VOL. LXXXVIII.] PHILOSOPHICAL TRANSACTIONS. 425 



bodies; but before mentioning my ideas on this subject, I shall give an account of 

 some experiments made on the flints, N° 6. These were coated with a yellowish 

 shining substance, which appeared to be pyrites; and as the flints could not have 

 contributed any metallic substance to form this coating, I was enabled by their means 

 to ascertain, whether the copper of the crust, formed on the wire and cuttings, had 

 been furnished by the pieces of copper, or by any thing in the vicinity of the water. 

 1 . I poured nitro-muriatic acid on some of the flints, in a matrass, so as completely 

 to cover them. 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. Prus- 

 siate of pot-ash produced Prussian blue; and the remaining part of the solution, 

 being supersaturated with ammonia, afforded an ochraceous precipitate of iron. 

 The supernatant liquor did not become blue, as when copper 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 solu- 

 tion any sulphur, and scarcely any iron ; it has not therefore been concerned in 

 forming the pyrites ; but it appears that the pyritieal 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. And, if sulphur, thus formed, should 

 meet with silver, copper, or iron, it will combine with them, unless the latter 

 should be previously oxidated. The sulphur has therefore, in the present case, 

 met with iron, in, or approaching, the metallic state, and has formed pyrites; 

 which, while in a minutely divided state, or progressively during formation, has 

 been deposited on bodies, such as the flints, when in contact with the mud. 



But an excess of sulphur appears to be present; for when copper is put into the 

 Mere, the sulphur readily combines with it; and at the same time a small portion 

 of iron appears to unite with the compound of copper and sulphur, possibly by the 

 mere mechanical act of precipitation. The incrustation on the copper wire and 

 cuttings is, in every property, similar to that rare species of copper ore, called by 

 the Germans Kupfer schwartze, (cuprum ochraceum nigrum) ; and I consider it as 

 absolutely the same. In respect to the martial pyrites on the flints, there can be 

 no hesitation ; and as in these 2 instances there were evident proofs of the recent 

 formation of ores in the humid way, I was desirous to ascertain the effect on silver. 

 I therefore wrote to Mr. Wiseman, to request that he would take the trouble to 

 make the experiment: and received from him the following answer, dated Diss, 

 8th Sept. 1798, accompanied by the specimens. 



VOL. XVIII. 3 I 



