168 ANNALS XEW YORK ACADEMY OF SCIENCES 



case of cement and reproduced with synthetic mixtures. What binding 

 power colloidal material may develop is strikingly seen in the case of 

 conglomerates and sandstones in which hydrous silicic acid, aluminic 

 hydroxide or ferric hydroxide has been the cementing material, so that 

 the theory is attended by a high degree of probability. 



On the other hand, it is also quite conceivable that the interlocking of 

 crystalline masses between the grains of cement may account in some 

 measure for the strength. There is definite evidence that calcium hy- 

 droxide does crystallize, and its mineralogical and crystallographic con- 

 stants have been determined (24). 



The two views are not entirely irreconcilable, and it is possible and 

 even probable that, mechanically, the strength of cement acquired by 

 hardening is due to both processes. Whatever be the chemical reactions 

 in detail by which these elements of the structure are produced, the main 

 condition for their occurrence is the presence of water. 



This paper is devoted to an enumeration of the factors which influence 

 the metamorphism caused by water in Portland cement, and the varia- 

 tions in the physical properties of the resulting rock, brought about by 

 varying these factors. 



IXFLUEXCE OF WATER UPOX METAMOKPIIISM 

 The action of water upon Portland cement is a resultant of 



1. The temperature of the water 



A. At first added 



B. That may subsequently come into contact with the system 



2. The quantity of water 



A. At first added 4 



a. Size of cement particles 



b. Mechanical agitation when water is added 



c. Total water added 



B. That may subsequently come into contact with the system 



3. The quality of water 



A. At first added 



a. Having material in solution 



B. That may subsequently come into contact with the system 



a. Having material in solution 



b. Having material in suspension 



4 Owing to the peculiar autoprotective reaction of cement against the action of water, 

 before alluded to, the quantity of water coming into contact with cement is a function 

 of the size of the particles and of mechanical stripping of protective films, as well as of 

 the ratio of cement to water. 



