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enclosed in the vessel with a cemented cover. It was found that 
the impurities deposited remained and accumulated, and there 
was no way of properly cleaning the filter. Animal charcoal after 
a time loses its properties, and actually gives back the impurities 
collected to the water ; it is also found to favour the growth of 
the low forms of organic life. We may therefore safely conclude 
that it is well to avoid the use of filters that are based upon the 
employment of charcoal only. 
There has been of late years a great advance in the construc- 
tion of filters, and their number is legion. I propose, therefore, 
briefly to note a few. 
Doulton’s Manganese Carbon Filter—One improvement in these 
filters consists in the fact that every drop of filtered water 
becomes available owing to the floor of the reservoir being formed 
with a slope towards the tap ; in most filters this is not the case, 
consequently the lowest stratum of water may lie unused, long 
enough to become positively harmful through the introduction of 
germs, which usually gravitate to the bottom of the water. 
This filter, though classed among the block system, claims to be 
exempt from the disadvantages attendant upon the use of charcoal 
in the ordinary block filters, and neutralizing the property that 
animal charcoal possesses of favouring the growth of low forms of 
organic life ; in porous blocks after a time the purifying power 
becomes diminished, and water left in contact with the medium 
is apt to take up impurity again. 
The principle of this filter is the combination of manganese 
with carbon in the block, and this professes to prevent the 
growth of organisms and also to improve with use. 
Silicated Carbon Filter.—This is another filter on the block 
principle—the block is formed of a mixture of carbon, iron, silica, 
and alumina. Professor Wanklyn states he has such confidence 
in this filter, that he has passed a solution of strychnine through 
it and drunk the filtrate. This filter claims to remove lead and 
also to soften the water appreciably. 
