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fucceffion,® it firft liquefies and mere watercomes over, after which a confiderable quan-tity of ammoniacal gas is given out, and if thefait in the retort be then examined, it is foundto be fulphat of ammonia with excefs of acid,and may be diffolved in water and cryftallizedwith this excefs, forming a fuper-fulphat. Butif the heat is continued, after the ammonia haspaffed over there rifes a denfe white cloudwhich fills the veffels and concretes into mi-nute glittering cryftals of volatilized fuper-ful-phat. After this rifes a great quantity of ful-phurous acid and water, the greater part ofwhich condenfes in the receiver, and withthem a quantity of azotic gas, all of which con-tinue till nothing remains in the retort. Duringthe diftillation the contents of the retort arealways liquid, and when the procefs is over,the receiver contains fulphurous acid, water,and ammonia, and in the neck of the retort isa quantity of fublimed fuper-fulphat of am-monia.
In the above procefs feveral decompofitionstake place. At firft a part of the ammoniafeparates from the fait leaving the latter withexcefs of acid; after which, as the heat is in-creafed, part of the fuper-fulphat in the retortis totally decompofed, the ammonia is refolvedinto its elements, azot and hydrogen, theformer of which paffes off in a gafeous form,and the hydrogen unites with part of theoxygen of the fulphuric acid to form water,and the acid with a diminished quantity ofoxygen becomes fulphurous acid. The entireprodu&s therefore are ammonia, water, ful-phurous acid, together with fome fuper-ful-phat that has efcaped compleat decompofition.
All the other ammoniacal falts Suffer this de-compofition of the alkali, totally or in part,when expofed to a high heat.
Sulphat of ammonia is decompofed by thefixed alkalies and by the alkaline earths. Itscompofition according to Kirwan, is 14.24 percent, of ammonia, 54.66 of acid, and 31.x ofwater.
The native fulphat has been already de-scribed under the article Heavy Spar, and itappears to agree very exaftly in chemical com-pofition with the artificial fulphat, for if anygiven weight of heavy fpar be decompofed by acarbonated alkali, and the carbonated barytesthence arifing be diffolved in muriatic acid, andagain precipitated by fulphuric acid in the form• Hatchett, Phil, Tranf. for 1796. p. 31c.
of a fulphat, the weight of the latter very ex-actly correfponds with that of the native ful-phat if pure, and if an equal degree of heathas been employed in the deficcation.
Sulphat of barytes is formed whenever anybarytic fait comes in contaft with fulphuricacid in any combination, and being perfectlyinfoluble in water, and in all acids, except themoll concentrated, it precipitates totally andfpeedily in all common cafes, and may be col-le£ted, edulcorated, and dried with great eafe,and without rilk of lofs. It is then quite freefrom fmell and tafte.
Sulphat of barytes is the heavieft of all theearthy falts. It undergoes no change by beingheated red-hot, without addition, except thelofs of the water which it may contain. In avery ftrong fire and before the blow-pipe itmelts into_an opake milky globule.
This fait is perfectly unchanged by any ex-pofure to air. None of the acids when at alldilute have any effeft upon it, but if it isheated with concentrated fulphuric acid to theboiling point of the acid, it diffolves thereincompleatly, forming a clear colourlefs denfefluid. f On dilution with water the fulphat ofbarytes again feparates totally and unchanged.The fulphuric folution expofed to the air forfome days depofits the fulphat of barytes inbeautiful radiated cryftals, and this is the onlymethod in which it can be brought to cryftallizeby art. This is doubtlefs effected by the ab-forption of water from the atmofphere, whichdilution being gradual allows the fulphat to befeparated in a regular form.
No fingle agent, neither acid, nor alkali, norearth, can feparate the fulphuric acid from ba-rytes except perhaps the fixed acids fuch as thearfenic and fluoric, in a very ftrong heat, butthis fulphat is readily decompofed by doubleaffinity by the carbonated fixed alkalies; andalfo by fufion with chart oal. In the formercafe the decompofition may be effe&ed eitherby repeatedly boiling the fulphat in fine pow-der, with a folution of carbonat of potafh andfoda, or by mixing the fulphat with two orthree times its weight of the dry carbonatedalkali, and giving the mixture a moderate redheat (which need not be urged to fufion) forhalf an hour, and then lixiviating the falinemafs.
In both inftances a faline folution is formed,which confifts of fulphat of potafh or fodawith fome undecompofed alkaline carbonat,and an infoluble powder is obtained, which
f Withering, Phil. Tranf. for 1784,