which would render it impossible to draw any conclusion as to the exact temperature, yet still the experiments appeared to offer, on any view, interesting results; and I was the more desirous of performing them, as I believe the nature of the fluid and aeriform matters included in rock crystals and other siliceous stones, has never been accurately ascertained.

Having purchased some crystals, and having had others committed to my care by the liberality of my Brother Trustees of the British Museum, and of my friend Prof. Buckland, I proceeded to make the necessary experiments upon them. It will be improper for me to take up the time of the Society by a minute description of my manipulations. Holes were drilled in the crystals by the use of diamonds, generally by Mr. Newman, under distilled water, or mercury, the gas was expelled by the introduction of wires, and the fluids included in the cavities were drawn out by means of fine capillary tubes, and experiments were afterwards made to determine the space they occupied, which had been accurately measured and marked upon the crystal. The chemical nature of the fluid and gas was determined by processes which were necessarily difficult from the smallness of the quantities operated upon; but which are too well known to the chemical philosophers of this Society to need description.

The first three crystals that I examined were from Schemnitz, in Hungary; the cavities that they contained were proved not to be permeable to the atmosphere, by exposure to rarefied air, alone, and under water, in the receiver of an air-pump, a circumstance which it was necessary always to attend to, in order to render the experiment availing,

A cavity in one of the crystals was pierced under oil, three under distilled water, and one under mercury. In all of them the fluid rushed in when the cavity was opened, and the globule of elastic fluid contracted so as to appear from six to ten times less than before the experiment. The fluid in all the crystals (in two it was minutely examined) was found to be water nearly pure, containing only a minute portion of the alkaline sulphates. The elastic fluid, as well as I could ascertain from the very minute quantities I could procure, appeared to be azote, unmixed any

other substance, The largest cavity, which was in the crystal put into my hands by Prof. Buckland, contained a space equal to 74.5 grains of mercury; the water in it equalled in volume 48•l grain measures of mercury; and the globule of air, after the experiment, equalled in diameter a globule of mercury weighing 4-2 grains, so that the elastic fluid had contracted at least between six and seven times.

In the other experiments, the cavities being much smaller the quantities of air and Auid could not be accurately measured; but there seemed to be nearly the same relation between the space

with

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filled by fluid, and that containing aeriform matter; and in all of them the contraction of the globule of aeriform matter was evidently greater, and in one instance to less than 1-10th of its original bulk.

The fourth crystal that I experimented upon was of unknown locality; but I have reason to believe that it was from Guanaxuato, in Mexico, as it strongly resembled some that Mr. Heuland showed me from that place. The cavity in it was extremely small, and when pierced into, under distilled water, the globule of gas, from being one-eighth of an inch in diameter,* diminished so as to be less than 1-25th ; so that its rarefaction was much greater in this than in the other instances; the water was too small in quantity to be minutely examined; it seemed to be nearly pure, producing a cloudiness barely perceptible in solutions of nitrate of silver and muriate of baryta.

It was an interesting point to ascertain whether the same circumstances occurred in productions found in rocks which have been generally considered as of igneous origin, such as the basaltic rocks in the neighbourhood of Vicenza, the chalcedonies of which so often afford included water. I found it much more easy to make experiments of this kind, and to procure specimens, which were abundantly supplied to me from the same sources as those I have just referred to; and though some of these specimens proved to be permeable to the atmosphere, and to have been filled with water artificially, yet many occurred, in which the sides of the cavity were absolutely impervious to air or water.

The results that I obtained were very analogous. Water containing very minute quantities of saline impregnations, occasioning barely a visible cloudiness in solutions of silver and of muriate of baryta, was found to be the fluid; the gas was azote, but it was in a much more rarefied state than in the rock crystals, being between 60 and 70 times as rare as atmospheric air.

The quantity of water was to the void space in greater propor-tion than in the rock crystals. In the instance in which the most accurate experiment was made; namely, on the great specimen preserved in the collection of the British Museum, and which weighed 380 grains, the quantity of water was 29.9 grains, the space occupied by aeriform matter was equal to 11.7 grains of water, the volume of the globule of gas at the common pressure was to that of its rarefied volume as 1 to 63.

It occurred to me that atmospheric air might have been originally the elastic fluid included in these siliceous stones and in the crystals, and that the oxygen might have been separated from the azote by the attraction of the water, and a direct experiment

seemed to confirm this idea. A chalcedony which had been bored was placed in water free from air under a receiver, which was exhausted till a portion of gas from the interior of the crystal had escaped into a proper receptacle. This gas examined by nitrous gas was found to contain nearly as much oxygen as atmospheric air ; so that there is every reason to believe that the water had emitted oxygen during the exhaustion.

I endeavoured to find some calcareous secondary rocks, or crystals belonging to them, containing cavities, on which experiments of the same kind might be made ; but in a number of trials, I have as yet found none impermeable to the atmosphere; and the cavities of such, when bored, are always found to contain atmospheric air in a common state of density.

I was surprised to find that this was the case even with cavities in calcareous spar in the centre of a limestone rock ; yet these cavities which contained atmospheric air did not fill with water when the stone was placed in water under an exhausted receiver. When, however, it was dry, and placed in a receiver alternately exhausted and filled with hydrogen, the air that was produced by piercing the cavities, was found mixed with hydrogen; proving that the substance of the stone was permeable to elastic fluid.

I hope soon to be able to make further researches on this subject; but in reasoning upon the vacuum, or rarefied state of the aeriform matter in the cavities of these rock crystals and chalcedonies, it appears difficult to account for the phenomenon, except on the supposition of their being formed at a higher temperature than that now belonging to the surface of the globe; and the most probable supposition seems to be, that the water and the silica were in chemical union, and separated from each other by cooling

Water in the temperature of the arctic winter is constantly a crystallized body. As a fluid, its solvent powers are increased as its heat becomes higher, and, when elastic, the density of its vapour is exalted in proportion to its heat; so that an atmosphere of steam, supplied from an indefinite source above water, would render it capable of receiving a very high degree of heat. Lime retains water in combination at a heat above 250° Fahrenheit; baryta retains it (even under ordinary pressures) at a strong red heat, and fuses with it. It is extremely likely that a liquid hydrate of silica would exist, under pressure, at high temperatures ; and like all 'liquid bodies in the atmosphere, would pro

; bably contain small quantities of atmospheric air; and such a supposition only is necessary to account for the phenomena presented by the water in rock crystal and chalcedony.

As, however, steam or aqueous vapour may be considered as having a share in these results, if it be supposed included in the cavity, no exact conclusions can be drawn from the

apparent degree of contraction of the water; particularly as the late inge

nious researches of Mr. Perkins show, that water is much more compressible than was formerly imagined; and the volume of water, however high its temperature, must be influenced by the pressure to which it is exposed; so that a certain compressing weight may, not only impede, but altogether counteract, the expansive force of heat.

Many speculations might be indulged in on this subject, but I shall not at present enter upon them; and I shall conclude by observing, that a fact, which has been considered by the Neptunists, above all others as hostile to the idea of the igneous origin of crystalline rocks, namely, the existence of water in them, seems to afford a decisive argument in favour of the opinion it has been brought forward to oppose.

APPENDIX. Since the foregoing pages were communicated to the Royal Society, I have made some new experiments on the same subject; all of them, except two, offered results of the saine kind as those I have detailed, and upon such I shall not enter; but these two, from their peculiarity, will not, I trust, be thought unworthy of a particular notice.

In examining, with Mr. Heuland, the beautiful specimens of rock crystals in the collection of Charles Hampden Turner, Esq. I observed one crystal which, Mr. Heuland informed me, was from La Gardette, in Dauphiné, that contained a considerable cavity, in which there was a viscid brownish liquid, resembling in its appearance and consistence linseed oil. As the void space or cavity filled with aeriform matter appeared considerable in proportion to the fluid, I expressed a desire to pierce the crystal; and Mr. Turner, hearing of my wish, was so kind as to gratify it in the most polite and liberal manner, by presenting to me the specimen. With Mr. Newman's assistance I made the usual experiments upon it. The cavity was pyramidal, and nearly the third of an inch in diameter. I soon ascertained that the fluid was not water, as it congealed and became opaque at a temperature of 56o. When the crystal was pierced under distilled water, the water rushed in and entirely filled the cavity, so that no other aeriformn matter but the vapour of the substance could have been present : the water was rendered white and cloudy, apparently by the substance. I endeavoured to collect some of it for chemical examination, but it was too small in quantity (not equalling in volume one-sixth of the volume of the cavity), to be submitted to analysis. It swam on the water, had no distinct taste, but a smell resembling naphtha; a portion of it taken out mixed with the water, when exposed to heat acted like fixed oil

, and it seemed to have a high temperature of ebullition. It inflamed, producing a white smoke.

The fact, of almost a perfect vacuum existing in a cavity con

taining an expansible but difficultly volatile substance, may be,
considered as highly favourable to the theory of the igneous,
origin of crystals: the other experiment is of a nature entirely,
different, though its result may be explained in the same suppo-
sition.

In examining a crystal in the collection of the Royal Institu-
tion, and which from its characters I believe to be from Capab
d'Olanda, Province of Minas Geraes, Brazil, I observed that the
quantity of aeriform matter was unusually small in proportion to
the quantity of fluid, in two or three cavities not occupying one-
tenth or one-twelfth of the space; and from the peculiarity of
its motion, it appeared to be more likely to be compressed than
rarefied elastic fluid; and in piercing the sides of the cavities, I
found that this was the case; it enlarged in volume from ten to
twelve times ; the fuid was water, but the gas was, too minute

;
in quantity to be examined.

It will be interesting to ascertain under what circumstances,
and in what situations, crystals of this kind are found.

If they be supposed of igneous origin, they must have been formed under an immense weight of atmosphere or fluid, sufficient to produce a compression

much more than adequate to compensate. for the expansive effects of heat, a supposition which, in consequence of Mr. Perkins's experiments, already alluded to, may be

, easily formed.

ARTICLE V.

On Grey Whin. By N. J. Winch, Esq.

(To the Editor of the Annals of Philosophy.) DEAR SIR,

Newcastle-upon-Tyne, Dec. 18, 1822. THOUGH I believe it to be generally known to such of your readers as have paid attention to the geology of Britain, that the workmen engaged in the collieries and quarries of the north of England and Scotland apply the term whin not only to basalt or greenstone, but to niost other species of hard stone, yet I am not aware that a peculiar rock called by them grey whin has ever attracted particular notice. The rock constituting the stratum, or possibly strata in question, consists of minute grains of hairbrown compact felspar or clinkstone, with a few spangles of silvery mica scattered through it. From the close cohesion of its small particles, it might be mistaken at first sight for clinkstone, strongly resembling the well-known rock of Lamlash, but by a lens, the granular texture is detected, and the difference between them easily proved. Owing to this compact texture,

New Series, vol. V.

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