MATHEMATICAL, PHYSICAL, AND NATURAL SCIENCES.

ART. VII.-On a new Hydrated Silicate of Potash, and on some of the conditions under which the Reniform Structure in Minerals may be developed. By WILLIAM K. SULLIVAN.

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[Read before the Royal Irish Academy, December 9, 1861.]

BOUT two years ago I wanted a solution of silicate of potash for some experiments with which I was then engaged, and accordingly prepared it, by fusing a mixture of finely powdered vein quartz with about four times its weight of purified pearl ash, in a Cornish crucible. The melted glass was poured out on a cold plate of iron, and when cold was broken into lumps, and put into a large glass jar about half full of water. On being stirred about from time to time during a couple of days, the smaller fragments nearly all completely dissolved, while the larger lumps were only superficially acted upon. The solution thus formed having been found strong enough for the purposes for which the silicate was prepared, was poured off and fresh water poured upon the lumps, which were frequently stirred during two or three days, by which a second solution, but very much weaker than the first, was obtained. At this period my experiments were interrupted, and the jar containing the solution and the undissolved lumps was put away in a cupboard, where it remained undisturbed for nearly a year. I then found that some of the lumps still remained, to a great extent, undissolved, but a great number had softened into a pasty mass, in which were disseminated here and there the unsoftened lumps. The whole of this pasty gelatinous mass was not immediately derived from the softening of the lumps, as a part appeared to have been precipitated from the supernatant liquor, so that the uneven surface formed by the original pasty mass was filled up and partially covered over by a thin layer of gelatinous silica, like that formed by precipitating a solution of basic silicate by soluble carbonates or by a solution of sal ammoniac. Upon the top of this pasty mass, beautiful white warty concretions had formed, the whole being covered by about six inches. of water. The borders of the warts were serrated, the serrations being produced by the projecting ends of fine prismatic needles. In every instance the warts formed over a lump of

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undissolved silicate, being largest where the lump came closest to the surface of the pasty mass.

The jar, tightly covered with writing-paper, was again laid aside, but in a place where it could be frequently examined. The warts gradually increased in number, each new one appearing to commence over a lump, or where the pasty mass was thickest and most granular, until at length they extended into a continuous snow-white crust. The positions of the warts in this crust were marked by raised prominences. raised prominences. The crust thus formed continued to increase in thickness, the fresh depositions appearing to begin, as at first, over the lumps, so that the raised prominences became more and more marked, until a distinct reniform structure was developed. While this growth was taking place, the water had gradually evaporated, until not more than an inch covered the crust, and the pasty mass had become quite gelatinous.

The supernatant liquor, which was a solution of carbonate of potash, containing only a mere trace of silica, was poured off, and the crust removed as carefully as possible. The latter was very fragile, the slightest pressure reducing it to a pulpy mass. The gelatinous mass upon which the crust rested had a yellowish colour; left in the jar, it gradually dried and cracked." Part of it, when dried, consisted of an opaque whitish gray substance, mottled with pure white, which was very friable when dried for some minutes in a water bath. Another part, however, was semi-translucent, hard, and very like some varieties of opal, and contained water even after having been exposed to dry air for several months. A very hard semi-translucent fragment contained, when first removed from the jar, 23.27 per cent. of water, which would correspond to SiO,,HO; but after some months exposure to dry air, it was reduced to 9.59 per cent., or 3SiO2,HO. In both cases the fragment still contained some carbonate of potash, so that no very accurate analysis of it could be made. The gelatinous precipitate formed by passing carbonic acid through soluble silicate of potash, even when exposed to the air in considerable mass until it became dry, yielded only an amorphous white anhydrous powder, or one containing only small and variable quantities of water. A hydrate containing 16.5 per cent. of water, and which may be represented by the formula 3SiO2,2HO, (=SiO,,HO) appears, however, to have been obtained by dropping slowly hydrochloric acid into a solution of basic silicate of potash of moderate strength, and drying the gelatinous precipitate in a vacuum or in dry air. This hydrate consisted of a white powder; but M. Doveri obtained a similar hydrate in the crystalline state by precipitating a solution of silicate of copper dissolved in hydrochloric

acid, by sulphide of hydrogen, and evaporating the perfectly limpid solution of silica over quick lime in a vacuum. When the hydrate 3SiO2,2HO in the form of a white powder was exposed for some time to the temperature of 100° to 120° Cent., it lost half its water, and formed a definite compound, represented by the formula 3SiO,,HO (=2SiO,,HO), that is, the same compound as that which was formed by the exposure of my hard semi-translucent silica for some months to dry air. The latter, to which I have above assigned the formula SiO2,HO (=2SiO3,3HO), has the same composition as the remarkable glassy hydrated silica obtained by Ebelman by exposing silicic ether to the slow action of moist air. So far as I am aware, the two hydrates which I have described are the only examples of definite hydrated silica having been obtained in the form of opal. A strong solution of silicate of potash put into a Briet's apparatus, charged in the ordinary way with bicarbonate of soda and tartaric acid, and left undisturbed for a few months, and then exposed to the air until it dried, was horny here and there. The quantity of water in many varieties of opal and hyalite is so small that some mineralogists consider it not to be chemically combined in those minerals. In what state, then, is it? Hydrated water may be held with so feeble a force as to appear attached merely by cohesion. Mr. A. Gages, in a paper read before the British Association at Leeds, described an opaque silicious skeleton which he obtained by the long continued action of acids upon a mineral, and which became transparent like hydrophane when plunged into water. The quantity of water necessary to effect this change appeared to be definite; the phenomenon was certainly an excellent example of mechanical cohesion passing into chemical. Opal, hyalite, etc., as well as the semi-translucent gummy hydrated silica just described, probably belong to the same category. The formation of some horny hydrated silica in the Briet's apparatus, is interesting, as showing that time influences the combining power of water and silica. A similar influence appears to be exerted upon carbon.c acid dissolved in water under pressure, because, the longer it is subject to the pressure, the more slowly it appears to be evolved when the pressure is removed.

The gummy silica which adhered to the white crust, was removed as carefully as possible while the crust was still moist; the latter was then placed upon dry filtering paper, which was frequently renewed so as to imbibe all the moisture. A portion was broken into small fragments, and laid upon dry filtering paper under a bell-glass along with a sulphuric acid desiccating dish filled with water. The air being always saturated with mois

ture, the carbonate of potash in the substance deliquesced, and was absorbed by the filtering paper. The operation was repeated until dry paper was no longer wetted by the crust. So completely was the carbonate of potash removed by this process, that even after an exposure of several months to the air under a large bell-glass, which was frequently lifted in order to allow the substance to be moved about on the paper, it only yielded a few minute bubbles of carbonic acid when treated with acid.

Thus dried, it formed small porous lumps, which crushed between the fingers into a snow-white gritty crystalline powder, formed of extremely fine oblique prismatic needles. Heated in a crucible to a red heat, it lost water; heated in the blow-pipe flame, it fused into a milky-looking glass, which under a very strong heat became transparent. Thus fused, it was scarcely acted upon by boiling oil of vitriol, even though boiled with it for some hours. In the hydrated state, it was decomposed by boiling concentrated hydrochloric acid, but only very slowly; it was readily attacked by oil of vitriol. For the purposes of analysis a small quantity of the powder, produced by crushing the lumps between paper, was shaken up with distilled water for some minutes, in order to remove as far as possible all traces of carbonate of potash, placed upon filtering paper, and repeatedly pressed, and then dried at a temperature of about 60° Cent. in a current of air. The substance was decomposed by concentrated hydrochloric acid, and the silica and potash directly determined, the latter being weighed as chloride. The results of the analysis led to the formula KO,5SiO2,14HO, as the following table shows:

A portion of the unbroken crust under which the filtering paper was changed only a few times, was left to dry gradually. As it did so, some carbonate of potash effloresced on it; this was derived from the mother liquor, and not from the decomposition of the compound, as a portion of the latter left to dry for several months, and then well washed, had the same composition as that above given. During the drying the crust exfoliated into thin layers, which were often perfect shells wherever there was a reniform prominence. In many of those shells a fibrous structure could be distinctly traced, the fibres appearing to converge, as in globular minerals having a fibrous structure, such as wavelite, etc.

The formation of this hydrated silicate of potash may perhaps

be attributed to two, or even three causes. Firstly, the carbonic acid of the air was gradually absorbed and combined with the potash of the basic silicate, by which gelatinous silicate was precipitated upon the lumps of undissolved silicate. Secondly, the lumps, in slowly dissolving, formed an almost concentrated solution of basic silicate in their neighbourhood; this solution produced a diffusive current, which slowly brought a portion of the solution of carbonate of potash from the surface, where it had continued to absorb more carbonic acid after the precipitation of the gelatinous silicate; this solution must therefore have contained some bicarbonate of potash, and on coming in contact with the solution of basic silicate, must have produced carbonate of potash, and a less basic silicate of potash, which, if rapidly formed, would be precipitated as a powder, but being very slowly formed, crystallized out in obedience to any direction impressed upon the molecules by the molecular forces in action in the solution and underlying mass. This change would of course take place more rapidly where the solution would be densest, that is, near the undissolved lumps, and hence the warty crystallizations would begin there. But a third cause may also aid in producing the latter result. We know that a glass rod, a piece of glass, or other object projecting from the bottom of a vessel containing a saline solution, will generally induce crystals to form upon it: a crystal of the salt in solution dropped into it will still more strikingly act in the same way. It may be, then, that the lumps acted as so many centres of cohesive force, which acted the more rapidly the nearer they were to the surface of contact of the pasty mass and supernatant liquor.

ART. VIII.—On the Structural Anatomy and Physiology of the Muscular System of Animal Life. By THOMAS HAYDEN, F.R.C.S.I.

IT is proposed in the present article to consider a few of the

many points of interest relating to the Physiology of the Muscular System which still remain to be definitely settled.

It is obvious that, as a preliminary step to an inquiry of this nature, having for its object the elucidation of the vital and physical endowments of Muscle, a full and definite comprehension of its structure becomes indispensable; but, as many and different opinions are still held upon this subject by distinguished