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In fact, the copper thus precipitated on iron will serve directly to preserve it, to give a beautiful appearance to objects of the locksmith's production, to balconies, balustrades, grates, chimney utensils, &c.

Besides, it can, we are assured, enable us to enclose iron in an envelope or case of brass. It is sufficient to make a deposit of copper and zinc on cast iron, then to heat the piece to a red heat in powdered charcoal. Brass is thus produced, and constitutes a metallic varnish less alterable than copper, and of a colour which we can vary at will.

In conclusion, at any time when we wish to go to the expense that the combustible which produces this latter operation exacts, we may be enabled to produce on the metals deposits in the alloys as casily as deposits of pure metal. This is a point of view which M. de Ruolz has not considered, but it is one to which we recommend his zeal and penetration.

The Precipitation of Lead.-In acting upon a solution of the oxyde of lead in potash, by means of the pile, we can lead iron plates, iron, and all the metals in general. The fabrication of chemical products will be benefitted by this discovery, by thus obtaining cauldrons of iron plates lined with lead, and where the solidity of the iron will be united to the resistance which lead offers to the chemical action of saline solutions and feeble acids.

In fine, there are but few circumstances in which lead obtains the preference over other metals, except for its low price and the facility with which it is managed. The new processes with which we are occupied will have, then, for their object rather to avoid the employment of lead than to increase it.

Tinning.We have not yet said much of tin. The new processes may extend its applications, by giving an easy and prompt means of tinning copper, bronze, brass, iron, and even cast iron, by operating with it cold, and on all kinds of utensils.

Again, for a long time the workpeople who tin pins have, without knowing it, made use of a truly galvanic process, for they put among the pins grain tin, and water charged with cream of tartar. The two metals constitute a real pile, where the negative pole formed by the pins attract the tin to such a degree that it becomes dissolved, and being obliged to precipitate itself, the pins are thus covered with the tin.

The tinning of iron, as well as zinc, would be impossible by such a procass; it is then neeessary to have recourse to a real pile, independent of the metals employed.

On the contrary, in order to copper the metals which are negative with respect to tin, we can make a voltaic pair with the tin itself and the metal to be tinned, and by making use of cream of tartar to dissolve the tin, as is practical in the process of tinning pins, from a solution of the oxide of tin in potash, as propssed by M. Böttiger.

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Cobaltizing-Nickelizing.–The Academy will remark with some interest the metallic pieces covered over with nickel or of cobalt among the specimens on its bureau.

Cobalt, whose colour approaches so near to platinum, has been employed in the recovering of musical instruments of copper, and it furnishes, in these cases, a metallic varnish agreeable to the eye, durable, and at a cost very little enhanced. However, all our experiments lead us to believe that platinum, gold, or silver, will obtain the preference; but cobalt will be able to find its place in such applications as a means of varying the tints.

Experience has proved, again, that by thus changing the surface of sonorous instruments, and by recovering the metals which form them with a coat of another metal, we do not modify in any point their properties, in a musical point of view. The most practised ear cannot recognize any change in this respect.

Nickel has especially been tried upon objects in the locksmith's branch, or in ornaments for harness. As it is not dear, and there does not require much to resist the air, it is well to note here that this metal may be applied very well on iron—a fact which may possibly become important in its application to locks for great security, to large clocks, to counters, and even to many parts of machines which we wish to preserve from the action of the air, without being obliged to grease them often.

Zincing.--Among the processes of M. de Ruolz, those which he applies to the zincing of metals, and of iron in particular, have highly interested your Commission.

The zinced iron acquires the faculty of resisting the oxydizing action of the air, and especially of humid air or of water. The fact is, that the zinc, which is more oxydable than the iron, preserves this metal from oxydation, and is scarcely at all oxydized itself ; for when it becomes covered with a layer of sub-oxyde, all ulterior alteration is arrested.

In the greater part of the applications attempted by M. de Ruolz, the metal deposited is found on the contrary negative, with regard to the metal thus covered. All the guarantees which the metallic varnish promises in similar cases depends on its perfect integrity or connexion ; for if it enters upon any point whatever, and the humid air can arrive at the interior of the metal, the superficial layer, far from being a preserver, will become, on the contrary, a determining cause of oxydation.

Zinc, applied on iron, preserves it doubly then, as long as it is in contact, like varnish, and when it is performed by a galvanic action. This particularity accounts for the success which the zinced iron, in all its applications where iron, or iron plates, being employed cold, have not lost any of their tenacity, and might support a supplement of expense.

In general, the zinced iron ought not to be employed for containing cold water ; the galvanic action of the two metais determines

very rapidly the oxydation of the zinc, and the iron in its turn becomes red with a singular activity. This remark is intended, and ought to direct artisans to the employments they may make of the new processes, and is doubly sufficient to make them avoid mistakes except in very rare circumstances, but even then, less susceptible of being apprized of it by experiment alone.

The zincing of iron has hitherto been performed by immersing the iron in a bath of zinc, which is melted with some inconveniencies besides. The iron becoming attached to the zinc, thus constitutes a very brittle superficial alloy : the iron then loses its tenacity, a circumstance which is not at first perceived, until we attempt to zinc a very fine wire of iron or of iron plates very thin. Besides, the surface thus clothed with a layer of a metal slightly fusible, is always deformed.

Thus, by this process, we cannot zinc a fine wire of iron; it would become fragile and misshapen. Nor can we zinc balls or bullets ; they would be misshapen, and no longer of the same calibre. The zincage of iron is not, by this process, applicable to objects of art : all their forms would be destroyed.

The industrial arts, the military art, the fine arts, will receive, then, with a high degree of interest, the processes of M. de Ruolz, by which is accomplished, and that economically, the zincing of iron, steel, and cast iron, by means of the pile with the solution of zinc ; by operating with the solution cold, and in respecting, consequently, the tenacity of the metal; by applying it in very fine layers, and by the preserving of the general forms of the objects, and even the aspect of their smallest details.

There is, then, nothing to hinder us from zincing the iron wire employed in numerous ways, and which, far from rusting, will be preserved, at any rate, during many years, without doubt. Thus, the cords of suspension bridges and lightning conductors may be made of iron wire covered with zinc. We may say as much for metallic cloths employed in the fabrication of sieves, bolters, and of those which we ly in the construction of safety lamps. In the latter case, even the workmen charged in the mines with the care of cleaning the lamps, will be enabled, without sensible expense, to be supplied with everything that is necessary to restore the zinc, from time to time, without dismounting the lamp.

All the parts of machines, whose dimensions are so strong or so small as to render improper the zincing by the hot method, will be, on the contrary, susceptible of being easily zinced by the humid method.

The thinnest plate may receive this preparation without becoming cased ; this will permit of the production of artificial slates of plate zinc perfectly applicable, and applicable with great economy, to the roofs of buildings.

The Commission were desirous of being convinced that it was possible to zinc cast-iron, and bullets in particular. It was certain

that this application would excite all the interest of the minister of war, and of that of the marine especially ; for the bullets alter so rapidly at sea, that their dimensions are soon modified in such a manner as to be prejudicial to the truth of the aim and to the duration of the pieces. It deposits a zinced bullet on the bureau.

In fine, the zincing of iron and of cast iron are of great importance to architecture and the arts of imitation. Every one knows with what promptitude the nails and bars of iron employed in buildings become oxydized, and consequently lose their tenacity; and we all comprehend to what extent it is useful to preserve, with an eye to cheapness, all the pieces of iron disseminated in the walls of a building, for they are destined to give it a solidity which will become thereby durable and susceptible of being calculated with precision. In the same manner, grates and balustrades of cast-iron, receiving a coat of zinc in place of one of paint, which requires frequent renovation, will be thus found better guaranteed against the action of water or air.

It is especially desirable that these new means are called into use to preserve statues of cast-iron, of which we have recently seen the attempt in several of our monuments, and which, in some cases, have been submitted to the application of plasterers or painters, very ill calculated with regard to science, and with an effect very deplorable in reference to art.

The processes of M. de Ruolz for zincing may be applied not only on objects small and open, but it will be possible farther to make use of them for monuments in their place, and of large dimensions, by taking some precautions easy to foresee.

Your Commission is far from having sought to enumerate here all the applications which this new means of the zincing of iron is susceptible of presenting ; it has limited itself to those most essential, but they will very well suffice to make the Academy appreciate all the extent of the works of M. de Ruolz on this point.

Before quitting a subject so important, we will recall to mind the fact, that M. Sorel, on one hand, and M. Perrot, on the other, had already attained the art of covering iron with a coat of zinc by means of the pile, but still using, in all cases, solutions altogether different from those which M. de Ruolz believes to be preferable, and which have enabled him to act with economy, a point which is here truly important. M. M. Sorel and Perrot have even anno

nounced, on this occasion, that they occupied themselves on the general problem of fixing the metals one on the other; we will hope, that by making known their processes, they will add to the perfection of an art which already appears so far advanced.

The Academy will see, with the highest interest, an industrial art destined to spread itself in the world under all its forms ; to put to profitable use the pile of Volta, which had not hitherto been

industrially applied except at the metallurgic works of our colleague, M. Becquerel, and to galvanoplastik processes.

By the variety of his applications, M. de Ruolz gives to the pile an opportunity of multiplying itself and of spreading, which will become, we doubt not, a very certain cause of perfecting, both as to the construction of this apparatus, and as to the means of rendering it economic.

In conclusion, your Commission thinks itself obliged to declare that, forced as it has been to limit the time which it could consecrate to this examination, since it acted as a Commission for the prize Montyon, and as it could no longer withhold its report, it was bound to limit itself to trace here the summary history of these experiments, without pretending to make a systematic exposition of the state of the science on the point on which it has been occupied.

That which it has had in view is the economic application of it. All its researches have been in this direction : this was its duty.

Under this aspect, the experiments of M. de Ruolz have presented it with a character really novel. Their utility has appeared to him to be worthy of all the attention of the Academy. The Academy will be pleased to recollect also, that the author of these experiments has given proof, in this long work, of a remarkable penetration, and of a perseverance worthy of being crowned with complete success.

The Commission comes, then, to demand of you to decide with confidence that the memoir of M. de Ruolz be admitted to form a part of Recueil des Savants etrangers.

But it would require still more of you—and that in the view of public interest easy to comprehend—to decide that a copy of the present report be addressed to M. M. the Ministers of War, of Marine, of Finances, of Public Works, and of the Interior, who will be enabled therein to find tokens of a nature to interest the services of which the high direction is to them confided.

The conclusions of this report are adopted.

On the Powers of Large and Very Small Horse-shoe Electro

Magnets. By C. H. PFAFF, of Kiel.*

So long as the hope exists of bringing electro-magnetism into use as a motive power, there will be an interest instilled on experimental enquiries respecting the determination of the most favourable circumstances for the production of still more powerful electro-magnets. With the exception of the powerful electro-magnet described by the

* Poggendorff's Annalen der Physik and Chemie. Band. 52. x. 2.

1841.

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