1102 A TREATISE ON METAMORPHISM. 



These observations of Pumpelly convinced me some years ago that 

 the copper was reduced by the ferrous compounds. These conclusions 

 have been later confirmed by experimental work. Biddle, in a thick-walled 

 flask, reduced both cupric and cuprous chlorides by ferrous chloride in a 

 saturated solution of potassium bicarbonate." More recently Stokes, by 

 heating an acidified solution of cupric sulphate and ferrous sulphate in a 

 closed tube, has produced metallic copper at the cold end of the tube and 

 pure hematite at the hot end of the tube. The reactions involved are as 

 follows: b 



2CuS0 4 +2FeS0 4 £Cu,S0 4 + Fe, ( S0 4 ) 3 



The Cu 2 S0 4 is decomposed on cooling to Cu and CuS0 4 , while Fe 2 

 (S0 4 ) 3 f decomposes on heating, thus: 



Fe 2 (S0 4 ) 3 +3H 2 0=Fe,0 3 +3H 2 S0 4 



Stokes further was able to reduce cupric sulphate to metallic copper 

 by heating with hornblende in a closed tube to a temperature of 200° C. 

 The reduction of the copper he attributes to the ferrous iron silicate of the 

 hornblende. Thus experimental work completely confirms the conclusion 

 that under natural conditions copper may be reduced from its salts by 

 ferrous compounds, and that the metallic copper of the Lake Superior 

 region was probably reduced both by ferrous solutions and by the ferrous 

 iron of the solid compounds. 



In the reactions written above it is supposed that where the copper 

 salts are reduced by ferrous salts, fen-ic sulphate or hematite is produced. 

 However, this is not necessary, nor where the ferrous salts are in excess is 

 it believed to be probable that these are the common reactions. The 

 natural reaction under such circumstances would be to produce magnetite, 

 a compound not oxidized to the extent of ferric salts. The reaction may 

 be represented as follows: 



CuS0 4 +3FeSO i +4H 2 0=Cu+Fe 3 4 +4H 2 S0 4 



By this reaction three molecules of the ferrous salts are required to 

 produce one molecule of metallic copper, whereas if ferric salts be pro- 

 duced only two molecules of ferrous compound are needed. It is needless 



"Biddle, H. C, The deposition of copper by solutions of ferrous salts: Jour. Geol., vol. 9, 1901, 

 pp. 430-136. 



6 Stokes, manuscript. 



