PHYSICAL AND CHEMICAL PROPERTIES. PARTS IV, V. 177 
In order to secure the greatest early strength, it is necessary 
to sinter or fuse the raw materials at a high temperature. 
The endurance of great early strength, increases in strength 
with age, and constancy in volume are the more satisfactory 
the less free lime or free magnesia the indurated cement con- 
tains. This is corroborated by the fact that in the laboratories 
of many manufacturers it is known that if the material has been 
burned so that the freshly ground product is sound, tests for 
strength are not necessary. We believe that the manufacturers 
should be required to produce a Portland cement which is sound 
when fresh and which accordingly needs no curing whatever 
to enable it to pass the hot tests. 
In order to secure the formation of desirable quick-hardening 
compounds and a minimum of free lime, raw materials must 
be of proper chemical composition, finely ground, very thor- 
oughly mixed, and hard burned. The finished product must be 
ground to extreme fineness and properly packed. Therefore, 
efficiency is obtained at a corresponding expense to the man- 
ufacturer, and cements should be purchased on a basis of quality 
rather than upon a mere consideration of quantity. 
