the Water of the Mere of Diss. 573 
My first experiments were made on the incrustation of the 
copper wire, mentioned in Mr. Wiseman's first letter. 
This incrustation was easily detached from the wire, and, 
being reduced to powder, was digested with nitro-muriatic acid, 
in a gentle heat : a green solution was formed, and there re- 
mained a residuum, of a pale yellow, which proved to be sulphur. 
The solution being diluted with two parts of distilled water, 
was supersaturated with pure ammoniac, by which, a few brown 
flocculi of iron were precipitated. The supernatant liquor was 
blue ; and, being evaporated, and redissolved by sulphuric acid, 
the whole was precipitated by a plate of polished iron, in the 
state of metallic copper. The component parts of this coating 
were therefore copper, and a very small portion of iron com- 
bined with sulphur. 
I could not extend these experiments, as the whole quantity 
of the coating that I was able to collect, amounted only to 
three grains and an half.* 
The next experiments were made on the black crust of 
No. 2, 3, and 4. 
This I found to be exactly the same as that formed on the 
copper wire ; viz. it consisted of copper combined with sulphur, 
and a very small portion of iron. 
The copper wiie, when the coating was removed, was perfectly flexible, and the 
surface did not appear unequal or corroded : this is commonly the case under such, cir- 
cumstances ; for, when sulphur has combined superficially with a metal, the compound 
is observed to separate easily, so as to leave the metal underneath not injured in quality, 
and very little, if at all, affected in appearance. Those who diminish silver coin, make 
use of the following method. 
They expose the coin to the fumes of burning sulphur, by which a black crust of 
sulphurated silver is soon formed, which, by a slight but quick blow, comes off like a 
scale, leaving the coin so little affected, that the operation may sometimes be repeated 
twice or thrice, without much hazard of detection, if the coin has a bold impression. 
