CHEMICAL PROPERTIES OF CLAY. 69 



Alkalies alone seem to exert little or no< coloring influence on 

 the burned clay, although in some instances potash seems to 

 deepen the color of a ferruginous clay in burning. 



Titanium. 



Titanium is an element which is found in several minerals, 

 some of which are more common in clays than is usually 

 imagined, although they appear rare because they are seldom 

 found in large quantities. Among the titanium-bearing minerals, 

 the commonest is rntile, which is an oxide of titanium (Ti0 2 ), 

 containing 60 per cent, of metallic titanium and 40 per cent, of 

 oxygen. So- far as known, it is never found in clays in suffi- 

 ciently large grains to be visible to the naked eye, although a 

 microscopic examination may often show its presence in the 

 form of little needles or grains. Its frequent occurrence is, no 

 doubt, due to the fact that it is quite resistant to> weathering. 



It may be asked, why, if the material is so widespread, the 

 presence of titanium is so rarely shown in an analysis of clay. 

 This is because its determination by chemical methods is attended 

 with more or less difficulty and is rarely carried out. In the 

 ordinary process of chemical analysis it is included with the 

 alumina. Very few state geological surveys, in investigating 

 their clay resources, have made special determination of this 

 mineral, but in an investigation of clays of New Jersey, made 

 in 1877, Prof. Cook found that in 21 clays examined (p. 276), 1 

 it ranged from 1.06 to- 1.93 per cent. In a series of Pennsyl- 

 vania fire clays 2 the percentage of titanium oxide ranged from 

 0.87 per cent, to 4.62 per cent. The clay at Hackensack con- 

 tained 0.85 per cent., and analyses of a number of fire bricks 

 from this State gave percentages ranging from 0.85 per cent, 

 up to 4.30 per cent., so' that the probable effect of such a wide- 

 spread substance is well worth investigation. 



Unfortunately, but little experimental work seems to 1 have 

 been done along this line, although some years ago, Messrs. 



1 Report on the Clays of New Jersey, 1878, Cook and Smock. 



2 Second Geological Survey of Pennsylvania, Rept. MM, pp. 261 et seq. 



