RETORT-BENCH APPURTENANCES 263
reference to Fig. 179. It will be seen that the tar-box casting is attached to the side of the hydraulic, seal regulation being effected by the running socket, as shown. Owing to the greater density of the tar, the height of the liquid level in the tar box
Fig. 178.—Typical Weik Valve.
will be slightly below that of the liquor in the hydraulic main. An important feature is the equilibrium pipe between the tar box and main, which ensures the same conditions prevailing above the two columns of liquid. Tar boxes of this type are, at the present day, very seldom erected, as they are not always reliable in their action and entail a good deal
Fig. 179.—Showing Principle of Action ok Tab Box.
of attention. . They are, moreover, expensive in the first instance; and have largely given way to more modem principles.
TAR TOWERS
Probably one of the most striking features of present-day retort-bench equipment is the manner in which the Dillamore tar tower—an appliance originally introduced many years ago, but with. mixed results—has forced its once-despised merits upon the attention of the gas engineer, so that it is now looked upon as fumishing a most effective means for seal regulation and tar and liquor disposal. It may be said that each engineer who favours tar towers has his own particular way of fitting them up; hcnce no hard and fast rules can be laid. down. In general, however, it will be found profitable to aim at leaving the interior of the tower as unencumbered with pipework as possible, and with. this end in view the author suggests the scheine shown in Fig. 180 as being the least costly and the most satisfactory from the stand-