November 15,1934
I N D U S T R I A L A N D E N G IN EE R I N G CHE MISTR Y
the reaction between iodoacetone and thiosulfate can be used to raise the iodometric method t o quantitative accuracy. The stoichiometric relations are fortunately such that errors due to the discussed side reactions, occurring because of presence of acetone, presence of moisture, or local deficiency of iodide, are corrected automatically. Thus, it is immaterial whether the acid is formed by hydrolysis of phosgene, by iodination of acetone, or by the action of phosgene on acetone. The following may prove helpful as a suggested procedure: Absorb the phosgene, freed from acid gases, in a saturated acetone solution of potassium iodide containing at least several times as much iodide as iodine to be liberated. Add an excess of iodate and then a measured excess of 0.01 N thiosulfate. Let stand for half an hour or more. Make sure that the solution contains more water than acetone, add several drops of starch indicator, and titrate back with 0.01 N iodine t o a distinct coloration. (Since excess iodate is present, 0.01 N hydrochloric acid probably could be used instead of iodine.) Finally, a t once discharge the iodine color with thiosulfate. The total
459
thiosulfate minus the equivalent of the added iodine then represents the phosgene exactly as if the side reactions did not occur. (1)
LITERATURECITED Anonymous, Jahresber. chem.-techn. Reichsanstalt, 5,
11-20
(1926).
(2)
Dawson et al., a large number of articles beginning with J.
Chem. SOC.,95, 1860-70 (1909). (3) Kolthoff and Furman, “Volumetric Analysis,” Vol. 11, pp. 38992, John Wiley & Sons, N. Y., 1929. (4) Matuszak, J . Am. Chem. SOC.,56, 2007 (1934). ( 5 ) Morley and Muir, “Watt’s Dictionary of Chemistry,” Vol. IV, p. 481, Longmans, Green and Co., N. Y . , 1894. (6) Olsen, J. C., Brooklyn Polytechnic Institute; private communication. (7) Olsen, Ferguson, Sabetta, and Scheflan, IND.ENQ.CHEM., Anal. Ed., 3, 189-91 (1931). (8) Rose, Ann., 205, 230-47 (1880). (9) Slator and Twiss, J. Chem. Soc., 95, 95 (1909). (10) Wallauer, Chemisoh-technischen Reichsanstalt; private com-
munication.
RECDIVPD April 21, 1934. Published by permission of the Director, U. S. Bureau of Mines. (Not subject t o copyright.)
A Volumetric Method for Determination of Cobalt and Nickel J. T. DOBBINS AND J. P. SANDERS, University of North Carolina, Chapel Hill, N. C . HE reaction between pyridine, the thiocyanate ion,
T
and several metal ions (cobalt, copper, cadmium, manganese, nickel, and zinc) which results in the formation of complexes of the general formula M(Py)d(CnS)z has been the basis for quantitative determinations of these ions developed by Spacu. Obviously the method is not applicable for one ion in the presence of any other. As all the methods of Spacu were gravimetric, it occurred to the authors that these reactions would also serve for indirect volumetric methods. As there is no reliable volumetric method for either cobalt or nickel, they were chosen to test the method. Since completion of the work, Spacu (1) has published a variation of the method in which he titrates the excess thiocyanate in the whole filtrate. This method did not give satisfactory results for tho authors, as it was not possible to wash all the excess thiocyanate out without dissolving some of the complex salt. Spacu (2) has also published a potentiometric method for nickel for which he claims an error of less than 0.5 per cent.
SOLUTIONS STANDARD AMMONIUMTHIOCYANATE. An approximately 0.1 N solution of ammonium thiocyanate was repared and standardized by titrating it against a standard sogtion of silver nitrate. Potassium thiocyanate may be used in place of the ammonium salt, as later work has shown. STANDARD SILVERNITRATE. A 0.1 N solution of silver nitrate was prepared and standardized against c. P. sodium chloride. INDICATOR SOLUTION.This solution was prepared by dissolvin~10 crams of ferric alum in a mixture of 80 cc. of water and 20 cc. ;f 6 “N nitric acid.
PROCEDURE The sample, which should contain from 0.05 to 0.1 gram of cobalt as some cobaltous salt, is dissolved in about 150 cc. of water in a 250-cc. volumetric flask. The solution is made just acid to litmus with nitric acid, 3 cc. of pyridine are added, and an excess of standard ammonium thiocyanate is run in. Upon the addition of the thiocyanate, the cobalt is precipitated as pink C O ( P ~ ) ~ ( Cwhich ~ S ) settles ~ rapidly and filters very easily. The solution is diluted to the mark and mixed thoroughly. A portion of the solution is filtered through a dry filter and the first few
cubic centimeters of the filtrate are discarded. An aliquot of 50 cc. of the filtrate is transferred to a beaker and diluted to 100 cc., 1 cc. of concentrated nitric acid is added, and an excess of standard nitrate is immediately run in. Five cubic centimeters of indicator are added and the titration is completed in the usual way. The error introduced by the presence of the precipitate in the solution is negligible. The weight of cobalt may be calculated from the formula: g =
[(cc. of NHdCnSXN)
- 5 (cc. of AgNOtXN)]0.02947
In order to test the precision of the method, three solutions of cobalt sulfate were made and 25-cc. portions were analyzed by this volumetric method and also by the electrolytic method of Brophy. The results are given in Table I. TABLE I. DETERMINATION OF COBALT SOLUTION I1
SOLUTION I
Gram
SOLUTION I11
Gram
Gram
VOLUMIOTRIC METLIOD
0.1059 0.1062 0.1057 0.1056 0.1063 0.1058 0.1059
0.1328 0.1330 0.1326 0.1329 0.1326 0.1330 Av 0.1328
0.1596 0.1598 0.1594 0.1595 0.1593 0.1594 0.I595
DLDCTROLYTIC M l T H O D
Av. 0.1329
0.1596
0.1060
The same procedure may be used for the determination of nickel. A comparison of the results of the method and the dimethylglyoxime method is seen in Table 11. TABLE 11. DETERMINATION OF NICKEL SOLUTION I
SOLUTION I1
Gram
Gram VOLUMDTRIC METHOD
0.0128 0.0125 0.0126 0.0123 0.0127 0.0126 Av. 0.0126
0.0505 0.0507 0.0510 0.0510 0.0503 0.0504 0.05065
D I X D T H Y L G L Y O X I Y E METHOD
Av. 0.0125
0.0506
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 R E M A I N I N Q
RATEOF AIR FLOW
First bottle
Second bottle
%
% T E M P E R A T U R E , 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 T E M P B R A T U R E , 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.
