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not prove it to be necessary that every substance, or any substance containing the basis or elements of salts, should undergo this process, and be formed into salts, before it can be in a state to constitute Food fit for the reception and nourishment of Plants.
Salts are various in their nature and general effects, when placed in contact with other substances.
I have made many experiments with sea salt, nitre, soda, barilla, &c. &c. and feel myself justified in concluding, from the results, that salts are not in any degree an essential in the Food of Plants.
The opinions of Drs. Smith and Pearson on this subject, appear rational : they say, that salts, as they operate in promoting vegetation, are analogous to mustard, cinnamon, ginger, &c. which are not of themselves at all, or necessarily nutritious, but contribute to render other things nutritious by exciting the action of the stomach, and other organs of digestion and assimilation. Dr. Pearson
-" I have no doubt of the truth of the position, that no living thing, neither Plant nor Animal, can grow or live in a state of visible action, without supplies of matter that has been alive; in other words, living Animals and Vegetables can only live on dead Animals and dead Vegetables ; no Plant nor Animal has ever been known by experience, nor in the nature of things does it seem reasonable, that they can be nourished
by mere water and pure air, as some persons have asserted.”
Notwithstanding all that has been said to establish the opinion that salt is a valuable manure, am convinced it never can, as an article of food, contribute to the increase of any vegetable, but as a chemical agent, by destroying and hastening the decomposition of animals and vegetables, and by its deliquescence, 'it may in many instances increase the fertility of soils.
Mr. Kirwan, in an Essay on Manures and the Food of Plants, as applicable to Agriculture, takes a very correct and comprehensive view of his subject.
Sir Humphry Davy also has favoured the world with a very luminous work on agricultural chemistry.
Both those eminent chemists appear to have maturely considered the nature of Manures and the Food of Plants, and, no doubt, have explained their opinions and detailed their experiments with great clearness and perspicuity.
Were it possible for me, in a work like this, to convey an adequate idea of the information contained in either of those works, it may appear conceited and presumptuous to attempt it; but as I could not claim the merit of having done my best to elucidate my subject, without a reference to such splendid authorities, and finding it difficult to explain their arguments, experiments, and results, in any language equal to their own, I trust I shall be
excused in making considerable literal extracts. Although in the general opinions and principles of those eminent chemists there appears to be a great: coincidence, I trust it will be admitted that there is a sufficient difference to shew, that the subject cannot be considered as finally arranged, or at rest, and that I may be justified in offering a commentary, and an explanation of my own ideas.,
Mr. Kirwan observes, “ The first essential requisite to a fertile soil is, that it contain a sufficient of the three or four simple earths, and of the soluble carbonaceous, principle: the other requisites are, that the proportion of each and general texture of the soil be such as, to admit and to retain as much water as is necessary to vegetation and no more."
Sir Humphry Davy says, “ The surface of the earth, the atmosphere, and the water deposited from it, must either together or separately afford all the principles concerned in vegetation, and it is only by examining the chemical nature of these principles, that we are capable of discovering, what is the Food of Plants, and the manner in which this food is supplied, and prepared for their nourishment."
He also says, “ By methods of analysis, dependent upon chemical and electrical instruments discovered in late times, it has been ascertained that all the varieties of material substances may be resólved into a comparatively small number of bodies, which, as they are not capable of being decompounded, are considered, in the present state of
chemical knowledge, as elements. The Bodies incapable of decomposition, at present known, aré forty-seven ; of these, thirty-eight are metals, six are inflammable bodies, and three, substances which unite with metals and inflammable bodies, and form with them acids, alkalies, earths, or other analogous compounds. The chemical composition of Plants has, within the last ten years, been elucidated by the experiments of a number of chemical philosophers, both in this and other countries, and it forms a beautiful part of general chemistry, if the organs of Plants be submitted to a chemical analysis; it is found that their almost infinite diversity of form, depends upon different arrangements and combinations of a very few of the elements, seldom more than seven or eight belong to them, and three, constitute the greatest part of their organised mat
« All the varieties of substances found in Plants are produced from the sap, and the sap of Plants is derived from water, or from the fluids in the soil, and it is altered by, or combined with, principles derived from the atmosphere.”
66 Soils in all cases consist of a mixture of dif. ferently divided earthy matter, and with animal or vegetable substances in a state of decomposition, and certain saline ingredients. The earthy matters are the true basis of the soil; the other parts, whether natural, or artificially introduced, operate in the same manner."
Sir Humphry also says, “ What may be our ul
timaté view of the laws of chemistry, or how far
Kirwan states, “ All Plants, (except the sub-