5 i6 AUSTIN F. ROGERS 



school of mineralogists, recognized colloids under the name poro- 

 dine substances as early as 1817. 1 He called attention to the 

 fundamental differences between the crystalline and amorphous 

 conditions and divided amorphous substances into two groups : the 

 hyaline (glasses) and porodine ("guru-en" or gels). Breithaupt 

 knew of the researches of Graham before the publication of 

 the latter' s discovery of dialysis and stated that his group of 

 "guhren" was identical with the laboratory products of Graham. 

 The application of colloid chemistry to mineralogy has been 

 pointed out by Cornu and others in a series of papers published in 

 1909 2 , and more recently Marc and Himmelbauer 3 have contributed 

 an excellent summary and bibliography of the whole subject. 



CONFUSION OF THE TERMS AMORPHOUS AND COLLOIDAL 



While the study of the amorphous condition involves a study 

 of the colloidal or "dispersed" state, the terms amorphous and 

 colloidal are not synonymous. Amorphous is the broader term. 

 Ordinary glasses are amorphous but not colloidal, although some 

 varieties of glass may be colloidal (e.g., opalescent glass). Col- 

 loids are microheterogeneous systems made up of two phases, one 

 dispersed through another. 



Most of the amorphous minerals are hardened hydrogels. The 

 water present is usually considered to be adsorbed water. It 

 may be adsorbed water when the colloid is first formed (even this 

 fact is doubted by Robertson), 4 but after hardening, the water may 

 be present in solid solution. 5 Hyalite opal, for example, is appar- 

 ently a microhomogeneous substance, and there is no reason why 

 it may not be looked upon as a true solution of water in silica. 

 Hence it is possible, and even probable, that the mineral hydrogels 

 are not, properly speaking, colloids, but only colloidal in origin. 



1 Cornu, Zeit.f. Chem. u. Ind. d. Kolloide, IV (1909), 300-4; Hunt, Systematic 

 Mineralogy, New York, 1891, p. 10. 



2 Ibid., IV, 15, 89, 187, 188, 189, 275, 285, 291, 295, 298, 300, 304, 306. 

 ^ Fortschritte der Min., Krist., u. Petrog., Ill (1913), n, 3 2 - 



4 Zeit.f. Chem. u. Ind. d. Kolloide, III (1908), 49. 



s The fluorin content of collophone mentioned later in this paper is an argument 

 in favor of the solid solution theory of hydrogels. 



