IRON ROASTING. 



blade into the solution ; if it has not, a film of copper will 

 be left on the knife. 



Weight of copper 100 = P crcenta S e of copper 



Weight of ore sample in fc he ore. 



Iron. 



To assay an iron ore by the wet method, the standard 

 solution of bichromate of potash is, by means of a graduated 

 burette, added to the iron solution (the powdered ore dis- 

 solved in hydrochloric acid); but like the other burette 

 assays, this requires so much practice in order to secure 

 reliable results, that there is no occasion to enter into 

 details concerning it. The prospector will rarely require to 

 know the exact amount of iron in an ore, and his own sense 

 will perhaps guide him nearly as well as an assay, as great 

 quantity and good quality are both necessary to make an 

 iron ore payable. 



Roasting. 



In roasting the powdered ore much care is necessary in 

 order that the sulphur, &c., may be expelled. The powdered 

 ore placed in an open and shallow vessel, if possible, should be 

 exposed to a low heat at first, and after a time the tempera- 

 ture may be raised. During the operation free access of 

 air is requisite, and the ore must be constantly stirred by 

 means of an iron wire bent at one end, or other suitable 

 apparatus, so as to prevent clotting. When fumes cease to 

 be given off the operation is finished, about a quarter of 

 an hour being the usual time necessary. 



Mechanical Assay of Ores. 



This is performed by crushing the ore and subjecting it 

 to the action of water. If the powdered ore be subjected 

 to the action of water running on an inclined plane or 

 trough with a slope, the heavier particles of metals may be 

 caught up in their descent by means of thin boards (riffles) 

 fastened across the trough. Rough hides, with the hair 

 upwards, may be used to intercept the heavier portions. To 

 " pan " gold, see GOLD, Chap. V. 



