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purity of the substances employed, but did not prevent a similar recurrence: ammonia was always found. Now, on the old principle of the simple elementary nature of the metals, no ammonia could exist in the substances examined; but, if the base of metals be hydrogen, then, as potass contains oxygen, the materials of ammonia may be traceable: this, however, will involve another condition; and with it, the confirmation of another of Sir Humphry Davy's conjectures,—that Azote, (one of the constituents of ammonia, see No. 100,) is an oxide of hydrogen. I will not, however, anticipate inquiries, which of right attach to subjects referrible to the Section on the atmosphere.

The presence of the alkalies in the ashes of plants, alluded to at No. 90, appears to furnish the most conclusive evidence in favour of the agency of hydrogen in the formation of metals, for to what other source can we trace these alkaline substances? It may be contended that plants absorb them from matters in the soil, and particularly in the manures employed; but ferns, and many other wild plants, and underwood of all descriptions, grow in places where manure is never by any chance applied; and yet such plants and shrubs produce abundance of potass. What, then, is the source of these metallic oxides? Can it be the oxygen?—If the answer be in the affirmative, then oxygen must form an oxide of itself—a thing impossible; for substances possessed of one common electricity, refuse to unite. Can it be from the carbon? This substance is a distinct product of incineration, or burning, as well as the alkalies ; they possess no sensible property in common. What is left, then, but the hydrogen, or the small proportion of azote which is traceable in some plants?—but what is azote? They who know what it is, are alone fully qualified to assert, that it is not an oxide of hydrogen. But plants,—though these alkaline substances cannot be traceable to any of their own constituent parts, may absorb such substances from the soil; and, indeed, Sir Humphry Davy shows that alkalies do occasionally exist in the soil; two things, however, must be considered ;—first, that it is in the ashes that alkalies are found; and, second, that the quantities yielded by different plants vary so much, that it may be considered as very doubtful, whether alkalies, purely such, exist at all in the vessels of the living plant. According to the table in Daw's Agric. Chem. (page 104), 10,000 parts of oak yielded but 15 parts of potass, while the same quantity of fern, wormwood, and fumitory, yielded respectively 62, 730, and 790 parts. There is much of astonishing mystery in all these natural phenomena; but it appears to me, that the more we press our inquiries, and the deeper we go in our researches, into first principles, the more evident cause do we find for believing, that nature has formed all her decomposable productions from the elements of that universally diffused fluid,—water; and that, in effecting these surprising transmutations, she has employed but one primary agent,—the electrizing principle of the sun's rays.

the upper part of the tube. In this experiment, then, ammonia, which is well known to yield azote by its decomposition, appears to have been formed without its presence; and if so, the azote must have been derived from the combination of the elements enumerated."—See Penny Cycl., Article Azote, vol. iii., 207, The above is the experiment alluded to by the Lecturer,

(c.) The third head, comprises the phenomena which attend the decomposition of water in the immediate neighbourhood of the spongelets, and remotest fibres of the roots of plants. Their food requires preparation: manures are deposited in the soil, and these must be laborated by the process of fermentation; and that process is effected by the decomposition of water. Carbon (charcoal) constitutes one of the most important parts of vegetable aliment, and it is totally insoluble in fluid water; but of this fact, experience appears to warrant a doubt: plants which bleed, (as the vine,) just prior to the expansion of the leaves, yield drops, like tears, that may be collected. If these be made to fall into a phial containing pure lime water, no milkiness, or chalky deposit is produced, that I have been able to detect; were carbonic acid present, pellucid lime water would instantly reveal it. The pores also in the fibres are so very minute, that no solid food can by any possibility, be supposed capable of passing into them. Sir Humphry Davy (Agric. Chem. 243) says; "I tried an experiment on this subject; some impalpable powdered charcoal, procured by washing gunpowder, and dissipating the sulphur by heat, was placed in a phial containing pure water, in which a plant of peppermint was growing: the roots of the plant were pretty generally in contact with the charcoal. The experiment was made in May, 1805; the growth of the plant was very vigorous during a fortnight, when it was taken out of the phial; the roots were then cut through in different parts, but no carbonaceous matter could be discovered in them, nor were the smallest fibrils blackened by the charcoal, though this must have been the case had the charcoal been absorbed in the solid form."—If wo consider all the facts stated in this extract, we can scarcely doubt that some powerful agent, such as the descending currents of solar and atmospheric electricity, by day and night, must induce those chemical affinities, by which the constituents of the manures form new compounds exactly suitable to vegetable nutrition. Our views must also be extendod: for, not only is the food prepared, but electric agencies are simultaneously developed? and these constitute the ascending current wnichpropels and carries forward the aliment, so prepared, and deposits it in the vessels appropriated to the purposes of assimilation and distribution. It must ever be recollected that no one state of electric excitation, can, by any possibility, exist, without exciting another of an opposite character. If these be excited in masses, they exhibit the attractive and repulsive powers of electricity: such are, without exception, the ordinary phenomena produced by the electrical machines and apparatus in common use among electricians: but if the divellent powers (from divello, to separate,) of natural electricity be excited,—those that induce the nicest and most subtile processes of chemical decomposition and affinity, among mixtures consisting probably, of six or eight binary and ternary compounds, (terms expressing the union of opposite substances—such as acids with alkalies,hydrogen, with carbon and oxygen, 'e., in certain definite proportions); the several electricities so disturbed and developed, by changing and interchanging relations, produce effects, which must startle the most apathetic mind, if but one ray of light dart through it, so as to reveal a glimpse of the wondrous work,—and yet, these divellent powers are excited, and have induced such surprising changes in every common heap, or compost mass of fermenting materials, daily, and from the earliest period of time.

I have thus endeavoured to recall to the reader's recollection the influence of electric induction, as experimentally demonstrated in natural phenomena, with a view to render as perspicuous as possible the mode by which the nutritive fluids are prepared, and carried into the minute vessels of the root: it remains to condense the substance of what has been said, and to bring it into the form of a theory of vegetable nutrition; but previously, I again refer to the experiments of Dr. Faraday; they evince that a volume of electricity enters into every compound matter, and forms the bond which ties its components together.

The oxygen and hydrogen gases developed by the decomposed water, seize upon the carbon produced by the decomposition of the manures, and form gaseous bodies, consisting of carbonic acid, carbonic oxide, and carburetted hydrogen; ammoniacal gas, is also frequently evolved, and a variety of liquid compounds are produced, at a time, and in a state, the most suitable to the purposes of vegetable introsusception. (See No. 16). Electricity is also developed during these processes, and serves to propel the aliment into the finest vessels of the plant. Thus Dutrochet's first theory—that of electric currents—is corroborated, and these, at the same time are proved to be coincident with the laboration of the food, and with its introsusception into the vegetable pores and tubes. This wordintro, susception (from intro, within, and susceptio, a taking up), and another, in frequent use, capillary attraction (from capillus, a hair), through tubes, fine as a hair—are terms which imply a cause or causes in active operation; but according to their usual acceptation, they express phenomena the causes of which remain involved in mystery. Do not these phenomena result from electrical currents? and as no effect can be produced without an efficient cause, may we not find that cause in the agency of electric propulsion*, induced by electric attraction? I think we may, and that such agency will fully elucidate all the phenomena of introsusception and capillary attraction,—effects which can be explained or accounted for by no other agency whatsoever.

104. General properties of water. Water is said by Parkes to exist in four separate and distinct forms: "viz. in the state of ice; in that of a fluid; in the state of vapour; and in the state of chemical combination with other bodies. The most simple form in which it is probable that water will ever be exhibited, is that of ice; for by the mere combination of ice with caloric, fluid water will be formed, and a further portion of caloric will convert the fluid into steam; the most attenuated aqueous vapour being nothing more than ice divided and rarified by the solvent and expansive power of caloric."—{Essays, vol. i. 361.) This opinion should be received with some caution, for it is founded entirely upon the doctrine of latent caloric; a doctrine which, if examined with that degree of critical acumen its assumptions seem to require, will scarcely be able much longer, to furnish satisfactory evidence of being founded upon philosophic truth. The electrolyzation of water and the developement of its elements, by the passing of a definite quantity of voltaic electricity, has opened the road to truth, and leaves the mind free to trace effects to real causes.

Ice differs essentially in its characters from those of water; and the phenomena which the latter displays in its approach to the freezing point, are remarkably different from those of other fluid bodies. Water contracts in cooling, and increases in density till it is reduced to about 40° of Fahrenheit: below that point, it expands,

• The reader who possesses an electric machine may readily convince himself of the influence of propulsion, by means of a small apparatus termed the electrical paQ; it is a little brass bucket, to be suspended from the conductor by a chain; a small tube projects horizontally from one side, near the bottom. If water be put into the pail, it will scarcely ooze through the fine orifice in the tube; but the instant that the machine is excited, the water is projected in a well defined stream of ai r inch or more in length.

and becomes less dense. Ice is lighter than water, and consequently floats upon it. Its expansive force is such, that heavy pavement stones are raised, trees are split, and rocks rent asunder by it. By this expansion the most beneficial effects are produced on the soil; for as every interstice is occupied by the water, the act of freezing forces the particles of the soil apart; and as these possess no elastic property, they are found when the thaw takes place, to be broken up, more finely divided, and in a state much more manageable by the labourer, and in every respect better prepared for the purposes of vegetable growth.

105. Ice and snow are bad conductors of electricity. At 18° below zero, ice becomes a non-conductor, and at a much lower degree of temperature, it has been found to be an actual electric, affording sparks of fire, upon being excited. Is it possible then, that a substance, which as a solid, is specifically lighter than the fluid upon which it floats—which, when its temperature is very much reduced, may be ground into powder so fine, as to be blown about by the wind—and which from being a very ready conductor of electricity, has become itself an excitable electric; can this substance be identical with a fluid, possessing properties altogether dissimilar? And shall we, when our feelings, and our instruments convince us that the aqueous vapour held in invisible solution in the atmosphere during the coldest day of winter; when our thermometers demonstrably prove that this vapour, and the ponderous masses of solid ice, six or eight inches thick, are both, at one and the same individual moment, reduced to a temperature of 8° or 10"; shall we, under such circumstances, with such evidence, be constrained to acknowledge, that "the most attenuated vapour is nothing more than ice, divided and rarified by the solvent and expansive power of caloric V Such may be the fact, but of what value then are our instruments! I would rather suggest that ice, water, and vapour, are bodies possessing different electric conditions; and that, as chemical changes depend upon electric agency, the three are essentially different, and must remain so, till atmospheric changes take place, antagonist to those which had induced the various phenomena of frost.

106. In the fluid state, water possesses a solvent power, which, when exerted in the soil, is of great importance. Plants will not continue to vegetate, unless their roots are supplied with water; and if they be kept long without it, the leaves will droop, and assume B withered appearance. Tulips, hyacinths, and a variety of plants, with bulbous roots, may be reared, if the roots be merely immersed in water. Du-Hamel, Bonnet, Van Helmont, and Boyle, con

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