326 COX, REIBLING, AND REYES. 
Quarry débris, soft stone, and volcanic tuff are often suitable 
sources of silica and in many instances are capable of being 
crushed into desirable sand at no greater cost than that required 
for the installation of the division method. Siliceous sands, soft 
sandstone, and volcanic tuff are plentifully distributed through- 
out the Philippine Islands. 
Richly colored siliceous materials naturally give bricks of a 
similar color, but otherwise a pleasing white to gray is obtained 
which is more or less spotted according to the color, quantity, 
and shape of the coarse grains. The color is permanent, unless 
oxidizable mineral pigments such as iron are present. 
Lime.—In ordinary lime mortar, magnesia is not considered 
detrimental, but it can not be substituted for calcium oxide in 
the sand-lime brick industry on account of its slow slaking prop- 
erties. Other impurities in the limestone, such as sand, clay, 
and iron oxide, should also be avoided. They tend to produce 
slow slaking, fluxed and overburned lime,® as well as to decrease 
the efficiency by dilution. On the other hand, a comparatively 
pure calcite limestone gives the best results, and can be burned 
and slaked with the least expense and difficulty. It is absolutely 
necessary that the free lime be thoroughly hydrated before the 
bricks are molded; otherwise, the expansion due to subsequent 
hydration is very apt to cause the bricks to swell or crack and 
split. 
In the Philippines, the most generally distributed calcareous 
material is a hard limestone of Miocene age which is usually 
associated with shales and sandstones. It occurs abundantly 
on nearly every island of the Archipelago and is uniformly 
remarkably pure.*° Its fitness for the sand-lime brick industry 
is demonstrated by the analyses given in Table III. 
*The evil effect of free lime and magnesia in sand-lime brick is in 
all respects similar to their effect in indurated Portland cement, and 
the slaking properties of free lime under all conditions of burning, grind- 
ing, and seasoning are important considerations. Cf. Reibling W. C. 
and Reyes, F. D., This Journal, Sec. A (1910), 5, 117-142; (1911), 6, 
207-252; (1912), 7, 185-191. 
* Cox, A. J., This Journal, Sec. A (1909), 4, 211; Pratt, W. E., Min. 
Resources P. I. for 1910, Bur. Sci., Div. Min. (1911), 61. 
