with each other by means of platina wires, one of which was introduced into the chlorate of potassa in the one tube, and the other into the potassium in the other. The position of the tubes in the tray are represented Fig. 1. I now filled the tray with plaster of Paris and coal-ash, and upon this mixture I placed an iron plate, on which were laid two weights, forty pounds each. The tray with the weights was placed on a common fire, the fireplace of which was so constructed, that an intense heat might at any time be produced. As oxygen would come off from the chlorate of potassa, when the temperature of that salt was raised, I inferred that the intense heat to which the oxygen and potassium would be subjected, would disunite positive electricity from the oxygen, and negative electricity from the potassium; and that the two electricities thus set free would escape by the platina wires, and unite with each other, heat being the product. After the tray which had been brought to a red heat had cooled down sufficiently, I proceeded to examine its contents. Both tubes were entire. I opened at one extremity the tube which contained the potassium, a portion of which fell out, and presented very much the external characters of carbon. Its metallic lustre was gone; and when thrown upon water, there was

neither combustion nor action of any kind. I introduced a sharp-pointed wire into the tube, with a view of extracting what remained of the potassium ; but the instant that I touched the potassium with the wire, the whole exploded in my hand. How is it that the properties and external characters of this substance were so very different from the properties and external characters of potassium? Is it that potassium, deprived of its negative electricity, possesses properties and external characters, such as I have described? I now examined the contents of the other tube. It was evident that oxygen had been disengaged from the chlorate of potassa, and that the residual constituents were those of the chloride of potassium. The only other change which had taken place was, that the surface of the tube appeared to be bedewed with moisture.

5. This first experiment was an earnest of what I might realise when provided with a suitable apparatus, and with those tubes which resist an intense heat, without fusion and without fracture. In the prosecution of my experiments, I found that flint glass tubes were not suitable, as they contained lead in their composition, which renders them easily fusible, and the materials which I introduced into them were generally blown out, or a rupture of the

tubes took place. From some difficulty, which I could not explain, I failed to obtain, though every effort was made on my part, those tubes which contain no lead in their composition, and which resist fusibility while exposed to an intense heat. Having, however, partially succeeded in my first experiment, I persisted in operating with such tubes as I could procure, unsuitable though they were, resolved either to verify my views on electro-chemistry, or prove them fallacious; and it was not until after years of toil and failure, I at last obtained a positive result, which proves that there is a latent electricity existing in bodies as well as a latent heat.

6. At the close of 1856, I procured one of those German glass tubes that contain no lead in their composition, and into which I poured a small portion of nitric acid; but as another tube was required, I substituted a tube of iron, into which I introduced a few grains of caustic potash. Both tubes were hermetically sealed, and contained platina wires which were not joined together externally as is represented in Fig. 1., but were kept apart from each other, and made to project beyond the tray, through two small perforations in one of its sides, as is represented in Fig. 2.

The iron tube deposited in the tray was insulated by inclosing it in a tube of glass, while the platina wires which passed through the small perforations in the side of the tray were encased in capillary tubes. The extremities of the wires which projected beyond the tray dipped into a small bent tube that contained a solution of the iodide of potassium. In every other respect the experiment was conducted precisely as that which I had performed in 1849. In the course of the experiment, I found that the solution of the iodide of potassium was decomposed; the appearance of the iodide was first made manifest in the limb of the tube into which the wire from the tube containing the nitric acid was introduced. From what source was the electricity derived by

which the iodide of potassium was decomposed? There can be no escape, I should think, from the conclusion that the positive electricity was derived from the acid, and the negative electricity from the alkali.

7. The materials with which I operate are necessarily so very small in quantity, particularly when I introduce liquids into glass tubes, that the results, though positive, may be thought trivial. Thus when I introduce nitric acid into a glass tube, I first fill it with acid, which is afterwards decanted, and the tube is kept inverted until all the acid has dropped from it, leaving only as much acid as adheres to the platinum wire and the internal surface of the tube. The quantity of acid which remains is not more than two grains, or one grain and a half; if more than this, the rupture of the tube, when exposed to an intense heat, generally take place. It indeed requires a nice adjustment in respect to the quantity of the materials with which I operate, as well as the requisite hardness and thickness of the tubes which I employ, in order to resist, without fusion and without fracture, the degree of heat to which, in the course of my experiments, they are subjected.

8. In October, 1857, I obtained what I had hitherto failed to procure-those German glass tubes