84 The Rev. N. J. Callan on a new Voltaic Battery. 



of the solution of nitre, make a most powerful exciting mix- 

 ture for platina, but give comparatively little power to plati- 

 nized lead. I endeavoured to find among the sulphates a 

 substitute for sulphuric acid, but did not succeed. The vol- 

 taic current from a platinized lead battery, excited by two 

 parts of sulphuric acid, three of sulphate of soda, and three 

 of nitrate of potash, is very powerful, but considerably inferior 

 to that which is produced by the concentrated acids. 



On finding that platinized or gilded lead and platinized 

 platina were superior to platina, I saw that the cause of the 

 superiority was that, in the platinized or gilded lead, and in 

 the platinized platina batteries, the acting metals were, not 

 lead or platina and zinc, but gold or platina powder, and 

 zinc; and that the gold or platina powder was more negative 

 compared with zinc than platina is. Hence I inferred, first, 

 that a leaden plate coated with any of those substances which 

 are more negative and cheaper than platina or gold, would 

 act as powerfully as platinized or gilded lead ; and secondly, 

 that any other metal to which the platina or gold powder 

 would adhere might answer as well as lead. I therefore 

 coated, by the galvanic process, leaden plates with antimony, 

 arsenic, chromium, molybdenum and borax. The plates 

 coated with arsenic and molybdenum were much inferior to 

 platina : those that were coated with antimony and borax 

 appeared fully equal to platinized lead, but they soon lost their 

 power. The first plate which I chromed acted as well, and 

 retained its power nearly as long as platinized or gilded lead. 

 I afterwards coated a great number of plates with chromium ; 

 but all of them were far inferior to the first. The power of a 

 leaden plate is greatly increased by being coated with mer- 

 cury, or even with clay boiled in aqua regia, or with any other 

 substance which I tried ; but I have not found any substance 

 to answer as well as the chloride of gold or platina. 



I have compared with platinized lead, the other cheap me- 

 tals coated with gold or platina, or chromium ; and with the 

 exception of cast iron, they were all inferior to it. Platinized 

 or chromed cast iron answers as well as platinized lead ; and 

 without being chromed or platinized, cast iron appears to act 

 as powerfully as platina. The power of a cast iron battery in 

 magnetizing our large electro-magnet, and in driving an elec- 

 tro-magnetic machine, was compared with that of a Grove's 

 battery of the same size. In the two batteries the exciting- 

 mixture was the same. The power of the former appeared to 

 be fully equal to that of the latter. 



From the results of several experiments which I have made 

 on the relative power of platinized silver and platinized lead, 



