MAY 1.5. 1936
ANALYTICAL EDITION
I n E-%, the per cent of oxygen was nearly doubled without apparent effect upon the recovery of nitric oxide. At a certain large coke plant, not included in the previous discussion, the gas was being experimentally treated for nitric oxide removal on a full plant scale. It mas known that the method employed gave uniform and nearly complete removal of nitric oxide under optimum conditions. A series of routine efficiency tests, run daily upon this treater by this method for a period of about one week, showed removal efficiencies of 94, 93,97,93,96, and 95 per cent.
Summary An improved method for determination of the traces of nitric oxide usually found in coke-oven gas and the procedure used t o check this analytical method, b y adding extremely small measured amounts of nitric oxide to nitric oxide-free coke-oven gas, have been described.
167
By use of this analytical method approximately one-half of the nitric oxide actually in the gas is recovered and determined b y a colorimetric method. Therefore, a factor of 2 is applied to the observed value to give the actual content of nitric oxide. The effects of variables such as delay time, added oxygen, temperature, etc., have been described.
Literature Cited (1)
(2) (3) (4)
(5)
Fulweiler, 15’. H., Am. Gas Assoc. Proc., 15, 829-46 (1933); G‘as Age-Record, 72, 411-13, 422 (1933). Schuftan, P., Brennstof-Chem., 13, 104-8 (1932). Shaw, J. A., IND. ENG.CHEar., Anal. E d . , 6, 479-80 (1934). Treadwell and Hall, “-4nalytical Chemistry,” 6th ed., Vol. 2, pp. 306-7, Yew York, John TTiley & Sons, 1924. Tropsch, H., and Kassler, R . , Brennstoff-Chem.,12, 345-8 (1931).
RECEIVED March 21, 1936.
Titration of Silver with Potassium Iodide Ceric Ammonium Sulfate and Starch as Indicators ALBERT BLOOM AND WALLACE M. McN.4BB The John Harrison Laboratory of Chemistry, University of Pennsylvania, Philadelphia, Pa.
CCORDING to Shapiro (4, in the determination of chlorides by the Volhard method, excess silver may be titrated in a nitric acid solution with potassium iodide. The end point is detected in the presence of starch when the nitric acid oxidizes the iodide to iodine. Schneider (3)suggests the use of palladium nitrate as an indicator, noting the end point by the formation of a red-brown precipitate of palladous iodide. Fleury and Courtois (1) and Josien ( 2 ) recommend the uae of starch-iodine-potassium iodide solution, in which
A
the silver solution must be added to the starch-iodinepotassium iodide solution. The method described by the authors consists of the titration of silver with potassium iodide in the presence of ceric ions and starch. Oxidation of the iodide ion to iodine b y the ceric ion is not permanent until the end point is reached. During the course of the titration a blue color appears, but is immediately discharged upon stirring. The method gave good results in the presence of ferric and cupric ions.
Analytical Procedure TABLEI. TITRATION OF SILVER ACIDITY N
0.1 N XI
0.1 N KI with Blank Correction
cc.
cc.
10 cc. of 0.1 N AgNOa solution in a volume of 110 cc. 10.14 10.04 0.2
10.04 10.14 0.5 10.16 10.06 1.0 10.18 10.08 2.0 10.06 10.16 3.0 20 cc. of 0.1 N AgNOa solution in a volume of 110 cc. 20.0s 19.98 1.0 2 0 . 11 20.01 2.0 20.12 3.0 20.02
Ten or 20 cc. of a 0.1 N silver nitrate solution were transferred to a 200-cc. beaker. To this were added water and a sufficient amount of sulfuric acid to give a volume of approximately 110 cc. (concentration of acid may vary from 0.2 N to 3 N ) , and then 3 cc. of 0.5 per centestarch solution and 0.1 cc. of an approximately 0.1 N ceric ammonium sulfate solution. It is important to add the sulfuric acid before the ceric ammonium sulfate. The silver was titrated with 0.1 N potassium iodide solution. The end point was sharp and easily detected when the last drop of potassium iodide gave a permanent blue-green color t o the
solution. Blank titrations were made under the same conditions omitting the silver nitrate. The blank consumed 0.1 cc. of the potassium iodide solution before a permanent color was obtained.
Summary TABLE 11. TITRATION OF SILVERNITRATE of 0.1 N AgNOa solution in the presence of cupric and ferric ions. Volume approximately 110 cc.. acidity approximately 0.5 N ) 0.1 N CuSOa6HzO and 0.1 N KI with Blank FeNH,1(S04)~.12Hz0 0.1 N K I Correction (10
00.
cc.
.
cc.
CC
10.10 10.13 10.14
10.00 10.03 10.04
10.15 10.12 30 50 10.17 50 F ~ N H I ( S O I ) Z . ~ ~10.12 H~O 50 CuSO4.5HzO
10.05
CuS04.5HzO 10 30
50 FeNH4(S04)z,lZHzO 10
10.02
10.07 10.02
A method is described for the titration of silver with potassium iodide, using ceric ammonium sulfate and starch as internal indicators. The acid concentration may vary in the titration from 0.2 Ar to 3 AT without appreciable error. The titration can be made in the presence of cupric and ferric ions.
Literature Cited (1) Fleury, Paul, and Courtois, Jean, Bull.
SOC.
chim.,4, 49, 860
(1931).
(2) Josien, M.-L., Compt. rend., 197, 1324 (1933). (3) Sohneider, L . , J. Am. Chem. SOC.,40, 583 (1918). (4) Shapiro, C. S., J.Lab. Clin. M e d . , 20, 195 (November, 1934). RECEIVED November 29, 1936.
