CHINA CLAYS. 121 



The clay fused at cone 27 in the Deville furnace. 



The clay has to be heated very slowly in burning in 

 order to prevent cracking. 



The tensile strength of the briquettes was tried in sev- 

 eral different ways. 



One lot was made from clay ground to pass through 

 a 20 mesh sieve, and these showed a tensile strength of 

 137 Ibs. per square inch, the maximum being 154 Ibs, 

 the variation in the different briquettes being 20 per 

 cent. A second lot was ground to pass through a 60 

 mesh sieve, and here the average strength was 138 Ibs. 

 per square inch, the maximum being 143 Ibs. and the 

 variation 12 per cent. 



A third lot was ground to pass through a 100 mesh 

 sieve and here the average tensile strength was 1 32 Ibs. 

 per square inch with a maximum of 150 Ibs. and a vari- 

 ation of 15 per cent. 



The chemical analysis of this clay yielded: 



Analysis of China Clay, J. R. Hughes. Gadsden. (No. 190.) 



Silica 67.95* 



Alumina 20.15 



Ferric oxide 1.00 



Lime 1.00 



Magnesia tr. 



Alkalies 3 .87 



Ignition 8.00 



Total fluxes. 



There are many points of a desireable nature to be 

 found in this material, viz., its high plasticity, its great 

 density on burning, and its good tensile strength, all ot 

 which would combine to make it a ball clay of good qual- 

 ity. The color on burning is not quite as white as could 

 be desired but no doubt washing would improve this. 



