negative cup, it was uniformly converted into limewater, or had a mixture of strontites, or a crust of barytes, carbonated by the contact of the atmosphere. Insoluble substances, containing very minute portions of acid and alkali, were next exposed to a similar process; and the negative side uniformly extracted the alkali, the positive side the acid, be the quantities ever so small. Soluble bodies were then examined in like manner, being subjected to the galvanic fluid in agate cups, and dissolved in pure water. The separation here went on much more rapidly, but it followed the same rules. The negative cup contained a solution of alkali, or a deposite of earth or metallic crystals, according to the compound neutral employed; the positive cup uniformly contained a great excess of acid; a muriatic salt gave oxymuriatic acid in the positive cup. The stronger the solution exposed in these experiments, the quicker was the change produced; but the smallest portion of acid and alkali was always detected; and the separation, at the end of the process, was as complete as at first.

Two foreign chemists of reputation, Messrs Hisinger and Berselius, had made an experiment, in which muriate of lime being exposed in the positive side of a siphon, and pure water in the negative, the action of the galvanic fluid made lime appear in the water: so extraordinary a discovery, merited every degree of attention. Mr Davy immediately pursued it, upon the plan of his former experiments. His first inquiry was into the manner of the passage here remarked, through a menstruum not chemically attracting the substance which passed over. An agate cup, for example, filled with water, was connected with a cup of sulphate of lime, by moistened asbestus: if the former was positively electrified, acid soon came over; if negatively, lime came over. Metals and metallic oxides passed over to the negative cup, like alkalis and alkaline earths; and, in one beautiful experiment, where nitrate of silver was placed in the positive side, the amianthus between the cups appeared covered with a thin silver film. The transference went on slower, in proportion to the body of water through which it was performed: when the wires were only an inch asunder, sulphuric acid came over from sulphate of potash in five minutes; nor was contact with either electrified surface, necessary in these experiments. A vessel of solution of muriate of potash, being connected by amianthus with two glass tubes filled with water, the one negatively, the other positively electrified; by degrees, the alkali went over into the former, and the acid into the latter. But one of the most singular parts of this process, is, thatthe acid and the alkali, in passing from one vessel to another, through any intermediate body of water, or over the surface of the amianthus, do not change the vegetable colours in their way, except in so far as they come in contact with them at the positive

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and negative sides respectively; e. g. the acid passes over the negative portion of a solution of litmus without reddening it; and the alkali does not render turmeric brown by passing over it at the positive side.

A considerable step was now made from the point at which our author had set out. He had satisfactorily ascertained the regular decomposition of bodies containing acids united with alkahis or metallic bases; the constant preference of the acid for the . positive side, and of the alkaline or metallic base for the negative; and the actual transference by perceptible motion of those substances from one part to another of the electrical circuit; circumstances which had been vaguely remarked by former observers. But he now was led a step further, and perceived a phenomenon perfectly different in kind from any thing which their experiments had made known. He found, that the action of the acids and alkalis on vegetable colours was suspended by the electrical state of those bodies; and that the influence of chemical affinity, in this instance at least, was superseded by the powers of electricity: for on what, but chemical affinity, does the action of salts upon cofours depend? This singular fact, however, deserved a more careful examination, and obviously suggested a set of experiments upon the influence of electricity in various other processes of e

lective attraction.

The same general form of experiment was here again employed. Two glass tubes were connected with the positive and negative wires of the pile, and each was connected with a third vessel by films of amianthus. In the third vessel various substances were successively placed, having a known chemical affinity for the component parts of the substances in the two tubes; and those parts were made to pass through the contents of the third vessel, by the action of the galvanic fluid. Thus, sulphate of potash being placed in the negative tube, distilled water in the positive, and ammonia in the middle vessel, the action of the pile sent the acid over into the water, and through the ammoniacal solution, in a longer or shorter time in proportion to the strength of that solution. When it was weak, the acid would tinge the water in five minutes; but, even through the most saturated lixivium it never failed to come in a certain time. The other acids passed in the same manner; and by a similar process the alkalis and alkaline earths were sent through the acids according to the like rules; only that strontites and barytes passed with very great difficulty through sulphuric acid, and transmitted sulphuric acid with proportionate slowness, and in very small quantities. When the acids and alkalis were passed through neutral salts in the intermediate vessel, the alkali of the latter soon appeared in the

negative

negative tube, and the passage of the alkali from the positive tube went on slowly, sometimes never being completed; as when united with the remaining acid of the intermediate vessel and formed an insoluble compound, which fell immediately down be yond the sphere of the electrical action. Thus barytes could not be transmitted through sulphate of potash, though the galvanic process brought it from muriatic acid in the positive, to the sul phuric acid in the intermediate vessel, and at the same time brought the potash from the intermediate into the negative vessel. Animal and vegetable substances were quickly decomposed in similar experiments; and their constituent parts either separated purely, or recombined with other bodies exhibited to them, according to the general rules which the salts and metals follow.

A few experiments only were necessary to demonstrate, that in all the processes now described, the matter, or energy, or galva nism, or whatever it may be called, which operates in the pile of Volta, is identical with common electricity. Our author produced several of the same decompositions and transferences, by means of a powerful electrical machine, in the same manner as with the galvanic pile. It will be a general expression (says Mr Davy) of the facts that have been detailed, relating to the changes and transitions by electricity, in common philosophical language, to say that hydrogene, the alkaline substances, the metals, and certain metallic oxides, are attracted by negatively electrified metallic surfaces, and repelled by positively electrified metallic surfaces; and, contrariwise, that oxygene and acid substances are attracted by positively electrified metallic surfaces, and repelled by negatively electrified metallic surfaces; and these attractive and repulsive forces are sufficiently energetic to destroy or suspend the usual operation of elective affinity.' He thinks it further proved by his experiments, that a chain of homogeneous particles is kept up from one surface to another, along the circuit, by means of the electrical energy; for he observed, that so long as any of the matter transferred remained in the vessel, the chain of particles of that matter existed all along the circuit, and was only destroyed, or drawn over into the other vessel, af ter the first reservoir had been exhausted. That successive compositions and decompositions take place while substances pass through solutions of neutral salts, he conceives, is rendered very probable by the impossibility of completely bringing over such substances as form heavy compounds in their way, and fall down, so as to escape the limits of the electrical circuit.

The inquiries of our author are next directed to trace the analogy between the singular phænomena above described, and other known facts relating to the electrical changes superinduced in dif

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ferent bodies by their mutual contacts, and the tendencies to unite which opposite states of electricity may create. The various experiments which he instituted upon this subject, are incapable of a general abridgement. We shall only observe, that he found that the acids and alkalis, which could be exhibited in a solid state, gave plain indications of negative and positive electricity, respectively, upon being brought in contact with metallic plates. Thus, boracic acid, being touched with an insulated copperplate, became negative, and left the plate positive; lime, on the other hand, being treated in the same way, was positive, and the plate negative. Mr Davy is disposed, from these and similar considerations, to conjecture, that the chemical affinities of bodies depend on their natural state of electricity; that some being always, when in their natural state, positively, and others negatively electrified, the two classes combine in consequence of this; that when their natural electricity is augmented, their tendency to unite is increased, and that this tendency is destroyed by an electrization, of a contrary, and as it were, an unnatural kind. Thus, an acid and an alkali having opposite electricities, unite readily; if their degrees of electricity are nearly equal in opposite directions, they unite with the greater force; if those degrees of electricity are made stronger artificially, these bodies combine still more readily; if they are artificially reversed, and the acid made positive, and the alkali negative, no union is produced. Of the general theory thus hinted at, it is no small confirmation, that perfectly neutral salts show no symptoms of either positive or negative electricity; and that bodies having very strong degrees of opposite electricity, are restored to equilibrium, with an evolution of heat, and even of light and heat; while bodies show a similar phenomenon, when their union is effected by means of chemical action. It may likewise be observed, that Guyton de Morveau found the mechanical adhesion of the metals to mercury was in proportion to their chemical affinity with it. Mr Davy, admitting this to have been established by his experiments (though we wish he had repeated and varied them himself, as they were liable to a serious objection *), remarks, that it supports

his

Mr Davy hints at this in a note, obferving that amalgamation muft have interfered, but that the general refult feems diftinct." If we remember right, the polished plate of metal was let down upon the furface of mercury from one end of a delicate balance, and the weight ne ceffary to draw it up from the contact was marked. It is clear that there muft here have been a chemical union at the common furface, where the metal ufed had a confiderable affinity with mercury-The employment of mercury is itfelf a fufpicious circumftance. Polifhed plates of folid metal cohere ftrongly,--and why does the comparative trial not anfwer here?

his hypothesis; for he finds those metals which, in Mr Guyton's experiments, adhered most strongly to the mercury, are those which charge a condensing electrometer most highly.

Mr Davy's paper concludes with a number of ingenious and important observations on the general inquiries to which his experiments lead, the phenomena which they enable us to explain, and the more practical uses to which they may hereafter be applied. As this branch of the discourse consists of a series of detached remarks, we shall not attempt to analyze it, but shall content ourselves with extracting a few of them for a specimen.

A piece of muscular fibre, of two inches long, and half an inch in diameter, after being electrified by the power of 150° for five days, became perfectly dry and hard, and left on incineration no faline matter. Potafh, foda, ammonia, lime, and oxide of iron were evolved from it on the negative fide, and the three common mineral acids and the phofphoric acid were given out on the pofitive fide.

A laurel leaf treated in the fame manner, appeared as if it had been exposed to a heat of 500° or 600° Fahrenheit, and was brown and parched. Green colouring matter, with refin, alkali, and lime, appeared in the negative vellel; and the pofitive veffel contained a clear fluid, which had the smell of peach bloffoms; and which, when nentralized by potafh, give a blue-green precipitate to folution of fulphate of iron; fo that it contained vegetable pruflic acid.

A fmall plant of mint, in a ftate of healthy vegetation, was made the medium of connexion in the battery, its extremities being in contact with pure water: the procefs was carried on for 10 minutes: potash and lime were found in the negatively electrified water, and acid matter in the pofitively electrified water, which occafioned a precipitate in folutions of muriate of barytes, nitrate of filver, and muriate of lime. This plant recovered after the procefs: but a fimilar one, that had been electrified for four hours with like refults, faded and died. The facts show that the electrical powers of decompofition act even upon living vegetable matter; and there are fome phenomena which feem to prove that they operate likewife upon living animal fyftems. When the fingers, after having been carefully washed with pure water, are brought in contact with this fluid in the pofitive part of the circuit, acid matter is rapidly developed, having the characters of a mixture of muriatic, phof phoric, and fulphuric acids: and if a fimilar trial be made in the negative part, fixed alkaline matter is as quickly exhibited.

The acid and alkaline taites produced upon the tongue, in Galvanic experiments, feem to depend upon the decompofition of the faline matter contained in the living animal fubitance, and perhaps in the faliva.

As acid and alkaline fubftances are capable of being feparated from their combinations in living fyitems by electrical powers, there is every reafon to believe that by converfe methods they may be likewife introduced into the animal economy, or made to pafs through the animal or

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