21 



The mineral is rather harder than sume well-crystallised corundum 

 from Ceylon, which was available for comparison. Its specific gravity 

 varies from 3.75 to 3.90 according to the degree of the compactness of 

 its texture. The higher figure is e.xceeded by few specimens of corun- 

 dum, except ruby and sapphire, which reach 4.06. 



An analysis in the Scientific and Technical l>epartment of the 

 Imperial Institute gave the following results : 



Silica ... 



Alumina 



Lime ... 



Magnesia 



Combined water .. 



The percentage of alumina is greater than in any sample of 

 corundum which has been analysed, except ruby and sapphire. The 

 amount of water is, however, rather high. 



Corundum is used mainly for abrasive purposes in the same 

 manner as emery. The finer qualities are also employed in place of 

 gemstones in the movements of clocks and watches. It has been 

 pi'oposed to utilise it as a source of metallic aluminium, but at present 

 other less refractory and cheaper compounds of the metal are 

 preferred. 



In determining the value of coruu<lum for abrasive purposes, 

 whether it be employed as a loose powder or embedded in cement in 

 the form of discs, a trial on a large scale is absolutely necessary. In 

 no other way can it be ascertained if the mineral satisfies industrial 

 requirements, as not only hardness but toughness is important. The 

 liability of some varieties to split into thin plates along the pseudo- 

 cleavage that follows certain planes of decomposition is very objection- 

 able, as instead of irregular points and edges Avhich are effective for 

 grinding piirposes, flat surfaces aiv produced. 



This characteristic seriously diminishes the value of Indian corun- 

 dum, which was formerly exported in considerable amount to Europe, 

 but is now unable to compete with the extensive deposits of the mineral 

 which have been developed in the United States and Canada, and the 

 artificial products carburundum and alurundum. Corundum is now 

 mined in India mainly for local use and for export to China, only a 

 small quantity being sent to Europe or America. On the other hand, 

 the granular structure of the corundum from Perak seems calculated 

 to increase its value for abrasive purposes. 



The material from Kinta was sent to a commercial expert dealing 

 in corundum for his opinion as to its value. He stated that he 

 believed the material might be of value for abrasive work and it 

 might be woi'th from iil5 to =£25 a ton fur such purposes. If it 



