The practice of filling up hollow places with such materials cannot be too strongly deprecated if there is any chance of dwelling houses being erected on them, as the unsanitary condition of sites thus formed has been frequently demonstrated. Where towns are unable to dispose of their refuse by sale to farmers or market gardeners, the best method, and one which is gaining in popularity every day, is that of its destruction by fire. With this object in view a Mr Fryer has invented an apparatus which he styles a “Patent Carboniser, for the conversion of garbage, street, and market sweepings, also other vegetable refuse, into charcoal.” This apparatus consists of a structure somewhat resembling, externally, a brick kiln. It is divided into hopper-shaped compartments, which at the bottom are furnished with a furnace, fitted with a reverberatory arch. A fire is lighted in this furnace, the necessary combustion being obtained, and the heat maintained, by burning the cinders, which are sifted out of the house refuse for this purpose. All the street sweepings, refuse, garbage, &c., is then thrown in at the top of the kiln, and it is there and then completely destroyed by the action of the fire, and converted into charcoal, which is withdrawn through a sliding door fixed at the bottom of the kiln.[162] The next point which has to be considered, and which is the second in order of the list of duties I have given at the commencement of this chapter, is “the cleansing of earth closets, privies, ash-pits, and cesspools.” This is generally effected in conjunction with the collection of the house refuse and the work is carried out at night. Under the Goux-tub system the ashes of the house refuse are largely used as a deodorant or absorbent as a lining for the tub,[163] but in the pail systems this mixture is not effected until the tubs and refuse arrive together at the depôt. For descriptions of the manner in which the pail system for the collection of excreta is carried out in Birmingham, I must refer my readers to an article written by myself in a number of _The Sanitary Engineer_ of New York published on the 1st Sept. 1881, in which I have entered fully into the method there adopted and its advantages and disadvantages, but which are too long to recapitulate in this chapter. The next duty which has to be considered is that of “the proper cleansing of streets.” There is no doubt that for the sake of the appearance as well as the health of any town its streets cannot be too well cleansed. Muddy and wet streets cause dampness in the subsoil of neighbouring dwellings, and dust is not only injurious to tradesmen’s goods but also to the lungs of those who have to breathe an atmosphere loaded with silicate and organic impurities.[164]