The chemical character of so-called iodo-tannin compounds / by Frederick B. Power and Frank Shedden.

  • Frederick Belding Power
Date:
[1901]
Catalogue details

Licence: In copyright

Credit: The chemical character of so-called iodo-tannin compounds / by Frederick B. Power and Frank Shedden. Source: Wellcome Collection.

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    edit., Bd. ii., p. 1,017, it is stated:—“A solution of tannic acid takes up iodine in considerable amounts, forming a reddish- brown liquid, in which free iodine can no longer be detected by starch paste.” Practically the same statement occurs in Hager’s ‘ Handbuch,’ Bd. i., p. 134, with the additional conclusion that the liquid contains organically combined iodine, from the fact that the presence of this “element cannot be detected by starch.” Fliickiger, ‘ Pliarm. Chemie,’-2nd edit., pt. ii., p. 356, has recorded the following observation:—“1 part of powdered iodine affords with a solution of 7 parts of tannic acid in 50 parts of water, a turbid, reddish-brown liquid, which can be diluted without the separation of iodine, and produces no blue precipitate in solutions of starch.” The first study of the chemical changes which take place by the action of iodine on tannin appears to have been made by Socquet and Guilliermond, in a paper entitled “ Sur une nou- velle combinaison de l’iode ” (Journ. de Pharm. et de Chemie, 3 serie, t. xxvi., 1854, pp. 280-285). The notice given in Gmelin-Kraut’s ‘Handbuch der Cliemie,’ Bd. vii., 1862, p. 884, or in the Cavendish edition, 1862, vol. xv., p. 459, is apparently a brief abstract of the preceding paper. With reference to the observations of Socquet and Guilliermond (loc. cit.) the following points may be noted. They observed that the action of iodine upon tannin only takes place in the presence of water, and that in alcoholic solution no reaction ensues, how¬ ever prolonged may be the contact. They then further state that “ tannin, in aqueous solution, can thus dissolve considerable quantities of iodine—as much as half its own weight. What is remarkable in this absorption of iodine by tannin is that if it is arrested when a certain proportion exists between the two sub¬ stances one will see that a true chemical combination is effected.” They observed that from the iodo-tannin solution a sparingly soluble substance was separated, which was estimated to amount to about one-sixth of the weight of tannin employed. When washed with water and dried it did not retain any trace of iodine, which remained entirely in the solution from which it was deposited, but, as it had an acid character and retained some,of the properties of tannin, it was regarded as an altered tannin. The iodo-tannin solution was found to be more strongly acid than a solution containing simply the same amount of tannin, but to show the same deportment as the latter towards various re- agents_. It does not stain the skin, and the taste and odour do not permit of the recognition of iodine. It is capable of absorb-
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