ANALYTICAL EDITION
64
Vol. 4, No. 1
TABLEVIII. MAGNITUDE OF INTERFERENCE DUE TO SULFITEWASTES METHOD 1 to 300,000
(A, permanganate modification; B, regular Winkler procedure; C, alkaline-hypoahlorite modification) DILUTIONOF DIGESTER WASTE 1to 1 to 1 to 1 to 1to 1 to 1 to 1 to 1 to 1 to 150,000
60,000
P,p.m.
P.p,m.
P.p.m.
-0.06 0.03 0.00
0.00 0.07 0.05
-0.06
30,000
16,000
10,000
6000
3000
P.p.m. P.p.m.
P.p.m.
P.p.m.
P.p.m.
1500
1000
1t o 300
600
P . p . m . P.p.rn. P . p . m
1to 150
P.p.m. P.p.m.
APPARENTLOSS OF O X Y GEN” ~
A B C
0.10 0.02
0.12
0.M 0.00
0.34 0.02 0.04
0.46 0.90 0.07
0.77 0.24 0.06
1.68 0.54 -0.06
2.78 1.17 0.10
3.68 1.74 0.16
5.67 2.63 0.20
Average values in triplicate determinations. b Corresponding to the total absence of dissolved oxygen.
8.27, 4.69 0.30
7,‘h 1.10
a
contact with the manganous hydroxide should not exceed 40 to 60 seconds. 6. The titration should not be delayed, as a measurable loss of iodine occurs on standmg. Comparative results with the permanganate modification
(A), with the unmodified Winkler procedure (B), and with the alkaline-hypochlorite modification (C) are given in Table VIII. Satisfactory results are obtained by all three procedures when the concentration of digester waste does not exceed 1 part in 30,000 of water. The results with the permanganate modification are decidedly low at dilutions of 1 to 10,000, and the complete absence of dissolved oxygen may be indicated by this procedure at dilutions of 1 to 300. On the whole, the unmodified or regular Winkler method gives better results with sulfite wastes than the permanganate modification. Huge errors, nevertheless, are introduced a t dilutions of 1to 3000 or less. The alkaline-hypochlorite modification gives reasonably accurate results even in the presence of 1 part of digester waste in 300 parts of sample, corresponding to the situation which might be encountered at sampling points in the immediate vicinity of a paper mill. At dilutions of 1 to 150, however, this method also shows signs of failure. It will be noted that the values given in Table VI11 refer to the apparent loss of dissolved oxygen and not to the dissolved-oxygen content. The actual dissolved-oxygen content in all cases was in the neighborhood of 8.5 p. p. m. prior to the addition of digester waste. The possibility exists that, under rigid conditions of test, these apparent losses with different procedures might serve as an index to the
I
amount of waste present in a sample of river water. A less cumbersome and more sensitive test might be devised on the basis of the increase *in iodine-consuming capacity of a sample following a treatment with hydroxides. LITERATURE CITED (1) Alsterberg, G., Biochem. Z.,170,30-75 (1927).
(2) Bach, H., Oesundh.-Ing., 54, 39-41 (1931). (3) Bruhns, G.,Chem.-Ztg., 39, 845-8 (1915). (4) Chapin, R. M., J. Am. Chem. SOC.,38, 625-6 (1916). ( 5 ) Clark, H. W., 15th Annual Rept. of Dept. of Realth of Mass., p. 56 (1929). (6) Cooper, A. E.,Cooper, E. A., and Heward, J. A., Biochem. S., 13, 349-53 (1919). (7) Foerster, F.,et al., 2.anorg. Chem., 128,245-342 (1923). (8) Haaee, L.W., Qesundh.-Ing., 52, 846 (1929). (9) Haase, L. W.,Ibid., 53, 289 (1930). (10) Hendrixson, W. S., J. Ana. Chem. Soc., 47, 1319-25, 2156-9 (1925). (11) Lunge, G.,“Technical Methods of Chemical Analysis,” Vol. 1, pp. 776 et seq., Gurney and Jackson, 1908. (12) Meyer, J., and Schramm. W., 2. anwg. allgm. C h m . , 132, 226-38 (1923). (13) Noll, H., 2.angeto. Chem., 18, 1767 (1905). (14) Rideal, S.,and Stewart, C. G., Analyst, 34, 141-8 (1909). (15) Theriault, E.J., Pub. Health Bull. 151,18-29 (1925). (16) Theriault, E. J., Pub. Health Repts.. Suppl. 90 (1931). (17) Winkler, L. W., Ber., 21,2843-5413 (1888). (18) WinkIer, L. W., 2.anal. Chem., 53, 665-72 (1914). (19) Winkler, L. W., 2.Nahr. Genussm., 29, 121-8 (1915). (20) Winkler, L.W., 2. angew. Chem., 29 (I), 44-5 (1916). RECEIVED July 30, 1831. Presented before the Division of Water, Sewage and Sanitation a t the 81et Meeting of the American Chemical Society, Indianapolis, Ind., March 30 to April 3, 1931.
Volumetric Determination of Chloride J. STANTON PIERCE AND J.. L. COURSEY, Georgetown College, Georgelown, Ky.
D
\
ENIGES determined silver in a large number of compounds by adding excess standard potassium cvanide to an ammoniacal solution of the silver salt, and by titrating the excess cyanide with silver nitrate, using potassium iodide as indicator (1). Substances such as silver iodide, which are insoluble in ammonium hydroxide, were brought into solution by the addition of excess standard potassium cyanide to the ammoniacal solution. Silver salts insoluble in potassium cyanide, such as silver sulfide, were dissolved in nitric acid. The solution was then made ammoniacal and the silver was determined as above. Chloride, bromide, and iodide each were determined by precipitation with excess standard silver nitrate, filtration, and determination of the silver as above in an aliquot of the filtrate. Lestra (2) separated chloride, bromide, and iodide by means of the difference in the solubility of their silver salts in ammonium hydroxide, and determined all by a combination of the Mohr method and the method of DenigBs. Since the method of Denig6s ( I ) affords a convenient way to determine silver and many anions by use of only two stand-
ard solutions, a study was made of the method to see if the procedure could be modified slightly to make it more accurate and more convenient to carry out.
EFFECTOF VOLUME,AMMONIUM HYDROXIDE CONCENTRATION, AND INDICATOR CONCENTRATION Denigds carried out titrations in from about 125 to 250 cc. of solution, containing 10 drops of N potassium iodide, and from about 0.2 to 0.6 N in ammonium hydroxide. I n determining iodide in the presence of bromide, Lestra carried out titrations in about 6 N ammonium hydroxide. It takes 1.8 cc. more of 0.1 N silver nitrate to react with 24 cc. of 0.1 N potassium cyanide in 250 cc. of 6 N ammonium hydroxide than it does in 125 cc. of the same strength ammonium hydroxide, with 10 drops of potassium iodide as indicator, in each case. I n 3 N ammonium hydroxide, with the same amounts of indicator and potassium cyanide as above, it takes over 0.9 cc. more of silver nitrate in 250 cc. of solution than i t does in 125 cc. (In the absence of potassium cyanide, 0.02 cc. of 0.1 N silver nitrate causes a distinct turbidity in 250 cc. of 3 N
January 15, 1932
INDUSTRIAL AND ENGINEERING CHEMISTRY
ammonium hydroxide, containing 10 drops of N potassium iodide.) Even in 0.6 N ammonium hydroxide, with 10 drops of N potassium iodide as indicator (conditions used by DenigBs in some titrations), changing from 125 to 250 cc. causes a change of 0.16 cc. in the end point when titrating 24 cc. of cyanide. Thus, i t is evident that if 0.6 N or more concentrated ammonium hydroxide is to be used, with 10 drops of iodide as indicator, accurate results can be obtained only by carrying out standardization and analyses under almost identical conditions. Increase in potassium iodide concentration causes the effect of volume change to be lessened. The best results were obtained by using an amount of indicator proportional to the volume of the solution, and by carrying out titrations in fairly weak ammoniacal solutions. A satisfactory concentration of indicator was found to be 1 cc. of N potassium iodide for 50 cc. of solution. With this concentration, decrease in ammonium hydroxide concentration from 0.25 to 0.1 N has little effect on the end point. Also, in 0.25 N ammonium hydroxide, the effect of volume of solution on the end point is very slight. It is not convenient, frequently, to use a weaker concentration of ammonium hydroxide than this, so subsequent titrations were carried out in 0.25 N ammonium hydroxide, containing 1 cc. of N potassium iodide for each 50 cc. of solution.
TESTOF METHOD DenigBs showed that cyanide titration of silver ions can be used advantageously to determine all types of silver compounds and anions which form insoluble silver salts. Since in all cases the reaction is between silver ion and cyanide, with iodide as indicator, the conclusions reached above as to the most desirable ammonium hydroxide and potassium iodide concentrations should apply to all the determinations DenigBs made. For an analytical method to be of greatest value it should give consistent and accurate results over a wide range of concentrations of the substance being determined. Since silver nitrate can be readily and accurately standardized, it was chosen as a source of silver to test the method of DenigBs. The silver nitrate solution was standardized gravimetrically as silver chloride and the potassium cyanide solution was standardized by comparison with the silver nitrate. In samples of silver nitrate containing from 0.0504 to 0.4882 gram of silver, the maximum error was 0.3 mg. and the average error 0.15 mg. of silver. Thus, it is evident that the slightly modified method of DenigBs should give fairly accurate results for all soluble silver salts, when no interfering ion or substance is present. A solution of hydrochloric acid, approximately 0.05 N , wm standardized gravimetrically, and was used as a source of chloride in testing the method. Since the method varies slightly in detail from that of DenigBs, the procedure is given, as follows: Precipitate the chloride with silver nitrate solution containing nitric acid and wash free of acid-soluble silver salts, largely by decantation. Dissolve the precipitated silver chloride on the filter paper with dilute ammonium hydroxide, catching the filtrate in the beaker containing the bulk of the preci itate. If more concentrated than 0.25 N ammonium hydroxi& is used, dilute to approximately this strength. (Do not partially neutralize t o cut down the ammonia strength for, in the presence of a high concentration of a strong electrolyte, silver iodide has a tendency to coagulate, and the end point is determined with difEculty, Some of DenigBs' work was done in the resence of appreciable concentrations of strons electrolytes.) If all the silver chloride does not dissolve readdy in the ammonium hydroxide, start titrating with cyanide, using a policeman to crush the particles of silver chloride t o bring them into intimate contact with the solution, When the chloride is in solution, add a drop or two of indicator. (If iodide is added before the
65
recipitate is completely dissolved, coagulated silver iodide is Formed, and this dissolves slowly in potassium cyanide. Under the experimental conditions outlined in this procedure, the titration is carried out in a solution which has a low concentration of strong electrolyte. Under such conditions, the formed silver iodide does not coagulate, but remains in a very fine1 divided, readily soluble form.) If a. precipitate is obtained: continue titration with cyanide to its disappearance before adding the remainder of the indicator, 1 cc. of N potassium iodide for each 50 cc. of solution. Titrate till a very faint turbidity persists, using standard silver nitrate to back titrate, if necessary. By the above procedure, chloride was determined in volumes of the hydrochloric acid solution varying from 2.49 to 100.00 cc. The error varied from 0.0 to 0.2 mg. (average, 0.07 mg.) with weights of chloride from 0.0045 to 0.1800 gram. The same procedure with slight modifications was used to determine chloride in the presence of various substances which normally interfere with either the Volhard or Mohr method, or both (see Table I). OF CHLORIDE IN HYDROCHLORIC TABLEI. DETERMINATION ACID,IN PRESENCE OF OTHER SUBSTANCES
(Chloride present, 0.0899 gram) SUBSTANCE PRE~ENT Name Amount Gram Co++ C u t + N i t + 0.6 eaoh Fe(N& &3d3vBH10; 1 .O eaah FeNdr(903r. 12HaO 1.0 KnCnO7 1.0 KMnO4 Pb++, B i + + + 1.0 eaoh 1.0 NazHPO4.HaO XI 2 00. N KNOI 1.0 Gallio aoid 1.0 0.20 Fe(CN)s--'
CHLOBIDE FOUND Gam
0.0899 0.0897 0.0899 0.0899 0.0900 0.0898 0.0896 0.0898 0.0899 0.0886
It was necessary to neutralize the hydrochloric acid before the permanganate and nitrite were added. After the addition of the silver nitrate, these two solutions were acidified with nitric acid. It was necessary to make the solution more strongly acidic than is usually the case, to hold silver chromate in solution. I n the samples containing permanganate and bichromate, the precipitates of silver chloride were washed with sulfurous acid to remove impurities. Ferricyanide was reduced to ferrocyanide by sodium sulfite, in ammoniacal solution. Reduction of ferricyanide was not likely complete, for a similar test with ferricyanide alone yielded a slight amount of ammonia-soluble silver ferricyanide. Since the precipitate of silver ferrocyanide had a tendency to become colloidal in ammoniacal solution, the ammonium hydroxide washings of silver ferrocyanide were not added to the main filtrate. No doubt some chloride was left in the precipitate and the result obtained represents a balancing of errors. The method as outlined, therefore, is not to be recommended for accurate determination of chloride in the presence of ferricyanide. Chloride was separated from iodide and the formed ferrocyanide by the solubility of silver chloride in approximately N ammonium hydroxide, and the silver chloride was precipitated by the addition of nitric acid to the ammoniacal solution. ACKNOWLEDGMENT Grateful acknowledgment is made to the Dow Chemical Company for their financial assistance in carrying out this work.
LITERATURE CITED (1) Denighs, Ann. china. phys.. [7]6,399-428 (1895). (2) Lestra, BUZZ. sci. pharnaacol., 36, 209-21 (1929). RECEIVED July 21, 1931. Presented before the Division of Physioal and Inorganio Chemistry, Seotion B, at the 81st Meeting of the American Chemioal Society, Indianapolis, Ind., March 30 to April 3, 1931.
