USES. 1(^7 
The heat necessan^ for the fusion in making the vitrified wheel 
;il)parently has no elfect upon the corundum beyond a partial decok)r- 
ization and the expulsion of the slioht percentage of water m the 
corundum. 
CHElVriCAL WHEEL, 
Tn the process of manufacturing this wheel, called the silicate proc- 
ess, silicate of soda is used as the binding material. The silicate is 
mixed with the emery or corundum and some drying material and 
lamped into molds. It is then subjected to an "oven" heat for 
(wenty-four hours, after which it is removed and finished according 
(o the method described above for the vitrified wheels after they are 
removed from the kilns. Wheels over 2,000 pounds in weight have 
Ijeen made b}^ this process. 
CEMENT WHEEL. 
In the cement wheel, shellac, rubber, linseed oil, and other sub- 
stances are used as the binding material. This makes a soft wheel 
that is well adapted for roll and surface grinding wdien made with 
shellac, and for saw gummers and thin Avheels when made with oils. 
OTHER USES. 
An attempt has been made to use corundum as a source of alumi- 
num, but on account of its refractoriness and the percentage of ferric 
oxide and silica that it often contains, and on account of the cost of 
the ore, this use has not been found feasible. 
The late Mr. Alfred E. Hunt, of Pittsburg, Pa., made the following 
statement : " 
Tlie real difficulty which we find in the use of corundum for this manufacture 
is the cost of the raw material as compared with that of native bauxites. In 
this item we include not only the price of the corundum as it has been offered 
to us, but also the expense of grinding it to an imi)alpable powder, which must 
be done before it can be used directly in the manufacture of aluminum, and the 
cost of preliminary chemical treatment for purification — which latter opera- 
tion, however, is also required for bauxite. 
Corundum has also been used as the source of the aluminum in the 
manufacture of aluminum-copper and aluminum-iron alloys. In the 
manufacture of these the corundum, without undergoing any pre- 
vious treatment, was charged into an electric furnace with a mix- 
ture of carbon and copper or carbon and iron, according to whether 
alimiinum bronze or ferro-aluminum was desired. Since 1890, how- 
ever, when alumina began to l)e manufactured at a comparatively 
low^ price, this artificial oxide has been used in the place of the 
corundum. 
« Trans. Am. Inst. Min. I<]ng., vol. 28, 1898, p. 875. 
