162 On Gold Refining ly Chlorine Gas. 



small quartz pebbles, down nearly to the bottom of which the 

 pressure tube should extend ; on this layer should be placed 

 from seventy to a hundred pounds weight of binoxide of manga- 

 nese, in grains of about one-quarter inch cube, sifted from 

 powder. This quantity will he sufficient to effect many refining 

 operations, and will obviate the necessity of repeated dismantling 

 of the apparatus. 



Each generator should be suspended to about half its height in 

 a galvanized iron water bath. 



The chlorine gas is produced, when required, by pouring 

 common hydrochloric acid (sp. gr. 1T5) down the safety-tube; 

 the apparatus being warmed, by means of gas-burners beneath 

 the water baths. The gas is conveyed from the generators by 

 means of a leaden pipe fitted with branches to supply the several 

 furnaces ; all intermediate connections being formed by means 

 of vulcanized indiarubber tubing, which, if screened from the 

 direct radiation from the fire, stands the heat well, even imme- 

 diately over the furnace. All joints between the various pipes 

 and indiarubber tubes are easily secured, and rendered perfectly 

 gas-tight, with a cement consisting of a thin solution of india- 

 rubber in chloroform. 



Screw compression clamps on the indiarubber tubes give the 

 means of regulating the supply of gas as required, and enable 

 the operator to shut it off entirely as soon as the refining is over. 

 The chlorine then, having uo means of escape, accumulates in the 

 generator, and soon forces all the acid up the safety-tube into a 

 vessel placed above to receive it, and, the acid no longer acting 

 on the oxide of manganese, the supply of gas of course ceases. 



These generators are very convenient and manageable, and it 

 is questionable whether a gas-holder for the chlorine (even if the 

 practical difficulties in its use could be overcome) would be at all 

 preferable. Two such generators as are here described, and 

 three ordinary gold-melting furnaces have been found capable of 

 refining daily about 2000 ounces of gold, containing about 10 per 

 cent, of silver, between 9 a.m. and 2 p.m. 



Very many thousand ounces — (upwards of 200,000 ounces) — 

 have now been refined by this process, and the mode of operation 

 which has in practice been found the most advantageous has 

 been as follows : — 



The French crucibles (say size 17 or 18), duly prepared with 

 borax, having been placed in the cold furnace, and slowly and 

 carefully heated to dull redness, the gold (from 600 to 700 ounces 

 to each crucible) is introduced, and the fire urged until the metal 

 is melted (the necessary generation of chlorine having meantime 

 been commenced by the introduction of a little hydrochloric acid 

 poured down the safety tube into the generators). 



In order to fit the pots, and avoid the risk of splitting them by 



