He adds that the full benefit of the impervious pavements as regards the cost of scavenging has not yet been felt, for almost all the lines of streets so paved are intersected at short distances by streets of ordinary jointed granite setts or macadam, whence a quantity of mud and refuse is dragged by the traffic on to the asphalted jointed roadways, which are consequently debited with the cost of removal of some effete material not intrinsically belonging to them. He further adds that the credit reductions to be made in respect of the value of manure obtained from each description of carriageway is not readily ascertainable. In dry weather the value of manure collected from granite setts, with or without impervious joints, is about equal, but when the sweepings are wet, and consequently of little value for sale, the quantity yielded by the ordinary pervious jointed pavement is greater than from the impervious, and therefore the total value is relatively favourable to the latter class, whilst to get rid of the sweepings from macadamised streets is a source of additional expense. He concludes this portion of his valuable report by observing that the advantages of the new impervious pavements over the old kinds are especially shown after frost and snowfall, the results of which cause the setts of ordinarily jointed roadways to become loose, and allow a vast amount of mud to ooze up between the softened joints. The comparison is still more apparent in regard to macadam, which, unless a heavy rainfall succeeds the thaw, cannot be swept for some days without great destruction being caused to the metalling of the roadway.
The ultimate disposal of the material removed from the surface of a macadamised roadway, being principally composed of silicate, and consequently valueless as a manure, is a difficult matter.
In small towns, except during abnormally muddy weather, it may be mixed with the house refuse and sold to farmers, or the road scrapings themselves may be used as an excellent sand, if thoroughly washed, to mix with lime or cement to form mortar for public works; excessive accumulations of mud, however, must be got rid of in the most economical and speedy manner, and this is effected either by filling up old disused quarries with it, or depositing it upon waste lands, or forming embankments for new roads, but in no case should it be used, as I have before stated, upon building sites; it is difficult and expensive to destroy it or partially convert it into other matters by fire, so that if these methods which I have enumerated are impracticable, the only other method left for the disposal of the sweepings or scrapings from the streets is to take them out to sea in hopper barges and sink them in deep water.
In the City of Paris an area of about 13,000,000 square yards of streets are cleansed between three and six a.m. in the summer months and four and seven in the winter. This work in connection with the collection of the house refuse employs 2,200 men, 950 women, and 30 boys, besides 190 mechanical sweepers.
The Paris mud is said to no longer possess the manurial strength of former times, and in consequence the receipts derived by the municipality from this source have greatly diminished. At the present time it is disposed of by public tender to responsible contractors, who manage to take between them some 2,500 cubic yards daily.
The following additional particulars of the manner in which this work is carried out in Paris will, I think, prove of interest, especially with regard to the use of disinfectants, which are largely used in that city in connection with the cleansing of the streets, a practice which might be followed with advantage by the Sanitary Authorities of this country.
The cleansing of the public thoroughfares in Paris, which was formerly undertaken by the Prefect of Police, is now a function of the Prefect of the Seine. The staff consists of two chief engineers, one for each group of arrondissements, one group being sub-divided into three sections, each under the charge of an executive engineer, and the other into five sections similarly supervised. These sectional engineers have under them 51 superintendents and 61 overseers, whose employment costs annually £10,400. The scavenging plant is kept in a central depôt, where materials of every description are stored and classified for ordinary and extraordinary service, when snow and ice render additional assistants necessary.
The depôts contain supplies of chloride of lime, sulphate of zinc, sulphate of iron, and carbolic acid, as disinfectants; and hydrochloric acid and nitrobenzide, as cleansing agents. The chloride of lime, of a strength of 100° to 105°, is successfully employed for the disinfecting of places tainted with urine or faecal matter, also for cleansing gutters carrying any sewage water. Sulphate of iron and sulphate of zinc are both used under the same conditions. Sulphate of iron has the disadvantage of rusting objects to which it is applied, sulphate of zinc is stronger in its action, but it costs a little more; it produces no smell, nor does it leave any stain; it is much employed in summer for washing and watering the basements of the "Halles Centrales," which are used for fish, poultry, and offal. At a strength of one-eighth, and mixed with three per cent. of sulphate of copper, sulphate of zinc makes a good disinfecting liquor, which preserves its qualities a long time, and is of great use in private houses. Carbolic acid is not, strictly speaking, a disinfectant; it does not act like chloride on putrid matter, but it arrests and prevents fermentation, doubtless by destroying the spores, it is, therefore, always employed when it is desired to destroy the germs of putrid fermentation. It is used at a strength of about one-fortieth, say a gallon of acid to 40 gallons of water. At strengths of one-one hundredth and one-two hundredth it gives good results for watering once or twice a week in summer those parts of the "Halles Centrales" liable to infection; it is even used as low as one-one thousandth for watering streets and gutters. Hydrochloric acid is applied to urinals and slaughter-houses, in places much encrusted with tartar; it is used at a strength of one-sixth, lowered to one-tenth, it cleans smooth walls and flags efficiently, in ordinary rinsings a strength of one-fifteenth suffices; it leaves a disagreeable odour behind, which is, however, quickly dissipated. Nitrobenzide is more energetic than the foregoing, but it produces a disagreeable smell of bitter almonds and leaves a white film, which has to be washed off; it is used at the same strengths as hydrochloric acid. The annual cost for plant and disinfecting materials of all descriptions is £8,800.