52 



* No. 9. Copper precipitate thrown down by the immersion of 

 thin scrap iron in the cupreous solutions. (Contains on an 

 average 75 to 80 per cent, of metallic copper.) 



No. 10. Spent liquor, or liquid remaining after complete 

 precipitation of copper from solution. This liquor is run to 

 waste. 



167. Specimens illustrating the wet process of copper 

 extraction. 



1888. Exhibited by McKechnie, Duncan, fy Sons. 



Salt. 



Burnt pyrites. 

 Calcined ore. 

 Copper precipitate. 

 Lead precipitate. 



Silver precipitate. 



Silver residue. 



Purple ore. 



Best select copper (two bars). 



Refined lead. 



168. Specimens illustrating the manufacture of sul- 

 phate of copper. 



1888. Exhibited by McKechnie, Duncan, fy Sons. 



Copper shot. 



Sulphuric acid. 



Sulphate of copper (solution). 



Cupric chloride (solution). 



Sulphate of copper (crystals), ordinary. 



Sulphate of copper (crystals), telegraphic. 



Sulphate of copper, large mass of crystals. 



169. Model of apparatus employed for the manufac- 

 ture of chlorine, by Weldon's process. Scale, ^ in. = 1 ft. 



E. 8. 1889. Made by B. L. F. Potts. 



The leading idea of Weldon's process is the following. We 

 start with a solution of manganous chloride, i.e., ordinary still 

 liquor, after preparing chlorine by the action of HC1 on Mn0 9 . 

 This liquor is deprived of free acid by agitation with calcium 

 carbonate, and to this neutral solution is added milk of lime 

 more than sufficient to precipitate all the manganese as Mn(OH) 2 . 

 The pasty mixture is treated with a strong current of slightly 

 heated air when Mn0 2 is precipitated ; after settling the mud 

 which consists of Mn0 2 and CaO is again used in the chlorine 

 stills as if it were manganese ore. 



The following is a description of the model which illustrates 

 the arrangements for carrying out the above process. 



The three octagonal chambers on the ground, one of which is 

 shown in section, are called " mud stills." There is alongside 

 another smaller oblong still, which is used for treating man- 

 ganese ore only to make up for the loss in recovery. There is a 

 circular well near the mud-stills in which an agitator is worked 

 by the bevel gear above : this is the neutralising well in which 



