53 



One cu. ft. contains 12 x 12 x 12 = 1728 cu. inches. 

 A frame 36 in. x 48 in. (3 ft. by 4 ft.) by I in. high, 

 also contains 1728 cu. in. or i cu. ft. Therefore a 

 frame, as shown in fig. 25, 3 ft. x 4 ft. x 2 in. high, 

 will contain 2 cu. ft. of sand when filled and struck. 

 One sack of cement placed on top of this, spread 

 evenly and then, with the frame removed, thoroughly 

 mixed, would give an exact I to 2 mix. Another frame 

 could be built to contain 4 cu. ft. Make this 3 ft. by 

 4 ft. by 4 in. high or 6 ft. x 4 ft. by 2 in. high. While 

 the men are turning over the sand and cement, another 

 man can be filling the 4 in. frame with crushed stone, 

 striking this off, and wetting it. When the sand and 

 cement are turned for the last time, shovel it on top 

 of the 4 cu. ft. of stone and mix together. 



Always, if possible, wet the stone before mixing. If 

 you are cramped for room, or short of men, put one 

 frame on top of the other and assemble an entire batch 

 at once, 4 in. of stone in the bottom frame, then strike 

 this. Put on the 2 in. frame and put in 2 in. of sand. 

 Then spread a sack of cement over the top, lift the 

 frames and start in to mix. The heights of the frame 

 determine the proportion to one sack or i cu. ft. of 

 cement, because, as noted above, a frame 36 in. by 48 in. 

 by i in. high contains 1728 cu. in. or i cu. ft. 



Throughout this discussion, we have used sand and 

 stone as typical inerts. The same conditions apply, 

 whatever aggregates are used. 



In hand or machine mixing, always have an expe- 

 rienced man watching the concrete. This is a constant 

 check and is a factor for safety that cannot be dis- 

 pensed with. 



Concrete Hoisting Towers. There arc on the mar- 

 ket today, and well illustrated in trade publications, so 

 many good combinations to elevate concrete to the re- 

 quired floor level, that a discussion here is hardly 

 called for. A field-made tower with 4x4 uprights for 

 the corners, and sufficient cross bracing, is in general 



