102 Clarke — Constitution of Ptilolite and Mordenite. 



Reducing soda to potash in the Green Mt. ptilolite, and 

 potash to its equivalent of soda in the Silver Cliff minerals, 

 and recalculating to 100 per cent, we get a fair comparison 

 between the actual analyses and theory. 



Ptilolite. 





Green 



Mt. 





Found. 



Calc. 



Si0 2 



70-15 



69-22 



A1A 



11-86 



11-77 



CaO 



3-86 



3-88 



K o 



3-98 



4-3-1 



Na 2 











H s O 



10-15 



10-79 



Silver Cliff. 

 Found. Calc. 



68-45 67*64 



11-55 11-50 



3-35 3-16 



100-00 



100-00 



3-09 

 13-56 



100-00 



3-49 

 14-21 



100-00 



In mordenite, reducing Fe 2 3 to A1 2 3 and MgO to CaO,, 

 the comparison comes out as follows : 





Found. 



Calc. 



SiO„ 



66-88 



66-77 



A1A 



11-62 



11-35 



CaO 



2-17 



2-07 



K 2 



3-62 



3-49 



Na,0 



2-29 



2-30 



H 2 



13-42 



14-02 



100-00 



100-00 



Considering the scarcity of material, and the difficulties 

 attending its purification, these agreements are in the main 

 satisfactory. In the water determinations, however, there is 

 an uncertainty. In the theoretical composition assigned to the 

 Silver Cliff ptilolite, one seventh of the water, a trifle under 

 two per cent, is basic. But 3*10 per cent were found to be 

 stable at 300°. What weight can be assigned to this discrep- 

 ancy is not yet determinable, but it can hardly be regarded as 

 an insuperable objection to the proposed formulae. The 

 general character of the salts, their essential types, seems to be 

 fairly well established. 



