710
ELEMENTS OF MATERIA MEDICA.
parts of tartrate of potash, to form one equivalent or 220 parts of ferrotartrate ofpotash.
MATERIALS.
1 eq. Sesquioxide iof Iron....... 40 j
1 eq. ßitartrate IPotash....... ISO j
1 eq. Tartaric Acid. . 66l eq. Tartrate Potas/i 114
f 1 eq. Tartrate of Ses-i quiox. Iron___
Ulli
PRODUCTS.
1 eq. Ferrotartrate ofPotash. 230
The Edinburgh College orders of Sulphate of Iron, gv\; Bitartrate of Potash, 5v. and gj.;Carbonate of Ammonia in fine powder, a sufficieticy. Prepare the Rust of iron from the sul-phate as directed under Perrugo, and without drying-. Mix the pulpy mass with four pintsof water; add the Bitartrate; boil tili the rust of iron is dissolved; let the Solution cool; pouroff the elear liquid, and add to this the carbonate of ammonia so long as it oceasions effer-vescence. Concentrate the liquid over the. vapour bath to the consistence of a thick extract,or tili the rosiduum becomes on couling a firm solid; wbich must be preserved in well-closedvessels.
The explanation of the formation of hydrated sesquioxide of iron (here calledRust) has been already explained (see p. 690.) The theory of the other part ofthe process is the same as that of the process of the London Pharmacoposia.
The Dublin College Orders of Iron, drawn into thin vvire, one part; Bitartrate of Potash, invery subtile powder,/our parts ; Distilled Water, cight parts, or as much as may be suffi-cient. Let them be mixed, and exposed to the air during fifteen days in a wide vessel. Letthe mixture, whieli is to be oceasionally stirred, be kept constantly moist by the daily addi-tion of water, taking care that the iron shall not be entirely covered by tue water. Lastly,boil the product in a sufficient quantity of" water, and let the filtered liquor evaporate to dry-ness over a water bath. Let the Tartar of Iron be kept in a well-stopped vessel.
By the united agencies of air and water the iron is converted into the sesquioxide,which combines with the bitartrate of potash to form tartarized iron.
Properties. —It is an olive-brown inodorous powder, with a styptic inky taste.It reacts on vegetable colours, mildly alkaline. It is slightly deliquescent, pro-bably from the tartrate of potash which it contains. It dissolves in about fourtimes its weight of water, and slightly in alcohol.
Characteristics. —Ferrocyanide of potassium does not occasion any blue colourwith it, unless a few drops of acid be added. Potash, soda, and their carbonates,do not decompose it at ordinary temperatures, nor does ammonia or its carbonateeven hy the aid of heat. Tincture of nutgalls causes a dark-coloured precipitate,Sulphuric, nitric, or hydrochloric acid, throws down the sesquioxide of iron froma Solution of this salt; an excess of acid redissolves it: the Solution has then avery astringent taste. Tartaric acid causes the formation of crystals of tartar.Heated in a covered crucible, ferrotartrate of potash yields charcoal, carbonate ofpotash, and protoxide of iron.
Composition. —The following table exhibits the composition of this salt, ac-cording to Soubeiran and Phillips:—
Phillips,
Soubeiran.
Atoms.Tartrate of Sesquioxide of Iron 1 .Tartrate of Potash............ I .
Eq. Wt. Per Cent... 106 .... 48-18.. 114 ____ 51-82
Ferro.tarlrate of Potash .
220
100-00
Per Cent.
Sesquitartrate of Sesquioxide....... 45
Tartrate of Potash.................. 55
.................. 100
Soubeiran says it contains 13 per cent. of sesquioxide of iron; whereas, ac-cording to Mv. Phillips, the quantity is 18'18 per cent.
The ferrotartrate of potash is to be regarded as a double salt, in which tartrateof iron is the acid or electro-negative ingredient, and tartrate of potash the basicor electro-positive constituent. On this view, we comprehend why ferrocyanide