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"2dly, The friction of the piston, which is a greasy body, against a metallic substance, is not calculated to produce electricity.

"3dly, Experience demonstrates, that, unless during storms, the atmosphere seldom exhibits any signs of electricity at the height in which we breathe it; and that we must search for them with instruments in a more elevated region, or when electric clouds are passing over our heads. How then shall we estimate the infinitely small quantity of electric matter in a cubic inch of air, or even less, which the instrument contains ?

"4thly, It is not' without great difficulty, that we can kindle spunk with strong electric sparks. I have discharged a large jar on spunk strewed with powdered resin, and it has remained unkindled, though the resin caught fire, and burned entirely away.

"As long as the instrument was made with metallic substances only, we were obliged to confine ourselves to the exterior marks, of inflammation alone, without being able to assign the true cause, or at least furnish proofs of it. For to guess is not sufficient in natural philosophy; we must demonstrate, in order to give to facts: that degree of certainty, which befits science; and this we cannot do here, without seeing what passes at the very point of inflammation.

Nothing is necessary, but to
Those found in the shops being

"The means are very simple. substitute a glass for a metal tube. too slight, I applied to Mr. Laurent, the inventor of glass flutes, requesting him to procure me tubes of a similar quality. This artis, as much distinguished by his civility as by his talents, fur. nished me with three, which I fitted up. The first eight inches long by eight lines in diameter, did not kindle the spunk. The second, nine inches long by six lines and three quarters in diameter, kindled it completely. This being destroyed by accident, Itried the third, eight inches long by seven lines in diameter, which suc. ceeded equally well.

"When the instrument is made to act, and the spunk kindles, we see a bright flash, that fills the capacity of the tube; and this light is so much the more vivid, in proportion as the compression is more rapid. If the compression be less powerful, the spunk does not kindle, but we perceive in the upper part of the tube a light vapour, that falls in undulations on the piston. When this has disappeared, if we draw back the piston, the vapour will reappear, as long as there is any air in the tube. These effects may

be produced several times in succession, merely by pushing the piston with the hand. This vapour is so thin and diaphanous, that it is not perceptible in a strong light. It requires a sort of twilight to see it well.

"But whence arises this vapour, and what is its nature? As. suredly it is not furnished by the materials of the instrument; it can only proceed, therefore, from what it contains, from the atmospheric air. Now, according to the present state of our knowledge, the air contains only nitrogen, oxygen, and a very small portion of carbonic acid; all gassiform substances, which are kept in this state by the great quantity of caloric that penetrates them, and are consequently heavier than it. But in compressing the air con tained in the tube, what is the substance that must first give way? Is it not that which is lightest, the caloric, that general solvent, that principle of fluidity and volatilization, which gives wings even to metals to raise themselves in the air? Is then the vapour in ques tion caloric, rendered visible by the approximation of its particles, which are compressed by the surrounding air, as air becomes visible in passing through liquids? This idea, which I am far from presenting as a thing proved, acquires more probability from the fol. lowing experiments.

"I substituted hydrogen for common air, and the vapour showed itself as before; but the spunk did not take fire. With carbonic acid gass, and with nitrogen, the effects were the same. The latter, which contained a little nitrous gas, gave a somewhat denser vapour. Oxygen, lightly compressed, yielded a vapour more rare and transient than that from common air. It had scarcely fallen on the piston when it rebounded and disappeared. When I compressed oxygen with a proper force for producing in. flammation, the spunk, which commonly takes fire only at the anterior part, was almost entirely burned: yet for this experiment I used a copper instrument, the piston of which lost air so much, that it would no longer kindle spunk (with common air).

"Perhaps it will be said, that the vapour came from the greasy matter on the piston, which adheres to the sides of the tube; and that it is expanded by the heat produced by the friction. To this I answer, in this case, 1st. The vapour should not shew itself be fore the greasy matter is deposited on the sides of the tube; yet it appears at the first stroke of the piston, before the tube becomes greasy. 2dly, It should show itself below the piston, in the part

which the piston has left; but, on the contrary, it always shows above. 3dly. There is no vapour, when the piston loses much air, if the friction be ever so rapid. 4thly. The vapour should be more apparent, when the piston exerts its friction throughout the whole length of the tube, than when it is confined to a small part of its upper extremity; yet the reverse frequently happens. 5thly. When the air is entirely decomposed no more vapour appears, but it shows itself again, if ever so little fresh air be introduced.

"As it was essential to ascertain whether the vapour did not contain an acid principle, I fastened to the surface of the piston, with a little green wax, a piece of muslin dipped in infusion of litmus, and afterward dried. After twenty strokes of the piston the colour was not changed. I put on a second piece of muslin larger than the first, and the edges of which were loose. This was burned all round, without the colour of the rest being altered. Lastly, a third piece, which was wet, experienced no change of colour.

"From these experiments it follows, that no acid principle is developed; that all aëriform substances, as well as common air, produce a light vapour; that no other gass, except oxygen and common air, kindles the spunk; that oxygen produces a much more powerful combustion than common air, cousequently oxygen acts an important part in the inflammation; that as it can exert its action only when set free by the decomposition of the common air, of which it constitutes a fourth part, it follows, that the air contained in the tube is decomposed by the simple force of compres sion; that the vapour produced is not owing to the oxygen, since it shows itself equally in gasses that contain no oxygen; that this vapour is the effect of some agent common to all gasses; and that we may presume it is caloric itself, rendered visible by the sudden approximation of its parts in a small space, where it rises to a temperature that is increased in the oxygen so as to kindle the spunk.

"It sometimes happens, that the spunk is turned black without kindling. In this case, as well as when it is kindled, if we draw back the piston in the tube, a dense vapour, that may be smelt, issues out, which is not of the same nature as the former. That shows itself before the inflammation: this always succeeds it. That is the principle of the inflammation: this a product furnished by the combustion of the spunk, of which it has the smell."

[Le Bouvier. Desmortiers. Journ. de Physique.

CHAP. VIII.

PHOSPHORESCENCE, OR SPONTANEOUS ILLUMINATION, ANIMAL, VEGETABLE, AND MINERAL.

Tuis is a most extraordinary and interesting subject, and a perusal of the three preceding chapters will, in a considerable degree, enable the reader to understand its general principles, though there is much that has hitherto eluded pursuit, and still remains to be developed.

Phosphorescence, in its broadest latitude, imports light thrown forth from substances that at the same time emit little or no heat at the common temperature of the atmosphere, and which are denominated phosphoric.

The phosphorus properly so called, and which is usually understood in chemical books, and employed in chemical processes, is that commonly known by the name of Kunckel's phosphorus, and which we shall describe under that designation. But there are various other substances that possess, in different degrees, the same kind of illuminating power, and which it is hence necessary to take some notice of, as well as of the effects they produce.

Of these kinds the phosphorescent substances there are three leading divisions. The first comprehends those which require a previous exposure to the solar or other light, in order to become luminous; whence they are called solar phosphori: the second includes those which, without any necessary previous exposure to light, become luminous when moderately heated, which are denominated calorized phosphori, or phosphori from heat: the third comprehends those substances belonging to the animal and vegetable kingdoms, which emit light spontaneously at the common temperature, without the necessity of a previous exposure to light, and these are called spontaneous phosphori.

SECTION I.

Solar Phosphori.

A CASUAL discovery by Vincenzio Cascariolo, a shoemaker of Bologna, about 1630, was the first circumstance that attracted the notice of philosophers to this curious subject. This man being in

quest of some alchemical secret was induced to calcine a parcel of Bolognian spar (a sub-species of heavy spar or native sulphat of baryte), which he had procured from Monte Pateruo, in the neighbourhood of the city; and observed, that whenever this substance, thus prepared, was placed in a dark room, after having been exposed to the sun, it continued to emit faint rays of light for some hours afterwards.

In consequence of this interesting discovery, the Bolognian spar came into considerable demand among natural philosophers, and the curious in general, so that the best way of preparing it was found an object of some pecuniary importance. This seems to have been hit upon by the family of Zagoni, who supplied all Eu. rope with Bolognian phosphorus, till the discovery of more power. ful phosphoric put an end to their monopoly. Margraaf, some years afterwards, proved that other species of sulphated baryte might, under particular management, be made to produce a simi lar effect.

In the year 1677, nearly half a century after the discovery of the Bolognian phosphorus, G. A. Baldwin, a native of Misnia, observed, that if nitrat of lime were evaporated to dryness, and then formed into a compact mass by fusion at a red heat, it would exhibit the same property of imbibing and emitting light as the former, only somewhat inferior in degree: hence this preparation obtained the name of Baldwin's phosphorus.

Iu 1730, M. du Fay, who is justly celebrated for his electrical researches, directed his attention to this subject, and observed, that all earthy substances, susceptible of calcination, either by mere fire, or when assisted by the previous action of nitrous acid, possessed the property of becoming more or less luminous when calcined and exposed for a short time to the light: that the most perfect of these phosphori were limestones, and other kinds of carbonated lime, gypsum, and particularly the topaz; and that some diamonds were also observed to be luminous by simple exposure to the sun's rays, without being previously ignited; while flint, sand, jasper, agate, and rock crystal, were inphospho

rescent.

Not long after, M. Beccaria discovered that a great variety of other bodies were convertible into phosphori, by exposure to the mere light of the sun; not only the varieties of carburet and sul. phat of lime, but organic animal remains, and geodes lined with

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