In the case of household soaps, where the resultant product must be of good appearance and have a firm texture, the difficulty is to produce a bar fit for sale after the cooling has been performed, as soap which has been suddenly chilled lacks the appearance of that treated in the ordinary way. Several patents have been granted for various methods of moulding into bars in tubes, where the hot soap is cooled by being either surrounded by running water in a machine of similar construction to a candle machine, or rotated through a cooling medium; and numerous claims have been made both for mechanical appliances and for methods of removing or discharging the bars after cooling. In many instances these have proved unsatisfactory, owing to fracture of the crystalline structure. Moreover, in passing through some of the devices for solidification after chilling, the soap is churned by means of a worm or screw, and this interferes with the firmness of the finished bar, for, as is well known, soap which has been handled too much, does not regain its former firmness, and its appearance is rendered unsatisfactory. A form of apparatus which is now giving satisfactory results is the Leimdoerfer continuous cooler (Fig. 19). This consists of a fixed charging hopper, A, a portable tank, B, containing tubes, and a detachable box, C, which can be raised or lowered by means of a screw, D. The bottom of the hopper is fitted with holes corresponding with the cooling tubes, _e_, and closed by plugs _c_, attached to a frame _b_, which terminates above in a screw spindle _a_, by means of which the frame and plugs can be raised and lowered so as to permit or stop the outflow of soap into the cooling tubes. The tubes are closed at the bottom by slides _d_, and the box B, in which they are mounted, is carried on a truck running on rails. The charging hopper can be connected with the soap-pan by a pipe, and when the hopper is filled with liquid soap the plugs _c_ are raised and the air in the box C exhausted, thus causing the soap to descend into the cooling tubes. [Illustration: FIG. 19.--Leimdoerfer cooler.] The slides _d_ are closed, the screw D released, and the box B moved away to make room for another. At the end of the rail track is an ejecting device which pushes the cooled soap out of the tubes, and the truck is run back on a side track to the machine for use over again. In this way the apparatus can be worked continuously, the soap being received from the cooling pipes on a suitable arrangement for transport to the press or store room. A similar idea has been made the subject of a patent by Holoubek (Eng. Pat. 24,440, 1904, Fig. 20). The soap is run into frames or moulds having open sides, which are closed by being clamped with screws and pressure plates between cooling tubes through which water circulates. [Illustration: FIG. 20.--Holoubek's cooler.] CHAPTER VII. TOILET, TEXTILE AND MISCELLANEOUS SOAPS.