debted to Mr. Curr, steward to His Grace the Duke of Norfolk, for these particulars, who very politely attended me through the works in the year 1802, and assisted me in taking the necessary drawings, admeasurements, &c. This description will be better understood by reterring to a copper-plate engraving of these ovens in the second volume of my Chemical Essays, viz. Plate 11, page 329.

LI.

Of the Uses of Diamond.

The lapidaries employ a considerable quantity of diamond in powder, which they use with steel instruments, to divide pebbles and precious stones. The small pieces of diamond of which the powder is made, are worth 28 shillings a carat. The use of the diamond in this way is very extensive. Had nature withheld the diamond, the pebble, the agate, and a variety of other stones, would have been of little value, as no other substance is hard enough to operate upon them. In this way rock crystal from Brazil is divided into leaves, and ground and polished with diamond dust for spectacles, and other optical instruments. See page 262; also Mawe's Treatise on Diamonds and Precious Stones, octavo, London, 1815.

LII.

Of the Effect of Oxygen upon Colours.

Several of the effects of oxygen have been mentioned in different parts of this work; but its action on some colouring substances has not been noticed, though it is various and striking. When woollen cloths are taken out of an indigo vat, they are of a green colour; but they are scarcely exposed to the atmospheric air for one minute, before they imbibe a sufficient portion of oxygen to change that colour to a deep blue. In like manner the whelk (the buccinum of Linnæus,) which is used to dye purple, undergoes a change equally extraordinary. The liquor, though naturally yellow, becomes oxidized by exposure to the sun and air, passes through various shades of yellow, green, crimson, &c. and at length becomes purple. A good black cannot be given to cloth, without frequent exposure to the air. Light has a great affinity for oxygen: hence cloths frequently fade and lose their colours by the abstraction of oxygen by the agency of light. That part of the furniture of a bed which has been exposed to the sun will often be entirely faded, while those parts

which have not been so exposed will retain their original colours. This probably aris s from the loss of oxygen, and that the oxygen which existed in a solid form is rendered aeriform by the rays of the sun, and goes off in the state of oxygen gas. See Bancroft On permanent colours.

LIII.

Of the Gases emitted in Respiration.

Having shown that sheet of the work which contains page 57 to a friend, an ingenious chemist, he suggested that those remarks on the levity of nitrogen gas evolved from the lungs in respiration would have more force, were I to contrast this character with the su, erior specific gravity of carbonic acid gas, which is ejected at the same instant. For during that remarkable interval that always occurs in breathing, there is sufficient time allowed for these noxious fluids to separate; the first to ascend, while the other preponderates, leaving a space for a fresh current of uncontaminated atmospheric air. Thus every thing is prepared without any care or forethought of ours for a new inspiration.

"The air inhaled is not the gas

That from a thousand lungs reeks back to thine
Sated with exhalations rank and fell,
Which, drunk, would poison the balsamic blood,
And rouse the heart to ev'ry fever's rage-
But air that trembling floats from hill to bill,
From vale to mountain, with incessant change
Of purest element."
Dr. ARMSTRONG.

LIV.

Of Lutes.

Glazier's putty is a very good lute for all common purposes, but it is necessary that the whiting be made thoroughly dry be. fore it be mixed with the oil. Linseed oil and sifted slacked lime, well mixed, and made thoroughly plastic, form an excellent coating for retorts: if made thicker, this mixture is an impenetrable luting, that is not liable to crack.

Dr. Black recommends a mixture of four parts sand and one of clay, except where it is to be exposed to an intense heat, and in such situations to use six parts of sand to one of clay.

For fire-lute Mr. Watt directs the use of porcelain clay from Cornwall (not pipe-clay) to be pounded small, and mixed up to the consistence of thick paint, with a solution of two ounces

of borax in a pint of hot water. For want of this peculiar kind of clay, slacked quick-lime, mixed up in the same manner, may be used. This may be kept ready mixed in covered vessel. For cold-lute he directs to take equal parts by measure of the above clay and wheat flour, and to mix them to a proper consistence with cold water. This is more tenacious than his firelute, but does not keep so well.

A very excellent lute for many purposes may be made by beating up an egg, both the white and the yolk, with half its weight of quick-lime in powder. This lute is to be put upon a piece of linen, and applied as usual. It dries slowly, but becomes very compact, and acquires great hardness.

A mixture of martial pyrites and muriate of ammonia forms a good lute for stopping the cracks in iron utensils; but the tollowing artificial compound is preferred, on account of the exact proportions of the ingredients being more easily ascertained. To two pounds of iron turnings or filings, add one ounce of salammoniac, and one ounce of flowers of sulphur; blend the mixture with water till the whole is of a proper consistence, and use it fresh. This lute is employed by engineers to stop the joints of steam-engines and other machinery.

Just as this sheet was going to press, I received a letter from an intelligent stranger, informing me that a mixture of salt and whiting, properly kneaded with water, makes a very hard and durable lute for many purposes, particularly for securing the joints of the apparatus which is employed for the production of carbu. retted hydrogen gas.

LV.

Of the extreme Hardness of Ice in some Countries.

The following narration will show the solidity that water is capable of acquiring when divested of a large portion of its caloric: During the severe winter of 1740, a palace of ice, fiftytwo feet long, sixteen feet wide, and twenty feet high, was built at Petersburg, according to the most elegant rules of art. The river Neva afforded the ice, which was from two to three feet thick, blocks of which were cut, and embellished with various or◄ naments When built up, the different parts were coloured by sprinkling them over with water of various tints. Six cannons, made of and mounted with ice, with wheels of the same matter, were placed before the palace; and a hempen bullet was driven by one of these cannon, in the presence of the whole court, through a board two inches thick, at the distance of sixty paces."

* M. de Bomare.

"No forest fell,

Imperial mistress of the fur-clad Russ,

When thou wouldst build; no quarry sent its stores
T'enrich thy walls; but thou didst hew the floods,
And make thy marble of the glassy wave.
Silently as a dream the fabric rose;
Ice upon ice the well adjusted parts

Were soon conjoined; nor other cement ask'd
Than water interfused to make them one.
Lamps gracefully disposed, and of all hues,
Illumin'd ev'ry side. Long wavy wreaths
Of flowers, that fear'd no enemy but warmth,
Blush'd on the pannels, which were once a stream,
And soon to slide into a stream again.”

LVI.

A New Kind of Gunpowder.

COWPER.

Notwithstanding the accident which happened in France in the year 1788, (see note ◊ page 211,) the French have since, as I have been informed, actually employed, in one of their campaigns, gunpowder made with oxymuriate of potash instead of salt-petre. That this is practicable has been proved in this country by the Rev. Alexander Forsyth of Belhelvie, in Aberdeenshire, in Scotland. This gentleman, who has lately taken out a patent for a new kind of gun-lock, to be used without a flint, and has contrived to inflame such gunpowder merely by percussion, informed me, that ten years ago he discovered a method of making this gunpowder; and that he has himself been in the habit of using it ever since in killing game. The gun-lock is calculated for firing cannon as well as musquetry; it is contrived to hold forty primings of such powder; and the act of raising the cock primes the piece. Though each charge of priming contains only an eighth of a grain of oxymuriate of potash, that alone makes a very loud report; and the principle of the lock is such, that it can never possibly miss fire. This effect is entirely attributable to the large portion of oxygen which is con densed in this very singular salt.

LVII.

Of the Efficacy of Water in Vegetation.

That vegetables will grow in woollen cloth, moss, and in other insoluble media, besides soils, provided they be supplied

with water, has been reapeatedly shown since the days of Van Helmont and Boyle; but the experiments of a modern author, from their apparent correctness, seem more highly interesting and conclusive.

Seeds of various plants were sown in pure river-sand, in litharge, in flowers of sulphur, and even among metal, or common leaden shot; and in every instance nothing employed for their nourishment but distilled water. The plants throve, and passed through all the usual gradations of growth to perfect maturity. The author then proceeded to gather the entire produce, the roots, stems, leaves, pods, seeds, &c. These were accurately weighed, dried, and again weighed, then submitted to distillation, incineration, lixiviation, and the other ordinary means useful in a careful analysis. Thus he obtained from these vegetables all the materials peculiar to each individual species, precisely as if it had been cultivated in a natural soil,-viz. the various earths, the alkalies, acids, metals, carbon, sulphur, phosphorus, nitrogen, &c. He concludes this very important paper nearly in these extraordinary words: "Oxygen and Hydrogen, with the assistance of solar light, appear to be the only elementary substances employed in the constitution of the whole universe; and Nature in her simple progress, works the most infinitely diversified effects by the slightest modifications in the means she employs." See "Recherches sur la Force assimilatrice dans les Végétaux," par M. Henri Braconnot, Annales de Chimie, Fev. et Mars, 1808.

LVIII.

Of the Agencies of Galvanism.

The experiments of Sir Humphrey Davy, published in the first part of the Philosophical Transactions for 1807, have thrown considerable light on the agencies of electricity and galvanism. See note, page 432.

First. In opposition to the assertions of Pacchiani and others, he has demonstrated that muriatic acid is not produced in water by the agency of galvanism, but that water "chemically pure is decomposed into gaseous matter alone, into oxygen and hydrogen."

Secondly. By the agency of galvanism he decomposed sulphate of lime, sulphate of strontites, fluate of time, and other solid bodies, insoluble, or difficultly soluble in water. In each case the earth was found in one vessel and the pure acid in the other. Even glass was decomposed, and part of its alkali exhibited entire. Sulphuric, muriatic, nitric, and phosphoric salts