SOLUTION OF THE METALS. 1075 



arsenic, and antimony. All of these compounds are readily, or somewhat 

 readily, soluble, with the exception of lead sulphate, which is soluble only 

 to the extent of one part in 31,500 parts of water at 15° C. a But even this 

 degree of solubility is entirely adequate to account for the transportation of 

 the lead as a sulphate. 



While the effect of the oxygen is to transform the sulphides to sul- 

 phates, it is not supposed that the metals necessarily travel as such salts. 

 The well-known principles of physical chemistry make it certain that each 

 of the metals present in solution is combined in part with each of the acids. 

 For instance, if silver sulphide be oxidized to sulphate, and sodium car- 

 bonate be present in the underground solutions, as is sure to be the case, 

 then a part of the silver will be transformed to silver carbonate and the 

 sodium will travel in part as sodium sulphate. In this connection the point 

 is that the sulphides get transformed through the agency of oxygen to 

 compounds which are much more readilv soluble. 



It is further to be remembered that in the upper jaart of the course of 

 descending water, where oxygen is abundant, ic salts are produced. Of 

 these the sulphates are most abundant, but with them are chlorides also. 

 Of these ic salts, feme sulphate and chloride are very prevalent. 



In salts of this class metallic gold and silver are dissolved. The solution 

 is controlled by the law of mass action and by the temperature. The 

 greater the amount of the salts present, and the higher the temperature, 

 with a given amount of salts, the more gold and silver may be dissolved. 

 Thus, descending solutions are those in which ic salts are abundantly 

 formed and in which the temperature is increasing. Both the abundance 

 and the increasing temperature are favorable to the solution of gold and 

 silver. 



Therefore we conclude that the solutions which perform the first work in 

 the genesis of ore deposits, the dissolving of the metals, are descending. 



TRANSPORTATION OF THE METALS. 



Superimposed upon the downward movement of the waters is a lateral 

 one which, combined with the vertical movement, carries water sooner or 

 later to the trunk channels. The amount of water taking part in the lateral 

 movement is greatest near the surface of ground water, and from that 



a Comey, A. M., Dictionary of chemical solubilities: London, 1896. 



