334 — Cutbush on the Voltaic Lamp. 
tion has been completed, and sulphate of irou or of zine | 
formed, as the case may be, the quantity of water will al- : 
ways prevent its crystallization. Hence it is a matter of 
t to have the acid sufficiently diluted. 
n consequence of some defect or imperfection in the 
electrophorus cake, or of its splitting, which sometimes 
happens, I have found it necessary to remelt it, or to make 
a new one, by melting the best yellow rosin, and adding a 
small quantity of Spanish brown. Having melted the rosin, 
it was poured into a shallow dish made of tin plate, and left 
to cool undisturbed, not permitting however any bubbles to 
appear on its surface. 
The electrophorus belonging to my apparatus, when ex- 4 
cited will retain-its effect for many months. I excited it in 
the usual manner, by gently warming it, and rubbing it with 
a foxtail, catskin, or silk handkerchief ; the former of which 
{ found preferable. When thus excited, I have been suc- 
cessful in producing a spark even in the dampest weather. 
It requires, however, that the box, which contains the elec~ 
ra eka should be kept as tight as possible. 
ere is one defect which in fact is inseparable from the 
construction of the cock; namely, that however perfectly 
tight it may be, by frequent use it becomes loose, and suf- ’ 
rs the gas to escape gradually. To prevent this, and to 
make the cock as tight as possible, I have used various ex- 
pedients, but the following I find preferable : mix a portion 
of tallow with finely pulverized plumbago, so as to render 
the whole as stiff as possible; then apply it to the cock. 
From observation I have found, that hydrogen gas pre- 
pared by using zinc, makes its escape more readily than 
that prepared with iron filings; for, under the same cit- 
cumstances, the former I have discovered to disappeat 
sometimes in twenty-four hours, while the latter has re- 
mained more than a week. In consequence of this cir- 
cumstance, I employ iron filings in preference to those ol 
zinc, although we know that. the gas from the latter 1s 
much purer and consequently lighter, whereas that procur- 
ed by using iron filings contains more or less carbon, and J# 
consequently impure. 
: he lamp answers every purpose, and.I find it more eer 
_ tain for lighting a candle than any other contrivance, and 
therefore preferable to any which L have tried ; having used 
