52 



Mixers. A word as to different kinds of mixers. 

 They naturally group under the following heads with 

 self-explanatory names : 



(1) Gravity, 



(2) Continuous, 



(3) Batch. 



It is uncalled for in this work to enter into a com- 

 parison of the relative merits of these machines. As 

 noted, trade publications usually go into details much 

 more extensively. The same rules as to proportioning 

 the sand and aggregate apply .in these mixers. A con- 

 tinuous, however, naturally requires a continuous feed- 

 ing, correctly proportioned. 



Machine or Hand Mixing. It is perhaps pertinent 

 at this time, to invite consideration and thought on the 

 relative values of machine and hand mixed concrete. 

 There are on the market today so many small machines 

 run by hand or small engines, and even a traction 

 mixer, which can be loaded at the stock pile and mix 

 while being driven, that it seems a little uncalled for 

 to still employ the old method of hand shovel or hoe 

 mixing. 



Hand Mixing. If hand mixing is used, however, 

 take every precaution to have a carefully proportioned 

 mix. A frame is the best way of determining the pro- 

 portions required, using i cu. ft. as the unit of meas- 

 urement. 



F<>R MEASURING MATKRJALS OX THE 

 MIXING BOARD. 



