SODA. —Black-ash. Shanks Vats.

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of each vat can flow through the jug and its sidebranch into the next vat. The corresponding jugin the last vat (that to the right in the diagram),

cannot of course communicate direct with the firstone; but it does so by means of the horizontal piperunning back from the last to the first vat. The

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plugs are sometimes turned in the lathe to fit thebored out seat; but as this fit is easily disturbed byany dirt getting between the faces, it is better togroove the sides of the plug, and lap them withtarred spun-yarn, which closes the valve more safely.The second set of jugs are all in the front of thetanks; they have somewhat lower branches than theother jugs, and are on the outside either connectedwith taps or, as in the diagram, with several pipes,which can be turned up or down. As a rule theyare turned up, and only in that tank which isrunning strong liquor the pipe is turned down intothe spout carrying the lye away into the strongliquor well. Another spout runs underneath theoutlet cocks, and leads into the weak liquor well.Each well is provided with a pump. A cold water-pipe with a cock for each tank runs along their tops,and the delivery pipe of the weak liquor pump isconnected with this water-pipe, unless a specialrange of pipes is laid on for the weak liquor.Another range of pipes is laid on for hot water, orinstead of this (as in the diagram), a steam-pipesending a branch (or preferably two branches) intoeach vat. The tanks sometimes rest upon the floor;it is, however, preferable to mount them on brickwalls, so that any leakages may be more easilydetected.

It will be seen that all the tanks are on the samelevel, and the principle on which they are workedis as follows: — The ball-soda is placed in thetanks, on the top of the false bottom; and oncethere it is not removed, as in the process just de-scribed, but it remains in the same tank till it iscompletely exhausted. Thus it remains porous upto the very last, and allows the liquid to circulatefreely, and to penetrate into every part of the mass.This makes such a difference that four, or eventhree treatments, suffice for exhausting the black-ash, whilst ten or twelve treatments are requiredin Clement’s apparatus. The black-ash beingstationary, it follows as a matter of course that thenecessary change of liquid is produced entirely by

a removal of the lye from one tank to another. Itis the very great merit of Shanks’ tanks that theliquids are made to travel from one vat to the other,without raising the vats one over the other, butentirely by relying on the hydrostatic pressure of theliquids.

As the lye in its progress through the tanks is moreand more saturated by dissolving soda salts, itsspecific gravity becomes greater; and in consequenceof this the level of the liquid in the “ strong tanks ”is below that in the “weak” tanks. It has beenconsidered by some that the “declivity” from theweak to the strong tanks thus produced is the realmoving cause for the liquid; but this is entirelyerroneous, as each tank will find its exact levelaccording to the specific gravity of the lye con-tained in it, and the shorter columns in the strongtanks exercise precisely the same action as the longercolumns in the weak tanks. When the supply ofwater to the weak tank is stopped, the strong tankat once ceases running, although its level is muchbelow that of the weak tank. The real movingcause is the small head of water produced in theweak tank by the influx of the fresh water on theone side, and the running.out of the strong liquorfrom the strong tank below the level of the lye. Butthe immense advantage of Shanks’ system over thatof Clement’s is this—that the whole play of levelsbeing reduced to about 18 inches, or say one-fourthof the depth of the tanks, they can be, and alwaysare, arranged so that each tank may serve as a weak,an intermediary, or a strong tank, as will be seendirectly.

The practical operation is carried out as follows:—The balls, which should be cold enough to behandled (forty-eight hours is a very good timefor them to lie after being drawn out of the fur-nace), but which ought not to be kept longerthan necessary over and above that, are broken intopieces of the size of a man’s head, many small pieces,of course, being produced as well. These are filledinto barrows or small waggons, and tipped into the