V O L U M E 22, NO. 1, J A N U A R Y 1 9 5 0 the quinoline molecule ( 4 7 ) . This behavior of 8-hydroxyquinoline has been made the basis of a method for determining aluminum. The aluminum is precipitated with 8-hydroxyquinoline and t h e excess reagent used is determined polarographically (30). Quinoline-8-carboxylic acid has been studied in buffers ranging from p H 1 to 12 and behaves like 8-hydroxyquinoline in t h a t three waves are obtained (48). Determination of Metals. T h e addition of 2-naphthol, thymol, and diphenylamine changes the diffusion current and shifts the half-wave potentials of metallic ions. This behavior is ascribed to adsorbed films upon the electrode (19). LITERATURE CITED
Brdicka, R., Arkiv K e m i , Mineral. Geol., 26B, No. 19 (1948). Brdicka, R., Collection Czechoslov. Chem. Communs., 14, 130 (1949). Dennis, S. F.,Powell, A. S.,and Astle, M. J., J . Am. Chem. Soc., 71, 1484 (1949). Delelib. M..R a d . Hrvat. Akad.. 271. 21 (1941). . , Dragt, G., ANAL.CHEM.,20, 737 (1948). Elofson, R. M., Ibid., 21, 917 (1949). Elving, P. J., Warshowsky, B., Shoemaker, E., and Margolit, J., Ibid., 20, 25 (1948). Fields, AM., Valle, C., Jr., and Kane, M., J . Am. Chem. Soc., 71, 421 (1949). Francis, C . V., ANAL,CHmr., 21, 1238 (1949). Gerber, M. I.,Z h u r . A n a l . Khim., 2, 265 (1947). Hala, E., Chem. Obzor, 23, 145 (1948). Hartnell, E. D., and Bricker, C. E., J . Am. Chem. SOC.,70, 3385 (1948). Kalousek, M.,Collection Czechoslov. Chem. CommuPis.. 13, 105 (1948). Klumpar, J.,Ihid., 13, 11 (1948). Korshunov, I. A., and Kirillova, A. S., Z h u r . Ohshchei K h i m . , 18, 785 (1948). Korshunov, I. A., Ryabov, A. V., Sazanova, L. K.,and Kirillova, A. S., Zavodskaya Lab., 14, 519 (1948). Korshunov, I. h.,and Saaanova, L. N., Z h u r . Fiz. Khim., 23, 202 (1949). Landry, A . s.,ANAL. C H E Y . , 21, 674 (1949). Lashkarev, M.,and K r p k o v a , A., Z h u r . Fiz. Khim., 23, 209 (1949). Lewis, W. K., and Quackenbush, F. W.,J . Am. Oil Chemists' Soc., 26, 53 (1949). Lewis, W. R., Quackenbush, F. W.,and De Tries, T., Ax.4~. CHEM., 21, 162 (1949). MacKinney, G.. and Temmer, 0.. J . Am. Chem. SOC.,70, 3586 (1948). Mader, W.J.. and Frediani, H. h., ANAL.CHEM.,20, 1199 (1948).
33 Malyingina, N. I., and Korshunov, I. -4., Zhur. A n a l . Khim., 2, 341 (1947). Miller, E. W:, Arnold, A . P., and Astle. M. J., J . Am. Chem. SOC., 70, 3971 (1948). Neiman, M. B., and Gerber. M. I . , Z h u r . A n a l . K h i m . , 2, 135 (1947). Neiman, M . B., and Markha, Z.V . , Zavodskaya Lab., 13, 1174 (1947). Neiman, M. B., and Shubenko, M . A , Ibid., 14, 394 (1948). Page, J. E., Smith, J. W., and Waller, J. G., J . P h y s . and Colloid Chem., 53, 545 (1949). Parks, T. D., and Lykken, Louis, ANAL.CHEX., 20, 1102 (1948). Pearson, J., T r a n s . Faraday Soc., 44, 683 (1948). Ibid., p. 692. Ibid., 45, 199 (1949). Pittoni, A., A t t i BOC. med.-chir. Padova, 25, 125 (1947). Pittoni, A., Ricerca sei. e ricostruz., 17, 1396 (1947). Portillo, R., and Ortega, M., Anales fls. y gulm. (Madrid), 43, 855 (1947). Portillo, R., and Varela, G., Ihid., 40, i94 (1944). Ibid., p. 839. Ibid., 41, 1429 (1945). Ibid., 43, 850 (1947). Santavy, F., Collection Czechoslov. C'hem. Communs., 14, 145, (1949). Sartori, G., and Gaudiano, A , Gazz. chim. ital., 78, 77 (1948). Sartori, G., and Liberti, A., Ricerca sci. e ricostruz., 16, 313 (1946). Schranfstatter, E., Ezperientia, 4, 192 (1948). Schwabe, K., Z . Saturforsch., 3, 217 (1948). Skramovsky, St., and Teisinger, J., Arch. maladies profess., m6d. travail et se'curife' sociale. 8, No. 1, 22 (1947) : Chimie &- Industrie, 59, 48 (1948). Stock, J. T., J . Chem. Soc., 1949, 686. Ibid., p. 763. 71. 1519 Stricks, W., and Kolthoff, I. M., J . A.m. Chem. SOC., (1949). Vainshtein, Yu. I., Zavodskaya Lab., 14, 517 (1948). Ibid., 15, 411 (1949). Valyashko, N. A., and Kozuni, Y . S.. Zhur. Obshchei K h i m . , 18, 710 (1948). Vavrin, Z., Collection Czechoslov. Chem. Communs., 14, 367 (1949). Vavruch, I., L i s t y Cukrovar., 65, 171 (1949). Vlcek, A. K., Mansfeld, V., an$ Kckoskova, D., Collegium, 231, 245 (1943); Tech. Hlidka KozeluaskQ, 19, 165 (1943). Warshowsky, B., and Elving, P. J., IXD.EX. CHEX.,ANAL.ED., 18, 253 (1946). Warshowsky, B., and Rice, M.LY.,h s a ~C.H E Y . , 20, 341 (1948). Waweonek, S., and Fossum. $1. H.. .I. Electrochem. SOC.,96, 234 (1949). REcaIvEn November 17. l(l4!l
POTENT10METRlC TITRATIONS N. HOWELL FURMAN, Princeton University, Princeton, N. J .
T
HIS review covers the major advances in the field of potentiometric titrations subsequent to a review published in 1942 (73). Much progress has been made in this period in the direction of more convenient apparatus, and both automatic a n d recording titration assemblies have reached the stage of commercial availability. Much attention has been given t o titrations of various sorts in nonaqueous media. The major share of the papers have dealt with well established principles applied t o new situations. If classified by countries in which they were published, the distribution of effort was: United States of America 24.3%, Russia 22.6%, Germany 12.8%, France 12.4%, and England 10.7%. The remaining 17.2% of the papers appeared in Argentina, Brazil, Canada, Czechoslovakia, Finland, India, Italy, T h e Netherlands, S e w South Wales, Poland, Spain, Sweden, and Switzerland. GENERAL PRINCIPLES
The theoretical question of the offset between the inflection of a titration graph a n d the theoretical equivalence point has been
re-examined mathematically by Murgulescu and Dragulescu (139, 140). They found a slight offset between these two points in unsymmetrical types of titrations. T h e general theory and the applications of the potentiometric and related methods have been dealt with in a number of reviews by Carter (Sg), Fernando and Gumersindo (66), and Flatt (66). Special summaries have been published on the dead-stop end point by Bottger and Forche (18), on polarization end points by Evans (63),and on p H electrodes by Lauchlan (112). APPAHATU S
Electrodes. Perley (151-183) ha5 made important detailed studies of glass electrodes of special compositions. Glasses of good stability and low sodium ion errors contained 63 t o 67 mole % of silica, 1 to 4 mole yo each of lanthanum, calcium and barium oxides, 24 to 26 mole % of lithia, and 2 mole % of cesium oxide. Lykken and Tuemmler (126) have stressed the suitability of the glass electrode as a referenre half-cell in processes of types other
ANALYTICAL CHEMISTRY
34 than neutralization. A convenient rotating electrode has been described by Bruggemann (23). Hume and Harris (96) devised a simple bottle type of electrode with agar-filled salt bridge that has a low resistance, about one tenth that of a similar electrode with sintered-glass barrier. The electrode is finding much use in amperometric titrations. Lykken and Rolfson (125) devised an improved titration stand that utilizes commercially available electrodes. Vacuum Tube Voltmeters. Penther and associates (150) developed a vacuum tube voltmeter for use with electrodes of high resistance. Subsequently (149) this basic instrument was incorporated in a dual titration instrument with provision for two sets of electrodes. Titrations of the same or different types may proceed simultaneously with intermittent voltage readings. Buras and Reid (24) developed a line-operated titrimeter that is suitable for titrations. Lineweg (114) described a direct current instrument for use with electrodes of high resistance. Many alternating current line-operated pH meters and titration assemblies are now commercially available. This postwar development has been very rapid, and it has made the potentiometric method much more attractive for control, research, and instruction-for example, instruments of the Central Scientific Company, Macbeth Corporation, Sational Technical Laboratories (Beckman), Photovolt Corporation, Precision Scientific Co., etc. The use of simple magnetic stirrers has greatly improved the assemblies, particularly when titrations must be made Jl-ith an inert atmosphere above the solution. Most of the simplified methods of titration continue to be used, particularly the dead-stop method of Foulk and Baivden which obhas been reviewed (18). Galvanometric indication-Le., servation of changes of current flowing from the titration cell through a high resistance and a galvanometer-has again been found useful by Chirkov (58). Delahay's Methods. Delahay (48-50) has devised circuits for both potentiometric and conductometric titrations. The reagent is added at a constant rate, and the current, flowing through the cell, a condenser, and a sensitive meter, varies with time in a manner given approxiniately by: i = C dE/dt, where i is current, C is the capacity of the conI NO I C A T O R denser, E is the e.m.f., and t ELECTRODE is time. In potentiometric titrations there is a maximum value of i close to but beyond the equivalence point (48). Either indicating or recording assemblies may be based on this principle. Automatic and Recording A rapid deInstruments. velopment has occurred along lines of application of electronic devices to recording titration data or t o the devising of mechanized titrimeters. Pompeo and associates (169) have developed mechanized assemblies. Muller and Lingane (137) adapted the Schmidt trigger circuit t o the goal of stopping a titration as soon as the indicating electrodes reach a preIf this determined value.
value is exceeded by 2 to 3 millivolts, a relay is activated to control a buret, preferably of the motor-driven syringe type If the electrodes show a premature end point due to a local excess of reagent, the motor is activated by an impulse to a second relay and the titration is continued to a permanent change in e.m.f. Robinson (1'74) adopted the principle of adding reagent b? a motor-driven syringe buret operated in synchronism with thr drive of a recording potentiometer. The latter is so modified that reagent is added rapidly when the potential is changing slowly a t the indicator electrode; slow increments of reagent are made as the end point is approached. A limit switch stops the action at any desired point beyond the equivalence-point potential. Lingane (115) devised a similar automatic titration apparatus based upon the motor-driven syringe buret and a potentiometer recorder equipped with a switch t o stop the action a t any predetermined potential. The apparatus was shown to be well adapted t o titrations of various types and was utilized in titrations with chromous solutions (116, 180). A very high degree of precision was attained with the instrument. Lingane (117) also devised a multipurpose electroanalytical servoinstrumenl that may be utilized for a large number of analytical goals, including automatic potentiometric titrations. A plot of potential at the indicator electrode against timr during which reagent is added a t a constant rate has been used by Kale (103). Barredo and Taylor (6) applied this idea to automatic potentiometric titrations by amplifying the output of thr titration cell and registering the potential against time on )i recorder. Constant flow of reagent was attained with the aid of )i Mariotte flask as a constant pressure head. A galvanometer recording device such as that described by Lykken et al. (1231 for polarography should be of interest in registering current-time
v'y
50
GO.
HYPODERMIC
SYR I NGE
40 T H R E A D S / I N C H 3 12 R.P.M.
-
I Figure 1.
Autotitrator (115)
35
V O L U M E 22, NO. 1, J A N U A R Y 1 9 5 0
Syringe burets with revolution counters attached to the threaded drive shaft have been widely utilized in microtitrations. CONCENTRATION CELL METHODS
Swain and Ross (177, 806) found potentiometric titration useful in kinetic studies. Two similar electrodes, connected through a galvanometer, were placed in separate beakers connected by a salt bridge, and a blank solution in one beaker was titrated rapidly with a reagent that simulated the conditions that developed in the other beaker. The amount of reagent necessary t o balance the galvanometer was noted as a function of time. The hydrolysis of tel-t-butyl chloride and the oxidation of oxalate by ceric sulfate were studied in this manner.
EO
Dual Reoordomatic Ti plots and in coulometrio ' titraticms. Other automatic devices have been described by Portnov (160)and by Guntz (91, Q6). Coulometric Titration with Potentiometric Indication. The determination of a substance by oxidation, reduction, or other reaction a t a "generator" electrode by measuring the time at which a constant current has brought a specific reaction to completion is called coulometric titration by Swift and associates f187). T h e end of the process may be noted by change in pormtial with a pair of additional electrodes, or by other metho&e.g., amperometric. Epstein aud others (61) utilized the idea in t.he determination of acids by electrolytically generated hy~lroxyl. Oelsen and Gobbels ( 1 4 ) also used potentiometric in,lieation in this type of process. Shaffer et al. (188) have developed an automstic instrument t h a t electrolyzes mixtures af reagent and sample brought together in a oonstmt ratio. The alectrolysis current is inerewed or decreased in accord with signals fed hack from a pair of indicator-reference electrodes. The elecmalysis current may be indicated or recorded and calibrated in rerms of concentrations of a particular substance in the sample. The principles of the coulometric method are admirably adapted I,O mierodeterminations and to automatic indication or recording ,if content of a flowing solution or a gas stream. Titrations in Partial Vacuum. Apparatus has been devised by Kunst and Sprengel (109) for carrying out potentiometric titiarim* under a pressure of about 16 mm. in a nitrogen atmosphere. MICROTITRATIONS
Stock (608) has given an extensive review of the microchemical aspects of the dead-stop method (of. Bottger, 18). Frahm (71) discussed potentiometric methods in a general microchemical review. Ingold (98) attained accuracy, within *5%, in the titration of 0.300 t o 0.900 mg. of organic acids in a volume of I ml. The solution was placed in a re-entrant cup in a special glass electrode. Traces of acids or bases may be accurately titrated in unbuffered solutions, according to Kunst and Sprengel (108).
Acid-Alkali Processes. IN AQUEOUSMEDIA. The variation of pH with dilution in equilibria involving hydrogen ions and systems such as chromate-bichromate, polyvanadates, etc., has been subjected to mathematical analysis by Carpeni and Souchay (67). Jordan and Taylor (108) have devised a correction for the alkali required by the solvent in the titration of weak acids and bases. Their considerations are useful in studies of polypeptides. The galvanometric method with quinhydrone w. reference electrode, a high resistance, and a galvano by Eustigneev (66) and Gorbacheva. (81) of acids in colored media. Bereau and Taus (IO) have made studies of the further a p plicability of the quinhydrone and antimony electrodes in the titration of acids. Weiner and Mahr (6B) reported t h a t copper and nickel interfere with the use of quinhydrone electrodes in the titration of acids. Kauko and Komulainen (106) estimated carbonate alkalinity in water by direct p H measurement. Anderson and Robinson (6) derived a table of aotivity coefficients, fx+, to be used in connection with the determination of the alkalinity of sea water by titration of acid, where pH = -log Cm+ja+. Carbon dioxide and a small amount of hydrochloric acid in distilled water may he estimated by titration with barium hydroxide, according to Cuta and Kohn (@), and the data indicate the existence of barium bicarbonate. Giraut-Erler (80) found that weak acids a t very low concentration cannot be titrated accurately using a glass electrode. The titration of boric acid has been reinvestigated potentiometrically . hv . Ruehle and Schock (178). T h e boric acid complexes with mannitol with one and two molecules of mannitol per molecule of borate have association constants IG = 3 X lopand K, = 5.1 X IO4, respectively, and according to Deutsch and Osoling (61) these anionic complexes persist in alkaline solution. . Eitel (69) has studied the titration of acetone, acetaldehyde, o-chloro- and o-nitrobenaaldehydes, furfural, and salicylaldehyde with hydroxylamine hydrochloride using the glass electrodecalomel cell. The well known change in p H t h a t occurs in the titration of sulfate by barium chloride solution may be followed with either an antimony or a quinhydrone electrode (Sierra and Carpena, 198). Hypochlorite may be titrated in the presence of sodium hydroxide with standard acid if contamination due to carbon dioxide is avoided, according t o Rodriguez (176). Molybdates. Bye (655)states t h a t in the titration of sodium molybdate with hydrochloric acid the heteropoly anion may be or [HsMo,Oal------. CmriBre and Guiter [I-I,MO~O~~]---(68) found that basic salts are formed a t high p H and acid salts a t low p H in the titration of molybdic acid or molybdates in the presence of alkaline earth or lead ions. Carpeni (66) found that the presence of neutral salts decreased the first break in the titrsi tion curve of molybdic acid. The breaks were a t 0.5 and 2 eqiiivalents of base per gram-atom of molybdenum.
36
ANALYTICAL CHEMISTRY
tensive studies of titrations with the glass electrode as indicator in Precipitation of Hydrous Oxides. Numerous new studies of the course of p H during the titrations of various salt solutions have nonaqueous media with special reference to highly colored mixbeen made. Yadava and Chatterji (228) followed the stability of tures that are of interest in petroleum researches. The general colloidal solutions of aluminum and ferric hydroxide sols potentiotechnique and details of procedure are of considerable interest metrically. in all work with nonaqueous media. B benzene-isopropyl alcohol Moeller and Kremers (194) found the following basicities of mixture in 1 to 1 ratio with about 0.5% of water was found rare earth hydroxides relative to that of yttrium taken as unity: to be of general utility. Anhydrous acetic acid as a medium continues to be useful. lanthanum 1235, cerium 185, praseodymium 333, neodymium 23.5, samarium 8.4, europium 4.2, gadolinium 2.6, erbium 0.16, Kilpi and Puranen (106)found 2.8 X 10-13 for the self-ionization thulium 0.041, ytterbium 0.036, and lutecium 0.031. constant. Tomicek (210) made satisfactory titrations of sulMoeller and Rhymer (136)studied the precipitation of cadfonamides in this medium. Wittman (996)titrated basic nitrogen in oils with perchloric acid in this medium. mium from the nitrate, chloride, bromide, iodide, and sulfate. Virasoro (219) found that fatty acids in butanol may be tiExcess potassium iodide, bromide, or chloride may inhibit the precipitation completely. Carrikre et al. (29) studied the pretrated satisfactorily using the glass electrode. Izmailov and Tarcipitation of cadmium sulfate with sodium hydroxide. Quintin tyllo (101) found that sodium or potassium acetates may be ti(163) measured the concentration of both hydrogen and cadmium trated much more satisfactorily in alcoholic media than in water. Palit (146) utilized the solubilizing properties of glycol-hydroions during the precipitation of cadmium sulfate by potassium carbon solvents for many interesting types of titrations. A hydroxide. Precipitate and solution were separated after various glycol plus butanol, isopropyl alcohol, amyl alcohol, dioxane, or times of treatment. Time of contact of solution and precipitate chloroform is effective for the titration of salts of fatty acids, was found to have an important bearing on the p H of the solution a t various stages in the treatment. boric acid or borax, ammonia, aniline, etc. A glass electrode is Copper. Brouty (22) found evidence of the formation of used as indicator. Dioxane-water mixtures containing 50 to 65% of the former hydrated CuSO4.3Cu(OH)z in the potentiometric titration of were used by Gale and Lynch (76) in making careful titrations of copper sulfate. Guiter and associates (90) made detailed studies of the precipitation of copper from solutions of the sulfate, nivarious dibasic acids in solutions of constant ionic strengths. The ionization constants of oxalic, malonic, succinic, and glutrate, and chloride Basic salts of the type MXz.3CuO and Cutaric acids were derived from the data. The quinhydrone elecSO4.9Cu0 were reported. trode was used. Bordoni (20) studied precipitation methods for the determinaA new direction has been given to research in the nonaqueous tion of copper, iron, aluminum, zinc, nickel, chromium, and lead field by work of Moss et al. ( I % ) , who studied titrations in ethylions. enediamine. The sodium salt of ethanolamine was used as a Geloso and Fauchere (78) reported evidence of the existence of base. The medium is suitable for differentiating between carboxPb(NO&Pb(OH)2, Pb(N0&.3Pb(OH),, and a more basic salt, ylic and phenolic functions in resins. Amino acids give satispossibly Pb(NOa)z.9Pb(OH)2on the basis of titrations of lead factory titration curves. Either an antimony or a hydrogen nitrate"with sodium hydroxide. Various basic salts of uranium were reported by Guiter (88) in the titration of uranyl nitrate with sodium hydroxide. Uranyl acetate and sodium hydroxide gave a f i s t inflection corresponding to uranyl hydroxide and a second corresponding to Naz0.8U03 in Guiter's (89) experiments. Guiter (87) studied the titration of vanadic acid solutions with alkali in the presence of alkaline earth and lead ions. The reporting of basic salts on the evidence of titration data should be viewed with caution, for in many cases equilibrium conditions are not established. U ?;asanen (142) found that the precipitation of zinc hydroxide proceeds stoichiometrically in the presence of sodium, barium, or calcium ions, but that magnesium and sulfate ions interfere. Carrikre et al. (31) found that a correct determination of zinc could be made by titration of chloride or nitrate solutions of zinc with sodium hydroxide. They found a basic salt, ZnSO4.Zn0, a t pH 7.6 to 9.2 in sulfate solutions; it changed to zinc hydroxide a t pH 9.4 to 11.5 IK SONAQUEOUS MEDIA. Wolff (627) has pointed out that relative strengths of acidic or basic functions depend on both the charge type and the acidic or basic properties of the Figure 2. Apparatus for Potentiometric Microtitrations solvent, Uncharged acids (hydrofluoric, nitric, 1. Apparatus of Catch Cook, and Kitchener (34). Glass microelectrode g makes RCOOH) are of relatively constant strengths: contact with 0.1 to 0.2 ml.'of solution containing 2 to 5 ma. of acid or bane. r i s tip of in various media, whereas positively charged reference electrode. 2. Apparatus of Zircher and Hoepe (234) for titration of halide in single drop of acids such as hydrated cationq, NHcf, etc., liquid in depreasion on paraffin block, p . b buret, r reference electrode, M motor, s triangular section on motor shaft to vibrate solution in e. Silver wire indicator increase in acid strength as the dielectric conelectrode i s used. 3. Apparatus of Ingold (98)for microtitration of acids. 6 ia re-entrant glass stant of the medium decreases. membrane, c titration cell, b microburet, r reference electrode, d tube for withdrawLykken and associates (122,124)have made exing solution from fragile cell.
37
V O L U M E 22, N O . 1, J A N U A R Y 1950 electrode may be used, but the glass electrode is unsat,isf a c t o r y in t h i s
medium. Schaal and Itumpf (185) have studied titrations in nitrobenzene. P e t e r s o n et Ui. (154) proved that acids such as sulfur t r ioxi d P , ferric chloride, or stannicchloridta may be titrated potentiom e t r i a1 1 y w i t h 1)asessuch as quinoline, isoquinoline, or pyridine in a n anhydrous selenium o x y c h 1 o r i d t' medium. Precipitation and C o m p l e x Formation (see also hydrous oxide proc(2
PROCESSES VOLVING
A. REF'ERE 0. INDICATOR ELECTRODE C. MAGNETIC STIRRER D. 50 ML. 0URET E. T I T R A N T F. ASCARITE + DEHYDRITE C. 12/5 B A L L JOINTS H. 10/30 JOINTS
T
IS-
SILVEROR
H A L I D E SS. c o t t
Figure 3. Titrations in Ethglene(186) sct up a calidiamine as Solvent (136) l m t i o n graph t,hat 11-:is :ipproxiniately lintw for the estimation of c,hloritie i n \virter from 1 to 1000 p.p.ni. T h r electrode system was silver-silver chloride solution t o tx. tested :ind a 2 S magnesium sulf:tte-lead sulfate-lead amalgani. .I similar idea was proposed t>y LIitoff and Schaaf (133) usiriK the cell silver-silver chloride solution in a calomel half-cell. Th(J calibration line shows appreciable curvature. Gilbert (79 1 :tnd Itiedel (167) have also used the silver-silver chloride elwtrod(' in measurements of small concentrations of chloride ion. Thr w 1 1 established idea of using a quinhydrone electrode :it propclr pEI and a silver electrode to give zero e.m.f. at the entl point of the titration of chloride with silver nitrate ha? been wstudit'd hy Rocha (17.5). Dean and Hawley have developed a portahle apparatus for field determinations of cnhloride and tiic;solvcd oxygen in water ( 4 7 ) . The microtitration of chloride awurate to 0.02 ml. of I O molar silver nitrate has been described by Sorthrop (149). Simplified circuits have been applied to the determination of' cnhloride (Zhidkikh, 232) or in magnesium and its alloys (2717,218). Yeck and Iiissin (230) used the cell silver solution-potassium nitrate saturated with silver chloride, silver chloride-silver, and a v:icuuin tube voltmeter in the titration. Ot,hermodifications that have been recently utilized in the determination of chloride are : :I silver amalgam indicator electrode (Chirkov, 4 1 ) ; titration to R definite potential, in the estimation of chloride in copper solutions (Tao, 229); successive titration of oxalate and chloride (Shchigol and Rirnbaum, 1.90): rhloridc in presence of sulfur tliosidc (Rerkovic-h and Luzina, 1 2 ) ; and chloride in presence of hroniide nnd iodide in amnioniacal medium (Shchigol, 188). T h r w 1)rwksoccur, one a t the end of the precipitation of iodide, a scwnd at' the end of t,he bromide precipitation, and a third a t the (2nd of the formation of AgC1(SH3)2. Calcium may be estimated indirectly in the presence of magnesium by precipitation with standard oxalate solution, filt r:ttion, and titration of the excess oxalatr' with silver nitratc, : I ( % c o d i n g to Birnbaum anti Shchigol (717).
Sodium salts of lauric, myristic, palmitic, or stearic acid may be titrated potentiometrically with 0.02 to 0.1 S silver nitrate (Ekwall and J u u p , fi0). Ilavies and hrmst'rong (46) have confirmed the facut that mwcaptan (thiol) in the presence of sulfides may hi, titrated with silver nitrate. Phosphate may be determined iridirec~tlyby precipitation with excess silver nitrate in a borax hutTt'r of pH 9, adjustment to pH T to 8, filtration, and titration of cwess silver ion with st,andard potasaium bromide solution (Flatt,and Brunisholz, 67). Photographic developer solutions may lie analyzed potentiometrically for bromide [Crowell et al. (44) and Stott (203)jas well as for sulfate (203). Plasencia (155) separates silver and halides in emulsions 1)y alkali, and tit,rates the silver and the halides separately. Bellamy (8) has reinvc~ntig:itc~dtlic titratiori of silver wit,h thiocyanate solut,ion. Cynnidr. Processes. (iregory :+rid Hughan (83)estimate the silver in plating solutions by titration with cyanide. Chirkov (40) used the platinum-silver electrode pair in titrating copper or nickel in solutions of their ores with cyanide solution. The total cyanide in potassium cuprocyanide solutions may be titrated with mercuric nitrate, using an amalgamated platinum electrode as indicator. Free cyanide is estimated by titration with zinc chloride to a turbidity end point, according to Weiner (222). Gaguin (74) found lo-".' for the solubility product of silver cyanide and 0.395 volt for the Eo value of the procejs: .\g(CS),e = Ag 2C?;-, and 0.152 volt for that of .ig[Ag(CN)t] e = Ag (CY)*Ag. The titration of nickel w'th cyanide has heen reinvestigated by Chirkov and Soranovich (42). Fluoride Processes. The tit ration of aluminum with fluoride solution, using the ferri-ferrous indicator electrode, has been applied to ores and silicates t y Stefanovskil arid Svirenko (goo), to magnesium alloys by Marinchen (131), to ele~t~ron-type alloys Ijy Pollak (157),and to bronzes and steels after prior removal of interfering elements by Ivanov and Bezyaiko (99). Similar methods apply t o the determination of beryllium (Tarayan, %OR) and calcium (Tarayan, 209), and to the precipitation of lead as the chlorofluoride (Farkas and Lri, 6 4 ) . T h e determinat,ion of fluoride hy precipitation with ferric chloride according t o Treadwell's procedure has been utilized hy Talipov and Teodorovich (206). Ferrocyanide Precipitations. Yew studies have appeared on t,he titration of various metallic ions with standard potassium ferrocays ni d e soI u t i nns :
+
+
+
+
Cadmium. Bhattavhary and Gaur ( I $ ) , Rerkovich (11), Kale (104) Copper arid Lead. Bale (1OpI) Yickel. Tannaev and Levina (207) Thallium as CaT12 F e ( C S ) 6 2. Ripari and Poppev (170) Zinc. Shistermann and Kolesnikova (191); in aluminum dloys, Eisen (58); in bronze after removal of copper, tin, lead, and iron Pchelintsen (I,@)
.\liscellunroirs.
Lead may be determined indirectly I J adding ~
:in excess of a standard solution of potassium iodate; the excess
of the latter is determined with silver nitrate solution, according to Dragulescu and Latiu (5%). Sasanen has studied the soluM i t y of lead iodide in solutions of various perchlorates (lithium, sodium, barium, cadmium), anti nitrates (lithium, sodium, barium), and in sodium chloride by pot,entiometric technique ( 1 4 1 ) . The methods of preparation of electrodes of silver-silver chloride and silver-silver sulfide have been studied by Maltinea (132). According t o Druet (53) the variation in the end point in the determination of silver depends upon the age and nature of the electrode. Whrn ferric chloride is added to sodium moriohydrogen phosphatc solution, ferric phosphate forms directly, according t o Hubicki and Sykut (M), whereas in the reverse process 2FeP01.Fe(OH)3is formed. Oxidation-Reduction Processes. The work in this field is
38 suniniarized according to individual reagents arranged roughly in order of descending oxidizing power. Applications t o the analysis of precious metals and to the steel and ferroalloy fields are collected at the end of this section. CERICSULFATE. Copper(1) and antimony(II1) niay be t,itrated successively after prior reduct,ion with chromous chloride (Pribil and Chebovsky, 162). The arsenic(II1)-ceriuni(1V) reaction may be used for indirect catalytic estimation of iodine, according to Hahn (93). Cerium(1V) may be titrated with ferrous ion for the estimation of cerium in its alloys with iron (Raisin-Streden and MCillerGamillschweg, 164) and in steels (RIalov et al., 130). P o ~ a s s r u n PERJIANGASATE. i Pappas (147) found that acetate improves titrat,ion of uranium(1Y) in the presence of iron(I1). Manganese (11)is oxidized t o tripyrophosphatomangdnic(II1) ion, Mn(H2P207)2---, by pot assiuni permanganate a t pII 6 to 7 . Chloride and ions of cobalt, iron, chromium, copper, nickel, wolfram(VI), niolybdenuni(TI), uranium(TI), zinc, aluminum, magnesium, and cadmium do not interfere a r c a d i n g to Lingane and Karplus (118). The reverse titration of manganest:(III) pyrophosphate ion with iron(I1) may be used for the estiiiiation of manganese (Watters and Kolthoff, 221 ). lIanganese(I1) may be oxidized t o manganese(II1) in the presence of fluoride. Zvenigorodskaya and Gotsdiner (236) applied this process t o ores and slags. Treadwell and Kieriker (216, 616) have made a general investigation of the production of the ions of chromiuni of (11), uranium(III), uranium(IV), wolfram(IP), wolfram(V), and molybdenum(II1) by reduction with cadmium, follon-ed by oxidimetric titration. IXDICATORS. The formal potentials of o-phenanthroline anti bipyridine-frrrous complexes have been redet'ermined ( 9 7 ) . POTASSI~M BICHROMATE (see also analysis of steels). Oxford (f45)has restudied the titration of iron(I1). Zhivanovich (233) uses a plat,inum-ferric chloride reference electrode in bichromate titrations. HYDROGEK PEROXIDE \vas used by Gazulla (77) in the est'iniation of nitrites. was used by Reeves (165) t'o estiniatc3 LEADTETRAACETATE cis-glycols, the electrodes being lead us. platinum. PoTassIunr BROMATE. Arsenic(II1) and antimony(II1) were determined with bromate by Smith (195) using the polarized platinum-platinum electrode system. Thallium(1) may be titrated in presence of iron(II1) coniplexed by phosphate on a micro srale according to RienBcker and Knave1 (268). DuBois and Skoog (64) determined bromine numliers with standard potassium bromite-bromate solut'ion and mercuric chloride catalyst. 8-Hydroxyquinoline may be determined by the addition of excess standard bromate followed by back-titration with arsenite (Savioli, 184). The platinum-platinum black electrode conihirlation \vas usetl by Bielenberg and Kuhn (14, 15) in bromination of phenols. HYPOBROMITE was used by Chirkov (31) to t'itrate phenol. AND BROMIDE mixtures may be examiiird BROMATE, BROMINE, by titrating free bromine with aniline sulfate, then adding excess of antimony(II1) standardized solution, and titrating the excess with standard potassium bromate solution (Portnov antl Elkina, 161). HYPOCHLORITE. Maksiniyuk and Ptitsyn (12.q) have investigated the reaction between thiosulfate and hypochlorite. PoTAssIuar IODATE has been wed by Spacu and Spacu (1.Y6, 197) for the indirect determination of thorium or of lanthanuni (298). Singh and Rehrnann (194) used potassium iodat'e in the direct est,imation of aromatic amines. Spacu and Spac:u (18 8 ) used the reagent for the estimation of &ascorbicacid. FERRIC-FERROCS RE.KTIOSS. Ferric chloride or sulfate solutions have been found useful by Rius and Coronas ( 2 7 2 ) in the
ANALYTICAL CHEMISTRY estimation of niolybdenum(III), or of niolybdenum and vanadium (Rius and Martin, 173). Lannet (111) applied the met,hoti to titanium, and Weiss and Blum (224)to uranium(1V). Ferrous sulfate as reagent is used most frequently in steel analysis. Strouts and MacInnes (,god) determined nitric acid iii mixed acids with ferrous sulfate using a platinum-potassiuin iodate reference electrode. NcKinney et al. (128) developed a similar method for estimating nitric acid in oleum. IODISE-IODIDE REACTIOXS.Reagents containing iodine haves been used in t'he indirect determination of silver in micro or submicro amounts, based on the reaction 2Ag $- 1 2 = 2Ag1, folloived by titration of excess iodine with arsenite, using the dead-stop method (Lambert and Walker, 110). Sillars antl Silver (193) determined oxygen in water by the indirect iodine-thiosulfate procedure. Bates et uZ. (?) determined the amylose antl amylopectin coiitent of st,arch by standard iodine solution. Water by the Karl Fischer technique is best estimated wit11 the aid of the dead-stop end point as suggest,ed by Wernirnont and Hopkinson (2%) and by Carter and Williamson (33). Iieiinie and Markhain (166) applied the method to gunpowder.. glacial acetic acid, sawdust, and shellac. McComb (127) applied it to protein mat,erial, and Gukhman at ril. (RU) studied variouP applications. The folloiring titrations with at:tiidard potassium iodide have been investigated: chloramine, by Afanasev (1); copper, applied to indirect rstimation of iodine, by Hahn and Adler (S4);osniiuni in osmic. acid, by Ryahchikov (180); and selenates, by Ripan :ind Dragulescu (169) and de Salas (183). Major attentioil FERRI-A K D FERROCYANIDES AS IIE.WESTS. has been given t o the estimation of cobalt(I1) by titration with ferricyanide. Chirkov (39) studied t,his method and the cyanid(, method for nickel and cobalt. Ivanova and Malov (100) antl Bagshawe and Hobson (3)studied the application t o steels. The latter (3) consider the formal potentials and the interferences of manganese chromium(III), and ranadium(1V). Zvenigorodskaya (235) avoided the interference of manganese by oxidizing it to manganese(II1) in presence of fluoride with potassium prrmanganate. The standard ferricyanide ~olution was theii titrated with the solution of the alloy. Podlubnaya and Bukharov (156)estimate sugars by using thcair .iolutioris to titrate alkaline ferric)-anide solution. Murgulescu and Dragulescu (138) found that hexammine CI Ih:iltic salts may be used to t,itrate ferrocyanide. CCPRICION. Britton and Clissold (21) usrd cupric reagent, for the titration of phenyl hydrazine. POTAWIC-M MERCURICIODIDE, K?HgIA, may hr titrated wit li arspnite or antimonite in alkaline niediuni (72). hIoLYsnss-rhr(V) AS REDL-CTAXT. Tourky et al. (416) studie(! the stability of the solution and t,he titration of iron, and also (213) titration of iodate, bromate, bichromate, and vanadate. They later (224) investigated the titration of various mixtures of oxidant,s. Rius and Coronas (17 1 ) folloired potentiometrically the interaction of molybdenuni(V1) :ind niolybdenum(II1) ti, yield molgbdenum (V). THIOCYASATE. Gaguin (76) studied the reducing properties of thiocyanate ion a t various p H ranges. STANNOT'S CHLORIDE was used by Vasilev (217) for the indirec8t estimat,ion of phosphorus by titration of inolybdiphosphoric acid. 5 ) to the VASADOT-s SULFATE has been applied by Banerjee (4, titration of titanium and to the estimat,ion of organic substances. CHRo>rom S O L ~ T I O N have S been thP subject of in~estigat~ion. Apparatus and application of c.hroniiurn(I1) to the estimittion of molybdenum, Lvolfranl, uranium, vanadium, titanium, antimony, tin, and bismuth. Flatt and Sommer (68). Estimation of wolfram and vanadium. Flatt and Sommer (69). Estimation of iron, copper, titanium, vanadium, chromium, molybdenum, and wolfram. Flat,t and Sommer ( 7 0 ) . Titration of heteropoly acids of silicon and phosphorus Tourk). and El Shaniy ( 2 2 1 ) .
V O L U M E 22, NO. 1, J A N U A R Y 1 9 5 0 I
