Methods in chemical analysis : originated or developed in the Kent chemical laboratory of Yale university / comp. by Frank Austin Gooch.

  • Frank Austin Gooch
Date:
1912
Catalogue details

Licence: In copyright

Credit: Methods in chemical analysis : originated or developed in the Kent chemical laboratory of Yale university / comp. by Frank Austin Gooch. Source: Wellcome Collection.

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    reading. To render the plain iodine readings sharp a crystal of potassium iodide was added in the first two titrations. Titrations with and without Starch. Volume 125 cm.3 Nearly n/io I. Direct readings. Nearly »/10 I. Corrected readings. k/io I sol. Absolute n/10 I sol. Absolute errors in A, . . in B. n/10 As203. By iodine color, A. By KI- starch blue, B. A. B. amount calculated from So cm.3 A. B. cm.3 cm.3 cm.3 cm.3 cm.3 cm.3 cm.3 cm.3 5 10 IS 20 30 40 50 i drop* 4-94* 9.88 14-83 19.78 29.64 39-55 49.41 i drop 4.96 9.90 14-83 19.78 29.64 39-55 49.41 4.92 9.86 14.81 19.76 29.62 39-53 49-39 4-94 9.88 14.81 19.76 29.62 39-53 49-39 4-94 9.88 14.82 19.76 29.63 39-51 49-39 — 0.02 — 0.02 — 0.01 0.00 —0.01 +0.02 0.00 0.00 0.00 —O.OI 0.00 —0.01 + 0.02 0.00 * A crystal of KI was added. It is to be noted that the readings with plain iodine and with pure starch agree exactly except for the first two titrations, and here there is only a difference of a drop. The absolute errors are interesting, as they show how the absolute values fluctuate about a standard set by the 50-cm.3 readings. This fluctuation is lim- ited to a drop plus or minus. The statement has been made that starch from different sources has a varying power of absorbing iodine, e.g., that potato starch absorbs three times as much as rice starch.* To discover whether this fact has any bearing upon the use of the starch in- dicator, and at the same time to learn whether pure starch solu- tions made in the ordinary way (Gastine)f would give as delicate readings as that boiled with potassium iodide, solutions were made from pure potato starch, pure rice starch, pure arrowroot starch and a pure (so-called) soluble starch of unknown origin. The results of titration with these solutions as indicators are shown in the following statement. It is at once seen that these values are coincident within a drop, and that all the starch solutions are within the limits set by a plain iodine reading on the one hand and a potassium iodide * Girard, Ann. Chim., [6], xiii, 275. f Loc. cit.
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