368 Report S.A.A. Advancement of Science. 



11% to 15% moisture is reduced without difficulty to 2% by means 

 of Pape Henneberg driers. Ore with 4% moisture is workable with- 

 out drying. The driers are only used in the wet season. 



4. Expense incurred in fine crushing. This is frequently over- 

 done. Rand practice is gradually altering and coarser crushing is 

 gaining ground. At the Luipards Vlei Mill, pyritic ore crushed to 

 700 mesh per square inch was reduced in value to i^ dwts., indicating 

 aji extraction practically as good as the average obtained in Wet 

 Milling plants. 



5. Di-fficulty of dealing with coarser gold. This is of course 

 aji important and positive objection, when it does exist, but in the 

 majority of cases the gold is fine enough to be freely dissolved. Gold 

 which passes through a sieve with 200 or 300 meshes to the inch 

 can be dissolved without much difficulty, and coarser particles should 

 not escape if the sieves are working properly but be returned to the 

 crushers for further reduction. 



ADVANTAGES. 



1. Saving of power. This brings with it less capital outlay in 

 plant as well as in working cost. The economy will more than counter- 

 balance any possible excess in cost of renewals. 



At the Wanderer Mine, friable ore of ver)- low grade is economi- 

 cally crushed and cyanided when crushed tO' pass sieves with clear 

 apertures of 3/i6ths inch square, or 16 to the square inch. The final 

 residues do not exceed one dwt. in value per ton and the quantity 

 treated at present is 2,000 tons per week. 



2. Simplicity of operations for extracting gold. Plate and 

 battery amalgamation are not required. The smaller percentage of 

 slimes produced can be mixed with the sands, and the whole treated 

 by cyanide in one operation instead of two. The material produced 

 is more suited to the action of cyanide solutions and consumption of 

 this chemical is lessened. 



3. The amount of water required is very little ; the cost of pump- 

 ing is reduced to a minimum, and the large outlay in dams and 

 pumping plant inseparable from a stamp battery is reduced to a 

 minimum. The balance is decidely against wet crushing. 



A dry crushing plant is not recommended, however, for installa- 

 tions dealing with lesr; than 100 tons per day. 



