A pressure filter of the tank type is to be used. How many square feet of filter surface are needed to give 1400 gal of filtrate in a I-h filtration? The viscosity is that of water at 70°F. 30.8. The filter of Prob. 30.7 is washed at 70°F and 70IbJ/in.' with a volume of wash water equal to one-third that of the filtrate. The washing rate j~ 85 percent of the theoretical value. How long should it take to wash the cake?