CLAYS OF NEW YORK 



527 



the Pennsylvania clays the variation was fonnd to be from .87^ to 

 4.62^. It probably reaches a far higher amount in bauxites than 

 it does in clays, for analyses show a range commonly from 3^ to 5^. 

 In order to determine definitely what the effect of titanium was, 

 Seger and Cramer ^ mixed two parts of sample of Zettlitz kaolin 

 (which has 98.5;^ of clay substance) with respectively 5fo and lOfo 

 of quartz, and two other samples of the kaolin with respectively 

 Q.Q5/o and ISfc of titanium. These samples were molded into pyra- 

 mids which were heated to a temperature above the fusing point of 

 iron, with the following results. 



1 Pure Zettlitz kaolin burned tO' a white, sharp-edged dense body. 



2 100 pts kaolin and 10^ silica burned white. 



« Kd " 



4: " Q.5fo titanium oxid softened on heating 



and showed a blue fracture. 



5 100 pts kaolin and 13.3^ titanic oxid fused to a deep blue 

 enamel. [ 



It is therefore seen that titanium acts as a flux at lower tem- 

 peratures than silica, and it is suggested that the blue color given to 

 some stoneware clays by hard firing may not always be due tO' iron 

 oxid. 



Organic matter 



Organic matter affects not only the color of clay, but also its 

 plasticity, absorptive power and tensile strength. 



It generally consists of finely divided pieces of plant tissue, or 

 larger pieces of stems and leaves which settled in the clay during 

 its deposition. All surface clays contain plant roots in their upper 

 layers, but these do not directly influence the color of the clay. 

 Clays colored by organic matter and containing no iron burn 

 white, as the plant tissue passes off at bright redness; if such a clay 

 however be heated too quickly, before all the organic matter has had 

 an opportunity to escape from the interior, the surface becomes 

 dense, and it remains dark colored. 



1 Seger. Ges. Schrift, p. 411. 



