of the quality from which brass is made, and shots obtained from unrefined copper, were separately immersed in equal weights of muriatic acid. The immersion having been continued for 48 hours, the acid was poured off, and the copper washed repeatedly, and thoroughly dried. The pure copper had lost at the rate of 5 grains in 100. But the unrefined copper, on being weighed, seemed to have gained half a grain; so that either a mistake must have been made in the weighing, or else a portion of unexpelled moisture had remained in the porous flakes of the copper. Six ounces of unrefined copper were mixed with three times their bulk of charcoal, and exposed for six hours to a high heat of cementation much beyond what in the absence of the cementation would have sufficed to melt the copper. The flakes of copper were found surrounded by the charcoal, welded together without fusion, and soft and extremely flexible. Six ounces of the pure copper shots were treated in a similar manner, but the result was so far different that no adhesion of the masses had taken place, and the only perceptible change was a slight cracking or bursting upon the surface of the spheroids, which may be considered as a prelude to fusion. Both results were melted down with charcoal and run into iron moulds. The unrefined copper, when cold, was the strongest and softest; a bar of it, about ths of an inch thick, cut easily across with a knife, and in colour and general appearance it very nearly resembled Swedish copper. Another piece was flattened out thin when cold for the purpose of immersion in the muriatic acid. The pure copper was melted in rather a higher degree of heat, and although not teemed until it had assumed a creamy surface, and the crucible had fallen to a low red temperature, it was crystalized throughout the whole fracture. The surface and the fracture of this copper were of a red colour; the body weak, and tearing with facility into pieces. Fragments for immersion were cut off and flattened. The following specimens were then placed separately in muriatic acid. No. 1, Pure copper, cut off with a chisel, 53 grains 30 391 45 On the morning of the third day the following remarks were made upon their respective solutions: No. 1, Light green colour, very transparent when dashed against the sides of the glass. No. 2, equally transparent, but the green was brownish and not so decidedly cupreous. After continuing the immersion for 48 hours longer, the acid was poured off and the specimens were well washed and dried. No. 1, That weighed 53 grains, now weighed Loss 13 grains, equal to 25.4 per cent. No. 2, That weighed 30 grains, now weighed Loss 18 grains. Equal to 61.2 per cent. No. 3, Unrefined copper flattened, 39 grains, now weighed, Loss 20 grains. Equal to 50 per cent. 391 grains. 11/1/ } 19 grains 38 No. 4, Unrefined copper bar, 42 grains, now weighed, Loss 3 grains. Equal to 8.33 per cent. It would appear from this experiment that the unrefined copper resists waste in the muriatic acid, in the same way, and to nearly the same extent, as in the cementation with lime mentioned in my last previous paper. In corroboration of this fact, we may take the following abstract of another series of experiments, wherein the specimens were weighed three times, at intervals of 48 hours between each weighing. Unrefined copper, 1st immersion, lost, Ditto, 2nd ditto 15 per cent. 8 6 cent. 46.2 In favour of the unrefined copper, principally containing tin,-16.9 per Two pieces of copper, the one pure, the other unrefined, were immersed, under similar circumstances, for seven days. The unrefined copper lost 17 per cent., and the pure copper 45 per cent. To ascertain whether the greater indestructibility was owing to the tin which remained in the unrefined copper, I formed a bar of alloy as follows: Pure copper 2880 grains a proportion of tin about equal to 3 per cent. A piece from this bar weighing about 183 grains was exposed for seven days in muriatic acid, at the end of which time it was found to have lost 30 grains, or 16 per cent. The unrefined copper, above mentioned, lost in the same time and under similar circumstances, 17 per cent., which is a striking correspondThe same piece of tin alloy, at the end of five weeks, was found to have lost in all 76 grains, or 38 per cent. Pure copper by the foregoing results lost in seven days' immersion 46.2 and 45 per cent. ence. In the first instance I was inclined to attribute the indestructibility of the unrefined copper in the acid, partly to the effects of the charcoal in the cementation, seeing that the effect produced by that operation was much greater upon unrefined than upon pure copper. Whatever advantages may belong to the proper use of charcoal in the reduction and cementation of copper (and I consider them not unimportant), the addition of a small portion of tin will be sufficient to account for the superior resistance to waste which this alloy presents in the muriatic acid, over that of the common refined copper of this country. This incapacity to rapid oxidation which is presented by the alloy of tin with copper, suggests many useful hints to the artists and the manufacturers, of which advantage has already been taken in forming ship-sheathing and other articles. Lond. and Edin. Phil. Mag. Progress of Physical Science. Experimental researches in Electricity. Tenth Series. By MICHAEL FARADAY, D. C. L. F. R. S., &c. &c. [From Phil. Trans. 1835, Part. II.]* The subjects embraced are, on an improved form of the Voltaic Battery, Received by the Franklin Institute, through the kindness of the author. and some practical results respecting the construction and use of the bat tery. Mr. Faraday has previously shown that the chemical forces in the battery are two fold, one local and producing no useful effect, the other transferred and constituting the electrical current in the instrument. By ascertaining the quantity of zinc dissolved, compared with the decomposition produced, in a volta-electrometer, the ratio of the two effects just referred to, may be determined. In a battery of zinc plates, enclosed entirely by platinum ones, which do not touch metallically, and excited by dilute sulphuric acid, there would be no local action without transfer. If the surrounding metal be copper, and the exciting fluid dilute nitro-sulphuric acid, a very slight discharge takes place between the adjacent cop. pers, especially when the circuit is completed. The theory just stated induced the construction of a battery in which a thickness of paper was used to prevent metallic contact, and thus Professor Faraday was led to the re-invention of Doct. Hare's galvanic deflagrator. To the merits of this apparatus, and of its mechanical arrangements, Prof. Faraday does full justice, as full as if it had first originated with himself, while he refers the entire credit to its author Prof. Hare. A deflagrator of forty pairs of three inch square plates, was compared with a battery of forty pairs of four inch plates of the ordinary form with double copper plates, insulated, and proved to be its equal in igniting platinum wire, the discharge between charcoal points, the shock, &c. The power of the deflagrator diminished most rapidly, because but one seventh of the quantity of acid liquid was required to excite it, the solutions in its trough and in the cells of the other battery being of the same strength. To compare the two batteries, the amount of zinc dissolved for each equivalent of water decomposed in the volta-electrometer, was ascertained. Three acids were tried, sulphuric, nitric and muriatic. One cubic inch of the first dissolved 486 grs. of zinc, of the second 150 grs, and of the third 108 grains. A mixture of 200 parts, by bulk, of water, 4 of sulphuric acid, and 4 of nitric acid, was applied to the deflagrator before referred to, and to four troughs having plates of the size and construction before stated. One equivalent of water in the volta-electrometer, was decomposed for each 2 to 21 equivalents of zinc dissolved from each plate of the deflagrator, while 3.54 equivalents were required from each plate of the common battery, for the same effect. Twenty pairs of four inch plates in a deflagrator and twenty of the same size in a common battery, gave respectively 3.7 and 5.5 equivalents of zinc from each plate for the same effect. And with ten pairs, 6.76 and 15.5 equivalents, respectively, for the deflagrator and common trough. Prof. Faraday remarks: "1131. No doubt, therefore, can remain of the equality or even the great superiority of this form of voltaic battery, over the best previously in use, namely, that with double coppers, in which the cells are insulated. The insulation of the coppers may therefore be dispensed with; and it is that circumstance which principally admits of such other alterations in the construction of the trough as give it its practical advantages. "1132. The advantages of this form of trough are very numerous and great. 1. It is exceedingly compact, for 100 pairs of plates need not occupy a trough of more than three feet in length. 2. By Dr. Hare's plan of making the trough turn upon copper pivots which rest upon copper bearings, the latter afforded fixed terminations, and these I have found it very convenient to connect with two cups of mercury, fastened in the front of the stand of the instrument. These fixed terminations give the great advantage of arranging an apparatus to be used in connexion with the battery before the latter is put into action. 3. The trough is put into readiness for use in an instant, a single jug of dilute acid being sufficient for the charge of 100 pairs of four inch plates. 4. On making the trough pass through a quarter of a revolution, it becomes active, and the great advantage is obtained of procuring for the experiment the effect of the first contact of the zinc and acid, which is twice or sometimes even thrice that which the battery can produce a minute or two after. 5. When the experiment is completed, the acid can be at once poured from between the plates, so that the battery is never left to waste during an unconnected state of its extremities; the acid is not unnecessarily exhausted; the zinc is not uselessly consumed; and, besides avoiding these evils, the charge is mixed and rendered uniform, which produces a great and good result, and, upon proceeding to a second experiment, the important effect of first contact is again obtained. 6. The saving of zinc is very great. It is not merely that whilst in action, the zinc performs more voltaic duty, but all the destruction which takes place with the ordinary forms of battery between the experiments is prevented. This saving is of such extent, that I estimate the zinc in the new form of battery to be thrice as effective as that in the ordinary form. 7. The importance of this saving of metal is not merely that the value of the zinc is saved, but that the battery is much lighter and more manageable; and also that the surfaces of the zinc and copper plates may be brought much nearer to each other when the battery is constructed, and remain so until it is worn out: the latter is a very important advantage. 8. Again, as in consequence of the saving, thinner plates will perform the duty of thick ones, rolled zinc may be used; and I have found rolled zinc superior to cast zinc in action; a superiority which I incline to attribute to its greater purity. 9. Another advantage is obtained in the economy of the acid used, which is proportionate to the diminution of the zinc dissolved. 10. The acid also is more easily exhausted, and is in such small quantity that there is never any occasion to return an old charge into use. Such old acid, while out of use, often dissolves portions of copper from the black flocculi usually mingled with it, which are derived from the zinc; now any portion of copper in solution in the charge does great harm, because, by the local action of the acid and zinc, it tends to precipitate upon the latter, and diminish its voltaic efficacy. 11. By using a due mixture of nitric and sulphuric acid for the charge, no gas is evolved from the troughs; so that a battery of several hundred pairs of plates may, without inconvenience, be close to the experimenter. 12. If, during a series of experiments, the acid become exhausted it can be withdrawn, and re-placed by other acid with the utmost facility; and after the experiments are concluded, the great advantage of easily washing the plates is at command. And it appears to me, that in place of making, under different circumstances, mutual sacrifices of comfort, power and economy, to obtain a desired end, all are at once obtained by DR. HARE's form of trough."* The effects of the following circumstances are examined by Prof. Faraday under the new light thrown by his researches. 1. Nature and Strength of Acid. Nitric acid evolved no hydrogen, muriatic acid but little, and sulphuric acid most. They gave respectively for the equivalent of water decomposed, 1.85 eqs. of zinc for each plate, 3.8 eqs, and 4.66 eqs. by a mixture of 1 of acid to 200 parts of water. By adding to the mixture of water and sulphuric acid in proportions just referred to, 4 of nitric acid, the consumption of each zinc plate was reduced to 2.786 for each equivalent of water; 8 of nitric acid gave 2.26 eqs.; 200 water, 16 muriatic acid, and 6 nitric acid gave 2.11 eqs. per plate. This effect does not depend upon the strength of the acid solutions, the results being stated in equivalents. 2. Uniformity in the strength of the charge, is of great importance. A practical difficulty suggested by Prof. Faraday, of making a wooden trough tight under the frequent alterations of dryness and moisture, is entirely overcome by using a coating of cement in the interior as in the trough made by Dr. Hare. Cement duly applied will render unnecessary the glass sides proposed by Prof. Faraday, to prevent discharges from the edges of the plates. B 3. Purity of the zine is of great importance, its impurities making the action of the battery local. 4. Foulness of the zinc plates, interferes materially with the action of the battery. No old charge containing copper should be used. 5. New and Old Plates. The former are much the most efficacious. But after a few immersions the power of rolled zinc plates becomes nearly constant. This is not the case with cast zinc plates. 6. Vicinity of the Copper and Zinc. When the plates are at a less distance the facility of transference is increased. The intensity and quantity of the transferred current, are both increased for a given consumption of zinc. 7. First immersion of the Plates. This effect, independently of the newness of the plates, is produced by the mixture of the acid in the charge with that which has been neutralized. Hare's form of trough secures this advantage. 8. Number of Plates. The most advantageous number depends, mainly, on the resistance to be overcome in the decomposition, but the number admits, in any given case, of a maximum. 9. Large or Small Plates. The use of them will depend upon the facility of the transfer of electricity. If the most advantageous number is found, additions of zinc should be made to the size. Increase of size will raise the most advantageous number. 10. Simultaneous decompositions. When the number of plates exceeds the most advantageous number, more than one decomposition may be made with advantage. The conducting power of the body to be decomposed, of course, materially modifies the results obtained. The enlargement and proximity of the poles, and conducting power of the liquid, should be particularly attended to in the construction of the volta-electrometer. Recent Researches on Heat. M. MELLONI'S RESEARCHES.-Though the "thermo-multiplier" of M. Melloni has now been for several years before the scientific world, it is not yet perhaps so generally known to experimenters as it deserves to be. We shall deem it, therefore, not inappropriate to the nature of this article, to state briefly its principle. The essential part of it consists in a great number of pairs of small slips of antimony and bismuth soldered together, and combined in one case, so as to have their galvanic action excited by the application of heat. This thermo-electric effect is indicated and measured by its influence on a magnetic needle, placed below, and arranged as a galvanometer, by having many coils of wire passed round it, the wires communicating with the thermo-electric combination; the effect is increased in proportion to the number of pairs of plates. Thus the galvanic action on the needle is the measure of the amount of heat affecting the metallic combination; and the important and valuable part of the contrivance is, that degrees of heat, so small as to be quite insensible to the most delicate thermometers, are multiplied, as it were, by the multiplication of the number of pairs of metal plates, and thus produce a sensible effect on the galvanometer needle. The skill of artists has been exercised in reducing them to small dimensions. M. Gourjon of Paris, has succeeded in bringing them into so small a compass, that the end of the case which is exposed to the heat, is not greater than the section of the bulb of an ordinary thermometer. |