196 AMMONIA. —Sulphate op Ammonium.

cause it to sink into the layer of salt that depositsthereon; secondly, decomposition of any resinousmatters not completely destroyed in the dryingfurnace, whereby oily vapours would be liberated;and lastly, the accidental presence of ferrous or ferricchloride. The effect of the latter, however, is notgenerally on the first layer, but more frequentlyafterwards, when the temperature is higher.

The termination of the sublimation takes place infrom five to nine days ; but it is customary to raisethe caps every week, the fire being checked forsome hours previously. The salts are not sublimedto their last dregs, because the temperature required

would cause the decomposition of the carbonaceousimpurities, and emit vapours which would destroy' ina great measure the beauty of the sal-ammoniac.When a low temperature is used, or the compoundconsigned to the subliming furnace is impure, thechloride does not assume that compactness of grainwhich conduces to its transparency, but forms a kindof effloresced mass, though retaining the fibrous con-struction of the better quality.

When the sublimation has reached as far as isdesirable, the fire is allowed to go out that theapparatus may cool; the cover is then removed bymeans of the tackle before noted, and there is found

Fig. 17.

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in the interior a hard lining of the salt, from 2J to 3or 4 inches thick ; this is detached and conveyed tothe packing-house or store, and the residuary matterremaining in the body of the sublimers is removedto another part of the factory to be converted intosulphate of ammonia. The brown coating, arisingfrom the causes before alluded to, is separated fromthe cake by means of axes. The greater part ofthe chloride of ammonium manufactured is em-ployed by colour-makers and calico-printers, and bymakers of galvanized iron.

Sulphate of Ammonia. — Ammonium sulphate , sal-ammoniacum secretum, Glauber; (NTI 4 ) 2 S0 4 .—Thissalt forms crystals resembling those of potassiumsulphate, with which it is isomorphous. They be-long to the trimetric, i.c., the right prismatic system.

The prisms have six faces, and terminate in six-facedpyramids, belonging to the orthorhombic type.

Ammonium sulphate is colourless, has a sharpbitter taste, and is soluble in its own weight of boilingwater, or twice its weight of cold water. Inalcohol it is wholly insoluble. When heated itdecrepitates, and at 284° Fahr. (140° C.) melts. Above536° Fahr. (280° C.), it is decomposed into ammonia,nitrogen, water, and acid ammonium sulphite, whichlatter sublimes. ’When a solution of ammoniumsulphate is subjected to protracted boiling, it is inlike manner split up. At a dull red heat it is com-pletely decomposed, and yields sulphur, nitrogen,and water thus:—

Ammonium sulphate. Sulphur. Nitrogen. Water.

(NH 4 ). 2 S0 4 = S + 2N + 4H 2 0.