PART III.

Metallic Preparations. — Iron.

523

LIQUOR FERRI ALKALINI. Lond." Solution o/Al-caline Iron. 7,

** Take of iron, two drachms and, an half; nitric acid, twoJluid ounces; distilled water, six Jluid ounces; solution of sub-carbonate of potash, six Jluid ounces. Mix together the acidand the water, pour the mixture over the iron, and when theeffervescence has ceased pjur off'the acid solution. Add thisgradually, and at intervals, to the solution of subcarbonate ofpotash, frequently agitating until it become of a brownish redcolour, and no more effervescence is excited. Finally, set itaside for six hours, and pour off'the liquor."

Although this composition has been long known, yet it isnot well understood. The diluted acid 3 acts violently upon theiron and oxidizes it, while heat is evolved, and red fumes areextricated, consisting of nitrous gas and nitrous oxide. Ifthis action be moderated by the iron being in a lump, andputting the vessel in which it is dissolving into cold water, thesolution is of a pale green colour, and the iron is at the mini-mum of oxidizement; but if heat be applied, or the efferves-cence be allowed to proceed with violence, the solution isof a reddish brown colour, and contains oxynitrate of iron;a great excess of acid being present in both cases. On eachaddition of the solution of the subcarbonate of potash to eitherof these solutions, effervescence is excited by the disengage-ment of carbonic acid, and a red precipitate is instantly pro-duced, which is however kept suspended by agitation, andultimately redissolved by the excess of alkali. By allowing themixture to stand for six hours as directed, particularly if theweather be cold, the whole becomes involved in a spongy massof acicular crystals of nitrate of potash, from which the alka-line metallic solution is to be poured off: it is clear, and of adeep brownish red colour, if the acid solution contain the me-tal at the minimum of oxidizement: but if at the maximum,it is turbid and of a redder hue. The first of these is thepreparation of the London College.

Qiialities. — This preparation has an alkaline, slightly styptictaste, and excites the sensation of coldness in the mouth pro-duced by nitrate of potash, but in an inferior degree. Themetallic part is precipitated by water *; and the clear superna-

1 Teinture mar'iale alkaline de Staid (F ) Tiniuta ili marte alkalipa de Stahl (/.)

* This limine has been lust y criticised, as ■ i plying an unknown subs.anee, " alkalineiron;' 1 it should have been, Liquor alkalmus ferri -xidi.

3 Tile concentrated acid scarcely acts on iron.

+ This precipitate, when tile iron has been rapidly dissolved in the acid and heatemployed, is a combination of peroxide of iron and carbonic acid. It effervesces strong-ly with muriatic acid, and ghres off carbonic acid during the solution.

IO