390 COX, REIBLING, AND REYES. 
of lime are required for suitable results.t On the other hand, 
the durability of lime mortar is unquestionable. Lime-mortar 
brick buildings in Germany, England, and America which can 
be readily traced considerably over fifty years are still in 
excellent condition. More rapid and efficient methods of ac- 
complishing the same results have practically abolished this 
process of manufacture, but in some parts of the Philippine 
Islands the conditions are such that the old process might be 
employed with success. In Masbate, Surigao, Cebu, Benguet, 
and other provinces there are places where an abundance of 
firewood, limestone or seashells, and sand are available; and 
in such places the ordinary laborer could build his own lime- 
kiln and wooden molds and manufacture mortar brick without 
capital. 
When it was discovered that mortar brick hardened equally 
well in an atmosphere of carbon dioxide or waste furnace gases, 
the factor of time was largely eliminated. The process was 
further improved by molding the bricks under great pressure 
and also by hardening with carbon dioxide (CO.,) under pres- 
sure. We do not believe that any of these methods will ever 
become of commercial importance, because the conversion of 
lime into calcium carbonate is confined more or less to exposed 
surfaces of the mortar as well as to the individual particles, and 
this precludes the possibility of great strength and uniform and 
reliable results. 
CALCIUM HYDROSILICATE BINDER. 
In 1880 the researches of Michaelis Sr. of Berlin resulted in 
the process of making sand-lime brick in which the sand par- 
ticles are bound together by calcium hydrosilicate. The principle 
involved is very simple. Sand or finely crushed stone is thor- 
oughly mixed with about 10 per cent of slaked lime and the moist 
mixture molded under great pressure into any desired shape. 
When molded, the bricks are piled on trucks and wheeled into 
a large steel chamber where they are subjected to the action of 
live steam under pressure. The time required for proper steam- 
ing depends upon the steam pressure employed, but eight hours 
at 130 pounds per square inch (9.13 kilograms per square centi- 
“The crushing strength of lime mortar is only about 150 to 300 pounds 
per square inch (10.5 to 21.1 kilograms per square centimeter) and this 
maximum strength is attained in about one and one-half years. 
