262 CLARKE 



was actually observed in the analyses of barium and strontium 

 analcite. 



The presence of CI and NO3 in the substituted stilbite and 

 chabazite remains to be interpreted. The simplest explanation 

 of the facts is that adopted by Mr. Steiger in Bulletin 262, 

 where it is assumed that chlorides or nitrates as such are re- 

 tained or occluded by the residues. When' these substances 

 are deducted from the analyses, the remainders agree closely 

 with the theoretical composition of the derived zeolites. But 

 this explanation is not the only one possible. We may imagine 

 that new compounds have been formed, analogous to if not 

 identical wdth such silicates as sodalite or marialite : and it is 

 worth while to examine the data from this point of view. 



The simplest formula assignable to stilbite, regarding all 

 water as crystalline, represents the species as a mixture of the 

 two isomorphous salts 



Na,Al,(Si30,),.6H,0, 



CaAl2(Si303),.6H,0 ; 



with the calcium compound largely predominating. In chaba- 

 zite we have a similar commingling of 



(CaNa,)Al2(SiOj2.4H20, 



(CaNa,)Al2(Si308)2.8H20, 



the calcium and the trisilicate being most abundant. The true 

 formula} are probably multiples of these, and the anhydrous 

 salts are perhaps best figured by the following expressions, 

 which represent the salts as isomers of nepheline and albite, 

 with their equivalent calcium compounds : 



Al— SiO,=Al Al— Si30s=Al 



^Si04=Al ^SisOg^Al 



ySiO^^Al ySiaOg^Al 



Al— SiO,=Al Al— SiPs^Al 



\si04=Ca ^SL08=Ca 



Ca Ca 



I I 



ySiO^=Ca ySiaOg^Ca 



Al-SiO,=Al Al— Si30,=Al 



^SiO.sAl \si,0«=Al 



