FERRO-TARTRATE OF POTASH.

709

13. POTAS'SjE FER'RO-TAR'TRAS.—FERRO-TARTRATE OF POTASH.

(Ferri Potassio-Tartras, L. —Ferrum Tartarizatum, F..— Ferri Tartarum, />.)[Ferri et Potassaa Tartras, U. S.j

History. —This preparation was first described by Angelus Sala at the com-mencement of the seventeenth Century. Mr. R. Phillips 1 iraproved its mode of pre-paration. The late Dr. Birkbeck has described its medical properties. (Lora!.Med. Review, No. xix. July, 1812.) Besides the above, it has had variousother names; such as ühalybealed Tartar {Tartarus chahjbealus seu ferratus,)and Tartrate of Polash and Iran (Potassse et Ferri. Tartras-)

Preparation. —Soubeira'n ( iXouveau TrailP. de Pharmacie, t. ii. p. 447, 2 n * sed.) directs this Compound to be thus prepared: Take of Powdered Bitartrate ofPotash, one pari; Distilled Water, six parts; Moist Hydrated Sesquioxide ofIron, as rnuch as mau be sufflcient: digest them, at the temperature of from 120°to 140° F., until the liquor eeases to dissolve a fresh quantity of hydrate; thenfilter, and evaporate to dryness by a gentle heat.

The process of the London College, aecording to Mr. Phillips, {Translationof the Pharmacopaia.) is a modification of that of Soubeiran. It is, however,much more complex.

The London College Orders of Sesquioxide of Iron, giij.; Hydrochlorie Acid, Oss.; Solutionof Potash, Oivss., or as much as may be sufflcient; Bitartrate of Potash, ^xiss.; Solution ofSesquicarbonate of Ammonia, Oj., or as much as may be sufflcient; Distilled Water, Cong. iij.Mix the sesquioxide of iron with the acid, and digest for two hours in a sand-bath. Add tothese two gallons of the water, and set aside for an hour : then pour off the supernatant liquor.The Solution of potash being added, wash what is preeipitated frequently with water, andwhile moist boil it with the bitartrate of potash, previously mixed with a gailon of the water.If the liquor should be acid when tried by litmus, pour into it Solution of sesquicarbonate ofammonia until it is saturated. Lastly, strain the liquor, and with a g'entle heat let it evapo-rate, so that the salt may remain dry.

[The U.S. P. directs, Subcarbonate of Iron, three ounces ; Muriatic Acid, ten fluid ounces;Solution of Potassa, five pints and ahalf; Bitartrate of Potassa, seven ounces and a-half;Distilled water a gallon and a-half. The process is essentially the same as above.]

The theory of this process is as follows:—By the reaction of sesquioxide ofiron and hydrochlorie acid we obtain water and sesquichloride of iron (see p.692.) On the addition of caustic potash the sesquichloride is decomposed, hy-drated sesquioxide of iron is preeipitated, and Chloride of potassium is left in solu-,tion. These changes are illustrated by the following diagram:—

MATERIALS.

3eq. Totash___ 144 '

OOMl'OSITION.

3 eq. Potassium 1203 eq. Oxijgcn... 24

2 eq. Sesquichlo- £ 3 eq. Chlorine., 108ride lion..... 164 j 2 eq. Iron ...... 50

'S eq. ChloridePotassium.. 208

2eqSesqinox-ide Iron----- 80

Water.

308

308

When the hydrated sesquioxide of iron is boiled with bitartrate of potash, oneequivalent or 40 parts of the sesquioxide combine with one equivalent or 60parts of tartaric acid of the bitartrate of potash, and form an equivalent or 106parts of tartrate of sesquioxide of iron, which combine with an equivalent or 114

i An Eiperimental Examinetlion of the last editionofthe Pharrweoptela Lanxttneneis. 1811.