426 PHILOSOPHICAL TRANSACTIONS. [ANNO 1 798. 



" Sir. — Immediately on the receipt of your letter, (27th July) I laid some silver 

 plate, and silver wire, into the Mere; the whole weighed 235.6 gr. I took it out 

 on Thursday last, (Sept. 6th) and, after cleaning it carefully from mud and weeds, 

 I find it weighs 242.8 gr.; an increase of 7.2 gr. The silver plate you will find 

 much tarnished, in some parts almost black; the wire is in many places fairly in- 

 crusted, which crust on the pressure of the fingers, comes off in thin scales. The 

 whole appearance of the silver strongly indicates the presence of sulphur, which I 

 have no doubt abounds in every part of the Mere. The peculiar smell of the mud 

 gives reason to suppose, that a great deal of hepatic air is produced; which probably 

 uniting with the iron held in solution in the water of the Mere, may account for 

 the martial pyrites found on the flints. By what affinity the copper wire, laid in 

 this water, is attacked, I am not chemist enough to determine. I have begun a 

 set of experiments, with the view of producing the same effects on copper wire by 

 artificial means; but whether I shall succeed, I am not able at present to say. 



Benj. Wiseman." 



p. s. — By experiments I have lately made, I find hepatic gas precipitates carbonate 

 of iron in the form of a black flocculent matter: 71 parts of which are iron, and 

 29 sulphur. 



The silver plate I found, as Mr. Wiseman has mentioned, much tarnished, and 

 in many places almost black, but I could not detach any part of it. I succeeded 

 better with the wire, and collected a small portion of a black scaly substance, which, 

 as far as the smallness of the quantity would allow it to be ascertained, was sul- 

 phuret of silver; and was similar, in every respect, to the sulphurated or vitreous 

 ore of silver, called by the Germans glasertz. This effect on the silver was to be 

 expected; and I recollect to have read, not many months ago, in one of the foreign 

 journals, that Mr. Proust had examined an incrustation, of a dark grey colour, 

 formed in the course of a very long time, on some silver images, in a church at, 

 I believe, Seville. This incrustation he found to be a compound of silver with 

 sulphur, or, in other words, vitreous silver ore. The same principle is the cause 

 of the tarnish which silver plate contracts with so much ease, particularly in great 

 cities; for this tarnish is principally a commencement of mineralization on the sur- 

 face, produced by the sulphureous and hepatic vapours dispersed throughout the 

 atmosphere, in such places. 



To Mr. Wiseman's observations we are much indebted, as they make known the 

 recent and daily formation of martial pyrites, and other ores, under certain circum- 

 stances. It is not to be supposed that such effects are local, or peculiar to Diss 

 Mere; on the contrary, there is reason to believe that similar effects, on a larger 

 scale, have been, and are now, daily produced in many places. The pyrites in 

 coal mines have probably in great measure thus originated. The pyritical wood also 

 may thus have been produced; and by the subsequent loss of sulphur, and oxida- 

 tion of the iron, this pyritical wood appears to have formed the wood-like iron ore 

 which is found in many parts, and particularly in the mines on the river Jenisei, 



