Mr. A. B. Northcote on the Constitution of Allophane. 341 



proportion of the three constituents would remove the anomaly ; 

 or the very hygroscopic nature of the dried substance would of 

 itself be quite sufficient to account for such an excess of water ; 

 for I found that when, after drying, it was left for a day or two, 

 even in clamped watch-glasses in a balance-case, it had regained 

 half the weight which it had lost by drying. I may also state 

 here, that, on the authority of Brande, the neutral hydrate 

 of alumina sustains a temperature of 100° C. without loss of 

 water. 



Specimen II. Sp. gr. 1'84. 



99^98 



rWater .... 20^76 

 Loss percent, at 100°C.-< Carbonic acid exist- 1 ,.qt 

 \_ ing as bicarbonate J 



These constituents may be thus approximately arranged : — 



Alumina 37'30 



Silica 19-58 



Water fixed at 100° C. . . . 18^43 

 Water expelled at 100° C. . 20-76 

 Carbonate of lime .... 2-43 

 Carbonate of protoxide of iron. -17 



Carbonic acid existing as bicar-1 \.^\ 

 bonate j 



99-98 



The accidental constituents being, as in the former case, with- 

 drawn, we obtain as the composition of this specimen, — 



Alumina .... 37-30 49-53 



Silica 19-58 26-00 



Water fixed at 100° C. 18-43 24-47 



75-31 10000 



And the formula arrived at from these numbers is 



AP 08 . SSiQs, 4(A12 03 . 3H0) -}- 2H0. 



If the 2 HO are considered here, as in the former case, to be 

 due to erroneous determination, arising fronj one or more of the 



