820 SODA. —Black-ash. Ltxiviation.

three) tiers of iron tanks, one raised above the otherin the manner of steps, provided each with a cock ata certain height over the bottom. The lye from thetop tier was run on to the middle tier, from this on tothe bottom tier, and was then ready for evaporation.On the other hand, the black-ash was first tippedinto the bottom tanks; when these were run off theresidue was shovelled up into the middle tanks, andat last into the top tanks, whore fresh water wasrun on to it, and from whence the residue was takenout to be removed altogether. The only heating ofthe water or lye was by the black-ash itself.

This manipulation was not only very laborious, butit rendered, moreover, the mass very dense and com-pact, and thus seriously impaired its permeabilityfor the lixiviating liquid. The solutions thus ob-tained rarely exceeded 1T5 specific gravity. Aconsiderable improvement was effected by the appa-ratus of Clement-Desormes, which, indeed, held itsground on the Continent until quite a recent period.Instead of throwing the black-ash direct into thevats, where very soon a strong solution is formed atthe bottom, and very little further action goes on,Clement placed it in perforated baskets of sheetiron, which, with their contents, were immersed inthe water of the several vats, and kept suspendednear the top by means of handles and cross-bars.The vats themselves (generally ten or twelve in oneseries) were placed each slightly higher than theformer, and were connected by bent pipes in such amanner, that the bottom of each vat communicatedwith the top of the next lower one. Water was runinto the top vat, and this, after acting upon thecontents of the basket, flowed over from the bottomof the vat to the next lower one, and so forth, till itissued at the bottom as a concentrated solution ofball-soda. On the other hand, the black-ash travelledthe reverse way; each basketful was put in fresh atthe lowest vat. After a time the top one was takenout and emptied; it was replaced by that from thesecond, this by that from the third vat, &c.; thelowest one, which thus became empty, being pro-vided with a fresh basket. A travelling crane facili-tated the removal of the baskets. A steam-piperunning alongside the vats served to heat them,according to requirement. Each basket held from5G to 112 lbs. of black-ash ; each ton required there-fore the use of from forty to fifty baskets.

This plan gave very strong solutions, and thoroughlyexhausted the black-ash; but it had great drawbacks.The labour of continually lifting the baskets was veryconsiderable, and the space and plant required forthe operation in large works would be very large, asit goes on very slowly; but worse than that, theblack-ash, which during the lifting of the baskets lostthe hydrostatic support of the liquids, sunk downinto a more and more compact mass, and thus to agreat extent lost one of the most valuable propertiesof black-ash, viz., its porosity. Moreover, a greatdeal of fine stuff passed through the holes of thebaskets, and, on the one hand, rapidly plugged themlip, on the other hand, made the liquors muddy.

Shanks' Process .—Nobody who has once seen the

ordinary lixiviating tanks now in universal use in thiscountry, can wonder that they have entirely sup-planted Clement’s apparatus in all English works,and are doing so more and more on the Continentas well. The “tanks ” or “ vats ” now used are vastlysuperior to any previous arrangement by their cheap-ness, efficiency, and almost grand simplicity. Itseems that the inventor of this invaluable help toalkali-makers was the late James Shanks of St.Helens. I)r. Muspratt states it to be a foreigninvention, introduced by Dcnlop into the St. RolloxWorks at Glasgow about 1843 ; but this is probablya mistake, as nobody has ever claimed for himself orany one else the honour of this invention, exceptShanks, who has been rewarded for it by the greatestdistinctions of International Exhibitions. Shanks’vats, by applying the principle of leaving the ball-soda at rest and causing the liquor to travel throughit, obviates the labour of removing and the neces-sity of destroying the porosity of the black-ash.This is effected, not by the placing of the vats atdifferent levels, but by producing a flow of the liquorthrough them entirely by utilizing the difference inspecific gravity between water and weaker andstronger lyes.

The ordinary lixiviating tanks (sufficient for work-ing the produce of four or even five ball furnaces),are shown in Fig. 24, in an isometrical drawing.They consist generally of a set of four, made bydividing a long tank (40 feet long and 10 feet wideby 6 feet high), into four compartments of 10 feetsquare each.

Of course these measurements are only givenhere as very common, not as general ones. Thetanks are made of §-ineh iron plates, strengthenedby angle-iron at the top; T-shaped bars arerivetted at a distance of 6 inches from the bottom, asshown in the engraving, and these serve as supportsfor the perforated false bottom. The true bottomis made sometimes to slope towards the front,but more generally it is left level. The false bottomhas very frequently to be taken up for cleaningout the holes and the space underneath, andit must therefore consist of a number of plates,say 2 feet square, loosely laid side by side on theT.-shaped bars. The plates are sometimes made ofcast iron, but wrought iron (f-inch), is much pre-ferable, as the cast-iron plates break very easily.The holes are from one-fourth to one-half inch wide,and about 3 inches from centre to centre. Each tankhas an outlet cock of 3 inches bore, which must beso constructed as to admit of easy cleaning out bya red-hot iron when it is stopped up by crystals.Each tank has also two “jugs,” as shown in thediagram. One set of these serves as a means ofcommunication between the vats; the other forrunning off the strong liquor. The “ jugs ” consistof metal pipes 3 inches bore in the lower, and 4inches in the upper part, with a side branch, andwith a conical valve seat about midway up. A plugwith handle accessible from the top fits on the valveseat, and if put in, closes the communication ;whilst, when it is off, the liquor below the bottom