SODA—Glauber’s Salts. 795

The prepared salt is placed in iron cylinders,where it is subjected to the action of the gas. Thecylinders, not less than eight in number, are arrangedin a series, so that each in its turn becomes first,intermediate, and last. The salt lies upon movablegrids which are supported on tripods; these beingknocked away at the end of the operation, the saltcake falls and is readily withdrawn. The sulphurousacid is first admitted into the cylinder whose con-tents are most nearly converted into sulphate, andthe spent gases pass out from that which was lastcharged with salt, after passing through a successionof cylinders containing less and less sulphate.

The cylinders are arranged in two rows, and theground space between them is filled by an archcovered with ashes; the flues from the burners areprotected from loss of heat by the arch and thebulk of ashes.

Sulphurous acid direct from the pyrites kiln isfound to be too concentrated to be allowed to passdirect into the cylinders containing raw salt, sincethe action is then so violent as to fuse it into a hardmass. This is the reason that the nearly spent gasis made to play upon the pure sodium chloride andcover it with a coating of sulphate ; as the cylinderis brought nearer to the beginning of the series thiscoating increases in thickness, whilst at the sametime the reaction proceeds evenly and regularly.

The cylinders are heated by a small furnace. Thehot gases pass through a horizontal flue and ascendnarrow vertical flues; these flues are only 5 squareinches in section, the object being to reduce theheat-absorbing surface. They are, however, amplylarge enough to carry away all the products of com-bustion. After leaving the vertical flues the smokecirculates round the cylinder and charging holes, andpasses away to the chimney.

As the heat generated in the process is more thanenough to keep up the operation, and the losses ofheat are due to radiation and convection from thebounding surfaces of the apparatus, it is evident thatas the apparatus is enlarged so as to reduce therelative proportion of bounding surface to cubicalcapacity, the proportion of fuel per ton of sulphatemust decrease also, and it is only a question ofcarrying the principle far enough, to do altogetherwithout fuel for keeping up the temperature of thecylinders. This has been proved by experience ; anearly form of apparatus required 2 tons of fuel perton of sulphate, whereas 3 cwts. of fuel suffice withenlarged cylinders.

The pyrites burners are much like those used invitriol making; they are placed back to back, andexposure of iron to the direct heating effect of theburning pyrites is avoided as much as possible. Theoutside walls are 18 inches thick, preferably using5-inch fire brick lining and common bricks for theouter wall. The rate of conduction of commonbricks being less than that of fire bricks, a saving ofheat as well as cost in erection is effected. Theback of the arch is thrown lower than the front andthe gas flue placed in the depression, a wall is raisedover the burner fronts, and the entire space over the

burner covered with ashes to a depth of 2 feet ormore to prevent conduction of heat. The door isprotected from the heat radiated from the pyrites bya non-conducting lining.

The steam, before allowing it to mix with the gasfrom the burners, is superheated to 650° Fahr. bythe products of combustion leaving the cylinders,which are at a temperature of about 800° to 850°Fahr.

The hydrochloric acid and excess of other gasesare drawn from the apparatus by an aspirating ap-paratus.

Glauber's Salts —Crystallized Sodium Sulphate—Na 2 S0 4 + 10H 2 O.—A great deal of Glauber’s saltsis produced by the systematical treatment of seawater, according to the plans proposed by Balardand Merle, and carried out to some extent in thesouth of France . At a low temperature mag-nesium sulphate and sodium chloride in solutionform sodium sulphate, which crystallizes out, andmagnesium chloride, which remains in solution.Another large quantity of Glauber’s salts is gotby working up the “ pan scales ” of salt works,which consist mainly of sodium and calcium sulphate;by extracting with warm water the gypsum is leftbehind, to be sold for agricultural purposes, whilstsodium sulphate is dissolved. The lyes are obtainedmore concentrated by systematical lixiviation, andattain 25° to 26° Beaume. At that strength they willyield a good crop of Glauber’s salts in winter; butin summer they must be concentrated to someextent before they are run into the crystallizingcoolers. Before doing so the liquor is purified bysettling and filtering through canvas bags. Thecoolers are long, shallow troughs of wood lined withsheet lead, say 20 feet by 6 feet; the liquor onlystands 3 inches deep in them, as otherwise thecrystals become too large, which is considered adrawback. As soon as the crystallization sets in,a wooden spade is drawn once from one end of thecooler to the other; this slight motion causes singlecrystals to be secreted, which’afterwards, when quietis restored, grow principally in their longitudinalaxis, and thus acquire that acicular exterior which isexpected by the buyers of that article. The liquidmust not be moved or stirred about too much;otherwise only very fine crystal “flour” would beobtained. On the other hand, if the liquid is notdisturbed at all, the salt is principally formed onthe sides and the bottom in the shape of largecrystallized masses, which must be chiselled off witha great deal of trouble. When the liquid is quitecool the mother liquor is syphoned off, and a littlecold water is poured on the salt with a wateringcan, in order to wash off the mother liquor. Thesalt itself is then taken out and dried in the air (inwinter in gently-warmed rooms) on wicker-worktrays. This drying process must be interrupted themoment any efflorescence shows that it has gone farenough.

A good deal of Glauber’s salt is made by dissolv-ing commercial sulphate of soda (made on purpose orbrought from alkali works) in water of about 30° C.;