XVIII. Notes on Mineralogy.No. IV. On the Pitchstone Porphyry of Lough Eske, Co. Donegal. By the Rev. SAMUEL HAUGHTON, M.A., Professor of Geology in the University of Dublin*. URING a visit to the Co. Donegal in the summer of 1856, I observed a remarkable series of dykes of felspathic trap and porphyry intersecting the granite of Barnesmore Gap, exhibiting occasionally a tendency to pass into a description of glossy pitchstone. Subsequently I was favoured by James Wood, Esq., of Castlegrove, with some specimens from the mountains beyond Lough Eske, in the same locality, which are genuine pitchstone, passing into amygdaloidal, or rather oolitic porphyry, the cavities being filled with a white mineral which I consider to be stilbite. As the locality is a new one for pitchstone, and the mineralogical.composition of the rock unusual, I thought it might not be uninteresting to the readers of the Philosophical Magazine to place on record its analysis, and the result of my discussion of that analysis. totra Inas Analysis of Pitchstone from Lough Eske, Co. Donegal, viggie blow moto 911 to erodas en to Per-centage. 14tongool visva - 64-04 binow 9. on morbose bor 8 ei aid Magnesia won fi upitnoilage feniario di adder som dam sense Assuming this rock to be composed of quartz, felspar and stilbite, and writing Q, F, S for the number of atoms of each mineral respectively, we find, -098 on Quartz T Felspar Stilbite RO, SiO3 + R2 03, 3SiO3, RO, SiO3+ R2 03, 3SiO3 + 6HO, If we take 314 for the atomic weight of stilbite, which accords with its usual composition, we find the following to wola It would be very desirable that an investigation similar to the foregoing were made into the composition of the different varieties of the vast and heterogeneous family of trap rocks. The nomen clature of this class of rocks is a reproach to geological science; and no satisfactory classification can ever be made of these rocks which is not based on their chemical and mineralogical, as well as on their physical properties. Why should not such a body as the British Association undertake the task of reducing to order at least the British varieties of igneous rocks? The funds requisite for the investigation could easily be procured, and the zeal of the members of the Association would supply specimens from every locality of interest; and certainly an authorized nomenclature of igneous rocks proceeding from such a source would carry with it a weight which would go far to establish uniformity of language and precision of ideas on this important, but neglected, subject among British geologists. Let us take, for an example, the term clinkstone. This is a name given from a physical property common to it with many other rocks, including even limestones. The term was one formed in the infancy of geology, and has come to be used in a sense much more restricted than its original application; it now signifies a fine-grained felspathic rock, of conchoidal fracture, generally of a grayish colour, and containing zeolites as well as felspar. This is the correct meaning of the term clinkstone; and yet it is constantly applied to rocks which contain no zeo. lites, and some of which are not even of eruptive origin. This confusion as to the meaning of the term has led to the use of various synonyms, or quasi synonyms, of which it is sufficient to mention felspathic trap, hornstone and felstone,-the latter recently revived very usefully by the Government geological surveyors. Why should not all these terms, if retained at all, be used in definite senses? The republic of geologists is small, and many of its citizens are well educated; surely there could be no great difficulty in getting them all to use the same language. Trinity College, Dublin, January 14, 1857. IT. XIX. Chemical Notices from Foreign Journals. [Continued from vol. xii. p. 538.] T is known from the researches of Magnus that arterial blood absorbs about 10 times as much oxygen as does water. M. Fernet*, with the idea that this greater absorption was not owing entirely to the blood-globules (for many substances having only a weak affinity for gases may impart to water the property of absorbing them in a considerable degree), has made a series of experiments on the solubility of gases in certain saline solutions. He took successively solutions of different degrees of concentration of the principal salts found in blood, and determined their coefficient of absorption for gases, by means of an apparatus specially contrived by him for the purpose. For a description of this the memoir itself must be consulted. His experiments have as yet been confined to carbonic acid, A solution of chloride of sodium containing 15 per cent. of the salt, diminishes the solubility of carbonic acid by about one half. With phosphate of soda the volume of gas absorbed increases in a very rapid manner with the strength of the solution. All the numbers hitherto obtained appear to show that the coefficient of absorption for carbonic acid in solution of phosphate of soda, is deducible from the coefficient of absorption in pure water, added to the product of a constant coefficient multiplied by the strength of the solution. From this it would appear that there is, besides the solution of the gas in water, a true combination with the salt which complicates the phænomenon. This is also the case with carbonate of soda, with the exception that the coefficient is a different number. Schönfeldt has investigated the coefficient of absorption in water for sulphurous acid, sulphuretted hydrogen, and chlorine. The determinations were made by the chemical method, and not by the absorptiometert. With sulphurous acid, an arrangement was adopted by which the water could be saturated with the gas at constant temperatures. A measured quantity of this was taken, and the quantity of gas absorbed determined by a solution of iodine in iodide of potassium. As by the great absorption of gas the volume of the solution is very perceptibly altered, this circumstance must be taken into account. The absorption was determined between 0° and 40°. For chlorine the same arrangement for absorption was used; *Annales de Chimie et de Physique, August 1856. + Liebig's Annalen, July 1855. Phil. Mag. vol. ix. pp. 116 and 181. but as chlorine forms a hydrate at 10° C., the coefficient was only determined between 10° C. and 40° C. The chlorine was determined by mixing a measured quantity of the solution with a solution of iodide of potassium, and estimating the iodine set free. The absorption of sulphuretted hydrogen was made in a similar manner, and the gas absorbed estimated by mixing the solution with chloride of copper, and determining the sulphur in the sulphide of copper precipitated. Schönfeld has also made experiments on the absorption of mixtures of sulphurous acid and carbonic acid, and of sulphurous acid and hydrogen, and has found that the results obtained agreed well with the formula developed by Bunsen* for the absorption of gaseous mixtures. Carius has made a series of experiments on the absorption of various gases in alcohol, and has shown that the law of absorption is the same for this liquid. This is also the case with mixtures of gases. Carius determined the absorbability of a mixture of carbonic oxide and carbonic acid, of carbonic oxide and marsh gas, of carbonic acid and hydrogen, of sulphurous acid and hydrogen, and of a mixture of three gases, carbonic oxide, marsh gas, and hydrogen. In all these cases the results agreed with the numbers required by Bunsen's formulæ. The same chemist has also proved that the law of absorption is applicable in the case of ammonia. The determinations were made by the chemical method; the quantity of ammonia dissolved at a given temperature being estimated by a standard solution of sulphuric acid. With a mixture of hydrogen and of ammonia the law of absorption also prevails. Recent determinations of the atomic weight of antimony made by Schneider and Rose, will render necessary a material alteration in the number usually adopted. In Schneider's experiments, the material employed was a native sulphuret of antimony, of an extraordinary degree of purity, which occurs at Arnsberg, The only impurity it contains is about per cent. of quartz, which was always brought into calculation. The mode of determination was by reducing it to the metallic state and weighing it as such. The reduction was effected by heating it in a difficultly fusible glass tube, and passing hydrogen over it: the reduction takes place at a temperature at which only the merest traces of sulphuret of antimony are volatilized, and at which the glass is not melted. The sulphuret of antimony volatilized was collected and estimated, but when the current *Phil. Mag. vol. ix. pp. 116 and 181. of gas was not too rapid, its quantity did not exceed a millia gramme, even when the weight of sulphuret was 6 to 8 grammes. -It was with great difficulty that the last traces of sulphur were vexpelled from the antimony, and it was found necessary to estimate this by dissolving the residual metal in aqua regia; bthe quartz which remained undissolved was collected and (weighed.) The solution was then evaporated to dryness, the mass heated to expel free acid, and after treatment by boiling water, it was digested with pure carbonate of soda. The oxide of antimony which separated was filtered off, and the sulphuric acid contained in the filtered liquid estimated as sulphate of baryta. The quantity of sulphur deduced from the sulphate of baryta thus obtained, never exceeded of the weight of antimony. T 1000 Eight experiments made in this way, and with perfectly concordant results, gave a mean of 71.48 antimony and 28-52 bof of sulphur. Taking the equivalent of sulphur as fixed, the equivalent of antimony deduced from these numbers will be 1503 orgen scale, or 120-3 for hydrogen=1. The on last determination of Berzelius had fixed the equivalent at 1612.9, ad fixed or 129 on the hydrogen scale. + C90 In confirmation of Schneider's results, Rose has published* a determination of the atomic weight of antimony, which had been some time ago effected by Dr. R. Weber. He use used for this purpose the solid terchloride of antimony, SbCl. This was dissolved in water containing tartaric acid (since water alone Eldecomposes chloride of antimony), and the antimony précipitated by passing sulphuretted hydrogen through the liquid. In the -filtrate from the precipitate of sulphide of antimony, the chlorine was determined as chloride of silver. It was this found & that 58 15 parts of antimony corresponded to 46.85 of chlorine, from which Rose deduces the equivalent of antimony to be £ 1508,666, or 120.6 on the hydrogen scale. " It is interesting to notice that the arithmetical mean between the new equivalent of antimony 120-3, and the equivalent of & phosphorus (31-0 Schrötter), is 75 65, which is very nearly the equivalent of arsenic (75-0 Pelouze). There appears therefore to subsist between these three bodies a similar relation to that which exists between barium, strontium, and calcium. The new equivalent of antimony will give to many analyses of antimonial compounds which had appeared faulty their due value. Kermesite contains, according to the old equivalent, 76.25 per cent. antimony. Rose's analyses gave 75-06 per cent. antimony; on the new equivalent it contains 75-04 per cent. In a research on the antimoniates made some time ago, Heffter assigned to **Poggendorff's Annalen, June 1856. |