PHYSICAL AND CHEMICAL PROPERTIES. PARTS IV, V. 161 
in this connection the fineness of the cement must be taken into 
consideration, but provided the cements are ground to ordinary 
fineness the general relationship seems to exist regardless of 
the cause of the low density. 
The results given are characteristic of those obtained from our 
entire series of experiments. Aération seemed to effect the early 
compressive strength of the broken briquettes and the tensile 
strength in a similar manner. The results obtained by crushing 
larger specimens which had been stored in the same manner as 
the briquettes (Table L) are given in Table LI. 
TABLE LI. Compressive strength of 8” x 4 cylinders of 1:3 Pasig sand 
mortars showing the characteristic results obtained with aérated and 
nonaérated, soft and hard-burned cement. 
Compressive 
Constituents of 1:3 strength in 
3 mortars. pounds per 
Specific square inch. 
A Cement. gravi- 
x ty. e 
5 asig: 3 
& Saas Cement.| Water. Ponies 1 year. 
Grams. | Grams. | Grams. 
(e} Nstreceivedssesss=2226 82-222 tee 3.11 820 272, 125 2,880 | 3,.720 
Cc Aérated 3 months___ = 2.99 820 272, 130 1,728 | 2,982 
D As received ____-____ = 3 2.99 820 272 135 2,148 | 3,386 
D Aérated 3 months 2.91 820 272 150 1,104} 2,172 
The low gravity may be the result of premature caking or 
partial induration. It is well known that regauged cements 
harden very slowly. The addition of foreign substances to the 
cement, such as clay, sand, or slag, produces the same effects. 
Adulterated Portland cements are seldom met with, but sample 
B (see table of chemical analyses Appendix 1, Parts 1 and 2) 
must be considered as such since it contains 11.2 per cent of 
clay and sand. 
Decidedly underburned cements fresh from the kiln may have 
high specific gravities but such cements seasoned sound have a low 
Specific gravity, a high loss on ignition, and harden slowly. The 
proof that cements C and D are of this class lies in the fact that it 
is practically impossible to season good, hard-burned Portland 
cement clinker to the extent shown by these samples. Further- 
more, these cements contained so much free and slaked lime that 
which would necessitate the prolonged exposure of the cement in thin, 
frequently turned layers) to a low gravity and then regrinding it. Such 
treatment would often increase the efficiency of Portland cement both in 
sand-carrying capacity and constancy of volume, but it is too expensive to 
be practical. 
