PACINI, METAMORPHISM OF PORTLAND CEMENT 



217 



TABLE 26 

 Tensile Strength of 1:4 Mortars, stored in Rock Water 



TABLE 27 

 Analyses of Rock Waters in Previous Experiments 



The drinking water used to store the blanks contained in neither case 

 more than 100 parts per million of total solids. 



The most consistent reduction of strength, although a slight one, is 

 observed in the case of water B, a fairly typical sulphato-chloride water 

 according to Clarke's classification (18, p. 190). A strikingly high and 

 sudden reduction occurs at six months in water A, a sulphate water 

 charged with hydrogen sulphide, while water C, a chloride water, shows 

 no marked reduction of the strength, which, however, may be due to a' 

 low salinity. 



The six-month briquettes stored in water A showed superficially much 

 minute pitting, due to the removal of the sand grains, presumably by 

 solution of the matrix of the cement. Two sections were cut from one 

 of these briquettes, one transverse and one longitudinal, in the hope of 

 discovering whether any replacement of the original material by sul- 



