melts, and after losing its water of crystallization may be made to undergo the igneous fusion like common salt. Its constituents, (abstracting the water, which has not been determined), are 1 atom iodine 1 atom sodium 15.75 3 18.75 Sect. 1. 4. Iodide of barium. It is easily obtained by dissolving carbonate of barytes in hydriodic acid. It crystallizes in fine prisms similar in appearance to muriate of strontian. It is very soluble in water, and but feebly deliquescent. When long exposed to the air, a portion of the hydriodic acid is decomposed and dissipated, carbonate of barytes is formed, and hydriodate of barytes coloured by iodine may be dissolved by water. In close vessels it may be heated to redness without undergoing any alteration. But if air or oxygen gas have access to it while red hot, vapours of iodine are exhaled, and the salt becomes alkaline.* Its constituents are 5. Iodide of strontium. 25.375 This salt is very soluble in water. It fuses when heated to a temperature rather below redness. This fusion produces little alteration in close vessels; but in the open air vapours of iodine are exhaled, and the salt becomes alkaline+ 6. Iodide of calcium. This salt is obtained in a state of purity by saturating hydriodic acid with carbonate of lime. It is very soluble in water and very deliquescent. It may be dried in the air without undergoing decomposition.‡ 7. Iodide of magnesium. This salt is deliquescent and crystallizes with difficulty. When heated to redness, out of the contact of air, the acid flies off and leaves the magnesia. § 8. Iodide of glucinum. Glucinum, when heated in vapour of iodine, takes fire, and an iodide sublimes in white needles. 9. Iodide of iron. Described in vol. i. p. 493. 10. Iodide of nickel. Described in vol. i. p. 532. • Gay-Lussac, Ann. de Chim. xci. 57. + Ibid. p. 60. § Ibid. p. 63. Class IV. 11. Iodide of cobalt. red colour. This salt dissolves in water with a 12. Iodide of zinc. This salt is easily obtained by heating iodine with an excess of zine under water. The liquid at first acquires a deep brown colour; but if we continue the heat, more zinc is dissolved, and the whole becomes at last as colourless as water. It cannot be crystallized by evaporation. But if it be evaporated to dryness and fused, it crystallizes in beautiful prisms similar to those of white oxide of antimony. When thus heated, it is anhydrous iodide of zinc. When heated in the open air it is decomposed, the acid is driven off under the form of iodine, and oxide of zinc remains. The constituents of this salt are as follows: 13. Iodide of cadmium. Described in vol. i. p. 620. 22. Iodide of antimony. See vol. i. p. 324. 23. Iodides of molybdenum. See vol. i. p. 359. SECTION II.—OF IODO-STANNATES. From the experiments of Boullay it appears that iodide of tin dissolves in aqueous solutions of hydriodate of ammonia, iodides of potassium, sodium, barium, and strontium.† SECTION III.—OF IODO-PLUMBATES. Boullay has also observed that iodide of lead dissolves in the aqueous solution of iodide of potassium, and the solution, when concentrated, crystallizes in needles. Gay-Lussac, Ann. de Chim. xci. p. 65. SECTION IV.-OF IODO-HYDRARGYRATES. A few of these salts have been examined by Bonsdorf. The following are the results which he obtained. 1. Iodo-hydrargyrate of potassium. This salt may be obtained by saturating a cold solution of iodide of potassium with iodide of mercury, and abandoning the solution to spontaneous evaporation. It crystallizes in needles, which deliquesce in a moist atmosphere.* 2. Iodo-hydrargyrate of sodium. It may be obtained in the same way as the preceding salt. It crystallizes in rhomboidal prisms, has a saffron yellow colour, and speedily deliquesces when exposed to the air.† 3. Iodo-hydrargyrate of iron. This salt may be prepared like the preceding, but must not be exposed to the air, because it is decomposed when evaporated in contact with the atmosphere. It crystallizes in fine yellow prisms, which gradually becomes covered with a brown rust. 4. Iodo-hydrargyrate of zinc. It crystallizes in six-sided prisms, terminated by acute pyramids. It deliquesces even in a dry atmosphere. § CLASS V. FLUORINE ACID SALTS. As fluorine has not hitherto been obtained in a separate state, it is still to be regarded as a hypothetical substance. have stated in the first volume of this work (p. 88.) the reasons which have induced chemists to admit its existence. And in vol. ii. p. 197, I have given an account of the different acids into which this principle enters as a constituent; our object in this place is to describe the different genera of salts which these acids form with the various salifiable bases. SECTION I.-OF FLUORIDES, HYDRO-FLUATES, OR FLUATES. The properties of the acid called fluoric or hydro-fluoric || Sect. I. Class V. acid have been detailed in vol. i. p. 87. The salts which it forms were first examined by Gay-Lussac and Thenard,* and more lately by Berzelius.+ They have received different names, according to the opinion entertained respecting the nature of the acid which they contain. Those who consider it as a compound of a combustible base and oxygen, call these salts fluates; those that consider the acid as a compound of fluorine and hydrogen call them hydro-fluates; while those who are of opinion that fluorine is analogous to oxygen, and that when hydrofluoric acid comes in contact with a base a double decomposition takes place, (fluorine uniting with the base, while the oxygen and hydrogen form water), give them the appellation of fluorides. This last opinion is by far the most plausible; though it would be too much to affirm that it has been completely demonstrated. Sp. 1. Hydro-fluate of ammonia. This salt may be obtained by the following process, for which we are indebted to Berzelius. Mix in a platinum crucible 1 part of sal ammoniac and 2 parts of fluoride of sodium, both quite dry and in powder. Cover the crucible with an inverted lid filled with cold water. Apply a gentle heat. The hydro-fluate of ammonia sublimes and attaches itself to the lid of the crucible in the state of small prisms. It is not altered by exposure to the air. It is abundantly soluble in water, slightly in alcohol. When heated it melts before it begins to sublime. It corrodes glass vessels even when dry. ‡ 2. Bihydro-fluate of ammonia. It may be obtained in granular crystals by saturating hydro-fluoric acid with ammonia. and evaporating at the temperature of 100°. Half the ammonia escapes, and the bisalt remains in granular crystals. When heated it may be volatilized in thick white vapours. It precipitates the solutions of all the alkaline earths, and earths proper, in acids, because fluoric acid forms insoluble compounds. with all the earths. § 3. Fluoride of potassium. It may be obtained by saturating bicarbonate of potash with hydro-fluoric acid, and after evapor ating to dryness, exposing the residue to a red heat. This salt has a very sharp taste, crystallizes with difficulty, in cubes or rectangular prisms, is very deliquescent, and of course very soluble in water. When heated it undergoes first the aqueous *Recherches Physico-Chimiques, ii. 1. + Kong. Vet. Acad. Handl. 1823, p. 284. + Berzelius, ibid. p. 298. § Gay-Lussac and Thenard, Recherches Physico-chimiques, ii. p. 23, and then the igneous fusion. Sulphuric acid decomposes it, driving off fluoric acid in vapour.* 4. Bifluoride of potassium. It may be obtained by dissolving potash in an excess of fluoric acid, and concentrating the solution. By spontaneous evaporation it crystallizes in rectangular tables with bevelled edges, or in cubes. It is very soluble in water. When heated it melts, gives off its excess of acid, and again becomes solid. From the experiments of Berzelius, its constituents appear to be Sect. L. 5. Fluoride of sodium. This salt may be prepared most economically by mixing 100 parts of dry fluo-silicate of soda and 112 parts of anhydrous carbonate of soda with as much water as will reduce the whole to a thin pap, and boiling till all effervescence is over. When the whole has concreted to a solid mass, let it be pounded and boiled in water, to dissolve out the fluoride of sodium. By evaporation the salt is obtained in cubes and regular octahedrons. The crystals are transparent and have sometimes a pearly lustre. The salt is less fusible than glass. Water dissolves it very slowly. At 61° 100 parts of water dissolve only 4 parts of this salt. It is insoluble in alcohol.‡ 6. Bifluoride of sodium. It crystallizes in transparent rhomboids, has a sharp and acid taste, and is sparingly soluble in water. Its constituents are 7. Fluoride of lithium. This salt dissolves with difficulty in water, resembling in that respect carbonate of lithia. The solution is converted by evaporation into a white mealy looking mass, composed of opaque granules. Gay-Lussac and Thenard, Recherches, Physico-chimiques, ii. p. 18. + Kong. Vet. Acad. Handl. 1823, p. 292. Berzelius, ibid. p. 295. § Ibid. p. 294. |