338 ANNUAL REPORT 
No attempt was made to take into account the heats of the solution. 
We note here values running as high as 6.41 and as low as 0.47 per 
cent., but considering the many possible factors entering into the reac- 
tion it is a significant fact that the thermal values are quite low, not 
exceeding 10 calories. Now we might be led to the general conclusion 
that the higher calorific values are simply due to the hydration of the 
excessive amount of calcium oxide present. But we have no right to 
inmake such an assertion, and, furthermore, experiments quoted elsewhere 
have shown that the amount of lime contained in a cement stands in 
no direct relation to the heat evolved. Certain factors like the amount 
of silica present have a great influence on the heat of hydration. But 
taking the same cement, with the same clay base, the case is different. 
Here we may be able to detect any uncombined lime due to insufficient 
curing or underburning, and, hence, for a given cement we can establish 
a certain thermal limit and the calorimeter becomes a valuable aid. The 
significant fact is also to be noted here that aluminous cements show 
high heats of hydration which drop at once as soon as the clay base is 
enriched in silica. It cannot be denied that in doubtful cases where the 
boiling test is questioned the calorimeter is able to give important con- 
tributory evidence. ‘The calorimeter or an equivalent instrument should 
therefore form a valuable adjunct of every cement laboratory. Tetmayer 
has designed an instrument which is to be used in conjunction with the 
Vicat needle, which consists of a hard rubber casing and rubber cover. 
through which the thermometer is inserted and its readings noted, while 
in the meantime the time of setting is observed by means of the needle. 
This test is employed by a good many cement manufacturers, and the 
“writer was told by several superintendents that they never allow cement. 
to leave the stock house unless its rise in temperature on setting falls be- 
low a given limit. It is a curious fact that a second rise in temperature 
‘takes place with some cements, which often is quite considerable, up to 7 
or 8 degrees Centigrade. _ Just in how far this is related to the setting has 
not yet been determined. The curves of figure 64 show the temperature 
changes observed in four American cements. 
SETTING AND HARDENING. 
These two stages must be clearly distinguished. The first represents 
but a short period, from 15 minutes to 12 hours, while the second may 
extend for a period of years. If cement is made up with from 25 to 34 
per cent. of water, mixed thoroughly for about three minutes and made up 
into a pat, it will be found that after some time it begins to stiffen so 
that it becomes more and more difficult for a needle to penetrate into the 
mass. ‘This first period of the hardening we call setting and its begin- 
ning is determined by the point at which a wire, 1-12 of an inch in 
diameter, loaded with 14 pound, is supported by the cement without in- 
