69(3 GEOLOGY AND MINING INDUSTRY OF LEADVILLE. 



Skimmings — The t'ollowiug is all aualysis of skimmings collected iii the sipliou-tap 

 or lead-pot of one of the furnaces at the Grant smelter ; it is interesting because it con- 

 tains, in concentrated form, the metals which exist only in small quantity iu the bullion, 

 and thus more certainly proves their existence: 



Analysis XXIV. Skimmlngs. 



Lead 97.9172 



Silver 0.8657 



Copper 0.0:i59 



Bismuth 0.0160 



Iron 0.4-249 



Cobalt 0.0087 



Nickel Faint trace 



Zinc 0.0158 



Arsenic 1.187.S 



Antimony P. 1147 



Tin '. 0.0095 



Sulphur 3.3400 



Oxygen and loss (by tUflerence) 1.0ti41 



100.0000 

 Silver, 2b'i.o ounces to the ton. Gold, not a trace. 



Discussion — In the sklmmings, as in the bullion itself, part of the silver and 

 some lead exist in the state of sulphides; in fact, the skimmings are peculiar alloys 

 of metals, sulphides, and oxides. Although it was known from the analyses of the 

 ores by Dr. \V. F. Hillebraud, and of the hematites by the writer, that cobalt was 

 present in the smelting charge, the writer was extremely surprised not to find this 

 metal concentrated in the speiss or in any of the other furnace products, mattes, accre- 

 tions, etc. The preceding analyses show that it is in the skimmings tliat it must be 

 looked for. This curious fact illustrates a most interesting case of separation of nickel 

 from cobalt by the dry way, and by a method liitherto unknown and unsuspected. 

 Nickel, as will be seen, is concentrated iu the speiss, and cobalt accompanies the bullion, 

 from which it can easily be separated by the simple process of skimming. There would 

 seem to be no reason why tliis simple process should not be used in the rcetallurgy of 

 nickel and cobalt; for no cobalt is found either iu speiss or bullion. When the skim- 

 mings are cuitelled, the presence of cobalt is revealed by the formation of blue specks 

 of phos])hate of zinc and cobalt. This phenomenon is so rarely seen that it should 

 not pass unnoticed here. 



The skimmings are covered with a crystalline, yellowish-black scum, from which 

 tliey cannot be separated. When they are broken to pieces, the pieces are crystalline, 

 witli a white metallic luster, similar to lead. These pieces flatten under the hammer, 

 but the fattened portions are very brittle, with a crj-stalline structure and a blackish 

 color, due to small but very distinct crystals of galena. 



