The apparatus for accomplishing the evaporation varies with almost every mill. In some, it is very primitive and {181} crude, consisting perhaps of only a furnace for incinerating the residue, and over it a pan containing the liquor, the latter being heated and evaporated by the heat from the furnace. It is obvious that, with such an arrangement, a large quantity of heat must be wasted. To economise as much as possible of this waste heat, various plans have been suggested. That of Rœckner, of Newcastle, appears to be to a great extent efficacious. It consists practically of a series of shallow trays B (Fig. 67) placed in a brick chamber, alternated so as to allow the heated air from the furnace below to play upon the surface of each in succession, on its way to the chimney, with which the whole system is in connection. Above the chamber containing these trays, is a large tank C, containing a store of the liquor to be evaporated, placed there so as still further to economise the heat, and from which the liquor runs on to the trays. The furnace A is of the ordinary reverberatory kind; below it, and connected with it by a kind of damper, is a large chamber J, where the calcined residue from the furnace is put to cool, thus preventing any nuisance from the smell of the burning mass. The chamber is provided with a pipe L, through which the vapours pass into the furnace. Several pipes E from the furnace pass through the {182} tank, to assist in warming the liquor. The residue, when cold, is drawn through doors from the chamber below the furnace. Rœckner has devised an apparatus (Fig. 68), consisting of a small chamber containing a series of pipes A, through which a stream of cold water constantly runs, in connection with the flue from his evaporator, for the purpose of condensing volatile bodies, and thus preventing, to a certain extent, contamination of the surrounding air. A very economical form of evaporator is that invented by Porion, a French distiller, and named after him. It is shown in sectional elevation and plan in Figs. 69 and 70. It is largely used on the Continent, and also in England and Scotland. It consists of a large chamber _k_, the floor of which is slightly inclined from the chimney shaft, and through which the waste heat from the furnace _a_ passes. [Illustration: FIG. 69.] [Illustration: FIG. 70.] The liquor to be evaporated is run in at the end nearest the chimney from the tank placed above the chamber _c_. A number of cast-iron fanners _i_, dip into the liquor and revolve rapidly, usually at the rate of about 300 revolutions per {183} minute, producing and filling the chamber with a very fine spray, thus presenting a very large evaporating surface.