WASHING THE BUTTER 321 



filters is simple and inexpensive. The muslin is laundried and 

 used over again while the soiled cotton, charged with impurities, 

 is replaced by a new layer. These filters have the additional 

 advantage of taking up very little space. 



If the creamery is troubled with roily water, these cotton 

 filters are not practical, because they clog rapidly. In such cases 

 sand, gravel and coke filters are preferable. Home-made filters 

 of this type have been found somewhat cumbersome, owing to 

 the attention and extra work which their care involves. There 

 are on the market, however, very compact and practical specimens 

 of these sand, gravel and coke filters which require but little at- 

 tention and which are capable of freeing the water from its 

 grit and probably from much of its organic matter. They con- 

 sist of a closed iron drum which contains the filtering material 

 and through which the water is forced, and are equipped with a 

 rotary agitator. For cleaning, the current of water through 

 the filter is reversed and the agitator is rotated. The opera- 

 tion of cleaning the filtering material requires but very little 

 time (about 10 minutes) and if this is done daily, and in ac- 

 cordance with directions furnished by the manufacturer, these 

 filters can be depended upon to do the work expected of them 

 very efficiently. 



For the effective removal of micro-organisms from the water, 

 the efficiency of any of these filters is somewhat questionable. 

 Bacteriological analyses of the filtered water show variable re- 

 sults, probably depending on the condition and care of the 

 filter. Under ordinary creamery conditions they can hardly be 

 considered a reliable means to free the water from objectionable 

 germ life. 



In order to render water sterile or nearly so, high tem- 

 perature pasteurization of the water may be practiced, but it 

 requires considerable equipment, time and fuel, for heating and 

 cooling. Of late years, for the sterilization of drinking water, 

 water for swimming pools, etc, the ultra violet ray process has 

 been found very suitable and its use is rapidly gaining. Its 

 efficiency has been established by Government tests. 1 At the 

 present writing there are no creameries as yet which are using 



1 Public Health Report, Vol. 31, No. 41, Oct., 1916. U. S. Public Health 

 Service. 



