270 DR. FARADAY'S EXPERIMENTAL RESEARCHES IN ELECTRICITY. 



acid was used, each zinc plate lost 2- 16 equivalents ; when the charge with the same 

 battery was 200 water, 9 oil of vitriol, and 8 nitric acid, each zinc plate lost 2*26 

 equivalents. 



1142. I need hardly say that no copper is dissolved during the regular action of 

 the voltaic trough. I have found that much ammonia is formed in the cells when 

 nitric acid, either pure or mixed with sulphuric acid, is used. It is produced in part 

 as a secondary result at the cathodes (663.) of the different portions of fluid con- 

 stituting the necessary electrolyte, in the cells. 



1143. Uniformity of the charge. — This is a most important point, as I have already 

 shown experimentally (1042. &c.). Hence one great advantage of Dr. Hare's mecha- 

 nical arrangement of his trough. 



1144. Purity of the zinc. — If pure zinc could be obtained, it would be very advan- 

 tageous in the construction of the voltaic apparatus (998.). Most zincs, when put 

 into dilute sulphuric acid, leave more or less of an insoluble matter upon the surface 

 in the form of a crust, which contains various metals, as copper, lead, zinc, iron, cad- 

 mium, &c., in the metallic state. Such particles, by discharging part of the transfer- 

 able power, render it, as to the whole battery, local ; and so diminish the effect. As 

 an indication connected with the more or less perfect action of the battery, I may 

 mention that no gas ought to rise from the zinc plates. The more gas which is ge- 

 nerated upon these surfaces, the greater is the local action and the less the transfer- 

 able force. The investing crust is also inconvenient, by preventing the displacement 

 and renewal of the charge upon the surface of the zinc. Such zinc as, dissolving in 

 the cleanest manner in a dilute acid, dissolves also the slowest, is the best ; zinc 

 which contains much copper should especially be avoided. I have generally found 

 rolled Liege or Mosselman's zinc the purest ; and to that circumstance attribute in 

 part the advantage of the new battery (1134.). 



1145. Foulness of the zinc plates. — After use, the plates of a battery should be 

 cleaned from the metallic powder upon their surfaces, especially if they are employed 

 to obtain the laws of action of the battery itself. This precaution was always attend- 

 ed to with the porcelain trough batteries in the experiments described (1125., &c.). If 

 a few foul plates are mingled with many clean ones, they make the action in the dif- 

 ferent cells irregular, and the transferable power is accordingly diminished, whilst the 

 local and wasted power is increased. No old charge containing copper should be 

 used to excite a battery. 



1146. New and old plates. — I have found voltaic batteries far more powerful when 

 the plates were new than when they have been used two or three times ; so that a new 

 and a used battery cannot be compared together, or even a battery with itself on the 

 first and after times of use. My trough of twenty pairs of four-inch plates, charged 

 with acid consisting of 200 water, 4^ oil of vitriol, and 4 nitric acid, lost, upon the first 

 time of being used, 2*32 equivalents per plate. When used after the fourth time with 

 the same charge, the loss was from 3*26 to 4*47 equivalents per plate ; the average 



