Park. — Formation of Zones of Secondanj Enrichment. 97 



in 1869, and of E. Kohler* in 1903, who found that clays and 

 porous substances such as gelatinous silica, carbonaceous and 

 colloidal matter, possess the power of extracting metals from 

 their dilute aqueous solutions. As the subject is one having an 

 important bearing on the concentration of metals in the zone of 

 oxidation, and perhaps also in bed-impregnation and vein-filling, 

 it may be of interest to notice more fully the experiments made 

 by Skey in the New Zealand Government Laboratory in 1869, 

 1871, and 1874. Skey, it sho'uld be noted, was one of the pioneers 

 in this department of research, and it is a tribute to the marvel- 

 lous ability and skill he displayed in his research-work to find 

 his determinations so fully verified by investigators of later 

 date. 



In 1869 he proved experimentally f that finely pulverised mas- 

 sive quartz, rock-crystal, and silica possess the power of absorb- 

 ing or extracting the oxide of iron from its acetate solution. He 

 also found that prepared silica especially manifests this property 

 if ignited at a low temperature ; and, besides, takes oxides of 

 copper and chromium from their acetate solutions. The more 

 *^nely divided the silica the more apparent is the absorption. 



In 1871 SkeyJ found that when a weak ammoniacal solution 

 of copper containing a little caustic potash is poured upon a fi.lter 

 of Swedish paper (cellulose), the licjuid which passes through the 

 paper is quite or nearly colourless, and the filter is found to have 

 retained ail, or nearly all, the copper of such solution. 



In 1874 he showed that clay possesses the property of ab- 

 sorbing and fixing natural petroleum in such a way as to form a 

 substance resembling natural oil-shale, the oil being chemically 

 combined with the clay.§ He does not appear to have tried to 

 ascertain the absorptive power of clay upon solutions of the 

 metals, but his discovery that silica and porous substances, such 

 as cellulose, possess the property of absorbing metals from their 

 solutions has an important bearing upon the chemistry of ore- 

 deposition. 



* E. Kohler, Zeitschrift fiir Praktische (Jeologie, 1903, p. 49 et seq. 



•j- W. Skey, " On the Absorptive Properties of Silica, and its Direct 

 Hydration in Contact with Water," Trans. X.Z. Inst., Vol. ii, p. 151 : Wel- 

 lington, N.Z., 1869. 



J W. Skey, " Absorption of Copper from its Ammoniacal Solution by 

 Cellulose in Presence of Caustic Potash," Trans. X.Z. Inst., Vol. iv, 1871, 

 p. 332. 



§ W. Skey, " Notes on the Formation and Constitution of Tor- 

 banite and similar Minerals," Trans. X.Z. Inst., Vol. vii, 1874, j). 387. 



4— Trans. 



