Deductions

1. Particles of unground cement exceeding 1/50 of an inch in diameter may be allowed in cement paste without sand, to the extent of 50 per cent, of the whole, without detriment to its properties, while a corresponding proportion of sand injures the strength of mortar about 40 per cent.

Loaded partly along the bricks, and broke through them.

2. When these unground particles exist in cement paste to the extent of 66 per cent. of the whole, the adhesive strength is diminished about 28 per cent. For a corresponding proportion of sand the diminution is 68 per cent.

8. The addition of siftings exercises a less injurious effect upon the cohesive than upon the adhesive property of cement. The converse is true when sand, instead of siftings, is used.

4. In all the mixtures with siftings, even when the latter amounted to 66 per cent. of the whole, the cohesive strength of the mortars exceeded its adhesion to the bricks. The same results appear to exist when the siftings are replaced by sand, until the volume of the latter exceeds 20 per cent. of the whole, after which the adhesion exceeds the cohesion.

5. At the age of 320 days (and perhaps considerably within that period) the cohesive strength of pure cement mortar exceeds that of Croton front bricks. The converse is true when the mortar contains 50 per cent. or more of Band.

6. When cement is to be used without sand, as may be the case when grouting is resorted to, or when old walls are to be repaired by injections of thin paste, there is no advantage in having it ground to an impalpable powder.

7. For economy it is customary to add lime to cement mortars, and this may be done to a considerable extent when in positions where hydraulic activity and strength are not required in an eminent degree.