THE CLARIFICATION OF FRUIT JUICES. 15 



plate-and-frame filter presses handle such filtration problems suc- 

 cessfully^ but the cost of such equipment limits its use to commercial- 

 size installations. A pulp filter operated by a steam suction pump 

 failed to give satisfactory results. When first started, such a filter 

 permits the passage of particles of earth ; by the time this ceases the 

 surface of the pulp has become coated with a slimy, almost imper- 

 vious layer, and filtration becomes extremely slow. Increasing the 

 suction upon the filter merely hastens clogging by making this slimy 

 layer more compact. Attempts to use a small multiple-disk pulp 

 filter fed by gravity were equally unsuccessful; clogging and stop- 

 page occurred very quickly under gravity pressures ranging from one- 

 fourth to two atmospheres. The difficulty with such filters is two- 

 fold. The filtering medium is not sufficiently close in texture to re- 

 tain the finer particles until it has become reinforced by a layer of 

 earth. As the earth settles out of the undisturbed liquid, the larger 

 and heavier particles come down first, followed by the deposition of 

 successive strata of finer and finer particles. Such a layer of earth is 

 a highly efficient filtering medium in so far as preventing the passage 

 of suspended material is concerned, but its working period is short, 

 for the reason that there is soon built up on the surface a layer of 

 gummy, viscous material which practically stops the flow and necessi- 

 tates cleaning and repacking the filter. No satisfactory method of 

 overcoming this twofold difficulty in the use of pulp filters either of 

 the gravity or of the suction type has been found. 



SIMPLE AND EFFECTIVE METHODS OF FILTRATION WITH 

 DIATOMACEOUS EARTH. 



SMALL MULTTPLE-DISK FILTER. 



As a plate-and-frame type of filter press was not available in the 

 laboratory, a small multiple-disk pulp filter was so modified as to 

 make it essentially a plate-and-frame filter. The circular pulp disks 

 were replaced by filter cloths of a closely woven, rather light denim, 

 fastened in place at the outer edge and around the central opening 

 by rubber gaskets. When all were in place the press was closed and 

 water was passed through to wet the cloths thoroughly. A quantity 

 of earth sufficient to coat the cloths to a depth of about 0.5 cm. was 

 then thoroughly stirred into water and passed into the press. As the 

 filter was of the vertical type in which the disks rest one upon another 

 like a pile of coins, it was easy to effect uniform distribution of the 

 earth over the cloths by running it in while in suspension in water 

 under a head of 6 to 10 feet. Water was then passed in until earth 

 ceased to wash through. The juice to be filtered was then stirred 

 thoroughly with diatomaceous earth at the rate of two-thirds to 1 

 ounce per gallon (4 to 6 pounds per hundred gallons) and passed into 



