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CARBON AT OF AMMONIA; or Sal Vo-latile. Salt of Hartjhorn.

This, which is the belt known of all the arn-moniacal falts, is always prepared for generalufe by fublimation, and is found in the lhops inwhite compact irregular lumps, fontewhat re-fembling white fugar in appearance, and of aftriated texture.

Carbonat of ammonia is a copious product ofthe diltillation of all animal fubftances, almoftwithout exception, but is actually preparedchiefly from the refufe part of horn, ivory,bone, &c. Being volatile in a moderateheat it foon rifes in diltillation, and is founddiflolved in the natural watery and oily liquorswhich alfo diftil from thefe fubftances. It isnot from thefe however that this concrete faitis immediately prepared, but the impure am-moniacal oily liquor is firft converted into theMuri/vt of Ammonia (which fee) from whichthe pure carbonat is prepared by the followingprocefs. Mix together two parts of dry chalkwith one part of dry muriated ammonia inpowder, put them into a proper fubliming vef-fel, with the joinings carefully clofed, and ap-ply a gradual heat. A double decompolitionnow takes place, the carbonic acid of the chalkunites with the ammonia, and both rife togetheras a denfe white fume, which concretes on theupper and cooler vefl'el, and gradually collectsinto a hard tough cake. The refidue left in theheated veffel is the lime of the chalk, united toexcefs with the muriatic acid of the muriatedammonia, and is readily diflolved out by hotwater. The fublimation fhould be continuedtill the lower veffel is red-hot. The fame Ampleprocefs (with a fuitable apparatus) appears tobe adopted for the preparation of this fait inthe large way, as for experiment.

The carbonats of potafh or foda will anfweras well as chalk in the procefs, and lefs of themwill fuflice, but there can be no detriment tothe produft by ufing an excefs of the carbonatwhich is to decompofe the ammoniacal muriat.

The folid carbonat of ammonia thus preparedif it is dry, frelh made, or has been kept fromthe air, is very hard, tough, ftriated, white, andfemitranfparent. Its fmell is extremely pun-gent, and to moft perfons agreeable, but whentoo copioufly fnu-ffed up it excoriates the nof-trils. Its tafte is faline and ftimulating, butwith a fenfe of coldnefs. It gives the ufualtefts of alkalies with vegetable colours. It isvery foluble in water, and confiderable cold isproduced during the folution. At the heat of

* On the Aerial A<

55° water diflolves half its weight, and its owttweight at i2c°, but with conftant lofs by vola-tilization. When a folution of this fait is keptat a fcalding heat, a part of the alkali is con-ftantly flying off, and the folid fait thrown upona hot fhovel is totally volatile in denfe whitefumes. Even at the temperature of the air aconftant lofs is going on, as may readily be per-ceived both by the lofs of weight, and by thepenetrating ammoniacal fcent with which al'mall portion of the fait expofed to the air willfill a large room.

It is extremely difficult to procure this faitin any tolerably regular cryftalline form. Some-times by fublimation fmall needled cryftals arcfound cluftered together, but confufed. Thecommon method of faturating water when hot,and cryftallizing on cooling, will fcarcely anfweron account of the rapid volatilization of thefait from a hot folution.

Bergman fucceeded in obtaining tolerably re-gular cryftals a , by taking a concentrated folu-tion at a moderate temperature, faturating itwith carbonic acid, and expofing it to intenfecold. The cryftals, though not quite regular,appeared to be octahedrons with truncatedangles.

Carbonat of ammonia contains fo much car-bonic acid that it effervefces molt vehementlywith any of the acids.

This fait may be formed by a diredt unionof its two conftituents in their gafeous form,which furniffies a very beautiful experiment.Fill a jar half full of carbonic acid gas overmercury, then throw up as much ammoniacalgas, alfo over mercury, and as foon as the gaffescome together a very denfe white cloud of pre-cipitated carbonat of ammonia fills the jar,which is immediately followed by a total ab-forption of the gafles, fo that if they are pureand properly proportioned, the mercury rifesand fills the jar compleatly, leaving fcarcely avifible refidue. Some heat is given out by thisfudden condenfation.

As the ammonia is by much the lighted ofthe twogaffes,to produce the condenfation imme-diately it fhould be thrown up after the carbonicacid gas, and it will of courfe rife through thislatter, mixing with it in its paflage. If thisorder is reverfed, the two gafles remain feparatefor a while by the difference of their fpecific■gravities, and the white cloud and condenfationbegins from the point of contact of the two, andgradually fpreads upwards and downwards.

The fame experiment may be varied without

d Effays, vol, i,