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forter wires were calcined, the colours were more varied. A place is given of the stain 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 description can give an adequate idea.
On discharging the battery through eight inches of tin wire, i's of an inch diameter, extended over a sheet of paper, a thick cloud of blue smoke arose, in which many calcareous fila. ments were discernible ; at the same 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 surface for several seconds. The paper was marked with a yellowish clouded stain, immediately under the wise, and with streaks or rays of the same colour, issuing from it in every direction : some of these formed an uninterrupted line, others were made up of separate spors. In order to be certain that the colour of these streaks was not caused by the paper being scorched, the experiment was several times repeated, when a plate of glass, and a board covered with tin were placed to receive the globules. These, however, were stained exactly like the paper. On calcining five inches of the same kind of wire, the red-hot globules were thrown obliquely to the height of four feet, which afforded an opportunity of observing that each globule, in its course, diffured a matter like smoke, which continued to appear for a litele while in the parabolic line described by its fight, 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, issuing from their lower part, strikes against its surface, and, being elastic, forces them upwards again by its reaction. The clouded stain immediately under the wire, the Doctor attributes to the instantaneous calcination of its surface, whereas the remainder of the metal is melted into globules, which, while they recain their glowing heat, continue to be superficially calcined, and, during the process, part with this calcareous vapour.
Phenomena, something similar to the above, were observed on the calcination of a wire, of equal parts of tin and lead, eight inches long, and y'a 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 streaks of the same kind, but of a brown colour, edged with a yellow tinge. Some of these globules, though apparently not less hot, moved with less velocity than others, and were soon stopped in their course, by their burning a hole in the paper. In this case, a yellow matter was seen to rise from their
surface, surface, 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 seconds, to issue from the globules, and formed, on their surface, a kind of eflorescence, resembling the Aowers of sulphur produced by the folfaterra. The globules, from which these calcareous flowers had iffued, were found to be entirely hollow, and to consist of only a thin shell. When this mixed metal is calcined with a less charge of the battery, it leaves a stain upon the paper, something fimilar to that made by lead, and does not run into globules.
The Doctor has also given plates of the stains made upon paper, by the calcination of iron, copper, brass, silver, and gold.
Those 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, öö of an inch in diameter, were, by the explosion, reduced to a purple substance, of which a part rose like a thick smoke, and the remainder, falling on the paper, left a ftain diversified with different shades of this colour. Gold, silver, and copper, cannot easily be melted into globules; our author has once accidentally succeeded in this; but it required a degree of electrical force so very particular, that the medium between a charge, which only broke the wire into pieces, and one which entirely calcined it, could not be ascertained by the electrometer. .
In accounting for these 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. Ac. cording to this theory, of which, in an Appendix to this work, he has given an excellent analyfis, the metal, when, by the explosion, it has acquired a certain degree of heat, attracts, from the atmosphere, the principle of pure air (called, by M. Lavoisier, the oxiginous, or acidifying principle), in the same man. ner 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 absorbed in different degrees of calcination; and that this variety is much greater in calcination by electricity, than in the same operation by fire, may be accounted for, when we consider that, by the discharge of the battery, various degrees of heat are instantaneously acquired by different parts of the fame wire, which thus absorb 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 duit, which was diffused upon the wall, along which the wire had been conducted.
Though Dr. VAN MARUM was convinced, by M. Lavrifer's experiments, that metals, calcined in atmospherical air, abiorb from is that principle, which renders it fit for respiration ; yer he resolved further to investigate this point, by trying what would be the effect of a discharge of the battery through a piece of wire confined in phlogisticated air. For this purpose, he took air, in which a burning coal had been extinguished, and which had afterwards stood eight days upon water, that it might be entirely cleared from fixed air ; with this, he filled a glass cylinder, four inches in diameter, and fix inches high, closed at the upper end with a brass plate; from the center of this plate the wire was fufpended, on which the experiment was made. The cylinder was set in a pewter dish filled with water, and, to prevent is being broken by the expansion of the air, its lower edges were supported by two pieces of wood half an inch high. The lower end of the wire rested on the dish, which was connected with the outside coating of the battery.
On transmitting the charge, in this manner, through wires of lead, tin, and iron, of only half the length of thole which were calcined by an equal explosion in atmospheric air, no calcination took place. The first was reduced to a fine powder, which, upon trial by spirit of nitre, appeared to be merely lead ; the two other metals were melted into small globules.
The Doctor then tried the same experiment in pure, or dephlogisticated air, obtained from red precipitate ; thinking that, in this, the metals would be more highly calcined, than in common air. His expectation was aniwered only by the lead, which was entirely reduced to a yellow calx, perfectly resembling mafticor. 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 some reconds, even in the water, and to melt holes in the pewter dish into which they fell.
In nitrous air, calcination took place as easily as in common, or in dephlogisticated air; this was contrary to Dr. VAN MARUM's expectation; but he accounts for it, by observing that, from the experiments of Mr Cavendish, and of M. Lavoisier, pure air appears to be one of the component parts of the nitrous acid.
In order to illuftrate M. Lavoisier's theory, Dr. Van MARUM resolved to examine the phenomena resulting 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 surface, and the calx rose, like a cloud, through the water. This, he think's, is not so easily accounted for, by the theory of Stahl, as by that of M. Lavoisier, because, according to the former, water does not
readily either receive, or part: with phlogiston; whereas the latter supposes this fluid to be composed or the oxiginous principle, united with that of inflammable air: if this be true, nothing more is necessary to calcination, than that the metal thould acquire a greater affinity, with the oxiginous principle, than subfifts between this, and ihat of inflammable air, united with it in the composition of water. To collect che air, generated by these calcinations, was no easy matter; as the violence of the shock broke the glass receivers employed for this purpose ; at last, however, the Doctor contrived a method of receiving it in a glazed stone balon. From the first calcination of lead, about a quarter of a cubic inch of air was produced, which fewed no signs of inflammability; bur, on every repetition of the experiment, a less quantity of air was generated ; and, on an accurate trial of that produced by the fourth calcinacion in the same water, it was found to consist of one part of inflammable, and three of atmospherical air. Our author designs to repeat these experiments with water deprived of its air, by being boiled.
In order to imitate the phenomena of earthquakes, this ingenious philosopher followed Dr. PRIESTLEY's method, and made the electrical explosion pass over a board, floating on water, on which several columns of wood were erected, but this fucceeded only once. - Refecting that the electric explosion exerts the greatest lateral force when it passes through imperfect conductors, and that water is, probably, its principal subterraneous conductor, he laid two smooth boards upon each other, ooistening the fides in contact with water ; upon the upp:rmost, he placed pieces of wood, in imitation of builling:, the 'ales of which were 3 inches long, and 1 3 broad. When the char e of the battery was transmited between the boards, all there were thrown down by the tremulous and undu.atory motion of that on which they stood.
In the next chapter, Dr. VAN MARUM gives an account of his attempt to repeat that intereiting expernnen', made by Mr. Cavendith, in which he produced the nitrous acid, by a mixture of pure, with phlogisticated air *. Inttead of a syphon, the Doctor made use of a glais cube, one-(xin part of an inch in diameter, closed at one end, into which an iron wire, te of an inch in diameter, had been inserted : into this tube, filled wih mercury, and fixed in a veriical pofition, was introduced ine air, with which the experiment was to be tried. The dopnjo. gisticated air was obtained from red precipicace, and had been thoroughly puriñed, by alkaline falis, from any acid it might have contained. With a mixture of five parts of this, and
* See Monthly Review, vol. Ixxiv. p. 321.
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 same kind with that used by Mr. Cavendilb. The result was, that, after transmitting through the tube a continued stream of the eletrico! Auid during fifteen minutes, two inches of the air were al forbed by the lixivium : more air being introduced into the cube, till it was filled to the height of three inches, it was a vain electrified. This process was repeated, till 84 inches of air had been absorbed by the lixivium : this was now examined, and found to be, in some degree, impregnated with the nitrous acid; but it was very far from being faturated. With the same Jixivium, of which a quarter of an inch remained in the tuhe, the experiment was continued till 14 inches more of air had been absorbed; but its diminution was not perceived to decrease, 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 measures of air were absorbed by the alkali. But, notwithstanding this greater absorption, the lixivium was yet far from being saturated.
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 phlo. gisticated air, and lixivium added to the height of of an inch, Here, as in the former experiment, the diminution continued without any decrease; and the lixivium, after it had absorbed 22 inches, and consequently 178 times its own meafore 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 Thaking mercury with lead, he requested to be informed of the process by which it is generated; but Mr. Cavendish, not chusing to commupicate this at present, he determined to defer the repetition of the experimeni, will this ingenious philosopher shall bave pub. Jished his mode of obtaining the pure air used in it.
The following chapter contains a relation of some experie ments made by suffering the electric fluid to pass in a continued It:eain through various kinds of air, inclosed, for this purpose, in the little glass cube used in the last experiments.
Pure air, obrained the week before from red precipitate, being placed over mercury, and electrified for thirty minutes, was die minished by one-fifth, the surface of the quicksilver soon began to be calcined, and, towards the end of the experiment, the glass tube was so lined with the calx as to cease to be transparent. By introducing a piece of iron, the electric stream was made to pass through the air without immediately couching the mercury; yet this was equally calcined. This phenomenon the Doctor
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