FIRE CLAYS AND FIRE-BRICK INDUSTRY. 313 



8.5 of silica by weight), a mixture the fusion point of which was 

 the same as that of cone 37, he found that the refractoriness de- 

 creased until a mixture of 1 part alumina to 17 parts of silica 

 (10 alumina to 90 silica by weight) was reached. The fusing 

 point of this mixture was cone 29. A further increase in the 

 amount of silica began to increase steadily the refractoriness. 

 This shows that silica added to alumina in certain proportions acts 

 as a flux at high temperatures. 



Seger 







37 

 36 

 35 























o'uSILICfl 



with 































































33 



32 



Jl 



3C 



29 



21 



27 



Zt 

 Kaolin or 

 fffum/na 













X 























\ 





















\ 























\ 





















N 











nina ar 

 n and 



Td di/ia. 

 fSi/ica 



> 











1 





























1 

 1 



















V 



1 

 1 



>■/, <, 











r> 4 











r '3 



fllu 



40. Diagram showing effect of Silica on the fusion point, when mixed 

 mina and Kao/m, from Segers experiments. 



If now silica is mixed with kaolinite in the same manner, a 

 similar lowering of the refractoriness oi the mass takes place 

 down to a certain point beyond which the fusion point again 

 rises. These experiments of Seger are shown graphically in Fig. 

 40, in which the horizontal lines represent the different cone 

 numbers from 26 to 38 inclusive. The divisions on the lower 

 line represent percentages of alumina or kaolin measured above 

 the line, 100 per cent, being at the left end, and percentages of 

 silica measured below the line, 100 per cent, being at the right end. 

 The solid curve represents the mixture of silica and alumina, while 

 the dotted curve represents mixtures of kaolin and silica. An 



