Chemistry : general, medical, and pharmaceutical including the chemistry of the British Pharmacopœia a manual on the general principles of the science, and their applications in medicine and pharmacy / by John Attfield.

  • Attfield, John, 1835-1911.
Date:
1881
Catalogue details

Licence: Public Domain Mark

Credit: Chemistry : general, medical, and pharmaceutical including the chemistry of the British Pharmacopœia a manual on the general principles of the science, and their applications in medicine and pharmacy / by John Attfield. Source: Wellcome Collection.

    697/850 (page 663)
    Pevmangatiate of potassium is often used for tbe same purpose. Iodine acts indirectly, by taking hydrogen from water and liberating oxygen; the red chromate of potassium directly, by the facility with which it yields three-sevenths of its oxygen —as indicated by the equations and statements given on p. 666 ; permanganate of potassium by affording five-eighths of its oxygen in presence of acid, 2K2Mn208 4- Qfi^SO^ = 2K3SO^ + 4MnS04 + 6H2O + SOg. Standard Solution of Iodine. (Iodine, 1 = 127.) If pure iodine be not at hand, it may be prepared by mix- ing the commercial article with about a fourth of its weight of iodide of potassium and subliming. Sublimation may be effected by gently warming the mixture in a beaker, the mouth of which is closed by a funnel; the iodine vapour con- denses on the funnel; while fixed impurities are left behind, and any chlorine which the iodine may contain is absorbed by the iodide of potassium, an equivalent quantity of iodine being liberated. Small quantities may be similarly treated between two watch-glasses, placed edge to edge. Any trace of moisture in the resublimed iodine is removed by exposure for a few hours under a glass shade near a vessel containing oil of vitriol. Place 12'7 grammes of pure iodine and about 18 grammes of pure iodide of potassium (an aqueous solution of which is the best solvent of iodine ; the salt plays no other part in these operations) in a litre flask, add a small quantity of water, and agitate until the iodine is dissolved ; dilute to 1 litre. The following substances are officially estimated by this volumetric solution:— SulpJmrous Acid.—Operate on about 5 of a gi'amme of the acid, and dilute with water as usual. If the sulphurous acid be diluted to a less degree than 04 or '05 per cent., there will be some risk of the sulphuric acid formed being again reduced to sulphurous acid, with liberation of iodine. In delicate experiments the distilled water used for dilution should pre- viously be freed from air by boiling, to prevent the small amount of oxidizing action which dissolved air would exert. The solution of iodine is then added until a slight permanent brown tint is produced, showing the presence of free iodine.