526 NEW YOEK STATE MUSEUM 



The effects of free silica proper, or quartz, and sand on the 

 behavior of the claj are to be considered separately. 



Qnartz serves as a flux only at high temperatures, viz, 2800° F. ; 

 but at lower temperatures it tends to increase the refractoriness of 

 the clay, and this property is governed somewhat by the size of the 

 quartz grains and amount of fluxing material present, which will 

 fuse at lower temperatures. 



In connection with the fluxing action of silica at high tem- 

 peratures, the following experiments of Bischof's^ may be quoted. 

 Mixtures of alumina and silica were made in varying proportions, 

 and their fusibility determined. The fusion point of alumina alone 

 lies above cone 36, while the fusion point of silica alone is at cone 

 35. Bischof found that a mixture of one equivalent of alumina and 

 two of silica showed the greatest refractoriness. If the percentage 

 of silica increases, the fusibility is gradually lowered, till the mixture 

 of one alumina to 17 silica is reached, the fusibility of which is the 

 same as cone 30. With an increase of the silica, the refractoriness 

 of the mixture again increases up to the fusion point of silica alone. 



Titanium 



Titanium is probably of more widespread occurrence in clay 

 than is commonly imagined. The apparent freedom of the 

 clay from this impurity has resulted from the fact that in 

 the usual quantitative analysis it is ordinarily overlooked. Its 

 source is either the mineral rutile (oxid of titanium) or il- 

 monite (the titanium-bearing magnetic oxid of iron), or pos- 

 sibly titanite. Much more importance has at times been at- 

 tached to its presence than is really warranted, and some chem- 

 ists, on finding traces of it, delight in dwelling on the important 

 influence which it may exert on the properties of a clay. While it 

 is present in many clays, the percentage seldom exceeds 1.5^ to 2fl^. 

 The analyses of 21 'New Jersey clays showed it to range from 

 :l.06^ to 1.93^. (Report on clays of N. J. 1878. p. 277) In 



1 Seger. Ges. Schrift. p. 434. 



