shorter wires were calcined, the colours were more varied.

A plate is given of the ftain made by the calcination of eight inches of this wire, in which the cloud appears variously shaded with different tints of green, gray, and brown, in a manner of which no defcription can give an adequate idea.

On difcharging the battery through eight inches of tin wire, of an inch diameter, extended over a fheet of paper, a thick cloud of blue fmoke arofe, in which many calcareous filaments were difcernible; at the fame time a great number of red hot globules of tin, falling upon the paper, were repeatedly thrown up again into the air, and continued thus to rebound from its furface for feveral feconds. The paper was marked with a yellowish clouded ftain, immediately under the wire, and with ftreaks or rays of the fame colour, iffuing from it in every direction: fome of thefe formed an uninterrupted line, others were made up of feparate fpots. In order to be certain that the colour of thefe ftreaks was not caufed by the paper being fcorched, the experiment was feveral times repeated, when a plate of glafs, and a board covered with tin were placed to receive the globules. Thefe, however, were ftained exactly like the paper. On calcining five inches of the fame kind of wire, the red-hot globules were thrown obliquely to the height of four feet, which afforded an opportunity of obferving that each globule, in its courfe, diffufed a matter like fmoke, which continued to appear for a little while in the parabolic line defcribed by its flight, forming a track, in the air, of about half an inch in breadth.

From this phenomenon, Dr. VAN MARUM conjectures, that when the globules approach the paper on which they fall, the matter, iffuing from their lower part, ftrikes against its furface, and, being elaftic, forces them upwards again by its reaction. The clouded ftain immediately under the wire, the Doctor attributes to the inftantaneous calcination of its furface, whereas the remainder of the metal is melted into globules, which, while they retain their glowing heat, continue to be fuperficially calcined, and, during the procefs, part with this calcareous vapour.

Phenomena, fomething fimilar to the above, were observed on the calcination of a wire, of equal parts of tin and lead, eight inches long, and of an inch in diameter. This also was melted into red hot globules, which were repeatedly driven upwards again from the paper on which they fell, and marked it with ftreaks of the fame kind, but of a brown colour, edged with a yellow tinge. Some of thefe globules, though apparently not lefs hot, moved with lefs velocity than others, and were foon ftopped in their course, by their burning a hole in the paper. In this cafe, a yellow matter was feen to rife from their

furface,

furface, to the height of one or two lines, which extended itself. to the width of a quarter of an inch. This matter continued, during five or fix feconds, to iffue from the globules, and formed, on their furface, a kind of efflorefcence, réfembling the flowers of fulphur produced by the falfaterra. The globules, from which thefe calcareous flowers had iffued, were found to be entirely hollow, and to confift of only a thin fhell. When this mixed metal is calcined with a lefs charge of the battery, it leaves a ftain upon the paper, fomething fimilar to that made by lead, and does not run into globules.

The Doctor has alfo given plates of the ftains made upon paper, by the calcination of iron, copper, brafs, filver, and gold. Thofe made by copper and brass wires are remarkably beautiful, and are variegated with yellow, green, and a very bright brown. Eight inches of gold wire, of an inch in diameter, were, by the explofion, reduced to a purple fubftance, of which a part rofe like a thick fmoke, and the remainder, falling on the paper, left a ftain diverfified with different fhades of this colour. Gold, filver, and copper, cannot eafily be melted into globules; our author has once accidentally fucceeded in this; but it required a degree of electrical force fo very particular, that the medium between a charge, which only broke the wire into pieces, and one which entirely calcined it, could not be afcertained by the electrometer.

In accounting for thefe calcinations, Dr. VAN MARUM has adopted the theory of M. Lavoisier, to which he was converted from the Stahlian hypothefis, by attending upon the experiments of the French academicians in the year 1785. According to this theory, of which, in an Appendix to this work, he has given an excellent analyfis, the metal, when, by the explofion, it has acquired a certain degree of heat, attracts, from the atmosphere, the principle of pure air (called, by M. Lavoifier, the oxiginous, or acidifying principle), in the fame manner as when it is calcined by fire; the variety of colours, with which it ftains the paper, is owing to the various proportions of this principle abforbed in different degrees of calcination; and that this variety is much greater in calcination by electricity, than in the fame operation by fire, may be accounted for, when we confider that, by the difcharge of the battery, various degrees of heat are inftantaneously acquired by different parts of the fame wire, which thus abforb the oxiginous principle in different proportions.

This chapter is closed with an account, communicated to our author by M. Faujas de St. Fond, of the calcination of an iron bell wire by lightning, at Montelimar in Dauphiné, where the metal was reduced into a reddish brown duft, which was diffufed upon the wall, along which the wire had been conducted.

Though

ww

Though Dr. VAN MARUM was convinced, by M. Lavifier's experiments, that metals, calcined in atmospherical air, abforb from it that principle, which renders it fit for respiration; yet he refolved further to investigate this point, by trying what would be the effect of a difcharge of the battery through a piece of wire confined in phlogifticated air. For this purpose, he took air, in which a burning coal had been extinguished, and which had afterwards flood eight days upon water, that it might be entirely cleared from fixed air; with this, he filled a glafs cylinder, four inches in diameter, and fix inches high, clofed at the upper end with a brafs plate; from the center of this plate the wire was fufpended, on which the experiment was made. The cylinder was fet in a pewter difh filled with water, and, to prevent its being broken by the expanfion of the air, its lower edges were fupported by two pieces of wood half an inch high. The lower end of the wire refted on the difh, which was connected with the outfide coating of the battery.

On tranfmitting the charge, in this manner, through wires. of lead, tin, and tron, of only half the length of thole which were calcined by an equal explofion in atmofpheric air, no calcination took place. The first was reduced to a fine powder, which, upon trial by fpirit of nitre, appeared to be merely lead; the two other metals were melted into small globules.

The Doctor then tried the fame experiment in pure, or dephlogifticated air, obtained from red precipitate; thinking that, in this, the metals would be more highly calcined, than in common air. His expectation was answered only by the lead, which was entirely reduced to a yellow calx, perfectly refembling mafticot. The other metals were not more highly calcined in this, than in common air; but the globules of iron acquired fo great a heat, as to retain it for fome feconds, even in the water, and to melt holes in the pewter difh into which they fell.

In nitrous air, calcination took place as eafily as in common, or in dephlogifticated air; this was contrary to Dr. VAN MARUM's expectation; but he accounts for it, by obferving that, from the experiments of Mr Cavendish, and of M. Lavoifier, pure air appears to be one of the component parts of the nitrous acid.

In order to illuftrate M. Lavoifier's theory, Dr. VAN MARUM refolved to examine the phenomena refulting from the calcination of metals in water. This he tried with both iron and lead, and found that, in the moment of the explosion, a number of air-bubbles appeared on the furface, and the calx rofe, like a cloud, through the water. This, he thinks, is not feafily accounted for, by the theory of Stakl, as by that of M. Lavoisier, becaufe, according to the former, water does not readily

10

readily either receive, or part with phlogifton; whereas the latter fuppofes this fluid to be composed of the oxiginous principle, united with that of inflammable air: if this be true, nothing more is neceffary to calcination, than that the metal fhould acquire a greater affinity, with the oxiginous principle, than fubfifts between this, and that of inflammable air, united with it in the compofition of water. To collect the air, generated by these calcinations, was no eafy matter; as the violence of the fhock broke the glafs receivers employed for this purpose; at last, however, the Doctor contrived a method of receiving it in a glazed stone bafon. From the first calcination of lead, about a quarter of a cubic inch of air was produced, which fhewed no figns of inflammability; but, on every repetition. of the experiment, a lefs quantity of air was generated; and, on an accurate trial of that produced by the fourth calcination in the fame water, it was found to confift of one part of inflammable, and three of atmospherical air. Our author defigns to repeat these experiments with water deprived of its air, by being boiled.

In order to imitate the phenomena of earthquakes, this ingenious philofopher followed Dr. PRIESTLEY'S method, and made the electrical explofion pafs over a board, floating on water, on which feveral columns of wood were erected; but this fucceeded only once. Reflecting that the electric explosion exerts the greateft lateral force when it paffes through imperfect conductors, and that water is, probably, its principal fubterraneous conductor, he laid two smooth boards upon each other, moistening the fides in contact with water; upon the uppermost, he placed pieces of wood, in imitation of buildings, the bafes of which were 3 inches long, and 1 broad. When the charge of the battery was tranfmitted between the boards, all there were thrown down by the tremulous and undu.atory motion of that on which they ftood.

In the next chapter, Dr. VAN MARUM gives an account of his attempt to repeat that interesting expertinent, made by Mr. Cavendish, in which he produced the nitrous acid, by a mixture of pure, with phlogifticated air *. Instead of a syphon, the Doctor made ufe of a glais tube, one-sixth part of an inch in diameter, closed at one end, into which an iron wire, 13% of an inch in diameter, had been inferted into this tube, filled with mercury, and fixed in a vertical pofition, was introduced the air, with which the experiment was to be tried. The dephiogifticated air was obtained from red precipitate, and had been thoroughly purified, by alkaline falts, from any acid it might have contained, With a mixture of five parts of this, and

* See Monthly Review, vol. lxxiv. p. 321.

three

three of common air, the tube was filled to the height of three inches, to which was added of an inch of lixivium, of the fame kind with that ufed by Mr. Cavendish. The refult was, that, after tranfmitting through the tube a continued ftream of the electrical fluid during fifteen minutes, two inches of the air were abforbed by the lixivium: more air being introduced into the tube, till it was filled to the height of three inches, it was again electrified. This procefs was repeated, till 8 inches of air had been abforbed by the lixivium: this was now examined, and found to be, in fome degree, impregnated with the nitrous acid; but it was very far from being faturated. With the fame lixivium, of which a quarter of an inch remained in the tube, the experiment was continued till 14 inches more of air had been abforbed; but its diminution was not perceived to decreafe, though the lixivium had now absorbed 77 measures of air, each equal to its own; whereas, in the experiment related by Mr. Cavendish, only 38 meafures of air were abforbed by the alkali. But, notwithstanding this greater abforption, the lixivium was yet far from being faturated.

The experiment was repeated with pure air, produced by minium, moistened with the vitriolic acid, and deprived of its fixed air; seven parts of this were mixed with three of phlogifticated air, and lixivium added to the height of of an inch. Here, as in the former experiment, the diminution continued without any decreafe; and the lixivium, after it had abforbed 22 inches, and confequently 178 times its own measure of air, was very far from being faturated with the nitrous acid.

On this, Dr. Van Marum wrote to Mr. Cavendish, and finding, by his answer, that this gentleman had used pure air, obtained from a black powder produced by fhaking mercury with lead, he requested to be informed of the process by which it is generated; but Mr. Cavendish, not chufing to communicate this at prefent, he determined to defer the repetition of the experiment, till this ingenious philofopher fhall have published his mode of obtaining the pure air used in it.

The following chapter contains a relation of fome experiments made by fuffering the electric fluid to pass in a continued ftream through various kinds of air, inclofed, for this purpose, in the little glafs tube ufed in the laft experiments.

Pure air, obtained the week before from red precipitate, being placed over mercury, and electrified for thirty minutes, was diminished by one-fifth, the furface of the quickfilver foon began to be calcined, and, towards the end of the experiment, the glafs tube was fo lined with the calx as to ceafe to be tranfparent. By introducing a piece of iron, the electric ftream was made to país through the air without immediately touching the mercury; yet this was equally calcined. This phenomenon the Doctor

afcribes