MATERIALS. 117 



contents are thrown from side to side and end to end, and 

 thoroughly mixed. 



In Messent's machine the mixing-vessel is angular and of a 

 somewhat peculiar shape. When half filled with material, and 

 caused to revolve on its axle, the material, as in Coode's machine, 

 is made to turn over sideways as well as endways, thus ensuring 

 good mixing. 



Either of these machines may be geared for hand or steam 

 power as desired. 



Hoppers are generally used in charging them, and a small 

 overhead tank supplies the water, and at the same time ensures 

 the correct quantity being given to each charge. 



These machines are usually though not necessarily con- 

 structed to mix half a cubic yard at a time, experience having 

 shown that this quantity is more easily dealt with than larger 

 charges. A machine of this size will mix about 10 cubic yards 

 per hour. 



Of the latter type of machines, or continuous mixers, Ridley's, 

 Le Mesurier's, and Carey-Latham's are perhaps the best known. 

 A description of the last named will convey a good general idea 

 of a continuous mixing-machine, so it will not be necessary to 

 further refer to the others. 



This machine consists of a horizontal revolving mixing- 

 cylinder, within which are spiral ribs, carried upon radial 

 arms. These ribs revolve at a very much slower rate than the 

 cylinder itself, and from them the concrete material, as it is 

 brought up by the revolving cylinder, is thrown off, sideways 

 and forward, a number of times during its passage through the 

 cylinder, at the outer end of which it is delivered as concrete. 



Water is supplied about halfway down the cylinder, by 

 means of a central pipe or hollow shaft, at the end of which 

 is a star-rose. Thus the material is well mixed in the dry state 

 before it reaches the point where the water is added. 



The materials are automatically measured, and fed into a 

 hopper at the upper end of the cylinder. The sand and broken 

 stone or gravel are measured and lifted by means of buckets 

 attached to chains dredger fashion. One set of these buckets 

 the size and number of which may be made to suit any condi- 

 tions supplies the sand, and the other the broken stone or 

 gravel, while the cement is fed into the hopper by means of an 

 endless screw, its quantity being regulated to a nicety by means 



