On the Purification of Water hy means of Iron. 687 
aerated as much as possible, and where the depth should be so 
great as to allow four or five hours before it reaches the sand. 
The revolving purifier requires very little power to drive it, 
only a few inches of head to cause the water to flow through, 
and it is particularly suited for large water-works, and situations 
where power is to be had. 
The other form of purifier consists of placing the iron, for a 
depth of 4 or 5 feet, into a vertical pipe, a, Fig. 4, terminating 
Fig. 4. — Section of Filter-bed supplied by Vertical Purifier. 
in a cone at the lower end, like an inverted sugar-loaf. The 
water is forced through a jet or small aperture, B, in the apex of 
the cone, under a head of 8 feet or 10 feet, and issues by a 
lateral branch, c, at the top of the pipe. The rush of water 
keeps the whole of the iron, D, on the move, and consequently 
while the water becomes thoroughly exposed, the iron is kept 
perfectly clean, both by the washing and the rubbing action 
continually going on. After leaving the purifier, the water is 
poured into an ordinary sand-filter, E, in the same manner as 
from the revolving machine. 
This form of apparatus is best suited to situations in which a 
fall of some 10 feet can be spared, or where pumping power 
exists. The purifier requires no attention whatever beyond the 
occasional addition of a little iron, and it occupies very little 
space. 
The chemical effect produced is even more complete than in 
the case of the iron filter. Thus at Antwerp, in the water from 
a revolving purifier dealing with 166 gallons per minute, the 
free ammonia was reduced from 0'032 grains per gallon to 
0-002 grains, and the albuminoid ammonia was reduced from 
0'013 grains to 0-004 grains per gallon, or less than one-third. 
The size of the apparatus varies with the quality of the water 
which affects the time of contact required. At Antwerp three 
minutes' contact with the iron is found sufficient ; but some very 
bad and highly-coloured waters require as much as six minutes. 
