202 The Philippine Journal of Science 1921 
and 1,556 pounds at 58 to 59 days. It is interesting to note 
that there is practically no difference in the average compres- 
sive strength of the youngest specimens in the 1 : 2.5 : 5 and the 
1:3:6 series, these showing 1,098 and 1,068 pounds per square 
inch, respectively. With increasing age both give higher re- 
sults than the richer 1:2:4 series of corresponding ages. 
Briquettes made of the four Iloilo sands in the proportion of 
one part cement to three parts sand all give good tensile 
strengths. Table 2 shows that the 1 : 3 Iloilo sand mortars at 
28 days are, respectively, 79, 91, 95, and 105 per cent as strong 
as the corresponding Ottawa sand mortars. 
ISABELA 
Compressive strengths of concrete specimens from Isabela 
are low. The results given by test pieces coming from Echague 
School are consistent in that the 1:2:4 specimens are the 
strongest, and the 1 : 2.5 : 5 the weakest, the 1:2:5 coming be- 
tween. On the other hand there is very little difference be- 
tween the average strengths of 1 : 2 : 4 and 1:2:5 specimens 
coming from Cabagan Farm School which are aged 71 and 79 
days, respectively. No laboratory mixture of concrete made of 
Isabela aggregates was tested, nor has this laboratory ever re- 
ceived either sand or gravel from this province for test. 
JOLO 
Only two tests, both of laboratory-made mixtures, were made 
of .concrete composed of Jolo aggregates. No field specimens 
from this province have ever been tested at the Bureau of 
Science. Both results, as Table 8 shows, are low and unsatis- 
factory, due largely to the fine, soft, coralline beach sand. 
These and similar aggregates, which occur abundantly in the 
Philippines, should under no circumstances be used in concrete 
work. 
LAGUNA 
Results obtained from Laguna field-made test specimens, 
proportioned 1:3:6 and having ages ranging between 30 and 
39 days, show a higher average compressive strength than do 
those proportioned 1:2:4 and aged 28 to 33 days ; the respec- 
tive figures are 1,180 and 1,075 pounds per square inch. Field- 
made 1:2:4 test pieces aged 35 to 40 days average 1,266 pounds 
per square inch and are therefore not much better than the 
younger, 1:3:6 specimens. Disregarding possible errors, 
these results show that the 1:2:4 mixture is uneconomical, 
since the leaner mixture gives practically the same mean 
strength at a lower cost per cubic meter. The 1 : 2.5 : 5 field 
