8. Dr. Henry showed that when electric sparks are passed Class II. for some time through muriatic acid gas, it undergoes partial decomposition; a portion of chlorine and hydrogen gases being evolved. But this decomposition cannot be carried far, because when hydrogen and chlorine gases are accumulated in any quantity, the electric spark causes them to combine again. 9. When muriatic acid gas and oxygen gas are mixed together and passed through a red-hot porcelain tube, or when electrical discharges are transmitted through such a mixture, water is formed and chlorine gas disengaged. Dr. Henry found that the same decomposition was produced at the temperature of 250° when such a mixture was in contact with a platinum clay ball.+ 10. When potassium is heated in muriatic gas it liberates one-third of its volume of hydrogen. Davy found that when zine or tin is heated in this gas they are converted into chlorides, while a quantity of hydrogen gas is disengaged equal to one-half of the muriatic acid gas decomposed.‡ Charcoal even when ignited to whiteness, produces no change in this gas if it be perfectly dry. Nor is it probable that it would be decomposed by azote, phosphorus, sulphur, or selenium, though I am not aware that the experiment has been tried. It is decomposed by all the metals which decompose water, namely, iron, zinc, tin, and antimony, and also by the metallic oxides. In the last case water is formed and a metallic chloride. When these oxides consist of those of the more powerful bases, the decomposition is accompanied by the evolution of much heat. Thus if pure anhydrous barytes be put into this gas it becomes chloride of barium with the disengagement of light, while water is condensed on the inside of the jar containing the gas. 11. It is at present a subject of discussion among chemists Do muriates whether muriatic acid be capable of combining with bases, and forming muriates, or whether at the instant of combination a double decomposition does not take place; the hydrogen of the muriatic acid uniting with the oxygen of the base and forming water, while the chlorine combining with the other constituent of the base produces a chloride. In many cases of combination the phenomena are such that either explanation may be applied; while in others there can be no hesitation in adopting the last explanation as the true one. Thus if we dissolve 13.75 silver in nitric acid, and mix the neutral solution with 7.5 of common salt, we obtain 18-25 of a white matter, which must be chloride of silver. For it contains • Phil. Trans. 1812, p. 240. † Ibid. 1824. Ibid. 1810. exist? Chap. J, Silver 13.75 4.5 18.25 In the same way when 13 lead is dissolved in nitric acid and mixed with the requisite quantity of common salt, we obtain a white matter weighing exactly 17-5, and therefore chloride of lead. If we dissolve 4-25 zine in muriatic acid, and evaporate cautiously to dryness, we obtain a white matter weighing 9.875. If we heat this matter to incipient ignition in a glass tube it gives out 1.125 of water, and there remains 8.75 of chloride of zinc. We may therefore consider the white compound either The atomic weights and the elements are the same whichever of the two opinions we adopt. The only difference consists in the way in which these atoms are combined. This subject will come under our review more particularly hereafter, when we give an account of the different chlorides or muriates which possess saline properties. SECTION II.-OF OTHER CHLORINE ACIDS. I have no doubt that the number of chlorine acids will very much increase as soon as chemists turn their attention to the subject. But hitherto very few attempts have been made to determine whether those chlorides which contain acidifiable bases be capable of combining with, and neutralizing those chlorides that contain alkalifiable bases. 1. The chlorides of sulphur and phosphorus do not seem possessed of acid properties. At least the attempts which I made to combine them directly with alkaline chlorides did not succeed. It is evident from many chemical phenomena that the chlorides of potassium and sodium are alkaline bodies capable of combining with, and neutralizing various acid chlorides, as for example the chlorides of gold and platinum. But the chlo- Class III. ride of sulphur is incapable of dissolving these bodies even when assisted by heat. Neither did they dissolve one or two metallic chlorides which I exposed to their action. But no sulphuret was formed when the chloride of sulphur was digested over some metallic chlorides, whose bases have a very strong affinity for sulphur. 2. Bonsdorf has shown that corrosive sublimate* possesses acid properties, and is capable of combining and forming salts with a great variety of alkaline chlorides. This indeed has been long known, though Bonsdorf is the first who has explained the nature of these combinations in a satisfactory manner. I shall describe the new salts which he formed in a subsequent part of this work, when I come to describe the chlorine acid salts. 3. There can be little doubt that the chlorides of gold, platinum, palladium, rhodium, iridium, and osmium possess acid properties,+ and that the salts which have been distinguished by the name of double chlorides of gold and sodium or potassium, of platinum and sodium, or potassium and sal ammoniac, &c. are in reality salts formed by the union of a chlorine acid with a chlorine base. These salts, which amount to a considerable number, will be described in a subsequent part of this work, among the chlorine acid salts. 4. I have not had time to make any trials with the chlorides of arsenic and antimony; but should not be surprised to find them capable of combining and forming salts with the alkaline chlorides. The subject at any rate requires to be investigated. CLASS III. BROMINE ACIDS. Bromine has been known for so short a time, and is still so scarce and so dear, that we need not be surprised that this class of acids is still almost unknown. In fact there is only one acid belonging to this class which has been hitherto examined. It will constitute the subject of the following section. SECTION 1.-OF HYDROBROMIC ACID. This acid was discovered by M. Balard, and to him we are * Ann. de Chim. et de Phys. xxxiv. 142; xliv. 189, 244. + See Bonsdorf referred to above. Chap. I. indebted for every thing respecting it yet known. I have given a short account of its properties in the first volume of this work (p. 109), and I have nothing farther to add to that description. It is a compound of one volume of bromine vapour, and one volume of hydrogen gas united together without any alteration in the bulk. Hence its atomic weight is 10-125, and its specific gravity in the gaseous state must be 2.8125. This acid combines with bases, and forms a genus of salts which have been distinguished by the name of hydrobromates. It has not been yet determined whether these salts are really hydrobromates or only bromides, or compounds of bromine with the metallic bases of the alkalies. The difficulty is of the same nature as occurs with regard to the salts formed by means of muriatic acid. CLASS IV. 1ODINE ACIDS. the The analogy between oxygen, chlorine, bromine, and iodine, is so great that we can scarcely hesitate to admit that iodine, like the other three supporters, has the property of forming acids when it combines with various of the acidifiable bases. But except hydriodic acid, the properties of which have been described in the first volume of this work (p. 110), hardly any of the iodine acids have been hitherto investigated. M. Bonsdorf has shown that the periodide of mercury possesses characters of an acid, and is capable of combining with and saturating several of the alkaline iodides, as iodide of potassium, of sodium, of zine, of iron. Similar combinations have been made by M. Boullay. There can be no doubt that the number of iodine acids will increase rapidly, now that the attention of chemists is turned to the subject. It is known already that the iodide of arsenic possesses acid properties, and this will probably be the case with the periodide of antimony. would expect also the iodides of the family of noble metals to be acids, as this is the case with their chlorides. It were to be wished, therefore, that some chemist would set about the investigation of their properties, and of the salts which they may capable of forming. * Ann. de Chim, et de Phys. xliv. 260. We be Class V. Sect. II. CLASS V. FLUORINE ACIDS. I have given in the first volume of this work (page 89), the reasons which have induced chemists to believe that fluoric acid is a compound of fluorine and hydrogen; that fluorine is an electro-negative substance similar in its properties to oxygen, chlorine, bromine, and iodine, and capable like them of combining with the various acidifiable bases, and of converting them into acids. As fluorine has not yet been obtained in a separate state, this opinion cannot be considered as demonstrated, yet the opinion is so plausible and so strongly supported by analogy that it has been very generally adopted. We are at present acquainted with eight acids, which are considered as combinations of fluorine and an acidifiable basis. These are, 1. Hydrofluoric acid, 2. Fluoboric, 3. Fluosilicic, 4. Fluomolybdic, 5. Fluotungstic acid, 6. Fluochromic, 7. Fluocolumbic, 8. Fluotitanic. No combination of fluorine with the nine remaining acidifiable bases has yet been discovered. These eight acids will be described in the following sections. SECTION 1.—OF HYDROFLUORIC ACID. This is the acid which has been described in the first volume of this work (p. 87), under the name of fluoric acid. I have already given an account of the process by which it may be procured in a state of purity, and detailed its properties so far as they have been determined. Nothing farther remains but to give an account of the salts which it forms, and which have been examined in detail by Gay-Lussac and Thenard, and by Berzelius. They will occupy our attention in a subsequent part of this volume. SECTION II.-OF FLUOBORIC ACID. This acid was discovered in 1808 by Gay-Lussac and The History. nard.* Its properties and preparation have been already given in Vol. I. p. 218, of this work. It has not yet been analyzed, * Recherches Physico-chimiques, ii. 37. |