FIELD OPERATIONS 347 



and mop with hot pitch d the full width of the 17-in. lap, so 

 that in no case shall felt touch felt. (3) Coat the entire 

 surface with hot pitch e mopped on uniformly. (4) Lay 

 three full thicknesses of felt f, lapping each sheet 22 in. over 

 the preceding one and mopping with hot pitch g the full 

 width of the 22-in. lap between the plies, so that in no case 

 shall felt touch felt. (5) Spread over the entire surface of the 

 roof a uniform coat of pitch, into which, while hot, embed 

 the gravel or slag h. The gravel or slag in all cases must 

 be dry." 



The preceding specifications are designed for roofs having 

 an incline not exceeding 1 in. to the ft., and by adding the 

 words "such nailing as is necessary shall be done so that all 

 nails will be covered by at least two plies of felt," the specifi- 

 cations are suitable for inclines not exceeding 3 in. to the ft. 

 For surfaces steeper than 3 in. to the foot, nailing strips of 

 wood must be provided. These should be embedded in the 

 concrete from 3 to 6 ft. apart, running at right angles to the 

 pitch of the roof, and the felt nailed to these strips. 



FIELD OPERATIONS 



CONCRETE MIXERS 

 BATCH MIXERS 



Cube Mixers. One of the oldest and best-known forms 

 of batch mixer is the cube mixer. In Fig. 1 is shown what is 

 known as a Carlin cube mixer. The cube is driven by a belt a, 

 and gears b serve to reduce the speed of rotation. The cube 

 is shown in the position it occupies when being filled. The 

 trap door for filling and discharging is shown open and swung 

 back at c. The hopper above the cube is made in two parts. 

 The lower part is hung from one of the posts of the platform, 

 as shown. When the cube is revolving, this lower part can 

 be swung out of the way. At d is shown the water tank, 

 which feeds water into the cube through the pipe e. Below 

 the cube is shown a car f into which the finished concrete is 

 dumped. 



