non-oxidizable electrodes was most efficacious after the temperature of
the fluid acted upon rose 4° or 5°; but the cost of working made it
impossible on a large scale.

After a long series of experiments, iron plates were used as electrodes,
with remarkable results, for the compounds of iron formed not only
deodorized the samples of sewage acted on, but produced complete
precipitation of the matters in suspension, and also of the soluble
organic matter; the resulting effluents remaining perfectly free from
putrefaction. The first part of the process is well illustrated by the
small experiments now shown; the organic matter in suspension and in
solution separates into flocculent particles, which rise to the top of
the liquid and remain until the bubbles of hydrogen which have carried
them up escape, when the solid matter will precipitate. In the
arrangement adopted on a working scale, the separated particles
precipitate readily. As an illustration of the action upon organic
matter in solution I take a small quantity of dye, mix it with water,
and placing the connected iron electrodes in the mixture, the dye in
solution separates into flocculent particles. The electrolytical action
is of course easily understood, but the chemical changes that take place
need an explanation. At the positive pole, hypochlorite of iron seems to
be formed at first, but this is quickly changed into a protochloride,
and as at the negative pole an alkaline reaction takes place, the iron
salt is precipitated in the form of the ferrous hydrated oxide, together
with the organic matters in suspension and solution. Owing to the
carbonates that are always present in sewage, ferrous carbonate is also
formed.

The success of these laboratory experiments led me to a trial of the
process on a larger scale, for hitherto only a gallon at any one time