Max. 



Aver. 



7.29 



1.052 



4.80 



0.85 



6.25 



0.513 



2.42 



0.223 



CHEMICAL PROPERTIES OF CLAY. 67 



Amount of magnesia in clays. 



Quality. Min. 



Brick clays, 0.02 



Pottery clays, 0.05 



Fire clays, 0.02 



Kaolins, tr. 



Alkalies. 



The alkalies include potash (K 2 0), soda (Na 2 0) and 

 ammonia (NH 3 ). There are other alkalies, but they are prob- 

 ably of rare occurrence in clays. 



The amount of total alkalies contained in a clay varies from 

 a mere trace in some to 7 per cent, or 9 per cent, in others. The 

 range of alkalies in several classes of clays was determined to 

 be as follows •} 



Amount of total alkalies in clays. 



Range. Average. 



Kaolins, 0.1 -6.21 1.01 



Fire clay, 0.048- 5.27 1.46 



Pottery clays, 0.52 - 7.1 1 2.06 



Brick clays, 0.17 -15.32 2.768 



Ammonia is, no doubt, present in some raw clays, judging" 

 from their odor, and it may possibly exert some effect on the 

 physical structure of the clay, it being found that the bunches 

 of grains in a clay tend to separate more easily, when the clay 

 is agitated with water, if a few drops of ammonia are added. 

 As ammonia is easily volatile, it leaves the clay as soon as the 

 latter is warmed, and, therefore, plays no part in the burning 

 of the clay. The two other common alkaline substances, potash 

 and soda, are more stable in their character, and are, therefore,, 

 sometimes termed fixed alkalies. These have to be reckoned 

 with in burning, for they are present in nearly every clay. 



Several common minerals may serve as sources of the alkalies. 

 Feldspar may supply either potash or soda. Muscovite, the white 

 mica, contains potash. Greensand or glauconite contains potash. 



1 Bull. 35, N. Y. State Museum, p. 515. 



