On the uk of the Dynamic MultipUef. 359 



good as copper. But its liability to oxidation is an objection to its 

 use. Lead answers very well. I have batteries which were made 

 of lead and zinc plates nearly two months since, and have used them 

 often. Their power seems to improve by use. The lead plate be- 

 comes covered with metallic copper on the side towards the zinc. 

 Lead plates excited by sulphate of copper, will answer for com- 

 pound batteries. Mercury answers as well as copper. Bismuth 

 and antimony, also make a good series with zinc. Brass is nearly 

 equivalent to copper. Zinc with zinc makes a tolerable battery, 

 provided one of the plates much exceeds the other in surface. The 

 plate answering for a conductor, should be cut so as to leave narrow 

 parallel strips. Other metals have not been tried. A very active 

 arrangement is made by the nitrate of mercury and suphate of cop- 

 per, separated in a cell by a strip of membrane ; the connexion is 

 made by two strips of copper immersed in each cell. 



In copper or lead batteries, where the salts of copper are used, 

 the zinc plate should be movable, in order to clear it from the co- 

 pious deposit. To effect such an arrangement, and to give the bat- 

 tery at all times the benefit of fresh immersion, I have contrived a 

 revolving plate battery. 



Fig. 4, represents a side view of the revolving plate battery. 

 The zinc plate is raised from the box lined with lead or copper 

 holding the solution of the sulphate. The plate is of thick cast 

 zinc, a foot in diameter : d, is a copper disc attached to the axis of 

 the zinc plate, and when the plate is lowered, turns in a narrow mer- 

 cury cell, C, fixed to the side of the box, and connected by a strip 

 of metal with the mercury thimble, n : r, r, are two deeply grooved, 

 inclined rubbers on each side, to strip and lead off into the bowl 6, . 

 the deposit from the zinc plate. That side of the rubber which 

 presses against the zinc plate, is covered with leather, and the press- 

 ure is regulated by springs. After the zinc wheel has been immersed 

 a minute or two, it is turned over by its crank, which is on the side 

 opposite the copper disc, d. This battery combines the following 

 advantages, viz. the zinc plate and exciting liquid are kept clean, both 

 surfaces are opposed to the copper or lead plate, the conducting plate 

 exceeds the other in surface, the zinc plate will last a great length of 

 time, if properly turned, as only half of it is immersed at once, and 

 above all, if the zinc wheel turn accurately, it may come very near 

 the conducting plate ; whereas in batteries where the zinc plates are 

 permanent, considerable distance must be preserved, on account of 



