ANALYTICAL CHEMISTRY.1. INTRODUCTION.THIS is the first occasion on which this Report covers the advances made inall fields of Analytical Chemistry during the current year. The very largenumber of pages published annually on analytical topics (4200 abstractsappeared in British Abstracts, C, 1950) reflects activity in very manydirections, and the task of summarising the important advances in allbranches of the subject, for readers with varied and diverse interests, hasproved difficult owing to limitations of space; for this reason, it has beenassumed that fundamental aspects of each subject are well known. Thepublications appearing in a single year on a particular topic rarely constitutea major advance; such advances are usually recorded by a succession ofpapers over a period of many years (often by many different authors), andprogress of this nature is frequently influenced by factors other than thepurely scientific ones.This is particularly true of certain physical methodsof analysis, such as infra-red spectroscopy, which have only attained wide-spread importance since the production of commercially available instru-ments ; the pattern of this Report therefore differs in many respects from thatof previous Reports, which have consisted of periodic reviews of special topics.F. R. C.2. CHEMICAL METHODS (INORGANIC).Standardisation.-The scheme of standardisation bf volumetric solutionsused in the I.C.I. analytical laboratories is described.1 It is based on silveras the ultimate standard. The working standards referred directly tosilver are sodium carbonate, sodium chloride, and iodine, and arseniousoxide and potassium dichromate appear as secondary standards.Thepreparation of the working standards, and the reference of all the commonvolumetric solutions to one of the standards, are described in detail. Nutten 2lists numerous substances recently proposed as standards, and Underwood 3gives tables of the changes of pH with temperature between 0" and 60" forO.O5~-potassium hydrogen phthalate, O*OlM-borax, and O.O25~-phosphatesolution. McLellan * reports a comparison by eight chemists of commerciallypure potassium dichromate against Bureau of Standards samples, by reactionwith acidified potassium iodide and titration .with thiosulphate.Six ofthe eight analysts agreed to 1 part in 2000 or better, and four samples wereso pure that improvement by recrystallisation could not be detected. Anew standard substance has been proposed-propylenediamine ferroussulphate tetrah~drate.~ Its high equivalent weight, stability, and ease ofpreparation make it attractive.Metallurgia, 1949, 41, 111, 177, 237. 1 Strouts et al., Analyst, 1950, 75, 577.3 J . Ass. 08. Agric. Chem., 1950, 33, 225.6 Nutten, Analyt. Chim. Acta, 1949, 3, 433.6 Grossmann and Schuch, 2. anorg. Chem., 1906,50, 24.' Ibid., p. 224374 ANALYTIUAL UHEMISTRY.Reagents.-(When the emphasis is on the reagent, work is reviewed inthis Section; where the element determined is of greater importance, i t ismentioned under the appropriate heading.) The outstanding new reagentis Schwarzenbach's sodium ethylenediaminetetra-acetate. This salt (or thecorresponding acid) has great possibilities; it is outstanding as a complex-forming agent, and the complexes have in many cases widely differentproperties from the metal ions ; oxidation-reduction potentials are changedand precipitations with many reagents are profoundly modified ; some ofthe compounds have distinctive colours.Systematic investigations arebeing made by Pribil and his collaborators. The reagent alters the oxidationpotential of the Co++/Co+++ reaction, so that cobalt can be oxidised in acidsolution by means of ceric sulphate; ' other metals behave similarly, so thereaction cannot be always applied volumetrically, but Cr++ reduces thecomplex, and by potentiometric titration Co can be determined in presenceof many elements common in ferrous alloys.8 Chromium forms a wine-redcomplex, and this reaction may be used in the colorimetric determination ofthis meta1.O The complex with beryllium is one of the least Etable, andeven in presence of excess of reagent, ammonia precipitates the hydroxide :in this way beryllium can be quantitatively separated from many metals.10Similarly, the reagent prevents the precipitation by hydroxyquinoline inammonium acetate-acetic acid solution of all metals except W, V, Mo, Ti,and U : molybdenum, for instance, can be separated from a very largenumber of metals.ll Exactly analogous is its use combined with sodiumdiethyldithiocarbamate, which in its presence only combines with Hg, Pb,Cd, Cu, and Bi.Only the last two are coloured, and hence the colorimetricdetermination of copper can in many circumstances be much simplified .12The reagent combines with rare earths, and improved separations can bemade by adding just sufficient to keep the earths in solution, and fractionallyprecipitating with oxalic acid.l3 This reagent will also dissolve " insoluble "precipitates, e.g. barium sulphate, calcium oxalate, and lead iodate.14a-Benxoinosime l5 is applied to the photometric determination of copperin ferrous alloys, but nickel and cobalt interfere. a-Nitroso-p-naphthol isbeing studied as a volumetric reagent; l6 although the silver compoundadsorbs excess of reagent, a method of determination is possible, andpotentiometric and gravimetric methods for copper and iron are reported.The solubility and dissociation constants have been determined.Shorne l7aays that N-benzoylphenylhydroxylumine has advantages over cupferron : itis stable and soluble in water, and at pH -4 it quantitatively precipitatesCu, Fe, Al, and Ti. Bdsdimethyluminodiphenylmethune is recommended byPribil and Klubalova, ibid., p. 42.7 Pribil and Malicky, Coll. Czech. Chem. Comm., 1949, 14, 1413.* Pribil and Svestka, ibid., 1960, 15, 31.lo Pribil and Kucharsky, kbid., p. 132.l2 Sedevic and V&Ak, ibid., p. 260.l4 Budde and Patempa, AnaZyt. Chem., 1950, 22, 1072.l6 Dunleary, Wiberley, and Harley, ibid., p. 170.l6 Wenger, Monnier, and Jaccard, Helv.Chim. Acta, 1950, 33, 1154, 1458.1 7 Shorne, Ana7yst, 1960, 75, 27.l1 Pribil and Malat, ibid., p. 120.l8 Marsh, J., 1960, 1819WILSON : CHEMICAL METHODS (INORGANIC). 375Cornfield and Pollard 18 for determination of traces of manganese in planttissues, etc.; 0-5 pg. in 25 ml. of extract can be determined; potassiumperiodate in the cold oxidises the manganese, which in turn oxidises thereagent to form the colour. For cobalt and nickel, P-nitrososalicylic acid isrecommended as a colorimetric reagent.19 I n absence of iron and copper thetwo elements can be determined simultaneously, the brown cobalt complexbeing soluble in light petroleum, and the red nickel complex remaining in theaqueous phase. Copper can be determined by a reagent made by dissolvingsalicylic acid in pyridine.20 The copper complex dissolves in chloroform togive a green solution : Williams21recommends tetraethylenepentamine for determination of copper, particularlyin light alloys : i t is intermediate in sensitivity and reasonably free frominterference.Hoste22 finds that compounds with two pyridyl groups or apyridyl and a quinolyl or two quinolyl groups linked in the 2 : 2’-positionform intensely coloured compounds with Cu+, insoluble in water but solublein organic liquids. 2 : 2’-DiquinoZyZ is absolutely specific for Cu+ and verysensitive. The reagent dissolved in amyl alcohol extracts the copper froman aqueous solution at pH -3 and containing hydroxylamine. Extractionis quantitative and at 540 my.Beer’s law is obeyed. Antimony can bedetected by an acetone solution of gossipol, which, with a dilute hydro-chloric acid solution containing phosphate, gives a red colour. The reagentis stable, selective, and sensitive (limit of detection 1 : 100,000).23 Thio-acetumide is said to have advantages over hydrogen sulphide for the precipi-tation of bismuth,24 m~lybdenum,~~ antimony,26 copper,27 and arsenic.28For cadmium in micro-quantities, Dwyer and Gibson 29 recommend methyl-triphenylarsonium chzoride, 100-fold excess of zinc not interfering ; 1-10 yg.are determined turbidimetrically, but larger amounts are precipitated.Sodium mphthiomte 30 at pH 2-3 can be used to separate thorium from therare earths, and zirconium can be separated from thorium by means oft ~ n n i n .~ l Gordon et review the reactions of some dibasic organic acidswith thorium; tetruchlorophthalic acid is recommended; at 70-85” and apH of 1-1.2, a dense crystalline precipitate is formed ; double precipitationgives complete separation from the rare earths. Oesper and Klingenberg 33tested a number of glycollic acid derivatives ; substituted mandelic acidsproved useful reagents for zirconium, p-bromo-, p-chloro-, and unsubstitutedFe, Co, Ni, V, and Ag interfere.l 8 Cornfield and Pollard, J . SOC. Food Agric., 1950, 1, 107.2o Gordieyeff, ibid., p. 1166.22 Hoste, Analyt. Chim. Acta, 1950, 4, 23.23 West and Conrad, Analyt. Chem., 1950, 22, 1336.2* Flaschka and Jacobljevich, Analyt. Chim. Acta, 1950, 4, 351.25 Idem, ibid., p.356.27 Idem, ibid., p. 482.28 Analyst, 1950, 75, 201.30’ Venkataramaniah and Raghava Rao, ibid., p. 553.31 Purushottam and Raghava Rao, ibid., p. 558.32 Gordon, Vanselow, and Willard, Analyl. Chem., 1950, 22, 1323.a3 Ibid., 1949, 21, 1609.Perry and Serfass, Analyt. Chem., 1950, 22, 565.21 Analyet, 1950, 75, 425.26 Idem, ibid., p. 247.28 Idem, ibid., p. 486376 ANALYTICAL CHEMISTRY.mandelic acid being suitable. Hahri 3* also uses mandelic acid for zirconium.The reagent is almost specific.8-Hydroxyquinoline (“ oxine ”) is used in photometric determinations, ad-vantage being taken of the solubility of the chelate compounds in chloroform.Gallium and thallium solutions in chloroform are somewhat photosensitive ;the absorption spectra are given,35 but the thallium compound is too photo-sensitive to be of use.The same authors 36 deal with the ultra-violet spectraof chloroform solutions of the oxinates of Group IIIB elements. Photochemicalinstability increases with increasing size of the central metal ion. Gentryand Sherrington 37 determined the pH ranges for which a chloroform solutionof the reagent completely extracted Al, Cu, Fe(m), Mn, Nb, Ni, and Sn(Iv).For Sn(Iv), extraction a t pH 2-5-55 and photometry (max. extinction390 mp.) is a valuable procedure. 5 : 7-Dibromo-8-hydroxyquinoline is avaluable reagent for gallium, and enables it to be separated from aluminium 38by precipitation from a faintly acid solution. Although the complex issoluble in chloroform, has intense absorption a t 410 mp., and obeys Beer’slaw, direct extraction from the aqueous phase is not quite complete; itmust be precipitated first.Xodium diethytdithiocurbamate can be used as avolumetric reagent, in neutral or ammoniacal solution, with a silver wire asindicating electrode, and a calomel half-cell. It may be an advantage totitrate in presence of ether, which removes the heavy-metal salt as formed.Copper and cadmium, or copper and lead, can be titrated successively in thesame solution.39 Glen and Schwab have prepared seven “ carbates,”i.e., disubstituted dithiocarbamates, of which the piperazine, morpholine,thiazine, and-most promising-pyrollidine derivatives are new. Manymetals give insoluble compounds which are readily filtered off, are intenselycoloured, soluble in esters and-in contrast to xanthates-are stable inneutral or alkaline solutions.By varying the pH in presence of ammonia orRochelle salt, a new group separation is possible. Though the reagents havea family resemblance, they differ in speed of precipitation and solubility ofprecipitates. One or two new separations are possible, e.g., Ni++ can becompletely separated from GO++ by the pyrollidine compound in presence ofhydrazine, and tellurium can be separated from selenium. A specific testfor molybdenum is also possible. Excess of organic reagents in a solutioncan often be completely destroyed by persulphate catalysed by a littlesilver, by which, e.g., masking agents such as tartaric acid and precipitantssuch as oxine, can be oxidised, after which metals can be precipitated ashydroxides, etc.Some reagents are more resistant and mercapto-groupsare oxidised to elementary sulphur.41 Three papersg2 deal with thedistribution of ferric iron between hydrochloric acid and isopropyl ether.34 Hahn, Analyt. Chem., 1949, 21, 1579. 35 Moeller andCohen,ibid., 1950,22,686.36 Idem, J . Amer.Chem. Xoc., 1950,72,3547. 3 7 Analyst, 1950, 75, 17.3 8 Moeller and Cohen, Analyt. Chim. Acta, 1950, 4, 316.39 Sedivec and Vasak, Coll. Czech. Chem. Comm., 1950, 15, 52.4O Angew. Chem., 1950, 62, 320.41 Feigl and Schaeffer, Analyt. Chim. Acta, 1950, 4, 458.Myers, Metzler, and Swift, J . Arner. Chem. SOC., 1950, 72, 3767, 3772, 3776WILSON : CHEMICAL METHODS (INORUANIC).377The effect of changes of acidity, and the ultra-violet spectra of the ethereallayer under various conditions are discussed. Salicyli&enethiosemicarbazoneis proposed as a reagent; several metal salts are disc~ssed,*~ and a gravi-metric method for cadmium is put forward, but other metals interfere.44 Ithas also potential applications in colorimetry, e.g., for mangane~e.~~ Twonew oxidising agents for volumetric analysis are potassium fe~rate,*~ said tobe stable in solutions more alkaline than 5M. with respect to sodium hydroxide,used in conjunction with sodium arsenite solution, and potassium cupri-periodate K , C U ( I O ~ ) ~ . ~ ~ Lang** advocates the use of ruthenium as acatalyst in the titration of tellurous acid with permanganate.If cericsulphate is used, with chromate as catalyst, Te(rv) can be oxidised in presenceof Se(Iv), which is unchanged. Starke 49 finds that molten chlorides of somearomatic amines, e.g., pyridinium hydrochloride, dissolve metals and someoxides readily at convenient temperatures, and indicates possible analyticalapplications. Belcher 50 reports that tartrazine can be used as a reversibleindicator in the titration of arsenite with hypochlorite. For oxidationreactions there is a novel suggestion to use aiZ~xene,~l for when a minuteexcess of oxidising agent is added to a solution containing this substance thewhole solution emits light.Qualitative Analysis.-A review of tests for 24 anions has appeared62with comments on sensitivity and interferences.By heating small samplesin micro-burner flames, oxidising or reducing, asbestos fibres being used assupports, flame colours are noted, and by allowing the tip of the flame toimpinge on a test-tube full of cold water, sublimates of metal or oxide canbe collected from 18 metals, and identified by recommended microchemicalreactions.% k semimicro-scheme of analysis, including several of the" rarer " elements, which does not use hydrogen sulphide, is described.54Holness and Trewick 55 recommend a solution containing 1% of lithiumhydroxide and 5% of potassium nitrate as giving a cleaner separationbetween the copper and the arsenic sub-group than the older reagents.Potassium xanthate can be used to separate copper and cadmium, which issubsequently identified as sulphide.66 Nutten 57 describes a method ofremoving phosphate ion by a nitric acid solution of titanic hydroxide; heindicates the amount of common ions which remain in solution after theseparation.By extraction of a hydrochloric acid solution with ethylacetate, chloroauric acid is extracted : by evaporating the solvent, addingsodium metaphosphate solution, and applying a test-paper impregnated4a Hovorka and Holtzbecker, Coll. Czech. Chem. Comm., 1960, 15, 267.44 Idem, ibid., p. 275.O 6 Schreyer, Thompson, and Oekerman, Analyt. Chem., 1950, 22, 691.4 7 Beck, Mikrochem., 1950, 35, 169.40 Canadian J . Ree., 1950, €3, 28, 225.s1 Kenny and Kurtz, Anulyt. Chem., 1950, 22, 693.52 Odekerken, 2. anal. Chem., 1950,131, 165.63 Geilmann and Isermeyer, ibid., p.249.54 Badry, McDonnell, and Wilson, Analyt. Chim. Acta, 1950, 4, 440.O S Analyst, 1950, 75, 276.s 7 Nutten, Anulyt. Chim. A&, 1950, 4, 340.4 5 Idem, ibid., p. 280.Lang, 2. anal. Chem., 1949,128, 484.Belcher, Analyt. Chim. Acta, 1950, 4, 468.56 Rahn, 2. anal. Chem., 1950,181, 263378 ANALYTICAL CHEMISTRY.with p-rosaniline hydrochloride, a specific test for gold is obtained (limit5 pg.).68 Trich6 59 identifies calcium by coprecipitation of its carbonatewith silver chromate. Because of mixed-crystal formation, the latter saltdissolves much less readily in dilute ammonia. This phenomenon does notoccur with strontium or barium. Neu 6o reports that long-chain quaternarysalts, such as dodecylpyridinium bromide, precipitate metaphosphates froman acetic acid solution, but not ortho- or pyro-phosphates.A thoroughinvestigation of the etching of glass by hydrogen fluoride has shown thatthe reaction is in part catalytic, the silicon tetrafluoride formed reacting withmoisture to form more hydrogen fluoride. Though the reaction is notquantitative, yet by use of special apparatus, 1 pg. of fluorine can be detected.Freytag 62 detects hydrogen peroxide by its bleaching action on paperimpregnated with lead sulphide : as little as 1 in 5 x lo6 can be detected.Percarbonates are discussed by Partington and Fathallsh,63 who point outthat Riesenfeld's test, which attempts to discriminate between true per-salts(e.g., K2S20,) and salts containing hydrogen peroxide of crystallisation, byreaction with neutral potassium iodide solution (the former liberate iodine,the latter oxygen), is not sound.General Methods of Analysis.-In determining small amounts of aluminiumWillard and Dean 64 polarograph in presence of Pontachrom-Violet-SW(colour index 169) at pH 4.6 the half-wave potential being about -0-5 v.Many metals which interfere can be removed by electrolysis over a mercurycathode; the only anions present should be acetate and perchlorate.Thereaction of aluminium with alizarin-S has been reinvestigated. 65 BelowpH 3-9 one atom of aluminium reacts with one mol. of the reagent ; a t higherpH values, more complex compounds are formed. Calcium combines withthe aluminium alizarinsulphonates to form a new compound, between pH 3.9and 4-55, which is utilised in an improved colorimetric method.Berylliumis discussed in papers by Seguin and Gramme.66t 6 7 9 68 The first is general,and describes the chemical analysis of beryllium-copper alloys, the seconddeals with colorimetric methods, reporting that 1 : 2 : 5 : S-tetrahydroxy-anthraquinone is not a satisfactory reagent, and the third describes in detailemission spectroscopic analysis of copper alloys for beryllium. Accordingto Ellis, Zook, and B a u d i s ~ h , ~ ~ 1 : 1'-dianthrimide was the best colorimetricreagent for boron of forty tested. Azides can be titrated with silver nitrateby using daylight or ultra-violet light and the usual adsorption indicators,e.g., rh0damine-6B.~~ Lang and Annis 71 recommend the reaction withpotassium iodide and acid in the absence of air for the semimicro-determin-58 West and Carlton, Analyt.Chem., 1950, 22, 1055.6n Analyt,Chim. Acta, 1950, 4, 12.61 Williama,Anulyst, 1950,75,510.69 J., 1950, 1934.as Parker and Goddard, Analyt. Chim. Acta, 1950, 4, 517.66 SBguin and Gramme, Bull. SOC. chim., 1950, 17, 375.67 Idem, ibid., p. 384. 6B Idem, ibid., p. 388.69 Anolyt. Chem., 1949, 21, 1345. ' 0 Haul and Uhlen, 2. a d . Chem., 1949,129,21.7 1 Compt. rend., 1950, 230, 208.6o 2. anal. Chem., 1950, 131, 102.6a 2. anal. Chem., 1950, 131, 77.6* Analyt. Chem., 1950, 22, 1264WESON : CHJMICAL METHODS (INORGANIC). 379ation of nitrim; in determination of nitrates with m-4-xyleno1, Barnes 72avoids distillation by extracting the acid solution containing the nitroxylenolwith toluene.To determine free nitric acid in presence of aluminium nitrate,the use of potassium oxalate instead of fluoride is recommended as a, complex-ing reagent.73 Following Cotte and Kahane,74 who quantitatively reducenitrates to ammonia by ferrous hydroxide in presence of silver as catalyst, itis now proposed to determine the nitrate by titration of the excess of ferrousiron, after reaction is complete.75.MonojlwopJwq&ate. ion, FPO," , is rapidly hydrolysed in acid solution,7sand if the bleaching of peroxytihnate solution is measured a t 3-minuteintervals, by extrapolation back fo zero time both free F' and FPO," can beestimated. Fluoride ion can be accurately determined by its bleachingaction on solutions containing a ferrisulphosalicylate complex.A generallyapplicable method of analysis is described, which is applied after separatingthe fluorine from aluminium, etc., by di~tillation.~~ Sodium can bedetermined in calcined alumina after dissolution of the sample by heating ina sealed narrow-bore tube to 200" with excem of hydrochloric acid.78 Shell 7Ddetermines sodium in presence of lithium and phosphate by precipitating itwith magnesium uranyl acetate, and treating the precipitate with a solutionof hydrogen chloride in butanol ; lithium and phosphate dissolve, leavingsodium chloride insoluble. SiEiwn is determined 80 by diEtillation from alead still with sulphuric acid and fluoride, the distillate being hydrolysed byammonia.After addition of boric acid, silica is determined calorimetrically.Jewsbury 81 makes a similar use of boric acid in the analysis of hydrogenfluoride, etc., for silica. For determination of free sulphur trioxide in chloro-sulphonic acid, Seaman et a l . 8 2 measure the heat of reaction with hydrochloricacid. Traces of chlorides can be determined 83 by centrifuging out the silverchloride, reducing it with alkali and hydrazine, dissolving in nitric acid, andextractive titration with dithizone (diphenylthiocarbazone). The analyticalchemistry of chlorites is discussed.84 The similarity of C10, to NO, is pointedout ; e.g., there is an insoluble copper-lead-potassium chlorite analogous tothe well-known triple nitrite : many other reactions are described.Gale and Mosher B5 determine milligram quantities of vanadium inpresence of large amounts of uranium and other metals by titration withferrous sulphate, polarised platinum electrodes being used fo detect the end-point.In the determination of manganese by oxidation with persulphste,Analyst, 1950, 75, 388.73 Blaedel and Panos, Anulyt. Chem., 1950, t22, 910.74 Cotte and Kahane, Bull. SOC. chim., 1946, 13, 541.7 5 Szabo and Bartha, Nature, 1950, 166, 309.7 6 Hill and Reynolds, Andyt. Chem., 1950, 22, 448.7 7 Lacroix and LEabalade, AnaZyt. Chim. Acta, 1950, 4, 68.7 8 Jackson, Analyst, 1950, 75, 415. 70 Analyt. Chem., 1950, 22, 574.81 Analyst, 1950, 75, 257. Bonnier, Bull. SOC. chim., 1950, 17, 365.Seaman, Woods, and Bank, Ancrlyt.Chem., 1950,22, 549.Iwantscheff, Angew. Chem., 1950,62, 361.84 Morandot and Duval, Mikochm., 1950, 85, 202.Gale and Mosher, Analyt. Chm., 1950, 22, 942380 ANALYTICAL CHEMISTRY.metaphosphoric acid is used to stabilise permanganic acid.86 Iron isadvantageously precipitated as basic ferric formate, the hydrolysis of ureain the boiling neutral solution being used to adjust the pH ; good separationsfrom some other metals can be a~hieved.~' Cobalt is determined by thepolarograph, after oxidation to CO(III) with ammonia and perborate.Manganese and iron, precipitated as hydrated oxides, carry down cobaltand cause low results.88 Yardley 89 recommends potentiometric titration ofcobalt with ferricyanide as an accurate process. Norwitz says that withsuitable precautions copper and tin 91 can be safely electrodeposited fromhydrochloric acid solutions.The photometric determination of molybdenumis thoroughly discussed by Rasin-Straden and Popoff-As~toff.~~ Althoughthe maximum absorption of the thiocyanate colour is -470 mp., a t longerwave-lengths, changes with time and the influence of iron are less. Accuratercsults can be obtained even with high percentage of molybdenum, providedthat pure reagents are used, the iron concentration is constant, and a stricttime cycle is followed. Ellisg3 uses acetone as reducing agent in the thio-cyanate method for molybdenum. Also, this metal can be concentratedfrom very dilute solutions by being adsorbed on active alumina : a t pH5-5-6 adsorption is practically complete.It is recovered by washing withdilute ammonia.94 Traces of molybdate catalyse the reaction betweeniodides and hydrogen peroxide in neutral solution. This reaction is moresensitive than the well-known test with titanic sulphate : the peroxide canbe determined by measuring the extinction of the solution a t 353 mp.95Rhenium is discussed by Geilmann and Bode.g6e97 They do notrecommend precipitation in alkaline solution as the sulphide Re2S7, as this ismarkedly soluble, but distil from 80% sulphuric acid at 200" in a stream ofhydrogen chloride ; 97--98y0 of the rhenium is removed in 1* hours ; Re207is itself volatile, but more slowly. The same authors 98 have recommendedprecipitation of Re2S7 from dilute sulphuric and hydrochloric acid solutionwith thiosulphate : nitrates interfere. Tribalat 99 determined the distri-bu tion coefficient between water and chloroform of tetraphenylphosphoniumper-rhenate, and showed that traces of rhenium can be isolated.Phosphonium or arsonium chloride serves as a reagent. Gob! is separatedfrom copper, silver, and platinum by means of morpholine oxalate,lW whichreduces it to metal in slightly acid solution.The precipitate of platinumsulphide is shown lol to approximate in composition to PtS, if excess ofhydrogen sulphide is used, and it is more or less contaminated by sodium86 Jean, AnaZyt. Chim. Acta, 1950, 4, 360.87 Willard and Sheldon, AnaZyt. Chem., 1950, 22, 1162.88 Watters and Kolthoff, ibid., p. 1467.90 Norwitz, ibid., p.551.B2 OeSteTT. Chm. Ztg., 1950, 51, 1.9' Kulm, 2. anal. Chem., 1950, 130, 210.g5 Ovenston and Rees, Analyst, 1950, 75, 204.96 Geilmann and Bode, 2. anal. Chem., 1950,130, 320.97 Idem, ibid., p. 323.99 Analyt. Chim. Acta, 1950, 4, 228.89 Analyst, 1950, 75, 156.Dl Idem, 2. anal. Chem., 1950,131, 266.D3 Analyt. Chem., 1950, 22, 328.98 Idem, ibid., p. 232.loo Malorvan, Mikrochem., 1950, 76, 104.101 Jackson and Beamish, AnaZyt. Chem., 1950, 22, 813WILSON : CHEMICAL METHODS (INORGANIC). 381chloride, if present. For bringing iridosmine into solution, roasting of thesample mixed with sodium chloride in an atmosphere of chlorine isrecommended; lo2 provision must be made to trap any volatile compounds.For the precipitation of iridium, hydrolysis of the bromate is preferred.Osmium is determined colorimetricdly with thiourea, and transmission datafor the stable rose-red solution are given; lo3 of the platinum metals onlypalladium and ruthenium interfere in moderate concentration.Rutheniumcan be photometrically determined at 465 mp. in the red solution obtained byfusion with potassium nitrate and hydroxide; Beer's law is obeyed, andother platinum metals do not interfere.lo4 Ryan recommends Z-mercapto-4 : 5-dimethylthiazole for the colorimetric determination of rhdium, theoptical density being measured a t 430 mp.lo5 Platinum and gold areprecipitated by the reagent, palladium is removed by glyoxime, and iridiuminterferes somewhat. Ryan also discusses 2-mercaptobenzoxazole lo5 as acolorimetric reagent for rhodium in the presence of iridium, but platinum andpalladium interfere somewhat.Ayres and Young 106 have made spectro-photometric studies of the blue complexes of ruthenium with thiourea andwith dithio-oxamide ; spectral transmission curves, rate of colour develop-ment, and other particulars are given. Of the other platinum metals,osmium and palladium interfere with the thiourea method, and osmium withthe dithio-oxamide procedure.The precipitation of the cerium group of rare earths by sodium sulphatecan be extended by salting out. Brine is of great value in fractionatingmiddle (gadolinium) and heavy (ytterbium) rare earths.lo7 Followingwork lo8 on the stability of complexes of titanium, zirconium, and thorium,oxalate, citrate, and tartrate complexes of tantalum and niobium arediscussed.Tridot presents a thorough study on the precipitation of uranium fromaqueous solutions by alkaline hydroxides and sulphides ; besides a reviewof past work, some new determinations of the solubilities of uranium andthorium nitrates have been published,lll and the influence of bicarbonateon the colorimetric determination of uranium is shown to be negligible a t awave-length of 445 mp.l12 Hecht and Gerhold 113 describe the determinationof uranium in phosphates by removal of the phosphate with molybdate,evaporation almost to dryness to remove most of the MOO,, and extractionof uranyl nitrate from the filtrate with ether.The determination of brominein brines is fully described by Haslam and who also give data onthe bromine content of salt deposits and in-shore waters.The analysis ofbromine is also described.l15 For the potentiometric determination oflo2 Hill and Beamish, Analyt. Chew&., 1950,22,574. lo3 Ayres and Wells, ibid., p. 317.lo4 Marshall and Rickard, ibid., p. 795. lo5 Ryan, ibid., p. 599.lo6 fbid., pp. 1277, 1281. lo' Marsh, Nature, 1949,163,998.lo* Haissinsky and Jeny-Isong, Analyt. Chim. Acta, 1949, 3, 422.lo@ Idem, ibid., 1950, 4, 329. I1O Ann. Chim., 1950, 5, 358.ll1 Templeton and Hall, Canadian J . Res., 1950, B, 28, 166.112 Scott, Anulyat, 1950, 75, 100. 113 Mikrochem., 1950, 35, 359.11' Analyet, 1950, 75, 343. 115 Haslam, ibid., p. 371.Resistance to hydrolysis decreases in the order given.lo382 ANALYTICAL CHEMISTRY.chlorine and bromine in presence of one another, an improved form ofMuller's retarded auxiliary electrode system 116 is used.The determinationof rubidium in carnallite is described by D'Ans.117 After precipitation asperchlorate along with potassium chlorate, the rubidium content is calculatedfrom the ratio of chlorine to metals, after reduction of the perchlorate tochloride. Mercurous salts can be titrated with potassium mercurithio-cyanate, and mercurous and mercuric salts can be determined in the samesolution.lls I n the absence of other metals, cadmium can be titratedpotentiometrically with sodium sulphide solution in presence of a protectivecoll0id.1~~Analysis of Metsls.-Th&y l20 determines tin in aluminium alloys bydissolution in sodium hydroxide, followed by evaporation with nitric andperchloric acid, to render stannic oxide insoluble.The residue is dissolvedin sulphuric acid, and tin determined electrolytically, or by turbidimetrywith cupferron as reagent. Por determination of silicon in aluminium,following amalgamation attack with dilute hydrochloric .acid rapidly dissolvesaluminium and leaves silicon in solution as a colloid. The solution isunstable and silicon rapidly flocculates. It is filtered off, and ignited tosilica.121 Aluminium in zinc is determined by measuring the colour which itproduces a t pH 5.8 with solochrome-cyanine. The results quoted showsatisfactory accuracy.122 Traces of lead in zinc can be determined colori-metrically as colloidal sulphide, since in a strongly ammoniacal solution smallquantities of hydrogen sulphide do not precipitate zinc sulphide, but leadsulphide is readily formed.123 Short determines aluminium in iron byremoving most of the iron as trichloride with ether, and the remainder byprecipitation with cupferron and extraction with chloroform from a solutionof pH -0.2 ; aluminium is finally determined oolorimetrically.Chromiumin steel can be determined by direct measurement of the green colour of itssolution in sulphuric and phosphoric acids.12s Bacon 126 discusses thephotometric determination of phosphorus in low-alloy steels. A new systemof absorptiometric analysis for steel 12' is analogous to the " internal-standard " technique of emission spectroscopy.On various aliquots of thesample solution, optical-density measurements are made for the variouscomponents and for iron, after adding appropriate reagents. The com-ponents are determined with reference to 100 parts of iron and, the iron beingdetermined, can be calculated to percentages. By this internal-standardtechnique errors due to varying cell thicknesses and apparent deviationsfrom Beer's law due to non-monochromatic or stray light are eliminated.116 Muller, 2. physikal. Chem., 1928, 135, 102.118 Burriel-Marti and Lucena-Conde, Analyt. Chim. Actu, 1950, 4, 344.f19 Silver, Kethely, and Kriety, ibid., p. 389.121 Berthier, Bull. SOC. chim., 1950, 17, 363.122 Pollak and Pellowe, Mebllurgia, 1950, 41, 281.Hahn, Analyt.Chim. Acta, 1950, 4, 453.12s Vredenburg and Sackter, Cunad. Chem., 1950, 34, 119.146 Analyst, 1950, 75, 321.127 Berger, Pirotte, Muylle, and Juliard, Bull. SOC. chim. Belge, 1960, 59, 465.117 Angew. Chem., 1950, 02, 118.lZo Chim. unalyt., 1950, 32, 19.lZ4 Analyst, 1950, 76, 420WILSON : CHEMICAL METHODS (INORGANIC). 383The determination of very small amounts of carbon in steels engages attention.The first step is combustion; the carbon dioxide after absorption in barytasolution may be estimated turbidimetrically 12* or by the change in electricalconductivity of the solution.12Q Wells, however,130 after drying the exitgases from the tube furnace and removing sulphur dioxide, condenses thecarbon dioxide in a trap cooled by liquid oxygen, then transfers the carbondioxide to a McLeod gauge measuring system.A determination can becompleted in 20 minutes. Beeghly 131 determines aluminium nitride insteels after solution of the iron by bromine in methyl acetate; aluminiumnitride is unattacked, and nitrogen is determined on the insoluble matter.Two reports 1329 133 have been issued, by the " Methods of Analysis Committeeof the British Iron and Steel Research Association," on the determination oftin in highly alloyed steels and on the determination of silicon; referencemust be made to the original for details of these referee methods. Oxygenin chromium, after annealing a t 800" in vacuo, is present as chromic oxide,and is insoluble in hydrochloric acid.13* Oxygen in titanium metal isdetermined by heating in vacuo in a special apparatus with powdered graphiteand metallic tin to 1900".Induction heating is used, and the evolved gasesare collected and ana1y~ed.l~~ Oxygen (present as oxide) in metallic sodiumis determined by dissolving the metal in mercury in a special apparatus,leaving the oxide as an insoluble residue which can be dissolved andtitrated.136 Silver in silver solder, after solution in acid, is reduced to metalwith ascorbic acid; 137 the ascorbic acid in the filtrate does not interferewith the determination of cadmium, copper, zinc, etc. Minute traces ofmercury in copper alloys are determined by dissolving the alloy in dilutesulphuric acid with the aid of peroxide and distilling off the mercury (chloridesmust be absent) ; it distils in steam, is collected in permanganate-sulphuricacid solution, and determined by extractive titration with dithizone.la8Minerals a d Rocks.--In the analysis of sedimentary rocks the ignitedsample is dissolved in hydrochloric acid and treated with gelatin to removesilicon, then on aliquots of the solution Fe, Ni, Mn, P, V, and Ti are determined~olorimetrically.~3~ Koritnig l40 fuses the rock with sodium hydroxide,removes silicon, alumina, etc., with ammonium carbonate solution, and thenuses Steiger's method for determination of 0*001--0*1 yo of fluorine.Biffen 141determines alkalis in refractory materials by the flame photometer after aLawrence Smith fusion, with added lithium as internal standard. Resultsare as accurate as by the classical method, and quicker.Shell 142 says that128 Agassaut and Andrieux, Bull. SOC. chim., 1950,17, 253.120 Gardner, Rowland, and Thomas, Analyst, 1950, 75, 173.130 J . Iron Steel Inst., 1950, 166, 113.132 Anon., J . IronSteelInst., 1950,165,190.134 Short, Analyst, 1950, 75, 335.136 Yepkowitz and Judd, ibid., p. 1283.138 Miller and Wachter, Analyt. Chem., 1950, 22, 1316.la0 Blumer and Erlenmeyer, Helv. Chim. Actu, 1950, 38, 45.140 2. anal. Chem., 1950, 131, 1.141 Analyt. Chem., 1950, 22, 1014.131 Analyt. Chem., 1949, 21, 1513.133 Anon., ibid., p. 430.135 Walter, Analyt. Chem., 1950,22,297.lS7 Goldberg, Metallurgiu, 1950,41, 174.142 Ibid., p. 326384 ANALYTICAL CHEMISTRY.platinum or platinum-rhodium crucibles should not be used for fusingsilicates, etc., with borax and sodium carbonates, before determination oftraces of iron, as they retain iron.Silver crucibles are recommended.Mott 143 prescribes the concentration of reagents, etc., to be used in therapid determination of various forms of sulphur in coals. Allen andBeamish 144 discuss fire assay for rhodium. Losses on the fire assay are notconstant, and can be minimised by reworking the slags. Cupellation is liablet o lead to losses, and the lead buttons must be parted by wet methods.Removal of lead as sulphate leads to losses, but thiobarbituric acid precipitatesrhodium in presence of lead, or perchloric acid may be used to dissolve thelead. I n determination of uranium in rocks 145 the final measurement ismade after fusion with sodium fluoride and comparison of fluorescence inultra-violet light with standards.After removal of silica the uranium iscollected in Group 111, and separated by ammonium hydrogen carbonatesolution. Feherand Heuer 146 point out that 30% hydrogen peroxide has advantages overmany oxidising reagents since excess can be completely destroyed by boilingand no foreign ions are introduced; pH and temperature control areimportant. Zinc blende, for example, can be completely oxidised by per-hydrol, a little saturated oxalic acid solution being added as well.Fertilizer Analysis.-Hanson 14' obtains excellent results in the rapidroutine determination of phosphoric oxide by the stable yellow colourproduced with molybdic and vanadic acid, measuring the extinction a t470 mp.Epps 148 applies the same method to citrate-soluble phosphoricoxide. Frey 149 discusses the precipitation of ammonium phosphomolybdate,but his interesting paper has few numerical results. Iodine in phosphaterock can be determined by distilling with acid, and collecting the distillatein bromine water; all the iodine is converted into iodate and there are nointerferences : Morocco rock contains 8-104 parts per mi1lion.l" Potassiumin fertilisers is quickly and conveniently determined by flame photometry.151Hamence l52 measures the relative rates of nitrification in soils of manureswhich contain organic nitrogen. A standard soil containing added calciumcarbonate is used; the samples are compared against dried blood and thereal value of nitrogenous wastes can be assessed.Water Analysis.-The application of disodium ethylenediaminetetra-acetate to the determination of hardness is the most interesting advance inrecent years.Schwarzenbach first applied it by determining the pH changeon reaction. Later it was shown that a t a pH -10 certain dyes (e.g.,solochrom black WDFA) would act as indicators, and calcium and magnesiumcould be titrated by a dilute solution of the reagent, as excess is indicatedThe uranium content of a large number of rocks is given.lP3 Fuel, 1950, 29, 53.145 Erlenmeyer, Oppliger, Stier, and Blumer, Helv. Chim. Acta, 1950, 33, 25.146 Angew. Chem., 1950, 62, 162.148 Analyt. Chem., 1950, 22, 1062.l50 Kahane and Rasch, ibid., p.147.151 Brearly, Chem. T~ades J., 1950, 137, 724.114 Analyt. Chem., 1950, 22, 451.147 J.Soc. Food Agric., 1950, 1, 172.14s Bull. SOC. chim., 1950, 17, 685.15= J . SOC. Food Agrk., 1950, 1, 92WILSON : CHEMICAL METRODS (INORGANIC). 385by a colour change from wine-red to blue; excellent summarising articleshave appeared.154 There is no agreement yet aa to the “ best ” method,and reasonably good results are obtained in a wide range of conditions;other bivalent metals must be masked, e.g., by sodium sulphide, and byslight modifications from <1 to 2000 p.p.m. of hardness can be determined.Excessive amounts of peaty matter must be removed by active charcoal.Calcium alone can be titrated by using purpurin as indicator. Variousuncouth trivial names have unfortunately already appeared for the reagent ;the reporter most strongly advocatea the initials E.D.T.A.if “ Schwarzen-bach’s reagent ” is thought to be beyond English chemists’ pens or lips.Traces of lithium in water are determined 155 by adding sodium hydroxideand carbonate until the pH is 12.5, allowing the precipitate to settle, andpercolating the solution down a column of alumina, pretreated with alkalisolution of the mme pH. Other alkalis pass through, but lithium remains,is eluted with a 2N-solution of hydrochloric acid in dioxan, and finallyconverted into lithium borate and titrated. Various elements (particularlyK, Na, and Ca) can be very rapidly determined by flame photometry : toovercome the effects of other ions, a “ radiation buffer ” solution is added.156The bleaching of the aluminium lake of eriochrom-cyanine is recommendedfor the determination of jiwrine; the usual components of potable waterdo not interfere; l5’ another paper 158 discusses interferences with thezirconium-alizarin43 method.Clark 169 recommends titrating chloride withmercuric nitrate solution, using diphenylcarbazone as indicator. Houghton 160reviews current practice in the determination of “ residual chlorine.”Gas An&sis.-Shepherd, in three interesting papers,161 discusses theaccuracy of analysis of carburetted water gas by mass spectrometer andchemical methods. Kilday 162 presents a thorough study of the evolutionof carbon monoxide when oxygen is absorbed in pyrogallol.A specialsolution in 50% potassium hydroxide solution gives off less carbon monoxidethan other reagents, and bubbler pipettes are superior to the older Orsatpipette. The evolution of carbon monoxide markedly increases with thevolume of oxygen absorbed. Reed l63 describes a portable constant-volumegas analysis apparatus, and Towler 164 recommends sulphuric acid activatedwith silver sulphate or chromium trioxide for determining “ unsats.” inilluminating gas : he points out that most reagents for “unsats.” alsodissolve carbon monoxide.153 Schwarzenbach et al., Helv. Chim. Ada, 1949, 32, 839, 1046, 1175, 1324, 1484,1543, 1682 ; Biedermann and Schwarzenbach, Chimia, 1948, 2, 56.154 Connors, J . Amer. Water WorksAssoc., 1950,42,34; Diehl,Goetz,andHach,ibid.,p.40 ; Betz and Noll, ibid., p. 49 ; Heald, Coates, and Edwards, I d . Chem., 1950,26,428.lS5 Balkzo and Sinabell, Mikrochem., 1950, 24? 178.156 West, Folse, and Montgomery, Analyt. Chern., 1950, 22, 667.15’ Thinn, ibid., p. 918.168 Taras, ASCO, and Garnell, J . Amer. Water Works Assoc., 1950, 42, 583.150 Analyt. Chem., 1950, 22, 553.161 Shepherd,J.Ree. Nat.Bur.Stund., 1960,44,509; Analyt.Chern., 1950,22,881,885.laa J.Re8. Nat. Bur.Stan&., 1950,45,43. le4 Ibid.,p. 159.Analyst, 1950, 75, 180.163 Fuel, 1950,29, 166.REP.-VOL . XLVII . 386 ANALYTICAL CHEMISTRY.An apparatus for determining nitrous oxide on samples as small as0=2--0*4 ml. by reduction with hydrogen over a heated filament isdescribed.ls6 Another micro-apparatus (for binary mixtures and volumesas small as 10 mm.3) is described.ls6 I n the determination of sulphurdioxide and trioxide in flue gases, errors arise through catalytic oxidationof this oxide to the trioxide by traces of copper, when the gases are absorbedin O*B~-sodium hydroxide solution containing benzyl alcohol.Satisfactoryresults are achieved if a little benzaldehyde is added, and, just beforeabsorption is started, 30 mg. of p-aminophenol hydroch10ride.l~~Toxic GCMS a d Htu~ds.-A new procedure for estimating the carbonmonoxide content in air is given by Griffon and Capus,16* who measure thetime which elapses before a grey spot appears when air is drawn through afilter paper impregnated with palladous chloride. For nitrogen peroxide inair a method is based 169 on the absorption of dinitrogen tetroxide, but notnitric oxide, on silica gel.Fluorine in the atmosphere (<40 p.p.m.) isestimated 170 by aspiration through a paper impregnated with zirconiump-dimethylaminoazobenzenearsonate, wetted with hydrochloric acid justbefore the determination : the brown or yellow zirconium compound isdecomposed, and the red free acid liberated ; the amount of fluorine presentis deduced from the volume which gives a pink stain. At 2 p.p.m. the erroris &O-2 p.p.m., but increases a t higher concentrations.An apparatus which continuously records the sulphur dioxide content ofair in the range 0-01-1 p.p.m. is described by Katz; 171 the bleaching ofvery dilute starch-iodine solution is measured photoelectrically.It has beenfound that, if air is drawn through a filter-paper disc at a speed of 60 c. ft./hr.,from 90 to 97% of any sulphuric acid present is retained; it can then beextracted with water and titrate~I.l'~ Clark describes the testing of theatmosphere in theatres and cinemas.Recent Apparatus, etc.-An ingenious electrostatic precipitator is designedfor the continuous sampling of the atmosphere and the recording of theconcentration of air-borne electrolytes. The testing of the apparatus isdescribed ; its efficiency is about 85% a t 3 c. ft./min. and 100% a t 1 c. ft./min.Full details are given; the anode is a slowly rotating steinless-steel disc,which dips into a bath of water so that precipitated material is continuallywashed A portable small-scale Venturi scrubber washes very largevolumes of air with small volumes of water, and is efficient a t high rates;the total volume of circulating liquid is about 150le5 Burke, Mikrochem., 1950, 35, 135.166 Tompkins and Young, J .Sci. Inatr., 1950, 27, 224.16' Berk and Burdick, U.S. Bur. Mines, 1950, Rep. Invest. 4168.188 Chem. Abe., 1950, 44, 8823 (from Ann. Med. Legal Crim., 1950, 30, 187).168 Wade, Elkin, and Ruotob, Arch. Ind. Hyg. OCCU~. Med., 1950, 1, 81.1 7 0 Harold and Hurlburt, AnaZyt. Chem., 1949, 21, 1504.171 Ibid., 1950, 22, 1040.173 Mader, Hamming, and Baker, ibid., p. 1181.17* Schadt, Magill, Cadle, and Ney, Arch. I d . Hyg. Occup. Med., 1950, 1, 566.175 Magill, Rolston, McLeod, and Cadle, Analyt.Chem., 1950, 22, 1174.Analyst, 1950, 75, 525WILSON : CHEMICAL METHODS (INORGANIC). 387Haslam and Williamson 176 have devised an apparatus for the quantitativemeasurement and manipulation of liquids (e.g., bromine) of high vapourpressure. The filling of a pyknometer and subsequent quantitative transferof the liquid to a reagent solution are described.A vacuum fusion furnace for investigating the dissolved gas content ofmetals has a glass envelope, air-cooled; apart from this it is constructedof quartz, with a graphite crucible, and the sample is heated by induction.Wurzschmitt 178 describes a new type of bomb for combustions or fusionswith sodium peroxide. Rafter 179 states that fusion with sodium peroxidecan be safely and expeditiously carried out in platinum crucibles at atemperatdre of 340-540".Duval and his collaborators continue their researches with the Chevenardthermobalance into the drying and combustion of precipitates.Duvallmdescribes the balance with which changes in the weight of an object underincreasing temperature may be recorded, and mentions his previous researchesinto numerous gravimetric methods 181 which show the exact temperaturesa t which precipitates become constant in weight. He now examines thecombustion of filter-paper, the drying of asbestos, and the behaviour ofplatinum, which is shown to gain in weight owing to oxidation above 538",but to return to its original weight at 800". Filters of glass fibres remainconstant to 520". With his collaborators he has described the behaviour onheating of various precipitates of phosphates, arsenates, " oxinates,' ' 182silver salts,l= cadmium,lB4 gadolinium,18s titanium,ls6 germanium,l87 tin,188lead,lB9 molybdenum,190 vanadium, lgl and antimony.lQ2 The thermalbehaviour of beryllium oxide is described by Dupuis.lg3Accuracy of Sampling and Analysis.-Scheur and Smith lg4 discuss theaccuracy of spectrographic and chemical methods of analysis of alloys.Onplotting the coefficient of variation against the amount present, for allelements curves of similar characters are obtained for chemical results, adifferent family of curves being given by spectrographic results. The latterare the more accurate when less than 0.1 yo of an element is present. Furtherdata are quoted by van Someron.lg5 Riley,lB6 in an account of the routinespectrographic analysis of cast iron, includes a table of standard deviationsfor Si, Mn, Ni, Cr, Cu, and Mo, giving figures founded upon several years'observations.The accuracy of sampling and analysing fertilisers and feeds1'16 Analyst, 1950, 75, 383.17' Guldner and Beach, Anulyt. Chem., 1950, 22, 366.178 Chem.-Ztg., 1950, 74, 356.180 Mikrochem., 1950, 35, 242.l a 1 Analyt. Chim. Acta, 1947, 1, 408; 1948, 2, 92, 103; 1950, 4, 159.lS2 Duval and Dupuis, ibid., p. 256. lE3 Duval and Marin, ibid., p. 393.Duval, ibid., p. 190. lEs Duval and Dupuis, ibid., 1949, 3, 438.lE6 Idem, ibid., 1950, 4, 180. 1 8 7 Idem, ibid., p. 186.lE8 Idem, ibid., p. 201. lag Duval, ibid., p.159.lQo Duval and Dupuis, ibid., p. 173. lgl Duval and Morette, ibid., p. 490.lQ2 Duval and Morandat, ibid., p. 494.Compt. rend., 1950, 230, 937. lQ4 Metallurgia, 1949, 41, 44.Io5 Ibid., 1950, 42, 52. l o 6 Spectrochim. Acta, 1950, 4, 93.179 Analyst, 1950, 75, 485388 ANALYTICAL CHEMISTRY.has been investigated.lg7 It is stated that with normal fertilisers it isunnecessary to sample more than 20 bags however large the consignment.On a consignment of 1000 bags, the standard deviation (for P,O, analysis)on a 20-bag sample was 0-11%, on a 60-bag sample O*OS%, and by samplingevery bag was 0.06%. In the ordinary case it makes no difference howwidely spaced the samples are. The importance and utility of automaticsampling is discussed by Visman.lg8 The need for large numbers ofincrements of a minimal weight and the calculation of attainable accuracy inadvance are discussed, and an automatic sampler (for coal, from conveyerbelts) is described.H. N.W.3. CHEMICAL I16ETHODS (ORGANIC).This section comprises the reports on ultimate organic microanalysis andon functional organic analysis, and although convention has often relegatedmicroanalysis to the end of comprehensive reviews it has been consideredmore logical than this report should deal with the determination of elementsfirst. The published papers on functional analysis necessarily cover a wideand scattered field, and a glance at the list of references will show that avery high proportion of the work is of American origin. It is, in fact,apparent that in this country and in Europe, comparatively little attentionis being given to functional organic analysis. Considerable impetus has, ofcourse, been given to the elucidation of complex problems by the elegantpartition chromatographic technique developed by Martin and his co-workers at Leeds in 1944, and as a result considerable activity has beennoticeable in recent years in the fields of protein and sugar analysis. Paperson these topics have been rather less numerous in 1950 than in former years,and those which have appeared have been logically included in the sectionon chromatography.Ultimate Organic Microanalysis.Several recent reviews cover the microchemical field up to the end of1949.Collaborative results for various methods for carbon and hydrogen,and for Kjeldahl and Dumas methods for nitrogen, have been reported.2Specifications have been recommended by the American Chemical Societyfor the standardisation of microchemical apparatus and by the BritishStandards In~titution.~ The numerous papers on microchemistry read atthe Graz Congress in July 1950 5 are due to appear in Mikrochemie (formerlyMikrochimica Acta).Specially noteworthy is the fact that British Carbon and Hydrogen.lo7 Miles and Quackenbuah, J .A88. Off. Agric. Chem., 1950, 33, 424.lsS Fuel, 1950, 29, 101.1 Willits, Analyt. Chem., 1949, 21, 132; Willits and Ogg, ibid., 1950, 22, 268;Kahane, Bull. SOC. chim., 1950, 17, D 1; Ingram, Ann. Reports, 1949, 46, 280.Willits and Ogg, J .Assoc. 08. Agric. Chem., 1949, 32, 561.Steyermark et al., Analyt. Chem., 1949, 21, 1555.British Standard 1428, Parts A1 and D3, 1950. Besterr. Chem.-Ztg., 1950,51,94STAGG : CHEMICAL METHODS (ORGANIC). 389practice has not followed the German lead and the American trend towardsuse of automatic combustion techniques ; 7 Unterzaucher 8 has now developedan automatic procedure based on the method for oxygen : the combustionproducts traverse successive packings of copper oxide, copper, bariumchloride to remove water, and carbon to reduce carbon dioxide to carbonmonoxide, which is then determined by reaction with iodine pentoxide.Most recent publications concern the rapid combustion method with anunpacked tube, following the work by Belcher and Sp~oner,~ Co1son,l0 andIngram.11 Belcher and Ingram 12 have designed a new apparatus in whichthe combustion zone consists of a vertical double-surface chamber heatedby a special type of split furnace.The purification system has been con-structed to allow replacements to be readily effected. These authors l3have also reported a study of absorbents for nitrogen oxides, and selectedmanganese dioxide as being the most suitable ; in slow-combustion proce-dures, special care must be taken to avoid condensation of moisture in thebeak of the combustion tube or in the entrance to the water absorption tube;in rapid combustion methods particularly, sufficient time (or space in thetrain) must be allowed for complete formation of nitrogen peroxide fromnitric oxide and oxygen.Kirsten l4 has given a detailed account of a new rapid technique whichinvolves thermal cracking by heating to 1000" in a platinum capsule, andoxidation in a quartz combustion tube containing an inner nickel sleeve.The sample, in the capsule, is pushed into the furnace by means of anautomatically-travelling electromagnet ; halogens and sulphur oxides areremoved by silver in a nickel roll at goo", and nitrogen peroxide is retainedin a special sulphuric acid-chromic acid absorber.Among the manydetailed points considered are the design of the absorption tubes, and theneed for avoiding condensation of water a t the entrance to the waterabsorption tube (cf. Ingram). Naughton and Frodyma l5 have described amethod involving combustion of the sample in a modified Pregl apparatus,collection of the resulting water vapour and carbon dioxide in a solid carbondioxide trap and a liquid-air trap, respectively, and, after pumping out theexcess of oxygen, determination of the water vapour and carbon dioxidemanometrically at constant volume.The automatic combustion procedure for the Dumas method,16which is widely used in Germany and has been recommended by Bussmann,"has now been adapted by Manganey l* so that controlled combustions canbe done without recharging the tube after each test and without altering theBelcher and Phillips, B.I.O.S.Report No. 1606.Steyermark, I d . Eng. Chem. Anal., 1945, 17, 523; Clark and Stillson, Anulyt.Chem. Ing.-Tech., 1950, 22, 39.J . , 1943, 313; Fuel, 1941, 20, 130; Ind.Ghem., 1943, 19, 653.Nitrogen.Chem., 1947, 19, 423; Fischer, ibid., 1949, 21, 827.lo Analy8t, 1948,73,541. l1 Ibid.,p. 648. la Analyt. C1.h. Acta, 1950, 4, 118.l3 Idem, ibid., p. 401. Mikrochem., 1960, 56, 217.l5 Analyt. Chern., 1950, 22, 711. 16 Zimmermann, Mikrochem., 1943,31,42.l7 Helv. Chim. Ada, 1949, 32, 995. 1e Bull. SOC. chim., 1960, 17, 74390 ANALYTICAL CHEMISTRY.temperature. Kirsten l9 has.recommended a nickel-nickel oxide permanent,filling a t 1000" for use with all types of compound, with a quartz apparatuswhich allows a backward sweep with cakbon dioxide to save time and tolengthen the life of the filling. Modifications have been introduced 20 whichgive greater flexibility or strength; by increasing the size of the part of thetube in the hot furnace, more analyses can be carried out on one filling, andvery small amounts of nitrogen (0.03-0*007 yo) can be determined becauseof the greater oxidative capacity, which allows use of larger samples (-50 mg.).A rapid combustion method has been described by Colson; 21 thecombustion is carried out in a slow stream of carbon dioxide, and the nitrogenproduced is then swept out by a much faster stream of carbon dioxide thanis used in the normal Pregl-Dumas method; complete reduction of thenitrogen oxides during the combustion is effected by a four-fold increase inthe amount of hot metallic copper.I n a review of the manifold variations which have been proposed uponthe original Kjeldahl method, Kirk 22 emphasised the difiiculty of choosing aset of digestion conditions which can be applied to all nitrogenous compounds,and stressed particularly the circumspection which must be used in employingoxidising agents for speeding digestion.In 1949 Willitts, Coe, and Ogg,Z3in a study of the digestion of nicotinic acid, demonstrated the danger of lossof nitrogen when selenium catalysis (the mechanism of which is discussed bySchwab and Schwab-Agallidis 24) is employed in the digestion of refractorysubstances, and recommended mercuric oxide in conjunction with fixedamounts of sulphuric acid and potassium sulphate. Subsequent collaborativestudy of this procedure gave disappointing results in some cases, and areason for this has been found 25 in the lower temperature of digestion whichis obtained if the liquid is not boiled vigorously.In studying the digestion of compounds which require previous reduction,Secor, Long, Kilpatrick, and White 26 have shown that volatility of nitrogenis increased by pretreatment with hydriodic acid.Prolonged digestion anda high potassium aulphate-sulphuric acid ratio are especially dangerous inthese circumstances.For absorption of ammonia during distillation, boric acid continues tobe popular, although it is clear that care is necessary if loss of ammonia is tobe negligible in micro- and semimicro-work,27 and Silverstein and Perthell 28state that losses are reduced if the boric acid is contained in a Goessmantrap.29 Blom and Schwarz30 claim that if the ammonia is absorbed innickel ammonium sulphate sharper end-points are obtained in titration withacid.l9 Analyt.Chem., 1947, 19, 925.z1 Analyst, 1950, 75, 264.23 J . Assoc. Ofl. Agric. Chem., 1949, 32, 118.26 Ogg and Willits, J . Aasoc. Off. Agric. Chem., 1950, 33, 100.28 Analyt. Chern., 1950, 23, 949.as Massachmetts Agric. Exptl. Sta., Bulletin 54, 1898.so Acta Chem. Scand., 1949, 8, 1439.*O Ibid., 1950, 22, 358.29 Analyt. Chem., 1950, 23, 354.24 NatUTWiSS., 1949, 56, 254.Ibid., p. 872. 07 Machemer and McNabb, Anal. Chim. Acta, 1949, 3, 428STAGG : CHEMICAL METHODS (ORGANIC). 391Habgens. In the potentiometric titration of halogens by silver (followinga Parr-bomb fusion for decomposing the organic material) LBvy31 hasopposed the e.m.f.of the cell to that of a potentiometer standardised to thee.m.f. of a reference electrode containing the same quantity of sodiumsulphate and equivalent quantities of halogen and silver ions. White andSecor 32 have determined iodine by Carius digestion with nitric acid-mercuricnitrate mixture, followed by conversion into iodate and subsequent titrationof the iodine liberated on addition of iodide; a similar method has beendevelopedRickson34 has reported that low results obtained by thorium nitratetitration after separation of fluorine from interfering impurities by distillation,may be caused by some of the fluorine being present as the fluorosilicate ion,Sip,", which does not form an un-ionised compound with thorium. Thiserror can be avoided by carrying out the titration in a 50% alcoholic systembuffered a t pH 5.3, with gallocyanine as indicator.A considerable numberof different indicators for the thorium nitrate titration have been studied byWillard and H0rt0n,3~ who also report 36 a procedure for photofluorometrictitration of fluoride, using quercitin as fluorescent indicator.Neudorffer 37 has developed a semimicro-method for the simultaneousdetermination of sulphur and fluorine, in which the vapour of the compoundis mixed with hydrogen and burned in an atmosphere of oxygen; theproducts of combustion were determined by conventional means.Neudorffer's method for sulphur and fluorine simultaneouslyhas been mentioned above. Zimmermann 38 has described a simplifiedversion of his method ; 39 this involves decomposition by potassium,distillation of the hydrogen sulphide into cadmium acetate, and iodometrictitration.In a similar method40 the organic compound was decomposedby heating it with oxalic acid and metallic calcium. Kirsten 41 has given apreliminary report on a new method for sulphur, based on combustion ofthe sample in oxygen, reduction in an oxy-hydrogen flame a t 1100" tohydrogen sulphide, absorption in strong alkali, and determination oxidi-metrically with hypochlorite.Maybott and Lewis42 have compared the ter Meulen, Liebig,and Unterzaucher methods for determining oxygen in organic compoundsand have concluded that the last 43 is the most reliable. Oxidation catalystsused in preference to iodine pentoxide have included mercuric oxide,44 andsilica impregnated with iodine pentoxide and sulphuric acid.46 Harris,for bromine in organic compounds.SuZphur.Oxygen.31 Compi?.rend., 1950, 230, 1958.33 White and Kilpatrick, ibid:, p. 1049.3 5 Analyt. Chem., 1950, 22, 1190.Compt. rend., 1950, 230, 750.38 Ibid., 1943, 31, 15; 1947, 33, 122.4O Chernyi and Podoinikova, Biokhim., 1950, 15, 134.45 Ber., 1940, 73, 391 ; Aluise et al., Analyt. Chem., 1947, 19, 347.44 Deinum and Schouten, Analyt. Chim. Acta, 1950, 4, 288.45 Beseet and Pokier, Bull. SOC. chim., 1949, 16, D, 539.3a Analyt. Chern., 1950, 22, 1047.34 Analyst, 1950, 15, 84.36 Ibid., p. 1194.38 Mikrochem., 1950, 35, 80.Mikrochem., 1950, 55, 174. 4x Analyt. Chem., 1950, 32, 1051392 ANALYTIUAL CHEMISTRY.Smith, and Mitchell 46 have described a recording thermal conductivitymethod for determination of carbon monoxide in the resultant helium-carbonmonoxide mixture.Functional Organic Analysis.Hydroxyl Group.-AZcohols and GZycob.A new application of thepowerful reagent lithium aluminium hydride is described by Lintner, Schleif,and Higu~hi.~' Previously, this substance had been employed as analternative to methylmagnesium iodide in Zerewitinow determinations ofactive hydr0gen.~8 I n this new method the reduction potential producedon a silver or platinum electrode is used to detect an added excess of thehydride during titration of saturated alcohols in tetrahydrofuran as solventand to indicate the end-point in back titration with standard alcoholsolution.Use of p-aminoazobenzene as a colorimetric indicator is alsoenvisaged. The recoveries quoted are from 1% to 5% higher than theory,but in a later note Higuchi49 states that if oxygen is not rigidly excludedfrom the titration vessel, some hydride will be lost by oxidation.Determination of small amounts of ethyl alcohol in the Conway diffusionunit, using potassium carbonate to expel the alcohol, and alkaline per-manganate to absorb it, is described by M ~ L e o d , ~ ~ and successful applicationof ceric sulphate oxidation to the determination of tetrahydrofurfurylalcohol is reported by Haslam and Ruddle.61 Middleton and Stuckey 52describe the application of a cloud-point technique to determination ofethylene and dipropylene glycol in propylene glycol.Water must first beremoved. The method is claimed to detect O*lyo of either impurity, but asethylene glycol raises and propylene glycol lowers the cloud point, thepresence of both simultaneously can only be detected by examination ofdistillation fractions. A rapid method of determining glycerol with anerror of -+2% in fermentation solutions containing 2-8 pap.m. of glycerol isgiven by Lambert and N e i ~ h . ~ ~Three advances in the selective determination of phenols byiodination are reported by Willard and Wooten : for determining o-substituted in p-substituted monohydric phenols, coloured iodoquinones areformed by treatment with iodine and alkali.54 The formation of thequinone is dependent on linkage through the free p-position, thus preventinginterference by phenols substituted in that position.Resorcinol isdetermined by iodination a t pH 5-0 a t which most phenols do not interfere ; 55o- and m-dihydric phenols interfere, but catechol may be prevented fromdoing so by removing it with lead acetate. o-.and m-Dihydric phenols aredetermined by iodinating a mixture of the two, and adding acetone. A bluecolour is formed whose intensity is proportional to the amount of the lesser46 Analyt. Chem., 1950, 22, 1297.4 8 Zaugg and Harrom, ibid., 1948, 20, 1026; Krynitsky, Johnson, and Carhart, J .Amer. Chem. SOC., 1948, 70, 486; Hochstein, ibid., 1949, 71, 305.49 Analyt. Chem., 1960, 22, 955.I1 Analyst, 1949, 74, 569.63 Canadian J . Res., 1950,28, B, 83.Phenols.4 7 Ibid., p.534..w J . Biol. Chem., 1949, 181, 323.5* Ibid., 1960,75, 406.54 Analyt. Chem., 1950,22,423. Ibid.,p. 585STAGQ : CHEMICAL ME’l’HODS (ORGANIC). 393c~mponent.~~ Of 25 phenols tested only o- and Ira-dihydric phenols gave thereaction.Attention has been given by Siggia, Hanna,and Kervenski to the problem of determining primary, secondary, andtertiary amines in mixtures containing all three, and a scheme is described 67which has given good resulfs with known mixtures of aniline, monomethyl-aniline, and dimethylaniline ; aniline and mono- and di-ethylaniline ; anda-naphthylamine and its mono- and di-ethyl derivatives. In this scheme,three determinations of total bases are made by titrating with hydrochloricacid in a solvent consisting of equal parts of ethylene glycol and isopropylalcohol to accentuate ionisation of the bases : the first titration is made onthe sample itself, the second on the sample after condensing it withbenzaldehyde to remove secondary amine, and the third on the sampleafter primary and secondary amines have been rendered neutral byacetylation.Primary, secondary, and tertiary bases can then be obtainedby calculation.The titration of organic bases in non-aqueous solvents has been extendedby Fritz 58 to the determination of heterocyclic bases by titration withperchloric acid in dioxan. Pyridine, 2 : 6-lutidine, 2 : 2’-dipyridyl, 1 : 10-phenanthroline, and brucine have been determined ; an important featureof the method appears to be the formation of a precipitate of base per-chlorate. The same author shows 59 that Bandel and Blumrich’s method oftitrating weak bases in anhydrous acetic acid with perchloric acid in aceticacid 6o can be employed when the bases are dissolved in less polar solventssuch as nitrobenzene, hydrocarbons, chlorobenzene, etc.Another methodof determining pyridine in presence of ammonium salts 61 involves distillationof a solution adjusted to pH 4.8; pyridine is completely volatile butammonia is not. Ballard describes two cdorimetric methods, one dependingon the diazo-reaction and the other on condensation with p-dimethylamino-benzaldehyde, for determining p-aminophenol in metol a2 and primaryamines occurring as impurities in succinylsulphathiazole, Carbarsone, andGlycarsamideAmides and Amino-acids. The reaction of a mixture of nitric andhydrochloric acids with amides and amino-acids to yield nitrogen andnitrous oxide 64 has been applied to the determination of a number of simpleamides and amino-carboxylic acids,65 and Kay and Mills 66 have shown, in are-investigation of Pope and Stevens’s copper ealt method 67 for amino-acids, that reproducibility is improved by washing the copper phosphate.free from phosphate with borax buffer.Moubasher, Sina, Awad, andAmino-~~p.-Amines.6 6 Analyt. Chem., 1950, 22, 670.m Idem, ibid., p. 1028.61 Ashmore and Thickens, Coke and Gas, 1949,11, 307.aa Anulyet, 1950, 75, 430.64 Renard, Bull. Acad. roy. Belg., Chase mi., 1946, 81, 219.6 5 Renard and MBdart, Bull.SOC. roy. Sci. Lidge, 1949, 18, 409;66 Anarlyt. Chem., 1980, 22, 760.Ibid., p. 1296. 5 8 Ibid., p. 578.ae Angew. Chem., 1941, 64, 374.J. Pharrn. Plaarmaeol., 1950, 2, 98.Renard andDeschamps, oaterr. Chern.-Ztg., 1950, 51, 112.Bhchem. J., 1939, 88, 1070394 ANALYTICAL CHEMISTRY,Othman 68 have based a method of determining amino-acids on the observ-ation that many of them yield their amino-nitrogen quantitatively ontreatment with perinaphthindanetrione hydrate or its nitro-derivative.The formation of non-ionic silver complexes affords the basis of a methodfor cysteine and ~ y s t i n e , ~ ~ and a specific colorimetric method for hydroxy-proline 70 depends on oxidation with sodium peroxide and condensing theoxidation products with p-dimethylaminobenzaldehyde to form an intensered colour. An extensive study of the stability of tryptophan duringalkaline hydrolysis of proteins has been carried out by Spies and chamber^,^'and conditions are described for hydrolysis a t temperatures up to 185"without destruction of tryptophan ; a fluorimetric method for determiningtryptophan 72 depends upon the formation of a fluorescent product onreaction with perchloric acid.Carbons1 Group.-Little advance has been made recently in the generalmethods for determining carbonyl groups.Wanka, Jurevek, and Holanek 73in reviewing the phenylhydrazine, hydroxylamine, and semicarbazidemethods conclude that they share a common disadvantage in the difficultyof obtaining a sharp end-point in the titration of the liberated acid.How-ever, Maltby and Primavasi 74 claim that an alcoholic solution of hydroxyl-amine hydrochloride can be used satisfactorily to determine many commonand unfamiliar carbonyl compounds, bromophenol- blue being used asindicator. Lieb and Schoniger 75 studied the phenylhydrazine method uponbenzoin and vanillin and found that condensation does not proceedquantitatively or uniformly. Useful data on the rate of oximation offourteen aryl alkyl ketones in pyridine-methanol solution are given bySuratt, Proffitt, and Lester.76Aldehydes are determined in the presence of ketones by oxidising thealdehyde to carboxylic acid with silver oxide and titrating with alkali,77 andaldehydes in the presence of carboxylic acids by oximation followed bytitration of the liberated hydrogen chloride to pH 2-50.78Determination of formaldehyde by reaction with ammonium chloride 79and of formaldehyde and acetaldehyde in admixture by formation of theSchiff colour first a t pH 0.7 and then a t pH 2.7 8o are described, and theapplicability of the well-known chromotropic acid method for formaldehydehas been extended by Bricker and Vail's observation *l that the complexcan be evaporated to dryness without destruction, the purple colour beingreadily developed by treating the residue with sulphuric acid.68 J .Biol. Chem., 1950, 184, 693.139 Kolthoff and Stricks, J . Amer. Chem. SOC., 1950, 72, 1952.' 0 Neuman and Logan, J . Bio2. Chem., 1950, 184, 299.7 1 Analyt. Chem., 1949, 21, 1249.72 Gordon and Mitchell, J .Biol. Chem., 1949, 180, 1065.7 3 Coll. Czech. Chem. Comm., 1949, 14, 162.7 b Mikrochem., 1950, 35, 407.7 7 Mitchell and Smith, Analyt. Chem., 1950, 22, 746.7 8 Idem, ibid., p. 750.79 Cassini, Ann. Chim. appl., 1949, 89, 600.74 Analyst, 1949, 74, 498.'13 J . Amer. Chem.Soc., 1950,72,1561.Velrsler, J . Anal. Chem. U.S.S.R., 1950,5,32. 81 A d y t . Chem., 1950, 22, 720STAGG : CHEMICAL METHODS (ORGANIC). 396Colorimetric methods have also been described for glycollic aldehyde, 82pyruvaldehyde,m and acet01.~~Carboxylic Acids.-Advances in the analysis of carboxylic acids havebeen confined to individual cases, no new techniques for the generaldetermining of the carboxyl group having been reported.Conditions for the determination of acetic acid present as an impurityin refined formic acid have been described by Arthur and Struthers; 86 theformic acid is oxidised to carbon dioxide with mercuric oxide and the residualacetic acid is titrated with alkali.For determining acetic anhydride inglacial acetic acid, Benson and Kitchen s6 add an excess of aniline, and aftercondensation with acetic anhydride has taken place the remaining aniline isdetermined colorimetrically with furfuraldehyde : it is stated that smallamounts of ethylidene diacetate, copper acetate, acetaldehyde, and water donot interfere, but the possibility of the acetic acid itself interfering is notdiscussed. Determination of minute amounts of acetic acid in the Conwaydiffusion unit is described by Conway and D~wney.~'Two procedures have been described for the determination of oxalicacid : one, due to Burrows,88 depends on the fading effect of oxalate upon thegreen iron complex of 8-hydroxy-7-iodoquinoline-5-sulphonic acid ( " ferron ")and is in effect a modification of Lange's method 89 using ferric thiocyanate.The other method depends on reduction of the oxalic acid with magnesiumand sulphuric acid to glycollic acid, which is determined by Eegriwe's test.Wohnlich 91 gives a method for determining lactic acid colorimetricallyafter reaction with a-naphthol in concentrated sulphuric acid, and Troupeand Kobeg2 analyse lactic acid-lactic ester mixtures by studying thehydrolysis rates of the components.In the field of long-chain fatty acids, work leading to the development ofa method for determining saturated acids in the presence of unsaturatedacids has been described by Fitelson and Weber; 93 this involves non-disruptive oxidation of the unsaturated acids with performic acid a t 70-75"to form hydroxy- and formoxy-acids, which can be separated from thesaturated acids by a process of extraction and chromatography.Hydroxamates of long-chain fatty acids have been determined byhydrolysis to the acid and hydroxylamine with standard hydrochloric acid,followed by titration of the excess mineral acid.Q4Nitro-group.-A novel method for gravimetric determination of nitro-groups, based on reduction to amino-groups with tin and hydrochloric acid,.82 Dische and Borenfreund, J .Biol. Chem., 1949,180, 1297.84 Forist and Speck, ibid., p. 902.Thornton and Speck, Analyt. Chem., 1950, 22, 899.Canadian J . Res., 1949, 27, 266.Biochem. J . , 1950, 47, iv.Lange, " Kolorimetrische Analyse," 1941.Pereira, &err. Chem.-Ztg., 1950, 51, 111.8b Ibid., 1949, 21, 1209.8 8 Analyst, 1950, 75, 80.91 2. phy8iOl. Chem., 1950, 286, 138.O3 J . Amer. Oil Chm. Soc., 1950, 27, 1.O4 Roe and Swern, Analyt. Chem., 1950, 22, 1160.O2 Analyt. Chern., 1950, 22, 646396 ANALYTICAL CHEMISTRY.has been described by Vanderzee and Edge11,95 who have shown that, ifatmospheric oxidation is prevented, and the evolution of gaseous hydrogenis minimised by controlling the acid concentration, the consumption of tin isproportional to the nitro-group.After reaction, the excess of tin is weighed.Recoveries within &0-5y0 of theory are reported for several simple aromaticnitro-compounds, though interference was experienced if iodo- or aldehydegroups were present.In a study of the reduction of nitroguanidine, nitroaminoguanidine, andnitrourea with titanous chloride, Zimmermann and Lieber 96 found that thenitroguanidines gave inconsistent results except in the presence of ferrousion; by adjusting the concentration of ferrous ion to an amount dependingon the particular nitramide, reduction equivalents of 6H per nitro-groupwere obtained with errors of the order of &2%. Nitrourea on the other handconsumed only 2H per nitro-group whether ferrous ions were present or not.Sugars.-Heidt and Southam 97 have established conditions for determin-ation of reducing sugars with cupritartrate reagent buffered to low pH, andstate that the pH should be controlled to 0.01 unit, the optimum valuebeing 8-70.Bevenue and Washauer 913 in studying the effect of clarificationand dealcoholation of extracts before determination of reducing sugars,found that in many cases these steps are unnecessary and in many others asimple carbon treatment is all that is required. Thomas, Melin, and Moore ggalso found that clarification with lead can be omitted from the procedurewhen determining sugars in many forage plants, and suggested that anyonewho has to perform large numbers of sugar determinations will be welladvised to ascertain whether this step is necessary.A new colorimetric method for determining reducing sugars loo dependson reduction of triphenyltetrazolium chloride to triphenylformazan inalkaline solution.The amount of the red insoluble formazan is proportionalto the reducing sugar present, and it can be dissolved in pyridine and acidto give a red colour suitable for absorptiometric measurement.A scheme for determining glucose, galactose, and rhamnose in mixturesobtained by hydrolysis of flavonol glycosides is described by Porter andFenske; lo1 this employs Schoorl's copper reduction before and afterselective destruction of (a) glucose and ( b ) glucose plus galactose by ferment-ation. Sedoheptulose (D-aho-D-fructoheptose) can be determined, accordingto Nordal and Klevstrand,l02 by extracting the blue-green colour obtainedwith orcinol and hydrochloric acid into amyl alcohol and measuring it ; anda new method for hexosamines, based on deamination with nitrous acid anddevelopment of the indole colour from the resulting hexose 2 : 5-anhydrides,has been described by Dische and Borenfreund.lo3 This test is claimed tobe more sensitive than the Elson-Morgan test with acetylacetone andO 5 Analyt.Chem., 1950, 22, 572.O 7 J . Amer. Chem. SOC., 1950, 72, 589.O' Ibid., p. 1151.J . Assoc. Off. Agrie. Chem., 1950,33, 122.100 Mattson and Jensen, ibid., 1950, 22, 182.lo3 J . Biol. Cilem., 1950, 184, 517,Anulyt. Ch.em., 1949, 21, 1363.lol J . Assoc. Ofl. Agric. Chem., 1949,82, 714.102 Analyt. Chim. Acta, 1950, 4, 411STAGG : CHEMICAL METHODS (ORGANIC).397p-dimethylaminobenzaldehyde lo* and may be of special interest in view ofthe interference experienced in the latter from sugars and amino-acids.lO5Unsaturation.-The advantages of catalysed hydrogenation as a means ofmeasuring unmturation have again been emphasised in papers dealing withthe technique of microhydrogenation ; lo6 the interference of side reactionsin halogenation methods has also received attention : Braae 10' has shownthat the mercury-catalysed addition of bromine to isolated double bondsproceeds so rapidly that direct titration can be used in conjunction with anelectrometric end-point, the oxidising influence of an excess of bromine beingthus eliminated; and Lee, Kolthoff, and Johnson lo* employ a graphicalmethod to differentiate between the true iodine chloride addition and theabsorption in excess of theory which occurs as a result of decomposition inolefins which are branched in the vicinity of the double bond.For the specific determination of terminal unsaturation, Bricker andRoberts lo9 have combined th6 Malaprade reaction (whereby the terminalunsaturated groups are converted by permanganate into 1 : 2-glycols andthese are split by periodic acid into formaldehyde and a higher aldehyde)with the chromotropic acid method for determining formaldehyde, while forterminal unsaturation in styrene derivatives, especially those containinghalogen in the ring, Marquardt and Luce 110 recommend mercuric acetate inmethanol as a reagent.In the acidimetric determination of acetylene derivatives by reactionwith silver nitrate and titration of the nitric acid formed, advantage isclaimed 111 for the use of sparingly soluble silver salts (in particular silverbenzoate) in place of silver nitrate : insoluble complexes are formed withmany acetylides which do not give a precipitate with silver nitrate.Whereinterference is likely to arise in argentometric procedures from the presenceof silver reductants, precipitants, or complexing agents, Hanna and Siggia 112recommend a procedure based on reaction with potassium mercuri-iodide.Compounds of Biological Signiflcance.--AZkaloids. The effect of am-monium salts on the gravimetric determination of nicotine by precipitationwith silicotungstic acid has been studied by Ogg, Willits, and Ricciuti,113who showed that ammonium and other inorganic salts delay the formationof the precipitate; attempts to remove the ammonia, failed but conditionswhich minimise the salt-effect were found.However, in a later communi-cation, Willits, Swain, and Connelly 114 give a method for determiningnicotine spectrophotometrically at 259 mp. which is not affected by am-monium salts. A method for determining nicotinic acid in nicotinamide 115depends for its success upon the establishment of conditions for benzylatinglo4 Biochem. J . , 1933, 27, 1825.l o 5 Horowitz, Ikawa, and Fling, Arch. Biochem., 1960, 26, 226.106 Ogg and Cooper, AnaEyt. Chem., 1949, 21, 1400; Mead and Howton, ibid., 1950,107 Ibid., 1949, 21, 1469. log Ibid., 1949, 21, 1331.110 Ibid., p.1194.lI2 Analyt. Chem., 1949, 21, 1469. llS Ibid., 1950, 22, 336114 Ibid., p. 430.22, 1204.lo8 Ibid., 1950, 22, 995.ll1 Marszak and Koulkes, Bull. SOC. chim., 1950, 17, 364.us Cuke, Mikrochem., 1950, 35, 20398 ANALYTICAL CHEMISTRY.the tertiary nitrogen of the amide without benzylating that of the acid,which can then be determined by the Konig reaction. Koszegi and Salgo ll6note the formation of precipitates between potassium mercurithiocyanateand a number of purine bases, alkaloids, and primary, secondary, tertiary,and quaternary amines, and describe the volumetric determination ofstrychnine nitrate and quinidine sulphate. Preliminary results of a quali-tative study of the chromatographic separation of morphine, codeine, andheroin from each other and from barbiturates are given by Stolman andStewart .l17Pyrimidines, Purines, and Urea Derivatives. Soodak, Pircio, andCerecedo 118 have extended the WheelerJohnson test for uracil andcytosine 119 to give quantitative results and give conditions whereby cytosinecan be removed quantitatively from mixtures of these two pyrimidines byadsorption on Decalso ; Holt and Mattson 120 have obtained quantitativeresults within 1-2% of theory for uracil, thiouracil, and related compoundscontaining the -CO*NH-CO- and -CO*NH*CS- groupings by the colorimetriccobalt method described by Dille and Koppanyi.l21 Spinks l Z 2 determines'' Antrycide " in biological fluids by extracting the intensely fluorescent eosinsalt into chloroform-butanol solution and measuring the fluorescence.Alloxan has been determined in commercial samples by condensing it with2-amino4 : 5-dimethyl-1 -D-ribitylaminobenzene to give riboflavin andmeasuring the flu0re~cence.l~~ Pedley 124 prefers neutral mercuric per-chlorate to silver nitrate as a precipitant for the gravimetric determinationof barbiturates.Haurowitz and Lisie 126 have applied Kitamura's observ-ation 126 that thiourea is oxidised to urea by alkaline hydrogen peroxide, tothe determination of thiourea obtained by the action of ammonium thio-cyanate on proteins.Methods have also been given for the determination of amidines,12'methylaminoacridine,128 P-naphthoxyethanol in blood,129 a-pyridyl-carbinol,l3O and sulph~namides.~~~Hanna and Siggia 132 determine chloroform and bromoform bythe carbylamine reaction with aniline and caustic alkali and claim thatrecoveries approach theory more closely than those obtained by simplehydrolysis with alcoholic potassium hydroxide.Brain and Helliwell,l33dealing with determination of trichloroethylene in blood, give improvedconditions for the quantitative production of the colour from its reactionHalides.1l6 2. anal. Chem., 1950, 130, 403.118 J . Biol. Chem., 1949, 181, 713.120 Analyt. Chem., 1949, 21, 1389.122 Biochem. J . , 1950, 47, 299.123 Tipson and Cretcher, Analyt. Chem., 1950, 22, 823.124 J . Pharm. Pharmacol., 1950,2, 39.12E J . Phurm. Soc. Japan, 1935, 55, 300.127 Trought, Ashton, and Baker, Analyst, 1950, 75, 437.ll8 Anderson and Lederer, ibid.,p.318.130 Wollich, Kuhris, and Price, Anulyt. Chem., 1949, 21, 1412.131 Schaefer and Wilde, 2. anal. Chem., 1950, 130, 396.182 Analyt. Chem., 1950, 22, 569.117 Analyst, 1949, 74, 536, 543.119 Ibid., 1945, 159, 333.lal J . Amer. Pharm. ASSOC., 1934, 23, 1079.la5 Analyt. Chim. Acta, 1950, 4, 43.12s Spinks, Biochem. J., 1950, 46, 178.lS5 Riochem. J . , 1949, 45, 75CROPPER : PHYSICAL AND PHYSICOCHEMICAL METHODS. 399with pyridine and alkali. The specific determination of the y-isomercontent of technical benzene hexachloride (hexachlorocyclohexane) continuesto attract interest ; Davidow and Woodward l3* have co-ordinated theobservations of a number of other workers in developing a method based onhydrolysis to trichlorobenzenes and meaaurement of optical density ah threewave-lengths in the ultra-violet, while Monnier, Roesgen, and Monnier 136find that only the y-isomer and heptachlorocyclohexane are reduced polaro-graphically, and that the latter compound is destroyed a t pH 13 whereasy-benzene hexachloride is stable.H.E. S.4. PHYSICAL AND PHYSICOCHEWICAL METHODS.provide excellentsummaries of progress, to late 1949, in almost all the subjects discussedbelow. A comprehensive review on the determination of organic function-ality by molecular spectra covers applications of ultra-violet, infra-red, andRaman spectroscopy, micro-wave spectroscopy, and mass spectrometry ;a review on the same theme by Lykken deals with electrometric methods.Limitations of space make it impossible to review the 1950 literature in suchan exhaustive manner; attention has been given to advances in principlesand general techniques, although some applications have been noted whenconcerning important products, new features in technique, or improvedways of eliminating difficulties. Subjects in which there have been onlyminor advances, or which are still a t an early stage (such as micro-wavespectroscopy, acoustical methods) have been left for consideration insubsequent Reports ; radioactivation analysis was reviewed in detail in lastyear's Report .4The division of subject matter has been made on conventional lines, withno attempt to follow the more logical but unfamiliar classification given bySerfass, Steinhardt, and S t r ~ n g .~Further efforts have beenmade to improve the stability of the light source in spectrochemical analysis.Rouse has described the use of an induction heater to evaporate the samplefrom a carbon cup, and excitation of the vapour by a spark, so that the twomain functions of a source (evaporation and excitation) are controlledseparately ; a d.c. arc source with an automatic ~ontroller,~ and an improvedintermittent arc generator for steel analysisThe direct-reading instrument constructed by Crosswhite for measuringrelative spectral intensities employed two photomultiplier tubes with anelectronic pen-and-ink ratio recorder ; the fixed phototube served as alS5 Analyt. Chim. Acta, 1950, 4, 309.The recent Annual Reviews in Analytical ChemistryOptical Methods.-Emission Spectroscopy.have been designed.134 J .Assoc. Off. Agric. Chem., 1949, 32, 751.1 Analyt. Chem., 1949, 21, 1-173; 19.50, 22, 1-126.Coggeshall, ibid., p. 381.Smales, Ann, Reporter, 1949, 46, 285.6 J . Opt. SOC. Amer., 1950, 40, 82.8 Marti, Spectrochim. Acta, 1950, 4, 43.Ibid., p. 396.Analyt. Chem., 1950, 82, 966.Ibid., p. 122.' Fetterley and Hazel, ibid., p. 76400 AXAIJYTIOAL UHEIWSTRY.monitor while the moving phototube scanned the spectrum, so that intensityfluctuations of the source were cancelled out. Direct quantitative studies ofligh t-source properties were possible by this means, and the relativeintensities of over 1000 lines from a standard d.c.iron arc have been recorded.Sinclair lo has investigated the variations of spectroscopically significantproperties in pulsed-arc discharges produced by a condensed-arc source unit,particularly with respect to analysis of zinc alloys. A useful report has beenmade l1 on the effects of Variations in cathode dimensions and sampleweights on the intensities of trace element and internal standard lines, andon the intensity ratios; variations in electrode dimensions can alter lineintensities and intensity ratios, so that accurate determinations of traceelements will only be obtained if the dimenaions, and especially the boringdepth, are kept constant. Brode and Timma l2 have studied the effect ofvarying amounts of extraneous elements on the line intensity of differentelements, and claim that Slavin’s total-energy method makes possible a moreexact correlation than has been achieved by using the internal standardmethod; the effect varies with the amount of extraneous element, but notin a simple linear fashion.A survey of light sources has been made byKaiser .13A rapid method of assessing intensities of blackening of the photographicplate has been based l4 on visual comparison with standard density lines on aHilger Spectrum Projector ; the difficulties in detecting and determiningtrace elements in complex spectra, however, led Davis and Webb l5 todevelop an apparatus for presenting a picture of the blackening contour of aportion of a spectrogram on the screen of a cathode ray tube.The variability of density differences on different plates, and theconsequences of such variations on routine analyses, have been studied; l6statistical treatment of spectrochemical computation methods has shown l7that the inherent precision closely approximates to its maximum value whencomputations are carried out with y values which are the mean of fourindependent determinations.Kaiser 18 has reviewed methods for thecalibration of step filters, and has given methods for calculating filter factorsa t various wave-lengths with a minimum number of observations.Spectrochemical methods have been described for alkali metals in ironcatalysts,19 for cast iron,20 for boronY21 for impurities in berylliumin titanium,23 and in for trace elements in oil 26 and serum,26 and10 J .Opt. Soc. Amr., 1949, 39, 958.l 2 J . Opt. Soc. Amer., 1949, 89, 478.l4 Addink, Spectrochim. Acta, 1950,4,36.16 Dehio, Eggert, HonerjBger-Sohm, Hormann, and Kaiser, ibid., 1949, 8, 488.l7 Schmidt, ibid., p. 538.21 Roux and Husson, Compt. rend., 1950, 230, 1068.28 Smith and Fassel, Analyt. Chem., 1949, 21, 1095.*3 Peterson, ibid., 1950, 22, 1398.9 5 Carlson and Gunn, AwZyt. Chem., 1950, 22, 1118.11 Scott, Spectrochim. Acta, 1950, 4, 73.l8 Chimia, 1950, 4, 89.la Ibid., p. 13.1* Ibid., p. 518.20 Riley, Spectrochim. Acta, 1950, 4, 93. Fast, Analyt. Chem., 1950, 22, 320.L4 Walsh, Spectrochim. Acta, 1950, 4, 47,Pfeilsticker, Spectrochim Acta, 1950, 4, 100CROPPER : PHYSICAL AND PHYSICOCHEMICAL METHODS.40 1€or traces of thallium in muscular tissue; 27 bismuth has been determinedin its alloys after a preliminary concentration stage using cupferron,2* andberyllium in air dust has been measured by a procedure involving use ofoxine to remove certain metals.29 The use of photomultiplier tubes for thealmost instantaneous spectroscopic determination of carbon in steels hasbeen described by Breckpot,30 who has also reported a very rapid method fordetermining phosphorus in steels, using the 2 1 3 6 ~ . line and a photo-multiplier with an interposed fluorescent screen.31 A special chamber hasbeen designed to permit electrodes to be loaded with radioactive materialsbefore spark excitation, with minimum risk to operators.32Interest in flame photometry has been greatly stimulated in recent yearsby the production of the flame photometer attachment for the Beckmanspectrometer ; this photometer, now described in detail by Gilbert, Hawes,and BeckmanF5 has a simple detachable atomiser handling samples of 1 ml.or less, a heated spray chamber for evaporating the spray, and a versatileburner for oxygen-gas or other flames.Monvoisin and Mavrodineanu a4have improved the dispersion of the liquid particles in a flame source bybuilding an ultrasonic oscillator into the jet, and have stabilised the flameby heating the fuel inlet in the base of the burner. A simple, inexpensiveburner has been described35 for use with a medium spectrograph fordetermination of 15 elements in the dissolved ash of biological material; theBeckman flame photometer has also been used with a large Littrow spectro-graph for determination of sodium, potassium, and lithium in plant andanimal substances.36 Flame spectra, detection limits, and excitationcharacteristics have been given for several dozen elemenfsF3 and applicationsof flame photometry have been described for the analysis of refra~tories,~~1 37magnesite and b r ~ c i t e , ~ ~ water,a9 and blood ser~m.~OSchiiler 41 has described the use of a new type of discharge tube whichmakes it possible to observe the spectra of organic molecules instead of theusual glow discharge spectrum of molecular fragments ; results are illustratedby emission and absorption spectra of various benzene derivatives.The most important advance in absorptiometry (andalso in ultra-violet spectrophotometry) has been the use of high opticaldensity reference solutions as a means of attaining a high degree of precision.The early work of KortiimP2 has now been extended by Bastian, onAbsorptiometry.a 7 Jansch and Mayer, Mikrochem., 1950, 35, 310.28 Burriel-Marti and Ramirez-Muiioz, Analyt. Chim.Acta, 1950, 4, 428.29 Peterson, Welford, and Harley, Analyt. Chem., 1950, 22, 1197.3O Breckpot and Gobert, Bull. SOC. chim. Belg., 1950, 59, 102.31 Breckpot and Marzec, ibid., p. 280.3= Feldman, Hawkins, Murray, and Ward, Analyt. Chem., 1950, 22, 1400.33 Ibid., p. 772. 34 Spectrochim. Acta, 1950, 4, 152.36 Robinson, Newman, and Schoeb, Analyt. Chem., 1950,22, 1026.36 Schrenk and Smith, ibid., p.1023. 37 Biffen, ibid., p. 1014.38 Mosher, Bird, and Boyle, ibid., p. 716.39 West, Folse, and Montgomery, ibid., p. 667.40 Willebrand, Rec. Trav. chim., 1950, 69, 799.*l Specfrochim. Acta, 1950, 4, 86, 42 Angew. Chem., 1937, 60, 193402 ANALYTICAL CHEMISTRY.theoretical grounds, to copper in copper base alloys43 and to potassiumdichromate and potassium permanganate ; 44 a full theoretical treatment hasbeen given by H i ~ k e y . ~ ~ ' The mode of operation requires the measurementof the optical-density difference between the test solution and a referencesolution, both of high optical density, so that the concentration difference isevaluated; the error in the photometric measurement (and hence, in theconcentration difference) is the same as in ordinary absorptiometry orspectrophotometry, but when results are expressed as total concentration inthe test solution, a significantly improved precision (e.g., & 0-1-@2%) isobtained, far surpassing that given by any other photometric process andmaking light-absorption methods of this type comparable in accuracy withgravimetric and volumetric methods. The work published to date has beencarried out on a Beckman spectrometer, the slits of which can be widened toallow a larger section of the spectrum to fall on the photocell; with existingabsorptiometers, the fixed spectral intensity given by the source and filterresults in a greatly reduced light intensity falling on the photocell whenhigh optical density solutions are used, and this restricts the upper limit atwhich the work can be done.The Reporter has used this difference methodwith good results in the 290 mp. region on a Beckman spectrometer, and at434 mp. with a Spekker absorptiometer fitted with a mercury lamp; in thelatter case, the optical density of the reference solution could be no higherthan about 1-5. The need has now arisen for a commercial absorptiometerwhich will give adequate galvanometer response even when solutions areused with optical densities as high as 3.0.A detailed account of the improvements which have been made in thenew Spekker absorptiometer has been given by Isbell ; 46 photoelectricinstruments have been described for use in microanalysis 47 and for protein-bound iodine.48 A further contribution has been made 49 on the permanenceof glass standards of spectral transmittance, and a very useful study has beenreported on the isolation of the lines of the mercury arc by filters,50 so as togive more truly monochromatic light.Buc and Stearns 51 have given dataon the transmittance of interference filters.Although a considerable number of absorptiometric and spectrophoto-metric studies have been reported, mention can be made only of the work oncopper diethyldithiocarbamate, on cobalt-nitroso-R-salt complex and nickeldimethylglyoxime,52 and on methods for beryllium.53 Spectrophotometricdata have been given for 11 rare-earth elements in aqueous solutions as43 Bastian, Analyt. Chem., 1949, 21, 972.44 Bastian, Weberling, and Palilla, ibid., 1950, 22, 160.45 Ibid., 1949, 21, 1440.4g Analyst, 1949, 74, 618.4 7 Ellis and Brandt, AmEyt. Chem., 1949, 21, 1546. 48 Chaney, ibid., 1950,22,939.49 Gibson and Belknep, J . Res. Nut. Bur. Stand., 1950, 44, 463; J . Opt. SOC. Amer.,60 Nicholas and Pollak, Analyst, 1950, 75, 662.5 1 J . Opt. SOC. Amer., 1950, 40, 336.52 Ovenston and Parker, Analyt. Chim. Acta, 1950, 4, 135, 142.63 S6guin and Gramme, Bull. SOC. chim., 1950, 17, 384,1950, 40, 435CROPPER : PHYSICAL AXD PHYSICOCHEMICAL METHODS. 403chlorides, nitrates, acetates, and perch lor ate^,^^ and quantitative methodshave been outlined for mixtures of several of these elements.54* 5sWokes and Slaughter 56 have studied the performance ofthe new Spekker instrumenb with its fluorimetry attachment, and havestressed the difficulties encountered in obviating the errors induced by straylight in fluorimeters with large photoreceptive areas ; these have beenovercome, and sensitivity greatly increased, by replacing the barrier-layerphotocells by a photomultiplier tube.In a number of specific applicationsof the fluorimetric method, the effects of the many variables, the influenceof interfering substances, quenching, and decay, have been studied ; amongthese may be mentioned the work on pyru~aldehyde,~~ acet01,~~ alloxanmon0hydrate,5~ and traces of beryllium in biological material.60Considerable attention hasbeen directed towards avoiding the difficulties usually encountered in theanalysis of multicomponent mixtures, and in correcting for " background "absorption due to unknown impurities.Vaughn and Stearn 61 haveanalysed xylene mixtures by taking readings a t four wave-lengths, calculatingtwo pairs of differences between these measurements and using thesedifferences with a calibration chart (a ternary composition diagram) todeduce the required results, which are free from errors due to level back-ground absorption. A rapid and accurate method for xylenes has beendeveloped 62 in which only the mutual relationships of absorption co-efficients are determined instead of their absolute values. A method similarto that of Morton and Stubbs c3 has been used for determining anthracene inanthracene cakes,6* in which the background absorption was assumed to belinear over the spectral region used; the same principle has been applied inthe determination of vitamin A.65 Tunnicliff, Rasmussen, and Morse 66have presented an algebraic method for correcting for the effect of interferingbackground ; instead of assuming that the interference is linear over a smallspectral interval, it is assumed that the absorption curve of the interferingmaterial can be represented by a general expression which is a function ofwave-length.The function chosen to represent the interference must do soaccurately over the required spectral interval, and must not even approxi-mately represent the absorption curve of any one component or combinationof components to be determined.Results of a collaborative test on 28 Beckman spectrometers have beenreported ; 67 the individual results show a very wide variation (0*681-0*782)64 Moeller and Brantley, AnaZyt.Chem., 1950, 22, 433, 1393.5 5 Wylie, J. SOC. Chem. Ind., 1950, 69, 143.5 7 Thornton and Speck, AnaZyt. Chem., 1950,22, 899.5 8 Forist and Speck, ibid., p. 902.6o Klemperer and Martin, ibid., p. 828.6 z Perry, Sutherland, and Hadden, ibid., 1950, 22, 1122.63 Analyst, 1946, 71, 348.64 Hazlett, Hannan, and Wells, AnaZyt. Chem., 1950, 22, 1132.67 Photoelectric Spectrometry Group, Bulletin No. 1, April, 1949, and Bulletin No. 2,Fluorimetry .Ultra-violet A bsmption Spectrophtometry.5 6 Analyst, 1949, 74, 624.59 Tipaon and Cretcher, ibid., p. 822.61 Ibid., 1949, 21, 1361.McGillivray, ibid., p. 494. 6 8 Ibid., 1949, 21, 895.March, 1950404 ANALYTICAL CHEMISTRY.in for the maximum for potassium nitrate, the mean value (0-713)being about 2% higher than the generally accepted figure based on previouswork.The standard error of the mean of duplicate tests on an " average "instrument was found to be 1-69; the difference between the mean resultsof duplicate tests on two instruments would be greater than 2.8% on one-third of the occasions, and greater than 5.5% in one case in twenty. Thiswork, therefore, emphasises the need, when maximum accuracy is required,for careful checking of instrument performance by measurements on standardsubstances. The errors introduced in spectrophotometry by the use of slitsof finite width have been considered by Eberhardt,68 who gives theoretically-derived expressions to allow an estimate to be made of the magnitude ofthese errors.The method for increasing the accuracy of spectrophotometricwork by using test and reference solutions of high optical density has beenreferred to under Absorptiometry (see p. 401).The glycol saponification/ultra-violet spectroscopic method for analysisof polyene fatty acids, which was reviewed and improved by Hilditch,Morton, and Riley G9 five years ago, has been examined by eight collaborators,who tested four oil samples for conjugated diene, arachidonic, linolenic, andlinoleic acids; 7O the results were satisfactory, and a detailed procedure hasbeen recommended for adoption. The method has also been used on themicro-scale 71 but, to avoid interference due to background absorption, achange has had to be made from glycol-potassium hydroxide to aqueousalkali at high temperature and pressure.Analytical methods have been described for mixtures of quinine (orquinidine) and cinchonine (or ~inchonidine),~~ for pyridine in hydrocarbonsof the kerosene-naphtha range,73 for nicotine,74 and for chlorinated solvents.75A review of the techniques of microspectroscopy, particularly in theultra-violet region, has been given by Loofbourow ; 76 the various combin-ations of microscope and spectroscope optics for examining the spectra ofsmall samples are discussed (for emission spectroscopy and for absorptionmeasurements in the ultra-vioIet, visible, and infra-red regions) and examplesare given of the performance of particular instruments.The increasing popularity ofdouble-beam instruments, with percentage transmission recording devices,is reflected in the number of papers dealing with modifications to, and/orperformance of, commercial models, or with the building of new instruments.Hales 77 has described an improved Hilger D.209 instrument with a double-beam system, using twin thermopiles of high sensitivity and fast response,and has reviewed the various problems which arise with this type ofapparatus. Simple modifications have been made to a Perkin ElmerInfra-red Absorption Xpectrophotometry .68 J .Opt. SOC. Amer., 1950, 40, 172.7O Anon., J . Amer. Oil Chem. Soc., 1949, 28, 399.7 1 Berk, Kretchner, Holman, and Burr, Analyt. Chewt., 1950, 22, 718.7 2 Grant and Jones, ibid., p.679.74 Willits, Swain, Connelly, and Brice, ibid., 1950, 22, 430.7 5 Berton, Bull. SOC. chim., 1949, 18, 858.76 J . Opt. SOC. Amer., 1950, 40, 317.69 Analyst, 1945, 70, 68.73 Le Rosen and Wiley, ibid., 1949, 21, 1175.7 7 J . Sci. Instr., 1949, 26, 359CROPPER : PHYSICAL AND PRYSICOCHEMICAL METHODS. 405instrument 78 to convert it for double-beam operation, and to make itportable to facilitate rapid analyses at the site of laboratory experiment^.^^White and Liston 80 have given a very detailed account of the construction,performance, and applications of the new Perkin Elmer Model 21 double-beam instrument ; these authors have also modified a Perkin Elmer spectro-meter for the continuous determination of six components in a samplestream.a1 The recording spectrophotometer constructed by Brownlie,82which is basically similar to that of Baird Associates, used a Schwartzthermopile in place of the bolometer, slits of a new design, and a d.c.servosystem for the recorder. A simple scheme has been described 83 by whichany spectrometer is readily converted to a direct ratio-recording instrument ;a double-beam " slit illuminator " passes light from a, common source areaalternately over two identical paths to the spectrometer entrance slit, andthe signals corresponding to the two beams are amplified, " sorted," andrectified by synchronous switches, compared potentiometrically, and theratio recorded. The energy in the comparison beam is kept constant at anypredetermined level while a spectrum is scanned, by means of a simpleservo slit width control.Menzies B p has given an account of the Hilger instrument with cathode-ray presentation of the spectrum; Bullock and Silverman 85 have describeda spectrometer with cathode-ray presentation, in which the detector is alead telluride cell, and which works with scanning rates of 120 cycles persecond and a scanned interval of better than 1.5 p.The ultimate limits ofsensitivity of photoconductive cells have been discussed by Moss.8sBlout, Bird, and Grey 8' have described an experimental infra-redmicrospectrometer, based on a commercial macro-instrument which can bechanged from macro- to micro-work in a few minutes; the performancecharacteristics are also discussed in terms of the cross-sectional area andminimum volume which can be observed with satisfactory signal to noiseratio, and five ways are given in which the ratio of measured absorption tospectrometer noise can be increased, Elliott, Ambrose, and Temple s8 havedesigned an apparatus for spectroscopy in the 3-p.region (with lead selenidephotocell) which is particularly suited for measurements on small specimensof oriented materials with polarised radiation.The large number of individual spectra, published each year contributesto a general fund of information, and each spectrum is potentially useful tothe analyst engaged in qualitative and quantitative infra-red work ; mentionof those published in 1950 is not possible in this Report.The paper byKuhn,89 however, records the spectra of 79 sugars and sugar derivatives and'13 Savitzky and Halford, Rev. Sci. Instr., 1950, 21, 203.79 Chapman and Torley, AnaZyt. Ghern., 1950, 22, 987.J . Opt. SOC. Amer., 1950, 40, 29, 36, 93; Analyt. Chem., 1950, 22, 768.White, Liston, and Simard, ibid., 1949, 21, 1166.(12 J . Sci. Instr., 1950, 27, 215.8a Hornig, Hyde, and Adcock, J . Opt. SOC. Amer., 1950, 40, 497.8 8 J . Sci. Instr., 1950, 27, 21.Ibid., 1949,39,1060. Ibid., 1950,40,608. 8 6 Ibid., p . 603. 137 Ibid., p . 304.Analyt. Chern., 1950, 22, 276406 ANALYTICAL CHEMISTRY.concludes that infra-red spectroscopy is an excellent method for theidentification of sugars and of functional groups in the carbohydrate molecule,including cellulose; an example of the analytical value of this method isgiven in connection with the determination of nitrate group in nitrocellulose.The analysis of natural and purified methane streams for small amountsof ethane, propane, and n- and iso-butanes has been achieved on a BeckmanI.R.2 spectrometer specially adapted (and calibrated) with a methanecompensation ~ell.~O O'Neal 91 has described the analysis of C,-C, paraffin-mono-olefin hydrocarbon mixtures (including differentiation of cis- andtrans-but-2-ene) without the usual low-temperature distillation, by acombination of mass spectrometer measurement of hydrocarbon groups, andinfra-red measurement of the butenes.trans-Octadecanoic acids and esterscan be determined 92 by measurements a t 10.36 p., a t which wave-length thetrans-isomers show strong characteristic absorption, whereas the cis-isomers,and saturated acids, do not.Brief mention may be made of the work ondi-tert. -butylcresols,93 and on methylphenoxyacetic acid and its chloro-derivatives ; O4 the application of infra-red spectroscopy in the analysis ofdistillation fractions of an and the methods used in the Esso laboratoriesfor the analysis of complex hydrocarbon mixtures, have been de~cribed.~~Opler 97 has advocated the use of punched-card machines for rapid calculationof results for ten-component mixtures. Colthup 98 has published chartssummarising spectra-structure correlations in the infra-red region.Few improvements in instrumentation or techniquehave been reported since the review in Annual Reports for 1949.99 A photo-electric instrument has been described, loo incorporating a low-pressuremercury source, a three-prism monochromator, and a refrigerated photo-multiplier detector which actuates a two-recorder system through a d.c.amplifier.Braun, Spooner, and Fenske 101 have reported the Raman spectra of 119different compounds, supplementing the data on 172 compounds givenpreviously; lo2 such compilations of data are of much potential value, andtheir growth should stimulate the much wider exploration of the value ofRaman spectroscopy in analytical work.The detection and determinationof isomeric hexachlorocyclohexanes has been described.lo3Detailed reviews of theseRamn Spectroscopy.X-Ray Absorption and Diffraction Methods.O0 Stroupe, Analyt.Chem., 1960, 22, 1125. O1 Ibid., p. 991.O3 Hales, Analyst, 1950, 75, 146.Swern, Knight, Shreve, and Heether, ibid., p. 1261; J . Amer. Oil Chem. SOC.,O4 Sjoberg, Acta Chem. Xcand., 1950, 4, 798; an ultra-violet method is given by85 Lecomte, La Lau, and Waterman, Bull. SOC. chim., 1950, 17, 141.96 Bell, Analyt. Chem., 1950, 22, 1005.J . Opt. SOC. Amer., 1950, 40, 397.Woodward, Ann. Reports, 1949, 46, 216.Ibid., p. 1074.1950, 27, 17.Grabe, ibid., p. 806.O 7 Ibid., p. 558.loo Heigl, Dudenbostel, Black, and Wilson, AmEyt. Chem., 1950, 22, 154.lo3 Luther, Lampe, Goubeau, and Rodewald, 2. Naturforsch., 1950, 5, a, 34.108 Ibid., 1947, 19, 700CROPPER : PHYSICAL AND PHYSICOCHEMICAL METHODS.407subjects, up to late 1949, have been p~b1ished.l~~ The General ElectricX-ray photometer has been used for quality control of petroleum products,lo5particularly for determination of sulphur, tetraethyl-lead, and metallicadditives; very detailed accounts have been given lo6 of the technique andresults of X-ray absorption spectrophotometric determination of tetraethyl-lead in petrol. Birks has described 107 apparatus for measuring X-rayfluorescence spectra and has now reported methods for determining smallamounts of hafnium in zirconium, and tantalum in columbium,fO* and fortetraethyl-lead and ethylene bromide in aviation petr01.l~~Advances in apparatus for diffraction work include construction of apoint-focus monochromator for low-angle diffraction,l1° an optical centeringsystem,lll a, Geiger counter spectrometer for single-crystal measurements,lf2and a camera to eliminate spottiness from X-ray photographs of coarse-grained material ; 113 apparatus for operation at high temperatures has beendesigned by Goldschmidt and Cunningham,l14 by Williams,l15 and bySteward.ll6 A camera for low-temperature work,117 and a low-temperaturesingle-crystal technique 11* have also been described.X-Ray diffraction studies (for identification purposes) have been madeon di-p-~ylylene,~l~ and on the itmides,l20 anilides, and silver salts of thesaturated fatty acids up to C22.Data on certain complex alkyl sulphideeand sulphones show that X-ray diffraction may be used for identifyingalkyl halides from which the sulphides and sulphones were prepared.122Susich 123 has discussed the difficulties which arise, owing to polymorphism,in the identification of organic dyes, and has described applications todifficult problems in dye chemistry.Electxometric Methods.-Potentimetric and Conduetometric Titrations.Gran 124 has shown, both theoretically and in practice, that the equivalentpoint in a potentiometric titration can be determined more accurately fromAV/ApH or AV/AE versus V , rather than the usual AEIAV versus V , curves.Potentiometric titration of functional groups has been referred to abovelo4 Liebhafsky, Analyt.Chem., 1949,21,17 ; 1950,22,15 ; Kaufman and Fankuchen.lo6 Vollmar, Petterson, and Petrizzelli, ibid., 1949, 21, 1491.lo6 Calingaert, Lamb, Miller, and Noakes, ibid., 1950, 22, 1238; Hughes andlo' Birks and Friedman, Rev.Sci. Instr., 1948, 19, 323.lo8 Birks and Brooks, Analyt. Chem., 1950, 22, 1017.lo* Birks, Brooks, Friedman, and Roe, ibid., p. 1258.110 DuMond, Rev. Sci. Instr., 1950,21,188.lla Cochran, Acta Cryst., 1950, 3, 268.114 Ibid., p. 177.1l6 Ibid., 1949, 26, 371.118 Kaufman and Fankuchen, ibid., 1949, 20, 733.11# Brown and Farthing, Nature, 1949, 164, 915.Wurz and Sharpless, Analyt. Chem., 1949, 21, 1446.lal Matthews, Warren, and Mitchell, ibid., 1950, 22, 514.la2 Merritt, Cutter, Golden, and Lanterman, ibid., p. 519.les Ibid., p. 425.(p. 399).ibid., 1949,21, 24; 1950,22, 16.Hochgesang, ibid., p. 1248.111 Perrine, ibid., p. 262.113 Thewlis, J .Sci. Instr., 1950, 27, 72.115 Ibid., p. 154.117 Clifton, Rev. Sci. Instr., 1950,21,339.184 Acta Chem. S a n d . , 1950, 4, 559408 ANALYTICAL CH.RMIS!CRY.Rapid progress is now being made in the development and application ofhigh-fi-equency titrimeters, which have been reviewed at length.la5 Instru-ments giving good sensitivity, stability, speed and ease of operation havebeen built (operating up fa 40 Mc./sec.) ; their use has been exemplified byacid-base neutralisations, precipitation reactions, formation of complexes,and redox titrations.126 Blaedel and Malmstadt 12' have compared thepotentiometric, conductometric, and high-frequency titration procedures forthe determination of chloride by mercuric nitrate, and show that the high-frequency end-point is superior, although it is still inferior to end-points inargentometric titrations.A new titrimeter, operating a t 350 Mc. persecond, has also been described 12* by which it is possible to carry out accuratetitrations in presence of a considerable quantity of foreign electrolyte.The revival of interest in electroanalysis or coulometricanalysis has continued ; Lingane 129 has described an improved apparatus(" potentiostat ") for maintaining constant cathode potential, and anelectromechanical integrator which integrates the curve drawn by a recofdingp0tentiometer.l3~ Lamphere and Rogers 131 and Allen 132 have alsodescribed stable instruments which give constant cathode potential.Maxwell and Graham 133 have reviewed the applications of the mercurycathode and point out that the technique is especially useful in removinglarge concentrations of one or more elements before polarographic determin-ations of minor components.A review has been given of the advantagesand disadvantages of electroanalysis as a method of separation; 134 theproblems which arise in devising a quantitative separation by electro-analysis on the submicrogram scale have been discussed by Rogers.135The technique known as coulometric titration with amperometric end-point has received further attention ; this process involves timing a reactionoccurring with 100% current efficiency at the electrode, followed by a rapidincrease in current after the end-point has been reached. Farrington andhis collaborators have continued their work on the use of electrolytically-generated bromine1a6 and have extended the method to determination oftervalent arsenic by means of iodine and ch10rine.l~~ Cooke andFurman have described a similar technique for titration of ceric sulphateand potassium dichromate by means of ferrous iron generated a t a platinumelectrode.The methods of derivative and differential polarographyElectroanalysis.Polarography.lZ5 Analyt.Chem., 1950, 22, 734.lZ6 Anderson, Bettis, and Revinson, ibid., p. 743; Anderson and Revinson, ibid.,p. 1272; West, Burkhalter, and Broussard, ibid., p. 469 ; Blake,AnaEyst, 1950,75,32,689.127 Analyt. Chem., 1950, 22, 1410.lZg Ibid., 1949, 21, 497; 1950, 22, 1169.lS1 Ibid., p. 463.133 Chem.Reviews, 1950, 46, 471.la4 Ashley, Analyt. Ghem., 1950, 22, 1379.136 Wooster, Farrington, and Swift, ibid., 1949, 21, 1457.137 Ramsey, Farrington, and Swift, ibid., 1950, 22, 332.138 Farrington and Swift, ibid., p. 889.128 Idem, ibid., p. 1413.130 Lingane and Jones, ibid., p. 1220.13% Ibid., p. 804.135 Ibid., p. 1386.lS9 Ibid., p. 896CROPPER : PHYSICAL AND PHYSICOCHEMICAL METHODS. 409devised by Heyrovsky 14* and by Semerano and Riccoboni 141 have presenteddifficulties which have delayed more general adoption. Derivative polaro-graphy automatically gives curves representing A i l A E versus E , and id ofvalue in dealing with close half-wave potentials (e.g., for sodium and lithium)and for giving specific waves; differential polarography, on the other hand,compares two similar solutions so that (a) the effect of a major and moreeasily-reduced component is eliminated or ( 6 ) the concentrations of twosolutions can be compared more accurately.These techniques, potentiallyof great analytical value, require synchronisation of the drop formations toprevent appearance of a succession of nodes in the recorded polarogram.The use of capillaries with very short drop time, and Heyrovsky's streaming-mercury electrode, have not proved the complete answer to this problem.Airey and Smales 142 have given a very detailed account of their studies oncontrolled disengagement of a mercury drop, by electrostatic or * electro-mechanical means, and show that two capillaries can be accurately syn-chronised.Circuits are also given for modifying a Cambridge polarographfor work on derivative or differential polarography, and the performance ofthe modified instrument, with synchronised drops, has been described forboth methods ; this work will undoubtedly stimulate further research in thisfield, and publications on particular analytical problems can be expected.Snowden and Page 143 have given a detailed description of an improvedcathode ray polarograph, with results on inorganic and organic mixtures andalso on the use of the instrument for following rapid reactions; Delahay 144has constructed an improved apparatus and procedure for recording wavesa t high rates of potential variation, and also a portable electronic instrumentfor general purposes.145From a comparison of potentiometric and polarographic measurements,Stone 146 has concluded that pH effects may not be identical if reduced speciesare stabilised by resonance, and that buffer constituents play a vital r6le inthe polarographic reduction if a relatively stable species is formed betweenthe buffer anion and either the starting material or its reduction products.The value of Trilon B (ethylenediaminetetra-acetic acid) as a base solutionhas been emphasised; 14' it strongly displaces the reduction potentials ofnumerous elements, so that cobalt, for example, is reduced at a very lownegative potential and preliminary separation from other metals is notnecessary in the analysis of steel.A polarographic study has been made ofthe stability of the complexes formed between heavy metals and the' complexones " (ethylenediaminetetra-acetic acid and nitrilotriaceticacid) .I48The determination of small concentrations of zinc has been studied,149140 Chem.&sty, 1946, 40, 222 ; Analyst, 1947, 72, 229.141 cfazzettu, 1942, 72, 297.143 Anctlyt. Cilem., 1950, 22, 969.145 Anulyt. Chem., 1949, 21, 1425.14' Souchay and Foucherre, Analyt. Chim. Acta, 1949, 3, 252.148 Koryta and Kossler, CoEL Czech. Chem. Comm., 1950, 15, 241.142 Analyst, 1950, 75, 287.144 J . Phys. Colloid Chem., 1950, 54, 402.146 J . Electrochem. SOC., 1950, 97, 63.Champa and Wallach, Analyt. Chem., 1950, 22, 727410 ANALYTICAL CHEMISTRY.and methods have been given for determination of zinc in zinc ores,150 incompounded rubber,l51 in and in waters ; 153 polarographic methodshave been described for common impurities in refined lead,154 in calcium,155and in high-quality indium,l56 for cobalt in presence of excess of copper,iron, and nicke1,157 for trace metals in gelatins,15* for titanium in paintpigments (after removal of copper and antimony),159 and for uranium inpresence of iron, copper, and phosphates.ls0 Polarographic determinationof aluminium has been based on reduction of an aluminium di-o-hydroxyazo-complex.l6l Furness 162 has discussed the application of polarography tothe analysis of dithionites, and has outlined procedures for the determinationof thiosulphate, sulphide, and trithionate in presence of dithionite.Elving 163 has given recently a review on the polarographic behaviour oforganic compounds, adding to those already given by W a w ~ o n e k , ~ ~ ~ andmention is, therefore, made only of subsequent papers.The value ofpolarographic methods for the analysis of fine chemicals, for both inorganicand organic impurities, has been emphasised by Osb0rn.1~~ Carbon tetra-chloride gives two reduction waves corresponding to reduction to chloroformand to methylene chloride respectively, whereas chloroform only gives theone wave,166 so that analysis of mixtures of chloroform and carbon tetra-chloride can be done polarographically . The polarographic reduction ofdiazotised arylamines has been studied,ls7 and it is claimed that the measure-ment of concentrations of diazonium solutions by this means is moregenerally applicable than the gasometric or colorimetric methods.Sartori and Liberti le8 have shown that, in the polarography of mercapto-benzothiazole, the anodic reaction does not correspond to formation ofdisulphide, but to formation of the mercury compound, and also that theheight of the cathodic wave is proportional to [H+] of the buffer.Studieson quantitative polarographic methods have been made on g l ~ t a t h i o n e , ~ ~ Chloromycetin,l70 " Parathion ",171 n i n h ~ d r i n , l ~ ~ and cholesterol.173 Hall 17*150 Semerano and Gagliardo, Analyt. Chim. Acta, 1950, 4, 422.lS1 Poulton and Tarrant, Trans. Inst. Rubber Ind., 1950, 25, 328.lS2 Wiley, Deloney, and Winstead, Analyt. Chem., 1950, 22, 201.153 De Salas and Graells, Anal.Asoc. Quim. Argentina, 1949, 37, 208.lS4 Cozzi, Analyt. Chim. Acta, 1950, 4, 204.lS6 Haupt, Olbrich, and Nause, 2. Electrochem., 1950, 54, 67.15? Kolthoff and Watters, Analyt. Chem., 1950, 22, 1422.lS8 Michel and Maron, Analyt. Chim. Acta, 1950, 4, 542.15s Potts, Canadian J . Res., 1950, 28, F , 128.160 Block, Bull. SOC. chim., 1949, 16, 831.181 Willard and Dean, Analyt. Chem., 1950, 22, 1264.16z J . SOC. Dyers Col., 1950, 66, 270.164 Ibid., 1949, 21, 61; 1950, 22, 30.1~ Kolthoff, Lee, Stocesova, and Parry, Analyt. Chern., 1950, 22, 521.167 Elofson, Edsberg, and Mecherly, J. Electrochem. SOC., 1950, 97, 116.188 Ibid., p. 20.16@ Coulson, Crowell, and Friess, Analyt. Chern., 1950, 22, 525.170 Hess, ibid., p.649.172 UlEak, Spalek, and KrStkf, Coll. Czech. Chem. Comm., 1950, 15, 340.173 Talafant, ibid., p. 232.155 Stage and Banks, ibid., p. 551.163 Analyt. Chem., 1950, 22, 482.185 Analyst, 1950, 75, 671.171 Bowen and Edwards, ibid., p. 706.174 Analyt. Chem., 1960, a, 1137CROPPER : PHYSICAL AND PHYSICOCHEMICAL METHODS. 41 1has described the determination of traces of elemental sulphur in petroleumfractions, using methanol and pyridinium hydrochloride as an electrolyticsolvent miscible with hydrocarbons, and claims that the method is rapid,sensitive, and free from interference from organic sulphides, disulphides, andthiophen. The polarographic determination of tetraethyl-lead in petrolhas received attention; a rapid method has been described by Hansen,Parks, and Lykken,l75 and a direct-reading instrument, based on the use ofantimony as a pilot ion, has been developed by Offutt and S ~ r g .l ~ ~ Parksand Lykken 177 have reviewed the applications of potentiometric, ampero-metric, and polarographic methods for determination of common constituentsin petroleum products.The use of ethylene glycol monoalkyl ethers (Cellosolves) as non-aqueoussolvents for organic polarography has been a d ~ 0 c a t e d . l ~ ~ Gordon andJones 179 have reviewed previous work involving distribution between twoimmiscible solvents, followed by polarographic measurement on one of thephases; the name " partition polarography " is proposed, and formulae arededuced which predict the accuracy of the method and permit selection ofoptimum experimental conditions for each system with a minimum ofexperimental work.An improved amperometric titration cell, foruse with a dropping-mercury electrode, has been described 180 which usescontinuous gas flow for oxygen removal and solution mixing.A furtherreport has been made by Kolthoff and Liberti 181 on the titration of copperand ferric iron with cupferron ; conditions for the amperometric titration(dropping-mercury electrode) of zinc and indium with ferrocyanide havebeen studied.182 The rotating platinum electrode has been used for titrationof zinc by ferrocyanide 183 and for chromium and vanadium (after conversioninto chromate and vanadate) by means of ferrous ammonium sulphate.ls4It has been shown 185 that amperometric titration of thiols under theconditions described by Kolthoff and Harris 186 gives low results due topresence of oxidising agents in ammoniacal ethanol and dissolved air in thesilver nitrate solution.A modification of the method for thiol groups hasbeen developed for use with microgram quantities (in biological material),in which a vibrating platinum electrode is used as a combination electrode-stirrer.MIUS Spectrometry.-The mass spectrometer is rapidly growing inAmperometric Titrations.175 Analyt. Chem., 1950, 22, 1232.178 Parks and Hansen, ibid., p. 1268.lao Laitenen and Burdett, ibid., p. 833.lS1 Analyst, 1949, 74, 635; see J. Amer. Chem. SOC., 1948, 70, 1879.Nimer, H a m , and Lee, Analyt. Chem., 1950, 22, 790.lS3 Butenko and Rynskaya, Z h w .Anal. Khim., 1950,5,145; Chem. Abs., 1950,44,lE4 Parks and Agazzi, Analyt. Chem., 1950, 22, 1178.lS6 Strafford, Cropper, and Hamer, Analyst, 1950, 76, 55.17t1 Ibid., p, 1234.179 Ibid., p. 981.177 Ibid., p. 1444.6345b.I n d . Eng. Chem. Anal., 1946, 18, 161.Rosenberg, Perrone, and Kirk, AnaZyt. Chem., 1950, 22, 1186412 ANALYTICAL CHEMISTRY.importance as an analytical tool ; its applications have now expanded beyondthe limited fields of gas analysis and hydrocarbon analysis, and with improvedtechniques in handling samples of very low vapour pressure, the possibilitiesare immense. In addition to the reviews in Anulyticul Chemistry,l thearticle by Washburn 188 provides general information of special value tonewcomers to the subject.New instruments have been described byK e r ~ i n , ~ ~ ~ and by Duckworth,lg0 and an instrument has been developedfor the French Petroleum 1 n ~ t i t u t e . l ~ ~ Special interest must be given to thenew three-stage non-magnetic instrument, employing the principle of velocityselection, which has been developed by Bennett lg2 and which is small,simple in operation, and of high sensitivity; currents are of a magnitudewhich makes recording comparatively simple, and resolution is relativelyindependent of source slit width. Adaptation is being made to rapidscanning of the mass spectra, with display on a cathode-ray oscilloscope ;the instrument has been described as “ the poor man’s mass spectrometer ’’and although of more limited range and accuracy than the highly developedconventional instrument, it opens up innumerable possibilities for analyticalapplications.Improved methods of introducing liquid samples have been de-scribed,l939 lg4* lg5* 196 mainly in connection with the analysis of oxygen-containing samples ; results for synthetic mixtures of methanol, form-aldehyde, formic acid, methyl formate, and methylal were accurate only toabout 5%,lg4 whereas accuracy to within 2% is claimed in the analysis of3-, 4-, and 5-component mixtures of alcohols and other oxygenated deriva-tives containing 6 carbon atoms.lQ6 The “ internal standard ” method ofHindin, Grosse, and Kirshenbaum lg7 has been applied to the analysis ofliquid oxygenated C1-C5 mixtures, benzene being used as internal standard.lg5Several methods of introducing liquid samples of neohexane and of styrenehave been compared.lg8Satisfactory means of preparing deuterium-hydrogen mixtures in knownproportion, for calibration purposes, involved reducing deuterium oxide-water mixtures over zinc; 199 the deuterium content of water has beendetermined on a mass spectrometer after reaction with methylmagnesiumiodide to yield a mixture of methane and deuteriomethane.200Mohler has reported the mass-spectra data for ten C,H8 isomers 201 and188 “ Physical Methods in Chemical Analysis,” edited by W, G.Berl, Acad. PresslSg Rev. Sci. Inetr., 1950, 21, 96.lgl Bertein, Vastel, Reis, Buzon, and Nief, Rev. Inst.fran9. Pdtrole, 1950, 5, 59.lg2 Rev.Sci. Instr., 1950, 21, 578; J . Appl. Physice, 1950, 21, 143.lg3 Friedel, Sharkey, and Humbert, Analyt. Chem., 1949, 21, 1572.lo* Langer and Fox, ibid., p. 1032.lg8 Gifford, Rock, and Comaford, ibid., p. 1026.lg8 Wise, Reese, Dibeler, and Mohler, J . Res. Nat. Bur. Stand., 1950, 44, 215.lgB Alfh-Slater, Rock, and Swislocki, AnaEyt. Chem., 1950, 22, 421.201 Mohler, Bloom, Williamson, Wise, and Wells, J . Res. Nut. Bur. Stand.,Inc., 1950.190 Ibid., 1950, 21, 54.lg5 Thomas and Seyfried, ibid., p. 1022.lg7 Ibid., p. 386.Orchin, Wender, and Friedel, ibid., 1949, 21, 1072.1949,43, 533CROPPER : PHYSICAL AND PHYSICOCHEMICAL METHODS. 413for 35 nonanes,202 and points out that analysis of mixtures of nonanes willgenerally be impossible unless the material is a narrow cut containingcomparatively few components.Results have been given 203 showing the reproducibility and accuracy ofanalyses of a standard sample of carburetted water gas, by laboratories co-operating with a Sub-Committee d the American Society for TestingMaterials; low concentrations of solvents in air have been determined aftercondensation by liquid nitrogen.204 O’Neal 91 has described a combinationof mass-spectrometer measurement and infra-red measurement for theanalysis of C,-C, paraffins and mono-olefin mixtures.Radioactive Tracer Methods.-In addition to the general review articleon ‘‘ nucleonics ” by Gordon,2*5 monitoring instruments have been reviewedby Taylor 206 and Curtiss; 207 several reports have been given on thebehaviour of, or improvements to, counters,208 and an ionisation chamberhas been described by Tompkins, Wish, and B~rnett.~O~ Beamer andAtchison 210 have described quantitative techniques for 14C in compoundsof high specific activity, involving conversion into carbon dioxide and thenceinto barium carbonate, which is deposited on an aluminium plate ; measure-ment as carbon dioxide, admixed with carbon disulphide vapour, has beenstudied by EidenofK211 Radio-phosphorus has been used212 to show thatthe zinc and cadmium methods are equally eficient in separating ortho- frompyro-phosphate.Very small amounts of iodide have been determined 213 byconversion into iodate, reaction with excess of radioactive iodide of knownspecific activity, extraction of the radioactive iodine, and measurement byy-ray counting.A study of the precision attainable in P-activity counting,with special reference to the determination of cerium, has been made,214 andradioactive assays involving calcium 215 and elementary sulphur 216 havebeen reported. The use of radioactive silver in a radiometric titration hasbeen described by Langer.217Methods involving Separations.-Little new work has been published onmethods involving separation except in the fields of solvent extraction andchromatography. Rose 218 has reviewed the theory and practice of analyticaldistillation, and Starr, Anderson, and Davidson 219 have given it second1950, 44, 291.2O2 Mohler, Williamson, Wise, Wells, Dean, and Bloom, J. Res. Nut.Bur. Stand.,2os Shepherd, ibid., p. 509; Analyt. Chem., 1950, 22, 885.204 Happ, Stewart, and Brockmyre, ibid., p. 1224.a05 Ibid., 1949, 21, 96. 2 0 ~ J . Sci. Instr., 1950, 27, 82.207 U.S. Nat. Bur. Stand., Circular No. 490, 1950.208 Brown and Maroni, Rev. Sci. Instr., 1950, 21, 241 ; Laufer, ibid., p. 244; Bern-209 Anulyt. Chem., 1950, 22, 672.210 Ibid., p. 303.212 van der Straaten and Aten, Rec. Truv. chim., 1950, 69, 561.213 Raben, Analyt. Chem., 1950, 22, 480.a15 Shirley, Owens, and Davis, ibid., p. 1003.416 Kirshenbaum and Grosse, ibid., p. 613.217 Ibid., p. 1288. 218 Ibid., p. 1369.stein and Ballentine, ibid., p. 158 ; Wilkinson, J. Sci. Instr., 1950, 27, 36.211 Ibid., p. 529.a14 Freedman and Hume, ibid., p. 932.21D Ibid., 1949, 21, 1197414 ANALYTICAL CHEMISTRY.paper in continuation of their studies 220 on charging rates, distillation rates,and fraction cut-points.A review has been given 221 on the theory, scope,and methods of recrystallisation, and an apparatus has been designed 222 forseparations by sublimation under reduced pressure, the sublimate beingdeposited on a removable transparent plastic film. Mellon 223 has discussedsome general aspects of separations in analytical chemistry.The apparatus for counter-current liquid-liquid extraction, described by Craig and Post,224 has now been greatlyimproved ; 225 simple apparatus for similar purposes are described byRaymond,226 by Lochte and M e ~ e r , ~ ~ ' and by Nolan.228 Recent studies havebeen made of the distribution characteristics of 18 organic mono- and p l y -carboxylic acids between water and numerous organic solvents,229 and of 18polynuclear hydrocarbons between cyclohexane and 80% ethan01,~3O andapplications in analysis of mixtures within these classes have been given;the use of the Craig machine for determination of 2 : 4-dichlorophenoxyaceticacid has been described by Warskowsky and S ~ h a n t z .~ ~ ' Nichols 232 hasderived expressions for the prediction and evaluation of results from counter-current distribution experiments, including a method for determining thenumber of transfers necessary for a given degree of separation and pair ofpartition coefficients. Theoretical aspects of the simple extraction ofinorganic ions or complexes have been discussed by Sande11.233If the number of papers published be taken as a guideto the importance of a particular analytical technique, there is no doubt thatchromatography now ranks as foremost.The reviews which have appearedfrequently 234 should be consulted for earlier references in each particularfield of application.The detection and measurement of colourless bands as they leave thechromatograph column has continued to receive attention ; Holman 236 hasextended the range of concentrations dealt with by the Tiselius-Claessoninterferometric apparatus by introducing the effluent liquid, when itsconcentration is constant at each step, into the comparison cell. Automaticrecording flow refractometer apparatus for adsorption analysis have beendescribed 236 which, while not as sensitive as the interferometer, open upXolvent Extraction Methods.Chromatography.aao Analyt.Chm., 1947, 19, 409.222 Gettler, Umberger, and Goldbaum, ibid., p. 600.a23 Ibid., p. 1342.225 Craig, ibid., 1950, 22, 1346.227 Ibid., 1950, 22, 1064.229 Marvel and Richards, ibid., p. 1480.a31 Ibid., p. 460.z34 Martin, Ann. Reports, 1948,45, 267; Ann. Rev. Biochem., 1950,19,517; Lederer," ProgTBs RBcents de la Chromatographie," Part 1, Hermann et Cie, Paris, 1949 ; Cook,Nature, 1949, 164, 300; Strain, Analyt. Chem., 1949, 21, 75; 1950, 22, 41; Clegg, ibid.,p. 48 ; Biochemical Society Symposium, No. 3, Partition Chromatography, 1949 ;Discussions of the Faraday Society, No. 7, Chromatographic Analysis, 1949.am Tipson, ibid., 1950, 82, 628.224 Ibid., 1949, 21, 500.itas Ibid., 1949, 21, 1292.228 Ibid., 1949, 21, 1116.230 Golumbic, ibid., 1950, 22, 579.aa3 Analyt.Chim. Acta, 1950, 4, 504. Ibid., p. 915.e35 Analyt. Chem., 1950, 22, 832.as6 Hellstrom and Borgiel, Acta Ckm. Xcand., 1949, 3, 401 ; Thomas, O'Konski, andHurd, Anulyt. Chem., 1950, 22, 1221CROPPER PHYSICAL AND PHYSICOCHEMICAL METHODS. 415possibilities for extensive application. The polarograph, set a t the requiredvoltage, has been used237 for following concentrations of proteins in theeffluent from columns, and an ultra-violet sensitive photomultiplier tube hasbeen used to locate zones of methyl benzoate, benzaldehyde, and anisaldehydeon silicic acid and alumina.238 Harvalik 239 has studied the illumination ofcolumns by infra-red radiation, and has developed an electronic imageconverter to convert the infra-red radiation into visible light, so that colour-less zones can be detected by a process analogous to the use of ultra-violetfluorescence.A very sensitive micro-electrode, consisting of a smallplatinum electrode bearing a thin film of silica gel containing a trace ofquinhydrone, has been fitted to a chromatograph column to provide potentio-metric indication of change of concentration in the emerging effluent.240The “ carrier displacement ” method suggested by Tiselius 241 has beenutilised by Tiselius and Hagdahl 242 with promising results in the separationof amino-acids and peptides ; this method involves interposing between thezones to be separated a number of substances of intermediate adsorptionaffinities which would form part of the chromatogram and afterwards couldbe removed by evaporation or extraction.Apparatus has been described 243 for chromatography on narrow filter-paper strips or strips of mercerised cotton, glass, wool, or thin asbestos withboth ascending and descending solvent flows.Howard and Martin 244 claimto have widened the scope of partition chromatography for higher fatty acidsby using ‘‘ unwettable ” kieselguhr, obtained by treating it with dichloro-dimethylsilane vapour, as the support fir the static phase, which can be theless polar of the two phases. Boldingh 245 has used natural and syntheticelastomers to hold the static phase, e.g., benzene absorbed in vulcanisedrubber, with a strong polar solvent as flowing phase, for the separation of thesaturated fatty acids c($-c,8 and for separation of these from hydroxy-acids.Rutter 246 has described a useful improvement in paper chromatographyby the capillary run-out technique ; apparatus has been constructed for themass production of two-dimension paper chromatograms 247 and for applyingseveral ml.of solution to a sheet of paper as a narrow band, in work onmacro-q~antities.~~~ The separation of micro-quantities of mixed pigmentshas been carried out by chromatography on a restricted channel of paper,through which passed a beam of monochromatic light directed on to a photo-multiplier tube; this, in turn, operated a pen-and-ink recorder so thattime-transmittancy graphs were obtained.249 Silica-impregnated paper hasa37 Drake, Acta Chem.Scand., 1950, 4, 448.236 Sease, AnaEyt. Chem., 1949, 21, 1430.240 Kamienski, Compt. rend. MBd. Acad. polon., 1949, 1-2, 7 ; Compt. rend. Sci.241 Kolloid Z . , 1943, 105, 101. 24a Acta Chem. Scand., 1950, 4, 394.a43 Longenecker, Analyt. Chem., 1949,21,1402. a44 Biochem. J., 1950, 46, 532.a45 Rec. Trav. chirn., 1950, 69, 247. a46 Analyst, 1950, 75, 37.a47 Datta, Dent, and Harris, Biochem. J . , 1950, 46, Proc, xiii.a48 Yanofsky, Wasserman, and Bonner, Science, 1950, S, 61.24* Muller and Clegg, Analyt. CFem., 1949, 21, 1123.a39 Ibid., 1950, 22, 1149.math. nat. Acad. polon., 1949, 3-5, 11, 13416 ANALYTICAL CHEMISTRY.been used to achieve separations which could not be done on ordinary filterpaper, such as separation of the 2 : 4-dinitrophenylhydrazones of ethylmethyl, methyl propyl, and methyl isopropyl ketones.2mThe outstanding feature of the chromatographic techniques now availableis their wide applicability ; past reviews 234 have shown that chromatographyhas been applied to almost all subjects of great importance (e.g., fissionproducts of uranium, fatty acids, amino-acids, sugars, penicillins, carotenoids,to mention but a few), and there have been many recent refinements andimprovements in these applications; it is not possible, however, to reviewthem all in this Report (though each in its own way may present an advancein technique for dealing with particular mixtures) and mention can be madeonly of selected items published in 1950.Several important papers have appeared on the separation of the hydro-carbons in cracked petroleum ; Fink, Lewis, and Meiss 251 have made adetailed study of adsorption characteristics (and regeneration techniques) ofsilica gel for fractionating paraffins, olefins, and aromatic compounds by" frontal analysis " a t -40°, and have assessed the influence of the importantvariables affecting the efficiency of the process.Clerc, Kincannon, andWeir 252 have used " displacement development " and elution procedures onsilica gel for separating paraffins and mono-, di-, and tri-cyclic aromaticcompounds from petroleum oils. Petroleum fractions have also beenanalysed by chromatographic separation on silica into 4 parts, each of whichis then tested by conventional m e a n ~ .~ ~ 3 Adsorption on Florisil (syntheticmagnesium silicate) and elution by'pentane has been used 254 to separatehydrocarbons from nitrogenous and other heterocyclic compounds in shale-oil distillates ; the chromatographic method for analysis of shale oilnaphthas 255 has been improved 256 and consists of " displacement develop-ment " by octanol or cyclohexanol, at 70°, to separate paraffins, olefins, andaromatic CompoundB, followed by boiling-point and refractive-index measure-ments for determining the percentage of paraffins and cycloparaffins. All theabove methods use refractive index of the percolate to follow progress ofcolumn development.Frontal analysis and displacement development analysis of fatty acidshave been improved 257 by decreasing the solubility in alcohol by addition ofwater, or by lowering the temperature; adsorption on alumina has beenused to separate the 2 : 4-dinitrophenylhydrazones of aldehydes arising fromamino-acids treated with ninhydrin, as part of a method for determiningis0leucine.~5* Separation of water-soluble organic acids on a partitionKirchner and Keller, J.Amer. Chem. SOC., 1950, 72, 1867.251 Analyt. Chem., 1950, 22, 850, 858.253 Ibid., p. 864.252 Spakonski, Evans, and Hibbard, ibid., p. 1419.e54 J. R. Smith, C. R. Smith, and Dinneen, ibid., p. 867.355 Dinneen, Bailey, Smith, and Ball, ibid., 1947, 19, 992.256 Dinneen, Thompson, Smith, and Ball, ibid., 1960, 22, 871.z5' Hagdahl end Holman, J.Amer. Chem. SOC., 1950, 72, 701.258 Lohr, Biochem. Z., 1950, 320, 115CROPPER : PHYSICAL AND PHYSICOCHEMICAL METHODS. 417chromatographic column has been carried out 259 by making the developingliquid progressively more polar by adding increasing amounts of butanol tochloroform. A collaborative study of the partition method for volatilefatty acids has been reported.260The paper partition method attracts much attention. Since theappearance of the extensive general review by Clegg 261 further advanceshave been reported in some important applications ; further general inform-ation on inorganic separations has been given by Burstall, Davies, Linstead,and Wells,262 and conditions have been described for the separation of thecopper and the tin gr0up,~63 and nickel and ~ o b a l t .~ 6 ~ A method for deter-mination of potassium 2G5 depends on development with sodium leadcobaltous hexanitrite solution, and measurement by planimetry. For workon 1-2 ml. of solution, strips of paper pulp 6 mm. thick have been used, fordetermination of thallium. 266Block 2G7 has given detailed directions for the separation and determin-ation of all the common a-amino-acids on one- and two-dimensional paperchromatograms; reports have been made on the suitability of differentpapers 268 and water-miscible solvents 269 for use in amino-acid separations.The method has been used for the identification of the amino-acids fromphenylthiocarbamyl peptides,270 and for the determination (by planimeter)of the amino-acid residues of insulin.271 Paper chromatography has beenapplied 272 to the separation of p-iodobenzenesulphonyl derivatives formedfrom amino-acids with a reagent containing radioactive 1311 ; the recoverywas measured by adding known amounts of known p-iodobenzenesulphonylderivatives containing 35S, immediately after forming the 1311 derivatives ofthe amino-acids. The bands were located by radio-autographs, andconstancy of l311/355 ratios in successive portions of the bands provided atest of the validity of the analysis.Chloroacetic acid and a-chloropropionic acid have been separated onpaper with use of indi~ators,~~3 and zones containing keto-acids have beenmade visible by conversion into the semicarbazones and viewing under ultra-violet light; 274 the method has been applied to small amounts of hydroxy-259 Marvel and Rands, J . Amer. Chem. SOC., 1950, 72, 2642.260 Ramsey and Hess, J . Assoc. 08. Agric. Chem., 1950, 33, 848.261 Analyt. Chem., 1950, 22, 48.262 J., 1950, 516.263 Lederer, Analyt. Chim. Acta, 1949, 3, 476.264 Lacourt, Mikrochena., 1950, 35, 262.265 Beerstecher, Analyt. Chem., 1950, 22, 1200.266 Anderson and Lederer, Analyt. Chim. Acta, 1950, 4, 513.2 6 7 Analyt. Chem., 1950, 22, 1327.268 Kowkabany and Cassidy, ibid., p. 817.268 Bentley and Whitehead, Biochem. J . , 1950, 46, 341.270 Edman, Acta Chem. Scand., 1950, 4, 283.271 Archer, Fromageot, and Justisz, Biochim. Biophys. Acta, 1950, 5, 81.272 Keston, Udenfriend, and Levy, J . Amer. Chem. Soc., 1950, 72, 748.273 Renard, Bull. SOC. chim. Belg., 1950, 59, 34.274 Magasanik and Umbarger, J. Amer. Chern. Soc., 1950,72, 2308.REP.-VOL. XLVII. 41 8 ANALYTICAL CHEMISTRY.benzoic acids and amides 275 and to p-aminobenzoic acid derivatives.276The behaviour of numerous phenolic compounds has been studied277 andapplied to analysis of tea catechins 278 and wood extracts; 279 in a veryelegant analysis of certain flavonol 3-glycosides, the pigment zones werelocated under ultra-violet light, leached from the paper with aluminiumchloride, and the ultra-violet absorption intensities of the flavonoid-aluminium complexes were measured on a Beckman spectrometer.280Halogenated aliphatic and aromatic hydrocarbons, and n-octanol havebeen held as the static phase on acetylated paper, for the separation of thedinitrophenylhydrazones of the carbonyl fission products of sugars.281 Themethod of Goodall and Levi 282 for penicillins has been improved, by usingmixtures of pure penicillins as standards,283 or by conversion into thchydroxamic acid derivatives, separation on paper strips, development withferric chloride, and extraction of the iron complexes for colorimetric measure-ment ; 284 application of the latter procedure in penicillin production controlhas been reported.285 Progesterone has been determined 286 in commerciallyprepared oils, by paper chromatography, location by the m-dinitrobenzene-potassium hydroxide reaction, extraction, and measurement by its ultra-violet absorption.Chromatography on ion-exchange resins, applied in elegant ways byteams of American investigators on rare earths, and by several independentworkers on amino-acids, has been reviewed in detail quite recently byTompkins 287 and Schubert,288 and little can be added in this Report.Miscellaneous.Numerous papers have appeared on subjects outside the broad classific-ations given in this Report, but few can be mentioned. The use ofthermistors for cryoscopic measurements 289 and apparatus for micro-determination of melting, transition, and segregation points down to -40"have been described; 290 Siggia and Hanna 291 have devised a method foranalysis of one-phase ternary mixtures by titration with one of thecomponents (immiscible with the others) until a turbidity results. Anempirical relationship between refractive index and wave-length has been2 7 5 Bray, Thorpe, and White, Biochem. J., 1950, 46, 271.276 Keleman, Tanos, and Halmagyi, ibid., 47, 138.277 Bate Smith and Westall, Biochim. Biophys. Acta, 1950, 4, 427.278 Bradfield and Bate Smith, ibid., p. 441.279 Lindstedt, Acta Chem. Scand., 1950, 4, 448.280 Gage and Wender, Analyt. Chem., 1950, 22, 708.281 KoBtii and Slavik, Coll. Czech. Chem. Comm., 1950, 15, 17.282 Analyst, 1947, 72, 277.281 Baker, Dobeon, and Martin, ibid., p. 651.285 Albans and Baker, ibid., p. 657.286 Haskine, jun., Sherman, and Allen, J . Biol. Chem., 1950, 182, 429.287 Analyt. Chem., 1950, 22, 1352.2e8 Ibid., p. 1359.290 Tschamber, Mikrochem., 1950, 55, 353,291 Analyt. Chem., 1949, 21, 1086.283 Glister and Grainger, ibid., 1950, 75, 310.289 Zeffert and Hormats, ibid., 1949, 21, 1430CROPPER : PHYSICAL AND PHYSICOCHEMICAL METHODS, 419worked out 292 for calculation of one dispersion from any other, for use inhydrocarbon analysis ; the use of refractive index-density charts has beenextended to the analysis of liquid halogen and oxygen compo~nds.~~3 A newform of dew point-bubble point apparatus, for molecular weights and foranalysis of binary liquid and apparatus for precision pH measure-ment with a glass electrode295 have been noted. Tadayon, Nissan, andGarner 296 have described apparatus for determination of magneto-opticalrotation and its application to analysis of ternary hydrocarbon mixtures. Adetailed review has been given 297 on automatic operations in quantitativeanalysis from the point of view of the individual unit operations involved inany general method of analysis.F. R. C.P. R. CROPPER.H. E. STAOG.H. N. WILSON.Sankin, Martin, and Lipkin, AnuZyt. Chem., 1950, 22, 643.298 Gilmore, Menaul, and Schneider, ibid., p. 892.204 Feller and McDonald, ibid., p. 338.295 Kraus, Holmberg, and Borkowski, ibid., p. 341,Ibid., 1949, 21, 1532.Patterson and Mellon, ibid., 1950, 22, 136