TESTING OF PORTLAND CEMENT. 333 



provided with appliances for holding the briquettes. It 

 is preferable to have an automatic gear for increasing the 

 load. 



On Fig. 164 is represented a special machine by Messrs. 

 Bailey for cement testing. It will be seen that this is a 

 multiple-lever machine, provided with suitable holders for 

 taking the briquettes. The load is applied by small 

 leaden shot being allowed to run from a stationary reser- 

 voir into a can suspended at the outer end of the weighing 

 lever. When the sample breaks, an automatic catch stops 

 the flow of shot, and the contents of the lower can are put 

 into a weighing scale (as shown in Fig. 165), which is 

 calibrated to give at once, by its reading, the 

 breaking load on the specimen. A similar machine in 

 which the shot has to be supplied by hand is shown 

 on Fig. 166. There are also a pair of cement moulds 

 shown which are not quite the same shape as that on 

 Fig. 163, but have the form used in the German laboratories. 

 A third machine (Fig. 167), also by Messrs. Bailey, works 

 with water instead of shot, and the breaking load is given 

 by the height of the water in the suspended can when 

 fracture takes place. 



Messrs. Adie supply a single-lever machine pro- 

 vided with an automatic arrangement by which the 

 poise weight is moved outwards at a uniform rate. 



In addition to the care required in gauging the cement 

 and filling the briquette moulds, a considerable amount is 

 necessary in testing them. They must be placed in the 

 holders so that the pull may come on the specimen evenly 

 on the two faces, so that the stress is quite uniformly 

 distributed on the cross section of the briquette. Then 

 the load should be applied steadily at a uniform rate, all 

 shocks and vibrations being carefully avoided. As soon 

 as the briquette has fractured the breaking load should 

 be at once booked. It is the custom with many people to 

 write the breaking load on each half of the broken 

 specimen in pencil to prevent any possibility of mistake. 



174. Crushing Strength. Crushing tests are generally 

 made on 3in. or 4in. cubes, both of neat cement and 

 sand and cement, gauged in the same way as the 

 briquettes. 



