the Count de Bournon has thus been enabled to investigate and describe the various crystallizations, and other appearances, assumed by this remarkable substance. The Count observes that above twenty years have elapsed since the arseniate of copper was first discovered, either in Carrarach mine in the parish of Gwennap, or in Tincroft mine in the parish of Allogan. The matrix of the ores of these mines is a decomposed granite, in which the feldtspar has passed into the state of that argillaceous substance called kaolin. The matrix also of the one of Huel Gorland is siliceous, sometimes crystalline, and sometimes in an amorphous mass; occasionally, more or less mixed with all the known oxides of copper, with some of the oxides of iron, with grey vitreous copper ore, arsenical pyrites, and the rich deep coloured yellow copper ore: which, from its mamillated and botryoidal forms, as well as from some additional peculiarities, the Count de Bournon distinguishes from the other varieties of yellow copper ore by the name of yellow hematitic copper. Nature (fays the author) has established very remarkable differences between the arseniates of copper; and these take place not only in their forms, but likewise in their hardness and specific gravity. These differences arise, either from the manner in which the arsenic acid is combined with the copper, or from the different proportions in which these two substances are combined. I have been naturally led to follow the same order, and to divide the arseniates of copper into four different species: and the very interesting analysis of this substance made by Mr. Chenevix, has afforded me the most satisfactory sanction to this division. It is thus that the chemist and the naturalist, by freely uniting their labours, without jealousy or prejudice, ought in all cases to proceed, in order to attain that certainty which is the desirable recompense of their endeavours.' The Count de Bournon then proceeds to describe the following species of the arseniates of copper: Species 1. Arseniate of copper in the form of an obtuse octaedron. The most simple shape, under which this species appears, is a very obtuse octaedron, produced by the united bases of two tetraedal pyramids, with isosceles triangular planes; and this appears to be its original form. It varies in colour, from sky to Prussian blue, and frequently is of a fine grass green: it is seldom perfectly transparent; and its specific gravity is 2,881. Species 2. Arseniate of copper in hexaedral lamina, with inclined sides. This is of a fine deep emerald green colour; and the specific gravity is 2,548. Species 3. Arseniate of copper in the form of an acute octaedron. The colour of this species is usually brown or bottle-green, sometimes with a yellowish or golden tint:-the average spe cific gravity is 4,280. The author remarks that this is not always crystallized in a determinate form, but is an absolute proteus both with respect to the different shapes in which it appears, and the various colours which it exhibits. He then notices the five following varieties: 1. Capillary, of a determinate form, which is that of a very lengthened octaedron. 2. Capillary, of an indeterminate form. 3. In crystals perfectly regular for a part of their length, and fibrous at their extremity. 4. Amianthiform. 5. Hematitiform. Species 4. Arseniate of copper in the form of a triedrul prism. The colour of this is a very beautiful bluish, or deep verdigrise green; and the specific gravity is 4,280.-This species, as well as the former, is susceptible of many modifications in the figure of its crystals: but the nature of our publication will not allow us to enter into minute particulars. We must therefore here conclude the first section. of Count de Bournon's paper, and proceed to the second, which treats of the arseniates of iron. The Count observes that these arseniates are found in Muttrel mine, which is immediately contiguous to Huel Gorland. Hitherto they have been confounded with the arseniates of copper: but the result of Mr. Chenevix's Analysis (see the succeeding paper) proves, beyond a doubt, that they are com posed principally of iron combined wirh the arsenic acid. The present author then describes the two following species: Species 1. Simple arseniate of iron. The crystals of this species in general are perfect cubes, of a dark green, brownish, or yellowish colour. The specific gravity is 3,000. Species 2. Cupreous arseniate of iron. The crystals of this species are of uncommon brilliancy, and perfectly transparent. Their form is a rhomboidal tetraedral prism, having two of its edges very obtuse, and the other two very acute. The prism is terminated at each extremity by a sharp tetraedral pyramid. The crystals seldom occur singly, but are generally grouped in an irregular manner. The colour most commonly is a very faint sky-blue; and the specific gravity is 3,400. We doubt the propriety of this part of the Count de Bournon's arrangement; since, from Mr. Chenevix's analysis of these two arseniates, they do not appear to be distinct species, but rather varieties of the cupreous arseniate of iron. We shall more fully consider this part in our remarks on the following paper. Analysis of the Arseniates of Copper, and of Iron, described in the preceding Paper; likewise an Analysis of the Red Octaedral Copper Ore of Cornwall; with Remarks on some particular Modes of Analysis. By Richard Chevenix, Esq. M. R.I.A. R 3 We have have seen, in the preceding paper, the external characters of these arseniates, very accurately described by the Count de Bournon; and the present memoir, we think, will prove that the analysis of these substances has been not less ably performed by Mr. Chenevix. When the Count de Bournon (says Mr. C.) had completed what appeared to him to be the mineralogical classification of these copper ores, he gave me some specimens of each kind, numbered indiscriminately, for the very purpose of excluding prejudice: and it was not till my task was ended, that we compared our observations. If I had been admitted into any previous knowledge of the arrangement dictated to him by the principles of crystallography, I should have been afraid, that I had merely thought true, what I wished to be so. But I can, most conscientiously, indulge in the satisfaction which the according results of different means to prove the same proposition naturally excite; and which is justly due to the truth of the outward marks, however delicate, yet still to be perceived, that nature has left visible to those who will observe her. I shall now proceed to offer the result of a chymical analysis, undertaken with a view to determine what confidence the crystallo. graphical arrangement, adopted in the preceding paper, might merit; and to shew how far sciences so nearly allied, may receive new light and confirmation from reciprocal aid. I shall confine myself to detail only those general processes which, upon frequent trial, have been found preferable. By reducing to powder any of the arseniates of copper here spoken of, and then exposing them to heat in a platina crucible, the water of crystallization was quickly dissipated. But, as too great a degree of heat volatilized some portion of the arsenic acid, it was found necessary to moderate the heat; and, in order that every particle of water might be finally expelled, to prolong it. When the diminu tion of weight was ascertained, the residuum was dissolved in acetous, or, still better, in dilute nitric acid, and nitrate of lead was poured in. Arseniate of lead and nitrate of copper were thus formed, by double decomposition; but, when more nitric acid had been used than was strictly necessary to dissolve the arseniate of copper, no precipitate appeared, till the liquor had been evaporated. When the evaporation was pushed too far, part of the nitric acid, contained in the soluble nitrate of copper flew off; and that nearly insoluble cuprecus nitrate, first mentioned by Mr. Proust, was produced. To obviate both inconveniences, alcohol was added, immediately before the liquor was quite evaporated, and long after the precipitate had begun to appear; in a few minutes, all the arsenic of lead fell to the bottom, while the nitrate of copper was held in solution. These new products being separated by filtration, the spirituous liquor was distilled; and, from the nitrate of copper, the quantity of that metal contained in the ore was obtained, by boiling the solution with pot-ash or soda.' Mr. C. afterward observes that he has given the preference to lead above every other method of combining arsenic, in order order to determine its quantity in any other body; having found arseniate of lime, which has been hitherto recommended, as well as all other earthy arseniates, to be nearly as soluble in water as sulphate of lime. He then relates some experiments which he previously made, to ascertain the exact composition of arseniate of lead; whence it appears that 100 parts contain Arsenic acid Oxide of lead 33 63 100 The above-described method of ascertaining the proportion of arsenic acid, in the arseniates of copper, is undoubtedly a very good one: but Mr. C. also points out the following mode, which may be deemed shorter, and perhaps even more accurate. After the quantity of water has been estimated, the remainder may be treated by either of the fixed alkalis, which will combine with the acid, and leave the brown, the only real, oxide of copper, in the same state as that in which it existed in the ore; the alkaline liquor may be neutralized, as above, and the proportions determined in the same manner.' Having thus stated the mode of analysis employed by the author, we shall proceed to give the results. No. 1. Third Species of the pre- | No. 4. Variety 5 of the third ceding Paper. Oxide of copper, Arsenic acid, Species. бо Oxide of copper, 39,7 Arsenic acid, Water, 99,7 No. 2. Fourth Species of the preceding Paper. Oxide of copper, Arsenic acid Water, No. 5. Second Species of the preceding Paper. Oxide of copper, 16 Arsenic acid, Water, 100 58 2,1 21 As the yellow hematitic copper ore, and the grey vitreous copper ore, so generally accompany the arseniates of copper and of iron, Mr. Chenevix thought it right to make an analysis also of these; and he thus states their composition : No. 7. Yellow Hematitic Cop- | No. 8. Grey Vitreous Copper per Ore. Ore, Sulphur, 12 Sulphur, 5 Copper, Iron, 30 53 12 84 4 100 100 The author is of opinion that the colour in some specimens of arseniate of copper may be explained on chemical principles; because, having observed that the colour of these corresponds with the proportion of water contained in them, and having considered the experiments of M. Proust*, with the addition of certain results deduced by himself, he concludes that we have never yet obtained, by art, any real salt of oxide of copper; for that all of those, which are generally considered as such, are compounds of the oxide combined with a certain portion of water (forming a particular substance, to which M. Proust has given the very improper name of hydrate,) dissolved in an acid. According to Mr. Chenevix, therefore, the blue salt which is denominated sulphate, nitrate, or muriate of copper, should be called sulphate, nitrate, or muriate of hydrate of copper; because it is not a compound of oxide with the acid, but of hydrate with the acid-This is a question which can only be fully resolved by future experiments; and we know that the existence of hydrates is much doubted by many chemists, particularly by M. Fourcroy, who has stated his objections in his Système des Connaissances Chimiques. Nevertheless, taking every circumstance into consideration, we are much inclined to adopt the opinion of M. Proust and Mr. Chenevix. From a general view of the foregoing analysis, it appears that the author considers No. 1. as the only real arseniate of copper; all the others being, in his opinion, arseniates of hydrate of copper. In the second section of this paper, Mr. C. gives the analysis of the arseniates of iron. Some preliminary experiments, which he relates, indicated the following ready method of decomposing the ore :-One hundred parts, boiled with potash, immediately became of a deep reddish brown: the liquor was separated from the residuum by filtration; and, after the usual • Annales de Chimie, vol. xxxii. p. 26. neutralizas |