SODA.— Reactions in Black-ash Furnace. 815

Na a S0 4 + CaC0 3 = Na 2 C0 3 + CaS0 4 ;

that the calcium sulphate is reduced by the coal tocalcium sulphide, with the evolution of carbonicoxide; and that the calcium sulphide joins withcalcium oxide to form a compound insoluble inwater, of the formula CaO,2CaS . This theory, atleast the latter part of it, is based on the assumptionthat CaS is soluble in water, and that, if it existedas such in black ash, it would, during the lixiviation,decompose the sodium carbonate, thus,—

CaS + Na 2 C0 3 = Na a S + CaC0 3 .

This assumption seems, however, never to havebeen verified experimentally by Dumas or any oneelse. Dumas expresses the final results of the fusionin the ball furnace thus (converted into the newnotation)—

2Na 2 S0 4 + 3CaC0 3 + 9C = 2Na 2 C0 3 + CaO,2CaS + 10CO.

The proportions of material corresponding to thisequation are, theoretically—

Sodium sulphate,.;. 100

Calcium carbonate,. 105*6

Carbon,. 38

Considering, in the first place, the impurity of thecommercial articles used in actual work, andsecondly, the fact that a portion of the coal is sureto be burnt before having done its work, theseproportions very fairly agree with the mixturesactually in use in alkali works.

This theory seems simple enough, and it wasadopted by Brown and by Unger in its essentialfeatures, although they differed in some particularsfrom Dumas’ opinions. But the whole theory wascombated by Kynaston (on the strength of researchesmade in Dr. Muspiiatt’s laboratory), by Gossage,and by Scheurer - Kestner , on the followinggrounds:—Pure calcium protosulphide, made byigniting gypsum with charcoal protected againstaccess of air, is in itself insoluble in water, and isalso very little acted upon by a solution of sodiumcarbonate. Furthermore, it is a well-known factthat the solution of black-ash always contains acertain quantity of caustic soda. It is certain thatno caustic soda exists pre-formed in the black-ash,for the latter would yield it on treatment withalcohol, which, however, dissolves little or no causticsoda from it. It is therefore generally admitted thatthe caustic soda is only formed during the lixiviation,by the action of the sodium carbonate upon theinsoluble part of the black-ash (“tank waste”).

If this were essentially CaO,2CaS , it must beexpected that the action of sodium carbonate wouldproduce sodium sulphide in the following propor-tions of two equivalents to one of sodium hydrate—

3Na 2 C0 3 + CaO,2CaS + H 2 0 = 2NaOH + 2Na 2 S + 3CaC0 3 .

It is, however, not the case that anything like thisproportion of Na 2 S is formed in the tank liquor, andthe above named chemists therefore assume thatDumas’ calcium oxysulphide does not exist, but that

it must be considered as a mixture of calcium sulphideand oxide, the latter causing the formation of acertain quantity of sodium hydrate (caustic soda) byits action on the sodium carbonate. Gossage has,furthermore, adduced this very forcible argumentagainst Dumas’ views:—That these views require, ofnecessity, the presence of three equivalents of calciumcarbonate for two of sodium sulphate in the ball-mixture, but that he, as well as two other practicalalkali-makers, have worked, both on the small andon the large scale, with equal equivalents of each,and have obtained real black-ash. lie does not denythat the extra chalk is useful, or even necessary forproper work, but only because it affords a largeramount of surface for reaction ; and thus expeditesthe fluxing reaction, and thereby prevents theformation of calcium polysulphide. The opinion ofGossage has been entirely borne out by the suc-cess of Mactear’s mode of working revolving ball-furnaces, since in this only the real equivalents ofcalcium carbonate is used.

The calcium oxysulphide found a new advocate inE. Kopp, who based his views on many analyses ofsoda waste, in which the proportion between CaO and CaS had always been nearly that required byDumas’ formula. The constancy of this proportionwas contradicted by Sciieurer-Kestner, but Koppurged again that the soda waste does not form witha solution of sodium carbonate either as much sodiumhydrate or sulphate as if CaO and CaS occurred freein it; that the soda waste does not, like free lime,precipitate Mn0 2 H 2 from a solution of MnCi 2 ; andthat an artificial mixture of 2CaS and ICaO forms amass which does not react either on sodium car-bonate or on manganese chloride, thus behaving likereal soda waste.

The question was further inquired into (1864-66)by Sciieurer-Kestner, J. Kolb, Pelouze, Th.Petersen, and Dubrunfaut, all of whom declaredagainst Dumas’ theory. Their researches establishedthe following facts beyond any doubt:—1. Calciumprotosulphide is very slightly soluble in water (1000parts of water dissolve at the ordinary temperatureonly 0*08 CaS, according to Sciieurer-Kestner;0*23 according to Kolb; 1 to 1*5 according toPelouze), and it is extremely slowly decomposedby a solution of sodium carbonate. 2. There iscertainly neither Na a O nor NallO in black-ash, foralcohol extracts nothing, even after the mass hasbeen moistened with water. 3. When black-ashis gradually lixiviated, the percentage of the solutionin sodium sulphate does not increase pari passu withthat of sodium hydrate; but at a very much slowerrate. 4. If equal quantities of black-ash are treated,a with milk-warm water, b with boiling water, thereare in both solutions equal quantities of sodiumhydrate, but in the latter also a large quantity ofsodium sulphide and less sodium carbonate (Pel-ouze). 5. If soda waste after lixiviation is treatedwith a strong acid, the expelled quantity of II 2 S andCO, is sufficient to saturate the calcium completely;but this would be impossible if there existed in it alarge quantity of CaO,2CaS , and if the caustic soda