Batteries composed of zinc and copper plates buried in the moist ground are said to be very constant. Such batteries, however, yield very weak currents, because the resistance to conduction between the plates is very great. Thus it is evident that the current of this battery will remain constant longer than when the plates were immersed in acid. Prince Bagration placed plates in vessels filled with sand, which he moistened moderately with a solution of sal-ammoniac. Garnier used such batteries successfully to keep electrical clocks in motion (Dingler's Journal, vol. 110, p. 177); here a very feeble current was powerful enough to impart sufficiently strong magnetism to a small electro-magnet. Garnier's apparatus was constructed as follows: The sand was in a small tub; the zinc and copper had the form of a cylinder, the zinc being on the inside. The surface of the copper was 1.5 and that of the zinc 1.3 square decimetres. Such an element kept the apparatus in motion two months and a half. By using a battery of many such elements the construction could be so arranged that a single pair of plates might be removed, and renewed without interrupting the current. Koppinsky (Dingler's Journal, vol. 101, p. 222; Technologiste, March, 1846, p. 241) was disappointed in his expectation of this battery. He probably wished to produce strong currents with it. The vapor of ammonia also annoyed him. The unfavorable results are to be ascribed, in his opinion, to insulation; because the battery cannot supply itself with electricity from the ground, and because it is not protected from exposure to the air, which neutralizes the electricity generated by contact of the plates. I cite this as an example of the loose and inconsiderate disquisitions on the galvanic current and battery to be met with in technical periodicals. The editors of these journals should be more critical in such cases, and statements which are only calculated to lead astray those having no well-founded physical knowledge should either not be permitted to appear, or should be accompanied with the requisite explanations. After condemning all other batteries, Koppinsky finally proposes to use for galvano-plastic purposes, zinc and copper elements, the plates of which are one square metre in surface, and immersed two or three millimetres apart in dilute sulphuric acid. This is one of the oldest forms of the battery with large plate, to which Hare subsequently gave the very convenient form of a spiral; thus, in this respect, Koppinsky's efforts resulted in nothing new. On the other hand, the proposal to place the acid in vessels of other than resinous wood and set them on moistened earth, is new, but of no value. The experiments of Weekes (Dingler's Journal, vol. 97, p. 194) show the feebleness of the current produced by burying in tolerably moist ground, plates of zinc and iron, each being 54 square decimetres in surface. A current was obtained which deflected the astatie needle of a multiplier 879, but the deflection soon fell to 61°; the current was therefore exceedingly weak. A pile of 36 pairs of this kind gave, between coal points, a light strong enough by which to read fine print at the distance of a metre. Comparing this exceedingly small effect with the brilliant illumination produced by 36 zinc and carbon, or zinc and platinum elements, it is difficult to comprehend how Mr. Weekes can cherish the hope that such batteries may become advantageous means of illumination. The plates of Mr. Weekes, it is true, were placed in rather dry ground; if placed in moister ground they would have yielded stronger current; but it could never be as strong as if the plates were immersed directly in water. By moistening the sand with a solution of sal-ammoniac the strength of the current will still never approach that which the same plates would produce if placed in the solution without the sand. Buried plates can be used profitably only when very weak currents are desired; but such currents can be obtained quite constant for a long time by using very dilute acid. Buried plates, however, have the disadvantage of being less accessible than those of other batteries. § 16. Smee's battery.-This battery was greatly praised in many quarters; it was represented to produce very strong currents, and to be far more constant than other batteries with one liquid. No measurements in support of this opinion were made, and I have not found it anywhere confirmed. The copper of Wollaston's battery is substituted in Smee's by platinum or silver, covered by a rough surface of platinum (platinmoor.) This coating of platinum is produced by immersing the perfectly clean plate in a solution of chloride of platinum and potassium in contact with the negative pole of a rather weak battery, the positive pole of which dips at the same time into the solution. The platinum deposites on the plate at the negative pole. If the positive pole be also a plate of platinum, it will be attacked by the chlorine, and the solution will be kept saturated. The two surfaces of Smee's platinized plate are placed at about one line distance from the zinc plates. The width of the zinc plates is to be only about three-quarters that of the platinized plate. What is to be expected to be gained by this I cannot see. It is not the case in the Smee element with which I experimented, the negative plate of which was platinized silver. I found this battery less constant than Wollaston's, and the variations of the needle were far greater. With the same liquid, Smee's battery gave the following results, obtained exactly as those already described in section 15. Assuming as a mean for the insertion 0 the deflection 26°, for the copper wire 12°.25, and the brass wire 5°.5, the electro-motive force of Smee's element is 212, which is scarcely greater than that of Wollaston's, which we have seen is 208. With equal surfaces, the resistances of the two elements are tolerably equal. From these experiments, it does not appear that Smee's battery deserves any preference over Wollaston's. It is yet to be determined whether platinized platinum gives better results than platinized silver. § 17. The zinc and copper battery with two liquids.-When the copper of a zinc and copper battery is placed in a concentrated solution of sulphate of copper, and this in dilute sulphuric acid, the two liquids being separated by a porous partition, the injurious effects of polarization are in a great measure removed; the electro-motive force becomes greater than in the ordinary zinc and copper battery, and the strength of the current is constant. The electro-motive force of Daniell's battery is— E 470. From Svanberg's experiments, (Pogg. Ann., LXXIII, 290,) it appears that the electro-motive force of Daniell's battery changes but little with the nature of the liquid. The copper being constantly immersed in a concentrated solution of sulphate of copper, and the zinc immersed in various liquids successively, the following values, expressed in an arbitrary unit, were obtained for the electro-motive force: For concentrated solution of sulphate of zinc For the same, much diluted....... For concentrated solution of sulphate of copper For slightly acidified water..... For more strongly acidified water ....... 15.6 15.9 16.6 16.2 16.0 16.7 For a square decimetre of mean metallic surface, the resistance of the element is R = 78 (acid = 1 part SO, + 10 parts HO.) By using an acid containing 1 part sulphuric acid to 5 of water, the resistance for the unit of surface can be reduced to R 30. This resistance is due to the earthen cells; for Stöhrer's cells the resistance would be about one-third; therefore Daniell's battery is, perhaps, the most constant of all, which is due partly to the acid being used up less rapidly; since the acid, set free by the decomposition of the sulphate of copper, passes in part at least through the porous cell to the liquid in which the zinc is immersed. Ryhiner (Dingler's Journal, vol. 110, p. 418) proposes to substitute iron for zinc, and to place it in a solution of common salt. The advantage of this combination is not clearly seen. Its electro-motive force is certainly less than that of the ordinary Daniell's battery. Ryhiner says of his battery: Though it has not a strong influence on the magnetic needle, it has, nevertheless, a greater reducing effect on metallic solutions than the ordinary zinc battery! (?) Mr. Ryhiner appears not to know that the chemical effect of a current is always proportional to its magnetic effect. Moreover, he proposes to substitute linen cells for clay cells, which is quite practicable. One is often in fact embarrassed to get clay cells. Those made by the potter are bad; good ones cannot be had everywhere; and this is the more annoying because the best cells are the most fragile. Ryhiner's cells are made in the following way: A bag, without ends, is formed of stout twilled linen cloth, and stretched over a tin cylinder; on this, three or four plies of stout paper are fastened with flour paste, and the whole covered with a piece of thin linen. The bottom is made of a flat wooden cylinder, with a groove on its edge, to which the linen is tied fast with twine. The tin cylinder is replaced and filled with hot sand. When all is thoroughly dried, melted wax or rosin is poured in, to stop the cracks in the bottom. The upper edge is soaked in amber varnish. Whether these cells are really to be recommended, I am unable to decide from my own experience. § 18. Grove's battery.-According to my measurements, given in section 9-which, however, for Grove's battery, have no claim to great accuracy-the electro-motive force of this battery is, in chemical measures, 829. Other observers have determined its force, not in an absolute measure, but compared with that of Daniell's battery. Making the electro-motive force of the latter equal to 1, we have for Grove's as follows: By Jacobi...... By Buff........... By Poggendorff. By...... do. Mean ..... 1.666 1.712 1.668 1.565 1.653 Assuming the force of Daniell's battery in chemical measure, according to my determination, equal to 470, we should have, in the same measure, that of Grove's equal to 470 X 1.653 = 777; while I found the value of the electro-motive force of this battery to be 829, or about 6 per cent. greater. The observers above named made no comparison of the resistance of Grove's battery with that of Daniell's. Such a comparison, however, can hold good only for an individual battery, since it changes with the nature of the earthen cells, and is dependent upon the degree of concentration of the liquid. A comparison of the resistance of these two batteries is of value only when earthen cells of the same size are used for both, and the same liquid for the zinc cells; while the copper cell of Daniell's battery should contain a concentrated solution of sulphate of copper, the platinum plate of Grove's should be in strong nitric acid. I have not made such a comparison for the Grove's battery, but I have for the zinc and carbon battery, the resistance of which under otherwise like circumstances may be considered equal to that of Grove's. Thus we will return to the comparison of resistance in the zinc and carbon battery. The proposition has been made to substitute for the nitric acid another substance also containing much oxygen, namely: a solution of bichromate of potash. With this liquid, Poggendorff found the electro-motive force of Grove's battery equal to 0.987", that of Daniell's battery being equal to 1; thus considerably less than with nitric acid. Hence, bichromate of potash is not to be recommended for Grove's battery. In the 106th volume of Dingler's Polytechnic Journal, page 154, it is stated, that in using Grove's battery for telegraphic purposes, it often happens that the nitric acid penetrates through the earthen cells, and attacks the zinc so powerfully that it has to be newly amalgamated every day. Crystals of Glauber salts cast into the dilute sulphuric acid are said to remedy this evil. The explanation of this may probably be that the Glauber salts are decomposed, and nitrate of soda is formed, the free nitric acid then disappearing. §19. Bunsen's battery.-As a mean of all my experiments, stated in section 9, the electro-motive force of the zinc and carbon battery was found to have, in chemical measure, the value 824. The force of Daniell's battery being made equal to 1, that of the zinc and carbon battery was found by Buff to be Poggendorff....... 1.712 1.548 Expressed in chemical measure the force of the battery, according to Buff, is........... which accords nearly with my mean; and according to Poggendorff is.... 805 727 The electro-motive force of the zinc and carbon battery, and that of Grove's, are so nearly equal, that in practical use the little difference may be disregarded. According to Poggendorff, the electro-motive force of Bunsen's battery remains almost the same, if for the nitric acid is substituted a solution of bichromate of potash; indeed, with the liquid it is somewhat greater, the proportion being 1,580 to 1,548. |