86 



The gravel is washed in a perforated drum revolving in a 

 trough. 



C. Bolle, the great milk [man 

 in Berlin (Germany) devised a 

 gravel filter shown in Fig. 82. 

 It consists of a large vessel 

 where the milk enters at A, 

 and passes through three lay- 

 ers, B, Bl, B2, of gravel of in- 

 creasing fineness. It is claimed 

 to treat 2,400 to 3,000 Ibs. per 

 hour and to reduce the number 

 of bacteria from one-third to 

 one-half. The gravel is washed 

 with boiling water, then with 

 muriatic acid and then again 

 with boiling water until all 

 trace of acid is removed. 



Dr. Backhaus uses cellulose in 

 Fi 82 a mush-like shape as filtering 



material. 



In Fig. 83 is shown the International Filter (Chicago) in 

 position for operation. It consists of two perforated plates 



with layers of flannel or 

 felting between, all en- 

 closed in a cast iron 

 casing, which can easily 

 be opened. The milk 

 has to have some pres- 

 sure, and hence the milk 

 vat is placed on the 

 floor above from whence 

 it enters the filter under 

 the lower perforated 

 plate, passes through the 

 felting and from there 

 into milk bottling tank. 

 This filter seems to me 

 the simplest possible and 



Fig. 83 . only the high price is an 



excuse for its not being 

 used more extensively. 



