His next questions are: But what becomes of that por- Farther ques tion of oxigen which is liberated? Does it unite with the tions. remainder of the oximuriatic acid, and so united, do they combine with the remaining oxide of potassium? or, is it attracted by the already saturated oride, and that too in the face of a superior affinity?" According to the explanation Answer on the which has been given by Mr. Davy, these objections cer- supposition that potassium. tainly present themselves; but if we agree with Mr. Mur- is united with ray, that potassium is the basis of the alkali united with hidrogen, hidrogen, a circumstance which I think that able chemist has proved from the experiments he has made, and from those of Gay-Lussac and Thenard, they are in a great measure removed. When hidrogen unites by combustion with oxigen, the product which is obtained is invariably water, which Mr. Davy supposes to be the union of these gasses in a neutralized state. Hence as the union of potassium with oxigen is always attended with combustion, there is great probability, that the hidrogen of the potassium unites with oxigen and forms water, and we obtain, instead of an oxide of potassium, as has been supposed, a hydrate; or pure alkali is the unknown base combined with water. That this is the case is also probable, from the very strong attraction alkali has for its water of crystallization, from which both Mr. Davy and Mr. Berthollet say it cannot be entirely freed at a very high temperature: after it has been freed from the water it holds in superabundance, I would suppose, it then requires the aid of a chemical agent, powerful enough to decompose the water it still retains, thus liberating the oxigen, whilst the hidrogen remains united to the unknown base, forming potassium. Again, as oximuri stic acid can unite with water, it requires no twisting of theory to suppose, that the hyperoximuriate of potash is a triple compound consisting of oximuriatic acid, water, and the unknown base, having, perhaps, by the combined affinity of the water and this base an excess of oximuriatic acid, and of course no evolution of gas would take place. This opinion might be extended a little farther, and we may secount for the disengagement of oxigen from the hyper See Mr. Murray's paper, Number for April. oximuriate Composition of the two muriates Boximuriate of potash upon the application of heat, by the combined affinity of the unknown base and oximuriatic acid for hide gen being enabled to overcome, by the aid of heat, the affinity of the oxigen for the hidrogen, which neither of them can effect separately. owing to the two acids coming over. tion of the fuming liquor of Libavius. His next observation is, that, as muriate of potash is a compound of mariatie acid and potash. "We must now suppose, that, when the oximuriatic acid first enters the solution of potash, part of it attracts from the water of the solution, a portion of hidrogen; and, being thus changed to muriatic acid, combines with the potash to form muriate of potash. The oxigen thus liberated unites to the other portion of the oximuriatic acid and the hyperoximuriate of potash is formed," which, he says, is a direct contradiction to the theory advanced to account for the liberation of oximuriatic acid in the retort. To account for the formation of the muriate of potash, there can be no occasion to have recourse to the decomposi tion of the water; for, as muriatic acid is extremely volatile, and as the action of the oxide of manganese is not instantaneous; it is evident, that part of the muriatic acid will rise and pass over with the oximuriatic acid, particularly in the first stages of the process, and hence we find both the mu riate and oximuriate of potash. Decomposi⚫ Mr. Davy, in accounting for the production of water when muriatic acid is passed over litharge, says, it arises from the superior affinity, which exists between the oxi muriatic acid and the lead, and the subsequent union of. the hidrogen of the one and the oxigen of the other. Next, . he accounts for the oxide of tin and muriate of ammouia, obtained by ammonia upon the addition of water to the fuming liquor of Libavius, as owing to the superior affi❤ nity between the oximuriatic acid and the hidrogen. Now your correspondent justly observes, that, "in the first place, water is composed because the affinity of oximuriatic acid for a metal is greater than the quiescent affinities, taken together, of oximuriatic acid for hidrogen and the metal for oxigen; and, in the second, water is decomposed because the affinity of oximuriatic acid for a metal is less than the now divellent affinities of oximuriatic acid for hidrogen and the metal metal for oxigen". Supposing the compositions of the wa ter in the first instance to take place according to Mr. Davy's views, then, in, the second, the oximuriatic acid is attracted from the tin by the ammonia, at the same time it attracts, in its turn, the hidrogen of the water; and as by the attraction of the ammonia the affinity between the oximuriatic acid and tin is weakened, the tin by this being enabled to attract the oxigen of the water, and the oximuriatic acid attracting the hidrogen, the water is decomposed, and the oxide of tis and muriate of ammonia are formed. Experiments on Allanite, a new Mineral from Greenland, by THOMAS THOMSON, M. D. F. R. S. E. Fellow of the Imperial Chirurgo-Medical Academy of Petersburgh.* ABOUT three years ago, a Danish.vesself was brought Collection of into Leith as a prize. Among other articles, she contained minerals in a Danish prize. a small collection of minerals, which were purchased by Thomas Allan, Esq., and Colonel Imrie, both members of this society. The country from which these minerals had been brought was not known for certain; but as the collection abounded in cryolite, it was conjectured, with very considerable probability, that they had been collected in Greenland. Among the remarkable minerals in this collection there One of these was one, which, from its correspondence with gadolinite, as supposed to be gadolinite. described in the different mineralogical works, particularly attracted the attention of Mr. Allan. Confirmed in the idea of its being a variety of that mineral by the opinion of • From the Transactions of the Royal Society of Edinburgh. + Der Fruhling, Captain Jacob Ketelson, captured on her passage from Iceland to Copenhagen. Count Description of it. Count Bournon, added to some experiments made by Dr. Wollaston, he was induced to give the description, which has since been published in a preceding part of the present volume. About a year ago, Mr. Allan, who has greatly distin guished himself by his ardent zeal for the progress of mi neralogy in all its branches, favoured me with some specimens of this curious mineral, and requested me to examine its composition; a request which I agreed to with pleasure, because I expected to obtain from it a quantity of yttria, an earth which I had been long anxious to examine, but had not been able to procure a sufficient quantity of the Swedish gadolinite for my purpose. The object of this paper is to communicate the result of my experiments to the Royal Society; experiments which cannot appear with such propriety any where as in their transactions, as they already contain a paper by Mr. Allan on the mineral in question. Sect. 1. I am fortunately enabled to give a fuller and more accurate description of this mineral than that which formerly appeared, Mr. Allan having since that time dis covered an additional quantity of it, among which he not only found fresher and better characterised fragments, but also some entire crystals. In its composition it approaches most nearly to cerite; but it differs from it so much in its external characters, that it must be considered as a distinct species. I have therefore taken the liberty to give it the name of Allanite, in honour of Mr. Allan, to whom we are in reality indebted for the discovery of its peculiar nature. Allanite occurs massive and disseminated, in irregular masses, mixed with black mica and felspar; also crystallised; the varieties observed are, 1. A four-sided oblique prism, measuring 117° and 63% { 2. A six-sided prism, acuminated with pyramids of four sides, set on the two adjoining opposite planes. These last are so minute as to be incapable of measurement. But, as nearly as the eye can determine, the form resembles fig, 1, Pl. II; the prism of which has two right angles, and four measuring 135°. 3. A flat prism, with the acute angle of 63° replaced by one plane, and terminated by an acumination, having three principal principal facettes set on the larger lateral planes, with which the centre one measures 125° and 55°. Of this specimen an engraving is given in the annexed plate, fig. 2. Specific gravity, according to my experiments, 3.533. The specimen appears to be nearly, though not absolutely, pure. This substance, however, is so very much mixed with mica, that no reliance can be placed on any of the trials which have been made. Count Bournon, surprised at the low specific gravity noted by Mr. Allan, which was 3,480, broke down one of the specimens which had been sent him, in order to procure the substance in the purest state possible, and the result of four experiments was as follows. 4.001 3.797 3.654 3.119 In a subsequent experiment of Mr. Allan's, he found it 3.665. From these it appears, that the substance is not in a pure state. Its colour is so entirely the same with the mica, with which it is accompanied, that it is only by mechanical attrition that they can be separated. Colour, brownish-black. External lustre, dull; internal, shining and resinous, slightly inclining to metallic. Fracture, small conchoidal. Fragments, indeterminate, sharp-edged. Opake. Semihard in a high degree. Does not scratch quartz or felspar, but scratches hornblende and crown glass. Brittle. Easily frangible. Powder, dark greenish-gray. Before the blowpipe it froths, and melts imperfectly into a brown scoria. Gelatinises in nitric acid. In a strong red heat it loses 3.98 per cent of its weight. Sect. 2. My first experiments were made on the supposi- Experiments, tion, that the mineral was a variety of gadolinite, and were to ascertain its pretty much in the style of those previously made on that substance by Ekeberg, Klaproth, and Vauquelin. composition. 1. 100 grains of the mineral, previously reduced to a fine Silex. VOL. XXIX.-MAY, 181). powder |
