CHAMBERS'S INFORMATION FOR THE PEOPLE. 



molecule of sulphuric acid. In ordinary circum- 

 stances, the affinity of the copper for the other 

 elements of the sulphuric acid is greater than the 

 affinity of the hydrogen for them. But when 

 any gas is being set free from a previous combin- 

 ation, its nascent or new-born state is a most 

 highly active one. Thus, the hydrogen which is 

 being liberated, at the copper plate, from the 

 water of the solution, is able to displace the copper 

 in it, and return to the bosom of the sulphur and 

 oxygen atoms to re-form sulphuric acid. The 

 copper, deposed from its place, is thrown on the 

 copper dish, and instead of hindering the action, 

 as the hydrogen would do, keeps the surface 

 bright with metallic copper, and so constantly fit 

 for service. 



The action of the battery is therefore to form 

 sulphate of zinc in the porous dish, and to con- 

 sume sulphate of copper in the outer. We must 

 thus keep the solution saturated with sulphate of 

 copper, by having some crystals of the salt lying at 

 the bottom of the cell. Usually, there is a small 

 shelf of copper gauze near the top of the copper 

 vessel, on which crystals may be placed for this 

 purpose. 



(5.) Grove's Battery has a greater electro-motive 

 power than any we have described, the plates 

 being platinum and zinc ; but it is inferior in con- 

 stancy to Daniell's. Fig. 22 shews an excellent 

 form of a Grove's cell. As in Daniell's, we have a 

 porous dish, d, but containing, in this case, the 



Fig. 22. 



Fig- 23. 



platinum plate, p, which is bent into the form 

 seen in fig. 23, to increase its surface. Outside of 

 d is the rolled-zinc plate, z, standing in a glass jar, 

 g. The liquids used are dilute sulphuric acid in 

 the outer dish, and strong nitric acid in the 

 inner. When the poles are joined, zinc sulphate 

 forms in the outer vessel, and an unhealthy gas 

 (vapour of hyponitric acid) at the platinum plate, 

 which must be kept from escaping by plugging 

 the mouth of the porous dish. The nitric acid 

 absorbs the hydrogen, and prevents polarisation 

 of the plate. 



Platinum is about four times the cost of silver, 

 and that is the only objection to the battery. But 

 it has the advantage of great power, and is very 

 easy to manage ; and the platinum does not get 

 useless, as other negative plates do, by the action. 



Iron, it is found, may be used for the platinum, 

 with almost equal effect Only, care must be 

 taken to keep the nitric acid concentrated, as it is 

 only then that it does not attack iron. 

 273 



(6.) Bunseris Battery was invented in 1843, and 

 is most powerful. It differs, in principle, from 

 Grove's only in the use of a carbon or charcoal 

 electrode for a platinum one. In the original 

 form, as devised by Bunscn, the carbon was in 

 the shape of a jar, and the porous dish with its 

 zinc stood inside it But the modified form, 

 most common here, 

 is shewn in fig. 

 24. The carbon ex- 

 actly takes the place 

 of the platinum 

 in Grove's element, 

 and a greater quan- 

 tity of electricity is 

 obtained from the 

 larger zinc surface. 

 Bunsen's is the most 

 energetic of all the 

 constant batteries, 

 and is almost uni- 

 versally employed 

 on the continent. 

 But it requires very Fig. 24. 



careful preparation, 



and extreme care in making the carbon connec- 

 tions. 



We need not describe the process of making 

 the carbon plates, as they are now easily obtained, 

 ready for use, from any electrician. 



Recent Forms of Battery Cells. The extensive 

 use of the telegraph within the last few years has 

 rendered the possession of a simple and cheap 

 battery of good power very desirable. Many 

 forms of cells have accordingly been suggested, 

 and adopted with more or less success. We have 

 here space to notice only those most favourably 

 received. 



(7.) The Daniell Trough has been adopted by 

 the Post-office, and is said to be a good and eco- 

 nomical battery. A wooden trough is divided into 

 cells by glass plates, or varnished slate slabs. 

 These are again subdivided by slabs of porous 

 earthenware. Cast zinc plates and dilute acid go 

 to one division, while copper and its sulphate go 

 to the other. The action is, of course, identical 

 with that of a Daniell. 



(8.) The Density Battery of Calland is derived 

 from Daniell's principle. Here the porous cell is 

 dispensed with, and the two liquids are kept apart 

 merely by their difference of density or weight. 

 The copper plate is placed at the bottom of the 

 cell among crystals of blue vitriol. A copper wire 

 soldered to it, and protected by gutta-percha, 

 passes up through the liquid to join the next zinc. 

 Over the crystals of copper sulphate is poured a 

 weak solution of sulphate of zinc, in which the 

 zinc plate is suspended so as not to reach the 

 copper solution. The zinc sulphate solution is 

 lighter than the other liquid, and so floats on it 

 without mixing. It is said to be very effective, 

 and to give a constant current for months. 



(9.) The Minotto Battery, somewhat like the 

 former, has also come into telegraphic use. 

 Coarsely powdered crystals of copper sulphate are 

 placed at the bottom of the cell, the copper plate 

 being under the crystals. A layer of clean sand 

 (or even sawdust) is put over the crystals, with a 

 piece of cloth or porous paper between, to prevent 

 mixture. 



The cell is filled with acid water, and a plate of 



