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 had been treated.

Small brick tanks were erected at my wharf at Peckham and iron electrodes fitted to them.

Wrought iron plates were fixed about an inch apart, and connected in parallel in the tanks, forming one big cell.  Sewage to the amount of about 200 gallons was run into the electrode tank and then treated, the results being so satisfactory that larger works were erected, when a supply of sewage equal to 20,000 gallons an hour could be obtained.

After a number of experiments had been carried out it was decided to run the sewage as rapidly as possible through electrodes, six cells or two rows in series fixed in a long channel or shoot, for experience showed that the motion of the liquid acted on reduced the back E.M.F. and hastened the formation of the precipitate.

A channel is kept at the bottom of the electrodes for the silt to collect, with a culvert at side to flush it into, so as to prevent any block occurring; the advantage of this is obvious.  The plates in each section may be from half an inch to an inch thick, and can be of any length up to 6 ft.  It may possibly be objected that a large number of plates is required.  This may be so, but the larger the number of plates, the less the engine power required, and the longer they last.  In each section the electrodes are in parallel, and any one section is in series with the other, the arrangement being exactly like that of a series of primary battery cells.