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completely iu the cone than in the old system.There is, of course, a system of spouts (mostly cast-iron ones) arranged over the cones, of which some-times several hundreds are placed in one shed, inorder to feed them with hot liquor; and anothersystem of spouts is laid in the ground, mostly levelwith it, in order to carry away the mother liquor.There are always strips of hoop iron laid over thecones, slightly hanging down into them, so thattjiey are covered by the liquor in filling the cones;they are laid crossways, and form a support for theformation of a crust, which soon covers the wholesurface of the cone, and ultimately becomes quite afoot thick. This crystal is generally the very bestand whitest. That attached to the sides and bottomis also broken off in as large lumps as practicable,and laid on a wooden bench to dry superficially fortwenty-four hours. It is then, still somewhat wet,packed into the casks, the interstices between thelarger lumps being skilfully filled up with the smallerfragments always occurring. It is sent out in casksholding from 2 to 8 cwts., and the custom on theTyne is not to tare the casks at all, but to invoicethe gross weight of the casks. The buyers, ofcourse, are aware of this, and generally assume that7$ per cent, of the weight invoiced is not soda, butthe tare of the casks. Each cone of the formershape yields about a ton, and those of the rectangularshape about 28 cwts. of soda crystals.
The French market requires a whiter and drierkind of crystal than the English one, and their modeof operation is- rather different from that used inthis country. The crystallizing cones are verysmall—sometimes round, sometimes square, andtapering to the bottom—about 18 inches wide and9 inches deep. They are mounted on woodenframes in three or four tiers, one over the other.After standing forty-eight hours (in summer thisoperation is not carried out at all in France ), theyare lifted off the stand, which can be done by oneman ; the mother liquor is poured off, and the coneis placed in a pan filled with boiling water, which,however, does not run into the cone itself. Aftera few moments the small cone is lifted out again;and as that portion of crystals immediately adheringto its sides has been melted by the heat,-the wholeof the crystallized contents can be tilted out as oneblock. These blocks are placed on edge on woodenracks, standing, one leaning against the other; andwhen completely drained, are transferred to a dry-ing chamber heated to about 30° C., where theyremain till they are quite dry, but not till theybegin to effloresce. This kind of work requiresmore labour than the English style, but the resultis better.
The mother liquors from the crystallizing conesare concentrated in an iron pan up to the saltingpoint, and furnaced exactly like white alkali. Theyyield a very white product, called mother alkali,which in winter, when the crystallization is verygood, only shows 30 per cent, alkalimetrical test ;but in summer the test comes up to 40 and some-times even to 44 degrees, which of course means a
corresponding loss of crystals. The low strengthof this mother alkali is caused by its large per-centage of sodium sulphate, which almost entirelyremains in the mother liquors; and it is thereforein good request by glass-makers, who only pay forthe alkalimetrical test, but to whom the sodiumsulphate, which they get for nothing, is almostequally valuable.
Sodium Bicarbonate. — Bicarbonate of Soda , Hydro-gen and Sodium carbonate, Ilydrosodic carbonate, Mono-sodic carbonate, Acid sodium carbonate —NallCOg.This salt may be obtained by passing carbonicacid through a concentrated solution of the neutralcarbonate, or by placing crystals of sodium carbonatein an atmosphere of the gas. In both cases bicar-bonate of soda separates after a time in minute crys-talline grains.
Sciiofeer’s process was to mix 1 part of commer-cial sesquicarbonate of ammonia (chiefly bicarbonate)with 3 to 4 parts of crystallized sodium carbonate.The semi-fluid mass thus obtained on being heatedgives off ammonia, and sodium bicarbonate remains.
Sodium bicarbonate is slightly alkaline, reddenslitmus, and has a feebly alkaline taste. At a mode-rate heat it loses half its carbonic acid and the wholeof its water, and is reduced to the state of neutralcarbonate. When the solution is heated to 70° C.carbonic acid is evolved.
Water at 10° C. dissolves about one-tenth of itsweight of sodium bicarbonate; the solution evolvescarbonic acid, if the temperature is increased to 70°C. the gas is given off rapidly, and at the boilingpoint the salt is reduced to neutral carbonate.
The process commonly followed for manufacturingbicarbonate of soda was suggested by Sciioffer.As the utilization of all the muriatic acid is verydesirable, this salt is made in several alkali workswhere soda crystals are manufactured, and where,at the same time, there is a considerable quantityof weak hydrochloric acid produced, of insufficientstrength to serve for the manufacture of bleachingpowder. The acid is allowed to act upon limestoneor chalk (of which the poorest kinds are availablefor this purpose) in large stone cisterns, laid in clayand well bedded. These are provided with a man-hole, with an inlet-pipe for the acid, which reachesnearly to the bottom on one side of the tank, withan overflow-pipe for the calcium chloride solution,and with an outlet-pipe for the gas. The man-holeserves for introducing the limestone, and for the occa-sionally cleansing of the cistern. The weak hydro-chloric acid, which generally comes direct from thecondensers, enters of course near the bottom of thecistern, where it at once disengages carbonic acid;and its supply is so regulated that it is completelysaturated whilst rising in the cistern, as it is dis-placed by the fresh acid flowing in underneath, andthus the calcium chloride solution overflowing atthe top is almost or quite neutral. The gas as it isevolved from the cisterns is often washed in a con-venient apparatus, and then conveyed in pipes tothe boxes containing the soda crystals. These boxesare mostly made of iron, and in various shapes,