304 ANNUAL REPORT 
is gradually heated till boiling and kept so for at least three hours. If the 
cement is sound the pat, though it may come off the glass plate, should 
be straight, free from radical cracks, and if a piece is broken off the edge 
it should break with a clear, sharp sound. If the pat is soft or cracked 
or partially disintegrated or warped, the cement is not considered sound. 
” i 
JANN. 5 
a Fig. 73. Partial vertical cross-section 
through mechanism of Martens appara- 
Fig. 72. Vertical section through Mar-= tus, showing method of transmitting and 
tens apparatus for measuring constancy magnifying changes of length of cement 
of volume. block on which the apparatus rests. 
The steam test differs only in that the pat is placed on a wire netting 
in an atmosphere of steam at about go° C., without contact with water. 
This test is not as severe, as it eliminates the mechanical action of the 
boiling water. 
In the warm water test the pat is placed in water at about 45° C-. 
and kept there for 24 hours. : 
In the normal water test the pat simply remains in water at about 
21° C. for 28 days. Any of the evidences mentioned under the boiling 
test will disqualify a cement. Warping may be detected by applying a 
straight edge to the surface which was in contact with the plate. 
The boiling test is the most severe test and it may be said that, 
roughly speaking, nine out of ten cements which stand this test will be 
