378 ANNUAL REPORT 
breaks the briquette before the ultimate strength is reached. Care must 
be taken that the clips and the sides of the briquettes be clean and free 
from sand or dirt, which would prevent a good bearing. The load should 
be applied at the rate of 600 pounds per minute. The average of the 
briquettes of each sample tested should be taken as the test, excluding 
any results which are manifestly faulty. 
CONSTANCY OF VOLUME. 
69, Stenificance.—The object is to develop those qualities which 
tend to destroy the strength and durability of a cement. As it is highly 
essential to determine such qualities at once, tests of this character are 
for the most part made in a very short time, and are known, therefore, as 
accelerated tests. Failure is revealed by cracking, checking, swelling or 
disintegration, or all of these phenomena. A cement which remains 
perfectly sound is said to be of constant volume. 
70. Method.— Tests for constancy of volume are divided into two 
classes: (1) normal tests, or those made in either air or water maintained 
at about 21° C. (70° F.) and (2) accelerated tests, or those made in air, 
steam or water at a temperature of 45° C. (115° F.) and upwards. The 
test pieces should be allowed to remain 24 hours in moist air before immer- 
sion in water or steam. 
Fine How these tests, pats, about 72cm 9(2.O5em)) sit) sciamever: 
14% cm. (0.49 in.) thick at the center, and tapering to a thin edge, 
should be made, upon a clean glass plate (about 10 cm. (3.94 in.) 
square), from cement paste of normal consistency. 
72. Wormal Test.—A pat is immersed in water maintained as near 
21° C. (70° F.) as possible for 28 days and observed at intervals; the 
pat should remain firm and hard and show no signs of cracking, distortion 
or disintegration. 
73. Accelerated Test.—(a) A pat is placed on a shelf in a suitable 
vessel filled with fresh water, but without allowing it to touch the bottom. 
The water is then gradually raised to a temperature of 45° C. (115° F.) 
and maintained at this temperature for 24 hours; or (b), a pat is exposed 
in any convenient way in an atmosphere of steam, above boiling water, in 
a loosely closed vessel, for 3 hours. 
74. lo pass these tests satisfactorily, the pats should remain firm 
and hard, and show no signs of cracking, distortion or disintegration. 
75. Should the pat leave the plate, distortion may be detected best 
with a straight-edge applied to the surface which was in contact with 
the plate. 
76. In the present state of our knowledge it cannot be said that 
cement should necessarily be condemned simply for failure to pass the 
accelerated tests; nor can a cement be considered entirely satisfactory 
simply because it has passed these tests. 
