202 ANNALS NEW YORK ACADEMY OF SCIENCES 



The effect of solution in percolation, then, is to a small degree de- 

 pendent upon the solubility of the components in pure water. This effect 

 diminishes as time goes on, because of the reversion of the soluble ma- 

 terial to a less soluble form and because of the protection afforded by the 

 insoluble portions of the system decreasing the exposed area of soluble 

 material. The washing away of these protecting films will of course 

 neutralize the second factor. The increased solubility of the components 

 of set cement in solutions of various electrolytes is the more important 

 element in percolation. Even a very dilute solution may have tremen- 

 dous total solvent power, when the time element is considered. In fact, 

 it may be that the action of a dilute solution will on the whole exceed 

 that of a concentrated solution, by reason of the greater cementing and 

 choking action of the latter, tending to diminish the quantity of water 

 that may come into contact with the soluble portions. A dilute solution, 

 therefore, with its more insidious attack, is probably more to be feared in 

 the end than the strong brine. 



Observation of the behavior of concretes and mortars during the per- 

 meability tests gives a clue to the balancing of these processes, whether 

 there is a preponderance of cementing and clogging on the one hand, or 

 of solution and erosion on the other. Attempts were made, in the experi- 

 ments noted below, to study chemically the reactions involved, by peri- 

 odical analyses of the percolating water. To this end nearly four hun- 

 dred complete analyses of the effluent water were made. Upon tabulation 

 of these it was observed that any deductions based upon them would be 

 inconclusive, as the chemical composition of the effluent water repre- 

 sented one of a great number of variable factors that might occur at any 

 point either within or without the concrete. The single qualitative 

 generalization, that lime was removed from the cement at a diminishing 

 rate, is the only permissible conclusion from the analytical data. 



The original purpose of these tests was to ascertain the suitability of 

 various aggregates for use in concrete, with reference to their stability 

 in the presence of percolating water. At the conclusion of the series, it 

 was found that the effect of water upon the various aggregates was prac- 

 tically negligible, during the period of observation, and that the action 

 had been confined to the cement of the mortar. The aggregates had been 

 protected from the action of water by the cement, it being probable, how- 

 ever, that a continuation of the tests would have revealed the action of 

 water upon these rocks, when the protective influence was removed. 



A series of sixteen aggregates was used, in as many concrete specimens. 

 Since it is not the purpose of this report to discuss the relative suita- 

 bility of these materials for concrete construction, but only to consider 



