P R U

P R U

( 256 )

with two other balloons in fucceffion, the firflof v/hich contained a folution of lulphat of iron,the fecond, fome of the lame folution acidu-lated, and the third, an acid nitrous folution ofiron. When the charcoal was red-hot, theammonia was palled through it, and the gas illpilling through the three balloons, produced alarge quantity of Prulfian blue in the firfl: (whichcontained neutral fulphat of iron) but none inthe fecoud or in the third. In another experi-ment the firfl balloon was filled before the ope-ration with l'ulphuric acid, largely diluted withwater, the fecond contained diflilled water, andthe third, cauftic fodain dilute folution. Whenthe operation was finifhed, the firfl balloon con-tained fulphat of ammonia (owing to the paflageof fome undecompofed ammonia) and alfo fomepruffic acid, fo as to give the blue prufliat onadding a folution of iron. The fecond appearedto hold pure pruffic acid, and gave Prulfian blueon adding a iolution of iron, and along with itfome alkali. In the third, the foda was foundcombined with a large quantity of pruffic acid.

This experiment was repeated by Bonjour, bwho on adding potafh and oxyd of iron to oneof the balloons, obtained in it after the diftilla-tion a fenfible quantity of cryftallized prufliatof potafli.

i he pruffic acid often makes its appearance(and is clete£ted either by the peach-flower fmellor by the blue precipitate which it forms withfplutions of iron) during a variety of decom-poling operations on animal fubflances eitherfpontaneous or artificial. Thus Vauquelin foundit produced by the action of nitric acid on ferum,and Fourcroy and others have detected it as anoccafional product (though rare) of animalputrefaction.

This acid is alfo contained in the vegetablekingdom in fmall quantity, in thofe fubflanceswhere the fmell would indicate it to be, that is,in bitter almonds, peach flowers, in the leavesof the lauro-cerai'us, &c. As thefe contain apoitonous principle, it has been conjecturedwith fome probability that it may refide in thepruffic acid, which is itfelf highly deleterious.

M. Schrader 0 detected this acid in thefevegetable fubflances by adding lime to the con-centrated infufion or diflilled water, then ap-plying a folution of iron and acid. Vauquelinalfo d obtained a notable quantity of the acid inthe diflilled water from the kernels of apricots,and that of bitter almonds. Ihefe waters weremixed with a folution of iron, then precipitatedentirely by ammonia, and after flirrmg the mix-

^Joarn. de l’Ecole Polytechnique 3d Cabiir. c J^urn. tie PI

ture and repofe for fome hours, fulphuric acidwas added, which diflolved the excefs of oxydof iron, and left an infolublejilne-green precipi-tate, which retained its colour for fome days,but immediately became blue in the heat ofboiling water. The alkalies took away the bluecolour and changed it to yellow, as they do thecommon blue prufliat of iron. As the heatemployed here was not fuperior to that ofboiling water, it appears more than probablethat the pruffic acid was merely expelled fromthe almond and other kernels by diflillation, andnot formed in the procefs, which therefore willentitle the pruffic acid to be confidered as oneof the immediate vegetable principles.

Prussiats. "We (ball now deferibe morefully the more important combinations of thisacid with the various bafes.

Prufliat of Iron. This fait cannot be madeby the direct combination of the pruffic acid andiron, but is always the -refult of the decompo-fition of the folution of iron in another acid.When the pure pruffic acid is added to any fo-lution of this metal, the prufliat of iron thusformed is at firfl green, and is foluble in acids,hence much of it, and often the whole, remainsin the folution, and no precipitate occurs. Buton expofure to the rays of light, or to fu'phu-reous acid, or if metallic iron is added to thefolution, the colour becomes blue, and theprufliat, which is now no longer foluble inacids, falls down. Hence it would appear thatpure blue prujfiat of iron (which may be diftin-guifted from Pntjfan blue by containing nothingbut pruffic acid and oxyd of iron) contains tbemetal in a lefs oxygenated ftate than in the.green folution.

Another Ample prufliat of iron has been no-ticed by Berthollet . When an alkali is digeftedwith blue prufliat, a divilion of its conftituentparts takes place-, c the alkali difl'olves out thegreater part of the pruffic acid, and a fmaller partof the oxyd of iron, and thefe three fubflances,when the folution is evaporated, unite to formthat triple fait, the prujfiat of potafh with iron ,which is commonly termed limply prvffat ofpotafi, and which will be prefently deferibed.The remaining and infoluble part of the blueprufliat, now confifts of pruffic acid, with anexcefs of oxyd of iron, and is of a yellow co-lour bordering on red. It may be termed withpropriety the fib-prufiat of iron, but though it)-f. tom 56. * Ann. Chim. tom. 4J . « Mem.de I'Acad. 1787.