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An Account of some Experiments on Galvanic Electricity made in the Theatre of the Royal Institution (1802?)1

in The Collected Works of Sir Humphry Davy, ed. John Davy (London: Smith, Elder and Co., 1839) II, 211-13.

{211} The apparatus employed in these experiments was composed of 150 series of plates of copper and zinc of 4 inches square, and 50 of silver and zinc of the same size. The metals were carefully cemented into four boxes of wood in regular order, after the manner adopted by Mr. Cruickshank, and the fluid made use of was water combined with about 1/100 part of its weight of nitric acid.2

The shock taken from the batteries in combination by the moistened hands, was not so powerful but that it could be received without any permanently disagreeable effects. Charges were readily communicated by means of them to coated jars, and to a battery; but in this case the effects produced by the electricity were much less distinct than in the case of immediate application.

When the circuit in the batteries was completed by means of small knobs of brass, the spark perceived was of a dazzling brightness, and in apparent diameter at {212} least 1/8 of an inch. It was perceived only at the moment of the contact of the metals, and it was accompanied by a noise or snap.

When instead of the metals, pieces of well-burned charcoal were employed, the spark was still larger and of a vivid whiteness, and evident combustion was produced, the charcoal remained red hot for some time after the contact and threw off bright corruscations.

Four inches of steel wire 1/170 of an inch in diameter, on being placed in the circuit became intensely white hot at the point of connection, and burnt with great vividness being at the same time red throughout the whole of their extent.

Tin, lead, and zinc, in thin shavings were fused and burnt at their points of contact in the circuit, with a vivid light and with a loud hissing noise. Zinc gave a blue flame, tin a purplish, and lead a yellow flame violet at the circumference.

When copper leaf was employed it instantly inflamed at the edges with a green light and vivid sparks, and became red hot throughout the whole of its diameter when it did not exceed four inches.

Silver leaf gave a vivid light, white in the centre and green towards the outline, with red sparks or corruscations. Platina in thin slips, when made to complete the circuit, became white hot, and entered into fusion, and gave scintillations at the edges; but whether any part was converted into oxyde could not be accurately determined.

When gold leaf, attached by gum-water to white paper was burnt by the spark, the light was of a bright yellow and the noise comparatively loud; the gold was converted into an oxyde of a purplish brown colour, which firmly adhered to the paper, and by regulating {213} the course of the spark by means of the communicating wire, letters and figures were traced by the combustion, which appeared semi-transparent when exposed to the light.

When the galvano-electric spark was taken by means of two pieces of charcoal partially covered with cotton, the cotton was readily inflamed; whether in its simple state, or sprinkled over with resin or sulphur.

Fulminating mercury and gunpowder were deflagrated by means of the communication of charcoal; and hydrogen and the compound inflammable gases, were readily made to burn when simply in contact with the atmosphere and to detonate when mixed with oxygen.

A few only of these results have any claim to originality. On the phenomena of the combustion of bodies by galvanism we have been already furnished with many striking experiments, by our own countrymen, and by the German and French philosophers. And after the path is once discovered in researches of this kind, to pursue it requires but little ability or exertion. An account of common facts, under new circumstances, particularly when they are accompanied by striking phenomena, can however never be wholly useless; and it sometimes gives a novel interest to the subject, and tends to awaken curiosity.

Notes.

1. [From Journals of the Royal Institution, vol. i.]

2. Messrs. Van Marum et Pfaff, Journal de Chemie par Van Mons, have attempted to show, that acids are less efficacious than muriate of ammonia in increasing the power of the pile; but their experiments were made with cloths, a case in which the series can only be constructed slowly, and where, when they are numerous, the acid in those first formed must be wholly or in a great measure decomposed, before the last are put together. To those who have been accustomed to operate with boxes, troughs, or glasses in which the communication by the fluids is very speedily effected, there can be no doubt of the superiority of the nitric and muriatic acids over muriate of ammonia, muriate of soda, and the alkalies in increasing all the sensible galvanic effects.