1889-90.] ARSENIC AND SULPHUR. 145 



the volatile or combustible substances are expelled and as much oxygen 

 becomes combined at the same time with the ore as it possibly can 

 absorb." But we are aware of the weak affinity of the precious metals 

 for oxygen, they are therefore reduced direct to the metals. In 

 accordance with this he says further on, that " Sulphuret of Silver is easily 

 liberated from its sulphur and forms metal ; the same is true of gold." 

 Roasting was resorted to but very little in the treatment of ores of the 

 precious metals until lately, and even where it is used the benefit that 

 might accrue from it is lost by restraining the temperature from rising 

 above a certain point, for fear of sintering and thus causing extra expense 

 in the working of it. 



Well, to go into detail of how I intend to roast these ores. They 

 must either be roasted in piles or kilns. I prefer the pile as a larger 

 portion of ore can be operated on at once and more easily manipulated 

 than if in kilns, and there is also very little outlay in preparing the bed 

 to receive the same ; but it all depends on the metallurgist who is con- 

 sidering the question, as one man can see an advantage where another 

 could not. I shall go no further into details than to say that the pile 

 will be merely the ordinary one, with special attention paid to its draught 

 canals which shall be two feet apart. We shall commence by building 

 up the foundation from i8" to 2ft. in height, of hardwood, the height it is 

 to be built depending on the amount of sulphur contained in the ore, the 

 more sulphur the less fuel, and vice versa for the other extreme. The top 

 should be easily reached so that the fines that form the covering could be 

 easily manipulated. When the pile is all ready for lighting, we shall 

 light it at one end only and not all round as is usually done, as the fire 

 will spread soon enough for our purpose. When the end is well lighted 

 let it have the benefit of a full draught by opening four draught canals 

 (2 on each side), and clearing the fines of the top, for four feet, when the 

 ore having this great draught will sinter ; when it has pretty well sintered, 

 turn three or four jets or streams of water on it, this will cause it to crack 

 and crumble, then let men with long iron hooks pull the crumbling parts 

 away so that the water may the better get at the other parts, and keep 

 continually clearing away as it is possible to do so ; when within one foot 

 of that part of the pile, whose draught canals are not open, stop putting 

 on water, open two on each side, pull fines off top as before, let sinter, 

 put on water, and pull and clear away as ready, repeating this until the 

 pile is finished. 



The ore which has been done in the meantime is carried off to the mill 

 and fed to the stamps ; there may be sluices having hardwood riffles, 

 leading from the mill to settling tanks, or it may be stamped dry, and 



