216 ANNALS NEW YORE ACADEMY OF SCIENCES 



The general deductions from these experiments for the period covered 

 are that the high silica cement, notwithstanding its slower rate of har- 

 dening, resists the action of these dissolved salts better than the low 

 silica cement, and the finely ground cement better than the coarsely 

 ground. Moreover, with the concentrations used, the stronger solutions 

 in nearly every case had a more destructive effect upon the strength of 

 the mortar than the weaker. 



The strengths here obtained by storage in salt solutions are in general 

 decidedly greater than those obtained by storage in fresh water. Ex- 

 amination of the cubes, when removed from the solutions at the end of 

 the test period, revealed under a lens that the exterior was being at- 

 tacked, minute pittings being quite distinct. 



The strength attained by these specimens may be considered as a re- 

 sultant of the balancing of two effects : the deposition of crystallized or 

 precipitated material in the voids, which by packing the spaces with 

 solids will increase the compressive strength; the creation of additional 

 voids by direct solution or by the disruptive effect of metathetically pro- 

 duced material. It is probable that the disintegrating effect for these 

 concentrations is reached considerably beyond three months' exposure. 

 From the increases in the compressive strength, it is likely that at this 

 period a great deal of crystallization or precipitation has proceeded, 

 overbalancing in the main the disruptive effects. This is a general 

 deduction, and single instances are notable in which the reverse holds 

 good. 



In the case of the finely ground cement, the density of the mortar 

 made therefrom has prevented the disruptive effect to a greater degree; 

 and thus the deposition, while not necessarily as much as in the coarser 

 cement mortars, has had a more marked effect in increasing the strength. 



Effect of storage in rock water upon the strength of lean cement 

 mortars. — A series of briquettes of 1 : 4 Ottawa sand mortars was made 

 up, using a normal Portland cement of high quality. The mix was made, 

 lean purposely to accelerate whatever disintegrating effect might occur. 

 Batches of the briquettes were stored in bottles in the laboratory for the 

 7-day and 28-day tests, and additional series were stored in the field, for 

 the longer tests, at stations where the waters in question were encoun- 

 tered. The field series were stored in running water, and the action 

 upon these should be more severe than upon the laboratory specimens 

 stored in still water. In each case a parallel test was made by storing a 

 series in pure drinking water. 



