An abstract of the abbé Hauy's memoirs on the crystals, ufually called the ftones of the crois, the cruciform fchorl of De Lifle, follows. Thefe cryftals our author would ftyle croifettes, as they form a mark which diftinguishes this fofil from the fchorls with which it has been hitherto confounded. Its form is a rectangular hexaedral prifm, two angles of the bafe being larger than the four other angles: thefe prifms ufually crofs each other in pairs.

M. de la Croufe's letter relates to a different refult of the fame experiment in the hands of M. de la Metherie and M. Haffenfratz, refpecting the change in the nature of vital air by ftanding in water. The letter maintained, that its properties were not altered nor its quantity diminished, a refult confirmed by M. de la Croix.

Some account of a work entitled a Chemical Analysis of the Sulphur Water of Enghien follows; but this we have already confidered in a separate article, which has been accidentally delayed. (See p. 513.)

M. Klaproth's note to M. Schurer we fhall tranfcribe, as it is not long. M. de la Metherie has given his readers, in the Journal de Phyfique for November, p. 399, a definition of the pechblende, and the green glimmer, as the fubftances, which afforded me the new metal, the uranium. I take the liberty of obferving to M. de la Metherie, that the pechblende of Cronstedt, which is a true ore of zinc, is not the fofil of Johan-Georgenstadt and of Joachim Sthall, which contains the uranite, while what has been improperly ftyled green glimmer differs effentially from the true mica of this colour. The fubftances which I have employed, are the black fulphur of Uranium, and the green fparry calx of Uranium. Cronstedt was acquainted with neither. Sage has defcribed the last under the title of green heavy fpar, and the pretended brown earthy ore of iron, is the brown calx of Uranium-Uranium ocroceum,

M. Fourcroy has, it seems, been treated unfairly. We long ago noticed the deficiencies in the animal chemiftry; and our au thor, with his pupil M. Vauquelin, who have made great additions to this branch of science, and often mentioned the facts in their courfes, have had reafon to regret their candid communications, as their difcoveries have been published by others; they have therefore taken the precaution of fending an account of their difcoveries to the academy, to be preferved in the fecretary's office; and the editor of the Annals' has inferted a copy-we fhall mention them fhortly, as they occur. The oxygenated murratic acid, and the nitric acid, convert gum arabic into the citric and oxalic acids, refpectively, a difference we now know to be owing to the proportion of vital air (for we at laft are obliged to drop phlogiston, and to

declare

declare, that we are become converts to the new doctrine) in the feparating acids. The fecond fact relates to the calces of Tournefol. Thefe, he obferves, which are the fæculæ of the eroton tinctorium, appear blue, as they contain a mild foda; and acids redden the tincture only by faturating the foda to which the blue colour was owing. The extractive matter of vegetables is found not to be a foap. It is feparated by expofure to air, and absorbs oxygen, which renders it indiffoluble. The oxygenated muriatic acid converts it readily into a concrete yellow fubftance, diffoluble in alkalis and alcohol, but indiffoluble in water. The fourth fact is an account of a method of forming the pruffic acid, with ferum of blood and the nitric acid. The oxygen of the acid certainly contributes to the new production, as it is decompofed. The laft fact is a very fingu lar one, and will contribute greatly to derange a large part of the received fyftem of phyfiology. We fhall faithfully trans-. late an account of the experiment, On coagulating by means. of fire, blood united to one-third of its weight of water, a liquid feparates from the coagulum, which by a careful evaporation (une évaporation ménagée) affords a liquor fo much like the gall of an ox, that many perfons, without any previous information, have recognised the smell, the colour, and the taste, of this fecreted fluid; and, in every other refpect, by a chemical analysis, it fhows the fame propertics.-Serum, expofed to heat after being mixed with half its weight of water, coagulates in part. The portion of the liquid that does not coagulate, contains a gelatinous matter, which on cooling becomes a jelly. It is mixed with a mild foda and common falt.

Our readers may recollect our having formerly mentioned, that the Royal Society of Medicine at Paris had offered a reward for an analyfis of milk, particularly for a comparative account of the properties of different milks. An abstract of the fuccessful differtation is contained in this volume, and it is in many refpects important: we fhall felect only what is new, or lefs generally known. The pellicles which arife when fkimmed milk is put over the fire, refemble, after drying, the internal membrane of an egg, foon become putrid, glairy, and intolerably foetid. On analyfis, they leave an earthy refiduum infoluble in acids, and unalterable in the fire, moft probably a phosphoric falt. When fresh, carefully washed, and put on hot coals, they burn with the odour of hartthorn: distilled they produce water, oil, and volatile alkali, and are confequently clearly of an animal nature. The cheesy matter is intimately combined with the ferum, and only depofited when its dificlyants are deftroyed, or difperfed: thefe are the fugar of milk, and the acid formed in confequence of the fpontaneous coagulation. When the glutinous matter is boiled with pot afh or

6

cauftic

cauftic foda, it affumes a deep red, and may be faid to be blood teproduced, though the refemblance is in appearance only. During the folution of the foda, the smell of volatile alkali is very fenfible, but this falt feems to be formed during the ope ration. On feparating the combination of cheefy matter with the falt of foda, by means of acids, fome hepatic gas feems to be formed, and, as the resemblance of this gluten to the white of an egg is confpicuous, it may be fuppofed that the former contains fulphur as well as the latter. But no fulphur could be discovered in it. The phofphoric acid our authors, M. M. Parmentier and Deyeux, could not find, and Scheele, who first mentioned it, is faid never to have defcribed the process by which he obtained it. The fugar of milk is the true effential falt of milk the acid is only formed in the fpontaneous changes, or of fome of the ingredients, from the acids employed in the more violent analyfis. The differences in the other milks are foon defcribed. The cream of goats and theep's milk is thicker than in cows in the milks of women, the afs, and mares it is lefs copious and more fluid. The butter from the cream of sheep is always foft; that of women, affes, and mares milk, is al ways in the state of a cream, and scarcely can be ever brought to feparate, or to continue uncombined. The cheese from the cow and goat is firm and gelatinous; that from the sheep vifcous. Cheefe from women's milk has fcarcely ever any confiftence; from affes' and mares' milk, it holds the middle rank between thofe of the moft and leaft firmnefs. The ferum varies in quantity and nature; it is the fugar of milk that alone appears invariable.

M. Chaptal's Elements of Chemistry, analyfed in the next article, we have already noticed. M. Berthollet has commu nicated alfo fome additions to his defcriptions of the process of bleaching, which are too minute and mifcellaneous, to admit of an analyfis.

A very excellent memoir, by M. Berthollet, on the action. of the oxygenated muriatic acid on the colouring particles of different fubftances, follows. We fhall only give a concife ab ftract of the principal objects to be collected from it. The threads of hemp and cotton are bleached in confequence of their being deprived of the colouring particles, which form from one-fourth to one-third of their weight. But a very fmall part only of these particles are capable of being diffolved by foap, and, to effect this union, they must have attracted pure air from the atmosphere, from the dew, or the oxygenated acid; hence the neceffity of alternating the actions of lixives and the oxygenating process. When these particles are dif folved by the alkali, they may be precipitated by lime water, and combined with metallic oxids, by means of metallic folu

tions. Acids precipitate these colouring particles from alka lis, and the precipitate is of a fawn colour; but, when dry, it is black before their folution in the alkali, they appear white, and affume the fawn colour by the heat of the lixives. The oxygenated muriatic acid bleaches alfo the green parts of ve getables, but ebullition renders them yellow; it acts fimply by combining with them, diluting, rather than changing, the co lour; or, if it changes the colour at all, this is owing to the deftruction of the hydrogen. When the oxygenated muriatic acid affumes a yellow, nut, or brown colour, it produces this effect, by rendering the coal predominant, for it takes place only after the fubftance has been expofed to an intense heat, or a flight combuftion.

The nitric and the fulphuric acids give the yellow, nut, brown and black colours to the fubftances they act on, equally in augmenting the proportion of coal, and diminishing that of hydrogen. The cauftic metallic oxids act in the fame way on the animal fibres. All thofe phenomena, with fome others in which there is a flight combustion, depend on this: that, at a low temperature, hydrogen combines more readily and eafily with oxygen than coal; though, by the concurrence of different affinities, the contrary fometimes happens, particularly in ref piration, and the fpirituous fermentation.

The diminution of hydrogen is not fhown by a change of colour, if the fubject changed does not contain coal, as in the deftruction of the volatile alkali: it is not even changed, if the substance does contain coal, if the oxygen is fixed in a large proportion. When the nitric acid alters the nature of fome of the vegetable acids, it seems principally owing to the diminu tion of hydrogen, which, with coal, forms their radical. The green part of the leaves, and the fecond bark of trees, seems the principal fource of the colouring particles found in the wood and bark. This green part affumes a nut colour, by the actions of oxygen, and by the combination of this action, which produces a kind of combuftion; it finishes with lofing, particularly in the bark, the property of circulating in the veffels: it is thrown to the surface, and makes the most folid part of the bark.

M. Weftrumb, who still retains the phlogiftic fyftem of Stahl, has defcribed numerous experiments, in which different bodies burn in the oxygenated muriatic acid: from thefe he has fince endeavoured to fupport the fallen doctrine. In this part he is replied to by M. Berthollet. Our author adds fome remarks on the nature of the acid, and particularly endeavours to show that its gas is not truly air, but the acid brought into an aerial ftate by the matter of heat.

The analysis of caffia by M. Vauquelin is not very interest

ing. It contains, like other vegetable fubftances of a fimilar kind, gluten, jelly, gum, extractive matter, fugar, &c. Some flint was found in the analysis by fire, which our author attri butes to the crucible; but having found a filiceous substance in the tabasheer already formed, we would recommend the ana lyfis to be repeated in a black-lead crucible. The acid in the caflia diffolved the copper of the veffels, and tinctured the matter with a pretty confiderable cupreous impregnation.

Nitric acid is formed in the mutual decompofition of a mer curial oxid and a volatile alkali, for each fubftance, in the precipitation of the calx approaching to the metallic ftate, is de compofed. Azotic gas is produced, which arifes from the ammoniac. But M. Fourcroy, to whom we are indebted for these remarks, obferving that the quantity of gas was too finall in proportion to the oxid reduced, examined the fubject more clofely. Mr. Milner's obfervation came to his aid; the expe riment, we mean, where, from alkaline gas paffing through manganese in a hot iron tube, nitrous gas was obtained. M. M. Vauquelin, Seguin, and Sylveftre, with a porcelain tube, procured nitrat of ammoniac in vapour from azotic gas and water. Another chemist declares that he obtained nitric acid with ammonia and an oxid of lead. Our author explains these facts according to the new system, and indeed it is fufficiently obvious, that the ingredients of the nitrous acid are found in the substances employed, and that only a separation and a new combination is neceffary. The azotic gas in the original ex periment confequently contributed in part to form the acid, and our author affigns the reason why it was not observed in his former trials. He has fince difcovered that nitric acid is formed in another way, viz. by pouring the concentrated fulphuric acid on the cauftic mineral alkali faturated with the Pruflic acid.

The last effay in this volume is on the mechanifm of felt making. Though every hair appears in the microscope smooth, it is certainly, from a well-known experiment, fcaly; and the fcales are always in the fame direction. The fibres of wool are fimilarly conftructed, and it is from thefe fcales which, as the hairs in the manufacture of hat-making are fcattered in every direction, that the firmnefs of the felt is derived: the fibres are united and locked together by means of the little la mellæ. To render the texture more firm, thefe fibres muft af fume the shape of curves, &c. or indeed any figure except a rectilineal. For this purpose, before the wool is feparated, it is rubbed with a brush moiftened with nitrated mercury: the fur of the hat is laid on afterwards, and the wool for this purpofe does not undergo the laft operation. The effect of the

mercury