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NEW YORK STATE MUSEUM 



• Magnesia also tends to prevent the development of a red color 

 in bricks. 



A white or light-colored brick is sometimes produced if the 

 clay contains a large amount of organic matter which will 

 reduce the iron. Efflorescence is due to the dissolving of the sul- 

 phates of magnesia and the alkalies by permeating water, and 

 their deposition on the face of the brick when the water 

 evaporates. 



A similar whitish coloring noticed on brick freshly burnt may 

 be due to the reduction of the iron by smoke from the arch fires. 



Titanium and lithium are never present in quantity. The 

 latter occurs as titanic acid. Lithium occurs in the clay in a simi- 

 lar form and its presence was first detected in the Cretaceous 

 clays of New Jersey. 



Clays weigh 110 to 125 pounds per cubic foot. They have a 

 specific gravity of from 1.75 to 2.00. 



Clays may be divided into three kinds : 



1 Clay. Mostly alumina and silica in varying proportions, 

 with a small percentage of salts of iron, lime, magnesia, pot- 

 ash, etc. 



2 Loams or sandy clays. 



3 Marls. Clays containing a large amount of lime. 



The refractoriness of a clay is not alone dependent on its com- 

 position but is also influenced by its density and fineness of grain.* 

 When two clays are of the same density and fineness, their 

 refractoriness is inversely proportional to the detrimental impuri- 

 ties present, when the latter are equated as to their proper flux- 

 ing values. This Professor Wheeler calls the " Fusibility factor " 

 and deduces the formula : 



N being the sum of the non-detrimentals or total silica, alumina, 

 titanic acid, water, moisture and carbonic acid gas. 



D=sum of detrimental impurities as iron, lime, magnesia, 

 alkalies, sulphuric acid and sulphur. 



D'=sum of the alkalies. This latter is added because the 

 alkalies have about twice the fluxing power of the other detri- 

 mentals. The effect of FeO is not considered as it is quickly 



* H. A. Wheeler, " Calculation of the Fusibility of Clays. 1 ' Eng. and Mix Jour., March 10, 1894. 



