68 SCHALLER AND BAILEY: INTUMESCENT KAOLINITE 



planation is that the liquids used were not checked for their 

 indices. It is very essential to redetermine frequently the index 

 of these liquids. It was found, for instance, that our liquids 

 had increased 0.003 from the value determined a year ago. 

 Dick 3 gives the mean index as 1.563 with a birefringence of 0.006. 

 Further Dick gives (7 — (3) = 0.004 (on basal plane) and (/3 — a) 

 = 0.002, values identical with those found on the material from 

 Oklahoma. The value 1.54, given in some books as the mean 

 index of kaolinite is doubtless too low. 



The mineral after intumescence, examined microscopically, 

 is opaque and nearly all of it has lost its perfect crystal outline. 

 Most of the pieces have a form which suggests that during the 

 heating (and intumescence?) the escape of the water took place 

 in such a way as to practically disrupt the crystal structure of the 

 mineral. 



The chemical analysis, by R. K. Bailey, gave the results shown 

 under (1), and for comparison under (2) is given an analysis of 

 kaolinite from Saitzewo near Nikitowka (Donez-Becken) by 

 Samojloff, 4 and under (3) the theoretical composition. 



(1) (2) (3) 



Si0 2 46.55 46.51 46.50 



A1 S 3 38.90 39.45 39.56 



H 2 O a 14.04 b 14.10 13.94 



99.49 100.06 100.00 



a Loss on ignition. 

 b Average of the two determinations, 13.97 and 14.10. 



A comparison of the figures given above shows the chemical 

 identity of the mineral from Oklahoma with kaolinite. The water 

 in it apparently behaves normally, for it was found that the total 

 loss on heating the mineral to 330° was insignificant, the total 

 loss of water being 0.09 per cent at 145°, 0.11 per cent at 220°, 

 and 0.12 per cent at 330? 



3 Dick, A. B., Supplementary notes on the mineral Kaolinite. Mineral Mag. 

 16:124-127. 1908. 



4 Samojloff, J., Uber das Wasser des Kaolinits. Bull. Acad. St. Petersburg, 

 3:1137-1152. 1909. 



