The Annals of Electricity Magnetism and Chemistry and Guardian of ...

nevertheless, that the one now described stands next for convenience and simplicity. There remains to be made known, however, that by this arrangement there is one disadvantage experienced, by our not being able to renew the porous vessel without interrupting the action of the whole apparatus: and it is necessary, now and then, to change these porous vessels, and soak those last used in clean water, in order that their pores may be well cleansed of the crystallised salts that lodge in them. This process will occupy five or six days, according to circumstances; which, however, I have found is a sufficient length of time, even after I have kept a battery frequently from fourteen days to three weeks in uninterrupted activity, and in such uniform action, that the small deviations in the direction of the magnetic needle, and variations of temperature (Temperaturveränderimgen) in the liquids, were too trifling to describe.

The size of the apparatus here spoken of becomes limited, in consequence of the difficulty in procuring porous cylinders of considerable dimensions, and at the same time having thin sides or walls; thick walls offer a considerable resistance to the currents, and consequently lessen the action. It is, therefore, preferable to unite several smaller apparatus into one common action, by connecting all the copper cylinders together on one hand, and all the zinc cylinders on the other, so that they may form but one voltaic pair. Fig. 32 represents a ground plan of an apparatus of nine elements, placed in one common reservoir, and which can be properly united by clamp screws, or by any other convenient method, so that they may form one single pair, of nine times the surface presented by each individual element. The method of combining the metals is not shewn in the figure, in order to prevent confusion. It is true, this apparatus requires much liquid to keep it in action; notwithstanding, however, it is so much the more durable, and is easily managed.*

For whatever purpose the galvanoplastik art may be used, we shall see, by what follows, that it is capable of very extensive application. The hitherto known methods of obtaining metallic copies, by casting or stamping, may be entirely superseded by this process; and the certainty, sharpness, and accuracy, in every case, is such as by the old methods could not be accomplished; and in regard to the beauty of polish, it surpasses coins or medallions from the finest steel dies. If we take a plate of gold, silver, or copper, of the highest polish, and employ it as a cathode in the galvanic circuit, the copper that becomes reduced upon it, not only exhibits the exact polish of the original, but it finds out the finest microscopic scratches which the polishing process left unfilled up. If we touch with the finger a highly polished plate of metal, a small dull speck,

*There are a few more lines of this section, which it would be useless to translate, as they merely refer to the supposed cost of keeping up the action of the apparatus in Russia, by turning to account the sulphate of zinc and other products. TRANS.

which shews the pores of the skin, will be left behind even this speck will be so accurately copied by the galvanic process, that the keenest microscopic observation can detect no difference from the original. It is well known, that to obtain metallic copies by striking with dies, is a very expensive process, and the truth of the original is always encroached upon; but by the galvanic casting the most accurate copies are produced at a very trifling cost.

When we are about to multiply copies from a deeply engraved plate, we must, in the first place, make a galvanoplastik picture, in relief, of the original engraving; and upon this first galvanoplastik we can again, at pleasure, obtain other plates, which will be precisely identical with the original; and they may be printed from it in the same manner, and the impressions will be as good as those taken from the first engraved plate. I will also make a few remarks in this place respecting the separating of the galvanoplastik from the original plate. The two will always separate very well, when the new plate is allowed to become sufficiently thick, if the copper of the original be not spongy, porous, or scaly, and, finally, if the design be not engraved too perpendicular, or, rather, be not undercut. There are essential circumstances to be attended to in all cases where engraved copper-plates are intended as models for forming galvanic copies on.

If the galvanic copper be slowly and cautiously reduced, it attaches itself very excellently to every part of the engraved plate, and allows of being easily loosened. There is no difficulty whatever in making galvanic plates, especially where an already engraved copper plate serves for the original. By this means we get rid of the tiresome labour of grinding and polishing, requisite processes which the original engraved plate has already passed through; at the same time, such original plates should have obtained an uniformity of texture which surpasses that possessed by the best mercantile copper. With common copper, it frequently happens that the galvanic plate adheres so firmly to the original, if not throughout the whole surface of contact, at least in many places, that the separation of them can be accomplished by no other than forcible means, and it is possible only at the expense of the original. Sometimes a thin film of fat, or oil, laid over the original plate, prior to its being submitted to the galvanoplastik process, facilitates the separation of the two. Strong coverings of wax, lac, &c., can only be used where sharpness and accuracy is not of much consequence. The galvanic plates are easily removed from silvered or gilt plates, on which they have been formed. It appears, also, that for this purpose the gilding performed by the wet process has an advantage over that in which the amalgams of gold are used. An exposed covering of thin gold leaf, or gold size, over the face of the copper, answers, also, to facilitate the separation, and may be used for that purpose, where it can be done without injuring the sharpness of the design. These precautionary measures, after all, are not necessary

when the copper of the original is of a good quality. As soon as the galvanic plate has acquired the requisite thickness, and the parts grown over the edges of the original are filed away, it springs loose of itself, without any further trouble. It hardly need be mentioned, that a casting of gypsum would answer all the purposes of copper plate, provided it were nicely managed, and taken from an original engraving that was not under-cut.

(To be continued.)

On Voltaico-Electric Quantity and Intensity. By Dr. BUFF. (Ann. der Pharm., t. 32, p. 1.*)

The author has had in view the study of that species of mysterious property which Faraday conceives to be found in voltaic electricity, by virtue of which it is more easily transmitted; a property which he has named intensity, and which he distinguishes from quantity. He has found that this property is, as I have already indicated, only an effect of conductibility, by virtue of which the neutralization of two electricities accumulated at the poles of the pile is more or less easy.

The experiments of Dr. Buff are not all new, but they are interesting, as they confirm those which have already been made on the same subject by other philosophers.

He arrived at the conclusion, by varying the number of pairs in a pile, that if the circuit is closed by an imperfect conductor, the facility which this possesses of transmitting the quantity of electricity which can be developed by the battery is universal in proportion as the number of pairs is augmented.

The effects of tension observed by Dr. Buff are more numerous and more remarkable. He has at first studied them on a pile, the poles of which were insulated. The centre pair gave the same tension as it possessed when alone; two pairs, apart from the middle of the pile, gave a stronger tension; three, a still stronger; and so on to the poles, where the electricity attains its maximum. The author appreciated the electrical state of each pair in diverse manners, and in particular by means of a copper wire soldered to zinc, which he put in contact with the inferior plate of the condensor, whilst he touched the superior one with the finger.

By making the poles communicate with each other by distilled water, the same distribution of free electricity in the pile has been found, only it was a little more feeble. With acidulated water placed between the poles, and which was decomposed, the electricity of tension was still found in those pairs nearest to the poles. But no portion of it could be found when the poles had been metallically united.

Archives De L'Electricitie, No. 1.

The same effects have been obtained by charging the pile with diluted sulphuric acid, in place of ordinary water. By reuniting the poles by distilled water, the tension was still feebler, and no decomposition took place in any part; but when reunited by acidulated water, decomposition took place in all parts, in the troughs of the pile, as well as in those into which the poles were inserted. The tension has in all cases been stronger at the poles.

The author remarks the analogy which exists between these effects and those of an ordinary electric battery, charged with electricity from a machine; and he thence concludes that the greatest tension, or the static intensity of the pile, only proceeds from the resistances which the circulation of the electricity meets with. We conceive, then, that it is at its maximum at the poles, and that, without being obliged to attribute to the current a mysterious property, there exists for the two electricities, accumulated at the two poles, a tendency to neutralization, more or less strong, and consequently a greater facility for the current which results from this neutralization to traverse the imperfect conductors.

On an Advantageous Manner of Constructing Grove's Pile.
C. A. GRUIL. (Ann. der Physik, tome li. p. 381.)*

The author at first constructed this pile by placing a cylindric ring of platinum, in a porous earthen tube, closed at its lower extremity, and filled with nitric acid. The porous tube was introduced into a cylindrical jug, filled with diluted sulphuric acid, in which was also inserted a cylinder of amalgamated zinc, which enveloped the tube without touching it. This piece of apparatus, which is almost similar to a calorimeter, gave powerful results, but it presented this inconvenience: the thin layer of nitric acid, comprised between the surface of the cylindric ring of platinum. and the interior partition of the porous tube, became rapidly heated, entered into a state of ebullition, and emitted nitrous vapours.

The author then substituted, for the cylindric ring of platinum, two plates of the same metal, cutting each other at right angles, following the axis of the tube, and forming a cross. He has, even at a later period, added a third plate, in such a manner that the three plates crossed each other at the axis, by making angles of 60° with each other. They were thus disposed around the axis, like the leaves of an open book round the back of the book.

After this disposition, all the nitric acid being in the circuit was much less heated. This pair would act during several hours without any disengagement of gas or decrease of the force of the current, when even the nitric acid had taken a deep green colour.

Archives De L' Electricitie, No. 1.

- Day of month.

By W. H.

A Register of the Electric State of the Atmosphere, in relation to its
Meteorological Phenomena, for the Month of June, 1841.
WEEKES, Esq.