8 EFFECT OF WATER ON ROCK POWDERS. 



esting point was whether the increased binding power of ordinary 

 rock dusts was due to analogous if not similar causes. 



Before describing further experimental work it will be necessary to 

 present some of the physical-chemical theories, which are advanced to 

 account for the constitution and structure of all substances formed 

 from an originally fluid or molten condition. To quote Van't Hoff: a 



We are certainly entitled to speak of solid solution in certain definite cases, where 

 the complete homogeneity combined with the possibility of varying composition, 

 which are characteristic of the state of solution, are found. In colored specimens of 

 glass and in isomorphous mixtures of two alums, for example we are just as little 

 able, even with the help of the microscope, to perceive the presence of more than 

 one substance, as in a solution of sugar in w r ater. It is a familiar fact that the ordi- 

 nary colorless alum, when crystallizing from solutions containing the highly colored 

 chrom-alum, forms octahedra more or less tinted with chrom-alum; and yet the 

 most minute observation reveals no gross irregularities in the physical distribution 

 of the material, or any other evidence of lack of homogeneity. In such a case, 

 therefore, we speak of the existence of a solid solution. When the substance is 

 amorphous, as in the case of colored glass, the analogy to a fluid is so complete that 

 the two are connected by a series of more or less viscous mixtures in such a way that 

 no sharp distinction can be drawn. Of course, when the solid solution is crystalline 

 it must be admitted that it differs from a fluid solution fundamentally, in so far that 

 an arrangement of the molecules according to some definite order has taken place. 

 The essential point is that the laws of fluid solutions have been successfully applied 

 to solid ones. 



In accordance with these ideas it is now held that glass is a homo- 

 geneous solid solution of lime, silica, and the alkalis, or better, per- 

 haps, of an alkaline silicate in a calcium silicate in which no crystalline 

 aggregates form as the orginal fluid mass cools. The constitution of 

 igneous rocks is explained by considering that from the original mol- 

 ten magma costal line aggregates, such as feldspar, mica, augite, etc., 

 separate at different temperatures on cooling, though these ma} T be 

 more or less modified by substances retained in solution. In addition to 

 the crystalline constituents, glass-like amorphous bodies occur, which 

 are in the nature of true solid solutions. 



As a result of Richardson's 6 brilliant researches into the constitution 

 of Portland cement, we now know that hydraulic cements consist of 

 solid solutions of certain calcic aluminates in certain calcic silicates. 

 These are formed by the more or less rapid cooling of the cement 

 clinker, which results from heating the proper mixture of lime, alu- 

 mina, and silica to a point where diffusion is complete among these con- 

 stituents. The essential characteristic of such a cement is that when 

 ground to a fine powder and treated with water certain reactions take 

 place at once, which lead in the case of Portland cement to a trydraulic 

 set, that is to say, the cement sets to a solid stone-like mass under 



a Decennial Publications Univ. of Chicago, 2d series, 18 : 59. "Physical chemistry 

 in the service of the sciences." 

 & Cement, 5 : 3, et seq. 



