248 

 The following communications were read : — 



1. On a new Galvanic Battery, and an improved Voltameter. 

 By Martyn Roberts, Esq. Communicated by Sir John 

 Robison. 



Electrical observers have experienced three important defects in 

 the common galvanic trough battery, as constructed by Cruick- 

 shanks, namely, that the zinc is deposited on the copper plates, that 

 the zinc plates become gradually covered with a coating of oxide 

 of zinc, and that the hydrogen formed by the decomposition of 

 water adheres in globules to the surface of the copper; the result 

 of all which circumstances is, that the galvanic action quickly de- 

 creases in force. These inconveniences have been in part removed 

 in the battery of Professor Daniell, in which the zinc plates are 

 covered by an animal membrane, and sulphate of copper is substi- 

 tuted for acids to form an exciting solution. l?y the former pre- 

 caution, the deposition of zinc on the copper plates is prevented ; 

 and by tb.e latter, hydrogen is no longer evolved so as to ad- 

 here to the copper plate. These contrivances, however, do not 

 prevent the zinc plates from becoming gradually covered with oxide 

 of zinc, as in the battery of Cruickshank; and, besitles, the improve- 

 ments made by Profei^sor Daniell are attended with their own in- 

 conveniences in turn. Copper is gradually deposited on the ziuc 

 plates ; the animal membrane obstructs in some measure the free 

 transmission of the electric current, and it is also apt to putrefy iu 

 no long time ; the cleaning of the plates is trouMesome ; and the 

 expense of employing a battery of considerable size must also be 

 taken into consideration. 



The author proposes to obviate all the inconveniences hitherto 

 noticed, by resuming the original construction of Cruickshanks, 

 rendering the plates circular and moveable on a common axle, 

 which is turned slowly by a handle at one end of the trough, and 

 attaching a rubber of cloth along the margin of the trough, by which 

 the plates are constantly kept clear equally of metal, oxide, and hy- 

 drogen gas. By this contrivance, the power of a battery may be 

 maintained without diminution for any length of time which is de- 

 sired. He has found that an equal quantitv of water may be de- 

 composed in one fourth part of the time by his method, compared 

 with what is required when the plates are left at rest, so that the 

 biittery is converted into the battery of Cruickshanks. Among 



