PACINI, METAMORPHISM OF PORTLAND CEMENT 171 



lishing whether "wet" or "dry" mixes best resist the disruptive effects of 

 frost during setting. The results reported are discordant. An excess of 

 water has been found by one investigator to enhance the effects of frost 

 (85), while by another it has been found to diminish them (11). Theo- 

 retically, Mie disruptive effects of freezing should be enhanced by the 

 presence in the mass of larger quantities of gaging water. On the other 

 hand, it can be assumed from the colloidal standpoint that an increase in 

 the amount of water present will result in the formation of a greater 

 quantity of colloids and a greater elasticity of the resulting mass, to- 

 gether with a smaller total breakage of cell-wall material. 



TEMPERATURE OF THE WATER THAT MAY SUBSEQUENTLY COME IXTO 

 CONTACT WITH THE SYSTEM 



The action of hot and boiling water upon set cement is strongly 

 marked in the case of cement which contains free lime, producing after 

 a few hours, swelling, distortion and cracking and even total disintegra- 

 tion. A normal cement so treated, however, preserves its original form 

 and volume after short periods of exposure to the boiling temperature. 

 The viscosity of water at high temperatures is greatly diminished, and 

 the liquid is thereby enabled to penetrate more rapidly the capillary and 

 subcapillary voids, thus reaching more quickly a larger internal area. 

 If, as in the case of an unsound cement, free lime is thereby reached, this 

 is slaked much sooner than it would be under normal conditions, and 

 moreover with great violence, owing to the higher temperature of the 

 water, producing internal disruption, and perhaps thus opening up fur- 

 ther avenues to the penetration of water, with a repetition of the slaking 

 process. 



The boiling test here described is a very important one in the testing 

 of cement for construction, but it is perhaps less reliable in the case of 

 unsoundness from the presence of excess of magnesia. 



In cements stored in waters of relatively high temperature, it is prob- 

 able that the processes of solution act more rapidly, from the two reasons 

 mentioned above ; but evidence is lacking to show that any significant 

 decrease in ultimate strength is thereby occasioned. 



Data as to the storing of cement in waters of low temperature, yet not 

 subjected to the action of frost, are not available in the literature, but 

 they would be interesting. 



In the case of exposure to the action of frost, the process is quite 

 similar to that which goes on in the disintegration of natural rocks and 

 depends, in like manner, upon the initial mechanical resistance of the 



