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duced only 15; the same experiment was made with stock July flowers and other plants with equal success. The manner in which fixed air acts in promoting vegetation scems well explained by... Senebier; he first discovered that fresh leaves exposed to the sun in spring water, or water slightly impregnated with fixed air, always produce pure air as long as this impregnation lasts; but as soon as it is exhausted, or if the leaves be placed in water out of which this air has been expelled by boiling, they no longer afford pure air, from whence he infers, that fixed air is decomposed, its carbonic principle retained by the plant, and its pure air is expelled. It appears to me also, by acting as a stimulant, to help the decomposition of the water. Hazenfraz, indeed, denies its decomposition ; but his arguments do not appear to me conclusive, for reasons too tedious and technical to mention here.
Sir Humphry Davy admits that the presence of fixed air is necessary to preserve health and sustain the vigorous growth of plants, but he seems to consider it more as a necessary sustenance to be taken into the system by the leaves, than as Food by the Roots.
“ When a growing plant, the roots of which are supplied with a proper nourishment, is exposed in the presence of solar light, to a given quantity of atmospheric air, containing its due proportion of carbonic acid, the carbonic acid after a certain time is destroyed, and a certain quantity of oxygene is found in its place , if new quantities
of carbonic acid gas be supplied, the same result occurs, so that the carbon is added to plants, from the air, by the process of vegetation in sunshine, and oxygene is added to the atmosphere.” He adds, “ This circumstance is proved by a number of experiments made by Drs. Priestly, Ingenhouz and Woodhouse, and M. T. de Saussure, many of which I have repeated with similar results. The absorption of carbonic acid gas, and the production of oxygenes are performed by the leaf. And leaves recently separated from the tree effect the change, when confined in portions of air containing carbonic acid, and absorb carbonic acid and produce oxygene, even when immersed in water holding carbonic acid in solution."
The opinion that fixed air is consumed by plants, seems to be unanimous, and to those who believe in the doctrine of the circulation of the
may appear necessary to support their theory, that the carbonic acid should be absorbed by the leaves. But Kirwan's observations do not lead us to conclude that it is at all necessary that the leaves should possess such powers, and I shall hereafter endeavour more clearly to show that this is the fact, when treating of the leaves of plants.
Animal and vegetable manures, when placed in contact with plants, in a recent or undecomposed state, are generally more productive of evil than good; for if death or disease does not immediately ensue, the plant grows to such a gross and bloated state, as to be very far from prolific; indeed, ex.
perience proves that the most productive and perfect state of plants is produced and sustained by a mixture of animal and vegetable matter that has been perfectly decomposed, and which has been for a long time (say twelve months at least) turned over and exposed to the sun and air.
I am inclined to infer from these and other observations, that nitrogene in combination is the injurious principle, and that before manure can be reduced to a wholesome state, this must be expelled. To corroborate this idea it may be mentioned, that gum appears to be the only vegetable substance which contains nitrogene, and gum is the production of disease.
It is well known that fermentation reduces animal and vegetable manures to a more wholesome and immediately nutritive state than a cold and aqueous putrefaction; and that during fermentation ammonia is created and passed off; and as ammonia is formed of nitrogene and hydrogene, this again corroborates the idea that nitrogene is poisonous to plants, and that any method of facilitating its escape is more requisite than that of its retention; and therefore the suffering manure to remain on the surface of the soil, until it is reduced to a proper state to be carried to the roots as food by water, must be much more conducive to health and fructification, than burying it before it is perfectly decomposed; and it shows that that which is by some supposed to be a loss by evaporation is in fact a gain.
Acthough this subject has engaged the attention of so many eminent philosophers, none of them appear to have established a theory, that will generally accord with actual observation, or from which we can form a scientific arrangement of practical rules; but the following elementary principles, which are universally admitted, enable us to trace effects, ascertain causes, and to draw conclusions, that will be found applicable to every existing case or positive result.
All things that constitute animated nature, are reducible to the same primitive or elementary principles, viz. oxygene, hydrogene, nitrogene, carbon, and earth. The three first are permanent elastic fluids, the fourth a permanent substance; and although the earths are proved by Sir 'Humphry Davy, to be compounds of highly inflammable metals and oxygene, it does not appear that they are found in any other state, than as such compounds, in vegetables or animals, nor that it is neces
sary they should be further subdivided, either for the reproduction, or sustenance, of vegetables or animals. I shall therefore take the liberty, in the arrangement of my system, to consider the earths as elementary principles.
Oxygene is the vital air of life, the principle of combustion, and the vehicle of heat, the pure air of Kirwan.
Hydrogene is the basis of inflammable air, and is the lightest of all ponderable things, the inflammable air of Kirwan.
Nitrogene, or azote, is the opposite of oxygene, and is incapable of supporting combustion and animal life.
Carbon is the basis of common charcoal, divested of all its impurities.
Atmospheric air is compounded of the two different permanent substances oxygene and nitrogene in certain proportions, rendered aerial by the expansive power of heat.
Water is composed or formed of hydrogene and oxygene in certain proportions, and, in its common state, always holds a portion of earth in a state of solution, and generally of carbon also.
Vegetable substances are reducible to oxygene, hydrogene, carbon, and earth.
Animal substances are reducible to oxygene, hydrogene, nitrogene, carbon, and earth.
With these elementary principles in view, tracing the composition and decomposition of animals and vegetables, it will clearly appear, that matter, in