264 Mr. Nortlicote on the Constitution of Thermophyllite. 



that eveu in the experienced hands of Professor Miller of Cam- 

 bridge, who has kindly investigated this point for nie. Every 

 fractnre, with the exception of the one above-mentioned cleavage, 

 he found to be extremely irregular : the single face obtained was 

 so curved as to render it impossible to obtain any distinct reflexion 

 from it ; and no natural faces were observable. Its hardness is 

 between 1"5 and 2'0, and its specific gravity 2"61, as detemnined 

 by M. Nordenskiold's observation. When heated before the 

 blowpipe, this mineral swells up more than pyrophyllite, and 

 assumes fantastic forms ; it loses only 0'3 per cent, of its water 

 when exposed to a heat of 100° C, and is scarcely acted on by 

 hydrochloric acid, a small quantity of iron being almost all that 

 is removed. Its analysis was therefore effected by fusion witli 

 an alkaline carbonate, and with the hydrate of barium for the 

 determination of the sodium. The constituent elements were as 

 follows: — sodium,magaesium,alumiaium,iron,hydrogen,oxygen, 

 silicon ; and the atomic weights employed were, for sodium, 23 ; 

 magnesium, 12 j aluminium, 13"7 ; iron, 28; hydrogen, 1; 

 oxygen, 8 ; and silicon, 22. Nordcnskiokl has given yttrium 

 as one of its components, an observation which I have been un- 

 able to verify. The following determinations were in the present 

 instance made : — 



I. II. Mean. 



Soda 2-98 2-70 2-84 



Magnesia 37-39 37-45 37-42 



Water not expelled at 100° C. 10-73 10-43 10-58 

 Water expelled at 100° C. . -32 -28 -30 



Alumina 5-54 5-44 5-49 



Silica 41-52 41-44 41-48 



Protoxide of iron .... 1-71 1-47 1-59 



99-70 



The composition thus arrived at, when calculated to 100 parts 

 v.'itli and without the water expelled at 100° C, is slightly 

 altered as follows — the loss of water is so slight as to be obvi- 

 ously immaterial to the composition of the mineral : — 



Including the 0'3 per Excliuling the O'S per 

 cent, of water ex- cent, of water ex- 

 pelled at 100° C. pelled at 100° C. 



Soda 2-S4 2-85 



Magnesia .... 37-53 37-65 



Alumina . . . ^ 5-50 5-53 



Protoxide of iron. . 1-59 1'60 



Water 1092 10-65 



Silica 41-62 41-73 



100^ 100-00 



