STATE GEOLOGIST. 300 
found satisfactory in practice, but it is liable to reject cements. which 
are really good. Thus a silicilous cement may not pass this test simply 
because in the 24 hours its hardening has not progressed sufficiently to 
withstand the mechanical action of the water, while at. the same time a 
rapidly hardened aluminous cement may test normally. In all these tests 
the mere coming off of the pat from the glass should not count against 
the cement. 
| | lll rn | 
| 
R = 5 y 5 ¥ c teed = 5 ~ % “ a ip 
Ros, IY L OAK 
Fig. 74. A Martens apparatus, showing ten cement blocks under observation for 
change of volume, 
The last word has not yet been said in regard to these tests and 
future work will clear up many difficulties attending our tests for con- 
stancy of volume. . 
In Europe still more rigid tests are practiced, like the hot flame test 
and the high pressure steam tests. 
Calorimeter Test.—An auxiliary test made mention of before is the 
determination of the heat of hydration. It is well known that aluminous 
