LIME AND CEMENT INDUSTKIES 73 5 



Portland cements, is considerable (at least seven days, if a reason- 

 ably reliable indication is to be obtained), and, as work is usually 

 carried on, is frequently impracticable. For this reason, short 

 time tests are allowable in cases of necessity, though the most 

 that can be done in such testing is to determine if the brand of 

 cement is of its average quality. It is believed, however, that 

 if a neat cement stands one day tensile test, and the tests for 

 checking and fineness, its safety for use will be sufficiently indi- 

 cated in the case of a brand of good reputation; for, it being 

 proved to be of average quality, it is fair to suppose that its sub- 

 sequent condition will be what former experiments, to which 

 it owes its reputation, indicate that it should be. It can not be 

 said that a new and untried cement will by the same tests be 

 proved to be satisfactory; only a series of tests for a considerablo 

 period, and with a full dose of sand, will show the full value of 

 any cement; and it would be safer to use a trustworthy brand 

 without applying any tests whatever than to accept a new article 

 which had been tested only as neat cement and for but one day 

 only. 



The test for compressive strength is a very valuable one in 

 point of fact, but the appliances for crushing are usually some- 

 what cumbersome and expensive, so much so that it seems un- 

 desirable that both tests should be embodied in a uniform method 

 proposed for general adoption. Where great interests are at 

 stake, however, and large contracts for cement depend on the 

 decision of an engineer as to quality, both tests should be used 

 if the requisite appliances for making them are within reach. 

 After the tensile strength has been obtained, the ends of the 

 broken briquets, reduced to one inch cubes by grinding and rub- 

 bing, should be used to obtain the compressive strength. The 

 adhesive test, being in a large measure variable and uncertain 

 and therefore untrustworthy, is not recommended. 



The strength of a cement depends greatly upon the fineness to 

 which it is ground, especially when mixed with a large dose of 

 sand. It is, therefore, recommended that the tests be made with 

 cement that has passed through a no. 100 sieve (10,000 meshes 

 to the square inch) made of no. 40 wire. Stub's wire gage. The 

 results thus obtained will indicate the grade which the cement 

 can attain, under the condition that it is finely ground, but it 

 -does not show whether or not a given cement offered for sale 

 shall be accepted and used. The determination of this question 



