218 TESTS ON CEMENT 



Molds. Cement briquets are made in molds that come 

 either single or in gangs of three, four, or five. The gang 

 molds are preferable, as they tend to produce greater uni- 

 formity in the results. Molds should be made of brass or of 

 some other non-corrodible material; those made of cast iron 

 soon rust and become unfit for use. 



Method of Making Briquets. First, 1,000 g. of cement is 

 carefully weighed and placed on the mixing table in the form 

 of a crater, and into the center of this is poured the amount 

 of water that has previously been determined to give the 

 correct normal consistency. Cement from the sides of the 

 crater is then turned into the center, by means of a trowel, 

 until all the water is absorbed, after which the mass is 

 vigorously worked with the hands, as dough is kneaded, 

 for 1J min. When sand mixtures are being tested, 250 g. 

 of cement and 750 g. of sand are first weighed and thor- 

 oughly mixed dry until the color of the pile is uniform; then 

 the water is added and the operation is completed by vigor- 

 ous kneading. 



After kneading, the material is immediately placed into the 

 molds, which should first have been wiped with oil to pre- 

 vent the cement from sticking to them. The entire mold is 

 filled with material at once not compacted in layers and 

 pressed in firmly with the fingers without any ramming or 

 pounding. An excess of material is then placed on the mold 

 and a trowel drawn over it under moderate pressure, at each 

 stroke cutting off more and more of the excess material, 

 until the surface of the briquets is smooth and even. The 

 mold is then turned over, and more material placed in it and 

 smoothed, as before. The mixing and molding should be 

 performed on a surface of slate, glass, or some other smooth, 

 non-absorbent material. During the mixing the operator 

 should wear rubber gloves, so as to protect his hands from 

 the action of the lime in the cement. 



Storage of Briquets. For 24 hr. after making, the briquets 

 are stored in a damp closet so that the cement can harden 

 in a moist atmosphere. The damp closet is simply a tight 

 box of soapstone with doors of wood lined with zinc, or some 

 similar arrangement, with a receptacle for water at the 



