C. Barus — Note on Volcanic Activity. 483 



Art. XLY. — Note on Volcanic Activity • by C. Bakds. 



1. Last year* I published a brief discussion on the origin 

 of volcanic heat containing, as I think, certain features of 

 sufficient interest to deserve a more definite statement. The 

 remarks were based on the experiments which I described some 

 time ago,f showing that water glasses may be made in the 

 laboratory which melt (aqueous fusion) even below 200° C. 

 In their general physical properties like density, hardness, 

 refraction, etc., these glasses need not differ remarkably from 

 ordinary igneous glasses, in spite of the content of water in the 

 first case. The solution takes place under a contraction of the 

 system (liquid water and glass) of from 20 to 30 per cent ; and 

 it occurs more rapidly as the temperature of the system is 

 higher, the observations extending from between 180° and 

 300° C. 



That water may be kept liquid near the shores of an ocean, 

 even if it should, by some accident, penetrate as far as an iso- 

 therm of several hundred degrees C, will at once be granted. 

 Similarly other properties of this volcanic mechanism fit the 

 actual occurrences fairly well, as was pointed out in the articles 

 cited. Thus the contraction of the system is favorable to the 

 evolution of heat ; a region of activity comparable in depth with 

 the depth of the ocean may be inferred ; etc. 



2. My purpose in the present note, however, is to dwell more 

 specifically on the phenomenon of diffusion. I have argued 

 that since water is more rapidly soluble in glass at 300° than at 

 200°, diffusion of liquid water would take place from the lower 

 to the higher temperatures, and that the larger vapor pressures 

 associated with the higher temperatures would have no appre- 

 ciable bearing on the phenomenon. However we may approach 

 the order of values of osmotic pressure, they are usually to be 

 estimated in thousands of atmospheres. 



In the case of dilute solutions (for which there is an adequate 

 theory) the increase of a diffusivity D, with temperature, 0, 

 is sufficiently well substantiated. If we take J*\ ernst's expres- 



n x +n; 



sion, D increases both with the absolute temperature 6 and with a 

 mobility, O x and U 2 of the ions. True the case of solution of 



* Science, xxiv, p. 400, 1906. 



t This Journal, xlvi, p. 110, 1891: vii, p. 1, 1899: ix, p. 161, 1900; Phil. 

 Mag., xlvii, pp. 104, 461, 1899. 



Am. Jour. Sci.— Fourth Series, Vol. XXIV, No. 144.— December, 1907. 

 34 



