found in gold or silver by fusing the slightest scrapings of them with a little lead, &c., &c.

Cut into very small, very acute triangles, clay affords a substitute for Saussure's sappare.

AN IMPROVED METHOD OF MAKING COFFEE.

From Thomson's Annals of Philosophy, Vol. XXII; New Series, Vol. VI, 1823, page 30.

June 4, 1823.

SIR: From the highly fugacious nature of that part of coffee on which its fine flavour depends, a practice has become very generally adopted of late years of preparing the liquor by mere percolation.

This method has not only the great defect of being excessively wasteful, but the coffee is likewise apt to be cold. Coction and the preservation of the fragrant matter are, however, not inconsistent. The union of these advantages is attainable by performing the operation in a close vessel. To obviate the production of vapour, by which the vessel would be ruptured, the boiling temperature must be obtained in a water-bath.

In my experiments I made use of a glass phial closed with a cork, at first left loose to allow the exit of the air. Cold water was put to the coffee.

This process is equally applicable to tea.

Perhaps it may also be employed advantageously in the boiling of hops, during which, I understand, that a material portion of their aroma is dissipated; as likewise possibly for making certain medical decoctions.

This way of preparing coffee and tea presents various advantages. It is productive of a very considerable economy, since by allowing of any continuance of the coction without the least injury to the goodness, all the soluble matter may

be extracted, and consequently a proportionate less quantity of them becomes required. By allowing the coffee to cool in the closed vessel, it may be filtered through paper, then returned into the closed vessel, and heated again, and thus had of the most perfect clearness without any foreign addition to it, by which coffee is impaired. The liquors may be kept for any length of time at a boiling heat, in private families, coffee houses, &c., so as to be ready at the very instant called for.

It will likewise prove of no small conveniency to travellers who have neither kettle, nor coffee-pot, nor tea-pot, in places where these articles are not to be procured, as a bottle will supply them.

In all cases means of economy tend to augment and diffuse comforts and happiness. They bring within the reach of the many what wasteful proceedings confine to the few. By diminishing expenditure on one article, they allow of some other enjoyment. which was before unattainable. A reduction on quantity permits indulgence in superior quality. In the present instance, the importance of economy is particularly great, since it is applied to matters of high price, which constitute one of the daily meals of a large portion of the population of the earth.

That in cookery also, the power of subjecting for an indefinite duration to a boiling heat, without the slightest dependition of volatile matter, will admit of beneficial application, is unquestionable.

A DISCOVERY OF CHLORIDE OF POTASSIUM IN THE EARTH.

From Thomson's Annals of Philosophy, Vol. XXII; New Series, Vol. VI, 1823, page 258.

SIR A RED ferruginous mass, containing veins of a white crystalline matter, part of a block which was said to have been thrown out of Vesuvius during a late eruption, was brought to me, with a request that I would tell what it was.

This red ferruginous rock was a spongy lava, in the substance of which was here and there lodged a crystal of augite or pyroxene of Haüy, or of hornblende.

The white matter filled most of the larger cavities, and was more or less disseminated through nearly the whole of the mass.

It had a saline appearance; a tabular fracture could be seen in it with a lens, and in some few places regular cubical crystals were discernible.

I supposed it to be chloride of sodium, or muriate of ammonia.

Heated in a matrass, it decrepitated slightly, and melted, but little or nothing sublimed.

This white matter dissolved entirely in water. Laid on silver with sulphate of copper, it produced an intense black stain.

Chloride of barium added to the solution caused only a very slight turbidness, due probably to some sulphate of lime which is present.

Tartaric acid occasioned an abundant formation of crystals of tartar. Chloride of platinum immediately threw down a precipitate, and distinct octahedral crystals of the same nature afterwards appeared.

On decomposition by nitric acid, only prismatic crystals of nitrate of potash could be perceived. On a second crys

tallization, a few rhombic crystals were discovered; but nitrate of potash sometimes presents this form.

It appears from these experiments, that this white saline matter is pure, or nearly pure, chloride of potassium.

I am inclined to attribute its introduction into the lava to sublimation.

As chloride of potassium is a new species in mineralogy, I shall send the specimen to the British Museum.

A METHOD OF FIXING PARTICLES ON THE SAPPARE.

From Thomson's Annals of Philosophy, Vol. XXII; New Series, Vol. VI, 1823, page 412.

October 24, 1823.

SIR: When the species of minerals are ascertained by their physical qualities, they mostly undergo no injury, or but a very slight one; as that attending the determination of their hardness, the colour of their powder, their taste, &c. This is certainly a material advantage, and would highly recommend this method, was it constantly adequate to its purpose. That it is not so, however, we have a proof in the great errors into which have fallen those best skilled in it. Mr. Werner, its principal and most distinguished professor, was unable by its means to discover the identity of the jargon and the hyacinth; of the corundum and the sapphire; of his apatite and his spargelstein; and while he thus parted beings, as it were, from themselves, he forced others together which had nothing in common.

The chemical method justly boasts its certainty; but it carries destruction with it, and often bestows the knowledge of an object only at the expense of its existence. The sole remedy which can be opposed to this defect is to reduce the

scale of operating; and thus render the sacrifice which must be made as small as it is possible.

M. de Saussure's* ingenious contrivance for subjecting the most minute portions of matters to fire, by fixing them on a splinter of sappare, appeared to fulfil the conditions of this problem, and to have accomplished all that could be desired. It has, however, been scarcely at all employed, owing to the excessive difficulty in general of making the particles adhere; and in consequence the almost unpossessed degree of patience required for, and time consumed by, nearly interminable failures.

That such should be the case could not but be a subject of much regret, for besides economy of matter, of time, of labour, and the great beauty of deriving knowledge from so diminutive a source, and attaining important results with such feeble agents; reduction of volume became, in this instance, productive of increase of power, and thence, of an extension of the series of qualities by which substances are characterised.

A slight alteration which I have made in M. de Saussure's process has removed the objection to it. To water, saliva, gum water, which he employed, the last of which is not sensibly superior to the former, I have substituted a mixture of water and refractory clay.

be

Small triangles, or slender strips, of baked clay may used in lieu of sappare, which is not at all times to be procured; or a little of the moist clay may be taken up on the end of a platina, or other wire, and the object to be tried touched with it. This way may be applied to pieces of the ordinary size, and supersede the use of the platina tongs.

But a proceeding which I have only recently adopted appears to deserve the preference. Almost the least quantity of clay and water is put on the very end of a platina wire, filed flat there. With this, the particle of mineral lying on the table can be touched in any part chosen; for a moment

* Journal de Physique, par Rozier, tome 45.