THE MANAGER ON THE WORKS. 87 



magnifying glass, it will be seen that the revivification is on 

 the surface only, and that the middle is quite black. And 

 this surface revivification should not be confounded with 

 through or complete revivification, but the oxide should be 

 worked for some time after changing colour. If there are 

 three boxes, sufficient oxide should be provided for five; and 

 it is a good plan to keep each heap separate, and to 

 distinguish it by a small lettered label. A proper record of 

 purifier changes being kept, it is possible at any time to 

 see the age and the work done by any particular heap, and 

 to judge the position as to requirement of new oxide. 

 After a time, the heap may swell to such an extent that a 

 surplus remains after filling the box. This can be put on 

 one side for admixture with new oxide. After eight or ten 

 alternate foulings and revivifications, the material shows 

 signs of getting old, and in a small works this usually 

 happens when it has accumulated 40 to 50 per cent, of 

 sulphur. There is a general idea that oxide cannot be 

 worked up to 50 per cent, or more on the small scale, but 

 there is no foundation for it. T!:e explanation is that it 

 does not get so much attention in the matter of revivifica- 

 tion, and as the oxide gets old the action gets more feeble. 

 The buyers of spent oxide require 50 per cent, or more of 

 sulphur, and it is as easy to get the oxide up to this point, 

 if the boxes are of sufficient capacity, on the small scale as 

 on the large. 



When an oxide purifier is opened, the contents should 

 be removed without delay, and if the job cannot be finished 

 before night and a part must be left till next day, the lid 

 should be put on and the air valve closed. The exact 

 treatment varies with the nature of the oxide. Natural 

 ores, such as bog ore, clay iron ores, etc., differ somewhat 

 in their action from the various artificial materials that are 



