Volume 12 (1866) (428 pages)

402 The Mining wid Srientifie Press. Gouunurications. In TH1g Derartuert we invite the FREF vIscussiON of all Proper subiects—correspondents alone being responsible for the ideas and theories they advance. {Written for the Mining and Scientific Press.) Source of the Electric Current in the Voltaic Battery, BY EDWARD PIQUE. Whenever two different metals, for instance, copper and zinc, are immersed in a fluid capable of conducting electricity, and the two metals touch each other, either within or without the fluid, an eleciric current will at once be establisbed, aud a chemical decomposition of the fluid will take place at the eame time, in such a way that one of the constituents of the Auid, wbich necessarily must be a compound body, will be attracted by one metal, and the other constituent by the other metal. If tbese metals possess sufficient affinity for the constituents of the fluid, they will form a conngetion with them; in the contrary case, the separated elements of the compound solution will be eliminated. If these effects do not appcar by using one pair of different metallic plates, they are sure to take place by using a number of thein, and connecting them in the proper way, whereof the explanation can be found in auy treatise, on electro-metallurgy. To make this better understood, let us connect about ten pairs of copper and zinc plates, in the manner generally adopted by any electrician, with a piece of platinum attached to eacb end of the battery. If we dip these two pieces of platinum in water, slightly acidulated by sulphuric acid, the water will be decomposed into its elements, the oxygen will rise in bubbles on the positive platinum—that ig the one attached to the last plate of copper— and the hydrogen on the negative platinum, which is attacbed to tbe last zioc plate. The reason is that the platinum has no affinity for eitber of tbe constituents of the water ; tbcrefore, the water being decomposed, both the above gases escape. If the terminal platcs are made of copper, instead of platinum, the hydrogen will appear in bubbles on the negative plate ; but no oxygen will appear on the positive copper plate, because the copper connects witb the oxygen, forming oxyde of copper, which dissolves in the dilute sulphuric acid» exposing again a metallic surface to renewed action, until all the positive copper plate is dissolved. Ifwe employ a solution capable of being decomposed by bydrogen—as, for instance, a solution of sulphate of copper—no hydrogen will escape; but it will connect with tbe oxygen of the oxide of copper, and at tbe negative pole metallic copper will be deposited. These actions being understood, it appears that whether bydrogen and oxygen, both of them' or only one of tbem, or neither of them, are evolved, the original influence is always the same ; the appearances only being modified by tbe disappearance of the oxygen in connecting with the positive metal, if this be oxydizaable, or the reducing action of the hydrogen on some oxyde contained in the solution. In seeing these changes going on, no one will doubt fora eingle moment that a chemical action is taking place. Just as plain are the evidences of an electric currect being active, wbich can be easily proved in different ways. One proof ie by applying the galvanometer. Tbis consists of a rectangular coil of copper wire, containing about twenty convolutions, the wire being covered with cotton or silk, to, prevent the lateral escape of the current. .4 magnetic needle, supported on a pivot, is placed in the center of the coil, and a card, graduated into 360°, is fixed to the board on which the coil regta, eo that a line drawn from 360° to 180° coincides with its long axis. We place this instrument in such a position that the wire coil is precisely in the magnetic meridian, and consequently the needle and coil, both, will be parallel] ani point nearly north and south. We form now a galvanic pair by immersing a copper anda zine plate in water, slightly, acidulated with eulphuric acid ; but instead of forming immediately a metallic connection be‘tween the two metallic plates, we solder a copper wire to each of tbe plates, separate the plates from each other, and fasten these two wires each to one end of the coil-of wire surrounding the maguet, the ends of which must be latd bare from their silk covering, so tbat metal shull touch metal. The moment that these connections are completed, the ueedle will move to the east or west, which is a positive proof of an electric current traversing the wire. 4 Another satisfactory proof of the same fact, is given by the calorific effects of clectricity. We take two plates of copper and zine, which for this purpose ought to be at least four inches long aud two broad, the larger the better; we olace them, separated, in the dilute acid, then connect them by a piece of very fine platinum wire, half aninch in length. Tbe platinum wire will become brilliantly ignited ; and this is a positive proof of an electric discharge taking place through it. Some more proofs of the existence of an electric cnrrent in this casc could be produced, but those already given are quite sofficieut. Now no one denies that ina galvanic battery an electric current is established, and a chemical action takes place ; but which of the two is the cause, and which the effect, is a question which the most learned men have fcr a nuinber of years disputed, withuut beiug able to agree in opinion. Dr. Wollaston, Dr. Faraday, and several others, believe that the chemical action of the acid solution on the zine, or rather of the zinc on the water of the acid solution, is the source of the electric current in the voltaic battery ; and this is termed the cuemr cHL TuHgory of tbe pile. Other philosophers, following the opinion of-the illustrious discoverer, Prof. Volta, of Pavia, believe that the chemical action is the effect of the electric current, and that the power is produced by the contact of two dissimilar metuls—this latter has received the name of thecontactTHEory. It is certainly a matter of the greatest importance to know tbe source or origin of a power that has been applied to so many uselul purposes, and which promises for the future so many additional uses ; and it is very much to be regretted that learned men cannot unite in one opinion, because when two exist, one must be rigbt and the other wrong, and the student gets bewildered, not knowiug which opinion should be received. If our ideas ahout the source of voltaic action were clear aud correct, we might be enabled to produce and regulate that power with more certainty, and perhaps more economy ; but as long as we do not know the source ot power, we shall always be groping in the dark. Tbe great obstacle in clearing up our notions about any mysterious law of nature, has always been the vanity of some learned men, who, fond of some preconceived notion, cannot bear that any oue should contradict their pet idea. A curious instance of this trnth is lound in the early stages of chemistry. In the begianing of the eighteenth century, a German chemist, uamed Stahl, founded the phlogistic theory of chemistry, asserting that every com-bustible body, as, lor instance, the metals, contain a matter which he called Phlogiston. Observing that the metals, when oxydized by combustion or otherwisc, lose their metallic properties, Stab] and his followere believed that the metals gave up their phlogiston, and losing this they are no more metals. In the year 1783, Lavoisier proved that the metals, when oxydized-by combustion, or otherwise, weigh beavier than they did before; Tor instance, one pound of copper, when thoroughly roasted, will give a pouud and a quar-. ter of a black powder, etc,, etc. Now, although any man in his right senses, when seeing tbat four pounds of copper, after being burned, weighed five pounds, must have been convinced that it gained something ; still, for about tweuty years after this discovery, some of the most learned men disputed this fact, and firmly believed that the metals under these circumstances actually lost something. Such was the opinion held by many uatil the discovery of the different gases and their properties of counecting with solid bodies, put an end to these ridiculous controversies. If we seek for truth, neither vanity nor prejudice should iufluence us. We cannot make nor change the laws which the Almighty has impriuted upon nature; we are fortunate if we can only trace them. It would be useless for ns to describe all the numerous experiments which have been made, to prove that almost every chemical action produces a current of electricity; in most cases, however, of very weak tension. It is certain that electricity produces chemical action, when the current traverses different bodies capable of being decomposed, and tbe electricity is of the proper tension; no difference whether the electricity be generated by friction or a galvanic battery, or the motion of a magnet, or by any of the numerous ways that will generate electricity. Our object is to iuquire into THE SOURCE OF THE ACTION IN *A GALVANIO . BATTERY. Is it a chemical action which starts the electricity, or is it electricity which here produces decomposition? To decide this point, I wisb to answer three questions. The first question is—Will two different metals, by mere contact, produce electricity witbout any exciting fluid whatever?’ My auswer is—yes. ¥ Two disks of different metals, when pressed together und suddenly separated, assume opposite electric etates. ‘l’o demonstrate this, take a plate of copper and one of zinc, about four inches in diameter, each furnished with a glass handle fixed in its center; now connect a gold leaf electrometer with one plate, A, of the condenser, allowing the otber plate, B, on the condenscr, to be connected with the eartb. Press the copper and zine plates together, holding them by their insulating handlee; suddenly separate and apply one of them to the plate, A, of the condenser; again press them together, having previously touched them witb the finger to restore their electric equilibrium, and reapply the sume plate to tbe same condenser. Repeat this about six times; then draw back the uninsnlated plate, B, and the gold leaves of the electrometer will diverge with positive electricity if the zine, and with the negative if the copper plate has been applied to the céndenser.—[Dr. Bird's Natural Philosophy.) T’be second question to be answered is—In . constructing a galvanic battery, are we making . arrangements favorable to a chemical action ? J answer—No. If we dip a plate of zine in dilute sulphuric acid, it will cause a rapid evolution of hydrogen gas, which will escape along the plate of zine, until all the zine will be dissolved—if a sufficient quantity of acid be present. ‘This is called a chemical action, and every chemist knows that the zinc contbines with the oxygen of. the water, that the oxyde of zine so formed is dissolved in the dilute sulphuric acid as sulphate of zine, and the hydrogen, thus set free, escapes along the ziue. We now place a plate of copper in the same acidulated liquid, separate it from the plate of zinc, and connect the two plates together outside the fluid by a wire previously fastened to each plate. What will be the result? We shall see hydrowen escaping from both plates —the copper as well as the zinc—and we say, that the hydrogen escapes from the copper in consequence of an electric current, as the copper-plate does not undergo the slightest change ; neither does tke copper gain or lose anything. Chemistry cannot account for this, and it is universally acknowledged, that only the quantity of hydrogeu escaping from the copper, is in proportion to the electricity, and therefore it has been used to ascertain the relative quantity of electricity which isaclive. The hydrogen escaping from the zinc, cannot be taken in account. It is an unnecessary waste, and therefore means have been devised to prevent the localaction of the acid on the zine, by coating the zine plate with mercury. The snrface of the zine is cleaned with a little acid, and a few globules of merenry are rubbed over it, and we call it then amalgamated. If we dip this amalgamated zine plate in dilute sulphnric acid, it ussumes a grayish tint from its becoming covered with myriads of excessively minute bubbles of hydrogen gas, which mechanically adhere to its surface, and thus form a gaseous covering, which shields it from the further actiou of the acid. We can see quite plain that there is an end to the -kind. chemical action. We now immerse a copper plate in the same dilute acid, and form a me-. tallic connection between the copper and the amalgamated zinc plate, when in an instant a torrent of bubbles of gas is evolved from the copper, no evolution of gas from the zine taking place. The copper, however, remains’ chemically unacted npon, and the zinc is alone dissolved, in proportion to the quantity of hydrogen escaping from the copper. This answers my second question, wbether in constructing a galvanic battery we are producing conditions favorable to chemical action. We do not. On the contrary, we arrange it so as to impede the chemical action ; we. coat the zinc with mercury, and this preveots the dilute sulphuric acid from acting on the zinc, which is not at all consumed or in any way altered, natil we dip another more negative metal, for instance copper, in the same fluid, and form a metallic connection between the two metals. If it were: true, that ina galvanic battery chemical action produces electricity, would it not he reasonable to expect, that uncoated zine sbould produce a larger amount of eleetricity than the amalgamated zinc; since the uucoated zinc gives rise to a very powerful action, when dipped in dilute aeid, while the amalzamated zinc excites no chemical action whatever. We employ a similar proceeding in the protected sulphate of copper batteries. In using, . for instance, porous cells, ft is not necessary to amalgamate tbe zinc; but then we must not allow an acid solution to bein contact with the zinc, because it would consume the zine, . without giving us anybenefit. We ought only to use solutions that have no cbemical infuence on the zine ; for instance a solution of common salt, or sulphate'of zinc, and so on. We do rot want the zine to be touched by any solution capable of actjng on it. Flow can we then reasonably imagine, that the chemical action of the zinc on the surrounding fluid excites electricity, if no chemical action of any . kind ie present ? The third question I wish to answer, is from which plate originates the power? Is i: the zing or the copper plate? By what I have already said, it is clearly understood, that the action sbowing itself on the negative or copper plate, is regarded as an electric action, because it cannot be explained by the laws of chemistry. This action migbt consistin tbe evolution of hydrogen, or in tbe reduction and deposit of a ‘metal on the negative plate, which amounts to the same, as far as the kind of power is concerned that produces these effects. Itis likewise understood that the action on the zinc or positive plate, is considered a chemical action, and consists in the oxidation of the zine, which cousequently is dissolved by the acid, which fornis a constituent of the liquid surrounding it. To answer our question, let us suppose we have a vessel divided into two copartinents by a porous diapbragm, it migbt be a bladder, unglazed earthenware, or anything else of this In one division of the vessel we put a solution of sulphate of copper, and in the other division a solution of sulphate of zinc. In the first solution we immerse a copper plate, and in the last solution a zine plate, and connect the two plates by a copper wire. What will be the result ? The copper of the solution will be deposited on the copper plate, and the solution of sulphate of copper will be in the end so exhausted, that hardly anythiug but water will be left mn‘its place. On the other side the zinc will be dissolved, and the solution surrounding it will be concentrated, and contuin so mucb snlphate of zinc, that. if proper precautions be not taken, it will even crystallize. Now let us try to explain this final result by two different and opposing suppositions to find out which is the correct one. [To be Continued.) [Written for the Mlulng and Scientifte Press.) Mining in Aurora. Enitors Press:—My letters of late have been few and far between, owing to the scarcity of subject matter bereabonts. My abject is only to write you of matters of interest in general on miuing.For the past three or four months, work has been going steadily on in this district, that will eventually test the value of the mines, and prove the existence or non-cxistence of ite mineral wealth. Past experience teaches the futility of gouging out mines on their surface, with any hope of making theni permanent paying institutions. It is only by sinking to the core, where the real formation of mineral lice, that will give any lasting stability to a mine. This now seems to be the determination of the owners of at least a few of the leading lodes here, and if their efforts should be crowned with success (of which I have not the least doubt), hundreds will follow in their wake. There are many mines working that pay tbeir way, independent of those sinking Toro test. Among the former, THE PHILADELPHIA COMPANY Is driviug its work along witb a vigor and force very creditable to the superintendent, Mr E. O. Tuylor. Their sbaft, intended to be 500 feet deep, before they commence drifting into the hill, is situated in Wide West Gulch, a short distance above tbe famous Wide West mill, on the west side of Last Chance Hill. They are now down aboot eighty feet, and are making from three to four feet a day. The strata through which they are working requires but little blasting, being composed of a mixture of decomposed quartz and bed-rock. The shaft is eigbt by four and a halfin the clear, and as fine a piece of work as I have have ever seen. ‘This company have a tunnel running into the hill from where ttheir shaft is located, sonie 600 feet long; and in tbat tunnel they have six well defined ledges. When they attain the depth of 500 feet, I predict for them a brilliant success. Mr. Taylor is now in San Francisco, looking after the shipment of some $50,000 worth of machinery, which he started for this purpose prior to his leaving Philadelphia. THE COLNEN AGE AND EMPIRE COMPANY, On the simmit of Last Chance, are driying their work bravely on, under the able management of Capt. George Benson. They are run-

402 The Mining wid Srientifie Press. Gouunurications. In TH1g Derartuert we invite the FREF vIscussiON of all Proper subiects—correspondents alone being responsible for the ideas and theories they advance. {Written for the Mining and Scientific Press.) Source of the Electric Current in the Voltaic Battery, BY EDWARD PIQUE. Whenever two different metals, for instance, copper and zinc, are immersed in a fluid capable of conducting electricity, and the two metals touch each other, either within or without the fluid, an eleciric current will at once be establisbed, aud a chemical decomposition of the fluid will take place at the eame time, in such a way that one of the constituents of the Auid, wbich necessarily must be a compound body, will be attracted by one metal, and the other constituent by the other metal. If tbese metals possess sufficient affinity for the constituents of the fluid, they will form a conngetion with them; in the contrary case, the separated elements of the compound solution will be eliminated. If these effects do not appcar by using one pair of different metallic plates, they are sure to take place by using a number of thein, and connecting them in the proper way, whereof the explanation can be found in auy treatise, on electro-metallurgy. To make this better understood, let us connect about ten pairs of copper and zinc plates, in the manner generally adopted by any electrician, with a piece of platinum attached to eacb end of the battery. If we dip these two pieces of platinum in water, slightly acidulated by sulphuric acid, the water will be decomposed into its elements, the oxygen will rise in bubbles on the positive platinum—that ig the one attached to the last plate of copper— and the hydrogen on the negative platinum, which is attacbed to tbe last zioc plate. The reason is that the platinum has no affinity for eitber of tbe constituents of the water ; tbcrefore, the water being decomposed, both the above gases escape. If the terminal platcs are made of copper, instead of platinum, the hydrogen will appear in bubbles on the negative plate ; but no oxygen will appear on the positive copper plate, because the copper connects witb the oxygen, forming oxyde of copper, which dissolves in the dilute sulphuric acid» exposing again a metallic surface to renewed action, until all the positive copper plate is dissolved. Ifwe employ a solution capable of being decomposed by bydrogen—as, for instance, a solution of sulphate of copper—no hydrogen will escape; but it will connect with tbe oxygen of the oxide of copper, and at tbe negative pole metallic copper will be deposited. These actions being understood, it appears that whether bydrogen and oxygen, both of them' or only one of tbem, or neither of them, are evolved, the original influence is always the same ; the appearances only being modified by tbe disappearance of the oxygen in connecting with the positive metal, if this be oxydizaable, or the reducing action of the hydrogen on some oxyde contained in the solution. In seeing these changes going on, no one will doubt fora eingle moment that a chemical action is taking place. Just as plain are the evidences of an electric currect being active, wbich can be easily proved in different ways. One proof ie by applying the galvanometer. Tbis consists of a rectangular coil of copper wire, containing about twenty convolutions, the wire being covered with cotton or silk, to, prevent the lateral escape of the current. .4 magnetic needle, supported on a pivot, is placed in the center of the coil, and a card, graduated into 360°, is fixed to the board on which the coil regta, eo that a line drawn from 360° to 180° coincides with its long axis. We place this instrument in such a position that the wire coil is precisely in the magnetic meridian, and consequently the needle and coil, both, will be parallel] ani point nearly north and south. We form now a galvanic pair by immersing a copper anda zine plate in water, slightly, acidulated with eulphuric acid ; but instead of forming immediately a metallic connection be‘tween the two metallic plates, we solder a copper wire to each of tbe plates, separate the plates from each other, and fasten these two wires each to one end of the coil-of wire surrounding the maguet, the ends of which must be latd bare from their silk covering, so tbat metal shull touch metal. The moment that these connections are completed, the ueedle will move to the east or west, which is a positive proof of an electric current traversing the wire. 4 Another satisfactory proof of the same fact, is given by the calorific effects of clectricity. We take two plates of copper and zine, which for this purpose ought to be at least four inches long aud two broad, the larger the better; we olace them, separated, in the dilute acid, then connect them by a piece of very fine platinum wire, half aninch in length. Tbe platinum wire will become brilliantly ignited ; and this is a positive proof of an electric discharge taking place through it. Some more proofs of the existence of an electric cnrrent in this casc could be produced, but those already given are quite sofficieut. Now no one denies that ina galvanic battery an electric current is established, and a chemical action takes place ; but which of the two is the cause, and which the effect, is a question which the most learned men have fcr a nuinber of years disputed, withuut beiug able to agree in opinion. Dr. Wollaston, Dr. Faraday, and several others, believe that the chemical action of the acid solution on the zine, or rather of the zinc on the water of the acid solution, is the source of the electric current in the voltaic battery ; and this is termed the cuemr cHL TuHgory of tbe pile. Other philosophers, following the opinion of-the illustrious discoverer, Prof. Volta, of Pavia, believe that the chemical action is the effect of the electric current, and that the power is produced by the contact of two dissimilar metuls—this latter has received the name of thecontactTHEory. It is certainly a matter of the greatest importance to know tbe source or origin of a power that has been applied to so many uselul purposes, and which promises for the future so many additional uses ; and it is very much to be regretted that learned men cannot unite in one opinion, because when two exist, one must be rigbt and the other wrong, and the student gets bewildered, not knowiug which opinion should be received. If our ideas ahout the source of voltaic action were clear aud correct, we might be enabled to produce and regulate that power with more certainty, and perhaps more economy ; but as long as we do not know the source ot power, we shall always be groping in the dark. Tbe great obstacle in clearing up our notions about any mysterious law of nature, has always been the vanity of some learned men, who, fond of some preconceived notion, cannot bear that any oue should contradict their pet idea. A curious instance of this trnth is lound in the early stages of chemistry. In the begianing of the eighteenth century, a German chemist, uamed Stahl, founded the phlogistic theory of chemistry, asserting that every com-bustible body, as, lor instance, the metals, contain a matter which he called Phlogiston. Observing that the metals, when oxydized by combustion or otherwisc, lose their metallic properties, Stab] and his followere believed that the metals gave up their phlogiston, and losing this they are no more metals. In the year 1783, Lavoisier proved that the metals, when oxydized-by combustion, or otherwise, weigh beavier than they did before; Tor instance, one pound of copper, when thoroughly roasted, will give a pouud and a quar-. ter of a black powder, etc,, etc. Now, although any man in his right senses, when seeing tbat four pounds of copper, after being burned, weighed five pounds, must have been convinced that it gained something ; still, for about tweuty years after this discovery, some of the most learned men disputed this fact, and firmly believed that the metals under these circumstances actually lost something. Such was the opinion held by many uatil the discovery of the different gases and their properties of counecting with solid bodies, put an end to these ridiculous controversies. If we seek for truth, neither vanity nor prejudice should iufluence us. We cannot make nor change the laws which the Almighty has impriuted upon nature; we are fortunate if we can only trace them. It would be useless for ns to describe all the numerous experiments which have been made, to prove that almost every chemical action produces a current of electricity; in most cases, however, of very weak tension. It is certain that electricity produces chemical action, when the current traverses different bodies capable of being decomposed, and tbe electricity is of the proper tension; no difference whether the electricity be generated by friction or a galvanic battery, or the motion of a magnet, or by any of the numerous ways that will generate electricity. Our object is to iuquire into THE SOURCE OF THE ACTION IN *A GALVANIO . BATTERY. Is it a chemical action which starts the electricity, or is it electricity which here produces decomposition? To decide this point, I wisb to answer three questions. The first question is—Will two different metals, by mere contact, produce electricity

witbout any exciting fluid whatever?’ My auswer is—yes. ¥ Two disks of different metals, when pressed together und suddenly separated, assume opposite electric etates. ‘l’o demonstrate this, take a plate of copper and one of zinc, about four inches in diameter, each furnished with a glass handle fixed in its center; now connect a gold leaf electrometer with one plate, A, of the condenser, allowing the otber plate, B, on the condenscr, to be connected with the eartb. Press the copper and zine plates together, holding them by their insulating handlee; suddenly separate and apply one of them to the plate, A, of the condenser; again press them together, having previously touched them witb the finger to restore their electric equilibrium, and reapply the sume plate to tbe same condenser. Repeat this about six times; then draw back the uninsnlated plate, B, and the gold leaves of the electrometer will diverge with positive electricity if the zine, and with the negative if the copper plate has been applied to the céndenser.—[Dr. Bird's Natural Philosophy.) T’be second question to be answered is—In . constructing a galvanic battery, are we making . arrangements favorable to a chemical action ? J answer—No. If we dip a plate of zine in dilute sulphuric acid, it will cause a rapid evolution of hydrogen gas, which will escape along the plate of zine, until all the zine will be dissolved—if a sufficient quantity of acid be present. ‘This is called a chemical action, and every chemist knows that the zinc contbines with the oxygen of. the water, that the oxyde of zine so formed is dissolved in the dilute sulphuric acid as sulphate of zine, and the hydrogen, thus set free, escapes along the ziue. We now place a plate of copper in the same acidulated liquid, separate it from the plate of zinc, and connect the two plates together outside the fluid by a wire previously fastened to each plate. What will be the result? We shall see hydrowen escaping from both plates —the copper as well as the zinc—and we say, that the hydrogen escapes from the copper in consequence of an electric current, as the copper-plate does not undergo the slightest change ; neither does tke copper gain or lose anything. Chemistry cannot account for this, and it is universally acknowledged, that only the quantity of hydrogeu escaping from the copper, is in proportion to the electricity, and therefore it has been used to ascertain the relative quantity of electricity which isaclive. The hydrogen escaping from the zinc, cannot be taken in account. It is an unnecessary waste, and therefore means have been devised to prevent the localaction of the acid on the zine, by coating the zine plate with mercury. The snrface of the zine is cleaned with a little acid, and a few globules of merenry are rubbed over it, and we call it then amalgamated. If we dip this amalgamated zine plate in dilute sulphnric acid, it ussumes a grayish tint from its becoming covered with myriads of excessively minute bubbles of hydrogen gas, which mechanically adhere to its surface, and thus form a gaseous covering, which shields it from the further actiou of the acid. We can see quite plain that there is an end to the -kind. chemical action. We now immerse a copper plate in the same dilute acid, and form a me-. tallic connection between the copper and the amalgamated zinc plate, when in an instant a torrent of bubbles of gas is evolved from the copper, no evolution of gas from the zine taking place. The copper, however, remains’ chemically unacted npon, and the zinc is alone dissolved, in proportion to the quantity of hydrogen escaping from the copper. This answers my second question, wbether in constructing a galvanic battery we are producing conditions favorable to chemical action. We do not. On the contrary, we arrange it so as to impede the chemical action ; we. coat the zinc with mercury, and this preveots the dilute sulphuric acid from acting on the zinc, which is not at all consumed or in any way altered, natil we dip another more negative metal, for instance copper, in the same fluid, and form a metallic connection between the two metals. If it were: true, that ina galvanic battery chemical action produces electricity, would it not he reasonable to expect, that uncoated zine sbould produce a larger amount of eleetricity than the amalgamated zinc; since the uucoated zinc gives rise to a very powerful action, when dipped in dilute aeid, while the amalzamated zinc excites no chemical action whatever. We employ a similar proceeding in the protected sulphate of copper batteries. In using, . for instance, porous cells, ft is not necessary to amalgamate tbe zinc; but then we must not allow an acid solution to bein contact with the zinc, because it would consume the zine, . without giving us anybenefit. We ought only to use solutions that have no cbemical infuence on the zine ; for instance a solution of common salt, or sulphate'of zinc, and so on. We do rot want the zine to be touched by any solution capable of actjng on it. Flow can we then reasonably imagine, that the chemical action of the zinc on the surrounding fluid excites electricity, if no chemical action of any . kind ie present ? The third question I wish to answer, is from which plate originates the power? Is i: the zing or the copper plate? By what I have already said, it is clearly understood, that the action sbowing itself on the negative or copper plate, is regarded as an electric action, because it cannot be explained by the laws of chemistry. This action migbt consistin tbe evolution of hydrogen, or in tbe reduction and deposit of a ‘metal on the negative plate, which amounts to the same, as far as the kind of power is concerned that produces these effects. Itis likewise understood that the action on the zinc or positive plate, is considered a chemical action, and consists in the oxidation of the zine, which cousequently is dissolved by the acid, which fornis a constituent of the liquid surrounding it. To answer our question, let us suppose we have a vessel divided into two copartinents by a porous diapbragm, it migbt be a bladder, unglazed earthenware, or anything else of this In one division of the vessel we put a solution of sulphate of copper, and in the other division a solution of sulphate of zinc. In the first solution we immerse a copper plate, and in the last solution a zine plate, and connect the two plates by a copper wire. What will be the result ? The copper of the solution will be deposited on the copper plate, and the solution of sulphate of copper will be in the end so exhausted, that hardly anythiug but water will be left mn‘its place. On the other side the zinc will be dissolved, and the solution surrounding it will be concentrated, and contuin so mucb snlphate of zinc, that. if proper precautions be not taken, it will even crystallize. Now let us try to explain this final result by two different and opposing suppositions to find out which is the correct one. [To be Continued.) [Written for the Mlulng and Scientifte Press.) Mining in Aurora. Enitors Press:—My letters of late have been few and far between, owing to the scarcity of subject matter bereabonts. My abject is only to write you of matters of interest in general on miuing.For the past three or four months, work has been going steadily on in this district, that will eventually test the value of the mines, and prove the existence or non-cxistence of ite mineral wealth. Past experience teaches the futility of gouging out mines on their surface, with any hope of making theni permanent paying institutions. It is only by sinking to the core, where the real formation of mineral lice, that will give any lasting stability to a mine. This now seems to be the determination of the owners of at least a few of the leading lodes here, and if their efforts should be crowned with success (of which I have not the least doubt), hundreds will follow in their wake. There are many mines working that pay tbeir way, independent of those sinking Toro test. Among the former, THE PHILADELPHIA COMPANY Is driviug its work along witb a vigor and force very creditable to the superintendent, Mr E. O. Tuylor. Their sbaft, intended to be 500 feet deep, before they commence drifting into the hill, is situated in Wide West Gulch, a short distance above tbe famous Wide West mill, on the west side of Last Chance Hill. They are now down aboot eighty feet, and are making from three to four feet a day. The strata through which they are working requires but little blasting, being composed of a mixture of decomposed quartz and bed-rock. The shaft is eigbt by four and a halfin the clear, and as fine a piece of work as I have have ever seen. ‘This company have a tunnel running into the hill from where ttheir shaft is located, sonie 600 feet long; and in tbat tunnel they have six well defined ledges. When they attain the depth of 500 feet, I predict for them a brilliant success. Mr. Taylor is now in San Francisco, looking after the shipment of some $50,000 worth of machinery, which he started for this purpose prior to his leaving Philadelphia. THE COLNEN AGE AND EMPIRE COMPANY, On the simmit of Last Chance, are driying their work bravely on, under the able management of Capt. George Benson. They are run-