18 BULLETIN 1025, U. S. DEPARTMENT OF AGRICULTURE. 



A FILTER FOR USE ON A SEMICOMMERCTAL SCALE. 



A similar arrangement for use on a larger or semicommercial scale 

 was made from a pulp filter operated by a steam suction pump by 

 removing the pulp packing and replacing it with a heavy nickel- 

 wire screen fastened permanently in place. Upon this as a support 

 was placed a piece of heavy closely woven denim. Diatomaceous 

 earth in the form of a thick paste was then poured in and packed 

 into a firm disk about 3 to 2>\ cm. thick by gentle suction and press- 

 ing down with a wooden rammer. A few minutes' washing with 

 water under full suction removed all traces of earth from the lower 

 surface of the cloth. Such an arrangement filters rapidly, can be 

 restored to the original rate of filtration when partial clogging occurs 

 by scraping off the accumulated slime together with a thin layer of 

 the compact disk, and when necessary can be taken out and replaced 

 in a very short time. In setting up and operating such a filter it is 

 necessary to observe a few rather obvious precautions. The wire 

 screen used as a support should be of a metal which is not attacked 

 by the acids of the juice, though in default of a satisfactory screen 

 a wooden lattice may be used. Whatever the material used, the 

 support must be rigid, in order that the filter disk may not be dis- 

 placed or broken by starting or stopping the suction pump. The 

 cloth used as a backing should be of firm closely woven texture, in 

 order that particles of the earth may not wash through it into the 

 filtrate, and should be thoroughly wetted before it is put into place. 

 The earth used in packing the filter should be made into a paste 

 with as little water as possible, as it then holds together like putty, 

 does not pass through the cloth, and can readily be molded into a 

 uniform layer, making close contact with the side walls of the con- 

 tainer. When the earth is so packed very little washing is necessary. 

 In filling the filter with juice, care must be taken not to allow the 

 entering stream to strike the disk with sufficient force to wash holes 

 in it. The liquid on the filter should be thoroughly stirred from 

 time to time. Care must be taken not to allow the disk to become 

 dry, as the earth then shrinks considerably and will crack and pull 

 away from the side walls of the container if not kept thoroughly 

 moist. In cleaning the surface of the filter when it becomes coated 

 with slime, a broad-bladed putty knife or some similar instrument 

 which permits the operator to pare off a uniform thin layer from 

 the top of the disk should be employed. When the removal of the 

 disk is necessary it should be allowed to become rather dry ; it may 

 then be lifted out practically entire. The cloth used as a backing 

 should be taken out and thoroughly washed before the filter is re- 

 placed. The disks which have become clogged from use, together 



