THE TESTING OF ROAD MATERIALS. 



jar for twent} T -four hours. About 25 grams of this dough is placed in 

 a cylindrical metal die. iio mm in diameter, which can be seen in fig. 

 4. A closely fitting plug, supported by guide rods, is inserted over 

 the material, which is then subjected 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 a special machine has been designed 

 (fig. 5). The die is placed on an iron platform supported by a piston 

 rod, which is connected directly with a hydraulic piston below. Water 

 Irom a tank is admitted to the hydraulic cylinder through a small 

 orifice in the pipe. As the piston rises the platform and die are car- 

 ried up with it, the plug of the latter coming in contact with a yoke 

 attached to a properly 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. One 

 minute is required to com 

 press 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 2f> 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 

 FIG. 4.-Briquette die. fa d,-y twelve hours in air and 



twelve hours in a -team bath. After cooling in a desiccator they are 

 te-ied by impact in a machine especially designed forthe purpose (fig. ti). 



It consists of a 1 kg (_'.:.' pounds) hammer (17)., which is guided by t\\<> 



vertical rod- ( />). The hammer (//), which ends in a small cone at the 

 top ( /.). is caught on the lower side of the cone by two spring bolt- 

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

 A vertical rod (/'). which i> directly over the hammer cone, can be 

 adjusted by thumbscrews to give a drop to the hammer varying from 

 a fraction of a millimeter to in cm. This rod has a hollow coin 1 at it- 

 lower end into which the cone of the hammer head is thrust when the 

 hammer U lifted by the cm head (/). When the cone of the hammer 

 head is brought into the cone of the adjusting rod the hammer is 



