32 The ratio dud Oazo Process. 



silver is formed at all, as none was found in a torta left for four 

 months on the patio, during which time he constantly examined 

 the piles. Mr. Boweringsays, in support of this theory, that when 

 only two of the reagents, sulphide of silver, chloride of so- 

 dium, or sulphate of copper are mixed together, no effect is 

 produced, and that when three are mixed in a small vessel, the 

 mercury combined with just half of the chlorine in the chloride 

 of copper, and formed sub-chlorides of both metals. As the 

 chloride of copper has the property of absorbing oxygen, he 

 concludes that it is the principal reagent. According to this 

 theory the mercury acting on the chloride of copper makes sub- 

 chlorides of both. The chloride of copper absorbs oxygen, which 

 acts on the sulphide of silver and makes sulphuric acid, and 

 leaves the silver in a metallic state to be absorbed by the mer- 

 cury. The sulphuric acid set free acts on the chloride of so- 

 dium, and forms sulphate of soda. Chlorine is given off, combines 

 with the sub-chloride to make a chloride of copper, which is again 

 decomposed, and so on. In this case the sub-chloride acts just 

 as nitric acid does in the manufacture of sulphuric acid. The ac- 

 tion of the chemicals in the pile is especially slow if sulphide of 

 silver is present, in which case the loss of mercury is also very 

 large. When the whole of the silver is in the state of sulphide, 

 a large part of it, which may sometimes be as high as 40 per 

 cent., is lost. The mercury transforms the chloride of copper into 

 sub chloride, which, like chloride of silver, is soluble in an ex- 

 cess of salt. The sub chloride in this state acts more energeti- 

 cally on the sulphide of silver than the chloride. A sulphide 

 of copper is formed, while the silver is precipitated, and the 

 chloride of copper formed again by giving up half the copper, 

 which becomes a sulphide. This advantage is gained only at the 

 expense of a very large quantity of mercury ; and in order to 

 prevent this loss, experiments were made of not introducing the 

 mercury until much later in the process, but this did not succeed, 

 as the extraction of the silver was not so well done. 



The next day after the first treading, another one is made. The 

 torta is then allowed to rest for a day, with occasional spadings, 

 quite as much to make the mixture as to ascertain whether the ore 

 is not getting too stiff from evaporation. As the heat of the sun is 

 depended on for a part of the chemical action, water, when added, 



