SECONDARY PRECIPITATION OF GOLD 265 
cipitation would, in general, depend on the concentrations of 
permanganate, gold chloride, and manganous salt, and the acidity 
of the solution; a complex relationship which has not as yet been 
worked out. 
V. OTHER INORGANIC SUBSTANCES 
The number of inorganic substances capable of chemically 
precipitating gold, and occurring in ore deposits or mine waters, 
is doubtless rather large, but the more important ones only have 
been discussed. 
Sulphur dioxide is used as a precipitant for gold, and either 
crystalline or colloidal gold may be formed by the action of this 
substance or sulphurous acid on solutions of gold chloride, the 
state of the gold depending upon conditions of temperature, con- 
centration, etc.’ Sulphur dioxide however is comparatively rare 
in mine waters, and probably may be neglected so far as precipi- 
tation of gold in an ore body is concerned. Similarly arsenious 
acid, and doubtless a great number of substance may be disregarded. 
VI. ORGANIC COMPOUNDS 
That a very great number of organic compounds can precipi- 
tate gold is very well known, and the idea that such precipitations 
occur in nature is by no means new. Rickard’s experiments with 
the Rico shale? have been frequently referred to in the literature 
of ore deposits. Practically all organic compounds found in nature 
are reducing agents, and a very great number are strong enough 
to precipitate gold. Formic acid, oxalic acid, acetylene, glucose, 
and a host of others belong to the list. 
Just what compounds are present in a carbonaceous shale, 
and just which of those present cause the precipitation, is at 
present impossible to say, but that many of them can cause pre- 
cipitation seems unquestionable. 
Amorphous carbon is capable of taking gold from gold chloride 
solution by absorption.s This seems to be a physical action 
t See Gmelin-Kraut, op. cit. 
27. A. Rickard, Trans. Am. Inst. Min. Eng., XXVI, 978 (1896). 
3S. Brussow, Zeztschr. Kolloid Chem. Ind., V, 137-38 (1909). 
