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during the decomposition of nine grains of water, an amount of electricity is thus set free far greater than that which is called into terrific action in the production of the vivid lightning-flashes and appalling thunder-sound of the dread-inspiring tempest.

But, to descend to positive proof, it has been shown by Becquerel, and subsequently by myself, in a paper read some years ago before the Royal Society, that the electricity evolved during the decomposition of a few grains of common salt was, when properly managed, capable of producing chemical changes which, in the hands of the illustrious Davy, required for their demonstration the vast voltaic battery of the Royal Institution. The element necessary for the production of these phenomena, appears to be simply a weak current with continuity of action.

Let me draw your attention to the glass vessels before you, in which a few grains of common salt have been undergoing decomposition during the last few hours. The current evolved has been made to traverse a solution of hydrochlorate of ammonia. The result of this has been the decomposition of the salt, and the evolution of its curious theoretical base, the compound metal, ammonium. It has in the central tube appeared as an amalgam with mercury, a globule of which had been previously entangled in the folds of the

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platinum conducting-wire. The compound here appears as a gray ash-coloured sponge, like spongy platinum, so light as to float in water. And observe another effect of these weak currents: the amalgam remains in the midst of water unchanged, whilst, under ordinary circumstances, a moment's immersion in that fluid is sufficient to destroy it; the weak current which produced it is effective in retaining it unchanged. By untwisting a wire I cut off the current; chemistry comes into play, the spongy amalgam vanishes

Fig. 10. Battery or source of the electric current consisting of: A, vessel containing solution of common salt; B, glass cylinder, closed with a plug of plaster of Paris, and containing a solution of sulphate of copper; C, copper plate; Z, zine plate. **Decomposing cell: D, vessel containing solution of common salt, having a zinc plate, E, immersed, and connected by a wire, G, with the copper plate, C, of the battery; F, glass tube, closed at the lower extremity with plaster of Paris, containing a solution of hydrochlorate of ammonia, the amalgamated platinum wire immersed in it passing through the cork, and connected with plate, Z, of the battery. The direction of the positive current is shown by the arrows.

amidst a torrent of bubbles of hydrogen.

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more let me unite the wires, the electricity from the decomposing salt again traverses the solution; again chemical forces are paralysed, and we shall soon see the spongy amalgam of ammonium and mercury reappear.

We have just noticed the fact that, under the influence of a weak current, salts can be resolved into their component elements. In this way a compound can be separated into its constituent acid and base. Now, it is a remarkable fact, that if an acid and alkaline solution be so placed that their union be effected through the parietes of an animal membrane, or indeed any other porous diaphragm, a current of electricity is evolved. This fact was first noticed by Becquerel, and has since been found to be true, not only with nitric acid and potass, during whose combination he observed this disturbance of electric equilibrium, but with all other acids and soluble bases. anxious to demonstrate the accuracy of this statement to you, although I fear the test I shall use, the deviations of the needle of an astatic galvanometer, will not be visible to all. I have here a glass tube closed at one end by an animal membrane-a piece of bladder. I fill it with a weak solution of soda, and immerse it in a glass vessel containing some diluted nitric acid. The soda and acid are gradually combining through the

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Fig. 11.

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walls of the membrane. I now plunge a plate of platinum into the acid, and connect the wire fixed to it to one screw of the galvanometer. Fixing the wire of a second plate to the other screw, I plunge it into the alkali; the needles of the galvanometer instantly start into motion, and traverse a considerable arc, pointing out the existence of a current of positive electricity from the acid to the alkali through the conducting-wires. Now, with the exception of the stomach and cæcum, the whole extent of the mucous membrane is bathed with an alkaline mucous fluid, and the external covering of the body, the skin, is as constantly exhaling an acid fluid, except in the axillary and perhaps pubic regions. The mass of the animal frame is thus placed between two great envelopes,

Fig. 11. A, a glass vessel containing a solution of soda, in which is immersed a tube, B, closed at its lower end by a piece of bladder, and filled with dilute nitric acid. Into these are immersed plates of platinum connected by the wires, C D, with the astatic galvanometer, E.

the one alkaline and the other acid, meeting only at the mouth, nostrils, and anus. This arrangement has been shown by Donné to be quite competent to the evolution of electricity; and accordingly he found that if a platinum plate connected with the galvanometer be held in the mouth, whilst a second be pressed against the moist perspiring surface of the body, the needles will instantly traverse, just as they did in the experiment I have shown with the acid and alkali. The current thus detected by Donné at once explains the cause and confirms the accuracy of the celebrated experiment of Professor Aldini, to which I have already drawn attention. I refer to that in which he excited convulsions in a frog by holding its foot in the moistened hand, and allowing the sciatic nerve to touch the tongue. His curious experiment with the head of an ox admits of a similar explanation.

A remarkably energetic current also can be thus detected when the platinum plates are plunged, one into the acid contents of the stomach of an animal, the other into the alkaline secretion of the liver. This gastro-hepatic current is of so very remarkable a character that it will once more occupy our attention.

Founded on the development of electricity by the mutual reaction of acid and alkaline fluids, Baron Liebig has expressed his opinion that the

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