688 On the Purification of Water by means of Iron. 
Sand-filtration is not always necessary ; subsidence in large 
tanks or reservoirs frequently answers equally well, for the iron 
possesses the property of curdling together the impurities like 
isinglass, and causing them to subside quickly, which, before 
treatment, they would not do in any reasonable time. 
The stock of iron required on the system described is very 
small ; a machine to deal with 500 gallons per minute holds a 
charge of about one ton and a quarter, and the rate of use, in- 
cluding fine particles washed away in the first instance, is, with 
the worst waters, less than 15 lbs. weight per million gallons. 
The cost of the iron is about 6Z. per ton for large quantities, and 
8Z. for small. 
With respect to the effect of iron on the sanitary condi- 
tion of water, it is daily growing more and more certain that 
the views held by Professor Bischof, Dr. Frankland, Dr. de 
Chaumont, Dr. J. Lane Notter, Dr. Voelcker, Mr. Hatton, and 
others who have examined the matter, are correct, namely, that 
not only does the iron oxidize or burn up obnoxious organic 
impurities held in solution, and therefore incapable of separa- 
tion by mere filtration, and throw down salts which cause hard- 
ness, but that the germs and living organisms, both animal and 
vegetable, are killed, after sufficient, though by no means long, 
exposure. 
In the interesting discussion which followed the reading of 
my paper at the Institution of Civil Engineers, Dr. Frank- 
land dwelt upon the extraordinary vitality of germs and 
organisms exposed to the action of powerful alkalies and acids, 
and expressed surprise that they should be so powerfully 
affected by a substance so neutral as iron. 
It is certain, however, that the water in the purifiers is largely 
deprived of its free oxygen, and the inference is highly probable 
that many living organisms cannot consequently exist, and are, 
in fact, smothered for want of air. In the revolving purifier it 
is necessary to provide a cock for periodically letting off the 
gases which collect. These gases are found to extinguish the 
flame of a taper instantly, and on analysis are proved to contain 
only 8^ per cent, of oxygen. It is satisfactory to find, as a con- 
firmation of the views of the eminent men above quoted, that the 
inhabitants of Antwerp have been free from all epidemics, 
although they have been for three years supplied with water 
taken from a most offensive and discoloured tidal river, a river 
which flows through and drains a highly-farmed country, and 
which takes the sewage of several large towns and many 
villages. 
There is no doubt that, by adopting purification of water by 
spongy iron, almost any source can be made thoroughly fit for 
