39^ REVIEWS 



The brilliant investigations of Vant' Hoff along this line do not seem 

 to have been applied as yet to the problems of petrology. 



After showing that the law from which he calculates the rate of 

 molecular diffusion is good only for dilute solution, Dr. Becker says: 

 " Magmas must be regarded as solutions of a series of very similar sub- 

 stances, and it is known that in such cases the solubility of each is 

 diminished by the presence of the others." 



This law holds only for salts dissolved in a dielectric, and is due to 

 equilibrium relations between free ions and the undissociated portion 

 of the salts. By "a series of very similar substances" is evidently 

 meant a series of salts the members of which have some common ion or 

 ions. If the data in the paper on the change of electric conductivity 

 observed in rocks of different composition, while passing from liquid 

 to solid, by Carl Barnes and J. P. Iddings,' are sufficient to prove that 

 there is electrolytic dissociation in igneous magmas, then Dr. Becker's 

 method is correct, and we need only to examine his assumptions on the 

 viscosity, etc., of the lavas. If these data are insufficient to close the 

 subject then Dr. Becker is reasoning from premises not yet proved. 



Admitting, however, that the weight of evidence is with Dr. Becker 

 on this point we may examine his views on the viscosity of lavas, for 

 although of importance to his conclusions regarding segregation of 

 miscible liquids, the value of his objections to segregation oi immiscible 

 liquids, depends upon the correctness of his assumptions on this point. 

 He states that "There is some reason to think that the viscosity of even 

 the most fluid lavas is more than fifty times as great as that of water." 

 This is drawn (i) from a comparison of the speed of the flow of lava 

 from Kilauea, with that of a stream of water of the same cross section 

 and flowing down a slope of the same grade. (2) Since banded rhyol- 

 ites show no diffusion of their layers into each other, it follows that if 

 they had viscosity fifty times that of water they would show appreciable 

 diffusion. 



It does not seem probable that the viscosity of an extruded lava 

 would be the same as that of one highly treated and supercharged with 

 vapors. The erupted lava has crusts forming on both outer and inner 

 surfaces. It has lost much of its superheated steam and other vapors, 

 and more or less crystallization has already started throughout its mass. 

 The unerupted lava is permeated with superheated gases, and is at a 

 very high temperature. Of course pressure increases the viscosity and 



' Amer. Jour. Sci. (3), XLIV, 242-249. 1892. 



