaks, of those times of disorder and of tumult of the elements, which preceded the appearance of orgarlised beings upon the earth?

But scarcely are the carbonic acid and the nitrate of ammonia produced, than a form more calm, although not of inferior energy, comes to put them in action ; it is light. Through her influence, the carbonic acid yields its carbon, the water its hydrogen, and the nitrate of ammonia its azote. These elements unite, organized matters form, and the earth puts on its rich carpet of verdure.

It is, then, by continually absorbing a real force, the light and the heat emanating from the sun, that plants perform their functions, and that they produce this immense quantity of organised, or organic matter--pasture destined for the consumption of the animal kingdom. And if we add, that animals on their part produce heat and force in consuming what the vegetable kingdom* has produced, and has slowly accumulated, does it not seem that the ultimate end of all these phenomena, their most general formula, reveals itself to our sight?

The atmosphere appears to us as containing the primary substances of all organization, volcanoes, and storms; as the laboratories in which were first produced the carbonic acid and the nitrate of ammonia which life required for its manifestation, or its multiplication.

In aid of these comes light, and developes the vegetable kingdom, immense producer of organic matter ; plants absorb the chemical force which they derive from the sun to decompose carbonic acid, water, and nitrate of ammonia; as if plants realised a reducing

"Le règne animal," in the original; but this is obviously an error.

apparatus superior to all those with which we are acquainted, for none of these would decompose carbonic acid in the cold.

Next come animals, consumers of matter and producers of heat and force, true apparatus for combustion. It is in them undoubtedly that organized matter puts on its highest expression. But it is not without suffering from it that it becomes the instrument of sensation and of thought ; under this influence organized matter undergoes combustion; and in reproducing the heat and the electricity which produce our strength, and which are the measure of its power, these organized, or organic matters become annihilated, in order to return to the atmosphere whence they came. Thus the atmosphere constitutes the mysterious link which binds the vegetable to the animal kingdom.

Vegetables, then, absorb heat and accumulate matter which they have the power to organize.

Animals, through whom this organized matter only passes, burn or consume it, in order to produce in its aid the heat and the different powers

which their movement turns to account. Suffer me, therefore, if, borrowing from modern science an image of sufficient magnitude to bear comparison with these great phenomena, we should liken the existing vegetation (truly a storehouse in which animal life is fed,) to that other storehouse of carbon constituted of the ancient deposits of pit-coal, and which, burnt by the genius of Papin and Watt, also produces carbonic acid, water, heat, motion: one might almost say, life and intelligence.

In our view, therefore, the vegetable kingdom will constitute an immense depot of combustible matter, destined to be consumed by the animal kingdom, and in which the latter finds the source of the heat of the locomotive powers of which it avails itself.

Thus we observe a common tie between the two kingdoms, the atmosphere; four elements in plants and in animals—carbon, hydrogen, azote, and oxygen; a very small number of forms under which vegetables accumulate them, and under which animals consume them ; some very simple laws, which their connexion simplifies still more : such would be the picture of the most elevated state of organic chemistry which would result from our conferences of the present year.

You, like myself, have felt, that before separating we have need of collecting our thoughts, of fixing with precision all the facts, of bringing together and summing up the opinions which explain and develope these great principles ; lastly, that it was useful, as regarded your future studies, to give you in writing, and in a clearer form, the expression of these views, which were partly brought into existence under the stimulus of your presence, and consequently reduced into form with the hesitation which so often accompany the first enunciation of our thoughts.

Since the causes of] all the phenomena of life are exerted upon matters which have for their base carbon, hydrogen, azote,

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oxygen ; since these matters pass over from the animal kingdom to the vegetable kingdom, by intermediary forms, carbonic acid, water, and the oxide of ammonium ; lastly, since air is the source whence the vegetable kingdom is fed, and the reservoir in which the animal kingdom is annihilated, we are led to take a rapid survey of these different bodies with a special view to general physiology.

Composition of Water. Water is incessantly formed and decomposed in animals and plants ; to appreciate what results from this, let us first see how it is composed. Some experiments founded on the direct combustion of hydrogen, and in which I have produced more than two pounds of artificial water: experiments which are in truth very difficult and very delicate, but in which any errors would be unimportant with regard to the circumstances which we are engaged upon : make it very probable that water is formed, in weight of 1 part hydrogen, and 8 parts oxygen, and that these whole and simple numbers express the true relation according to which these two elements combine to form water.

As substances always present themselves to the eyes of the chemist by molecules, as he always endeavours to connect in his thoughts, with the name of each substance the weight of the molecule, the simplicity of this relation is not unimportant.

In fact, each molecule of water being formed one molecule of hydrogen, and one molecule of oxygen, we arrive at these simple numbers, which cannot be forgotten.

A molecule of hydrogen weighs 1 ; a molecule of oxygen weighs 8; and a molecule of water weighs 9.

Composition of Carbonic Acid. Carbonic acid keeps incessantly forming in animals, and is continually undergoing decomposition in plants; its composition, therefore, deserves a special notice in its turn.

Now, carbonic acid, like water, is represented by the most simple numbers. Experiments founded on the direct combustion of the diamond, and on its conversion into carbonic acid, have proved to me that this acid is formed of the combination of 6 parts by weight of carbon, and 16 parts by weight of oxygen. We

are, therefore, led to represent carbonic acid as being formed of one molecule of carbon weighing 6, and two molecules of oxygen weighing 16, which constitute one molecule of carbonic acid weighing 22.

Composition of Ammonia. Lastly, ammonia, in its turn, seems formed in whole numbers of 3 parts of hydrogen and 14 of azote, which may be represented by 3 molecules of hydrogen weighing 3, and by i molecule of azote weighing 14.

Thus, as if the better to show all her power, Nature operates in the business of organization only upon a very small number of elements, combined in the most simple proportions.

The atomic system of the physiologist revolves on these four numbers—1, 6, 7, 8. 1 is the molecule of hydrogen ; 6 that of carbon, 7 or twice 7, i. e. 14, that of azote; 8 that of oxygen.

These numbers should always be associated with these names, because for the chemist there can exist no abstract hydrogen, nor carbon, nor azote, nor oxygen. They are beings in their reality which he has always in view; it is of their molecules that he always speaks ; and to him the word hydrogen depicts a molecule which weighs 1 ; and the word carbon, a molecule which weighs 6; and the word oxygen, a molecule which weighs 8.

Composition of the Air.

Does atmospheric air, which performs so great a part in organic nature, also possess as simple a composition as water, carbonic acid, and ammonia ? This is the question which M. Boussingault and I have recently been studying. Now we have found that, as the greater number of chemists have thought, and contrary to the opinion of Dr. Prout, to whom chemistry owes so many ingenious views, air is a mixture, a true mixture.

In weight, air contains 2,300 of oxygen for 7,700 of azote; in volume, 208 of the first for 792 of the second. The air, besides, contains from 4 to 6 10,000ths of carbonic acid in volume, whether it be taken at Paris or in the country. Ordinarily, it contains 4 10,000ths. Moreover, it contains a nearly equal quantity of the carburetted hydrogen gas, which is called marsh gas, and which stagnant waters disengage perpetually.

We do not speak of aqueous vapour, which is so variable : of oxide of ammonium and of nitric acid, which can only have a momentary existence in the air, because of their solubility in water.

The air, then, is constituted of a mixture of oxygen, azote, carbonic acid, and marsh gas.

The carbonic acid in it varies, and indeed, greatly, since the differences in it extend almost from the simple to the double, from 4 to 6 10,000ths. May not this be a proof that plants take from the air this carbonic acid, and that animals take back a part of it? In a word, may not this be a proof of that equilibrium of the elements of the air attributed to the inverse actions which animals and plants produce upon it?

It has, indeed, been long since remarked, that animals borrow from the air its oxygen, and give to it carbonic acid : plants in their turn, decompose this carbonic acid, in order to fix its carbon, and restore its oxygen to the air.

As animals breathe continually; as plants breathe under the solar influence only; as in winter the earth is stript, whilst in summer it

is covered with verdure, it has been supposed that the air must transfer all these influences into its constitution.

Carbonic acid should augment by night, and diminish by day. Oxygen, in its turn, should follow an inverse progress.

Carbonic acid should also follow the course of the seasons, and oxygen obey the same law.

All this is true, without doubt, and quite perceptible as to a portion of air limited and confined under a jar; but, in the mass of the atmosphere, all these local variations blend and disappear. Accumulated centuries are requisite in order effectually to put in action this balance of the two kingdoms, with regard to the composition of air; we are then, very far from those daily or yearly variations, which we had been apt to look upon as being as easy to observe as to foresee. With regard to oxygen, calculation shows that, exaggerating all the data, not less than 800,000 years would be required for the animals living on the surface of the earth to consume it entirely.

Consequently, if we suppose that an analysis of the air had been made in 1800, and that during the entire century plants had ceased to perform their functions on the surface of the whole globe, the animals at the same time all continuing to live, the analysts in 1900 would find the oxygen of the air diminished by 1-8000th of its weight: a quantity which is beyond the reach of our most delicate methods of observation, and which, assuredly, would have no influence whatever on the life of animals or plants.

As to this, then, we cannot be deceived ; the oxygen of the air is consumed by animals, who convert it into water and carbonic acid ; it is restored by plants, which decompose these two bodies.

But nature has arranged everything so that the store of air should be such, with relation to the consumption of animals, that the want of the intervention of plants for the purification of the air should not be felt until centuries have elapsed.

The air which surrounds us weighs as much as 581,000 cubic kilometres of copper; its oxygen weighs as much as 134,000 of these same cubes. Supposing the earth peopled with a thousand millions of men, and estimating the animal population at a quantity equivalent to three thousand millions of men, we should find that these quantities united consume in a century only a weight of oxygen equal to 15 or 16 cubic kilometres of copper, whilst the air contains 134,000 of it. It would require 10,000 years for all these men to produce a perceptible effect upon the eudiometer of Volta, even supposing vegetable life annihilated during all this time.

In regard to the permanence of the composition of air, we may say with all confidence, that the proportion of oxygen which it contains is secured for many centuries, even reckoning for nothing the influence of vegetables, and that nevertheless, these restore oxygen to it incessantly, in quantity at least equal to that it loses, and perhaps more ; for vegetables live just as much the expense of the carbo

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