17. Golte fiin. Gallic acid readily dissolves carbonate All The solution has a dark green colour, and when lack matter behind, which does not yield LT OF BARYTES, A consider" le number of the salts of barytes are insoluble 1. They are white or transparent, and in general affect a crystale form. 2. If a little of the solution of sulphate of soda be let fall into a salt of tes, a white powder immediately precipitates, which is insoluble in nitric acid. 3. When heat is applied to a salt of barytes, it is not completely dissipated. If the acid be combustible, carbonate of barytes remains belin: if the acid be not combustible or vold How the salt remains behind undecomposed. 4. Prussiate of potash occasions no precipitate in a salt of barytes: unless the acid happens to contain a metallic basis. The same remark applies to hydrosulphuret of potash when dropped into a salt of barytes. 5. Most of the salts of barytes are poisonous. 6. When a fusible salt of barytes is heated before the blowpipe. it tinges the flame yellow. The same change of colour is produced when alcohol, containing any soluble salt of barytes in solution, is burnt. 7. Oxalate of ammonia, when dropt into a solution of a barytes salt, does not occasion an immediate precipitate. 1. Sulphate of barytes. This mineral occurs in considerable quantity, chiefly in veins, and very frequently accompanies galena and grey copper ore. Its nature was first ascertained by Assessor Galin. It often occurs crystallized, and the primary form is a right rhombie prism, the faces of which are inclined at angles of 101° 42′ and 78° 18'. It cannot be crystallized by art. This salt is insoluble in water, or at least only soluble in 43000 times it weight of water at the temperature of the atmosphere. Sulphuric acid dissolves it when concentrated and boiling, but it is precipitated by the addition of water. * Gmelin, Gilbert's Annalen, lix. p. 415. + Kirwan's Min. i. 136. Thus it forms a kind of supersulphate, capable of crystallizing, as Withering first observed. Mr. Hume has also mentioned it in Phil. Mag. xiv. 357. The fact was well known to chemists. This solution, however, When suddenly heated, it breaks in pieces and flies about with a crackling noise. This phenomenon, which is called decrepitation, is occasioned by the sudden conversion of the water which it contains into steam. When heated very violently it melts, and before the blow-pipe is converted into a white opaque globule. According to Saussure, a heat equal to 35° Wedgewood is required to fuse it.* When formed into a thin cake with flour and water, and heated to redness, it phosphoresces in the dark. This was first observed in a variety of this substance known by the name of Bologna stone. Lemery informs us, that the property was discovered by an Italian shoemaker named Vincenzo Casciarolo. This man found a Bologna stone at the foot of Mount Paterno, and its brightness and gravity made him suppose that it contained silver. Having exposed it to the fire, doubtless in order to extract from it the precious metal, he observed that it was luminous in the dark. Struck with the discovery, he repeated the experiment, and it constantly succeeded with him. It is evident that by the calcination it must be converted, at least partly, into sulphuret. I found that when sulphate of barytes was obtained by precipitation, and after being well washed was dried by simple exposure to the air in a damp room, it retained 3 per cent. of water lodged mechanically in its pores. The constituents of this salt are 2. Sulphite of barytes. A tasteless white powder, insoluble in water. When heated it gives off sulphur. It dissolves in aqueous sulphurous acid, and crystallizes in needles. Its constituents are Sect. V. It contains about 2 per cent. of water lodged mechanically 3. Hyposulphite of barytes. This salt may be obtained by is but very imperfectly entitled to the name of supersulphate of barytes; as it parts with its excess of acid at a moderate heat, which by no means is the case with supersulphate of potash. * Jour. de Phys. xlv. 15. Class I. pouring muriate of barytes into a concentrated solution of hyposulphite of lime. It falls in the state of a white brilliant. scaly powder. It is very slightly soluble in water. When the muriate of barytes is poured into dilute hyposulphite of lime, no precipitate appears at first, but small crystalline grains gradually fall, speedily followed on brisk agitation by a copious separation of the barytes salt. Mr. Herschell, to whom we are indebted for every thing at present known concerning this salt, considers it to be a bihyposulphite.* Hence its constitu ents must be Acid 10 9.5 19.5 4. Bihydrated hyposulphate of barytes. This salt is obtained when hyposulphate of manganese is digested over barytes. The oxide of manganese, and all the sulphuric acid, is separated, and the liquid contains only a solution of hyposulphate of barytes. By evaporation the salt may be obtained in crystals, by keeping the liquid for some time in a hot place. The crystals are usually four-sided prisms, deviating only 6° 45' from a right angle by Dr. Heeren's measurement. They are terminated by irregular four-sided pyramids, the faces of which are set on the edges. There is another variety of crystallization, with faces usually convex, and not easily described.† It is not altered by exposure to the air. When heated it strongly decrepitates. It dissolves in 11 times its weight of boiling water; in 404 times its weight at 64°, and in 7·17 times its weight at 47. It is insoluble in alcohol. When strongly heated, water and sulphurous acid are driven off, and sulphate of barytes remains. Its constituents, as determined by GayLussac and Welter, with which the analysis of Heeren agrees, 5. Quater hydrated hyposulphate of barytes. When a solution of hyposulphate of barytes is set aside in a temperature not Edin. Philos. Journ. i. 20. † Figures of both these crystals have been given by Heeren in Poggendorf's Annalen, vii. 173. The figures are in Tab. 11, figs. 4, 5, 6. exceeding 41°, crystals are gradually deposited, containing Sect. V. twice as much water as the preceding salt. The crystals are large, and are in four-sided prisms, terminated by four-sided pyramids, approaching very nearly to the shape of sulphate of barytes. The inclination of the faces of the prism, measured by a common goniometer, are 102° and 78°.* When heated it decrepitates strongly, but does not melt, but is converted into sulphate of barytes without altering its shape. Its constituents, as determined by Heeren, are 1 atom hyposulphuric acid 1 atom barytes 4 atoms water 9 9.5 4.5 23 6. Nitrate of barytes. This salt was formed immediately after the discovery of barytes. Vauquelin has added considerably to our knowledge of its properties. It is usually prepared by dissolving native carbonate of barytes in nitric acid, or by decomposing sulphuret of barytes by means of nitric acid, and evaporating the filtered solution till the nitrate crystallizes. Its crystals are regular octahedrons, sometimes cubes, and often they adhere to each other in the form of stars. The summits of the pyramids are often truncated. Sometimes it crystallizes in three-sided tables with the angles truncated. Sometimes it is obtained in small brilliant plates. Its specific gravity is 2-9149.+ It is very easily reduced to powder. Its taste is hot, acrid, and austere. 100 parts of water at 32° dissolve 5 parts of it; at 58°, 15.8 parts; and 120°, 17 parts; and at 215°, 35-2 parts of this salt, according to the determination of Gay-Lussac. It contains no water, but is a compound of It is insoluble in alcohol of the specific gravity 0.800. It is but little altered by exposure to the air. When thrown on burning coals it decrepitates, undergoes a kind of fusion, and then becomes dry. When strongly heated in a crucible, the whole ⚫ See a description and figure of the crystal by Heeren, in Poggendorf's Annalen, vii. 176. He considers the primary form an octahedron, but we might also assume a right rhombic prism with angles of 98° and 102°. Hassenfratz, Ann, de Chim. xxviii. 12. Class I. of the acid is gradually driven off, and the barytes remains pure. It detonates less violently with combustibles than most of the other nitrates. 7. Chlorate of barytes. The best method of obtaining the chlorate of barytes is to pour warm water on a quantity of the earth procured by Vauquelin's method, and to pass a current of gas through this mixture kept warm. By this method the usual mixture of chloride and chlorate is obtained. Now these two salts, when barytes is their base, possess the same degree of solubility, and resemble each other in the form of their crystals, so that they cannot be obtained separate by repeated erystallizations. Mr. Chenevix succeeded by the following ingenious method: Phosphate of silver, when boiled in solutions of the earthy chlorides has the property of decomposing them; the phosphoric acid combines with the earth, and the chlorine with the silver. But this salt produces no such change on the earthy chlorates. Now both the phosphate of barytes and the chloride of silver are insoluble in water. Of course, when phosphate of silver is boiled in a solution of chloride and chlorate of barytes, the whole muriate is decomposed into chloride of silver and phosphate of barytes, which are insoluble, and the only substance which remains in solution is chlorate of barytes. It crystallizes in square prisms, terminated by an oblique face. Its taste is sharp and austere. It dissolves in about four times its weight of cold water. The solution is neither precipitated by nitrate of silver nor muriatic acid. This salt is insoluble in alcohol. When heated, it loses 39 per cent. of its weight, owing to the escape of oxygen gas. The residue possesses alkaline properties.* From the analysis of this salt by Chenevix, its constituents are S. Bromate of barytes. This salt forms acicular crystals, soluble in boiling water, but little soluble in cold water. burning coals it fuses with a green flame. On It has not been |