80 



A TREATISE ON METAMORPHISM. 



0° C. and 100° C. are shown by fig. 2, taken from Ostwald. For various 

 substances the maximum capacity for solution lies between 60° and 140° 

 C, and for many substances it is probably below 200° C. It therefore 

 follows, in respect to underground solutions, that a general statement can 

 not be made as to how change of temperature may affect solubility. 

 However, it is highly probable that up to temperatures of 100° C, and 

 therefore under normal conditions to depths of 3,300 meters, increase of 

 temperature increases the average capacity of underground water to hold 

 material in solution; and it is probable that the average capacity of 

 ground water increases to temperatures considerably above 100° C, and 

 therefore to depths greater than 3,300 meters. But when water passes 

 downward to the deeper parts of the zone of fracture the increase in temper- 

 ature may lessen the average capacity for holding material in solution, 



provided the joint effect of pressure be 

 barred. But it has been seen that increas- 

 ing pressure with increasing depth pro- 

 motes solubility. It is almost certain that 

 high temperature and pressure combined 

 greatly increase the capacity of water for 

 solution. This is proved by the experi- 

 ments of Barus upon the solubility of 

 glass. He has shown that at temperatures 

 above 185° C. and below 200° C it is possible "to impregnate glass 

 with water to such an extent as to make it fusible below 200° C. The 

 solution occurs with contraction of bulk relatively to the ingredients and 

 increasing compressibility." . . . "If these solutions are sufHcientlv 

 concentrated they coagulate at ordinary temperature and the congealed 

 aqueous glass is not different in general appearance from common glass. 

 The melting" point of the coagulated aqueous silicate frequently lies below 

 200° C, probablv above 150° C, depending on the glass." And he con- 

 cludes that "Glass as a colloid is miscible in all proportions with water." 6 



Since glass is one of the important silicate rocks which occur in nature, 

 these statements are directly applicable to one set of rocks. They may 



"Ostwald, W., Grundlinien der anorganischen Chemie, Engelmann, Leipzig, 1900, p. 222. 

 t> Barus, C, Remarks on colloidal glass: Am. Jour. Sci., 4th ser., vol. 6, 1S98, p. 270. See also Am. 

 Jour. Sci., 4th ser., vol. 9, 1900, pp. 161-175. 



10° 20° 30° 40° 50° 60° 70° 80° 90° 100° 

 Temperature. 



Fig. 2.— Quantitative relations between solution and 

 temperature. After Ostwald. 



