132 



Molding. 



39. Having worked the paste or mortar to the proper 

 consistency, it is at once placed in the molds by hand. 



40. Method: The molds should be filled at once, the 

 material pressed in firmly with the fingers and smoothed 

 off with a trowel without ramming; the material should 

 be heaped up on the upper surface of the mold, and, in 

 smoothing off, the trowel should be drawn over the mold 

 in such a manner as to exert a moderate pressure on the 

 excess material. The mold should be turned over and the 

 operation repeated. 



44. A check upon the uniformity of the mixing and 

 molding is afforded by weighing the briquettes just prior 

 to immersion, or upon removal from the moist closet. 

 Briquettes which vary in weight more than 3 per cent 

 from the average should not be tested. 



Storage of the Test Pieces. 



42. During the first 24 hours after molding, the test 

 pieces should be kept in moist air to prevent them from 

 drying out. 



43. A moist closet or chamber is so easily devised that 

 the use of the damp cloth should be abandoned if possible. 

 Covering the test pieces with a damp cloth is objection- 

 able, as commonly used, because the cloth may dry out 

 unequally, and in consequence the test pieces are not all 

 maintained under the same condition. Where a moist 

 closet is not available, a cloth may be used and kept 

 uniformly wet by immersing the ends in water. It should 

 be kept from direct contact with the test pieces by means 

 of a wire screen or some similar arrangement. 



44. A moist closet consists of a soapstone or slate box, 

 or a rnetal-lined wooden box the metal lining being cov- 

 ered with felt and this felt kept wet. The bottom of the 

 box is so constructed as to hold water, and the sides are 

 provided with cleats for holding glass shelves on which to 

 place the briquettes. Care should be taken to keep the air 

 in the closet uniformly moist. 



45. After 24 hours in moist air, the test pieces for longer 

 periods of time should be immersed in water maintained 

 as near 21 C. (70 F.) as practicable; they may be stored 

 in tanks or pans, which should be of non-corrodible ma- 

 terial. 



Tensile Strength. 



46. The tests may be made on any standard machine. 

 A solid metal clip, as shown in the figure, is recommended. 



