III. It cannot, when perfectly dry, be made to act on, or unite with, charcoal. IV. In most, if not in all cases of its evolution, a portion of water is formed. Each of these will be the subject of separate examination. I. Of the conversion of Oxymuriatic Gas into Muriatic Acid, by the action of Hydrogen. It is stated in Dr. Thomson's System of Chemistry,* that water is an essential ingredient of muriatic acid; and that, hitherto, all attempts to procure it in an insulated elastic form have failed. M. Berthollet remarks, that, after having been exposed to a cold equal to 10° of Fahrenheit's scale, the proportion of real acid was to the water as 26.6 to 34.9.† This proportion, as Dr. T. observes, is probably excessive; but it must be noted, that the means employed by Berthollet were not adequate to the condensation of water held in the elastic form by an affinity so powerful as that between the muriatic acid and its water appears to be. Dr. Thomson considers the proportion of 25 per cent. given by M. M. Gay-Lussac and Thenard ‡, as being probably near the truth. Mr. Dalton is, however, inclined to believe that muriatic acid gas contains no aqueous vapour; and the reasoning employed by him is to the following effect. § If oxygen, hydrogen, nitrogen, or any of the other gases which are not readily, and in considerable quantity, absorbed by water, be brought into contact with that fluid, the vaporific force of the heat to which they may be exposed will raise a portion of it into the interstices of their particles; but if fluoric, muriatic, sulphuric, or nitric acid, in the state of gas, be placed in similar circumstances, an attraction is exerted between it and the water; in consequence of which the acid assumes the liquid form. "Hence," adds Mr. Dalton," it should seem that these acid gases, so far from obstinately retaining their vapour, as is commonly imagined, cannot be induced to admit any vapour at all, in ordinary circumstances." This reasoning is very plausible, and certainly highly ingenious; but it seems to me not unobjectionable. The gas experimented on by Mr. Dalton was of necessity previously saturated with aqueous vapour; and, therefore, could not admit into its constitution an additional quantity. No one would hazard the assertion that muriate of lime contains no water of crystallization, assigning as a reason, that, if a very small portion of water be added to the crystals of this salt they assume the liquid form. Yet it appears to me *Vol. v. p. 778. + Troisième Suite des Recherches sur les Lois de l'Affinité, p. 103, &c. that this assertion and proof would be exactly analogous to those offered by Mr. Dalton. Since, then, unless we adopt the recent views of Sir H. Davy, his experiments,* in conjunction with those of Dr. Henry,† M. M. Gay-Lussac and Thenard, M. Berthollet, § Mr. Murray, and Dr. Bostock, ** may be looked on as proving satisfactorily the existence of water in muriatic acid gas; let us examine the relation, in regard to quantity, subsisting between it and the oxygen, which oxymuriatic gas used to be supposed to contain. According to the analysis of Chenevix,++ oxymuriatic gas consists of 77.5 of muriatic acid, united to 22.5 of oxygen by weight. If to this compound a quantity of hydrogen be added, and if the mixture be then exposed to the sun's light, muriatic acid is produced. In Mr. Dalton's detail of his experiments on this subject (which are by far the most complete set that have fallen under my notice), he mentions that he always employed a quantity of water to condense the residual muriatic acid: he could not, of course, easily ascertain whether or not any water was evolved along with the acid. By calculation, I am led to believe there was not: for 22.5 of oxygen are capable of forming, by union with 3.76479 of hydrogen, a quantity of water equal to 26 26479, which approaches singularly near to the estimate of M. M. Gay-Lussac and Thenard; and which may acquire some additional probability from the eircumstance that all others who have experimented on the quantity of water in this gas, have stated it as being greater than that which is assigned by these chemists. I Let us pursue the subject a little farther. Mr. Dalton, speaking of the quantity of hydrogen necessary to decompose oxymuriatic gas, says, "From the mean of five experiments, I am induced to conclude, that 100 measures of hydrogen require 94 measures of oxymuriatic acid gas. In every one of the experiments the acid was less than the hydrogen."§§, I have already stated that 3-76479 of hydrogen are sufficient to unite with the oxygen which 100 of oxymuriatic gas has been thought to contain. Now 3.76479 grs. of hydrogen occupy, according to Phil. Trans. 1809, p. 92, 458. Nicholson's Journal, 4to. vol. iv. p. 247. ** Nicholson's Journal, vol. xxxii. ++ See Thomson's Syst. vol. ii. p. 257. It may not be unworthy of notice that I cubic inch of bydrogen, by union with very nearly 2 inches of oxygen, forms a quantity of water, whose weight is to that of the real muriatic acid contained in 2 inches of the acid gas, as 26 to 100. §§ New System, p. 307. the estimate of Kirwan,* nearly 144'04 cubic inches, and 100 grs. of oxymuriatic gas, as appears from Mr. Dalton's experiments, † are equal to 137.9 inches, which, being reduced, give a proportional bulk, as 100 of hydrogen to 957 of oxymuriatic gas. Thus we see that Mr. Dalton's experiments agree almost exactly with the result of calculation; and if the hydrogen he employed was contaminated by the slightest admixture of extraneous matter, the quantity of oxymuriatic gas condensed by it must of course have been proportionally lessened. Mr. Dalton, having denied the existence of aqueous vapour in muriatic acid gas, ascribes the appearance of hydrogen during the action of certain bodies on that gas to the decomposition of the acid, which he looks on as a quaternate compound of oxygen and hydrogen. While, however, he admits the fact as stated by Sir H. Davy, that "when potassium was heated in muriatic acid gas as dry as it could be obtained by common chemical means, the gas wholly disappeared, and from one-third to onefourth of its volume of hydrogen was evolved, and muriate of potash was formed." He questions the accuracy of an experiment detailed in the Bakerian lecture for 1809, by which this conclusion was established. In this experiment it was found that 8 grs. of potassium absorbed 22 cubic inches of muriatic acid gas, and gave out 8 inches of hydrogen. Before proceeding to examine Mr. Dalton's reasoning on this experiment, it may be well to take a view of it, unconnected with his speculations on the nature of muriatic acid. According to the analysis of Sir H. Davy, § 8 grs. of potassium may be converted into potash, by union with about 1.29152 grs. of oxygen. In order to furnish this oxygen, if water be its source, 1495934 grs. of that fluid must suffer decomposition; and this quantity is sufficient, at the rate of 25 per cent. to give the gaseous form to 5.983736 grs. or in the proportion of 26-26479 to 5.6459 grs. only of muriatic acid gas. At the same time that the oxygen of this water is absorbed by the potassium, its hydrogen, amounting to 204414 of a gr. or 7.82297 inches, must be set at liberty. Thus it appears that the hydrogen evolved was almost exactly equal in quantity to what could be afforded by a portion of water sufficient to oxydate the potassium employed. The experiment appears, however, to be inaccurate, with regard to the absorption of the 22 inches of muriatic acid gas: for 9-29152 grs. of potash are capable of combining with the real acid contained in 5·59055 grs. of muriatic acid gas, which Essay on Phlogiston, p. 30. New System, p. 297. measure 9.641375 cubic inches only. And if we suppose that none of the acid condensed in consequence of the loss of its water entered into union with the potash, and that the acid thus employed carried all its water with it, we have only in addition to this quantity either 5.983736 grs. measuring 10-0062 inches, or 5.6459 grs. measuring 9-42625 inches, making in all a con densation of either 19-643675 or 19.067625 inches. But it is obviously more natural to suppose that the acid deprived of its elasticity from the loss of its water afterwards entered into union with the potash in which case the results of the experiment should have been 13.76396 grs. of muriate of potash, an evolution of 7.82297 inches of hydrogen, a condensation of 1.328152 grs. of an-hydrous muriatic acid, and not less than 11.9977 cubic inches of residual muriatic acid gas. It will be seen by a reference to page 290 of Mr. Dalton's work, that he infers by calculation that during the oxydation of a quantity of potassium sufficient when in the state of potash to unite with 22 inches of muriatic acid gas, were water the source of the oxygen, nearly 16 inches of hydrogen would be evolved; while if the acid gas suffered decomposition 8 inches would appear. This, however, is not perfectly accurate: for the quantity of real acid contained in 22 inches of the gas is capable of combining with 23.0872 grs. of potash, and, for the formation of this, 28175 grs. of oxygen are requisite. Now this quantity of oxygen is, in the state of water, combined with not less than 18.0444 inches of hydrogen. On the other hand, if Mr. Dalton's view of the nature and constitution of muriatic acid be correct, and if this body were the source of the oxygen, there should have been an evolution of 6.0148 inches only, from the oxydation of 20-2697 grs. of potassium. If, however, the 22 inches of muriatic acid gas were the sole source of the oxygen, 16.917 grs. only of potassium would have been required; and the evolution of hydrogen could not have exceeded 4.3739 inches. As, however, the quantity of oxygen required by 8 grs. of potassium is almost exactly sufficient to form water with 8 cubic inches of hydrogen, and as it is certain that 9.29152 grs. of potash cannot form muriate of potash by union with the real acid of 22 cubić inches of muriatic acid gas, is it not better to argue upon á foundation in some degree known, and from phenomena consistent among themselves, than to build speculations on a part of an experiment, which is almost demonstrably impossible? In the only other experiment of this sort detailed by Sir H. Davy, 5 grs. of potassium took nearly 14 inches of muriatic acid gas, and gave about 5 inches of hydrogen: 5 grs. of potassium may unite with 8072 of a grain of oxygen; which in the state of water hold in union 13505 of a grain, or 5·115 VOL. II. N° I. B inches of hydrogen. Now 94225 of a grain of water are capable of giving the gaseous form to either 3.769 grs. (measuring 6.3027 inches) or 3.55609 grs. (measuring 5.94564 inches) of muriatic acid gas; and 5.8072 grs. of potash can unite with the real acid contained in 2.9045 grs. or 4.857 inches of muriatic acid gas: so that the condensation could at most amount to only either 11.1577, or 10.80364 inches. If the condensations were not independent of each other, the results ought to have been 87117 grs. of muriate of potash, 5-115 inches of hydrogen, 8645 of a grain of an-hydrous muriatic acid, and 7.6973 inches of residual muriatic acid gas. Mr. Dalton has, in a subsequent part of his work,* joined with the French chemists in supposing potassium to be a hydruret of potash. He does not, however, look back to the reasoning in page 290, to inquire whether, from the action of potassium on muriatic acid gas, so much hydrogen be evolved, as might, besides the quantity ascribed to the conversion of the potassium into potash, leave a surplus to be accounted for from the decomposition of the acid. It is probable that there is not: and this probability will the better appear, if, for an instant, we admit the truth of Mr. Dalton's atomic theory. In every binate compound, the weights of the combined elements are proportional to those of their atoms. Mr. Dalton has stated the weight of the atom of hydrogen at 1, and that of potash at 42; of course, that of hydruret of potash must be 43. The amount of the hydrogen evolved in Sir H. Davy's first experiment, should therefore have been of 8 grs. or 1860465 of a grain; a quantity less than that noted by Sir H. Davy, by 0183675 of a grain, or about 702 of a cubic inch; and falling short of the result of calculation on the data of the experiment, by only 52477 of a cubic inch. It is almost superfluous to say that this slight discrepancy is not to be wondered at, in an investigation which is as yet only in its infancy. Mr. Dalton, however, says that water is a binate compound; therefore if 8 grs. of potassium contain as many particles as 204414 of a grain of hydrogen, and if the number of particles in this be equal to that contained in 1.29152 gr. of oxygen, it follows that, in these quantities of oxygen and of potassium, there exists an equal number of particles, and potash may still be an oxide of potassium. The hydrogen which appeared may of course have come entirely from the water, without any decomposition of the acid. † * Page 484-486. I would not be understood as having any reference here to Mr. Murray's views of the nature of potassium; but merely as arguing against its being a hydruret of potash. (To be continued.) |