Chemistry. 181 
been much relied on for the discovery of arsenic, prepared it in 
the usual way with sulphate of copper and subcarbonate of 
potash. In one experiment a decided precipitate was produced 
from a stfmgeTj and in another a scarcely perceptible one from 
a weaker arsenical solution. Coifee was then added to the so- 
lution of copper, and of carbonate of potash, but without ar« 
senic, and the effect resembled that of the stronger arsenical 
solution, more than this last was resembled by that of the weak- 
er. But what was still more important. Dr Pester found, that 
in the production of Scheele’s green by arsenic, sulphate of 
copper and carbonate of potash, — chromate o/* potash might 
be substituted for the arsenic, and that it produced a precipi- 
tate not to be distinguished by the eye from Scheele’s Green. 
He ascertained also, that even Mr Hume’s celebrated test, 
nitrate of silver, (as modified in its application by Dr Marcet,) 
gave with chromate of potash a yellow precipitate, which, when 
placed side by side with one produced by arsenic, could not be 
distinguished by their colour and appearance. — American Jour- 
nal ofSciencCy Vol. III. No. 2. p. 354. 
14. Camphor.' — In the last Number of the Philosophical 
Journal, you did me the honour to insert some experiments of 
mine on the Solubility of Phosphorus in Sulphuret of Carbon. 
Permit me now to add, that if a drop of the sulphuret is 
brought in contact with a chip of camphor while moving on 
water, the rotatory motion is instantly checked, and a film of 
camphor diffuses round the spot to some distance. I have 
sometimes observed, when a small portion of floating sulphuret 
of carbon is touched by a minute fragment of camphor, that it 
glances off with extreme rapidity, and is speedily lost in a rota- 
tory circle. If the camphor, when dropped on the sulphuret of 
carbon, be too large, both fall together to the bottom of the 
vessel. Here the camphor is mantled and dissolved by the sul- 
phuret, and the instant the liquid spherule is raised to the sur- 
face of the water, it darts a film of camphor around it, and dis- 
covers uneven ridges throughout.”— J. Murray. 
15. Chemical examination of a Liquid from the Crater 
of Vesuvius, — During my sojourn at Naples, I scaled Ves- 
uvius at the period of a slight eruption, and passing a 
stream of running lava in the crater, got with considerable 
