No. ^ (1921) MANUFACTURE OF FISFt OIL AND GUANO ^2^ 



bright and should be passed at once into its storage receptacles. 

 With these presses the kieselguhr is really the filtering medium, 

 and filtration improves as the layer of material consolidates in the 

 chambers. When it becomes obvious that the deposit has become 

 excessive, the frame is slackened so that the plates can be released ; 

 the solid cakes of material are then removed, the filter cloths 

 cleaned, and the press again put together ; the cakes may also be 

 treated to recover any contained oil, and the kieselguhr washed for 

 further use. 



It is suggested, in view of observations made on the extra- 

 ordinary anti-enzymic action of asbestos on nitrogenous and other 

 substances (British Medical Journal, November 22nd, 1913) that, for 

 very fine oils, asbestos, which is abundant and cheap in India, may 

 be used in powder as filtering material ; a sufficient quantity may 

 be intimately mixed with the impure oil and left in contact for at 

 least one night ; the mixture may then be passed through the filter 

 press. According to the observations mentioned in the Journal 

 the exudate (filtrate) should be free from nitrogenous matter as 

 such. 



A small filter press is available in the Tanur Yard. 



129. The value of filter presses lies in the great eff'ectiveness 

 and rapidity of their action by which fluids which would take 

 many months to clear by ordinary gravity settlement may be more 

 effectively purified in a few minutes or hours, so that a minimum 

 of storage room and receptacles is required, capital is locked up 

 for a minimum of time, and the manufacturer is ready at any 

 moment to take full advantage of the market. But filter presses 

 are expensive and not always necessary though desirable for first- 

 class edible goods ; when ordinary filtering may be desirable, 

 their place can be taken by a variety of filters of very simple 

 character and cheap material. A simple and most effective filter 

 is composed of nothing but cloth, moss, cotton waste or pulp, 

 paper pulp, coir, charcoal, and even clean sand, put together in 

 layers in a wooden tub or box through which the filtrand is passed 

 by gravity. The containing vessel may be of iron (preferably 

 galvanized) or wood and may be of square or cylindrical section ; 

 it must be well made, strong, and water-tight but with open top. 

 The bottom is usually cone shaped and is provided with an inlet 

 cock and a wash-out cock ; above the cone is a perforated plate, 

 resting on lugs or on a rim in the container ; on the perforated plate 



