CLAYS OF NEW YOKE " 511 



Chemical properties 



The chemical composition, and indirectly therefore the minera- 

 logic composition, may influence the fusibility of a clay, its color 

 in burning, shrinkage, and perhaps plasticity. 



The compounds which may be found in clay are silica, alumina, 

 iron oxid, lime, magnesia, potash, soda, titanic acid, sulfuric acid, 

 manganese oxid, phosphoric acid and organic matter. Compounds 

 of chromium^ and vanadium^ may also' be present in small amounts, 

 and even lithium (N. W. Lord. /. A. I. M. E. 12:505) and 

 cerium, yttrium and beryllium oxids {Jour. pr. chem. 33: 132) 

 have been recorded. Phosphoric acid is also known.^ ITot 

 all of these are present in every clay, but most of them are. 

 Pure clay would contain silica, alumina and combined water. The 

 purest clays known contain traces of iron oxid, lime and alkalies, 

 , All of the constituents of clay except alumina, organic matter, 

 and water, may exert a fluxing action on the clay wh-en burned, 

 the intensity of this action depending on the amount of fluxing 

 material and the temperature. Consequently the impurities of 

 clay are often divided into fluxing and non-fluxing. 



Fluxing impurities 

 Pure clay, theoretically composed altogether of the mineral 

 kaolinite, is very refractory. This mineral contains two molecules 

 of silica and one molecule of alumina. A higher percentage of 

 silica tends, up to a certain point, to increase the fusibility provided 

 it is in a finely divided condition. If the silica percentage how- 

 ever gets above a certain point, the refractoriness of the clay in- 

 creases with the increase in silica up to the point at which tlie 

 mass contains nothing but silica. This has been demonstrated 

 by the experiments of Seger. (Tlionindustrie zeitung, 1893. 



no, 17) 



Other substances act as far more powerful fluxes than the silifi, 

 and these fluxes include not only elements but also definite chcmi; al 



' Some Brazilian clays. 

 5 See p. 509. 



3 Some pleistocene clays near Baltimore, Md., contain much vivianite. 



