118 Day and Allen — Isomorphism and Thermal 



feuille) at as low a temperature as practicable, after which the 

 excess of sulphate was extracted with water aud the product 

 dried (the temperature was raised to a dull red heat to remove 

 all water) and analyzed. 



Calculated. 

 SiC) 68-74 68-68 



A1 2 3 and 

 FeO 



Found. 



68-74 



19-56 



11-73 



•02 



•16 



19-49 



Na 2 11-73 11-83 



S0 3 



wo 3 .._. 



100-21 



The specific gravity of it was 2*604, which may be corrected 

 as before for the remaining trace of tnngstic acid assumed to 

 be in the form of the sodium salt. The value then falls to 

 2-601. 



A second portion of the same albite was purified by another 

 process. Instead of fusing with acid sodium sulphate, the 

 powdered sample was first digested for a short time with dilute 

 hydrochloric acid (1:1), which set free tungstic acid. The 

 excess of hydrochloric acid was removed with water, the 

 tungstic acid with ammonia, aud finally the excess of reagent 

 and the ammonium tungstate by further washing with water. 

 When dried at a low red heat, the preparation had the follow- 

 ing composition ;• 



Si0 2 

 A1.0, 



Fe 2 3 

 Na 2 



wo 3 



HO 



Found. 





Calculated 



68-91 





68-68 



18-95 \ 



•18 \ 



19-13 



19-49 



i 

 11-59 





11-83 



•22 







•13 







99-98 



The specific gravity determination gave 2'615, which when 

 corrected for a small amount of sodium tungstate becomes 

 2-612. If, as is possible after the above treatment, the 

 tungstic acid is present as the anhydride, sp, gr. 7*1, the cor- 

 rection would lower the value to 2*605, in excellent agreement 

 with the other determinations. 



The products of both methods of purification were carefully 

 scrutinized by the microscope, but no conclusion could be 

 reached as to which was the purer. Neither the sodium sul- 



