ion show that the chief
advantages of this system of putrefaction are:

"First.--The active agent, hydrated ferrous oxide, is prepared within
the sewage itself as a flocculent precipitate. (It is scarcely necessary
to add that the inorganic salts in solution are not increased, as in the
case where chemicals in solution are added to the sewage.) Not only does
it act as a mechanical precipitant, but it possesses the property of
combining chemically with some of the soluble organic matter and
carrying it down in an insoluble form.

"Second.--Hydrated ferrous oxide is a deodorizer.

"Third.--By this process the soluble organic matter is reduced to a
condition favorable to the further and complete purification by natural
agencies.

"Fourth.--The effluent is not liable to secondary putrefaction."

Mr. Alfred E. Fletcher also investigated the process subsequently, and
reports as follows:

"The treatment causes a reduction in the oxidizable matter in the
sewage, varying from 60 to 80 per cent. The practical result of the
process is a very rapid and complete clarification of the sewage, which
enables the sludge to separate freely.

"It was noticed that while the raw sewage filters very slowly, so that
500 c.c. required 96 hours to pass through a paper filter, the
electrically treated sewage settled well and filtered rapidly.

"Samples of the raw sewage, having but little smell when fresh, stank
strongly on the third day. The treated samples, however, had no smell
originally, and remain sweet, without putrefactive change.

"In producing this result two agencies are at work, there is the action
of electrolysis and the formation of a hydrated oxide of iron. It is not
possible, perhaps, to define the exact action, but as the formation of
an iron oxide is part of it, it seemed desirable to ascertain whether
the simple addition of a salt of iron with lime sufficient to neutralize
the acid of the salt would produce results similar to those attained by
Webster's process.

"In order to make these experiments, samples of fresh raw sewage were
taken at Crossness at intervals of one hour during the day. As much as
10 grains of different salts of iron were added per gallon, plus 15.7
grains of lime in some cases and 125 grains of lime in another, and the
treated sewage was allowed to settle twenty-four hours; the results
obtained were not nearly as good as the electrical method."

During the present year a very searching investi