Allen and Clement — Bole of Water in Tremolite. 103 



an essential constituent. While work on this subject was in 

 progress, Penfield and Stanley- published the analyses of a 

 number of amphiboles, including two tremolites, all made on 

 very carefully selected material, in which it was found that all 

 contained notable quantities of water and fluorine. While our 

 results conlirm theirs in regard to water, it may be noted in 

 passing that fluorine is entirely absent from one of our speci- 

 mens and occurs in quite insignificant quantities in one or two 

 others. It is not, therefore, to be counted an essential constit- 

 uent. 



The role of the water. — The next question to present itself 

 is : What part does the water play in the constitution of the 

 mineral? Is it chemically combined or dissolved, i. e., does it 

 escape at one or more temperature 

 points with a sudden change in phys- 1 



leal properties, or is it given off grad- 

 ually through a range of temperatures, 

 the physical properties varying with 

 the change in composition ? 



Tammann,f in attackiug a similar problem 

 with the zeolites, used the method originated 

 by Yan Bemmelen. The powdered minerals, 

 in small beakers, were left to stand, at con- 

 stant temperature (19°), in desiccators with 

 sulphuric acid of various concentrations, the 

 vapor pressures of which were known, until 

 the weight became constant. This method 

 had the disadvantage of removing only a frac- 

 tion of the total water, 1*1 per cent to 23 per 

 cent, according to the mineral, leaving one 

 still in doubt about the major part of the 

 water. This difficulty is obviated by the more 

 direct method of Friedel,;}: who heated the 

 zeolites, at progressively higher temperatures, 

 in a current of air which was saturated with 

 water at an approximately constant tempera- 

 ture, this temperature remaining nearly the 

 same in all the experiments of any one series. 

 Be found thus for several zeolites true 

 equilibria at every temperature. Thti4oe[ement. " 



The Apparatus. — Some preliminary experi- 

 ments on tremolite suggested that the vapor pressure, even at 

 higher temperatures, would probably fall practically to zero 

 within a limited time. We therefore adopted Friedel's method, 



*This Journal (4), xxiii, p. 23, 1907. 



fZeitschr. Phys. Chem., xxvii, 328, 1898. 



{Bull. Soc. Min., xix, 363, 1896 ; xxii, 5 and 86, 1899. 



