CEMENTATION TEST. 





revolved at the rate of 2,000 revolutions per hour. It was found by 

 experiment that grinding rock thus prepared for two and a half hours 

 is sufficient to reduce it to a powder which will pass through a 0.25 mm 

 mesh. The dust thus obtained is mixed with water to about the con- 

 sistency of a stiff dough, and is kept in a closed jar for twenty-four 

 hours. About 25 grams of this dough is placed in a cylindrical metal 

 die 25 mm in diameter, shown in figure 2. A closely fitting plug, 

 supported by guide rods, is inserted over the material, which is sub- 

 jected to a pressure of 100 kg per square centimeter. 



It is most important that these briquettes should be compressed in 

 a uniform manner, and for this purpose a special machine has been 

 designed (fig. 3). The die is 

 placed on an iron platform 

 supported by a piston rod, 

 which is connected directly 

 with a hydraulic piston be- 

 low. Water from a tank is 

 admitted to the hydraulic 

 cylinder through a small ori- 

 fice in the pipe. As the pis- 

 ton rises, the platform and 

 die are carried up with it, the 

 plug of the latter coming in 

 contact with a yoke attached 

 to a properry weighted lever 

 arm. When the lever arm is 

 raised one-eighth of an inch 

 it closes an electric circuit 

 which trips a right-angle 

 cock, shutting off the water 

 and opening the exhaust. 

 About one minute is required 

 to compress a briquette, and the maximum load is applied only for an 

 instant. By this device practically uniform conditions are obtained. 



The height of the briquette is measured, and if it is not exactly 25 

 mm the requisite amount of material is added or subtracted to make the 

 next briquette the required height. Five briquettes are made from each 

 test sample and allowed to dry twelve hours in air and twelve hours in 

 a steam bath. After cooling in a desiccator they are tested by impact 

 in a machine especially designed for the purpose (fig. 4). It consists 

 of a 1 kg (2.2 pounds) hammer (//), which is guided by two vertical 

 rods (D). The hammer (11), which ends in a small cone at the top (Z), 

 is caught on the lower side of the cone by two spring bolts (S), and 

 is lifted by a crosshead (I) which is joined to a crank shaft above. 

 A vertical rod (P), which is directly over the hammer cone, can be 



FIG. 2. Briquette die. 



