On Gold Refining ly Chlorine Gas. ' 163 



the wedging of the ingots at their contracted bottom, the gold 

 for refinage is cast in moulds of a peculiar form. Two inches 

 from one end, the sides and bottom of the iron ingot moulds 

 converge so as to produce a slipper-shaped ingot, two of which 

 placed face to face fit conveniently into the pot. 



As soon as the gold is melted, from two or three ounces of 

 borax in a state of fusion are poured upon its surface. If the 

 borax is added sooner it acts too much on the lower part of the 

 pot, and if thrown in cold is apt to chill the gold. The clay pipe 

 which is to convey the chlorine to the bottom of the melted gold 

 is now introduced. (It is necessary to carefully heat the lower 

 portion of this pipe for some ten minutes before introducing it 

 into the molten gold, or it is apt to split.) At the moment of 

 its entering the melted gold, the screw compression clamp is 

 slightly lossened, so as to allow a small quantity of gas to pass 

 through it, and thus prevent any metal rising and setting in the 

 pipe, which is then gradually lowered to the bottom of the 

 molten gold, where it is kept by means of a few small weights 

 attached to the top. The compression tap is now quite relaxed, 

 and the gas is heard bubbling up through the melted metal, 

 which it does quietly and without projection of globules from the 

 pot. 



Sufficient hydrochloric acid must be added to the generators 

 from time to time to keep up a rapid evolution of chlorine. A 

 rough general rule is to allow 1 imperial quart of acid of 1*15 sp. 

 gr. to every 10 ounces of silver in the alloy operated on. 



The column of liquid in the safety tube, acting, as it does, like 

 a barometer, affords a ready means of knowing the pressure in 

 the generator, and of judging of the rate of production of the 

 gas, as well as at once showing by its fall if anything irregular 

 has occurred, such as a leak or a crack of the chlorine pipe or 

 pot. From sixteen to eighteen inches in the safety tube corre- 

 spond to, and balance, one inch of gold in the refining crucible. 

 When the chlorine is first introduced into the melted gold a 

 quantity of fumes are seen to pass up from the holes in the 

 crucible lid ; these are not chloride of silver, but the volatile 

 chlorides of some of the baser metals, and they are especially 

 dense when much lead is present in the alloy under treatment, 

 forming a white deposit on any cold substance presented to 

 them. After a time, longer or shorter, according to the impuri- 

 ties in the gold these fumes cease. So long as any decided 

 quantity of silver is present in the molten gold, the whole, or 

 nearly the whole, of the chlorine is absorbed, little, if any, 

 appearing to escape and to be thus wasted ; and it is found that 

 the better the supply of chlorine the quicker is the operation. 



It is a curious circumstance that, though in toughening with 

 corrosive sublimate, this substance is only thrown on the surface 



