FILTRATION OF WATER. 325 



My objections to the old method of filtering by putting 

 water into the filtering stone are, that the dirt falls to the 

 bottom, and fills up, or chokes the pores of the filtering* 

 stone, so that the stone requires frequently to be cleaned 

 with a brush and sponge to allow the water to pass, after 

 which the water passes through the stone in a muddy state 

 for two or three days ; it likewise requires to be frequently 

 filled, and as it empties less water comes into contact with 

 the stone, and therefore a smaller quantity, in such a state, 

 can only pass through. Likewise a filtering stone used in 

 the common way soon becomes useless, from the filth in- 

 sinuating itself into the internal parts of the stone, out of 

 the reach of the brush. 



In the method I propose and practise, the filtering-stone Improved m©» 

 is placed within the water to be purified, which presses upon^ ° ' 

 the outside of the filter, and the stone does not require to 

 be supported in a frame as it needs on\y to stand within the 

 water cistern ; it will thus filter, in an equal time, double 

 j ^- the quantity of water procured in the common mode; it *" 



fills itself, and requires no cleaning. I have upon this plan 

 used one for more than three years with great success, 



I am, Sir, 



Your humble servant, 



WILLIAM MOULT, 



No, 37, Bedford Square J 

 April IS, 1810, 



Certificates. 



We, the undersigned, having inspected and examined a Testimonies of 

 new mode of employing the ordinary filtering-stone, dis-.^^^**^^"^^^^ 

 covered by William Moult, are of opinion that its supe- 

 riority over the customary method is so great as to entitle 

 it to particular notice. 



That it not only supplies an infinitely greater quantity of 

 purified and limpid water, but is capable of preserving its * 



porosity free and pervious for years together, by an occa« 

 sional self-operation. 



That by this valuable process the principal objections io 

 drip^stones is removed, viz. the constant labour they require 



to 



