720 Kl ;1 ^ BTATl MUSEUM 



I on top of the Boft cement projecting above tie mold." 

 The loading block is shaped to the mold with V-r o f m in,,]l t * lt ' ar " 

 . be placed on the oement symmetrically; after load- 

 ing the surplus oement La to be cut off with a trowel or a knife, 

 and tlit' briquet smoothed level with the top of the mold. "With 

 f the j st can-, the handmade briquets do not 

 compare with those made with the machine/ 1 



Another advantage of machines is the rapidity with which the 

 in be made, and an additional advantage of this is that 

 a lot of material can be mixed np at once. 



In making briquets by hand enough material is usually mixed 

 to make four or five briquets at once, and this is necessary if the 

 material is at all quick setting. 



All tensile test briquets should be kept in a moist atmosphere 

 for 24 hours, and then kept the remainder of the period in water. 

 It is important that the water used in mixing and also the bath in 

 which the briquets are immersed should be kept at a constant tem- 

 perature, so that uniform results may be obtained. Thus it has 

 been fonnd that in Portland cement the time of setting is shortened 

 by increasing the temperature of the mixing water, while the 

 strength attained in a given time may be greatly increased by rais- 

 ing the temperature of the bath from 40° to SO 01 . In case of 

 ' normal mortar, lC: 3S, this increase at two months was from 100 

 to -'■'>" pounds per square inch. 



Briquet machines. The object of these is to bring about uni- 

 formity <.f pressure in the molding of the briquets. A number of 

 such machine- have been devised but comparatively few of them 

 are in use. The Bohme hammer is a machine much used in Ger- 

 many for this purpose (pL 23). According to M. Gary 8 it con- 

 sists of a tilt hammer with automatic action. The hammer is 

 driven by a cam wheel of 10 earns actuated by simple gearing, and 

 the wrought iron handle of the hammer is let into the crosshead 



i Johnson. Materials <>f construction, p. 408. 



.11-. Am. M -1. 



