Kaolin Incrustation on. Pyrolusite. 363 



free from quartz. To bring about a perfect separation it was 

 fdund advisable to wash away from the powder the constituents 

 of which are to be separated all the very fine particles so as to 

 leaA-e the grains about one size. 



The result of the above experiments is to show that a separa- 

 tion of two constituents of the powder having specific gravities 

 within .04 of each other, and haiving particles of maximum 

 diameter .015 mm. is impossible by means of Sondstadt's 

 solution useless the centrifuge be used as above described. 



3. The isolated incrustation was examined. Au analysis gave 

 the following results : — 



We see that the approximation of the composition of the 

 material to that represented by the formula Al.^O;^ . 2H.jO . 2Si0.2 

 is very close. 



The specific gravity was determined approximately in the fol- 

 lowing manner: — Some Sondstadt's solution was diluted down 

 until it was seen that particles of the incrustation just floated. 

 The specific gravity of the liquid was found to be 2.61 by 

 Sprengel tube. Hence we may call this the specific gra.vity of 

 the kaolin. 



The account of the examination of the optical properties of 

 the incrustation has already been given. 



4. It was found, as a result of this investigation, that this 

 inci'ustation is kaolinite. 



Its percentage composition, specific gravity and optical proper- 

 ties under the microscope, together with the property of retaining 

 its combined water at 150 deg. C, though parting with it at a 

 red heat, agree with those given in Dana for kaolinite. Further, 

 its properties under the microscope correspond with those of a 

 known specimen of kaolinite mounted as a microscope slide 

 for comparison. 



