SAL

SAL

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faturated with fulphuric acid, either by the ad-dition of the mother liquor from the green vitriolmakers (confifting for the raoft part of red ful-phat of iron); or dill more economically bymeans of calcined and pulverized gypfuin : inthis latter cafe after mixing the materials andftirring them well together, they are to be leftat reft for fome hours, during which a doubledecompolition takes place, the fulphat of limeyielding part of its acid to the ammonia, and at(he fame time depriving this latter of its car-bonic acid. The folution of fulphat of ammoniathus produced is then mixed with common fait,by which another decompofition takes place,the alkali of the former and the acid of the latteruniting to form muriat of ammonia, while thetwo remaining ingredients produce by theircombination fulphat of foda.

The liquor containing thefe two falts is thenclarified by fubfidence and decantation, andtransferred into oblong leaden boilers, about 9feet long, 3 wide, and 9 inches deep. Theboilers are fet for about f of their length oniron plates, heated by a fire beneath, the re-maining part being fupported by flat tiles de-fended by folid brick-work from the accefs ofthe heat. As the water evaporates the Glauberfait begins to cryftallize, and is fwept from timeto time to the cool extremity of the boiler,whence it is (hovelled out into baflcets arrangedover the end of the boiler, that the liquor whichdrains from the fmall granular cryftajs may notbe loft. The evaporation is continued forfeveral hours, till as much as poffible of theGlauber’s fait has been feparated, and the muriatof ammonia begins to cryftallize on the furfaceof the liquor in the form of feathered liars.The remaining fluid is then run off into coolers,and depofits little elfe than muriat of ammonia,till it gets below the temperature of 70° Fahr,at which time the cryftals are to be removed,left they (hould be mixed with Glauber’s fait,which now begins to be again depofited. Afterthe muriat of ammonia has been fuffered todrain in the baflcets, it is removed to a kind ofoven, or even an open tiled hearth heated frombelow, where the water of cryftallization isdriven off, by which the fait becomes fpungy,friable, .and of an afh or Hate colour, interfperfedwith fmall white filaments.

The fait is now removed while hot into glo-bular glafs receivers, or more commonly glazedearthen jars, fitted with a cover (having a holeof above half an inch diameter in its centre)luted on with a mixture of clay and horfe-dung.Thefe are fet in iron pots over a ftrong fire, in

a furnace of eithrr a circular or oval form, andcapable of containing from fix to eighteen, fur-rounded with fand up to the edge of the pot,and aji'o having about two and a half inches offand on the cover, confined by an iron ring aboutthree inches deep, and two inches lefs in dia-meter than the cover, in order that if the luting(hould give way in any part, it may be repairedwithout fuffering the covers (which (hould bekept during the fublimation at about 320 0 ) tobe cooled by the removal of a large portion ofthe fand. Thefe earthen pans may be filled towithin two inches of the top, with the driedfait gently prefi'ed in, but not rammed clofe;and the fire, which has been lighted fome timebefore, is now to be raifed gradually till theiron pots are of a pretty ftrong red heat allround, being fo placed in the furnace that theupper part may be firft heated, the bottom redingon folid brick-work. During the firft impref-fion of the heat a portion of the fait carryingwith it a quantity of watery vapour not fepa-rated on the drying place, will efcape throughthe hole in the cover, which muft be left opentill all the aqueous particles are exhaled : this isknown by bringing a piece of cold fmooth ironplate near the hole in order to condenfe thefublimate, which, becoming more and more dry,at length attaches itfelf firmly to the plate, inthe form of a dry femi-tranfparent cruft. Atthis time the hole is to be (lopped with a bit oflute, more fand is to be put on the cover, andthe heat continued till it is judged that nearlythe whole of the muriat of ammonia is fublimed.The time requifite for this purpofe depends onthe ftrudlure of the furnace, the fize of the pots,the brifknefs of the fire, and other circumftancesonly to be learnt by experience. The procefs(hould be (lopped before the fublimation hasentirely ceafed, as the heat in fome parts of thejar may be too groat when it is nearly empty,and either by burning a part of the fait itfelf, orelevating a portion of foreign matter from whichit can never be kept wholly free, give the cakea yellow tinge, and a fcorched, opake, crackledappearance. The fame defedts are likely tohappen, when any part of the luting havinggiven way, is obliged to be repaired by wet lute,when the fublimation is pretty far advanced :confequently glafs veffels are preferable, excepton account of the expence, as they muft alwaysbe broken to pieces in order to get out the cake :the jars on the contrary will ferve for feveralfublimations, even the covers, if well glazed,will laft .two operations. The fublimationbeing finifhed and the apparatus having become