$2 InviJIigattift of the EfftEls prtdudd upmt 



in producing the effeas which he has obferved, and the quantity was too fmall to be fub- 

 jeded to a regular analyfis; I noted, however, what follows : 



I. It has a very ftrong hepatic flavour and fmell. 2. A plate of polifhed filver, put into it, 

 became black in a few hours. 3. It became faintly bluifh with prufliate of potafli, after 

 ftanding five or fix hours. 4. Tin£lure of galls produced a faint purple cloud. 5. Solu- 

 tion of acetite of lead aflForded a brown precipitate, 6. Nitrate of filver produced the fame. 



7. Potafli, and ammoniac caufed a precipitate ; but that of the former was the moft copious, 



8, Oxalic acid produced a precipitate. 9. Muriate of bvirytes had alfo a flight eiFefl:, 



The water, No. 5, cannot, therefore, be confidered as a chalybeate (the quantity of iron 

 contained in it being fcarcely perceptible) ; but it appears to be a water containing feme 

 liepatic gas, together with fubftances fimilar to thofe contained in No, i. From the above 

 experiments it is evident, that the water, No, i, does not contain any of the component parts 

 of the cruft formed on the copper- wire and cuttings, although it is certain that the incruftatioii 

 took place during the immerfion of thofe bodies ; but, before I mention my ideas on this fub- 

 jcft, I fhall give an account of fome experiments made on the flints, No. 6. Thefe were 

 coated with yellowifh fhining fubftance, which appeared to me to be pyrites ; and, as the 

 flints could not have contributed any metallic fubflance to form this bating, I was enabled 

 by their means to afcertain, whether the copper of the cruft, formed on the wire and cuttings, 

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



1. I poured nitro-ciuriatic acid on fome of the flints, in a matrafs, fo as completely to cover 

 them. The coating was rapidly diflblved, with much efFervefcence ; and, when the flints 

 appeared perfeftly uncoated, and in their ufual ftate, I decanted the liquor. 



2. A yellow matter fubfided, which proved to be fulphur. 



3. Prufliate of pota(h produced Pruffian blue } and the remaining part of the folution, 

 "being fuperfaturated with ammoniac, afforded an ochraceous preci[)itate of iron. The fuper- 

 natant liquor did not become blue, as when copper is prefent, nor was the fmalleft trace of it 

 aiForded by evaporation. 



Martial pyrites is, therefore, the only fubftance depofited on bodies immerfed in the water 

 of Difs Mere ; and the copper of the cruft, formed on the wire and cuttings, was furniflied 

 ty thofe bodies. 



It is proved by the analyfis, that the water of Difs Mere does not hold, in folution, any 

 fulphur, and fcarcely 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. Wifeman fays in his letter, that " the Mere has received the filt of the ftreet for 

 ages," Now it is a well-known fail, that fulphur is continually formed, or rather liberated, 

 from putrefying animal and vegetable matter, in common -fewers, public ditches, houfes of 

 office, &c. &c. ; and this moft probably has been the cafe at Difs, Moreover, if fulphur 

 thus formed fhould meet with filver, copper, or iron, it will combine with them, unlefs the 

 latter fhould be previouily oxydatcd. The fulphur has, therefore, in the prefent cafe, met 

 with iron, in, or approaching, the metallic ftate, and has formed pyrites ; which (whilft in 



a minutely 



