6 
Davis,] 102 [April 6, 
On the Conversion of Chlorine into Hydrochloric Acid, as observed in the 
Deposition of Gold from tts Solutions by Charcoal. By Wm. Morris 
Davis. 
(Read before the American Philosophical Society, April 6, 1883.) 
The simple fact of such conversion, while of interest in a chemical point 
of view, would not justify me in occupying the time of this meeting in dis- 
cussing it. 
But in its technical application to the cheap and effective deposition of 
gold from its solution, both from the novelty and usefulness of the method 
it is deemed worthy of your attention. 
Preliminary to the description of the process, and necessary to an appre- 
ciation of its value in a technical sense, the following facts have an im- 
portant bearing. 
It has been estimated that only about one-tenth of the gold of our coun- 
try exists in an uncombined state (as free milling ores), or as dust and 
grains of gold in river sands, or placer washings; such gold is largely 
obtained by amalgamation processes. 
The remaining nine-tenths is found in veins of the older geologic period, 
and is held in combination by sulphides, arsenides and tellurides ; to these 
ores the process of amalgamation with mercury has been found inapplica- 
ble ; hence they are generally known as refractory ores. 
Two methods have been adopted for working these refractory ores, viz.: 
Smelting or fusion with lead, and chlorination ; that is by first reducing the 
combined sulphides, &c., to oxides, and then dissolving the gold by means 
of chlorine. 
The process of smelting is applicable to refractory ores only, when they 
varry a high value in gold, because of the high cost attending the method. 
Crooks and Roéhrig’s ‘‘ Metallurgy’’ teaches that ‘‘ores containing combined 
gold to the amount at $20 per ton cannot be profitably fused with lead; 
even could they be raised without mining cost.’’ Asa rule in this coun- 
try this process is not applied on ores below the value of $40 per ton. 
By chlorination, ores carrying $20 per ton, can be profitably worked, 
mining costs included. 
Without entering into the question of chlorination, it may be remarked 
that various methods have been devised whereby the solvent powers of 
chlorine have been applied to the extraction of gold from such ores. The 
process is an old one, is one which has been long in use, and the excel- 
lence of the method is admitted; it has been found that the solvent power 
of a chlorine solution is much increased by operating with the gas under a 
pressure equal to two or more atmospheres. 
By such proceeding it is evident that the chlorine solution employed in 
the chlorinating apparatus will be highly saturated with the gas; it was 
with such supercharged solutions that the following experiments with car- 
bon were conducted. It is taught that water at ordinary temperatures will! 
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