40 FILTERING MACHINE. 



VIII. 



Pefcription qf a Filtering Machine invented By Profejjfor Parrot 

 of Paris. In a Letter from a Correjpondent. 



To Mr. NICHOLSON. 

 SIR, 



Filtering ma- 1 ENCLOSE you a drawing of a filtering machine invented 

 frlTer^feSi" by Profeiror Parrot, of Paris, wliich for fimplicity and uti- 

 tity feems fuperior to any other I have met with. You will 

 perceive that from the curvature of its form, it purifies the 

 water both by defcentand afcent, and fs, confequently, a clofer 

 imitation of the operations of nature than thofe in which the 

 water penetrates in but one direftion. Among the advantages 

 which he afcribes to it, he infiances the *' prolongation of the 

 flratum of fand, which does not confiderably diminith the pro- 

 duct of the filtre, but contributes remarkably to the purity of 

 the fluid/* and that ** the difference of its water-level has an 

 eflential influence on the quantity of purified water obtained 

 in a given time;*' he therefore recommends an apparatus of 

 eighteen inches long from A to D, two inches thick, and four 

 broad, which, he fays, will yield fix (Paris) pints of pure 

 water every hour: a machine of this {\z6 requires onlyadift 

 ference of two or three inches in the height of the water, 



I am^ Sir, 



Your conflant reader, 

 London, Augujl 20, 1804. A. A. 



Defcription of tlie Machine. 



The refervoirG. Cfig- 1* P^ate IV.) may be of any form or 

 dimenfion which is convenient J the principal part of the ma- 

 chinery confiding of a fquare vetfel bent in the form of an in- 

 verted fyphon. The curve may be circular, elliptic, or in any 

 other direftion. This veflel is to be filled with fine pure fand 

 lo nearly the height of the dotted line x y, which denotes the 

 afcent of the water to D, whence it flows into the receiver. 

 To the part marked A B, which muft always be above this 

 line, a woollen bag is attached, open at the top and reaching 

 to the fand : this colled^s the coarfeft impurities, and prevents 

 the fand from becoming foul for a longer time. In large ma- 



' chines 



