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340 ANNUAL REPORT 
denting the surface, while the close of the setting is fixed by the point . 
at which a wire 1-24 of an inch in diameter no longer indents the cement. 
Starting from this condition the cement gains in hardening for one or 
more years. In European practice the Vicat needle is employed exclu- 
sively for the determination of the time of setting. This instrument 
consists of a weighted cylindrical rod which slides up or down in guides 
and is provided with an indicator and set screw. (See Fig. 70, p. 372). 
they cross section is) 0 sq. cm. and the weieht) of thes rod: sisy 200 
grams. The cement is molded in a conical recptacle, 65 mm. 
in diameter on top and 75 mm. at the bottom and 40 mm. high. If the 
rod penetrates 5 to 7 mm. the cement is said to have standard con- 
sistency. The lower part of the rod is now replaced by a needle I sq. mm. 
in cross section and enough weight is added to keep the total weight 
equal to 300 grams. As soon as the needle cannot penetrate the cement 
complete setting is said to begin, and when it cannot penetrate the mass 
at all the final setting is considered finished. Some advocate the use of 
thermometric measurements in place of the needle tests, considering the 
setting finished when the temperature of the cement begins to fall. This, 
however, is quite liable to be erroneous and deceiving. | 
The rapidity of the setting of cement is influenced by a number 
of factors, which are as follows: 
~ 
~ 
Amount of water used. 
Temperature of water and air. 
Fineness of the cement. 
Composition of the cement. 
Time and manner of curing cement. 
Catalytic agents added to the cement. 
7. Composition of the water. 
| 
ODS SRE SEES Nr 
In brief, the more water is added above the amount required, the 
slower will be the setting. 
Warm water invariably hastens the setting and it has been found 
by Erdmenger that lukewarm water also increases the ultimate strength 
of the cement. Boiling water, on the other hand, decreases the strength 
of the cement, owing to increased porosity. Cold water causes the set- 
ting to take place more slowly, as we find it to be true in most of the 
chemical reactions. 7 
Fine cement invariably sets faster than coarse cement. 
As we have seen already, aluminous cements set very quickly, as 
well as cements high in lime, while, on the other hand, silicious cements 
tend to set slowly. 
Cement fresh from the kiln is much more rapid than cement which 
has been cured. This is due to the slaking of any uncombined lime as 
well as to the absorption of carbon dioxide. Cured cement when heated 
strongly resumes its initial rapidity of setting. Slow setting cement 
