LIME AND CEMENT INDUSTRIES 723 



3 They must be so rigid that they will not spread appreciably 

 when subjected to their maximum load. 



Placing hriquet in machine. This should be carefully done, 

 seeing that not only is the briquet in straight, but also that it 

 has a full bearing surface. The pressure should be applied slowly, 

 not faster than 500 pounds a minute. A note should be made 

 of the number of pounds required to break the briquet and also 

 of the character of the break. When the fracture is uneven, or 

 does not occur at the minimum section, a note is always made 

 of the fact, and the cause of this should be ascertained if possible. 



Sand used. Two kinds of sand are used in cement tests, de- 

 pending on the object for which the tests are being made. In 

 the one case, when the cement is to be used in a particular piece 

 of work, then it should be mixed with the sand that it will be 

 mixed with in the actual work of construction. 



If the cement is being tested simply for comparative purposes, 

 or there is uncertainty as to the quality of the sand, then standard 

 sand should be used. The standard is clean crushed quartz of 

 such size that it will go through a no. 20 sieve, but be retained 

 on a no. 30 sieve. 



After molding and removal from the molds the briquets are 

 set on non-absorbent slabs for 24 hours under a damp cloth, after 

 which they are removed, half of them being put under water. 

 The style of the tanks or pans used varies with the arrangement 

 of the laboratory and the fancy of the person making such tests. 

 The briquets when placed under water are always set on edge. 



Temperature of briquets. I n cements there may be a slight 

 increase in temperature following the molding, which is due to 

 the presence of free lime. In good Portland cements this rise 

 in temperature is very slight, but is often sufficient to be felt 

 by placing the hand on the briquet. In light burned natural 

 cements there is often an appreciable rise in the temperature. 



