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antiquary, and keeper of the Pontifical Museum. Young Visconti shewed early the talents which afterwards so much distinguished him; his childhood was spent in decyphering inscriptions, explaining medals, and describing monuments. An exhibition of this knowledge, made at the age of twelve, before an assembly of cardinals, excited the utmost astonishment. He reached maturity at the moment when the successful researches of Winckelman, Lanzi, and other learned men, had opened a wide field of antiquarian inquiry. "A man, however," says Rochette," was still want ing who should collect the scattered discoveries, and should unite in himself all the different species of science, necessary to fix our knowledge of the ancients and their arts on a solid basis."

Such a man was Visconti, who, in his description of the Museum Pioclementinum, erected a monument, which will always do honour to his memory. Texts, medals, inscriptions, statues, basso-relievos, are all admirably classed, and made to illustrate ancient religious and political institutions, and mythological traditions. The highest degree of enthusiasm for these pursuits was combined in him with solid judgment and deliberate inquiry. He published afterwards

the Monumenti Gabini, the description of the Villa Borghese, and other works of equal merit. When the French carried off these monuments of art to Paris, they removed Visconti along with them, and he was appointed Keeper of the Museum. During his stay in France, he contributed most valuable accounts of the antiques contained in the Musée Francois and Musée Royal. His last work, which promised to prove the greatest, was his Greek and Roman Iconography, one of the most remarkable works of the age, both for its magnificence in point of art, and for the original and curious information contained in it. Only one volume in folio appeared before the lamented death of the author. Besides his works, his learned contemporaries peculiarly valued him for the ready and sure information to be obtained from him upon every subject. "It was not," says one of them, “ a learned man that we consulted; it was a book always open; a sort of library open to all the world." His opinion bore almost the authority of an ancient. In this view it was anxiously sought by the English government, in its investigation of the value of the Elgin marbles. M. Visconti left a widow, with two children, and only a moderate inheritance.

CHAPTER III.

VIEW OF IMPROVEMENTS IN SCIENCE DURING THE YEAR.

Oxygenation of Acids and of Water.-Constitution and Analysis of Mineral Waters.-Impressions of Cold from the Higher Atmosphere, and the New Instrument called the thrioscope.-Operations for determining the Figure of the Earth.

OXYGENATION OF ACIDS and of

WATER.

ONE of the most interesting trains of research in experimental chemistry that have recently appeared, is that of the indefatigable chemist, Thenard, on the oxygenation of the acids and of water. The final result is the obtaining of oxygenated water, or, a deutoxide of hydrogen, as the atomic chemists denominate it, from the idea, that in a state of purity this compound has a double proportion of oxygen (compared to the hydrogen) that water or the protoxide has. The leading instrument by which he was enabled to accomplish this combination was the peroxide of barium; and, as the process is somewhat long, and apparently complicated, we shall describe its different stages in a regular and deliberate manner. It is thought complicated, chiefly because several of its steps depend on comparatively recent discoveries, all of which require to be well understood; but many of those facts in chemistry which are reckoned plainer and easier would present

equal complication if all the steps of manipulation, by which the ultimate products are obtained from the substances in their natural and crude state, were reported to us for the first time. These have become easy in consequence of certain steps being already familiar to us, or certain intermediate products being well known. This is not exactly the case in the present instance; and, therefore, though with those whose chemical knowledge was acquired some years ago it requires more care to reach the conclusion, it is to be recollected that each of the intermediate steps is to be considered as a separate discovery, and that the greater time and attention demanded for the ultimate object is rewarded with the knowledge of a series of scientific acquisitions, all of them elegant. This series may be divided into these distinct stages:I. The obtaining of barytic earth, or pure barytes.-II. From this the obtaining of the peroxide of barium.— III. The oxygenation of different acids; and, IV. The oxygenation of water.

1. Barytes is obtained from the heavy spar, found to be a sulphate of barytes, which is for this purpose pounded, mixed with charcoal, and subjected for a length of time to an intense heat. The acid is decomposed by the charcoal, and its radical, the sulphur, combines with the barytic earth to form a sulphuret of barytes. This is treated with nitric acid, which combines with the barytes to form a liquid nitrate of barytes, and from which crystals of that barytic salt are obtained by evaporation. For the purpose of procuring this salt in a very pure state, and, above all, free from any iron or manganese, it should be again dissolved in water, a small excess of barytic water added, and the solution filtrated, and then crystallized. The pure nitrate thus obtained must be decomposed by heat, to extract the barytes. This must be done, not in an earthenware retort, because this contains both iron and manganese, but in a retort of fine white porcelain. If four or five pounds of the nitrate are thus treated, the operation should last three hours, after which BARYTES remains. It is combined with some silex and alumine, from the fusion with the retort, but free from iron and manganese, which is an essential circumstance.

II. The pure barytes thus obtained has been found, by galvanic analysis, to consist of a peculiar metal, in combination with oxygen. The metal is called barium. This metal is found to have the property of combining with a larger proportion of oxygen than that which forms this earth. It now forms a peroxide of barium. The formation of the peroxide is accomplished by exposing the pure earth to oxygenous gas, under an elevated temperature. The barytes is cut into pieces about the size of the end of the finger, is put into a luted glass tube, long and wide enough to contain

about 4lbs. troy. When this is made moderately red-hot, a current of oxygenous gas is past over it by squeezing a bladder which is filled with that gas, and tied over one of the cool ends of the tube. If an empty bladder is tied over the opposite end, that portion of the gas which does not combine with the barytes passes into it, and by compressing this in its turn, the current is passed and repassed till the whole is combined, which is done with extreme facility. When the tube is cooled, the contents are to be taken out. These are now a greyish white PEROXIDE OF BARIUM, and must be kept in an accurately closed bottle.

III. The peroxide of barium thus obtained, is soluble in various liquid acids the nitric, phosphoric, and muriatic. It is first moistened with a little water, which makes it fall readily into a powder, without much increase of temperature. This powder may be added by degrees to the nitric or muriatic acid, and is by them quickly dissolved, forming li quid nitrate, or muriate, of the peroxide of barium. If the barytes is now precipitated, a liquid combina tion of the acid with oxygen will be obtained. Such precipitation is effected by adding sulphuric acid in the requisite quantities. Sulphate of barytes is formed, and a copious precipitate of this compound is separated, the superabundant oxygen remaining in combination with the liquid acid. After one quantity of the barytes has been thus separated from the solution by being converted into a sulphate, and one dose of oxygen has been left in combination with the acid, more of the peroxide may be added, from which the barytes may be in like manner precipitated, and an additional dose of oxygen made to combine with the acid. The operation may be several times repeated, as often at least as

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seven, without the loss of any oxygen. Afterwards the impregnation with oxygen may be rendered successively stronger, by further repetitions of the process, but a little oxygen is now lost. These oxygenated that acids cannot well be concentrated by heat, as heat has the effect of separating the oxygen; but they may be Concentrated by evaporation under exhausted receiver, containing quicklime, or some other hygromethe Eric substance, to absorb the moisture evolved by the removal of the atmoSpheric pressure. The oxygenated nitric acid thus obtained does not, like the nitro-muriatic acid, act on gold; but it readily dissolves those metals which simple nitric acid is capable of dissolving, and the solution takes place without the disengagement of oxygenous gas, and without the production of heat. When muriatic acid is treated in the same manner, a liquid is obtained possessed of properties wholly different from hose of chlorine, the substance so Jong known under the name of oxymuriatic acid. It does not, like chloine, dissolve gold and platinum. It very acid, colourless, and almost destitute of smell. A boiling heat converts it into oxygenous gas and muriatic acid. These experiments are considered by some chemists as setting at rest the question of the nature of chlorine, and proving it to be wholly different from a combination of muriatic acid with oxygen. M. Thenard has frequently given the acid as many as 125 volumes of oxygenous gas. The oxygenated acid dissolves zinc without effervescence, the oxygen in combination with the acid being taken up by the metal to form an oxyd, in preference to the oxygen of the water, which, with the simple liquid muriatic acid, takes place, occasioning an effervescence by the evolution of hydrogen gas.

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The oxygenation of sulphuric acid is not obtained with equal simplicity. When that acid is brought into contact with the peroxide of barium, it forms sulphate of barytes by combining with the barytes, which is the protoxide of barium, and the overplus of oxygen is disengaged in the gaseous form, exactly in the same way as this acid operates on the black oxide (or peroxide) of manganese, combining with an inferior oxide of that metal, and setting oxygenous gas at liberty. In order to effect the oxygenation of the sulphuric acid, we first procure an oxygenated muriatic acid, which should be kept in a glass surrounded with ice. We must also be provided with a solution of sulphate of silver. This solution is to be added drop by drop to the oxygenated muriatic acid. (It is absolutely necessary that the sulphate should not contain any uncombined oxide of silver.) An instant decomposition takes place. The muriatic acid quits the liquid state and the oxygen to combine with the oxide of silver; thus producing that very insoluble salt, the muriate of silver. In the meantime, the sulphuric acid being disengaged, becomes liquid, and combines with the which the muriatic acid had quitted, and we thus have oxygenated sulphuric acid. This, which is turbid while the sulphate is adding, becomes limpid the moment that the whole of the muriatic acid is combined with oxide of silver. It is equally important, on the other hand, that no excess of sulphate of silver should be added beyond what is required to engage the muriatic acid. Alternate trials must be made with the tests of nitrate of silver on the one hand, and muriatic acid on the other, on single drops taken from the whole liquid, till the point of saturation is exactly hit; the liquid is then to be filtered, the filter itself pressed through cloth, and the

oxygen

turbid drops which it yields passed through paper, and added to the rest. We have now a liquid composed solely of OXYGEN WATER, and sulphU

RIC ACID.

IV. From the liquid compound now mentioned we have to separate the sulphuric acid, and then we shall have oxygenated water. For this purpose we treat it with an aqueous solution of barytes, i. e. barytic water. The barytes and the sulphuric acid are now precipitated in mutual combination, and THE OXYGEN REMAINS IN UNION WITH THE WATER. Another plan, and one which renders the oxygenation of the water less dilute in the first instance, is to put the liquid in a glass mortar surrounded by ice, to rub into it gradually a little caustic barytes, previously slacked and ground to powder, till the sul phuric acid is nearly precipitated, (which is known by the liquid hardly reddening litmus,) then filter the liquid, and complete the separation of the sulphuric acid by adding a few drops of barytic water.

It is expedient at first to have a slight excess of barytes in the liquid, that any trace of iron or manganese which may have escaped the former operations may now be separated, after which a few drops of very dilute sulphuric acid will remove the excess of barytes; and the operator should so manage as rather to leave a slight excess of acid than of base, as the acid tends to fix the oxygen, but the base to disengage it.

By a repetition of the process now described, on the same quantity of liquid, the proportion of oxygen may be increased. But in order to concentrate this curious substance more powerfully, another process is required-that of evaporation under an exhausted receiver, containing a hygrometric substance, such as a vessel of strong sulphuric acid or powdered muriate of lime, according

to the experiment of Professor Leslie. (See our former volume, p. 262.) In this situation a part of the water is evaporated, while none of the oxygen is disengaged. This is a fact which we should not have anticipated, knowing that the oxygen is easily separated by heat. It shews that the oxygen is not kept in its state of condensation, in any degree, by the pressure of the atmosphere. A low temperature, however, has a great influence on the stability of the compound. By keeping the oxygenated water a sufficient length of time under such a receiver-for example two daysthe liquid remaining will sometimes contain two hundred and fifty times its volume of oxygen. After the concentration has been carried to a certain pitch, part of the oxygen separates in bubbles, which burst with difficulty. The separation of a part of the oxygen, when it takes place, will be ascertained by the rising of the mercury in the mercurial gage of the air-pump. An earlier disengagement of it is sometimes occasioned by the presence of foreign matter, and is stopped by adding two or three drops of very weak sulphuric acid.

The highest point of concentration to which the author has brought the liquid is that of containing 475 times its volume of gas, at a medium temperature and pressure. The proportion is ascertained by introducing a portion of it previously diluted into a tube inverted over mercury, and passing up a little oxide of manganese diffused in water. The whole oxygen is immediately disengaged, and on comparing its volume with that of the compound before it was diluted, we calculate the proportion expressive of its strength.

Oxygenated water is heavier than pure water; it sinks in it like sulphuric acid, and has the same sluggish consistence. The property which

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