discover the exact quantity of the sulphuric acid. It is well known, that the oxides of gold and platina allow themselves to be entirely precipitated, if, to a mixture of their solutions and of sulphuric acid, we add muriate of barytes. I know not the nature of that affinity by which the sulphate of barytes carries these oxides along with it. I dare not hazard any conjecture respecting the nature of their union; but it does not seem improbable, that several substances, which in mineralogy are considered as foreign, may have been introduced by a similar affinity. But, to return from this digression, to examine the analysis of our double salt:-I have said that we ought likewise to know the composition of neutral carbonate of magnesia. I procured this salt by allowing a solution of magnesia in liquid carbonic acid to evaporate spontaneously. The carbonate deposited itself on the bottom and sides of the glass, in the form of small pellucid crystals, which I dried upon blotting paper. The dry salt was next introduced into a small apparatus, such as I have already described, and heated by the flame of a spirit-of-wine lamp. At the first application of the heat, the salt gave out a great quantity of water, and became milk-white, but preserved the form of its crystals. This salt has the property of efflorescing in dry air, where it loses its water of crystallization, without losing any part of its acid, as I have proved by a direct experiment. I make the observation in this place, because it might be imagined that the efflorescence of the salt was in reality only a transformation of it into magnesia alha. The salt contained in the small cornute was kept in the flame, till it had been red for a quarter of an hour. The two recipients had gained 38.9 per cent. of water. The glass bulb which held the magnesia was anew exposed to a stronger heat, in a crucible of platina, among burning coals. There remained in it 29.6 per cent. of magnesia, entirely deprived of carbonic acid, The loss, 31.5 per cent., was therefore carbonic acid. The portions of oxygen contained in these quantities of magnesia, carbonic acid, and water, are 11.457, 22.89, and 34.33; or proportional to 1, 2, and 3. Consequently, the acid contained 2, and the water 3 times the oxygen of the base. The composition of neutral carbonate of magnesia may therefore be expressed by the formula, Mg C+6 Aq; whence we infer that it contains, It still remained for me to determine the quantity of water, combined with the crystals of the bicarbonate of potash. When treated in the same apparatus as the salts already analyzed, those crystals yielded 9 per cent. of water, and 69 per cent. of carbonate of potash. This result agrees exactly with the formula, KC4+2 Aq†, which denotes that the carbonic acid contained 4 times the oxygen of the base, as well as of the water. These different points being adjusted, we again proceed to examine the result of our analysis of the double carbonate, in order to discover its true chemical composition. The 18.28 parts of potash contain 3.0987 parts of oxygen; and the 15.99 parts of magnesia contain 6.1894, or twice as much. The 34.49 parts of carbonic acid contain 25.57 parts of oxygen, or, with a slight error, 8 times the oxygen of the potash. If we seek to connect the acid with its two bases, we shall find, that it must be divided between them, in such a manner that they may contain equal quantities of it; the potash, however, being at a higher point of saturation, or forming a bicarbonate, whilst the magnesia forms only an ordinary carbonate. This becomes evident, if we consider that the bicarbonate of potash was employed in producing the salt; and that, if the carbonic acid were divided proportionally between the bases, it would give degrees By applying the law stated in page 65. note 2. the quantities found by the experiment are sufficiently correct to indicate that, in conformity with this law, Mg C+6 Aq, is the exact formula; or that (1 atom of magnesium with 2 of oxygen, or) 1 atom of magnesia joined with (2 atoms of carbonium, each containing 2 of oxygen, or with) 2 atoms of carbonic acid, must be combined with 6 atoms of water, in order to form carbonate of magnesia. But the weight of these several atoms being already ascertained, by numerous and varied experiments, the error of the analysis is rectified accordingly.-TRANSL. The meaning of this expression may be collected from the preceding Note, and that to which it refers.TRANSL. of saturation which are improbable, if not contrary to expe rience. It may be observed, that the quantity of water found in this double salt was greater than that contained in the two salts separately; and, as it is to be 'presumed that the strong base, rather than the weak one, would combine with a more than usual quantity of water, this bicarbonate of potash must have contained three times as much water as in its isolated state; and the water in each of the two salts must have contained three times as much oxygen as the base. The composition of this double salt may therefore be expressed by the formula KC1 Aqʻ + 2 Mg C2 C* Aq*: from which we conclude its exact composition to have been, I have been minute in describing the examination of a salt which may appear uninteresting and obscure; but I thought it right to be so, because a careful and exact examination of what allows itself to be determined with ease, enables us to judge of what ought to happen in cases where a similar examination is not equally possible. The analysis of this double salt is highly important in two points of view. In the first place, it shews that two salts formed by the same acid, at different degrees of saturation, with different bases, may unite and constitute a double salt. And this fact confirms those formulas, which have been deduced from the analyses of several substances in the mineral kingdom; of the emerald, for example, the apophyllite, the mesotype, the tremolite, and others; the composition of which being found with sufficient accuracy, connects silica with earths which serve it as salsifiable bases, and exhibits siliciates in different degrees of saturation. Secondly, our analysis proves that the quantity of water which exists in a double salt, is not always the same as that which exists in its component salts, taken These symbols have already been explained.-TRANSL. separately; an important circumstance in analysing those bodies, the composition of which is multifarious and complicated. (To be continued.) ART. XII.-Comparison between the length of the Seconds Pendulum, as determined by Mr Whitehurst and Captain Kater. By EDWARD TROUGHTON, Esq. F. R. S. IN examining Mr Whitehurst's experiments on the length of the Seconds Pendulum, Mr Troughton observed, that the result admitted of various corrections, which were not applied by the gentleman who calculated the length of the pendulum from these experiments*. He therefore proceeded to compute the amount of those corrections, and obtained the following results. The length of the Seconds Pendulum, as calculated by Dr Rotheram, and examined and approved of by Dr Hutton, was 39.11960 inches, when vibrating in a total arc of 6° 40′, and in air at the temperature of 60°. Whitehurst's length of the pendulum,.... Correction for circular arcs,.................. Correction for the weight of the wire rod,............................ Sum of positive corrections,..... Sum of negative corrections,.... Inches. 39.11960 + 0.01654 0.00080 0.00052 + 0.00404 + 0.00030 Difference to be added to the length of the pendu lum,...... Whitehurst's length of the pendulum,.............. + 0.01956 39.11960 Whitehurst's length of the pendulum corrected, .................... 39.13916 • The object of Mr Whitehurst was not to obtain the length of the simple pendulum; but, from two pendulums of different lengths, to obtain a measure, in such a way, that every other person who used the same means could obtain the same measure, He had no occasion, therefore, to apply any corrections to his results. Now, the length of the pendulum, as obtained by Captain Kater, is 39.1386, at the temperature of 62°; but Mr Troughton has proposed a slight correction upon this length, for the following reasons. Captain Kater's pendulum was composed of three different kinds of brass, as stated in the following table. From these numbers Captain Kater deduces 8.469 as the specific gravity of the pendulum, and uses this number in his calculations; but, it is obvious, that the true mean of the above specific gravities, taking into account both the quantity and quality of the brass, is only 8.2601. Beside this circumstance, Captain Kater has omitted to carry the deal ends of his apparatus to the account of buoyancy. When these two sources of error were calculated by Mr Troughton, he found their amount to be 0.00017, which, added to 39.13860, gives 39.13877 for the true result of Captain Kater's experiments. Hence, we have, Whitehurst's length of the pendulum corrected,................. 39.13916 Captain Kater's length of the pendulum corrected,........ 39.13877 Difference,........ 0.00039 If Captain Kater's table of specific gravities is wrong printed, as Mr Troughton suspects, from the circumstance that no workman was likely to use brass so porous as to have its specific gravity so low as 7.816, then the most material part of the correction of 0.00017 is without foundation. A result nearly the same as that of Captain Kater and Mr Whitehurst, has been recently obtained at Greenwich by our celebrated astronomer-royal Mr Pond. His experiments were made with the apparatus which had been used in France, and which was left at the Royal Observatory by M. Arago in the summer of 1817.-In our next Number, we expect to be able to present our readers with an abstract of his results. १ |