ANALYTICAL CHEMISTRY Stenger, V. A., Kramer, W. R., and Beshgetoor, A. W., IND. ENQ.CHEM.,ANAL.ED., 14, 797-8 (1942). Stevens, R. E., and Carron, M. K., U. S. Geol. Survey, Bull. 950, 91-100 (1946).
Strong, F. C., ASAL.CHEM.,19, 968-71 (1947). Stumper, R., Chem.-Ztg., 65, 239-40 (1941). Stumper, Robert, and Mettelock, P., Compt. rend., 224, 1 2 2 4 (1947).
Tabak, Salomao, Qulmica (Brazil), 1, 146-7 (1945). Tamayo, M. L., and Marques, 3. G., Anales fis.
y quim. ( M a d r i d ) , 43, 1011-16 (1947). Tananaev. I. V..Zavodskawa Lab.. 12. 248-9 (19461. Tananaev; I . V., and Abiiov, S. T., J . Appiied Chem. (U.S. S.R.), 15, 61-70 (1942). Tananaev, I. V., and Deichman, E. N., Zavodskaya Lab., 12, 30-7 (1946). Tananaev, I. V., and Karabash, A. G., IbicE., 13, 20-4 (1947). Tananaev, I. V., and Misetskaya, I. B., Ibid., 12, 529-33 (1946). Tananaev, I. V., and Sil'nichenko, V. G., Ibid., 12, 140-1 (1946). Tamnaev, N. A,, and Lotsmanova, M. H., Zhur. Anal. Khim., 1,206-8 (1946). Tassieur, Arnold, Compt. rend., 214, 80-2 (1942). Termansen, J. B., Arch. Pharm. Chem., 50, 373-88, 393-417 (1943) ; Chem. Zentr., 1943, 11, 1982. Thiers, R. E., and Beamish, F. E., AXAL.CHEM.,19, 434 (1947). Thistlethwaite, K.P., Analyst, 72, 531-40 (1947). Tompkins, E. R., Khym, J. H., and Cohn, W. E., J . Am. Chem. Soc., 69, 2769-77 (1947). Touhey, W. O., and Redmond, J. C., ANAL.CBEM.,20, 202-6 (1948). Tournaire, M., Ann. chem. anal., 27, 9-11 (1945); Chimie et Industrie, 54, 249-50 (1945). Traub, K. W.,IND.ENG.CHEM.,ANAL.ED.,18, 122-4 (1946). Trombe, Felix, Compt. rend., 215, 539-41 (1942). Ubeda, F. B., Gonzales, E. L., and de la Sota, Herrera, Anales ffs. II ougm. ( M a d r i d ) . 41. 498-529 (1945). . Vasil'ev, A . A , , and Sudilovskaya, E.'M., Zavodskaya Lab., 11, 802-3 (1945). I
_
(337) Vasil'ev, K. A., and Vegrin, M. L., Ibid., 9, 627-8 (1940). (338) Veselovskit N. V., Hydrochem. Material. (U.S.S.R.), 12, 2-23, 35-41 (1941). (339) Vlodavets, N. I., T r u d y Inst. Geol. N a u k . Mineral.-Geokhim. Ser. 1940, No. 17 (No. 4 ) , 1-18; K h i m . referat. Zhur., 4, No. 9, 83 (1941). (340) Voight, Adolf, 2. anorg. allgem. Chem., 249, 225-8 (1942); Chem. Zentr., 1942, I, 3237-8. (341) Weiss, Igor, Rev. brasil. qulm., 20, 337-8 (1945). (342) Weiss, Ludwig, and Sieger, Hans, 2. anal. Chem., 119, 245-8 (1940). (343) Weissler, Alfred, IXD. ENG. CHEM.,ANAL.ED., 16, 311-13 (1944). (344) Wenger, Paul, Helv. Chim. Acta, 25, 1499-500 (1947). (345) Wenger, Paul, and Duckert, Roger, Ibid., 25, 1110-14 (1942). (346) Wheeler, W. C. G., Analyst, 68, 246 (1943). (347) Wichers, Edward, Schlecht, W. G., and Gordon, C. L., J . Research ATatl. B u r . Standards, 33, 451-6 (1944) (Research Paper 1621). (348) Wijs, J. C. de, Rec. trav. chim., 62, 188-92 (1943). (349) Willard, H. H., and Freund, Harry, Ibid., 18, 195-7 (1946). (350) Willard, H. H., and Gordon, Louis, ANAL.CHEM.,20, 165-9 (1948). (351) Willard, H. H., and Zuehlke, c. TV., IND.ENG.CHEaf., ANAL. ED.,16, 3 2 2 4 (1944). (352) Killiams, Dwight, and Haines, G. S., Ibid., 16, 157-61 (1944). (363) Wirts, Hubert, Metal. u. Em, 41, 84-6 (1944). (354) Witte, M. C. de, Rec. hav. chim., 62, 134-6 (1943). (355) Wright, E. R., and Delaune, R. H., IND.ENG.CHEM.,. ~ N A L . ED.,18, 426-9 (1946). (356) Wylie, -4. W., Analyst, 72, 250-2 (1947). (357) Wylie, A. W., Nature, 160, 830 (1947). (358) Yien, C. C., and Shing, S. S., J . Chinese Chem. Soc., 8, 12-14 (1941). (359) Yoe, J. H., and Jones, A. L., IXD.ENG.CHEM.,ANAL.ED.,16, 45-8 (1944). (360) Young, R. S., and Hall, 4 . J., Ibid., 18, 262-4 (1946). (361) Young, R. S.,and Hall, A. J., J . SOC.Chem. Ind., 66, 375 (1947). (362) Zil'berman, Ya. I., and Markova, N. G., Zavodskaya Lab., 11, 150-2 (1945).
ORGANIC GRAVIMETRIC ANALYSIS JOHN F. F L A G G ZCnolls Atomic Power Laboratory, General Electric Co., Schenectady, N . Y .
D
EVELOPAIENTS in the field of carbon and hydrogen analysis are considered together in this review, as these elements are usually determined together. A survey of publications on the subject for the preceding &year period reveals a constant search for improvement in the chemistry of combustion, and an increasing degree of automatic control and instrumentation, designed to standardize conditions in the conventional combustion procedures, and permitting use of relatively unskilled personnel in determinations formerly calling for a high degree of skill and experience. Willits (47) discusses developments in microdetermination of carbon and hydrogen in his review of organic microchemistry. Most workers continue t o prefer filled tubes, and numerous modifications in fillings have been reported. The conventional copper oxide-lead chromate filling has been replaced with silver vanadate on small pieces of pumice (18). It is claimed that in microcombustions of compounds containing nitrogen and halogen or sulfur in addition, a better decomposition of nitrogen oxides is obtained. Promising results were also obtained with ctrium oxide-silver chromate and manganese oxide-silver chromate catalysts. T h e use of mixed iron-copper oxide catalysts has received some attention; a mixture of copper oxide plus 1% ferric oxide plus 20 parts of white kaolin has been stated t o be mere active and stable than copper oxide alone (6). A mixed copper oxide-iron oxide (1%) catalyst has been used successfully for the determination of gaseous hydrocarbon3 (28). The
modified catalyst permits lower oxidation temperatures (700 O compared with 900" C. for copper oxide alone), and in its application the method avoids the need for an oxygen supply of accurately known purity, as well as errors from incorrect measurement of oxygen volume or content of the oxygen supply. The explosion hazard is also eliminated. -4 comparative study, made using the copper oxide wire method, the slow combustion wire method, the platinized silica gel method, and the precipitated copper oxide method, showed that the latter method gives results equal or superior in accuracy and precision to the other three. A modification of the ter Meulen semimicromethod uses a 50-cm. layer of manganese dioxide, followed by a 9-cm. layer of lead chromate, over which the combustion products are passed at 450' C. (8). By this means 1-gram samples of refractory oils have been successfully analyzed. Use of platinized asbmtos, heated to 300" to 400" C., for the selective oxidation of hydrogen in a hydrogen-methane mixture has been reported (45),as well as the use of a high-temperature platinum wire for combustion of methane and hydrogen (44). The determination of carbon and hydrogen in an industrial plant is described (51) as being considerably simplified by use of a n electric furnace for graudal automatic heating of the sample tube. A unitized dual apparatus for macrocombustions has been described (43),in which a maximum control of the combustion
V O L U M E 21, NO. 1, J A N U A R Y 1 9 4 9 operations is sought as a means for improving speed, accuracy, and precision. Microrotameters monitor gas flow rates, furnace temperatures are closely controlled, rubber connections are limited, and oxygen is introduced a t two points in the combustion tube. Conventional tube packing and absorption bulbs have been used, and improvement in results is attributed to close control of mechanical factors. Critical studies of sources of error in the carbon-hydrogen micromethod have considered oxygen purity, combustion tube filling, and combustion time (7). On the basis of tests on commercial oxygen it was concluded that a copper oxide preburner cannot, safely be omitted from the system unless the oxygen is tested for impurities before use. Platinum gauze is recommended for use in the combustion tube when refractory compounds are being analyzed, and it was found that the lead dioxide could not be replaced by a permanganate absorber, a t least in the micromethod. Extension of the vaporization time up to 15 minutes may prove advantageous for oils and tars, as well as for low boiling hydrocarbons. Comparable vaporization times should be used for all analyses in a series to avoid errors resulting from removal of varying aniount,s of water from the water-lead dioxide equilibrium. The hygroscopic nature of asbestos and the manner in which it introduces positive errors in hydrogen determinations have been investigated, and data on the attraction and retention of water to and by asbestos a t various temperatures are given (26). Special methods have been reported in a few cases. The determination of carbon in organic fluorine compounds is carried out by a procedure in which the sample is burned in the presence of quartz powder, the water and silicon tetrafluoride are absorbed by sulfuric acid and potassium fluoride solution, respectively, and the carbon dioxide is finally absorbed in the usual way (SO). -4trend toward simplification of the hydrogen determination is reflected in the lamp method as applied to the analysis of hydrocarbons (14, 15). The procedure consists of collecting and weighing, in a phosphorus pentoxide absorber, the water formed upon burning several grams of the volatile hydrocarbon in a modified A.S.T.M. D90-41T sulfur lamp. Considerable improvenient in accuracy over the conventional combustion method is rioted (0.037Gagainst 0.1 to 0.2%)) and the method is well suited for use by unskilled operators. An extension of the lamp method to determine carbon as well as hydrogen has been re; the incompletely burned carbon gases are passed ported (40) through a heated combustion tube, and the emergent carbon dioxide and water are absorbed in the usual way. The method has been applied to both aromatic and aliphatic hydrocarbons, and the precision on 1-gram samples is of the order of 0.017,. Other Elements. Titrimetric methods seem more popular than gravimetric for elements other than carbon and hydrogen. The decomposition and analysis of organic halogen-containing compounds (including fluorine) have been studied by a method using sodium and liquid ammonia in a sealed tube a t room temperature ( 2 7 ) . Fluoride is precipitated from the product mixture as lead chlorofluoridc, but t,he determination is concluded volumetrically by titration of the chloride in the precipitate. Surface-active agents may be analyzed for organically combined sulfuric anhydride by digestion with nitric and perchloric acids unti! decomposition is complete, followed by precipitation of barium-sulfate (IO). ! 3ANALYSIS OF PARTICULAR SUBSTANCES
Hydrocarbons. A method has been reported for the determination of small quantities of acetylene in synthetic acetic acid (24). The sample is heated in nitrogen and the gases are passed through 60Y0 potassium hydroxide to remove acetaldehyde, then into a reduced ammoniacal copper solution containing hydroxylamine hydrochloride. Cuprous acetylide precipitates, and after
161 washing is analyzed either gravimetrically or volumetrically for copper. Styrene may be determined gravimetrically by precipitation as the nitrosite, C6H&H(KO)CH&O2 ( 2 ) . T h e reaction is specific for styrene in the presence of phenylacetylene and butadiene dimer, which frequently accompany styrene. Some diolefins react with the nitrogen trioxide used for the precipitation, but the products formed are soluble in cold alcohol and may be separated in this manner from the styrene nitrosite. The method possesses the advantage of being able to determine of styrene in comparatively low concentrations (up to 107~) niist,ures. A method for determining naphthalene in dilute air samples (25) involves measurement of weight losses in a naphthalencb tube as the air stream is passed alternately over active carbon and naphthalene. Aldehydes and Ketones. Studies have been carried out on the gravimetric microdetermination of "very small" amounts of aldehydes and ketones by precipitation with 2, Cdinitrophenylhydrazine (41); compounds determined included vanillin, acetophenone, fluorenone, cyclohexanone, menadione, and furfural. The same reagent has been used for the determination of methyl propyl ketone, although recoveries on milligram quantities are not particularly high ( I S ) . The Munson-Kalker method for determining reducing sugars has been applied to some of t'he less common sugars (mannose, galactose, xylose, arabinose, fucose, and rhamnose) as vie11 as to sodium glucuronate and glucurone (48). SerT tables for determining t'hese are given. The method has been restudied in connection with the determination of the more conimon reducing sugars, and slightly modified tables are given (11). Additional tables of sugar-copper equivalents have been given for 0 to 10 mg. of glucose, galactose, arabinose, xylose, and lactose, using the Bertrand micromethod (35). 4 comparative study of four such standard methods of reducing sugar analysis has been reported ( I ) . X method has been given for the determination of D-xylose by precipitation of that sugar as the dibenzylidene dimethyl acetal ( 3 ) . -4critical study of the method has been made (49),in which conditions necessary to obtain 82 to 1007c recovery are established. The precipitation requires 7 days for completion; during the last 24 hours the temperature must be held a t 4 " C. ~-Galacturorie and D-galacturonic acid do not interfere, but L-xylose does. Acids and Derivatives. The gravimetric determination of phthalic anhydride in alkyd resins has been carried out by saponifying the sample with alcoholic potassium hydroxide at 55' C. Potassium phthalate, with one alcohol of crystallization precipitates from the mixture; the alcoholate is decomposed by heating at 150" to 210" C., and anhydrous potassium phthalate is weighed (9, 12). Anhydrous conditions must be maintained, as the precipitate is appreciably water-soluble. Aconitic acid, CIH~(COOH),,a sugar cane product, and its salts have been determined by decarboxylation of the lead salt in glacial acetic acid-potassium acetate solution (34). The eiRuent carbon dioxide is absorbed in the usual type of train. The method is more rapid than a former ether extraction method: sources of error and interference have been studied, and the method appears capable of yielding satisfactory results. Precipitation with pyridine has been used for the determination of monochloroacetic acid; other halogenated derivatives react under the same conditions (3s). An interesting electrodeposition method has been reported for pectic acid and pectins ( 4 6 ) . These materials are negatively charged colloids, and in the method are deposited on a platinum gauze anode from a cooled solution of the material in water and alcohol. The deposit is washed with alcohol, dried, and weighed. Amines and Related Compounds. The separation and determination of primary, secondary, and tertiary alkaryl amines by a combination of gravimetric and volumetric methods have been
162 described (38). Aniline and its ring-methylated and S-methylated homologs are separated into groups of primary, secondary, and tertiary amines by forming the toluenesulfonamides of the primary and secondary amines in cold benzene-pyridine solution. The unreacted tertiary amines are removed by steam distillation, and the combined primary and secondary derivatives are weighed. The toluenesulfonamides are separated by extraction with 5odium hydroxide, in which the primary derivative is soluble. Following acid hydrolysis the free amines are titrated. The method offers advantages over the older Hinsburg method in that undesirable side react,ions are ahsent, and all the principal reactions go to completion. Two somewhat similar methods have been described for dct crmining melamine, (CX),(NH2)3 (21, 50). The test solution is acidified with acetic acid and heated, and melamine is precipitated as the picrate. Melamine picrate may be dried at 105 ' C. and weighed. The reaction is not specific for melamine, and provision is made for removing guanidine and dicyanodiamine. The formation of an insoluble dithiocarbamate serves for the gravimetric determination of 1-diethylamino-4-aminopentano (19). The precipitate forms in acetone in the presence of carbon disulfide, and is dried in vac,uum a t room temperature anti weighed as the hemihydrate, C1~H22N&. l/,H20. Sulfur-Containing Compounds. The mercaptan content of mixtures of primary mercaptans (thiols) has been determined by precipitation of silver mercaptides, which are dried and weighed (93). A novel feature of the method is the use of ai1 amperometric end point to indicate complete precipitation of the mercaptans as the silver nitrate is added. Sulfapyridine may be determined as the silver salt by precipitation with excess silver nitrate from weakly acidic solution. The precipitate may be dried a t 90' to 105' C. (BO). Phenols and Derivatives. For the gravimetric determination of a phenol, the sample is treated with formaldehyde and heated. The polymer that forms (resite) may be filtered, washed, dried at 140' C., and weighed ( 2 2 ) . It seems that such a method would hardly offer advantages over standard volumetric methods. .I rapid gravimetric determination of dinitrophenol has been described wherein the phenol is precipitated from a solution of its sodium salt by means of nitric acid (31). The precipitate may tie dried a t 90" to 100" C. and weighed, or dissolved in excess standard alkali, the remaining portion of which is titrated. Along somewhat more explosive lines is a method for determining trinitroresorcinol and trinitrotriazidohenzene (37). The former compound in solution is treated with a solution of phenylacridine hydrochloride. ITpon neut,ralizing and boiling, a precipitate forms which may be dried a t 80" C. for weighing. If one is dealing with lead triiiitroresorcinate, the lead is first precipitated with bicarbonate arid removed before adding the phenylacridine. Trinitrophloroglucinol is determined in the same way, and as trinitrotriazidobenzene may be converted t:) that compound by treating with dilute alkali, a means for dctormining it is also a t hand. Natural Products. A gravimetric method for cholesterol has been described in which the sterol is converted to a sulfonic acid derivative of cholesterilene in chloroform. This compound, finally obtained in a water solution, precipit>atesupon addition of barium acetate as Ba(C2~H4,03S)r, which is dried and weighr?.l 1.29).
An extraction procedure is reported for determining cdTeiric8 erva-mat6; the alkaloid apparently is not obtainod in a pure state for final weighing as the results are high. (6). Sicot,ine may be determined by precipitation with silicomolybdic acid, said t,o possess advantages over silicotungstic acid when used for The same purpose (4). h preliminary isolation is effected by *wain distillation of the alkaloid into hydrochloric acid, from which it is precipitated as (CIQHl&r)r.S O , . 121100,~H&, dried at 110" to 120" C.. and weighed. iri
ANALYTICAL CHEMISTRY Miscellaneous Determinations. The gravimetric determination of phenothiazine has been described, in which the material in alcohol is precipitated with chloroplatinic acid (32). The pre(elpitateof Pt(C12HgNS)2C14 is dried a t 100O C. before weighing. Leptazol (pentamethylene tetrazole) has been determined by precipitation with mercuric chloride and weighing of the mercuric cbhloride complex (17 ) . The determination of hexamethylene diisocyanate has been carried out by condensing it with aniline, steam-distilling out the oxcess aniline, and weighing the condensation product 142) The method may be used also for benzyl and cyclohexyl isocyanate. l-Proposy-2-amino-4-nitrobenzeneis a synthetic sweetening agent; it is insoluble in alkali, and may be extracted from aqueous .solution with ether, dried, and weighed (16). Appropriate modifications of the procedure are given if fat is present in the ,ample being analyzed. The analysis of carbowax compounds-solid polyethylene glycols-has been described using the precipitation reaction of these compounds with silicotungstic acid (36). The precipitates are ignited before final weighing, and the method is calibrated by use of knox-n samples to obtain the proper gravimetric factor. Benzidine hydrochloride has been used to precipitate the sodium salt of oleyl methyl tauride (Igepon T) from acid solution (44). The precipitatt. is washed with petroleum ether, dried, weighed. LITERATURE CITED
Blom, J., and Rosted, C. O., Acta Chem. Seand., 1, 32 (1947). Bond, G. R., J r . , ASAL.CHEM.,19, 390 (1947). Breddy, L. J., and Jones, J. K. N., J . Chem. SOC.,1945, 738. Brichta, M., Rev. b r a d . quim. (Sao P a d o ) , 18, 388 (1944). Buhrer, N. E., Arquiv. bid. e tecnol., Inst. bid. e pesquisas tecnol., Curitiba, Brazil, 1, 177 (1946). Chernyaeva, Y. I., Coke and Chem. (U.S.S.R.), 11, No. 5, 36 (1941). Clark, R. O., and Stillson, G. H., IKD.E m . CHEM.,ANAL.ED., 17, 520 (1945). Dam, H. van, Ing. chim., 26, 127 (1942). Doyle, C. D., IND.ENG.CHEY.,ANAL.ED.,16, 200 (1944). DuBose, B., and Hollard, V. B., Am. Dyestuff Reptr., 34, 321 (1945). Ekelund, S., Acta Agr. Suecana, 1, 239 (1946). ENG.CHEM.,ASAL.ED.,16, 198 (1944). Goldberg, 8 . I., IND. Heitzmann, P., Bull. matieres grasses inst. colonial Marseille, 29, 38 (1945). Hindin, S.G., and Grosse, A. V., ANAL.CHEM.,19, 42 (1947). ENG.CHEM.,ANAL.ED., Hindin, S. G., and Grosse, A. V., IND. 17,767 (1945). Hoeke, F., Chem. Weekblad, 43, 283 (1947). Horsley, T. E. V., Analyst, 71, 308 (1946). Ingram, G., J. Soc. Chem. Ind., 62, 175 (1943). ENG.CHEY.,ASAL.ED.,16, 431 (1944). Jones, R. G., IND. Khoromov-Borisov, N. V., Yurist, I. M., and Popova, L. P., Farmatsiya, 9, No. 1, 26 (1946). Korinfskii, 8. -4.Zavodskaya . Lab., 121, 418 (1946). Krahl, M., Kunststoff.-Tech. u. Kunststof-Anwend., 12, 190 (1942). Laitinen, H. A., O'Brien, A. S.,and Nelson, J. S., IND.ENO. CHEM.,ANAL.ED., 18, 471 (1946). Lazzari, G., A n n . chim. applicata, 32, 349 (1942). Linden, A. van der, and Klein, W. J., Het Gas, 66, 59 (1946). Lindner, J., Be?., 76B, 701 (1943). Miller, J. F., Hunt, H., and McBee, E. T., Ax.4~.CHEM.,19, 148 (1947). Murdock, R. E., Brooks, F. R., and Zahn, V., Ibid., 20,65 (1948). Nath, M . C., Chakraborty, M . K., and Chowdhury, S. R.. .Vature, 157, 103 (1946). Nikolaev, N. S.,Bull. m a d . sci. U.S.S.R., Classe sci. chim., 1945, 309; Chem. Age, 54, 309 (1946). Pastac, I., and Lecrivain, R., Ann. chim. anal., 26, 104 (1944). Payfer, R., and Marshall, C. V., J . Assoc. Oficial Agr. Chem., 28, 429 (1945). Iiamsey, L. L., and Patterson, W. I., Ibid., 29, 100 (1946). Roberts, E. J., and Ambler, J. A., ASAL.CHEM.,19, 118 (1947). Saint-Rat, L. de, and Corvasier, L., Ann. pharm. franc., 4, 47 (1946). Schaffer, C. B., and Critchfield, F. H., ANAL. CREM.,19, 33 (1947). 3
V O L U M E 2 1 , N O . 1, J A N U A R Y 1 9 4 9
163
(37) Schmidt, R., 2.ges. Schiess.- u . Sprengstoffw. Nitrocellulose, 38, 148 (1943). (38) Seaman, W., Norton, A. R., Woods, J. T., and Bank, H. N., J . Am. Chem. SOC.,67, 1571 (1945). (39) Shiraeff, D. A., Am. Dyestuf Reptr., 36, No. 12, Proc. Am. Assoc. Textile Chem. Colorists, 313 (1947). (40) Simmons, M. C., ANAL.CHEM.,19, 385 (1947). (41) Soeai, J. A., Analesfarm. u bioqulm. (Buenos Aires), 14, 41 (1943). (42) Stagg, H. E., Analyst, 71, 557 (1946). (43) Tunnicliff, D. D., Peters, E. D., Lykken, L., and Tuemmler, F. D., Ibid., 18, 710 (1946). (44) Vandoni, R., M e m . serz'ices chim. itat, 30, 18 (1943).
(45) Ibid., 30, 272 (1943). (46) Williams, K. T., and Johnson, C. M., IND.ENG.CHEM.,ANAL. ED., 16, 23 (1944). (47) Willits, C. O., ANAL.CHEU.,21, 132 (1949). (48) Wise, L. E., and McCammon, D.C., J . Assoc. Oficial Agr. Chem., 28, 167 (1945). (49) Wise, L. E., and Ratliff, E. K., ANAL.CHEM.,19, 694 (1947). (50) Zavarov, G. V., Khimicheskaya Prom., 1945, No. 2, 21. (51) Zimmermann, W., Mikrochemie ver. Mikrochim. Acta, 31, 140 (1943). RECEIVED November 23, 1948.
INORGANIC VOLUMETRIC ANALYSIS C L E M E N T J. RODDEN
National Bureau of Standards, Washington, D . C .
V"""'
I I E T R I C methods 89 applied t o inorganic analysis have seen, in the past several years, the usual modifications a n d reviews of existing methods, as well as some that are new and novel. Several innovations and improvements of existing apparatus have been made. Publications describing the results of European workers have been received irregularly. As a result, references are incomplete; hoyever, the work of Russian workers since the end of World War I1 has been discussed in French (212).
TITRATION
Reviews and examinations include a tsxt'book on titration methods (96); the precise measurements of volume (201); procedures and techniques for colorimetric titrations with photoelectric instruments (216 ) ; apparatus and techniques for amperometric titrations (191); potentiometric titration methods with special attention to microchemical applications (145, 192) and to arsenic and iron (62); new and existing methods for tungsten (26,146),thorium (139),and vanadium (148); potassium as cobaltinitrite, chiefly in plant ash (208); cobalt in steel by ferricyanide (8); the effect of iron in the reduction of molybdate in determining phosphorus (129) ; the Karl Fischer procedure for water (37, 177); and the iodomctric determination of thionalide as applied to bismuth, mercury, and copper (101). A discussion of the strength of acids in various organic solvents is of interest (224). A graphic procedure has been advocated as a means of determining the results of volumetric analysis (207). Apparatus and accessories (142) for automatic titrations, whereby it is only necessary to prepare and load feed units, have been described (118) and are on the market (157). The automatic recording of titrations as applied to potentiometric, amperometric, and absorptiometric titration has been made with recording potentiometers (73). Further work on the use of high frequency oscillators ( 8 7 ) ,which at one time promised to revolutionize volumetric analysis, has not been found. A simple apparatus, requiring only a battery, a microammeter, a variable resistance, and silver and copper wires for electrodes has been used with good results for the rapid analysis of chloride (49). Apparatus for polarization dead-stop end points has been described (58) n-hich is essentiallj- that of earlier n-orkers ( 6 5 ) . -4 cell suitable for conductivity determination of chloride in sea water is useful as a time-saver ( 4 ) . Titrations have been made using photoelectric colorimeters (160) which are a further application of previous work (149, 217). Among the several types of burets that have been suggested, are a n electrical solenoidoperated buret which avoids stopcocks but may be prone to leak ( 1 4 5 ) ; a rather complicated microburet, controlled by addition of
water to a mercury level (274); a syringe microburet (181); and a micropipet for titration of microgram samples (125). An 89sentially new technique for operation of a microburet appears useful (167). Electronically controlled apparatus for distillation of fluoride or hydrofluosilicic acid (218) is an important improvement. Several variations from the usual run of the mill methods are of interest. Among these are titrations in strongly colored solution by adding a solution of a complementary color ( 2 0 ) ; titration of dark colored solutions by extracting with ether prior to titration ( 9 9 ) ; extracting sulfuric acid from crude sulfonic acids with n-amyl alcohol, which is then extracted with water prior to titration (47); and titrating fuming sulfuric acid with water a t 10" C. (19). Aluminum has been determined in pigments by dissolving in ferric sulfate solution followed by permanganate titration (116). Free alkali in plating solutions is determined by adding excess barium chloride and alcohol and titrating to a phenolphthalein end point; after filtering, the precipitate is titrated with hydrochloric acid (184). hlagnesium can be titrated as oxalate after precipitation from 85y0 acetic acid with ethyl oxalate (76). Luminescent titrat,ion under ultraviolet radiation has been used to determine lead with sodium oxalate using fluorescein 89 an indicator (92). The use of photoelectric instruments instead of the eye for determination of end points (127), both colorimetric (127, 1 3 6 , 161, 217) and turbidimetric (43), has increased in Europe. Use has been made of anionic agents to titrate cationic agents and vice versa with appearance of turbidity a t the end point (102). The effect of various salts and acids on the iodometric estimation of persulfate and vanadate has been investigated. By adding cuprous iodide, oxalic acid, or ferrous sulfate, reactions are catalyzed to such an extent that iodometric determinations of persulfate and vanadate can be made ( 1 6 1 - 1 6 4 ) . Aniperometric titration of dilute chromate solutions (95) is another application of the interesting rotating platinum electrode. Determinations of arsenic by coulometric titration by electrically generated bromine using an amperometric end point have been made (144). Potentiometric methods have been advocated for beryllium by titrating with sodium fluoride (199); selenium and tellurium with chromous ion (125'); nitric acid in oleum (128); phosphate by an indirect method ( 6 3 ); and thorium with potassium iodate (190). .4n important study on conditions for potentiometric titration of titanium has been made using a mercury indicating electrode (119). When traces of certain elements are to be determined, the dithizone titration technique has been used for copper ( l 7 6 ) ,lead in copper, nickel, and cobalt ( 2 S 6 ) , nickel (227) and zinc (225) in cobalt. Another extraction method extracts iodine with chloro-
