minous effluvia very plentifully, and rather in a greater degree than the glass

tube.

If we conclude with the English philosophers, that fire is mechanically producible from other bodies, by collision, attrition, &c. or, according to Sir Isaac Newton, by putting the sulphureous particles of bodies into a very strong vibratory motion; by which means they become hot and lucid, i. e. affect us with ideas of light and heat; on this supposition may we not conclude, that the action on the glass tube, when it is rubbed, by putting the parts of it into such a vibration, and consequently agitating violently the sulphureous particles in it, may heat and kindle them? and may it not also be supposed, that when the air is in a due state, nitrous or other particles in the air may contribute to the kindling them? or perhaps, rather that subtil, active, elastic substance, which Sir Isaad Newton supposes to be the cause of the refraction, &c. of light, and which communicates heat to bodies, and is universally diffused; these effluvia being thus agitated and conveyed by a non-electric body intervening, in a due quantity, to the vapour of the warmed spirit, may be supposed to kindle them, without exciting any originally resident fire in the body immediately communicating with them; the luminous effluvia from the finger, or ice, &c. when brought near the inflammable body, being, as far as we can perceive, of the very same kind with those which proceed from the tube; or there is nothing appearing in them which may lead us to suspect they are not the very same, though in a greater quantity than what can come from the part of the tube approached with the end of our finger.

If we conclude, with some of the foreign philosophers, Boerhaave, Homberg, Lemery, Gravesande, &c. that fire is equally diffused throughout the universe by the Creator, pervading the interstices of all bodies, and that there is no fire mechanically produced de novo; then, may we not conclude, that whereas, by attrition of the glass tube, there is produced a very quick and strong vibration of its parts, which must necessarily affect the fire contained in its vacuities, by compression and relaxation; so that, as Boerhaave expresses it, there must be, in the bodies thus agitated, and in the fire contained in its pores, an exceedingly great motion excited, and the surrounding fire, from both these causes, must be agitated, and so much the more violently the nearer it is; may we not conelude, that its force will be hereby sufficiently increased to kindle the spirit to which it is conveyed?

In this, as in the former hypothesis, Dr. M. would not exclude the elastic materia subtilis from being supposed to have an influence on the effluvia. Which ever of the two hypotheses we embrace, Dr. M. inclines to think, that the kindling fire rather proceeds from the excited tube.

Tooting, Feb. 15, 1745-6.

An Account of a Book intitled, De quamplurimis Phosphoris nunc primum detectis Commentarius. Auctore Jac. Barthol. Beccario, 4to. Bolognia, 1744. Extracted and translated from the Latin by W. Watson, F.R.S. N° 478, p. 81. The ingenious author, in the work before us, does not treat expressly on those productions of the chemical art, which we usually call phosphori; but principally of such substances, whether natural or artificial, as imbibe the rays of light in such quantities, and in such a manner, as to appear luminous for a time, even in absolute darkness.

The author divides the phosphori into several kinds, some of which shine of themselves naturally, as the glow-worm and dates, or adventitiously, as the flesh of animals which most probably arises from a degree of putrefaction, sometimes too slight to be obvious to our senses. Other bodies become luminous by attrition, heat, the free access of air, and, lastly, by imbibing and retaining the rays of light. Those bodies that are luminous by attrition are, among others, some diamonds, and the hairs of animals; by heat, several sorts of gems, and mountain crystals; from the free access of air, the phosphori of Kraft and Homberg; from the aspect of light, the Bolognian luminous stone, the preparation by Christian Adolphus Baldwin of chalk dissolved in spirit of nitre, as well as several others discovered by the late Mons. Du Fay, who found, that whatever substances would, by calcination, be converted into a calx, or whose concrete, from a solution in the acid of nitre, would bear fire enough to become red-hot, these bodies were adapted to imbibe and retain light.

The greatest number of phosphori are of the last mentioned kind, and these are principally the subjects of this treatise. Some of these are natural, others artificial; but of these last, the preparation is so slight, as not to change the nature of their constituent parts. The natural phosphori are either fossil, vegetable, or animal. The fossil are, though very different in degree, some sorts of earths, white sand, lime-stones, stalactites, and several other figured stones, iceland crystals, flints, some species of agates, white arsenic; but no sort of metals, metallic or sulphureous bodies, as jet, amber; except the beforementioned arsenic. On the other hand, salts imbibe light, provided they are divested of every metallic principle; otherwise not, though pellucid as possible. For this reason, none of the vitriols will imbibe light; but other salts will, though with a considerable difference as to quantity; for sal gein. and rock-salt imbibe very little, sea-salt, if dry, and in crystals, much more; and in like manner sal ammoniac; more yet, sal catharticum and nitre; weak in the natron of the ancients, and alum; but brightest of all in borax.

In the vegetable kingdom we find very few phosphori; that of dry rotten wood, is weak, and not lasting; it appears chiefly on the edges and inequalities of the E &

VOL. IX.

surface. But this is most remarkable in the rotten wood of the fir-tree, and some others, where in the dark you see shining spots as large as tares; whereas in full light the whole surface appears alike. Some few barks are luminous, but not considerably so; but no fruits, seeds, or their meals. Cotton appears very bright, and the crystals of tartar; but fine loaf sugar appears the most luminous of all, both without and within. Gums and resins retain no light.

There is a vast variety of phosphori in the animal kingdom, such as the bones and teeth; to these may be added the shells of fish, egg-shells, the human calculus, bezoar, and in whatever parts of animals the terrestrial principle is very predominant. But where there is a considerable quantity of oily matter, as in the hoofs, horns, and feathers, no light is manifest.

The author, having gone through the natural phosphori, proposes some queries concerning them; of which the first is, in what and how great a light the object ought to be placed? He tried different phosphori in different degrees of light, and found them imbibe most light from the sun itself, next in quantity, when the sky was clear, and the least in foggy weather. These experiments should be made in the open air, and not in a house with the glass windows shut; because many bodies appear luminous, when the light has come directly to them, which will not have that appearance when the light has passed through the glass. He lastly tried what light they would imbibe from very bright flame, and found that alabaster itself, which is saturated more than any substance by the sun's rays, imbibed exceedingly little. The next query is, how long these bodies should remain in the light to be sufficiently saturated; 4 or 5 seconds were found the utmost length of time required for that purpose. The other query is, how long the received light will continue in these phosphori? it does not last the same time in all; but continues more or less, from 2 seconds to 8, in proportion to the strength of the phosphorus, and the quantity of light received.

We pass now to the phosphori which are produced by art: and first to those which are made by the maceration of plants alone, and without any fire; such as thread, linen cloth, but especially paper. The luminous appearance of this last is greatly increased by heat. This is confirmed by two experiments: the first is, by exposing the paper, spread on an iron grate, to the naked fire, yet not near enough to scorch it, and then laying a warm brick on it to retain the heat; by which means it was observed, that where the paper was not skreened by the iron grate it was most luminous; so that, by the lights and shades, might be distinguished in the dark the image of the iron grate a considerable time. The other experiment is the application of the paper to a plate of warm brass; from which, when in the dark, you might very easily, by its being less luminous, distinguish the margin of the paper, that had not been warmed by the brass.

The author proceeds to take notice of those phosphori which become so by

the assistance of fire. But the fire here spoken of is not great enough to dissolve their constituent parts, but only such as may affect the external parts of their texture, and that but gently; so that the process here mentioned is only drying or roasting. For it is not the watery or the saline part in bodies which is torrefied, but the oleaginous, with which many vegetables, and most animals, abound.

The white flesh of animals, such as that of chickens, becomes a phosphorus by roasting, as well as the tendons, and whatever parts of animals become glutinous by boiling, such as carpenter's glue, ising-glass, to these may be added cheese. Bones, though they imbibe light without any preparation, have that property in a much greater degree when burnt, and their luminous appearance is much more lively. But roasting has not this effect on feathers, hoofs, horns, or whites of eggs. The same operation which produces several phosphori from the animal kingdom, gives also several from the vegetable. Thus, by gently toasting gums, as myrrh, gum tragacanth, and others, appear luminous, though different in degrees: and this light is clear, in proportion to the gentle evaporation of their aqueous parts. By this treatment nuts of every kind, pulse, corn, coffee-berries, meal, bread, and wafers, also become phosphori. Turpentine, amber, and some resins, require more fire before they imbibe light; so that you must divest them of their acid, and their light ethereal oil, to make them appear luminous. But here great care must be taken that they boil no longer than from being white they turn yellow; for by proceeding longer, your labour is lost.

It is necessary to be acquainted, that those phosphori which are produced by torrefaction, soon lose their power, which perhaps neither time, nor a thorough dissolution of their parts, can deprive the natural ones of. In general, as long as the phosphori, gained by torrefaction, preserve their power, their light is more sharp and striking, but the natural more weak. But those that are gained by calcination, and Baldwin's Phosphorus, seem to possess both the striking light of those gained by torrefaction, and the weaker light of the natural phosphori: the last they preserve a long time, but the former is lost by degrees much sooner. The well calcined ashes of plants, or rather their terrestrial parts, remaining after the solution of their fixed salts by washing, and neutral salts, continue phosphori after many years. So that, as far as we can judge, the lumiminating power which is gained by calcination, though not so intense, continues perpetual; whereas that gained by torrefaction always decreases, and in a very little time is no longer visible. Some even, by this method, continue to imbibe light much longer than others. Gum Arabic, which continues longest, lasts 6 days; bread, not one; and coffee, only a few minutes. However, at any time, by a fresh torrefaction, you may recover these languid phosphori; in which pro

perty they greatly resemble the Bolognian stone, and other phosphori prepared by art. The phosphori gained by torrefaction, as well as that of Bologna, will not imbibe light, while they are warm; and this last does not appear so luminous when first prepared, as when it has been so some time.

The natural phosphori do not differ only in the beforementioned particulars, but also in the colour of the light itself. The light of the natural generally appears either perfectly bright, or somewhat inclining to yellow; the artificial produces a red, and sometimes a brown light; but there are some exceptions to both these rules. From these different appearances, the author conjectures, that there are two sorts of fire arising from different principles; viz. that in torrefied substances, from a sulphureous, and that of the natural, from a terrestrial principle.

In observing a piece of lapis tutiæ, which was rough and unequal on its convex side, smooth and somewhat polished on the concave; he found, to his surprise, that the rough side was luminous, and the smooth one not. He was very desirous of investigating the cause of this appearance. He remembered that some polished marbles did not imbibe light, or very little, and that at their edges; but, having lost their polish, they admitted and retained it. He therefore conjectures that bodies, according to the disposition of their surfaces for the reflection of the light, either suffer or prevent its entrance into them. If this position holds good in the reflection, why should it not with regard to the refraction? our author produces 2 experiments, which he apprehends not foreign to the present purpose, but is yet making others, for his further satisfaction. He exposed a glass bottle full of well-water to the light, and as soon as possible observed it in the dark. As he expected, it imbibed no light. On pouring into it some oil of tartar, it became turbid and whitish, from the well-water being usually impregnated with calcareous matter. On observing it then in the dark, after having been exposed as before, it retained enough of a pale light to distinguish the shape of the bottle. In a bottle of rain-water he dissolved some talc; which stone, by rubbing, will dissolve in water as salts do, without rendering it opaque; to this solution he added oil of tartar, and this mixture was luminous as the preceding. He therefore concludes, that so long as earthy corpuscles are very small, separate, and agreeing in their surfaces with the water in which they float, they readily transmit the light they receive; for which reason it is impossible they should retain light enough to appear luminous in the dark. But, by the affusion of the saline principle, the earthy corpuscles unite with the water and salt; and from the union of these principles the mixture grows thick, by which the ready transmission of light is prevented; so that if this mixture is without colour, or any thing metallic, the light will be stopped long enough to be visible in the dark. But if, instead of oil of tartar, we add sugar of lead,