case which are either much modified or are totally different in character to those prevailing in another.*

Although the conditions may be similar at the outset, although, indeed, the crude sewage to be dealt with in one district may be identical in composition with that in another, yet the method of treatment which gave satisfaction in the one case may be most unsuited to the other. This may be due to a variety of reasons, some of which are understood, whilst others still await elucidation. Difference in the nature of the water supply, in dealing with water-borne sewage, or slight differences in climate, or in physical environment, will be, in most instances, sufficient to render a method of treatment suited to one district inoperative in another.

Again, a slight difference in the chemical constituents of a particular water-borne sewage, due to the admission thereto, for instance, of liquid wastes from a brewery, or tannery, or manufacturing process, will probably call for some modification in the method of treatment, before it can be considered to have been satisfactorily dealt with.

Another factor, which has to be considered in the working of every installation, is the change which takes place both in constituents, volume and quality of the sewage to be disposed of in almost every hour of the day.

In installations connected with small towns it is easy also to detect the difference in the composition of the sewage on the chief local washing-day, when the presence of the various chemicals and fats which are used in the manufacture of soap make themselves felt, and interfere very materially with the methods of treatment employed on other occasions, if indeed they do not render it necessary in some way or other to alter or modify the treatment usual on other days.

Half a Century of Improvement.

It is scarcely too much to say. that to the improvements which have taken place in the methods of disposal of sewage matter in towns (the advance has not been so great in country districts) must be attributed a great deal of the improvement in public health which has taken place during the past halfcentury; and increasing knowledge in its scientific treatment must tend to yet further valuable results in the same direction. Half a century ago serious epidemics were of constant occurrence, and cholera and typhoid, more especially, demanded

*From the opening words of a Paper, by the writer, read before the Institute of Sanitary Engineers, Session 1910-11.

their toll of lives in one part of the country or another. Now, although not yet quite things of the past, as the typhoid epidemics at Maidstone, Gloucester, and Lincoln within recent years have shown, their virulence is much less in comparison.

The decrease in the death-rate furnishes ample evidence of the value of the advance which sanitary science has made during the intervening years, and the advance in the science of sewage treatment and disposal has played no mean part therein.

CHAPTER II.

Nature of Sewage Matter to be dealt with.

This will depend, primarily, upon whether conservancy, or water carriage, is the method employed in the collection of the sewage matter.

In the former, the night soil and urine only have to be dealt with, generally speaking; though, in some cases, house ashes, and, at times, waste vegetable matter are added to the contents of the pails to absorb the urine and facilitate conversion into portable manure.

Under conservancy methods, a system of sewers is necessary to remove the waste waters used for domestic purposes, washings from roofs, roads and streets, and also from stabling; the liquid wastes from slaughter-houses, business premises, and from manufacturing processes, if any.

These manufacturing and trade wastes are very varied in their nature. In most towns they consist of liquid refuse from one or several breweries, which render the treatment of the sewage with which it is mixed more difficult; as do, also, wastes from laundries, on account of the excessive amount of soap and various chemicals employed. Then most towns of any size, and others where leather dressing is a staple industry, possess one or more tanneries, the liquid wastes from which exercise retarding influences on the treatment of the ordinary town sewage with which they are mixed. Lastly, we have the trade effluents from various manufacturing processes, many of which are carried on in particular districts, each of which have special kinds of chemicals, dyes, fats, etc., used therein, as in the Lancashire cotton districts, the Yorkshire woollen and dyeing districts, etc., where such liquid wastes are admitted to the local sewerage system under the Rivers Pollution Prevention Act, 1876.*

In some cases the storm waters and washings from roofs, roads, and streets are conveyed away in separate pipes and receive but little treatment at the sewage works.

It will thus be seen that the composition and strength of the sewage to be dealt with and disposed of will vary to a very large extent in different districts.

*This Act applies to the United Kingdom (see p. 292).

The chief factors which influence the strength of the sewage are the number of water closets, the number of gallons of water supplied per head of the population of the particular area, and the nature of the liquid trade and manufacturing wastes (if any) to be treated with the ordinary domestic and town sewage.

Amount per Head.

Human excrementitious matter may be considered, by taking an average of all ages, and both sexes, as two to three ounces per head per day, and of urine two pints.

The late well-known chemist, Dr. Meynott Tidy, fixed the quantity of excrementitious matter in sewage, as quoted by Mr. Boulnois several years ago, as follows:

Every adult male person voids on an average 60 ozs. (3 pints) of urine daily.

The 60 ozs. contain an average of 2.53 ozs. of dry solid matter, consisting of—

Every adult male person voids about 1750 grains (or 4 ozs.) of fæces daily, of which 75 per cent. is moisture.

The dry fæcal matter passed daily is therefore about 1 oz. per adult head of the population. Of this dry fæces, about 88 per cent. is organic matter (of which six parts are nitrogen); and 12 per cent, inorganic matter (of which 4 parts are phosphoric acid), and some II per cent. is soluble in

water.

“Other experimentalists give about 35 ozs. of urine and 11⁄2 ozs. of fæcaľ matter for each person in twenty-four hours, and Messrs. Wolff and Lehmann, from investigations made with a mixed population of 100,000 persons for a year, give the following result:-3 ozs. of fæcal matter, and 26 ozs. of urine per day. It will thus be seen that there is some divergence of opinion as to the average amount of these matters voided daily by an adult, and it is really more important for

our purpose to ascertain what is the composition of waterborne sewage. This was given by the Rivers Pollution Commissioners in their first report of 1874, as follows:

TABLE I.

-

"This shows that there is, as a rule, only 116 per cent. of solid matters, in solution and suspension, in water-carried sewage in this country. It must not, however, be forgotten that this solid matter is of an extremely putrescible character, and hence the danger of untreated sewage, especially in cases where there may be in addition large numbers of dangerous pathogenic bacteria, or disease-producing germs."