pratt.] METHODS OF CLEANING AND USES. 75 
inclined surface that is just above the flames of the furnace and slides 
down this surface into an iron box. By the other method the wet 
product is thrown in at the upper cud of an iron cylinder, open at 
both ends, which revolves about a coil of steam pipes. One end of 
the cylinder is lower than 1 he other, and the wet mass is alternately 
carried up by the revolving cylinder and dropped on the hot coil of 
pipes, and so gradually worked toward the lower end, where it is 
caught in a hopper and conveyed by ('levator belts to the sizing room. 
Here it is automatically screened to the various sizes. 
On PL XIV, A and J5, are views of the exterior and interior of the 
corundum mill at Cullasagee. In the foreground of B are the boxes 
in which the ore is first washed and just beyond these are the mullers. 
Only within the last few years lias any attempt been made to 
improve the methods of concentrating and cleaning corundum. There 
are now a number of companies thai have installed complete con- 
centrating mills, similar to those used in concentrating gold ores, but 
modified to suit corundum ore. While all are using jigs for the 
coarser sizes of the crushed ore, some are using Frue vanners and 
others Bartletl or Wifley tables for the finer sizes. This method 
works very satisfactorily for concentrating the corundum, and if, 
during the crushing and rolling of the ore, the corundum is largely 
separated from the associated minerals, a nearly cleaned product 
is obtained. It is necessary, however, to subject the larger part of 
the concent rales to some process similar to 1 hat performed by mullers, 
to free the grains of corundum from other minerals attached to 
them. 
A hew machine — the Hooper pneumal ic concent rator — can also prob- 
ably be used to advantage in concentrating corundum ores. 
Any other minerals that will be likely to remain with the corundum 
in the concentrates, as garnet, pyrite, etc., can undoubtedly be sepa- 
rated by means of the Wetherill magnetic concentrator. Unless these 
minerals are unattached to the particles of corundum there will be a 
considerable loss of corundum by this separation. 
USES OF CORUNDUM. 
Corundum is used for only two general purposes, as gems and as an 
abrasive. 
The varieties of corundum that are of value as gems have been 
described on page :5!i, and the many uses that are made of the cut 
stones in the jewelry trade are too well known to need more than a 
passing notice here. One use of the corundum gem that is perhaps 
worthy of notice is in supplying jewels for watches. In a recent 
notice from the Swiss agency of precious stones for watches, Aarburg, 
Switzerland, it said that 75,000,000 watch jewels are required annually. 
With the increase of production of gem corundum in this country a 
