CASEIN PAINTS. 41 



substances with an alkaline reaction. Intimate mixture of 

 the various ingredients is an important feature in these paint 

 powders. The percentage of medium in these mixtures is 

 relatively small, and yet it must be distributed in a perfectly 

 uniform manner throughout the mass ; otherwise, if one 

 portion of the paint contained too much, and another too 

 little, the result would be noticed in the uneven character of 

 the coat of paint. Careful mixing is therefore an essential 

 feature. 



To secure this result, the medium and pigments are 



FIG. 9. Werner-Pfleiderer Sifting Mill. 



placed in a sifting mill like the Werner-Pfleiderer machine 

 illustrated in Fig. 9. This consists of a wooden box or other 

 receptacle, containing a spiral roller brush fitting and working 

 exactly in a semi- cylindrical sieve. The materials are fed in 

 at the top, and are carried round by the brush, all soft lumps 

 being broken up and passing though the sieve along with 

 the fine powder. On the other hand, all the hard lumps and 

 waste matters are discharged through an opening at the end 

 of the machine. From 1 to 30 cwt. per hour can be sifted in 

 this way, according to the size of the machine. 



