PHYSICAL PROPERTIES OF PORTLAND CEMENT. 611 



MOULDING. 



59. Having worked the paste or mortar to the proper consistency, 

 it is at once placed in the moulds by hand. 



60. The Committee has been unable to secure satisfactory results 

 with the present moulding-machines; the operation of machine mould- 

 ing is very slow, and the present types permit of moulding but one 

 briquette at a time, and are not practicable with the pastes or mortars 

 herein recommended. 



61. Method. The moulds should be filled at once, the material 

 pressed in firmly with the fingers and smoothed off with a trowel with- 

 out ramming; the material should be heaped up on the upper surface 

 of the mould, and, in smoothing off, the trowel should be drawn over 

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

 excess material. The mould should be turned over and the operation 

 repeated. 



62. A check upon the uniformity of the mixing and moulding 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. 



63. During the first twenty-four hours after moulding, the test 

 pieces should be kept in moist air to prevent them from drying out. 



64. 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 objectionable, as commonly used, because 

 the cloth may dry out unequally, and, in consequence, all the test pieces 

 are not maintained under the same condition. Where a moist closet 

 is not available, a cloth may be used and kept uniformly wet by immer- 

 sing 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. 



65. A moist closet consists of a soapstone or slate box; or a metal- 

 lined wooden box, the metal lining being covered 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. 



66. After twenty-four hours in moist air, the test pieces for longer 

 periods should be immersed in water maintained as near 21 C. (70 F.) 



