473 



*' When a zinc plate is put into the porous cell, and a learien 

 one coated with gold powder is placed on each side of it, in 

 the exterior cell, the effect of the voltaic current on the elec- 

 tro-magnet appears to be greater than that which is produced 

 by a single platina and double zinc. The voltaic current from 

 a leaden or platina battery is about fifteen times as great as 

 that of a Wollaston battery of the same size. In all the ex- 

 periments which I have described, the lead and platina plates 

 were about two inches by six. The lead and platina were ex- 

 cited by a mixture of concentrated nitric and sulphuric acid, 

 and the zinc by diluted sulphuric acid. The acids employed 

 in some of the experiments had been previously used. 



" When a platinized or gilded leaden plate is taken out of 

 the cell, and afterwards immersed in the acid, it does not pro- 

 duce its full effect until it has acted for about a minute. The 

 lead plate, after being used for a long time, requires to be again 

 coated with platina or gold powder. 



" Seeing that the concentrated acids, by dissolving a small 

 quantity of the lead, gradually removed the powder of gold or 

 of platina, and that the nitric acid was very expensive, I en- 

 deavoured to find a cheap substitute for it, which would not 

 act on the lead. The first that occurred to me was common 

 nitre. I dissolved about the eighth of an ounce of it in sul- 

 phuric acid, which I diluted with about an equal bulk of water. 

 I poured the mixture into a porous cell of a Grove's battery ; 

 after putting into the cell a platina plate, I sent the current 

 from the battery through the helix of the large electro-magnet. 

 The magnetic power given to the electro-magnet appeared to 

 be about equal to that which the same battery produced when 

 the platina was excited by a mixture of equal parts of concen- 

 trated nitric and sulphuric acid. The platina plate was taken 

 out of the cell, and a platinized leaden one of the same size put 

 in its stead. The magnetic power given to the electro-magnet 

 by this battery was greater than that which was given to it by 

 the platina battery when the platina was excited either by the 



