14.75 21. Succinate of cobalt. Succinate of soda when dropt into a concentrated solution of sulphate of cobalt, throws down a light red precipitate. 22. Benzoate of cobalt. The salts of cobalt are not precipitated by benzoate of ammonia or of potash. According to Tromsdorf, benzoic acid dissolves a very little of the carbonate of cobalt. The solution crystallizes like the pure acid. 23. Oleate of cobalt. This may be obtained by mixing hot solutions of oleate of potash and sulphate of cobalt together. The soap takes a long time to separate from the liquid in which it is formed. Its colour is greenish-blue at first; but it gradually becomes green. But Chevreul is of opinion that the true colour of this soap is blue.* 24. Pinate of cobalt. When nitrate of cobalt is mixed with pinate of potash, a blue precipitate falls, which may be agglutinated by heat. It dissolves in ether with a blue colour.† SECTION XXII.-SALTS OF OXIDE OF ZINC. Almost all the acids act with energy on zinc, in consequence of the strong affinity which it has for oxygen. The salts of zinc, therefore, are very easily formed; and as the metal forms only one oxide, they are not liable to change their state, like the salts of iron and tin. They may be distinguished by the following properties: 1. The greater number of them are soluble in water, and Characters. the solution is colourless and transparent. 2. Prussiate of potash occasions a white gelatinous precipi tate when dropped into these solutions. 3. Hydrosulphuret of potash and sulphuretted hydrogen gas occasion a white precipitate. 4. Gallic acid and the infusion of nutgalls occasion no precipitate when dropped into these solutions. 5. Potash occasions a white gelatinous precipitate, which is readily dissolved by sulphuric or muriatic acid, and by an excess of potash. Ammonia behaves in the same manner. II. *Sur les corps gras, p. 96. + Unverdorben, Poggendorf's Annalen, xi. 235. 2 R Class I. 6. Zine is not precipitated in the metallic form by any of the other metals. 7. Sulphocyanate of potash and hydriodate of potash occasion white precipitates when dropped into a solution of a salt of zinc. 8. Carbonate of potash throws down a white precipitate, not soluble in an excess of the carbonate. But it may be dissolved by potash or ammonia. 9. When a zine salt is heated before the blow-pipe on charcoal, after the acid is destroyed or dissipated, the remaining oxide of zine being reduced, gives out a brilliant light, and is gradually dissipated before the reducing flame, a white vapour condensing at the same time on the surface of the charcoal. 1. Sulphate of zinc. This salt, according to the best accounts, was discovered at Ramelsberg, in Germany, about the middle of the 16th century. Many ascribe the invention to Julius, Duke of Brunswick. Henkel and Neumann were the first chemists who proved that it contained zinc; and Brandt first ascertained its composition completely.* It is generally formed for commercial purposes from sulphuretted zinc, or blende, as it is called by mineralogists. This ore is roasted, which converts the sulphur into an acid; it is then dissolved in water, and concentrated so much that, on cooling, it crystallizes very rapidly and forms a mass not unlike loaf-sugar. This salt is usually called white vitriol. It is almost always contaminated with iron, and often with copper and lead. Hence the yellow spots which are visible on it, and hence also the reason that its solution in water lets fall a dirty brown sediment; a circumstance very much complained of by surgeons when they use that solution in medicine. It may be easily purified by dissolving it in water, and putting into the solution a quantity of zine filings; taking care to agitate it occasionally. The zine precipitates the foreign metals, and takes their place. The solution is then to be filtered, and the sulphate of zinc may be obtained from it in crystals by proper evaporation. The crystals are right rhombic prisms, deviating very little from rectangular, for the inclination of the two contiguous faces of the prism is 91° 7. The lateral edges of the prism are often replaced by tangent planes, and the crystals often terminate in pyramidal summits. The shape is precisely the same * Beckman's History of Inventions, art. Zinc. + See the measurement by Brooke, Annals of Philosophy (2d series), vi. 437. as that of the rhombic prisms of sulphate of nickel. The crys- Sect, XXII tals are large and transparent, and colourless, they redden vegetable blues, and have a peculiar and very disagreeable metalline taste. The specific gravity when crystallized is, by my experiments, 1-980. At the temperature of 60° 100 grains water dissolve 93-88 grains of the crystal. Boiling water dissolves any quantity whatever. When heated, it melts and speedily loses its water of crystallization, and, in a high temperature, loses part of its acid. The constituents of this salt are When the solution of this salt is too much concentrated it deposites on cooling a white solid crust, not so soluble in water as the crystals, and composed of When this salt is strongly heated it loses the whole of its acid and water, and the oxide of zinc remains behind in a state of purity. Probably pure sulphuric acid might be easily obtained by distilling this salt. For it parts with the whole of its water before the acid begins to separate. 2. Tris-sulphate of zinc. When the preceding salt is boiled with zinc or its oxide, or when a quantity of potash is added to the solution, not sufficient to decompose the whole salt, in either case, white scales are obtained having considerable lustre, very little soluble in hot, and not at all in cold water. These scales, according to Vogel, are composed of 3. Sulphite of zinc. Sulphurous acid dissolves the oxide of zinc with the evolution of heat, but without effervescence. The solution yields crystals of sulphite of zinc. These crystals have a less acrid, but more styptic taste than the following species. They are less soluble in water, and more easily crystallized. They are insoluble in alcohol. When exposed to 5. H f. Obtained by mixing solutions of of arytes, and sulphate of zine. The filtered when concentrated. deposites irregular crystals of of zine. They are not altered by exposure to dir: their taste is very harsh and disagreeable, and they in water. Their constituents, according to are very cf Heeren, are as follows: 1 atom hyposulj huric acid 9 5.25 6.75 21* 6. Nitrate fall. Nitric acid attacks zine with prodigious viclerce, ar i Las been said even to inflame it. It is necessary to moderate its action by using it in a diluted state: even then considera. le heat is evolved, and a strong effervescence is occasioned by the escape of nitrous oxide gas. The solution is transparent and colourless, very caustic, and Sect. XXIL yields by evaporation flat striated tetrahedral prisms, terminated by four-sided pyramids. The specific gravity of these crystals is 2-096.* They attract moisture very rapidly when exposed to the air. They are very soluble both in water and alcohol. When heated they melt and detonate on burning coals, emitting a red flame. When distilled, they emit red vapours of nitrous acid, and assume a gelatinous form. In a strong heat they are decomposed completely, giving out nitrous gas and oxygen gas. The constituents of this salt are 7. Octakinitrate of zinc. This salt may be obtained by evaporating the solution of the preceding salt nearly to dryness, or by pouring a small quantity of ammonia into it. It is a white powder, insoluble in water, and composed, according to the analysis of Grouvelle, of The zinc is rather less than 8 atoms; but the deficiency does *Hassenfratz, Ann. de Chim. xxviii. 12. |