Clarke and Steiger — Action of Ammonium Chloride. 29 



say. Neither have we any explanation to offer of the reten- 

 tion of chlorine by the ammonium derivative. Although the 

 amount of chlorine is small, it needs to be accounted for. 



If we discuss the composition of the stilbite and of its 

 ammonium derivative, the relations between them become 

 very clear. Neglecting the water as " zeolitic," to use Friedel's 

 phrase, and, therefore, as not a part of the chemical molecule, 

 and also rejecting the 1*37 per cent of soluble silica as probably 

 an impurity, the ratios derived from the analysis give this 

 empirical formula for the mineral : 



Na 40 Ca 110 Al SS! Si„,A«.- 



This corresponds to a mixture of ortho- and trisilicates in 

 which Si 3 O g : Si0 4 : : 286 : 43 ; and uniting these radicles under 

 the indiscriminate symbol X, we have, as a more general 

 expression, 



Na 4ffl Ca 140 Al iM X„ a ; 



or, combining monoxide bases, 



R "l60 A1 332 X 3 2 9> 



which is essentially R"Al a X a . Since the Si0 4 groups are 

 practically equal in number to the sodium atoms, the stilbite is 

 probably a mixture, very nearly, of NaAlSi0 4 and CaAl 2 (Si 3 8 ) 2 

 in the ratio of one to seven. This is in accordance with the 

 well-known theory of Fresenius as to the constitution of the 

 phillipsite group, to which stilbite belongs. Stilbite is mainly 

 a hydrous calcium albite, commingled with varying amounts 

 of corresponding orthosilicates of soda and lime. 



For the ammonium derivative similar relations hold. Tak- 

 ing analysis "B" for discussion, rejecting soluble silica and 

 chlorine as impurities, and neglecting all water except that 

 which belongs to the supposable ammonium oxide, the ratios 

 give this formula : 



(NH 4 ) aM Na 4 Ca 5B Al, 68 Si 88 ,0 8e8 , 



Uniting sodium and calcium with ammonium this becomes 



R', s ,Al aM (Si,0 8 ) 8 , < (Si0 4 ) 13 ; 



or, more generally, 



R' 5t ,Al a68 X 35 „ =1:1:1. 



The derivative, therefore, is a compound of the same order as 

 the original stilbite, with the ratio of 1 : 7 still holding between 

 the ortho- and trisilicate groups. This conclusion, however, 

 ignores the presence of chlorine, and is, therefore, inexact to 

 some extent. We are not dealing with ideally pure com- 

 pounds. 



