164 On Gold Refining ly Chlorine Gas. 



of the melted gold, yet the whole mass is toughened by its action, 

 it seems essential in using chlorine that the gas should pass to 

 the very bottom to effect a complete jrefinage. 



As soon as the operation is nearly over fumes of a darker 

 colour than those observed at the commencement make their 

 appearance, and the end of the refinage is indicated by a peculiar 

 flame or luminous vapour of a brownish-yellow colour (occasioned 

 by the free and now waste chlorine escaping,) which can be seen 

 on removing a small plug which fits into a hole in the lid of the 

 pot. This, however, of itself is not a sufficient indication : the 

 process is not complete until this flame imparts to a piece of 

 white tobacco pipe, or similar substance, when held in it for a 

 moment, a peculiar reddish or brownish-yellow stain. So long as 

 it gives any other colour the refinage is unfinished. 



When these appearances are observed, (usually for gold con- 

 taining about 10 per cent, of silver in about an hour and a half 

 from the introduction of the chlorine), tho gas is shut off, and 

 the pots removed from the fire, the white crucible lifted out of 

 the black one, and, together with its contents, allowed to stand 

 seven minutes, until the gold becomes cool enough to set or 

 solidify. The chloride of silver, which remains liquid much 

 longer is then poured off into iron moulds. The crucible is then 

 inverted on an iron table, when the still red-hot gold falls out in 

 the shape of a cone. This is slightly scraped, and then thrown, 

 hissing, into a concentrated solution of common salt, to free it 

 from any adherent chloride of silver. 



An alloy containing originally 89 per cent, of gold, 10 per 

 cent of silver, and 1 per cent, of base metals, will yield on an 

 average a cake of chloride, weighing, with a little adherent borax, 

 16 ounces for every 100 ounces operated on. 



It is necessary very carefully to dry and heat the moulds into 

 which the chloride of silver is poured, as the slightest moisture 

 causes the latter to be violently dispersed while red hot, to the 

 great risk of the bystanders. "With ordinary care this will never 

 happen, but attention is called to the point, as a very deliquescent 

 chloride of iron is apt to form on the moulds. 



The gold is now fine, and simply requires re-melting into 

 ingots. 



As before stated, it is found that all these operations can 

 readily be performed, and about 2000 ounces refined per day in 

 three common melting furnaces, between 9 a.m. and 2 p.m. 

 98 per cent of the gold originally contained in the alloy operated 

 on are then ready for delivery. 



The other 2 per cent, remain with the chloride of silver, par- 

 tially in the metallic state, and partly in a state of combination 

 with chlorine, and probably silver. 



To free the chloride of silver from this combined gold (that 



