178 HENRY G. SMITH. 



The constitution of kaolin is discussed in Percy's Metallurgy 

 {Fuel), page 93, but the arguments are principally based on the 

 above mentioned paper by Johnson and Blake. 



A figure of Kaolinite as it appears under the microscope is given 

 in Teall's British Petrography, Plate 44, but this only shows 

 isolated plates and scales such as may be found in ordinary clay. 



The following is one analysis I made of this mineral, it was 

 fused with the carbonates of sodium and potassium : — 

 •563 gram, gave -261 gram. Si 2 



•563 „ „ -2255 „ Al 2 3 with a trace of iron. 

 •563 „ „ -008 „ Mg 2 P 2 7 

 •563 „ „ -0727 „ H 2 

 = 46-359 per cent. Si 2 . 40-053 per cent. Al 2 3 

 •512 per cent. Mg O and 12-913 per cent. H a O 



= 99-837. 

 Another analysis gave almost identical results. 



The water was estimated three times, but in no instance did I 

 succeed in obtaining 13 per cent., the highest being 12*96 per 

 cent., the last portions are only driven off by long continued 

 heating. 



The magnesia does not appear to be an impurity, as it is a con- 

 stant quantity in all the samples of kaolin yet examined ; if a 

 portion of the water be considered basic, and the Mg O be calcu- 

 lated into this water the oxygen ratio is nearly 3:4:2, and the 

 formula is as usually written Al 2 3 2Si0 2 + 2H 2 O. The 

 alumina was a trifle high in all three estimations that I made. 



