Where large quantities of mortar are required, machine mixers are sometimes used. A very complete plant for mortar-making was used in building the Titicus Dam.1 In this case machinery was used in measuring the proportions of,cement and sand as well as in making the mortar. The measuring apparatus consisted of two cylindrical troughs, one for cement and one for sand. Each trough was divided, by means of six radial vanes and four discs, into eighteen equal compartments. These cylinders revolved in cast iron boxes which were so constructed as to serve as hoppers for filling the compartments. Three compartments were presented to the hoppers at once, and slides were provided by which any of the hoppers could be cut off at will. The cylinders being geared to the same pinion, it was possible, by means of the slides, to make any desired proportion of cement and sand from neat cement, to three parts sand to one cement.
1 Engineering Record, August 3, 1895.
The mixing machine "consisted essentially of a semi-cylindrical wrought-iron trough with extended flaring sides, with elements slightly inclined to the horizontal, and in its axis a revolving shaft with oblique radial blades set at an incline of ninety degrees to each other and of a length to just clear the bottom of the trough".
284. Another form of machine that is sometimes employed consists of a semi-cylindrical trough in which rotates an axis carrying a blade in the form of a screw. The materials are fed to the mixer at one end and the screw mixes them while working the mass toward the other end.