332 COX, REIBLING, AND REYES. 
the other. Our bricks were either tested in cubical form or 
standing on their smallest flat surface, and consequently the 
results represent a minimum strength. The strength obtained is 
considered as very satisfactory, and even the lowest is regarded 
as sufficient for ordinary local construction work, as a 1:2:4 
concrete mixture as ordinarily prepared from Philippine aggre- 
gate will crush under a pressure seldom exceeding 2,000 pounds 
per square inch (140 kilograms per square centimeter). On the 
other hand, the poorest result was much stronger than the best 
volcanic tuff. However, it is evident that a high molding pres- 
sure is essential if a strength above 2,000 pounds is required. 
A thorough investigation of the efficiency of the raw materials 
with respect to the fire-resistant properties of the sand-lime 
bricks has not yet been accomplished. Certain samples of the 
sand-lime bricks described in the following pages were heated 
for thirty minutes in a muffle furnace at about 1,100° and then 
quenched in water. Plate VIII shows five instances where the 
bricks remained perfectly sound after such treatment. 
RAW MATERIALS IN THE VICINITY OF MANILA. 
The high cost of land transportation throughout the Philippine 
Islands makes the location of the factory with respect to the 
market and raw materials a consideration of more than usual 
importance. Eventually, sand-lime brick factories should be 
installed at all of the principal commercial centers of the Archi- 
pelago where suitable raw materials are available in order to 
reduce the necessary transportation toa minimum. For several 
years to come the demand in the Philippines will probably not 
be great enough to support more than one, or possibly two, sand- 
lime brick plants; and since Manila appears to be the most 
desirable location for the first plant, the near-by raw materials 
have been given primary consideration. 
Lime.—The most available and important calcareous raw mate- 
rials in the vicinity of Manila are two exposures of Miocene 
limestone, one near Montalban, about 30 kilometers from Manila, 
on a line of the Manila Railroad Company and the other in a semi- 
mountainous country about 7 kilometers north of Binangonan, 
Rizal Province, and about 20 kilometers from Manila. There 
is communication between Binangonan and Manila by means of 
launches and scows via the Pasig River and Laguna de Bay. The 
limestones in both places are hard and crystalline, and the 
deposits are uniform in chemical composition. The analyses 
given in Table VI show that they are almost pure calcite. 
