18 BULLETIN 1025, U. S. DEPARTMENT OF -AGRICULTURE. 
A FILTER FOR USE ON A SEMICOMMERCIAL SCALE. 
3 .. 
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 34 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 lke 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 
