18 



wisco]srsi]sr academy sciEifCES, arts, aistd letters. 



I. is the clay just as it came from the pit, after drying at 100'^ 

 C. TI. is the fine or kaolinite portion of I. washed from the 

 coarse matter by repeated decantation and stirring. The separa- 

 tion is not perfect, but imitates what would be done in washing on 

 a large scale. III. is the coarse residue from this washing, its com- 

 position being calculated from the two preceding analyses after 

 finding that it constituted 67.1 per cent, of the whole clay. The 

 carbonic acid remains as a silent witness of the agency by which 

 the clay was formed. The following show II. and III., calculated 

 in percentages on the original unwashed clay, and indicate how the 

 various ingredients distribute themselves between, the fine clay and 

 coarse residue: 



II. III. I. 



Silica 16 . 33+62 . 50=78 . 83 



Alumina 12.03+ 1.40=13.43 



Sesquiox . Iron 



Lime 



Magnesia 



Potash 



Soda 



Water 3.75+17.0 



Total 



32.50+67.10=99.60 



