P R U

P R U

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Scheele, Berthollet , and others, which lead toan explanation of the nature of this Angularfubltance.

Thole of Scheele were the following (amongmany others of lefs importance).

Some pure pruffian blue was prepared anddiftilled per fe in a retort, to which was attacheda. receiver containing a little water. The firewas urged till the retort was red-hot. Thewater in the receiver contained fome undecom-pofed pruilic acid, and ammonia, and the airof the veffel was impregnated with the volatileacid, and with carbonic acid gas. The mafsthat remained in the retort was black and mag-netical. Hence ammonia appeared to be oneof the conftituents of pruffic acid, and the otherthe author was at firlt difpofed to believe to bean animal oil. He then endeavoured to eom-pofe pruffian blue by uniting ammonia withfome oily matter by diftillation of this alkaliwith fat, lard, oil of turpentine, &c. but to nopurpofe. This led to the further conjecturethat it was the carbonaceous part of the oilalone that was eflential, which was confirmedby the following experiments: two crucibleswere filled with a mixture of charcoal powderand alkali of tartar, and kept for a quarter of anhour at a red-heat. The contents of one werethen thrown into water, but into the other fomedry muriated ammonia was ftirred in, and heat-ed for a minute or two till no more ammoniacalvapours were given out. This was then lixivi-ated with water. On trying the lixivium fromthe firft crucible, with vitriol of iron, and acids,fcarcely any fenfible quantity of pruffian bluewas obtained: but the fecond gave it in abun-dance. In another experiment, plumbago wasfubftituted to the charcoal, and after calcinationwith potafh and fal-ammoniac, it yielded pruf-fian blue. From thefe interefting experimentsit appears that the pruffic acid is generated byfome peculiar action of charcoal on ammonia,a [filled, doubtlefs, by the operation of potafh,or in other words, that it is, probably, ammo-nia intimately combined with carbon. Hencewhen pruffian blue is mixed with fix times itsweight of black oxyd of manganefe and diftilled,nothing but carbonated ammonia comes overinto the receiver.

Berthollet purfued thefe ingenious refearches,calling in the affiftance of another and moltpowerful agent, the oxymuriatic acid. If thisacid is mixed with liquid pruffic acid preparedm the way_ given by Scheele , the oxymuriaticxad lofes its peculiar fuffogating fmell, and

becomes common muriatic acid, whilft the-liquor acquires a much more pungent odour,and appears to have become more volatile, andits affinity for alkalies to be leflened. In thisftate the precipitate which it forms with thefolutions of iron, is at firft green, but turnsblue by the aftion of light, or by fulphureousacid, that is (probably) by lofing a part of its -oxygen. When fulphat of iron is mixed w r ithoxymuriatic acid, and pruffiat of potafh is added,the green precipitate firft formed is rediflblved,but may be changed to the common infolubleblue pruffiat by Ample fulphat of iron, or ironfilings, or fulphureous acid. If pruffic acid isfully impregnated with the oxymuriatic and thenexpofed to the light, its properties as prufficacid are deftroyed, and new ones are acquired.-It now no longer combines with iron, anilaflumes quite a different and very peculiar fmell,,and when fhaken with water, a great partcol lefts at the bottom on {landing for a fewfeconds, and refembles in appearance an efl'en-tial oil. This Angular fu-bftance however is notinflammable, but at a moderate increafe of heatit refolves into a vapour immifcible with water. -If left to itfelf, in time it cryftallizes, but thenature of thefe cryftals is not known.

Though pruffic acid at firft contains no ammo--nia, as fuch, (at leaft not in a ftate.to be difen-gaged by lime or the alkalies, as is the cafewith all the known ammoniacal mixtures) yetwhen it has been brought by oxymuriatic acid-to that point at which it precipitates a greenpruffiat of iron inftead of a blue, and fixed alka-lies or lime are added, it now gives the volatilealkali in abundance, and lofes its peculiar peachflower fmell. At the fame time it effervefeeswith the ftronger acids, and carbonic acid isdifengaged. Hence it feems the moft probablefuppofition that pruffic'acid contains neither car-bonic acid nor ammonia ready formed, but theelements of thefe, (with the exception of oxy-gen) or in other words, that pruffic acid is a-combination of carbon with hydrogen and azot.

The method indicated by Scheele of com —pofing pruffic acid, by heating together ammoniaand charcoal, was repeated by Clouet a in adifferent manner, that is, by palling ammonia-cal vapour through red-hot charcoal. Thisvapour was difengaged from a mixture of limeand fal-ammoniac in an earthen retort, the neckof which w r as luted into a porcelain tube con-taining charcoal, and lying acrofs a fmall fur-nace. To the oppofite end of the tube wasluted a tubulated balloon,, which communicated':

* An. Chinn tom, xi.