ANALYTICAL EDITION
460
Vof. 6, No. 6
TABLE 111. DETERMINATION OF COBALT AND NICKELIN SAME and nickel sulfates to make two solutions, then analyzing for SOLUTION both by the volumetric method and determining nickel by (Volumetric method) the dimethylglyoxime method and calculating cobalt by the COBALT NICXEL difference. The results are given in Table 111. Present Found Present Found Cram Gram An examination of the tables shows that this method gives 0.0535 0.0532 0.0255 0.0254 excellent results for cobalt and nickel separately, and that 0.0536 0.0251 0.0538 0.0258 results in the presence of each other compare reasonably well 0.0639 0.0250 with accepted methods. The method is very rapid and re0.0540 0.0248 Av. 0.0537 0.0252 quires no expensive apparatus, as does the method of Spacu for nickel. Cobalt and nickel may be determined in the same solution LITERATURE CITED by precipitating them as the complex salts as outlined above, determining the nickel by the dimethylglyoxime method and (1) Spacu, BuZ. SOC. stiinte Cluj, 7, 377 (1934). calculating the cobalt by difference. The reliability of the (2) Spaou, 2.anal. Chem., 96, 245 (1934). method was tested by mixing standard solutions of cobalt RECIPIVED August 7, 1934.
Volatilization of Iodine from Dilute Iodine-Potassium Iodide Solutions W. A. HOUGHAND J. B. FICKLEN Chemical Engineering Laboratory of The Travelers Insurance Company, Hartford, Conn.
I
T IS WELL known that iodine is volatilized by the passage of gases through its potassium iodide solution. The purpose of this study is to determine the magnitude of the loss under different conditions of temperature, concentration, and rate of air passage. This loss, if substantial, would have a marked bearing on the determination of reducing gases, such as sulfur dioxide and hydrogen sulfide, in the air of rayon spinning rooms and other work places.
of iodine lost. Doubling the amount of iodine while keeping the amount of potassium iodide the same caused a loss of 5 per cent a t 7.6 liters per minute and 24" C., while tripling the amount of iodine caused the loss to increase to 13.5 per cent. A series of tests, run to determine whether increasing the total volume of solution in the first bubbler caused a change in the loss of iodine, showed that a t 7.6 liters per minuteand 24" C., the loss of iodine amounted to 10 per cent if the volume of potassium iodide solution were doubled.
PROCEDURE The apparatus used by the authors is a 500-cc. fritted-glass plate washing bottle of the Jena type. Suction is provided by a calibrated hand pump or motor driven suction pump and flowmeter. The air from the location to be investigated is sucked through the bubbler a t the rate of 4.5 liters per minute until the color of the solution has disappeared or a certain definite color is reached (starch indicator is added a t the beginning of the test). From the amount of air drawn through the bubbler and the amount of iodine used, the concentration of sulfur dioxide or hydrogen sulfide can be calculated. Employing a dilute iodine solution, a test of this sort can be run in 3 or 4 minutes. A standard iodine solution was prepared in 5 per cent potassium iodide. The iodine strength was determined by titrating with sodium thiosulfate solution which had been standardized against potassium dichromate solution. The strength of the iodine sohtion was 0.29035 gram of iodine per liter or 0.00228 N . In terms of hydrogen sulfide, 10 cc. of this solution are equivalent t o 0.000389 gram of hydrogen sulfide or approximately 0.25 cc. of this gas at standard conditions. Three gas-washing bottles were connected in series with a flowmeter and suction pump. Air was drawn from an uncontaminated atmosphere. The first bottle contained 60 cc. of 5 per cent potassium iodide, 5 cc. of 1per cent soluble starch, and 10 cc. of the standard iodine solution; the second and third bottles, 60 cc. of 5 per cent potassium iodide solution and 6 cc. of 1 per cent soluble starch solution. Air was passed through this system at various rates for 12-minute periods. The temperature of the first bottle was varied, while the other two were maintained at 6' to 10' C. The iodine remaining in each bottle at the end of the 12-minute period was titrated with sodium thiosulfate solution. Results are given in Table I.
Tests mere run to ascertain whether increasing the concentration of iodine in the first bottle affected the percentage
TABLEI.
VOLATILIZATION O F I O D I N E
IODINE REMAININQ
RATEOF AIR FLOW
First bottle
Second bottle
%
% TEMPERATURE, 8-10'
L./min. 7.6 5.0 7.6
C.
0
C.
98.7 98.5 T E M P E R A T U R E , 40-60'
%
T E M P I R A T U R E , 8-10'
0
100 TEMPBRATURE, 15'
a
C.
Third bottle
0
On
1.5
0
C.
0 2.5 0.5 99.5 0 5.0 99.7 0-3 0 7.6 98.7 1.3 I n this one instance the second and third bottles were not cooled.
CONCLUSIONS Air can be passed through dilute iodine-potassium iodide solutions a t room temperature and at rates higher than those usually used (about'4.5 liters per minute) in gas or vaporsampling procedures without loss of significant amounts of iodine. The loss can be cut to a minimum by reduction in temperature, in rate of air flow, or in concentration of iodine. Although no appreciable loss of iodine may result, it would appear desirable to ascertain whether a reducing gas such as hydrogen sulfide or sulfur dioxide is completely removed from the air stream and caused to react quantitatively with the iodine a t these high rates of sampling. An investigation covering this point is in progress in the authors' laboratories. RmcervIPD
July 12, 1934.
