577 
the Water of the Mere of Diss . 
The coating was rapidly dissolved, with much effervescence ; 
and, when the flints appeared perfectly uncoated, and in their 
usual state, I decanted the liquor. 
2. A yellow matter subsided, which proved to be sulphur. 
3. Prussiate of potash produced Prussian blue ; and the 
remaining part of the solution, being supersaturated with am- 
moniac, afforded an ochraceous precipitate of iron. 
The supernatant liquor did not become blue, as when cop- 
per is present, nor was the smallest trace of it afforded by 
evaporation. 
Martial pyrites is, therefore, the only substance deposited on 
bodies immersed in the water of Diss Mere ; and the copper of 
the crust, formed on the wire and cuttings, was furnished by 
those bodies. 
It is proved by the analysis, that the water of Diss Mere does 
not hold in solution any sulphur, and scarcely any iron ; it has 
not, therefore, been concerned in forming the pyrites ; but it 
appears to me, that the pyritical matter is formed in the mud 
and filth of the Mere; for Mr. Wiseman says in his letter, that 
“ the Mere has received the silt of the streets for ages." Now 
it is a well known fact, that sulphur is continually formed, or 
rather liberated, from putrefying animal and vegetable matter, 
in common sewers, public ditches, houses of office, &c. &c . ; 
and this most probably has been the case at Diss. Moreover, 
if sulphur, thus formed, should meet with silver, copper, or 
iron, it will combine with them, unless the latter should be pre- 
viously oxidated. 
The sulphur has therefore, in the present case, met with 
iron, iii, or approaching, the metallic state, and has formed py- 
rites; which (whilst in a minutely divided state, or progres- 
MDCCXCVIII. 4 E 
