1 1 24 A TREATISE ON METAMORPHISM. 



transportation of the compounds resulting- in the tellurides and of the pre- 

 cipitation of the tellurides have not yet been solved, there is little doubt 

 that careful chemical work will solve them. 



In view of all the foregoing facts, the most plausible suggestion which 

 I am able to make as to the development of the tellurides is as follows: 

 The gold is taken into solution by descending waters in the early part of the 

 journey in the form of a chloride, as explained on pages 1089-1091. The 

 tellurium is widely dispersed, possibly to some extent as metallic tellurium, 

 but more largely as a telluride, and is oxidized in the belt of weathering. 

 It there unites with an acid and travels as a soluble salt, perhaps, also, in 

 large part, as telluric chloride. That reactions of this kind take place with 

 reference to the tellurides in the belt of weathering are certain, as shown 

 by the abundant spongy gold at Cripple Creek, pseudomorphous after the 

 various tellurides, showing that such reactions have taken place there on 

 an extensive scale. The auric chlorides and telluric salts, such as telluric 

 chloride, may travel together without reaction, or they may come together 

 in the trunk channels. There they become mingled with reducing com- 

 pounds in solution, or, as has been suggested, come into contact with 

 reducing solids, such as the sulphides. It is believed the tellurium and 

 gold are simultaneously reduced under such conditions that they unite in 

 definite compositions, and thus produce the telluride minerals. 



Hall and Lenher were more successful in the production of telluride of 

 silver. An ammouiacal solution of silver chloride in contact with tellurium 

 at room temperatures resulted in the production of silver telluride according 

 to the following reaction: 



4AgCl+3Te=2Ag„Te+TeCl 4 



When the nitrate of silver was used "a greater range of temperature 

 was possible, and the solution was either boiled continuously or kept at a 

 temperature of about 80° C. for a long time." a The reaction in this case as 

 given by them is: 



4AgN0 3 +3Te=2Ag 2 Te+Te(N0 3 ) 4 



Since, however, it is difficult to understand how metallic tellurium can 

 be carried in solution, there is a possibility that the silver tellurides are 



«Hall, E. D., and Lenher, Victor, Action of tellurium and selenium on gold and silver salts: Jour. 

 Am. Chem. Soc, vol. 24, 1902, p. 922. 



