473 
** When a zinc plate is put into the porous cell, and aleaden 
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 zine. 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 zine 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- 
deayoured 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- 
phurie 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, anda 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 
