plained by the theory of crystallization, for which we are indebted to the sagacity of Mr. Hauy; a theory which, for its ingenuity, clearness, and importance, must ever rank high, and which must be considered as one of the greatest acquisitions which mineralogy, and even chemistry, have hitherto attained.

According to this theory, the additional matter which envelopes the primitive nucleus consists of thin slices or layers of particles laid one above another upon the faces of that nucleus, and each layer decreasing in size, in consequence of the abstraction of one or more rows of integrant particles from its edges or angles.

[Thomson.

CHAP. XI.

ON THE NATURE OF THE DIAMOND.

THE diamond is not more an object of attention to the jeweller or lapidary than to the chemist; for it is as singular in its compo sition among the crystals, as it is valuable, on account of its rarity and lustre, among the gems: having of late been fully ascertained to consist of nothing more than pure charcoal under a peculiar state of crystallization.

Upon this subject we shall copy Mr. Smithson Tenant's interest. ing paper, as communicated to the Royal Society in 1797.

Sir Isaac Newton having observed that inflammable bodies had a greater refraction, in proportion to their density, than other bodies, and that the diamond resembled them in this property, was induced to conjecture that the diamond itself was of an in. flammable nature. The inflammable substances which he employ. ed were camphire, oil of turpentine, oil of olives, and amber; these he called "fat, sulphureous, unctuous bodies ;" and using the same expression respecting the diamond, he says, it is pro. bably "an unctuous body coagulated." This remarkable conjecture of Sir Isaac Newton has been since confirmed by repeated experiments. It was found, that though the diamond was capable of resisting the effects of a violent heat when the air was carefully excluded, yet that on being exposed to the action of heat and air, it might be entirely consumed. But as the sole object of these

experiments was to ascertain the inflammable nature of the diamond, no attention was paid to the products afforded by its combustion; and it still therefore remained to be determined whether the diamond was a distinct substance, or one of the known inflammable bodies. Nor was any attempt made to decide this question till M. Lavoisier, in 1772, undertook a series of experi ments for this purpose. He exposed the diamond to the heat produced by a large lens, and was thus enabled to burn it in close glass vessels. He observed that the air in which the inflammation had taken place had become partly soluble in water, and precipi tated from lime-water a white powder which appeared to be chalk, being soluble in acids with effervescence. As M. Lavoisier seems to have had little doubt that this precipitation was occasioned by the production of fixed air, similar to that which is afforded by calcareous substances, he might, as we know at present, have in. ferred that the diamond contained charcoal; but the relation be. tween that substance and fixed air, was then too imperfectly understood to justify this conclusion. Though he observed the resemblance of charcoal to the diamond, yet he thought that nothing more could be reasonably deduced from their analogy, than that each of these substances belonged to the class of inflammable bodies.

As the nature of the diamond is so extremely singular, it seemed deserving of further examination; and it will appear from the following experiments, that it consists entirely of charcoal, differing from the usual state of that substance only by its crystallized form. From the extreme hardness of the diamond, a stronger degree of heat is required to inflame it, when exposed merely to air, than can easily be applied in close vessels, except by means of a strong burning lens; but with nitre its combustion may be effected in a moderate heat. To expose it to the action of heated nitre free from extraneous matters, a tube of gold was procured, which by having one end closed might serve the purpose of a retort, a glass tube being adapted to the open end for collecting the air produced. To be certain that the goid vessel was perfectly closed, and that it did not contain any unperceived impurities which could occasion the production of fixed air, some nitre was heated in it till it had become alkaline, and afterwards dissolved out by water; but the solution was perfectly free from fixed air, as it did not affect the transparency of lime-water. When the

diamond was destroyed in the gold vessel by nitre, the substance which remained precipitated lime from lime-water, and with acids afforded nitrous and fixed air; and it appeared solely to consist of nitre partly decomposed, and of aërated alkali.

In order to estimate the quantity of fixed air which might be obtained from a given weight of diamonds, 2 grs. of small dia. monds were weighed with great accuracy, and being put into the tube with oz. of nitre, were kept in a strong red heat for about an hour and a half. The heat being gradually increased, the nitre was in some degree rendered alkaline before the diamond began to be inflamed, by which means almost all the fixed air was retained by the alkali of the nitre. The air which came over was produced by the decomposition of the nitre, and contained so little fixed air as to occasion only a very slight precipitation from lime. water. After the tube had cooled, the alkaline matter contained in it was dissolved in water, and the whole of the diamonds were found to have been destroyed. As an acid would disengage nitrous air from this solution as well as the fixed air, the quantity of the latter could not in that manner be accurately determined. To obviate this inconvenience, the fixed air was made to unite with calcareous earth, by pouring into the alkaline solution a sufficient quantity of a saturated solution of marble in marine acid. The vessel which contained them being closed, was left undisturbed till the precipitate had fallen to the bottom, the solution having been previously heated that it might subside more perfectly. The clear liquor being found, by means of lime-water, to be quite free from fixed air, was carefully poured off from the calcareous precipitate*. The vessel used on this occasion was a glass globe, having a tube annexed to it, that the quantity of the fixed air might be more accurately measured. After as much quicksilver had been poured into the glass globe containing calcareous precipitate as was necessary to fill it, it was inverted in a vessel of the same fluid. Some marine acid being then made to pass up into it, the fixed air was expelled from the calcareous earth; and in this experiment, in which 24 grs. of diamonds had been employed, occupied the space

* If much water had remained, a considerable portion of the fixed air would have been absorbed by it. But by the same method as that described above, I observed, that as much fixed air might be obtained from a solution of mineral alkali, as by adding an acid to an equal quantity of the same kind of alkali.-ORIG.

of a little more than 10.1 oz. of water. The temperature of the room when the air was measured, was at 55°, and the barometer stood at about 29.8 inches.

From another experiment made in a similar manner with 1 gr. and a half of diamonds, the air obtained occupied the space of 6.18 oz. of water, according to which proportion the bulk of the fixed air from 2 and gr. would have been equal to 10.3 oz.

The quantity of fixed air thus produced by the diamond, does not differ much from that which, according to M. Lavoisier, might be obtained from an equal weight of charcoal. In the Memoirs of the French Academy of Sciences, for the year 1781, he has related the various experiments which he made to ascertain the proportion of charcoal and oxygen in fixed air. From those which he considered as most accurate, he concluded that 100 parts of fixed air contain nearly 28 parts of charcoal and 72 of oxygen. He estimates the weight of a cubic inch of fixed air, under the pressure and in the temperature above-mentioned, to be .695 parts of a grain. If we reduce the French weights and measures to English, and them compute how much fixed air, according to this proportion, 2 grs. of charcoal would produce, we shall find that it ought to occupy very nearly the bulk of 10 oz. of water.

M. Lavoisier seems to have thought that the aërial fluid produced by the combustion of the diamond was not so soluble in water as that procured from calcareous substances. From its resemblance however, in various properties, hardly any doubt could remain that it consisted of the same ingredients; and I found, on com. bining it with lime, and exposing it to heat with phosphorus, that it afforded charcoal in the same manner as any other calcareous substance. [Phil. Trans. 1797.

Since the above account, M. Guyton de Morveau having burnt the diamond in oxygen gas, by the solar rays, and thereby obtained carbonic acid without residue, presumed that he had ascertained the diamond to consist of pure carbon, or the pure principle of charcoal, that which yields the pure acidifiable basis of the carbonic acid. But it was Clouet who proposed the conclusive experiment of making soft iron pass to the state of steel, by cementation with the diamond. To this end he secured a diamond with some filings of iron, in a cavity bored in a block of soft iron, filling up the cavity with a stopper of iron. The

whole properly inclosed in a crucible, was exposed to the heat of a blast furnace, by which the diamond disappeared, and the metal was fused, and converted into a small mass or bottom of cast steel. [Editor.

CHAP. XII.

MANUFACTURE OF GLASS.

GLASS is a strictly chemical substance, and well entitled to our

attention as to its history, properties, and manufacture.

SECTION 1.

History of the discovery.

THE word glass is formed of the Latin glastum, a plant, called by the Greeks, isatis; by the Romans, vitrum; by the ancient Britons, guadum; by the English, woud. We find frequent mention of this plant in ancient writers, particularly Cæsar, Vitruvius, Pliny, &c. who relate, that the ancient Britons painted or dyed their bodies with glastum, guadum, vitrum, &c. i. e. with the blue colour procured from this plant. And hence the factitious matter we are speaking of came to be called glass, as having always somewhat of this blueishness in it.

At what time the art of glass-making was first invented is altogether uncertain. Some imagine it to have been invented before the flood: but of this we have no direct proof, though there is no improbability in the supposition; for we know, that it is almost impossible to excite a very violent fire, such as is necessary in metallurgic operations, without vitrifying part of the bricks or stones wherewith the furnace is built. This, indeed, might furnish the first hints of glass-making; though it is also very probable, that such imperfect vitrifications would be observed a long time before people thought of making any use of them.

The Egyptians boast, that this art was taught them by their great Hermes. Aristophanes, Aristotle, Alexander, Aphrodiseus, Lucretius, and St. John the divine, put it out of all doubt that