weeks together,) the clear portion afforded a crystalline salt on evaporation, having the characters of muriate of potash.

It may be remarked that this solution, when perfectly clear, contained no lead, on testing for it by sulphuretted hydrogen; but upon agitating or diffusing the fine powder of glass through water, holding the gas in solution, it was immediately discoloured, or blackened.

Flint-glass, although chosen for the above experiments, is not the only variety possessing this remarkable property, crown and plate-glass, white enamel, and what is more remarkable, Newcastle green-bottle glass, and tube of the same material, (in the composition of which there is, comparatively, little alkali,) also Reaumur's porcelain, made from the green bottle glass, possess the power of acting upon vegetable colours as alkalies.

These experiments, tending to prove that glass is a body of irregular composition, parting readily with its alkali by the action of water, it became a matter of some interest to determine how far certain natural combinations of potash with siliceous matter were equally active to the same tests, especially as in green-bottle glass, which contains little alkali, it is thus rendered evident. No analogous effect could, however, be produced by powders of felspar, basalt, green-stone, granite, obsidian, pumice, and some others, even when boiled with water, a method which never failed to produce it rapidly with glass, although cold water is perfectly sufficient.

Some interesting conclusions may be drawn from the above experiments, which may tend to explain several well-known phenomena, and may, perhaps, become matters of practical utility.

In the first place, with regard to the glasses employed in the laboratory, or for domestic uses, it must be evident that water has the power of acting upon and dissolving the alkali at the surface, and leaving an insoluble portion spread as a coating over the interior of the vessel, defending it from further immediate action.

Where, however, time can be allowed, the effect does not

appear to be confined to mere surface. In collections of ancient glass, specimens may be selected, exhibiting how extensively an analogous action has been going on during the period they have remained buried in the earth. These vitreous relics of antiquity are often covered, to a considerable thickness, with opal pearly scales of beautiful appearance, consisting almost wholly of silica, whose alkali had been removed probably by the action of the water*.

A fragment of transparent ancient glass was examined with regard to its alkaline property, which it was found to enjoy in a high degree, being sensibly alkaline (when in powder) to the tongue, and its hot solution acting upon the cuticle. It appeared to consist almost entirely of potash and silica; not the smallest trace of lead being discoverable in it; several other coloured specimens of ancient glass, upon examination, were, in every case, more highly alkaline than any modern glass containing lead, that has hitherto been examined.

The specific gravity of common flint-glass was taken by way of comparison with the ancient fragments above mentioned, the result of which is here given. Flint-glass, S.G., 3.208. Ancient glass, 2.375. It may here be remarked, that the latter acted powerfully upon the test-paper, by merely moistening it, without reduction to powder. It cannot be surprising, therefore, that ancient glass, which may almost be called pure silicate of potash, should be occasionally found in states of such rapid decay, as the specimens in collections often exhibit.

Another proof of the action of water, aided by other concomitant circumstances, in producing decomposition upon glass, is an account given in Vol. I. p. 135 of this Journal, of some bottles of wine found in a quantity of black mud at the bottom of an old well, full of burned wood, supposed, upon good authority, to be of anterior date to the fire of London. The siliceous earth, in this instance, separated in films on the surface of the bottle, in consequence of the abstraction of alkaline matter, probably

*The opal is an hydrate of silica: may not its formation have taken place by a similar agency acting upon natural combinations? The removal of alkali from siliceous compounds may have left opal thus constituted.

264 Mr. Griffiths on the Action of Water upon Glass.

by the action of water, aided perhaps originally by a certain degree of heat, and afterwards by the long period of their continuance, in a situation favourable to the decomposing agency.

In contact with ammoniacal, or decomposing animal matter, the disintegration of glass takes place more rapidly. Stablewindows, and bottles kept in such situations, often present a very beautiful iridescent appearance, in consequence of the siliceous matter being developed in thin plates on its surface, often amounting to a pearly, and sometimes almost metallic appearance; an effect which, it is believed, has not been hitherto investigated.

Solution of potash acts very rapidly upon glass, as the chemist often inconveniently learns by the effect produced upon the bulb of a thermometer, employed to determine its boiling point, and which is always found corroded to a considerable extent after the experiment.

It may also here be remarked (although not perhaps immediately connected with the subject), that from frequent observations by a person in the habit of using solid carbonate of ammonia, that the flint-glass bottles in which it has been for some time kept are invariably rendered much more brittle, and pieces of glass fall out upon very slight motion of its contents. This fact is merely mentioned as curious, and may probably be hereafter more fully examined.

ART. V.-Analyses of two Mineral Waters from Springs in Windsor Great Park. By W. T. Brande, F. R. S., Prof. Chem. R. I.

THESE waters were sent to me about a twelvemonth ago for analysis, and as I understand that since that period the springs have been much frequented, an account of their contents may not be unacceptable to those who have derived benefit from their use.

In taste, these waters exactly resemble each other, though one is manifestly more abundant in saline matter; their taste is

Mr. Brande on the Mineral Waters of Windsor. 265

salt and slightly bitter, without the smallest admixture of any chalybeate flavour.

The specific gravity of the stronger water is 1010.4; that of the weaker, 1007.7. Of the former, one pint measure (holding one pound avoirdupois of distilled water at 60°) afforded, on evaporation, 88 grains of dry saline residue; of the latter, a pint measure yielded 65 grains of residue. As the contents of these waters almost exactly resemble each other in quality, it will only be necessary particularly to describe the nature of the stronger spring.

On applying heat to the water, a small portion of carbonic acid escaped, it gradually became opalescent; and when it boiled, was turbid, and let fall a white powder, which was presumed to be carbonate of lime, deposited, as is usually the case, in consequence of the loss of the excess of carbonic acid previously holding it in solution. But on examining the precipitate, it was found to be carbonate of magnesia, the source of which was not at first very obvious, more especially as the water was slightly alkaline after having been somewhat reduced by evaporation.

A pint of the water mixed with excess of carbonate of ammonia, and boiled down so as to precipitate the earths of the earthy salts, afforded a mixture of carbonate of lime and of carbonate of magnesia, which being dissolved in excess of muriatic acid, neutralized by ammonia, and decomposed by oxalate of ammonia, yielded a precipitate, from which 1.25 grains of lime were obtained. The remaining solution, evaporated to dryness and exposed to a red heat, afforded a residue of 21.25 grains of magnesia.

The only alkali present in the water was soda, which, estimated in the state of sulphate, amounted to 10.52 grains of dry soda.

The quantity of sulphuric and muriatic acids present was determined by precipitation with muriate of baryta and nitrate of silver -the former furnished a precipitate equivalent to 33 grains of dry sulphuric acid-and the latter to 21 grains of muriatic acid. The combined carbonic acid in the water was estimated at 0.98 grains,

From the preceding statement it appears, that the substances present in a pint of the stronger water are as follow:

Various opinions may be formed respecting the nature of the saline combinations resulting from the union of these proximate elements. From the successive separation of the saline contents during the evaporation of the water, I am induced to consider them arranged as follows, forming the solid contents of a pint of the water, viz.:

Grains.

38.0

24.5

9.3.

10.8

3.0

2.4

88.0

The singular property of this water, that when boiled it throws down carbonate of magnesia, appears to depend upon the action of the carbonate of soda, which, though compatible with the earthy salts in a cold and dilute solution, decomposes them at a boiling heat, or when concentrated by evaporation. This has been verified by artificial imitations of this mineral water; and it has even been found that sesqui-carbonate of soda, in such excess as powerfully to redden turmeric paper, is compatible, not only in solutions containing the salts of magnesia, but also in those holding the more soluble salts of lime. In both these cases, precipitates are obtained by boiling, and by evaporation-otherwise the solutions remain transparent.