TO CORRESPONDENTS. "T. C. B."-There is no work on Mineralogy connected with the Collection in the British Museum. There is some notice of the minerals in the Synopsis, but not sufficient for study. "A CONSTANT READER."-Send us the means of writing to you. "G. M. R.," who writes about Sea Sickness, shall hear from us. LETTERS received from Dr. N; G. B.; Several Associates of the Pharmaceutical Society; An Early Subscriber; R. S. L.; An Agriculturist; F. R. S.; A Manufacturer; One interested in Mines, &c. &c. Those numerous Correspondents, who have communicated to us their intentions relative to the Pharmaceutical Society, have our thanks. TO SUIT the convenience of such of our readers as may wish for answers to questions sooner than can be obtained through the "NOTICES" in our Journal, we have determined on the following. Letters sent before the 10th of each month will be answered on that day by private letter; those which are sent after that time, on the 20th; after the 20th, letters will be answered in the Monthly No., or privately, on the 1st. Correspondents must send us their names and addresses; or initials, and the post-offices of their districts, will do. As this arrangement is for the benefit of our readers, postage stamps should be enclosed when private letters are requested in reply. THE CHEMIST. I. CHEMISTRY. NOTICE OF SOME EXPERIMENTS ON BY R. W. FOX, ESQ. stead of a considerable surface of metal, did not affect the direction or force of the currents; they were, moreover, constant in both these respects during more than eight months that the two veins were connected by the wires, and a part of this time the mine was filled with water in consequence of an acci READ BEFORE THE ROYAL CORNWALL PO- dent to the machinery. Ore-points in the LYTECHNIC SOCIETY. I HAVE already communicated to the Geological Society of London, some results produced by the electric action of two nearly E. and W. metalliferous veins which have been partially explored in Pennance mine. I have since made other experiments in the same mine, in which ore-points, consisting of copper and iron pyrites in the two veins, were connected by a pair of copper wires, which, in most instances, acted on a galvanometer or other apparatus at the surface, an end of each wire having been brought up through a shaft for the purpose:-about 50 fathoms of wire were employed, although the ore-points in the different veins were only about 14 to 18 fathoms asunder in a direct line. A galvanometer of not much sensibility was generally used; the needle, which was 2 inches long, moved on a pivot, and had a coil of fine wire passed 48 times round it. Another galvanometer, consisting of a suspended astatic needle, and 140 coils of wire, was also employed occasionally. When the former, which call No. 1, was placed in the circuit, the needle was deflected so as to become stationary at 14° to 15° from Zero; and it revolved rapidly round the circle when the circuit was broken and restored a few times, the direction of the electricity being from the south vein to the northern one. The other galvanometer (No. 2) suffered a permanent deflection of about 40°, when in the circuit. The interposition of a plate of platinum or zinc at either of the ore-points, or of a point, in *Communicated to THE CHEMIST. N. S. VOL. I.-No. VIII. August, 1843. two veins situated within two or three feet of the others respectively, were, at one time, connected by a second pair of copper wires of the same lengths as the first; both sets of parallel wires being kept apart, and insulated from the sides of the levels or galleries, by poles stretched across the latter at short intervals. When galvanometer, No. 2, was placed in the second circuit, No. 1 remaining in the other, the needle of the latter receded at least 20, standing at 12°, instead of 14° or 15°; and the former stood at 5° or 6° less than it did when only one circuit was established. On breaking either of the circuits, the deflection of the needle in the other circuit was increased to its original amount. And when both pairs of wires were connected with only one of the instruments, the effect was almost precisely the same as that produced by one pair alone,—not greater certainly. A copper and zinc pair of plates of about 6 inches surface, separated by a piece of cotton cloth moistened with water, was placed in the circuit, and when the currents from this source and the veins coincided in direction, the needle of galvanometer, No. 1, stood at about 10°, that is, at less than it did when acted upon by the subterranean electricity alone; and when the deflection caused by the latter was afterwards opposed by the action of the plates, the needle went back to Zero, and even sometimes passed a little beyond it in the opposite direction. These anomalies may perhaps be referred to the low conducting power of the moistened cotton, which, small as its thickness was, very probably interrupted the transmission 2 X of the electricity more than the 14 or 18 fathoms of strata or "Country." On taking the voltaic elements from the circuit, and connecting them with the galvanometer, so as to form a separate circuit acting in an opposite direction to the electricity from the mine, the deflection showed a difference in favor of the latter, and indeed, this was the case when the interposed cloth was moistened by a very weak solution of common salt. The electro-magnetic and decomposing effects of these subterranean currents also afforded unequivocal evidence of their energy. A helix of copper wire fixed round a small horseshoe-shaped bar of iron, was placed in the circuit formed by the wires from the veins, when the bar became so magnetized as to cause a compass needle 14 inch long, at the distance of nearly half an inch, to oscillate through an arc of about 70°, when the circuit was alternately made and broken a few times. A solution of hydriodide of potash was found to have been decomposed after it had been left in the circuit for rather more than a day. The endosmose action occurred in various experiments, but it may be sufficient to give one example. Sulphate of copper in solution was put into both branches of a Ushaped glass tube with clay in the bent part of it, the surface of the fluid in one branch standing half an inch above that in the other. A piece of silver wire was plunged into each of them, the upper end passing out through sealing wax, with which the extremities of the tube were stopped, and the apparatus was placed upright in the circuit, with the wire in the higher column of the fluid connected with the negative wire. In the course of a few days this column was found to have risen one eighth of an inch, the other having fallen in an equal degree, showing that the greater pressure of the higher column was superseded by the force of the electric action. When small cylinders of copper pyrites were substituted for the silver wires in the branches of the bent tube, not only did the endosmose action occur, but the copper ore, forming the negative pole, had its surface gradually changed to vitreous copper in the course of two or three days,* the other orepole remaining unaltered. The same change was produced, and apparently with equal facility, when solutions of other salts, as carbonate of soda, or common salt, were substituted for that of sulphate of copper, in both branches of the tube. The cylinders * Some of the ore thus changed was at the last Polytechnic Exhibition. of copper pyrites used in these experiments, were long enough for the upper ends to project above the mouths of the tube, where the opposite wires were attached to them respectively, and these were well coated with sealing-wax dissolved in alcohol, to prevent the access of moisture to any part of the metal; and, indeed, all but the lower portions of the ore were coated in like manner. In some instances, the cylinders of copper pyrites were allowed to remain in solutions of sulphate of copper in the bent tube for several weeks, when deposits of oxide of iron were found coating the inside of the tube about the negative pole. These results remind one of the ochrey appearance observed in rocks inclosing much vitreous copper,-a fact noticed by my friend Joseph Carne; and it may be worth while to inquire how far the proportion of "gossan" in copper veins may be connected with the quantity of vitreous ore contained in them. Since the foregoing experiments were made, I have obtained an electrotype copper plate 14 inch long, 14 wide, and of an inch thick, by the agency of these subterranean currents. The apparatus consisted of a porous earthenware vessel, resting on wooden legs in a larger one; both were partly filled with solutions of sulphate of copper, an engraved copper plate attached to the negative wire, being placed in the outer vessel, and another plate of copper attached to the positive wire, in the inner one. After a few days it was observed that crystals of copper had been formed on the negative plate, but it was nearly two months before the apparatus was removed from the circuit, when the deposited metal was detached from the plate, having received its impression, VI INSITA TERRÆ. Whilst this experiment was in progress at the surface, the water, as I have before mentioned, invaded the mine, but without interrupting the process; it appeared, indeed, that the electric action was rather increased than diminished by this circumstance. Before the influx of the water, an orepoint in the north vein was connected with rock near the south vein (generally the wall of the vein,) and an ore-point in the south vein was likewise connected with rock near the north vein, in both which cases currents more or less feeble were detected passing towards the latter through the wires, which were insulated, as before, by wooden poles stretched at intervals across the galleries. It is probable that the moisture on the rocks conducted the electricity from the ore to the metal, however imperfectly; and when different metals, as platinum and zinc, were successively substituted for the copper in contact with the rocks, the currents were modified in their force according to the metal employed, but were seldom changed in their direction. The action was most decided when the place of contact with the rock was near ore; and sometimes the end of the wire, or rather the piece of copper attached to it, was rubbed by an assistant against the walls of one of the veins, or the sides of a "cross-cut" between them. Under these circumstances the astatic needle was several times suddenly much deflected; and the parts of the rocks from which this increased action proceeded, having been marked, they were broken away, when iron pyrites was in every instance found imbedded in them; and there can be no doubt that the smallest branch of copper or lead ore might have been detected in like man ner. rents will traverse a very considerable thickness of rock or strata*, but in what degree this property may be modified by the nature or texture of the rocks, the saline contents of the subterranean water, or the proportion of ores included in the circuit, remains to be ascertained. If the influence of these different circumstances should greatly vary, electric currents generated by given elements might be rendered available on various occasions ;-to ascertain, for instance, the connection of saline springs not very distant from each other, often appearing at the surface, or in mines; or of a metalliferous vein discovered in one place, with a vein which has been worked for ore in another. The conducting power of the circuit at Pennance mine, already described, was, in this way, found to equal that of a tolerably strong solution of common salt, the current in the latter experiment having to traverse an inch of the solution and short copper wires to complete the circuit. The conducting power of the rocks or strata in this case, therefore, appeared to be very great. When some sulphate of copper was added to the solution, the conducting power of the latter exceeded that of the strata. Glass tubes filled with solution of salts in different known proportions, might be used as tests in experiments on the relative conducting power of different strata, and they might be referred to as standards in describing the results. TIONS BY M. PELOUZE ON THE On several occasions the ends of the opposite wires were placed in contact with the rocks near the two veins, when there still appeared to be a tendency in the currents to pass in the same direction, but often they could not be detected, or were too feeble for their direction to be determined with certainty. Pieces of copper pyrites attached to the wires, and imbedded in wood, were likewise used instead of the metal, for producing contact with the rocks, and with still less effect; and when the contact was made with platinum and zinc in succession, the currents were in opposite directions, and in accordance with the action of those metals respectively; so that the existence of independent currents under the circumstances described, though more than probable, was not clearly DISCUSSION OF SOME OBSERVAproved. Electricity, generated by a pair of zinc and copper plates, was transmitted through the rocks between the two veins from N. to S., and also from S. to N., in order to detect any independent currents traversing the rocks by a differential effect on the needle. This method appeared likely to be a very delicate test of electric action in rocks, but no decided results were obtained, the currents passing in opposite directions apparently with equal facility, at least, the few experiments hitherto made in this way, have not led to any satisfactory conclusions relative to the point in question. It should be remarked, however, that the astatic needle employed, was inconveniently sensitive, and was often set in motion when the cause was not very obvious. With needle, No. 1, the case was widely different, as it could scarcely be moved by any subterranean currents that were not tolerably energetic, such as were produced when both the wires were in contact with ore-points, and then, as has been stated, it often revolved rapidly. It has long been known that electric cur BY M. GAY-LUSSAC. Ar the sitting of the Royal Academy of * Many instances of this occur in my paper "On the Electro-magnetic Properties of Metalliferous Veins," published in 1830, in the Phil. Transactions, p. 399. I have long ago seen a very feeble current act on a sensitive galvanometer after it had traversed nearly a quarter of a mile of strata, and stronger currents would probably be detected in like manner, after having passed many times that distance under the surface. + Comptes Rendus, No. 6, February 6, 1843. talline States."* I fully join in the praises which the first part of M. Pelouze's Memoir merits; as to the second,-that containing some observations on the same bodies considered in the amorphous and crystalline states, I request permission to make it the subject of discussion. M. Pelouze has ascertained that oxide of mercury, precipitated from a mercurial solution, was violently attacked by chlorine, whilst the oxide obtained by the calcination of the nitrate or by the direct oxidation of mercury in the air, was acted on only after a long time, although it was in a state of extreme pulverisation. He is led to believe that this difference of action is due to two different states of the oxide of mercury. The precipitated, or amorphous oxide, would alone be susceptible of being decomposed by chlorine, at the ordinary or a low temperature, and the crystallised oxide would resist in the same circumstances. And the objection which would consist in the crystallised oxide of mercury, and especially its powder, giving with chlorine a small quantity of hypochlorous acid, does not appear sufficient to M. Pelouze for rejecting the preceding hypothesis; for this oxide might contain the amorphous modification. "I doubt," says he, "that the chemists who may repeat my experiments may attribute the differences which I have observed merely to a purely mechanical cause, as a greater number of reacting surfaces in the amorphous oxide. For my part, I should rather believe that pulverisation changes the nature of these surfaces, or sets at liberty small quantities of amorphous oxide concealed in the interior of the crystals." M. Pelouze was confirmed in his opinion, by calling to mind that Wöhler had found considerable differences in the points of fusion of the same compounds, according as they were amorphous or crystallised. It appeared to him, à priori, possible that something similar might be manifested in the terms of the composition of oxide of mercury. Indeed, he found that the amorphous oxide on which chlorine exerts so energetic an action is decomposed by heat much sooner than the crystallised oxide. The difference is such, that if these two oxides be placed in the same alloy-bath, or, more conveniently, in the muffle of a cupel furnace, at a properly maintained temperature, the amorphous oxide completely disappears, while the other has scarcely begun to be decomposed. "Thus, it is certain," continues M. Pelouze, "that the same compound, solely be * For which see THE CHEMIST, No. XLII. (VI. N. S.) page 241. cause it is amorphous or crystallised, ceases to manifest the same reactions on other bodies, and that it likewise presents great differences in the term of its decomposition by heat. That is the most active, if I may so express myself, which is soonest decomposed, and that is not peculiar to oxide of mercury. I have recognised the same property in the amorphous and crystallised binoxide of manganese, and in Iceland spar. The amorphous compound is decomposed before the same compound in crystals. "I hope that the experiments which I have detailed in this Memoir are of a nature to attract the attention of chemists. They prove how important it is to establish a distinction, even in a purely chemical point of view, between bodies which differ only by a peculiar state of aggregation. It was known, indeed, that certain insoluble bodies obtained by precipitation were more adapted for certain reactions than the same bodies prepared by the dry way; but the differences of cohesion alone were seen, and they were not considered also to extensively modify the chemical properties." The importance of the question raised by M. Pelouze has determined me to quote his own expressions nearly verbatim: I should have been fearful, in mutilating them too much, of altering the sense of his ideas. Now, it will be more easy for me to discuss them. I wished at first to verify M. Pelouze's experiments on the decomposition of amorphous and crystallised oxide of mercury by heat; for the disappearance of the amorphous oxide in the muffle of a cupel furnace, more speedily than that of the crystallised oxide, did not appear to me conclusive. I therefore submitted to the action of heat in the same fusible alloy-bath, two glass tubes, of equal diameter, containing equal weights, the one of well crystallised oxide of mercury, made directly by the air, and the other of oxide precipitated from the chloride and well dried.* The gases were conducted in small eprouvettes on to a water-bath. The temperature was slowly raised, and, nevertheless, at the same moment, or very nearly so, the metallic mercury exhibited itself in very fine globules on the upper side of the tubes, and oxygen began to be disengaged. Every time that the fire was lowered, then revived, the disengagement of oxygen ceased, or was resumed simultaneously in both tubes, and these alternations were very frequently repeated, with the same result. Only the decomposition proceeded rather more rapidly with the amorphous than with the crystal *M. Lariviere was kind enough to assist me in my experiments. |