STATE, GEOLOGIST. 343 
course, the general laws governing the sizing of the sand and the porosity 
with reference to the ultimate strength hold’ good for both kinds of tests. 
But, to illustrate, when clay is added to a sand used in making tensile 
tests the strength apparently is raised considerably, while with the same 
sand mixture the crushing strength, if it rises at all, shows but a small 
increase. 
Fig. 66. Amsler-Laffon machine for crushing test. 
The tensile strength of neat cement increases up to about one year, 
but it reaches its ultimate strength quite closely in three months. The 
tensile strength of the neat cement may vary from 600 to 1,100 pounds 
after three months in water. The crushing strength of neat cement may 
vary from 7,500 to 14,500 pounds per square inch after three months. 
Any decrease in the tensile strength of cement shows the presence of 
mechanical strains in the test pieces or chemical changes, and such 
