Febkuary 24, 1D22] 



SCIENCE 



213 



as to round, square or rectangular openings. Wire 

 cloth a failure in filtering certain colors. Filter 

 aids work well with wire cloth. Does not recom- 

 mend that wire cloth be rolled. 



Filter aids: C. P. Deeleth. The term filter 

 aid is defined and a list of materials used for 

 this purpose given. Materials to which the term 

 Kieselguhr is applied are discussed. Author 

 divides filtration problems into three classes on 

 the basis of whether the solids in the mixture are 

 rigid, non-rigid or a combination of the two. A 

 discussion is given as to the manner in which a 

 filter-aid may be used and the advantages accru- 

 ing therefrom, in each of the three cases. Desir- 

 able characteristics in filter-aids is given. Filter- 

 aids are said to improve clarity of filtrate, reduce 

 power consumption, reduce loss of liquid in cake, 

 reduce labor in cleaning cloths, increase life of 

 cloths, and increase rate of fiow. 



The feeding of filters: J. F. Speingee. Defines 

 ' ' feeding ' ' as consisting of the transmission 

 under pressure of the unfiltered liquor from a 

 point where it is received from storage to the 

 inlet aperture of the filter. Necessary equipment 

 is pipe-line, pump and power. Suggests that in 

 order to keep pump and valves clean from solids, 

 precipitation of the solids when possible ought to 

 be done either in filter or between pump and 

 filter. Suggests possibility of solids being dis- 

 solved before reaching pump and then again pre- 

 cipitated between pump and filter. Describes 

 feeding devices made of various materials and 

 the corrosive action of certain substances there- 

 on. Discusses suction, gravity and pressure 

 feeding and appropriate apparatus. Steam, 

 power-reciprocating, centrifugal pumps and 

 montejus are dealt with. 



Fundamental laws of filtration with sugges- 

 tions regarding research work: D. R. Speeet. 

 The writer develops a formula which is a state- 

 ment of the fundamental laws governing filtra- 

 tion. This is done to form a foundation upon 

 which filtration may be put upon a scientific 

 basis. Definitions of filtration, porous mass, 

 filter-base and filter are given. Three indispen- 

 sable conditions of filtration are difference ,iu 

 pressure between the two sides of the porous 

 mass, a filter base and a filter. A study is made 

 of the phenomena of filtration and it is found 

 that the rate of flow of filtrate at any instant 

 equals the rate of flow through the cake at that 

 instant were there only liquid above the cake. 

 With tjiis as a basis a study is made separately 

 of the laws of flow through cake and the laws of 

 building up of cakes. The two expressions are 



combined into one which is the fundamental law 

 of filtration as f oUows : Q = -^WPT + N^ — N 



(for constant pressure conditions) ; Q= 



WEM 



WP 



2M 



(for constant discharge conditions) ; 



where Q == total discharge, P ;= pressure, T ^^ 

 time, R z= resistance of cake, Rm z= resistance of 

 porous mass, c/o = per cent, of solids, M = con- 

 stant discharge rate, K = rate of disposition, 

 ^ 2K ^^ KEm 

 W = , N = . Units for measuring K, 



the rate of deposition, and R, the resistance of 

 cake, is given. A list of research suggestions 

 follows. 



Washing filter presses: Eustace A. Alliott. 

 Washing is used to recover a valuable liquor from 

 the solid particles which retain it or to free such 

 particles from impurities dissolved in the adher- 

 ing liquor. Generally wash water ought to be as 

 little diluted as possible; hence the smallest 

 quantity should be used. Adsorption, capillary 

 diii'usion, formation of chemical compounds, and 

 colloid formation on removal of electrolytes arc 

 disturbing factors in washing. Each of these 

 factors is discussed. Simple washing involves too 

 much space and care. For best washing results 

 plate and frame type filters should be used with 

 thorough washing. Air vents should be provided 

 at top of wash chambers, wash must leave at top 

 of press and enter at bottom. Considers various 

 mechanical appliances for washing, hydrometer 

 bowls, wash pumps, and montejus. TJnder ideal 

 conditions wash equal to one displacement volume 

 should effect complete washing. A number of 

 washing results is given from actual practice, 

 showing displacements volumes of 1.6 to 5.5. 

 Describes stage washing. Gives a number of 

 interesting wash curves, and cuts of mechanical 

 appliances for washing. 



Pulp or filtermasse filters: E. E. Finch. 

 Divides filters into two classes — those whose pri- 

 mary purpose is for clarification and those for 

 retaining solids. The pulp filter belongs to the 

 first class and uses cellulose as a filtering medium. 

 Gives a short history of the pulp filter. Origin 

 was probably in Germany. Gives a list of various 

 substances used as a filter-masse with appropriate 

 remarks. Concludes pure cotton masse the best. 

 Describes method of preparing and using filter- 

 masse. Pulp filters can be constructed for 

 handling liquids which must not touch the ordi- 

 nary metals. Discusses advantages of a clear 

 product for manufacturer. Filtration in pulp 



