13.32
CH?IKT,ES UASKERVILLE AND W. J. CROZIER.
portional to the absolute temperature. While there might be some minor corrections t o apply, these could be experimentally determined by observations on substances of known melting point. c
~ ~ R R K E L 1 . Y . 4L:L1OKh I i
THE RELATIVE STABILITY OF PRIMARY CADMIUM POTASSIUM IODIDE ArYD ITS APPLICATION IR THE DETERMINATION OF OZONE.' I % \ CH WLLS BASKERVILLE APID 1 %' J CROZIER
Received Julv 12 1912
Of the several methods which have been proposed for the determination of ozone, that of Schonbein, which consists in estimating the iodine liberated from metallic iodides, has been quite generally employed, although it is open to a number of serious objections. It is well known that when acid potassium iodide solution is employed, the potassium iodide-starch reaction is neither a qualitative nor a quantitative indication of the presence or amount of ozone; and that various agencies influence the liberation of iodine from the acidified potassium iodide solution, while chlorine, bromine and nitrites (frequently found in the air) also give the reaction These influences, of an order of magnitude safely disregarded in other analytical work, must be dealt with With regard to the reliability of neutral metallic iodide solutions, L e c h e r 2 maintained that unsatisfactory results were obtained when determining ozone with the aid of neutral potassium iodide solutions, as large quantities of iodine vapor were liberated This i i directly contrary to the results obtained by Ladenburg and Quasig,j who found that neutral solutions only give correct results. and that acid solutions give no sharp end-point and the results are too high They obtained good results. but used, apparently, only ozone of a high state of purity Baskerville and Hamorj have pointed out the objections to which potassium iodide is open as a reagent for hydrogen dioxide, and the authors have found that as a test for ozone, potassium iodide is subject to the same limitations, and, generaily, even t o a greater degree Baskerville and Hamor found that since primary cadmium potassium iodide (CdKI,.H,O) is unaffected by the presence of any likely amounts of acids in ethyl ether, and is much more stable in light than potassium iodide in solutions of comparable strength, its use is preferable for the detection of peroxidized compounds in ether. The authors have extended the observaRead brfore thc Eighth International Congress of -4ppiied Chemistry, New York, Sept, 1912 - Z. Elektrocheiri 17, 412 > 34, 1184 iIYo1) - Our experiments would tend to confirm these findings ' I Iizd Eng Ckcm , 3, No. 6 ( 1 9 1 1 )
STABILITY OF PRIMARY CADMIUM POTASSIUM IODIDE,
'333
tions on the stability of cadmium potassium iodide and have employed it as a reagent for the quantitative determination of ozone. The Comparative Stability of Potassium Iodide and Cadmium Potassium Iodide. The cadmium potassium iodide used in the experiments which follow was found to possess the following composition : I.
Water.
Calculated for CdKI,.H,O. , . . . . . . . . . . 3.2jyo Found. . . , . . . . . . . . . . . . . . . . . . , , . . . . . . 3 . 3 6
Cadmium. 21.17%
20.98
It was free from foreign metals, sulfuric acid, and hydriodic acid, and was soluble in about 0.95 part of water at 1 5 ~ .The potassium iodide used was also found to be pure. The statement is made in the literature' that solid cadmium potassium iodide assumes a slight yellow color on standing. In the experiments made by the authors on this point, the salt was from two different lots: (a) Some which, after.purification, had been standing for five years in a museum case, freely exposed to diffused light during most of every day. This sample possessed no yellowish tinge whatsoever, nor was there present any detectable free iodine. ( h ) Samples of a fresh lot of " cadmium and potassium iodide Merck." These were exposed to direct sunlight for periods ranging up to 2j days, and analysis showed that no decomposition occurred. We are therefore inclined to believe that pure primary cadmium potassium iodide uncontaminated with cadmium iodide, potassium iodide or water in excess, will not become colored upon storage. The next experiments were made on the rate of the decomposition of stock solutions of potassium iodide and cadmium potassium iodide under laboratory conditions. Tenth-normal solutions were kept in the ordinary diffused light of the laboratory for two months, at the end of which time the following comparative results were obtained in grams of iodine : Potassium iodide.
0.00053
Cadmium potassium iodide. 0.00046
A series of experiments was then made on the relative stability of cadmium potassium iodide toward various reagents.2 A 10% solution was prepared and the following tests were made with 2 cc. quantities, the exposures being to diffused daylight during the daytime : I. With 2 cc. of hydrochloric acid (density 1.20), no perceptible reaction occurred until after 30 hours. 2. With 2 cc. of sulfuric acid (density 1.84), a yellow coloration resulted a t once. 3. With z cc. of 10% sulfuric acid, after two days, the reaction was as strong as in 6. 4. With 2 cc. of concentrated nitric acid, the reaction %'as immediate. 5 . With 2 cc. of I : I O nitric acid, a reaction resulted. ' E. g., by Abegg and by Merck (1907Index, p. 1 1 0 ) . The results recorded are a t least the result of duplicate experiments.
'334
CHARLES BASKERVILLE AND W. J. CROZZER.
6 With z cc. of I 50 nitric acid, a reaction occurred after 40 hours. 7 Nitrogen tetroxide was found to give a prompt reaction, being apparently the same as in the case of potassium iodide 8 An equal volume of 99 smC acetie acid gave no separation of iodine even after 5 day 9 With IO cc of dilute hydrochloric acid, a slight reduction was noted after 3 days A 107;potaqsiurn iodide solution treated in the same way gave a strong reaction O\ er night I O Two small flasks were one-thud filled with (A,) 1 0 % potassium ~ iodide and (B,) IO%, cadmium potassium iodide, and then exposed to diffused sunlight. After 3 days, there was a faint yellow coloration in A,, but no separation of iodine in B, Titration gave the follom ing results
After 3 days kfter 7 daqs As in No. was added .4fter 11
Cc o o 1 N N a S O :'2
er
3 p
