diminution of size, and the saline beads on cooling assumed their usual opacity.

(D) A bit of Tabasheer was laid on a plate of silver, and a little litharge was put over it, and then melted with the blow-pipe. It immediately acted on the Tabasheer, and covered it with a white glassy glazing. By the addition of more litharge the mass was brought to a round bead; though with considerable difficulty. This bead bore melting on the charcoal, without any reduction of the lead, but could not be obtained transparent.

(E) The ease with which this substance had melted with vegetable ashes, led to the trial of it with pure calcareous earth. A fragment of Tabasheer, fixed to the end of a bit of glass, was rubbed over with some powdered whiting. As soon as exposed to the flame of the blow-pipe, it melted with considerable effervescence; but could not, even on the charcoal, and with the addition of more whiting, be brought to a transparent state, or reduced into a round bead.

Equal weights of Tabasheer and pure calcareous spar, both reduced to fine powder, were irregularly mixed, and exposed in the platina crucible to a strong fire in a forge for 20'; but did not even concrete together.

(F) When magnesia was used, no fusion took place at the blow-pipe.

(G) Equal parts of Tabasheer, whiting, and earth of alum precipitated by mild volatile alkali, were mixed in a state of powder, and submitted in the platina crucible to a strong fire for 20', but were afterwards found unmelted.

Examination of the other specimens.

No. I.

This parcel contained particles of three kinds; some white, of a smooth texture, much resembling the foregoing sort; others of the same appearance, but yellowish; and others greatly similar to bits of dried mould.

The white and yellowish pieces were so soft as to be very

easily rubbed to powder between the fingers. They had a disagreeable taste, something like that of rhubarb. Put into water, the white bits scarcely grew at all transparent; but the yellow ones became so to a considerable degree.

The brown earth-like pieces were harder than the above, had little taste, floated upon water, and remained opaque. Exposed to the blow-pipe, they all charred and grew black; the last variety even burned with a flame. When the vegetable matter was consumed, the pieces remained white, and then had exactly the appearance, and possessed all the properties, of the foregoing Tabasheer from Hydrabad, and like it melted with soda into a transparent glass.

No. II.

Also consisted of bits of three sorts.

(a) Some white, nearly opaque.

(b) A few small very transparent particles, shewing, in an eminent degree, the blue and yellow colour, by the different direction of light.

(c) Coarse, brownish pieces of a grained texture.

These all had exactly the same taste, hardness, &c., and shewed the same effects at the blow-pipe, as No. I.

27 gr. of this Tabasheer thrown into a red-hot crucible, burned with a yellowish white flame, lost 2.9 gr. in weight, and became so similar to the Hydrabad kind as not to be distinguished from it.

Some of this Tabasheer put into a crucible, not made very hot emitted a smell something like tobacco ashes, but not the kind of perfume discovered in that from Hydrabad, § IV. (E).

No. IV.

All the pieces of this parcel were of one appearance, and a good deal resembled, in their texture, the third variety of No. II. Their colour was white; their hardness such as very difficultly to be broken by pressure between the fingers.

In the mouth they immediately fell to a pulpy powder, and had no taste.

A bit exposed on the charcoal to the blow-pipe became black, melted like some vegetable matters, caught flame, and burnt to a botryoid inflated coal, which soon entirely consumed away, and vanished.

A piece put into water fell to a powder. The mixture being boiled, this powder dissolved, and turned the whole to a jelly.

These properties are exactly those of common starch.

No. V.

Agreed entirely with No. IV. in appearance, properties, and nature.

No. VI.

The pieces of this parcel were white, quite opaque, and considerably hard. Their taste and effects at the blow-pipe, were perfectly similar to those of the Hydrabad kind.

No. VII.

Much resembled No. VI. only was rather softer, and seemed to blacken a little when first heated. With fluxes at the blow-pipe it shewed the same effects as all the above.

Conclusion.

1. It appears from these experiments, that all the parcels, except No. IV. and V. consisted of genuine Tabasheer; but that those kinds, immediately taken from the plant, contained a certain portion of a vegetable matter, which was wanting in the specimens procured from the shops, and which had probably been deprived of this admixture by calcination, of which operation a partial blackness, observable on some of the pieces of No. III. and VI. are doubtless the traces. This accounts also for the superior hardness and diminished tastes of these sorts.

2. The nature of this substance is very different from what might have been expected in the product of a vegetable. Its indestructibility by fire; its total resistance to acids; its uniting by fusion with alkalies in certain proportions into a white opaque mass, in others into a transparent permanent glass; and its being again separable from these compounds, entirely unchanged by acids, &c., seem to afford the strongest reasons to consider it as perfectly identical with common siliceous earth.

Yet from pure quartz it may be thought to differ in some material particulars; such as in its fusing with calcareous earth, in some of its effects with liquid alkalies, in its taste, and its specific gravity.

But its taste may arise merely from its divided state, for chalk and powdery magnesia both have tastes, and tastes which are very similar to that of pure Tabasheer; but when these earths are taken in the denser state of crystals, they are found to be quite insipid; so Tabasheer, when made more solid by exposure to a pretty strong heat, is no longer perceived, when chewed, to act upon the palate, § IV. (A).

And, on accurate comparison, its effects with liquid alkalies have not appeared peculiar; for though it was found on trial, that the powder of common flints, when boiled in some of the same liquid caustic alkali employed at § IX. (A) was scarcely at all acted upon; and that the very little which was dissolved, was soon precipitated again, in the form of minute flocculi, on exposing the solution to the air, and was immediately thrown down on the admixture of an acid; yet the precipitate obtained from liquor silicum by marine acid was discovered, even when dry to dissolve readily in this alkali, but while still moist to do so very copiously, even without the assistance of heat; and some of this solution, thus saturated with siliceous matter by ebullition, being exposed to the air in a shallow glass, became a jelly by the next day, and the day after dried, and cracked, &c., exactly like the mixtures § IX. (D and E). And another portion of this solution mixed with marine acid afforded no precipi

tate, and remained perfectly unaffected for two days; but on the third it was converted into a firm jelly like that § IX. (F).

As gypsum is found to melt per se at the blow-pipe, though refractory to the strongest heat that can be made in a furnace, it was thought that possibly siliceous and calcareous earths might flux together by this means, though they resist the utmost power of common fires; but experiment showed that in this respect quartz did not agree with Tabasheer. But this difference seems much too likely to depend on the admixture of a little foreign matter in the latter body, to admit of its being made the grounds for considering it as a new substance, in opposition to so many more material points in which it agrees with silex.

Nor can much weight be laid on the inferior specific gravity of a body so very porous. The infusibility of the mixture § XIII. (G) depended also, probably, either on an inaccuracy in the proportions of the earths to each other, or on a deficiency of heat.

3. Of the three bamboos which were not split before the Royal Society, I have opened two. The Tabasheer found in them agreed entirely in its properties with that of No. I. and II.

It was observed that all the Tabasheer in the same joint was exactly of the same appearance. In one joint it was all similar to the yellowish sort No. I. In another joint of the same bamboo, it resembled the variety (c) of No. II. Probably, therefore, the parcels from Dr. RUSSELL, containing each several varieties of this substance, arose from the produce of many joints having been mixed together.

4. The ashes, obtained by burning the bamboo, boiled in marine acid, left a very large quantity of a whitish insoluble powder, which, fused at the blow-pipe with soda, effervesced and formed a transparent glass. Only the middle part of the joints was burned, the knots were sawed off, lest being porous, Tabasheer might be mechanically lodged in them. However, the great quantity of this remaining