INGENUITY AND LUXURY 



sand, gravel, and water are poured continuously into 

 the feeding-end in the required proportions. Owing 

 to the difficulty in measuring the various substances 

 accurately, many builders prefer " batch-mixers," 

 which have to be filled and emptied successively. The 

 general principle upon which all these machines work 

 is that of the time-honored churn, the contents of which 

 are jostled about in every direction. Some of the mixers 

 are barrel-shaped, having fixed paddles in the interior 

 which stir the contents thoroughly when the surround- 

 ing cylinder is revolved. Others are box-shaped, 

 the angles of the box performing the same functions 

 as the paddles when the machine is rotated. Still 

 others are in the shape of a long trough with a longi- 

 tudinal shaft upon which are placed several propeller- 

 like blades running through the center. Material 

 thrown into the upper end of this machine is thoroughly 

 mixed by the time it reaches the other end, so that 

 they are adapted for use as continuous, or batch- 

 machines, as the operator may prefer. A very simple 

 type of mixer is one in which the action of gravity is 

 utilized. This is in the form of an upright tube, or 

 box, along the inner surface of which projecting ob- 

 structions are placed at intervals. The material is 

 thrown in at the top and, striking against the obstruc- 

 tions as it descends, is jostled about until it emerges 

 from the lower end of the tube mixed perfectly. 



With all these machines great difficulty lies in feed- 

 ing them with the various materials in the correct 

 proportions. Mechanical measurers have been per- 

 fected that do this accurately and satisfactorily, but 



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