278 



EECIiBATIVE SCIENCE. 



Bt ood.* Whether electricity is to be regarded 

 as a material principle, and whether it com- 

 bines with other elements as the elements do 

 amongst themselves, has yet to be decided. 

 It will be sufficient to notice here, that when- 

 ever two metals are placed in a liquid which 

 acts unequally upon them chemically, the 

 electric equilibrium is disturbed. Positive 

 electricity comes off from the metal acted 

 upon most vigorously, while the metal itself 

 becomes negatively electrified. The fluid 

 then passes to the metal less acted on, and 

 from that through the connecting wire above, 

 till it reaches the former metal, and thus the 

 electric circuit is completed. In such an 

 arrangement — the chemical liquid containing 

 a metallic salt — the metal would always be 

 deposited on the plate which was least acted 

 upon by the liquid ; but the deposition is 

 irregular and uncertain. It is much improved 

 by immersing the negative metal in a diffe- 

 rent liquid, and separating this liquid from 

 the solution by means of a membrane, as 

 described above. This, however, is not a 

 convenient arrangement where a number of 

 experiments are to be made in succession, 

 although it does very well for a solitary 

 attempt. We will, therefore, conclude this 

 paper by describing one or tAvo modifications 

 of this " single-cell " apparatus, as it is called, 

 which add greatly to its efficiency. 



The membranous diaphragm with which 

 we have supposed the zinc-plate to be 

 covered is not effective in experiments which 

 last any time. Porous jars, such as may now 

 be obtained at any chemist's, are used in- 

 stead. They are cheap, and can be used re- 

 peatedly, especially if, when they are done 



* To those who are curious on this subject, we 

 recommend a perusal of a work which has come to 

 our hand, entitled " Electro-Chemistry, with Positive 

 Results ; in which it is demonstrated that there is a 

 latent electricity in bodies as well as a latent heat, and 

 that those bodies, when deprived of their latent elec- 

 tricity, indicate a change in their characteristic pro- 

 perties. By Charles Chalmers. Churchill, Burlington 

 Street." V^e nay have occasion to refer to this work 

 again. 



with, they are laid for a few hours in clean 

 water. If, however, a chemist's shop be not 

 easily accessible, the following way of making 

 very good porous diaphragms will be found 

 useful : — 



Let a core be turned out of a piece of 

 hard wood, of the shape a a (Fig. 6). Bind 

 round this core apiece of smooth 

 brown paper, B B, in such a way 

 as to leave a clear space round 

 the smaller part. The space thus 

 left is now to be filled with 

 plaster of Paris, which must be 

 added tiU it reaches the height c. 

 The plaster is thus prepared : — 

 Take it quite fresh, and drop it 

 piece by piece into a lipped jug 

 containing water; when it is 

 dissolved, the superfluous water may be 

 poured off. Mix the remaining water and 

 plaster with a clean stick, and pour it into 

 the mould. When it is firmly set, the paper 

 may be unwound, and the core withdrawn ; 

 a porous diaphragm will thus be formed, 

 which, with proper care, will serve for several 

 experiments. 



A better form of cell, too, might be easily 

 devised. A wooden box, lined with pitch or 

 well varnished, and furnished with a shelf to 



Fig. 6. 



Fig. 7. 



hold the crystals of sulphate of copper, the 

 shelf also having an orifice to receive the 

 porous diaphragm, would be found more 

 convenient. Such an apparatus, when at 

 work, would have the form shown in Fig. 7. 



