STUDIES IN HYDROTHERMAL ALTERATION 



189 



These tubes have a calculated bursting strength of 6,000 pounds 

 to the square inch and have proved highly satisfactory. They have 

 been practically unattacked except by sulphide solutions, in which 

 cases the tubes were found lined with beautiful chalcocite crystals. 1 

 They cost after sealing about one-half as much as Jena bombs of 

 similar size and can be used repeatedly. The oven will accommo- 

 date about fifty such tubes at one time. 



EXPERIMENTAL WORK 



Group I: Effect of pure water on feldspar and hornblende. — In 

 many hydrothermal processes it is not yet clear how significant a 

 role is played by the water independent of the dissolved matter. 

 Hence the first step in this investigation was an attempt to deter- 

 mine the efficiency of pure water in such processes. Accordingly 

 the powdered minerals were covered with 300 c.c. of distilled water 

 in open nickel crucibles with a device for maintaining the water at 

 constant volume. The crucibles were placed on electric hot plates 



TABLE I 



and the water kept boiling for 14 days. At the end of that time 

 the solutions were tested for alkalinity with neutral litmus paper 

 and phenolphthalein. No change of color appeared after five 

 minutes' standing. A similar pair of experiments at 180 C. in the 

 sealed copper tubes ran for 82 days and at the end of that time the 

 solutions were similarly tested and again no alkalinity developed. 

 The minerals were then examined under the microscope and com- 

 pared with slides of untreated mineral (Table I) . No change could 

 be detected. These results are not quite in accord with those of 



1 In certain cases a small amount of copper recrystallized on the plugs, probably 

 owing to the fact that the drawn copper has a higher solution tension than crystalline 

 copper. 



