RETORT-BENCH APPURTENANCES
265
Fig. 181.—Tower with Internal Seal.
shown in Fig. 180 is the possibility that the outlet pipe may become clioked, and, owing to the liquor flowing into a covered seal-pot, the stoppage may not be imme-diately noticed. In this case the tower gradually fills, with the result that a heavy seal is thrown upon all the dip pipes. It is scarcely necessary to mention that on all installations of the kind, bends in the pipework should be rigidly avoided, and plugged Grosses should be used wherever possible.
(/) It is always advisable to pro vide for a constant supply of liquor when towers are in use. Although this is frequently admitted at the liydraulic main, it is far preferable to arrangefor a small supplementary supply to the top of the tower as well.
(g) In cases where outside or inside sealing arrangements are provided, care must be taken to ensure that all possibility of syplioning is avoided. To this end, some portion of the pipework must be open, to the at-mosphere, whilst it will be noticed that in the system
shown in Fig. 180 this is
not necessary, as syphoning could not take place.
Sketches of the outside and inside seal types are given in Figs. 181 and 182, and the anti-syphon precautions will be noted. A decidedly uncommon and novel arrangement is that shown in Fig. 183. In this instance the depth of seal on. the dip pipes is entirely governed by the constant overflow of tar, the outlet pipe for the latter being brought up from the base of the tower to a point sufficiently high to maintain the seal. Accordingly, it is tar, and not liquor, which is constantly trickling away ; and since more liquor th.an tar is formed, a special draw-off cock for the former is provided about two-thirds of the way up the tower, and a certain amount of liquor is daily run off, so as to ensure there always being tar at the bottom of the tower. The chief advantage claimed is that the liquor may be worked up to greater strengt li than is the case with the more ordinary tower systems, whilst there is no constant stream of warm liquor running away to the wells.
An uncommon idea, infrequently met with, is that shown in. Figs. 181 and 185. It con-