126 CEMENT AND CONCRETE 



each time until it reaches the proper consistency. The only 

 objection to the hand method of mixing is that a great deal 

 of labor is involved, and this, in some cases, reduces the qual- 

 ity of the concrete because of the fact that the materials are 

 not mixed as thoroly as when mixed in a mixing machine. 



FIG. 139-a. Turning the mixture. 



FIG. 140. Batch mixer. 



120. Machine -Mixing. There are two types of ma- 

 chine mixers in use the batch mixer (Figs. 140 and 140-a) and 

 the continuous mixer. The latter type is not as satisfactory 

 as the batch mixer and is seldom used except on small jobs. 



