STUDIES IN HYDROTHERMAL ALTERATION 



191 



of one-half normal is equivalent to nearly 2.8 per cent. The 

 minerals in Nos. 5 and 6 showed no change under the microscope. 

 Tube No. 10 burst owing to defective sealing, but the mineral was 

 unchanged. In all the others crystals of analcite formed along the 

 sides of the tubes and around grains of feldspar as nuclei. Solution 

 No. 6 was not saved, but the solutions from Nos. 7, 8, and 9 were 

 placed in paraffin-lined bottles and on examination after several 

 weeks' standing showed heavy gelatinous precipitates. These pre- 

 cipitates were then examined and were found to consist of silica 

 and water. In spite of the fact that tube No. 10 burst, the results 

 obtained from later experiments, notably Nos. 33 and 34, make 

 it certain that similar results would have been secured had no 

 accident occurred. 



These facts indicate definite attack and solution of the feldspars 

 with loss of one molecule of silica from each molecule of feldspar 

 together with an exchange of the potash of the adularia for the soda 

 of the solution. The following equations, using empirical formulae, 

 indicate the reactions, which have positive experimental basis. 



KAlSi 3 8 +H 2 0+Na' -> NaAlSi 2 6 ,H 2 0+Si0 2 +K' 

 and 



NaAlSi 3 8 +H a O+Na' -» NaAlSi 2 6 ,H 2 0+Si0 2 +Na'. 



The analcite was identified optically and also by sifting out the 

 unchanged feldspar with its adhering analcite, gelatinizing the 

 remaining crystals with hydrochloric acid, and allowing a small 

 portion of the solution to crystallize out under the microscope as 

 sodium chloride; the remaining portion of the solution was tested 

 for alumina with ammonia water. After drying at no C, the 

 crystals yielded water in a closed tube. 



Group III: Sodium carbonate solutions on hornblende.- — -A series 

 of experiments, Nos. 11, 12, and 13, exactly like those in Group II, 

 were then tried with hornblende as the mineral (Table III). In no 



