66 



CLAYS AND CLAY INDUSTRY. 



Physical tests on Mackler's 



mixtures. 









*d 



V 



u 



'3 

 a 



V 



u 

 u 



V 



to 



V 



u 



a 



_s 



'u 

 .S 



W 



u 



< 



a 



bo 

 "S 



& . 



>*- be 

 p 

 "> 'u 



s« 



Fire shrinkage Cone Nos. 





010 



05 



1 3 



5 





28.8 







3-5 

 1.8 



1-7 

 3-o 

 3-7 



7-2 ! 7-9 



* 



6.7 



B. Clay + 25CaC0 3 (14 CaO), .. 



C. Clay +12.5 CaC0 3 (7 CaO),.. 



D. Clay + 21 MgC0 3 (ioMgO),... 



E. Clay +10.5 MgC0 3 (sMgO),.. 





33-6 



34-o 

 32.4 



8.3 



8.2 

 7-5 



10.4 



16.3 

 11. 1 



1.0 



06 

 i-7 



+ 

 11. 7 11. 9 

 11. 1 11. 3 



* 

 t 



* Melted. 

 t Warped. 



It will be seen here that the effect of magnesia was quite 

 different from that exerted by the lime. The mixtures contain- 

 ing magnesia did not vitrify suddenly, as did the limy clays, nor 

 did the magnesia exert as strong a bleaching action on the iron, 

 and the points of incipient fusion and viscosity were also sep- 

 arated. 



With a mixture of kaolin and magnesia, similar results were 

 obtained. The mixture of kaolin and magnesia showed a higher 

 shrinkage at the beginning of the burning than the kaolin alone, 

 and then increased but little until a high temperature was reached, 

 when the shrinkage suddenly began again. A hard body was 

 obtained at cone i with the kaolin-magnesia mixture. 



The effect of magnesia, therefore, if present in sufficient 

 quantity is to act as a flux and make the clay soften slowly 

 instead of suddenly, as in the case of calcareous clays. 



Of the various kinds of clay found in New Jersey, the brick 

 clays usually contain the highest percentages of magnesia, but 

 even in these it is 'rarely present in sufficient quantity to exert 

 a noticeable effect. The fire clays contain the least. 



The range of magnesia in several classes of clays, as figured 

 from a number of analyses, is as follows i 1 



1 Bull. N. Y. State Museum, No. 35, p. 524. Owing to an error in an 

 analysis of a brick clay the figures in this table have been recalculated. 



