ON THE rOEMATlOIT OF MOSS GOLD AND SILYEE. 129 



perature-^tliat between the melting points of tin and zinc 

 (770° E.) appeared to be the most favourable. At a higher 

 temperature the whole surface of the silver sulphide becomes 

 covered equally with a coat of metallic silver. 



The extrusion of the silver crystals cannot well be caused by 

 pressure from without inward, for neither the silver nor the 

 •silver sulphide undergo fusion or even softening ; neither can 

 the production of the filaments be due to the simple and ordinary 

 process of reduction by the removal of the sulphur as sulphur- 

 ous acid gas, otherwise the whole surface of the mass of heated 

 and more or less roasted sulphide should be covered with a coat 

 of reduced metallic silver, just as when the sulphide is reduced in 

 a current of hydrogen gas. But such is not the case ; the extruded 

 wires and filaments appear to be rooted in the sulphide, as if 

 they pushed their way out from within, and they usually project 

 out at nearly right angles to the surface of the apparently 

 unchanged dark lead-coloured silver sulphide, just as l)r. Percy 

 describes the formation of silver filaments, from the same com- 

 pound under the reducing agency of a current of hydrogen gas. 



It may be that their formation may have been determined by 

 the presence of nuclei of some sort, just as in the case of various 

 saline solutions. 



On even the most searching examination I cannot detect any 

 difierence between the filamentous silver thus artificially formed 

 and specimens of similar native silver. 



Since making my experiments, I find that De la Beche says, 

 in his " Greological Observer," p. 768 : — 



" Artificial sulphuret of silver was found to be readily decom- 

 posed by steam, and more easily so at a moderate heat. At a 

 temperature under the melting point of zinc this was soon 

 effected, and the silver efiloresced in such forms as to induce Mr. 

 Gustav Bischofi' to regard the moss-like and filamentous occur- 

 rence of native silver in veins as very probably the result of the 

 decomposition of sulphurets." 



Moss Copper. 



It is a well known fact that metallic copper occurs diffused 

 through certain kinds of copper regulus, in the form of minute 

 angular particles, which do not show the least trace of having 

 undergone fusion ; all the edges of these particles are sharp and 

 not in the least rounded, and where cavities occur the metallic 

 copper may be seen protruding into them in the form of minute 

 points and hair-like threads or filaments. 



Dr. Percy, in speaking of moss copper says* : — " In copper 

 works this term is commonly used to designate those accumula- 



* Percy's " Metallurgy," vol. i., p. 359. 



