28 Clarice and Steiger — Action of Ammonium Chloride. 



On boiling with sodium carbonate, 137 per cent of silica 

 went into solution. After ignition, only 1*03 per cent w T as 

 obtained. No silica, therefore, is split off when stilbite is 

 ignited. If the mineral were a hydrous acid metasilicate, 

 H 4 CaAl 2 Si 6 ]8 . 4H 2 0, as has been assumed by some authori- 

 ties, one-third of the silica should have been set free. Hence 

 the metasilicate formula is to be regarded as unsatisfactory. 

 The evidence here presented counts for something against it. 



Two samples of the ammonium chloride derivative were 

 prepared. In leaching with water the insoluble residue was 

 washed until the washings gave no reaction for chlorine. The 

 chlorine shown in the subjoined analyses is, therefore, present 

 in an insoluble form, and not as adhering ammonium chloride. 

 Dried at 50°, the two products gave the following composition: 



A B 



Si0 2 60-80 60-67 



A1 2 3 18-36 18-25 



CaO ]-86 1-46 



Na 2 -08 -15 



NH 3 5-12 5-13 



H 2 0_ 12-96 13-91 



CI 1-31 1-04 



100-49 100-61 



Less O -29 -23 



100-20 100-38 



Sample B was further examined as to the presence of soluble 

 silica, and 1*52 per cent was found. After ignition, only 

 1*62 per cent went into solution. These results conform to 

 those obtained with the original stilbite, and tend to show that 

 the ammonium derivative is a compound of the same order. 

 In the case of the unignited substance the residue remaining 

 after the removal of soluble silica was thoroughly washed, and 

 then examined for alkali. It was found to contain 9*30 per 

 cent of soda, which shows that the ammonium salt had been 

 transformed back into the corresponding sodium compound. 



From the foregoing facts it is clear that stilbite, like the 

 zeolites previously studied, is converted by the action of 

 ammonium chloride into an ammonium salt. That is, sodium 

 and calcium are removed as chlorides, ammonium taking their 

 place to form ammonium-stilbite. The reaction, however, is 

 less complete than it was in the cases of analcite and natrolite, 

 but whether this is due to a greater stability of the stilbite 

 molecule, or only to a different degree of fineness in the 

 powder upon which the operations were performed, we cannot 



