686 Oil the Purification of Water hy means of Ii'on. 
them, and the cost of cleaning entailed by the very impure 
character of the water operated on. 
To obviate these objections, I determined to try a method 
first suggested to me by Sir Frederick Abel, namely, that of 
shaking up the water to be treated with any iron in a divided 
state, instead of letting it filter through it. It is obvious 
that, inasmuch as the object to be obtained is to expose fresh 
clean surfaces to the action of the water, some arrangement by 
which the particles of the spongy iron would keep themselves 
clean by rubbing up against each other would present the best 
possible mode of application. 
The form which the apparatus has assumed is twofold. 
Fig. 3. — Section of Filter-bed supplied hy Revolving Purifier. 
In the first, Fig. 3, the iron fills about one-tenth of a cylinder, 
A, revolving slowly on hollow horizontal trunnions, B and C. 
The water to be purified is taken direct from the source, and 
passed into the cylinder through the trunnion, B, its course 
being checked by a spreader-plate, D ; the iron is caught up by 
numerous longitudinal shelves or ledges, E, fastened to the inner 
surface of the cylinder, and is constantly showered down through 
the water ; the rapid fall through which, combined with the 
attrition against itself and the surface of the cylinder and shelves, 
tends to keep the iron perfectly clean. The water passes slowly 
through the cylinder, and issues out through the trunnion, C, at 
the opposite end, entering it by means of an inverted bell, F, 
which effectually prevents any iron being carried over. The 
water from the revolving purifier is then allowed to flow on to 
an ordinary sand-filter, o, into which it should fall, so as to be 
