the Stony and the Vitreous Characters in Lavas. 287 and are stated in the annexed table, which may be depended upon, in every example, to within two, or at moft three degrees. The artificially cryftallized fubftances have been denoted, at Dr. Hope's fuggeftion, by the name of crystallite. The various fufibilities ftated in the table afford fome conclufions of confequence. The whins fubmitted to trial are more refractory than the lavas; though their excefs in this respect is not great, fince the most fufible of the former class equal the most refractory of the latter. The glaffes are all incomparably more fufible than the original ftones. This laft circumftance has long been known as a fact; but Sir James propofes to fuggeft the theory of it, and of all the peculiarities which occurred in those experiments, in a fecond communication which he means foon to lay before the Society. It is obfervable, that the lava No. 12 is fufible at 18; that is, it resembles in this property the moft fufible glaffes. And it is in fact a glass; for, being lifted in a soft state from a flowing lava of Vefuvius by Sir James Hall, it quickly cooled, and has of consequence affumed the vitreous character in every refpect: for, befides its easy fufibility, it poffeffes the fhining furface and fracture of glafs. This fubftance, being treated like the artificial glaffes of whin and lava, crystallized like these, and affumed the character of a stony lava, both in texture and in difficult fufibility, fince it foftened only at 35°. Here then is a proof beyond difpute, that the ftony character of a lava is occafioned folely by flow cooling. Although the internal structure of lava was thus accounted for, yet Sir James was embarraffed with the ftate of its external furface; which, though cooled in contact with the open air, is feldom or ever vitreous, holding an intermediate ftation between glafs and ftone;-but this difficulty was removed by a circumftance which took place in the courfe of thefe experiments. It was found that a small piece of glass of any of the lavas, or of several of the whins, being introduced into a muffle, the temperature of which was at any point between the 20th and the 224 degree of Wedgwood's fcale, the glass became quite soft in the space of one minute; but, being allowed to remain till the end of a fecond minute, it was found to have become hard throughout in confequence of a rapid crystallization, to have loft its character of glafs, and to have become by 12 or 14 degrees more infufible, being unaffected by any heat under 30, though the glass had been fufible at 18° or at 16. This accounted for the scoria on the surface of lavas; for the substance even at the furface, being in contact with the flowing ftream and surrounded with heated air; could not cool with exceffive rapidity; and the experiment shows, that should any part of the mass, in descending heat, employ more than one or two minutes in cooling from 22 to 20, it would infallibly lofe its vitreous character. The internal phænomena of volcanos being thus explained by the properties of common fire, and the resemblance, or identity, of many lavas and of whinstone being thus established, Sir James Hall conceives, that the powerful arguments advanced by Dr. Hutton, to prove the igneous origin of whin one and other mineral bodies, are very strongly corroborated; fince thefe experiments fhow that thefe fubftances may have been formed by a fimple extenfion of the fame caufes which continue at this day to agitate various parts of our globe. Independently however of any allufion to fyftem or to general theory, Sir James Hall flatters himself that thefe experiments may be of fome importance by fimplifying the history of volcanos; and above all by fuperfeding fome very extraordinary, and, he conceives, Pp2 unphilofophical 288 Remarkable Habitudes of Volcanic Products. unphilofophical opinions advanced with regard to volcanic heat, which has been stated as poffeffing very little intenfity, and as acting by fome occult and inconceivable influence, or with the help of fome invifible agent, fo as to produce liquidity without fufion. These fuppofitions, which have been maintained seriously by fome of the most celebrated naturalifls in Europe, have originated from the difficulty of accounting for the ftony character of lavas, when compared with that of glafs, which they affume in confequence of fufion in our furnaces. But now he hopes we may be relieved from the neceflity of fuch violent efforts of imagination, fince the phænomena have been fully accounted for by the fimple though unnoticed principle of refrigeration, and have been repeated again and again with cafe and certainty in a fmall chamber furnace. TABLE. The fufibilities, according to Wedgwood's pyrometer, ftated in the following table, were afcertained by heating the fubftances in a muffle, in which they could be diftinctly obferved, while expofed to the action of the heat. A fmall piece of the fubftance to be examined being put into the muffle, a pyrometer-piece was placed close befide it, and the heat raised gradually. The fubftance was touched at intervals with a flender iron rod; and when found fo foft as to yield easily to flight preffure, the pyrometer was withdrawn, and measured. [All the whins except No. 7. were taken from their original rocks in the neighbourhood of Edinburgh. ] Potafo and Soda found in Volcanic Products. 289 II. On the Analysis of Pumice, which is found to contain Potash; and of Bafaltes and Lava containing Sola. By Dr. KENNEDY *. ON the N the 5th of February 1798, an analyfis of pumice was communicated to the Royal Society of Edinburgh by Dr. Kennedy. By this analyfis he fhewed that the pumice contained potafh as one of its component parts. The fpecimen analyfed was of the common kind, having a fibrous texture and a fi.ky luftre. By a heat of 60° of Wedgwood, it was converted into a kind of glafy enamel; and in a muffle, even at a heat of 35 or 40, was so far altered, that its fibrous texture could no longer be diftinguished. Befides potash, it contained filex, argill, and a fmall quantity of iron; but no lime or magnesia. Several other varieties of the common kinds of pumice ufed in the arts, were found as fufible as the fpecimen above mentioned, and gave the fame kind of glaffy enamel. The refult of the analysis, with refpect to the earths and iron, correfponds very nearly with the refult of Mr. Klaproth's, published in the 2d vol. of his Beiträge; only he did not find potash in the specimen he analysed; in which, however, there was probably fome faline fubftance; for the fame kind of pumice melted in the porcelain furnace of Berlin; in which a compound confifting only of filex, argill, and a minute portion of iron, would certainly not have melted. The heat of this furnace was 136 of Wedgwood.-See Klap. Beytr. vol. 2d, p. 88. On the 6th of Auguft Dr. Kennedy announced to the Society, that he had difcovered mineral alkali in feveral varieties of bafaltes or whinftone. He found by chemical analyfis, that the alkali existed in these substances in a state of very intimate combination with their earthy bafes; and that it was with difficulty feparated, even by the strongest acids. Dr. Kennedy also analysed a specimen of lava from Etna, at the request of Sir James Hall, who thought it extremely probable that alkali would be found in lava, as well as in bafaltes, on account of the great resemblance which these two fubftances have to each other, both in external appearance and in many chemical properties. The fpecimen was broken, by Sir James Hall and Dr. Hume, from the celebrated current of lava which in 1669 deftroyed part of the town of Catania. It was found, like the basaltes, to contain foda. One of the fixed alkalis, potash, has already been difcovered in ftony fubftances by the celebrated Mr. Klaproth, to whom the world is indebted for so many analyses performed with the greateft fkill. The experiments above-mentioned fhow, that the other fixed alkali, foda, likewife exifts in ftony fubftances. * Abstract, by favour of the Author. This paper will appear in the 5th vol. of the Edinburgh Transactions, III, Experiments 290. Preparation of the Oxygenated Muriat of Potah III. Experiments and Obfervations on the Preparation, and some remarkable Properties of the Oxygenated Muriat of Pot-afh. By Mr. THOMAS HOYLE, jun. HAVING * AVING an opportunity in preparing the oxygenated muriatic acid for the purpose of bleaching, by a fmall extenfion of the apparatus, to prepare likewife the oxygenated muriat of potash, and to make experiments on that fubftance, I have been induced to digeft. the most material facts and obfervations which occurred, and to lay them before the Society: efpecially as I do not find much on the fubject in the writings of others, and as many have: probably been deterred from the investigation by the exorbitant price of the article, and by fome apprehenfions of danger attending it. A few experiments, which are not new, have been introduced, in order to bring under one point of view the principal chemical facts which relate to this falt. I have given in most cases an exact account of the quantities of the different ingredients compofing the. mixtures; and as perfons not much accustomed to fuch experiments may be inclined to repeat fonie of them, I would caution them not to use greater quantities than are here specified,, particularly where the terms violent detonation, explosion, &c. are employed. I would not by any means wish it to be understood that I have exhausted the subject: many more experiments and much labour and affiduity are required, before the nature and ufes of fo active a fubftance can be fully afcertained. I find it has been introduced into medicine with fuccefs; and I hope its good effects in that respect will not be frustrated by the high price of the article, as it may be procured at a much cheaper rate than it is commonly charged.. I. On the Preparation of the Salt, and its Solution in Water and the Acids. Finding that a quantity of gas escaped occafionally from our apparatus for making the: new bleaching liquor, more especially when the fire was not properly managed, or when by any other means a greater quantity of gas was produced than the liquor could abforb;: I thought it would be useful to adapt to the large apparatus a smaller one, in which this. fuperfluous gas might be condensed; as the escape of it was fometimes difagreeable to the workmen. This I did by filling an earthen-ware bottle with a strong folution of potash in water (confifting of about three pounds of alkali to the gallon), which I found entirely re-. lieved us from the disagreeable smell we frequently experienced before, and at the same time yielded a confiderable quantity of the oxygenated muriat. Though the production of the oxygenated muriat in this way be fomewhat precarious, depending upon the manage-. .ment of the perfon who conducts the procefs (it being the bleacher's intereft to condense. the whole of the gas in the liquor he wants for his business); yet I think, if the portion which commonly escapes were thus difpofed of, a confiderable quantity of this falt might be. made by bleachers with little additional expence, except what is incurred by the purchaseof the alkali, and fome more labour and attention. At fome of my first trials, about two years ago, I found the gas which efcaped from the materials of one diftillation fufficient to. faturate two gallons of the alkaline folution, from which I procured about fix ounces, and Manchester Memoirs, vol. v. part i.. fometimes fometimes more of the falt, after being purified by several crystallizations. But having made fome alteration in the apparatus, I now find that the fame quantity of alkali may remain for three or four diftillations before fufficient gas be furnished to form the falt; except the perfon employed be remarkably inattentive to his duty. I confider this as a valuable improvement, the making of the falt being only a fecondary object. The falt was chiefly formed during the diftillation. The alkali became warm toward the latter end of the procefs, efpecially if the abforption of gas was very rapid, a quantity of caloric being dif engaged. In this cafe, a confiderable part of the falt foon cryftallized, on the lixivium being fet in a cool place, and a great deal of gas appeared to escape; which on one occafion `I collected, and found that it precipitated lime from its solution in water, and extinguifked flame and therefore, though it had a flight fmell of the oxygenated muriatic acid gas, I believe that it confifted chiefly of carbonic acid, as the former occafions no precipitation of lime water, which the latter uniformly does. A glass jar containing 32 ounce measures of this gas, being left over water one night, was reduced to about one fourth its bulk. The gas that remained seemed to contain more oxygene than the air of the room; two meafures of it, with one of nitrous gas, gave 1.53, whilft an equal quantity of common air gave 1.9. Before any of the salt appeared to be formed in the alkaline folution, I have conftantly obferved a quantity of earthy matter to be precipitated. This was carefully feparated from the falt, and, after being washed repeatedly in boiling water, was fuffered to dry; but not having examined it with fufficient minuteness to say what it is, I fhall content myself at prefent with ftating fome of its properties. It did not detonate with fulphur, and was totally or nearly insoluble in water. The fulphuric acid diffolved it, and gave evident figns of muriatic acid, which appeared to be flightly oxygenated. After being exposed to a red heat for half an hour, the above properties ftill appeared the fame, except with the fulphuric acid. I thought the gas that was difengaged had more of the fmell of fimple muriatic acidgas, though along with it a little of the oxygenated gas might be perceived. The muriatic acid did not appear to diffolve any of this fubftance, either before or after its calcination. With the nitrous acid a strong smell of the oxygenated muriatic gas was produced. From a dram of this substance in an earthen retort exposed to a strong heat, about fix ouncemeasures of gas were produced, confifting of a mixture of carbonic and azotic gas, the latter of which was in the greateft quantity, forming by eftimate about three fourths of the whole. The form of the cryftals that first appeared in the folution of alkali were quadrangular plates what were afterwards formed, when the lixivium became cool, were needle-like, as were those that were produced by spontaneously evaporating the remainder of the ley: they appear to have the fame property of detonating as the firft. Thefe different forms of cryftals appeared on diffolving the falt in hot water, and, when cold, feparating the falt, and fuffering the water to evaporate fpontaneously. I frequently obferved, that unless the alkali began to part with a confiderable portion of gas without the admiffion of any from the apparatus, little or none of the oxygenated muriat was procured; and that as this gas (which I have before obferved to be chiefly the carbonic acid) efcaped, the crystallization took place, and increafed or diminished according to the evolution of that gas. This I found uniformly the cafe, whether mild or cauftic. alkali |