No. lU] 261 



Prof. Mapes— The English journals are filled with accounts of 

 experiments in the treatment of town sewerage, so as to render it 

 available for the use of the farmer; and the chemists seem to dis- 

 pute the ability of peat charcoal to absorb the ammonia and 

 other volatile gases of this sewerage. The only difficulty, evi- 

 dently, consists in the mechanical arrangement of the tanks, fil- 

 ters, &c. It must be evident to all that in so large a cistern as 

 would be used practically for such a purpose, the filtration of 

 millions of gallons, rapidly supplied, and rapidly parted with, 

 cannot be conducted practically by downward filtration, without 

 causing holes or openings through which portions of the fluid 

 will pass, without coming in contact homogeneously with the par- 

 ticles of peat charcoal, but rather continue to pass through a few 

 particles already saturated in the cornersof the cistern, or in such 

 positions as contain holes through the mass. 



By downward filtration the finer portions must coat the top of 

 the substances through which the fluid is passing, so as to render 

 it impermeable for a continued filtration. All this may be reme- 

 died by upward filtration. 



Suppose a tank with a false bottom filled with holes, and in 

 this tank, above the false bottom, the material for deodorizing, 

 through which the fluids intended to be passed shall be placed; 

 the fluid should be received in a secound cistern, as tall as the 

 first, but communicating with the first between the false and real 

 bottom. As soon as this lower place is filled, the more fluid por- 

 tions only will continue to rise through the deodorizing material 

 in their effort to find their level, and thus may be permitted to 

 run away from the top by such an arrangement. All the thicker 

 portions will settle between these bottoms, and may be taken out 

 by a side valve at any time. The filter will never become 

 stopped, because any particles rising against the bottom of the 

 filter will fall from it in preference to being crowded in between 

 the particles of the deodorizing material. This eflbrt of water to 

 find its level always renders its surface level while rising, and 

 hence every particle of tlie deodorizing material will be called on 

 to act equally. This may be taken out when surcharged, by back 



