of some recent discovery has happened to have been fortunate. 

 Thus the opinions entertained by Dr. Hutton, and by Dr. Playfair, 

 respecting the formation of pyrites, and the precipitation of pure 

 metallic substances, I trust, will be no longer tenable, when com- 

 pared with the ingenious experiments and observations of still more 

 recent date. 



The union of metals with sulphur, without the aid of fire, is dis- 

 coverable in many instances. A familiar instance is the violet tar- 

 nish which attaches itself to polished silver ; and which, being al- 

 lowed to accumulate, will form a crust which may be separated by 

 bending the silver, or striking it with a hammer. This pellicle has 

 been examined by Mr. Proust, who asserts it to be a sulphuret of 

 silver. The common sympathetic inks, formed of metallic solu- 

 tions, the writing of which, before invisible, is immediately dark* 

 ened by sulphuretted hydrogen, is also an instance of the union of 

 metal and sulphur, in the moist way. So also is that kind of shining 

 pellicle which forms on wainscots, painted with white lead, and which 

 have been exposed to the influence of sulphuretted hydrogen. 



An observation of Dr. Thompson, in his excellent System of Che- 

 mistry, affords us very decided evidence on the question which we 

 are about to discuss ; which is, Whether the natural combinations 

 of sulphur with the metals are effected, by means of fusion by heat, 

 or by solution by water ? Speaking of a combination of sulphur 

 with copper, he says, " This compound may be formed by mixing 

 copper filings and sulphur, and making them into a paste with 

 water, or even by mixing them together, without any water, and 

 allowing them to remain a sufficient time exposed to the air, as I 

 have ascertained by experiment*/' This point is also illustrated 

 by the well-known artificial earthquake of Lemery, in which a 

 mixture of equal parts of iron filings and of sulphur, being 



* A System of Chemistry, by Thomas Thompson, M. D. vol. i. p. 117. 



