STATE GEOLOGIST. a47 
Both the tensile and crushing strengths vary with the same cement, 
due to the influence of several important factors, which are: 
1. Amount of water used. 
2. Kind of sand employed. 
3. Mode of preparing the test piece. 
Amount of Water.—In German practice the proper proportion of 
water for a given 1:3 mixture is determined by mixing the sand and 
cement, dry, in a standard mixer, adding water, mixing wet for 12 minute, 
[| 
(rcs 
Tm 
in 
ml 
LICL LI 
BQliana 
Fig. 67. Portable machine for crushing large concrete cubes. 
and transferring to a cubical mold provided with a top plate. This plate 
is now subjected to a number of blows from a standard hammer and if 
between the goth and 11oth blow cement paste begins to leak out of the 
mold box the amount of water is considered sufficient. If not, another 
batch of cement is made up with more water. By experience, however, 
it becomes possible to tell without any elaborate apparatus just when the 
proper amount of water has been added. If an insufficient amount of 
water is used, hydration will not take place to its full extent and hence 
the cement will be weaker than its normal strength. If too much water 
is used the resulting porosity will be too great and hence the strength 
is again decreased. 
