218 ANNALS NEW YORK ACADEMY OF SCIENCES 



phates or sulphides was going on. The microscopic examination did not 

 reveal anything of the sort, the sections being in all respects similar to 

 sections cut from the briquettes stored in drinking water. It was con- 

 cluded therefore that the loss of strength was due to actual removal of 

 material by solution rather than by replacement with material which 

 would cause disintegration through a discrepancy in volume. 



The legitimate general deduction from these tests is that, over the 

 period of experiment, the effect of these waters is greater in void filling 

 by crystallization or precipitation than in disintegration by solution or 

 disruption. 



The void-filling material, if of a stable nature and not likely to return 

 into solution, should be in a measure a protection against the further 

 entrance of the saline solutions. It has been mentioned that this prop- 

 erty has been suggested of magnesium hydroxide (70). Probably upon 

 this possibility is based the reported effect of chemically inert fine ma- 

 terials, added to the cement for protection against such destructive 

 action. 



Summary of Experimental Eesults 



1. Increase of temperature of the water with which cement is mixed 

 causes acceleration of the set up to a certain maximum temperature, 

 then a retardation. 



2. Storage in cold water, without freezing, retards the hardening of 

 neat cement, and that of mortars more. 



3. Increase in the proportion of fine particles in a cement decreases 

 the permeability of mortar made therefrom. 



4. Mechanical agitation increases the strength of cement up to a cer- 

 tain maximum time; after which, if continued, it reduces it. 



5. The setting of cement is accelerated by dryness of the atmosphere. 



6. An excess of mixing water progressively reduces the strength of 

 cement. This effect is partly reversive of itself, and the reversion may 

 be increased by additional colloidal material in the original cement. 



7. Water percolating through concrete dissolves the lime of the ce- 

 ment chiefly, and this effect tends to neutralize itself by "healing." 



8. Percolation through concrete preferably follows the bedding planes. 



9. Salts in solution in the mixing water tend to lower the strength of 

 cement. This effect may be neutralized by precipitation in the pores. 



10. Storage in saline water affects low silica cements more than it 

 does high silica, and coarsely ground cements more than it does finely 

 ground cements. 



