176 ANNUAL OF SCIENTIFIC DISCOVERY. 



phurets, and then remark, " We have extended our investigations to 

 other metallic minerals, and can now assert that nearly all of them con- 

 tain silver, even when they do not come from strata from which this min- 

 eral is extracted ; for of over two hundred substances examined, in only 

 a twentieth part of the trials have we failed to detect silver." The in- 

 vestigation has been pursued with extraordinary care, among other 

 precautions, the purity of the reagents used being carefully determined. 

 In some experiments made upon the roasting of different sulphurets, it 

 was found that the silver contained in the blendes often undergoes a 

 loss, by sublimation, of more than half. It is found that, notwith- 

 standing all the precaution taken, a considerable portion of the silver 

 is always lost by clinging to the vessel, so that it cannot be removed. 

 Silver is unequally diffused in the different metallic substances ; thus 

 the oxides and the saline combinations always contain less than the 

 sulphurets, and among these latter those having a base of iron are gen- 

 erally less rich in silver than those having a base of lead, copper, or 

 zinc. The general diffusion of silver in the mineral kingdom induces 

 the belief that other metals may be equally diffused, and on examina- 

 tion of twelve specimens of galena, there were found, besides silver, 

 very perceptible quantities of iron, copper, and zinc. 



From various experiments upon the condition under which silver is 

 associated in small quantities with different metallic minerals, the au- 

 thors conclude that "silver is not found in the same form, in all the 

 sulphurets containing small quantities of it, but that it seems most 

 often to be combined as a sulphuret with the substance which it accom- 

 panies." It has also been demonstrated that the metallic sulphurets 

 cannot contain silver in the form of chloride and bromide, and some re- 

 markable reactions have been observed between the chlorides and the 

 sulphurets. The sulphurets of zinc, cadmium, lead, &c., react upon 

 the chloride of silver by double decomposition ; those possessing many 

 particles of sulphur, which they can abandon, such as the bisulphuret 

 of tin, undergo a partial reduction and are changed into protosulphu- 

 rets ; and those not saturated with sulphur and capable of absorbing it 

 partly reduce the chloride of silver and also act upon it by double de- 

 composition. The power of the sulphurets of decomposing the chlo- 

 ride of silver is more marked in those which act by reduction than in 

 those that produce a double decomposition ; this power appears to have 

 some relation to the electro-chemical state of the metals. The bromide 

 of silver exhibits the same phenomena of decomposition as the chloride, 

 and all these facts appear to depend upon a general law of the reaction 

 of the sulphurets upon the chlorides, and the insoluble upon the soluble 

 salts. These reactions take place in the dry as well as in the humid 

 way ; thus galena decomposes fused chloride of silver. 



In spite of the attention which has been paid to the amalgamation 

 of silver ores, there yet remain many obscure points, upon some of 

 which the authors think their experiments throw some light. The 

 matrix which accompanies the ores plays an important part ; the clayey 

 or argillaceous gangues are the worst, and the quartzose, or, in general, 

 those which have the least tendency to make a paste with water, are 

 the best. The proper quantity of water to be added is just sufficient to 



