Chemical treatment of sewage was first tried in Paris in the year 1740, and since then every effort has been made to extract a valuable and commercial manure from sewage and purify the effluent. Between the years 1865 and 1875 more than 400 patents were taken out in respect of these and other matters in connection with the sewage question. It is almost needless to say that but few of these patents were of any practical value. Those processes which have some merit and are now best known are, I believe, included in the following list:-- LIST OF CHEMICAL PROCESSES FOR THE TREATMENT OF TOWN SEWAGE. The A. B. C. (or Sillar’s) process Anderson’s process Bird’s „ Blyth’s „ Campbell’s „ Collin’s „ Forbes and Price’s process Fulda’s process Goodall’s „ Hanson’s „ Higg’s „ Hille’s „ Holden’s process Lenk’s „ Lundy’s „ Manning’s „ Scott’s „ Smith’s „ Spence’s „ Stothert’s „ Suvern’s „ Whitthread’s process Wickstead’s „ Space will not permit me to describe these processes, and probably most of them, if not all, are familiar to my readers. Suffice it to say that in nearly all cases the _modus operandi_ is that of mixing certain chemicals with the sewage by mechanical agitation, or by passing the sewage over “salmon ladders,” &c., then allowing the sewage to remain perfectly still whilst the solids are gravitating, and then dealing with the effluent in different manners. Amongst the numerous chemical ingredients which are used for this purpose may be mentioned the following:-- Alum, animal charcoal, ashes, blood, bone ash, carbolic acid, chalk, chloride of lime, chloride of zinc, chloride of iron, clay, creosote, hæmatite, hydrate of lime, lead nitrate, magnesian salts, oxide of manganese, perchloride of iron, salt, soda, sulphate of zinc, sulphate of iron, sulphuric acid, and tar. One of the great difficulties in connection with the precipitation of sewage is the disposal of the sludge which is left behind in the tanks.