ANALYTICAL CHEMISTRY.THERE is little of entirely novel character to report in analyticalchemistry during the year under review. Several improvementsand advances in potentiometric and conductometric determinationshave been recorded. The difficulties attaching to many of theprocesses of estimating and detecting substances by the ordinarymethods are again discussed and examined in detail. Micro-chemical determinations are likewise being actively investigated,with a considerable measure of success. Some attention has beendirected to the separations of the rarer alkali metals and a usefulmodification of the bleaching method for the colorimetric deter-mination of fluorine has been described. We have, in this Report,given a rbume' of the more important methods for the estimationof large and of small quantities of fluorine (excluding the well-known silicon fluoride method), since the accurate determinationof this element is becoming of increasing importance in manydirections.Inorganic Analysis.for the rapidand ready detection of certain metals by use of drops of the solutionsto be tested have now been extended to embrace all the commoncations; the scheme avoids the use of hydrogen sulphide.Theprecipitates produced in solutions of the heavy metals by 36 aliphaticand heterocyclic bases have been studied with a view to the possibleapplication of the results to the separation of various metals. Inparticular, the violet-blue precipitate yielded by glyoxaline withcobalt constitutes a delicate test for this metal.Diphenylthio-carbazone forms highly-coloured compounds with a number ofheavy metals most of which are soluble in chloroform and carbondisulphide. Sensitive and characteristic tests for zinc and copperare based on this rea~tion.~Traces of silver in ores can be detected by microchemical reactionsdue t o the formation of rubidium silver gold ~hloride.~ The form-1 N. A. Tananaev, Z. anorg. Chem., 1924, 133, 372; 140, 320; A . , 1924,2 Ulcraine Chem. J., 1926, 2, 27; A., 927.8 E. J. Fischer, W k . Ver6ff. Siemens-Konz., 1925, 4, 171; A., 1926, 492.6 W. Geilmann, 2. anwg. Chem., 1926, 155, 192; A., 1019.Qualitative.-The methods previously describedii, 671; 1925, ii, 324.Ibid., p. 158; A., 1926, 491.18ANALYTICAL CHEMISTRY.187ation of a copious white precipitate on addition of 1% brucinesulphate and potassium bromide t o a cadmium solution serves t odetect this metal in the presence of copper,6 and the reaction maybe utilised to differentiate between bromides and chlorides. Micro-scopic examination of the deposit on a copper wire acting as cathodeis capable of revealing mercury when present to the extent of O ~ Y0.5 mg. per litre.'Aluminium gives with an extract of dried alkanet root a charac-teristic purple lake when ammonia is added in excess.8Nickel sulphate gives with a large excess of concentrated hydriodicacid an intense red colour similar t o that of ferric thiocyanate;this colour disappears on sufficient dilution by water. Charac-teristic effects on the colour and absorption spectra of solutions ofcobalt salts are induced by hydrobromic and hydriodic acidsSBSolutions of cobaltous salts give with potassium ferrocyanide in thepresence of ammonia a red coloration, perceptible in very dilutesolutions, and the test is not vitiated by a considerable excess ofnickel salts.1° The sensitiveness of the borax bead test for cobaltcan be greatly increased by microscopical examination of minuteborax beads.11The sensitivity of a number of reagents for the strontium ion hasbeen worked out ; calcium can be detected, after removal of bariumand strontium as chromates by prescribed methods, by means ofpotassium ferrocyanide.12 Sodium ferrocyanide in the presence ofcalcium chloride gives a precipitate with aqueous solutions con-taining rubidium and cssium ; potassium and ammonium are onlyprecipitated from 50% ethyl-alcoholic solution, whilst sodium andlithium are not affected. These reactions afford a means of soparat-ing the alkalis.13 Thallium even in dilute solution also forms aprecipitate when calcium acetate is used with sodium ferrocyanide.14Complete qualitative separations of the various metals of thealkali group are described in a lengthy paper.15 Optimum con-e R.Meurice, Ann. Chim. anal., 1926, [ii], 8, 130; A., 703. ' H. S. Booth and N. E. Schreiber, J . Amer. (?hem. SOC., 1925, 47, 2625;* H. W. Estill and R. L. Nugent, ibid., 1926, 48, 168; A., 263.lo L. Minddev, Mitt. wiss.-tech. Arb. Republ. [Ems.], 1924, 13, 57; A.,A,, 1923, 40.G.Denig6s. Compt. Tend., 1926, 183, 55; A., 930.1926, 264.l1 J. M h , KoZZ.-Che+n. Beih., 1926, 23, 309; A., 1116.l* D. Raquet, Ann. Chim. anal., 1926, [ii], 8, 3; A., 262.Is T. Gaspar y Arnal, Anal. 2%. Q u h , 1926, 24, 99; A., 691; F. Diaz deRada and T. Gaspar y Arnal, &bid., p. 160; A., 702.T. Gaspar y Arnal, ibid., p. 153; A,, 703.S. At0 and I. Wada, Sci. Papers Imt. Phys. Chem. Rw., 1926, 4, 263;A., 929188 ANNUAL REPORTS ON THE PROGRESS OF CHEMISTRY.ditions under which the oxalate test for sodium should be carriedout are described; borax is the only common sodium compoundwhich does not respond to this test. Potassium pyroantimonateis a better reagent and may be used in presence of boric acid.ls Theprecipitation of sodium magnesium uranyl acetate in the presenceof alcohol is of value in the detection of small quantities of sodiumin the presence of potassium and magnesium, but is valueless forquantatitive work.1'For the microchemical detection of germanium, no characteristicreagent was discovered; the most practicable test was found todepend on the conversion into sodium fluogermanate or rubidiumgermanomolybdate following a preliminary separation from severalelements which normally give positive tests with fluorides andmolybdates.ls In the absence of iron and metals of the fist twoanalytical groups, the coloration given with pyrocatechol indicatesthe presence of cerium even in minute traces.19The hydrogen peroxide test for titanium is not suitable for spotanalysis on filter-paper ; for this purpose, the red coloration givenby chromotropic acid is most satisfactory.Copper, iron, andtitanium interfere with the ferrocyanide spot-test for uranium,but this difficulty may be obviated by reducing the former withpotassium iodide and decolorising the iodine with thiosulphateaaOThe lakes formed by " aluminon " (aurintricarboxylic acid) with anumber of the rarer metals have been more completely investigated ;with the exception of the beryllium lake, all are dissolved ordecolorised by ammonium carbonate.21 Reactions of a number ofhydroxyanthraquinone derivatives with zirconium and hafniumare described ; the reddish-violet solution obtained in the case ofalizarinsulphonic acid is a sensitive reagent for fluorides, which,by converting the zirconium into a complex fluoride, cause thesolution to become yellow.22 As the result of a study of the reac-tions between vanadic acid, hydrogen peroxide, and sulphuric acid,the best concentration of sulphuric acid for the detection of vanadiumby this test has been workedTraces of soluble ruthenium salts may be detected by heatingthe solution, rendered alkaline with sodium hydroxide, in a current16 N.Schoorl, Pharm. Weekblad, 1926, 63, 555; A., 814.1 ) E. Crepaz, Ann. Chim. Appl., 1926, 16, 219; A., 1019.15 E. M. Chamot and H. I. Cole, Mibochem., 1926, 4, 97; A., 1019.19 L. Fernandes, Cfazzetta, 1925, 56, 616; A,, 1926, 140.20 N. A. Tananaev and 0. A. Pantschenko, 2. anorg. Chem., 1926, 160,21 A.R. Middleton, J . Amr. Chem. Soc., 1926, 48, 2125; A., 930.22 J. H. de Boer, Rec. traw. chim., 1926, 44, 1071; A., 1926, 40.15 J. Meyer and A. Pawlettct, 2. anal. Chern., 1926, 89, 15; A,, 1020.163; A., 377. See also Ukraine Chem. J., 1926, 2, 43ANALYTICAL CHEMISTRY. 189of chlorine; a brown coloration in an absorbent consisting ofaqueous alcohol containing hydrochloric acid indicates ruthenium.24Reactions of the platinum metals with a number of typical organicand inorganic compounds have been tabulatedlZ5 and a schemefor the qualitative separation of these metals has been worked out.26Specific and delicate tests for nitrate and for hydroxylamine basedupon conversion into nitrite and application of the diazo-reactionhave been described, together with appropriate methods for thepreliminary removal of nitrites.27 A test for iodate, available inthe presence of bromate, chlorate, and nitrate, depends upon theliberation of iodine by reaction with thiocyanic acid.2* The effectsproduced by salts of cobalt, copper, and mercury serve to distinguishbetween carbonates and bicarboyates, sulphites and bisulphites.2QBromine, liberated by suitable methods from bromides, hypobromites,or bromates, may be detected in very small amounts by the cparac-teristic crystalline precipitate it produces in a solution of m-phenyl-enediamine in 5% sulphuric acid.3OQuantitative.-Pyridinium perchlorate may readily be obtainedfrom technical pyridine in a pure state free from homologues, andcan be used as an acidimetric ~tandard.~l Borax or potassiumiodate, used under appropriate conditions, is preferred to sodiumcarbonate for the standardisation of hydrochloric acid.32 Constant-boiling hydrochloric acid remains unaltered in strength for longperiods and is therefore available for dilution for standard solutions.33Two studies have been made of the variability of standard sodiumthiosulphate solutions.34 The high results obtained in the titrationwith thiosulphate of the iodine set free by potassium dichromate inacid solution are stated to be due to liberation of iodine by atmo-spheric oxygen in the presence of chromic salts ; normal values areobtained if the reaction solutions are first boiled and the processcarried out in an atmosphere of carbon dioxide.35Methods depending upon the formation of cyanogen halide have94 H. Remy, 2.angew. Chew, 1926, 39, 1061; A,, 1219.p 6 S. C. Ogburn, jun., J . Amer. Chern. SOC., 1926, 48, 2493; A,, 1117.26 Idem, ibid., p. 2607; A., 1117.2 7 J. Blom, Ber., 1926, 69, [B], 121; A., 375.*a J. Bicskei, 2. amrg. Chem., 1926, 151, 127; A., 375.29 T. Gasper y Amal, Anal. p68. Qukm., 1926, 24, 267; A., 928.80 C. W. Mason and E. M. Chamot, Mikrochem., 1926,4, 145; A., 1220.$1 F. Arndt and P. Nechtwey, Ber., 1926, 59, [B], 448; A,, 626.Is I. M. Kolthoff, J . A m . Chem. SOC.. 1926, 48, 1447; A., 813; Pharm.98 J. A. Shaw, I d . Eng. Chem., 1926, 18, 1066; A., 1220.8' C. M a p , 2. awl. Chem., 1926, 68, 274; A., 814; E. Schulek, ibid.,v6 K. Bottger and W.Bottger, ibid., 1926, 69, 146; A,, 1221.WeekblacE, 1926, 03, 37; A,, 1926, 139.p. 387; A., 1017190 ANNUAL REPORTS ON THE PROGRESS OF CHEMISTRY.been studied comprehensively and applied to the determinationof chloride, bromide, and iodide, alone or in Thetitrations of thiocyanic acid, of arsenious acid, and of antimonywith potassium bromate have been investigated from the point ofview of the optimum acidity ; the potentiometric method permitsof a wider range and therefore is preferred to the use of methyl-orange?'Extract of blue cabbage, used as an indicator, gives a series ofcolour changes between pH 2 and pH 11, ranging from red throughblue ( p , 6.8-7.1) and green ( p , 8) to yellow; it is, however, ex-tremely sensitive to carbon dioxide.38 An aqueous solution ofyatrenum (which consists of an iodohydroxyquinolinesulphonic acidwith an equivalent of sodium bicarbonate) is strongly colouredbetween p K 1 and p , 8, with maximum intensity a t pH 4 ; the possi-bility of its use, with buffer solutions, as an indicator is discussed.39Under special lighting conditions, quinine 40 and umbelliferone 4 1may be used as fluorescent indicators. The first is suitable forturbid liquids and both are available for coloured solutions.Vanadous sulphate is an even more powerful reducing agent thantitanous sulphate ; whilst the latter maintains its titre in 4iV-sulph-uric acid in a burette exposed to air for 12 hours, vanadous sulphatemust be used within 1 Uranous sulphate is a mild reducingagent the solution of which is stable in air.Its preparation anduse for the determination of ferric salts are described inDiphenylamine as an internal indicator has been applied in con-junction with reduction by liquid amalgams to the determinationof phosphoric acid, ferricyanide, chromic acid, and ferric salts.44" Citarin," the sodium salt of anhydromethylenecitric acid, canbe used for the quantitative precipitation of silver and of gold,owing to the liberation of formaldehyde from the hot alkalines0lution.~5 Small amounts of silver can be separated as metalfrom large quantities of lead or copper by boiling the alkalinesolution in the presence of glycerol.*656 R. Berg, 2. anal. Chem., 1926, 69, 1; A., 1017.5 7 T. Nakazono and 8. Inoko, J .Chem. SOC. Japan, 1926, 47, 20; A,, 1115.38 T. Milobedzki and S. Jajte, Rocz. Chem., 1926, 6, 177; A,, 927.39 IF. W. van Urk, Phamn. VeekbM, 1926, 63, 685; A,, 813.4 1 R. Robl, Ber., 1926, 59, [B], 1725; A., 1115.43 C. Vortmann and F. Binder, 2. anal. Chem., 1925, 67, 269; A., 1926,263.K. Someya, 2. anorg. Chem., 1926, 152, 368, 382, 386; A., 702, 706;see dso 8ci. Rep. TGhoku Imp. U n k , 1926,15,399, 417, 426; A., 1116, 1117.L. Vanino and 0. Guyot, Arch. Pharm., 1926, 264, 98; A,, 491.R . Mellet and A. Bischoff, Compt. rend., 1926, 182, 1616; A., 813.A. S. Russell, J., 1926, 497; A., 692.46 E. Donath, Chm.-Ztg., 1926, 60, 222; A., 491ANALYTICAL CHEMISTRY. 191Lead may be separated from silver as phosphate from slightlyammoniacal tartrate solution, the temperature of precipitationbeing less than 80' to avoid reduction of the silver ; silver may beseparated by addition of potassium iodide to the boiling ~olution!~The effect of varying concentrations of hydrochloric acid on theprecipitation of cadmium , bismuth, and lead by hydrogen sulphidehas been investigated once more and the requisite conditions fordirect separation of metals of this group are described!8Suggestions are given to prevent oxidation of cuprous iodide inWinkler's gravimetric method for the determination of copper ascuprous iodidenPg Benzoin monoxime does not separate coppercompletely from iron, aluminium, or zinc, its use in this connexionbeing critici~ed.5~ The micro-determination of copper by electro-lysis and iodometric titration is applied to 0.5 mg.and less.s1Bismuth solutions hydrolyse in the presence of bromide andbromate to basic bismuth bromide. This reaction, which is moredelicate than that due to hydrogen sulphide, has been applied tothe separation of bismuth from zinc, copper,'cadmium, and lead.6aThe methods for the complete removal of mercury from solutionby deposition on copper and subsequent determination by sublim-ation have been reinvestigated and placed on a satisfactory basissuitable for large or small q u a n t i t i e ~ . ~ ~ A number of papers dealwith the determination of very small quantities of mercury theseparation of which is effected by electrolysis on gold and weighingthe metallic mercury ; conversion into red mercuric iodide serves asa confirmatory testss4In the absence of gold, mercury, selenium, and tellurium, arsenicmay be precipitated by stannous chloride and determined as theelement, in which form it may be weighed; the results tend to behigh.65 With certain modifications, arsenic may be reduced to*' G.Vortmann and 0. Hecht, 2. anat. Chem., 1925, 67, 276; A., 1926,262; G. Vortmann, Analyst, 1926, 51, 456; A., 1019.W. Manchot, G. Grassl, and A. Schreeberger, 2. anal. Chem., 1926, 67,177; A., 1926, 40; see also S. Krishnamurti, J., 1926, 1549; A., 814.I. M. Kolthoff and H. A. Kuylman, Chem. WeekbEacE, 1926, 23, 185;A., 592.so E . Azzalin, Ann. Chim. AppZ., 1925, 16, 373; A., 1926, 140.I1 IT. Schoorl and H. Begem-, Rec. trau. chim., 1925, 44, 1077; A., 1926,64 L.Moser and W. Maxymowicz, 2. anal. Chem., 1925, 67, 248; A., 1926,6* B. S. Evana and S. G. Clarke, Analyst, 1926, 51, 224; A,, 704.64 A. Stock and R. Heller, 2. angew. Chem., 1926,89,466; A,, 703; A. Stockand E. Pohland, ibid., p. 791 ; A., 814; H. S. Booth, (Miss) N. E. Schreiber,and K. G . Zwick, J. Am?. C h m . rSoc., 1926, 48, 1815; A., 929.40; H. B. Dunnicliff and K. Ram, Kolloid-Z., 1926, 38, 168; A., 376.264.R. Fnidli, Pharm. Zentr., 1926, 67, 241; A., 591192 ANNUAL RBPORTS ON THE PROGRESS OB CHEMISTRY.element and determined in the presence of selenium.66 I n theGutzeit test, a freshly-prepared mercuric bromide paper is highlysensitive and preferable to mercuric chloride; 57 the use of glasswool in place of filter-paper and cotton wool in the purifying tubeof the Guteeit or Marsh apparatus considerably lengthens theeffective life of the tube.58 Arsenic acid may be determined byreduction with titanous chloride and back titration with ferricalum.59Iron may be titrated with titanous chloride in the presence ofcopper by the use of the chromic acid compound of s-diphenyl-carbohydrazide, which is reduced instantly by cuprous chlorideand very slowly by titanous chloride.60 Iron is quantitativelyprecipitated under certain conditions from 2N-acid solution con-taining 2% ammonium salt by the addition of an alkali salt ofbis-p-chlorophenylphosphoric acid ; the precipitate is Gnally con-verted into hydroxide by treatment with ammonia.61Aluminium can be satisfactorily separated from magnesium,even in the absence of added ammonium salts, by adding ammoniauntil p , 7 is reached (blue with bromothymol-blue), but magnesiumis carried down if pa exceeds 7.62 Chromium salts are completelyoxidised to chromic acid by boiling in alkaline solution with leaddioxide, the excess of which is readily removed by Htration.68 Adirect permanganate titration method similar to the Volhardmethod for chromium 6* and manganese 65 salts, depending uponthe use of excess of sodium acetate, has been worked out and isshown to be available in the presence of much iron. The varyingfactors influencing the oxidation of manganese salts to permanganicacid and the conditions for securing complete oxidation have beenstudied,66 and it is shown that sulphuric acid may advantageouslybe substituted for nitric acid in the determination of manganeseby the bismuthate method.676 6 R.Fridli, Pharm. Zentr., 1926, 87, 369; A., 702.G. Kemmerer and H. H. Schrenk, Ind. Eng. Chem., 1926, 18, 707; A,,928.66 T. J. Ward, Amlyst, 1926, 51, 457; A., 1018.59 A. W. Francis, J . Amer. Chem. SOC., 1926, 48, 665; A,, 490.O D L. Brandt, Stahl u. Eisen, 1926, 46, 976; B., 762.F. Zetzache and M. Na.chmam, Helv. Chim. Acta, 1926, 9, 420; A., 705.A. Lasieur, Ann. Chim. anal., 1926, [ii], 8, 97; Compt. rend., 1926, 182,E. Muller and W. Messe, 2. anal. Chem., 1926, 89, 165; A., 1222.B. Reinitzer and P. Conreth, ibid., 1926, 88, 81; A., 492.as Idem, ibid., p. 129; A., 705.A. Travera, Compt. rend., 1926, 182, 1088; Ann.Chim., 1926, [XI, 8, 56;B. Perk, I d . Eng. Chm., 1926, 18, 697; A., 704.384; A., 376.A., 704ANALYTICAL CHEMISTRY. 193The oxalate separation of calcium and magnesium continues toattract attention, and the effective separation is shown to be dueto the degree of supersaturation of magnesium oxalate; 68 it isimportant to note that calcium oxalate is rapidly and quantitativelyconverted into carbonate by heating in it current of dry carbondioxide a t 675-800°.6gThe cobaltinitrite method for the determination of potassiumis shown to be available in the presence of sulphate and is thusbetter than the perchlorate in this case ; further confirnation thatthe composition of the precipitate after drying at 100" isK2NaCo(N0,),,H,0 has been obtained.70 It has been foundadvantageous to replace the acetic acid by tartaric acid in preparingthe reagent.71 Determination of the cobalt in the precipitatedcobaltinitrite has been applied to the micro-determination of smallquantities of potas~iurn,~~ whilst for micro-determination of sodiumuse is made of the triple nitrite 6NaN02,9CsN0,,5Bi(N0,), throughelectrolytic separation of bismuth.73Rubidium may be precipitated quantitatively as silicotungstate,RbsSiWlzOez, by addition of sjlicotungstic acid, but in the presenceof more than 1% of potassium the precipitate requires furthertreatment with I)% salt solution to remove co-precipitated potass.ium.74 Both rubidium and cssium may be precipitated from thealcoholic solution of their chlorides and weighed as chlorostannates.If the two metals are present together, the cssium is subsequentlyseparated as a triple chloride with antimony and iron and thenconverted into and determined as perchlorate.The precipitateformed by the addition of sodium cobaltinitrite to a solution of arubidium salt contains varying proportions of sodium, but thecssium salt, precipitated a t 80°, is definitely CS,CO(NO,)~,H,O. 75Thallium also is quantitatively precipitated a t 80" by sodiumcobaltinitrite, the product dried a t 100-110" having the compositionTl;NaCo(NO,),. In other methods for determination of thallium,the metal is either weighed as element or estimated volumetrically,the thallium being precipitated by a measured excess of potassium6E W.M. Fischer, 2. anorg. Chem., 1926, 153, 6 2 ; A,, 703.H. W. Foote and W. M. Bradley, J. Amer. Cheni. Soc., 1926, 48, 676;A,, 491.'O M. A. Hamid, Artalyst, 1926, 51, 450; A,, 1019; L. le Boucher, Anal.Pls. Qlsim., 1925, 23, 540; A., 1926, 491.'l M. Wikul, 2. anorg. Chem., 1926, 151, 338; A., 491.M. Delaville and P. Cmlier, Compt. rend., 1926, 182, 701; A,, 491.78 E. Tschopp, Helv. Chim. Actct, 1925, 8, 893; A,, 1926, 39.7 4 P. Freundler and (Mlle.) Y. MBnager, Compt. rend., 1926,182, 1158; A,,76 W. Strecker md F. 0. Diaz, 2. anal. Chem., 1925,87, 321; A., 1926, 261.702.REP.-VOL. XXIII. 194iodide.'% Thallous salts are quantitatively oxidised by potassiumiodate in the presence of a large excess of hydrochloric acid and sodetermined,77 or by potassium bromate.Thallic salts may alsobe titrated potentiometrically with titanous chloride in the presenceof ammonium acetate.78The requisite but simple precautions for the accurate determin-ation of uranium gravimetrically as U,08 following precipitationas (NH4)2U207 or volumetrically by means of permanganate arediscussed. T9 Sodium cacodylate separates uranium from othermetals of the iron group. The precipitate is [(CH,),AsO],UO, andmay be weighed in this form.80 Zirconium may be quantitativelyseparated from all elements except hafnium as insoluble phenyl-arsinate from a solution containing 10% hydrochloric or sulphuricacid. The precipitate is ignited directly to zirconia. Double pre-cipitation is necessary for the complete separation from thorium,uranium, phosphoric acid, and iron.Thorium phenylarsinate isthe only rare-earth salt of the acid insoluble in excess of acetic acidand this is used in tho application of this reagent to the analysis ofmonazite.81 Zirconium citrate, although soluble in ammonia orcitric acid solution, is only sparingly soluble in water, whilst hafniumcitrate is readily soluble.s2 Zirconium hydroxide is soluble inammonium carbonate solution a t 70' ; this property has beenapplied to the separation from iron and aluminium. Thorium, ifpresent, accompanies the zirc0nium.8~ Niobium (columbium) canbe determined in the presence of tantalum by reducing it withhydrogen to the tetroxide and ascertaining the increase in weighton ignition; tantalum pentoxide is not reduced.The black colourof the tetroxide is a sensitive qualitative test for ni0kium.8~Palladium may be separated from the other platinum metals andfrom the commoner metals by means of benzoylmethylglyoxime.Precipitation is carried out in acid solution, with certain precautionsif antimony, molybdenum, vanadium, or tungsten is present.85ANNUAL REPORTS ON THE PROGRESS OF CHEMISTRY.76 W. Strecker and P. de la Pefia, 2. anal. Chem., 1925,67,256 ; A,, 1936,262.7 7 A. J. Berry, Analyst, 1926, 51, 137; A., 376.78 E. Zintl and G. Rienacker, 2. anorg. Chem., 1926,153, 276; A,, 703.G. E. F. Lundell and H. B. Knowles, J. Amer. Chem. Soc., 1925, 47,2637; B., 1926, 1016.8o E. Isnard, Bull. Sci. Pharm., 1925, 32, 131.A.C. Rice, H. C. Fogg, and C. James, J . Amer. Chem. SOC., 1926, 48,D. H. Drophy and W. P. Davey, Physical Rev., 1925, [ii], 25, 882; A,,R. Lessing, Z. and. Chem., 1925, 67, 341; A., 1926, 263.0. Ruff and F. Thomas, 2. attorg. Chem., 1926, 156, 213; A., 1222.J. Hand, A. Jilek, and J. Lukas, Chem. News, 1925, 131, 401; 1926,895; A,, 593.1926, 1117.132, 1; Chsm. &sty, 1926, 20, 68, 133; A,, 141ANALYTICAL CHEMISTRY. 195Titanous sulphte in the cold reduces salts of gold, palladium, andplatinum (and some base metals) t o the metallic state and thuseffects a separation from iridium; a method for the separation ofplatinum and rhodium depending upon this reduction is given.86The treatment of the iridium-ruthenium-iron alloy (obtained afterextraction of a lead button) necessary to isolate the iridium isdescribed in detail.87Except in very small concentrations of the metal, the brownish-red colour produced by hydrogen peroxide with solutions ofmolybdic acid containing excess of sodium hydroxide can beused, under certain conditions, for the determination of molyb-denum.Ammonium salts must first be removed by boiling thesolution with sodium hydroxide.88 A solution of quinquevalentvanadium in phosphoric acid is reduced quantitatively by theaddition of potassium iodide to the quadrivalent state, with liber-ation of the equivalent amount of iodine.89Tellurium is completely precipitated as the element by boilingits solutions in alkali sulphides with sodium sulphite ; in the presenceof potassium cyanide, separation from gold, copper, and seleniumcan be effected.Lead, bismuth, and mercury must f i s t be removedby appropriate methods.g0 Solutions of selenious or tellurous acidcan be determined in the absence of hydrochloric acid, by titrationwith permanganate in the presence of disodium phosphate ; if thetwo elements are present together, the tellurium is determined firstof all by dichromate.91In the absence of heavy metals, small quantities of bromides,chlorides, cyanides, and thiocyanates may be titrated with mercuricnitrate, sodium nitroprusside being used as indicator and theTyndall effect being employed to observe the end-point. Themethod is applied to perchloric acid after reducing it by means oftitanous sulphate and oxidising the excess with ammonium per-sulphate.92 Comparison has been made of several methods ofevaluating perchloratesg3 and full details for conversion into chloridewithout loss of chlorine by heating with sodium carbonate areI.Wade and T. Nakazono, Sci. Papers Inst. Phys. Chem. Res., 1923,W. R. Schoeller, Analyst, 1926, 61, 392; A., 931.A. D. Funck, 2. anal. Chem., 1926, 68, 283; A,, 815.8D T. Heczko, ibid., p. 461; A., 1926, 1020.A. Brukl and W. Maxymowicz, ibid., p. 14; A., 1926, 490.* l W. T. Schrenk and B. L. Browning, J . Amcr. Chem. SOC., 1926, 48, 2550;p2 I?. Konig, 2. anal. Chem., 1926, 88, 385; A., 1017.1, 139; A., 1926, 141.A., 1115.D. Dobroserdov, Ukraine Chem. J . , 1926, 2, 1 ; A,, 928196 ANNUAL REPORTS ox THE PROGRESS OF CHEMISTRY.givenaQ4 This reduction may also be effective by fusion with sodiumnitrate and gradual addition of copper powder.95Small quantities of iodide, bromide, and chloride may be estimatedwith fair accuracy when present together by releasing the halogensone a t a time by increasingly powerful oxidising agents.Thoseselected are acid ferric sulphrtte for iodine, cold chromic anhydridefor bromine, and permanganic acid for chlorine, the halogens beingremoved by aspiration after treatment.90 Iodides may be titrateddirectly in sulphuric or phosphoric acid solution by permanganate,ethyl acetate being present to extract the iodine liberated, therebyenabling the end-point to be discerned ; manganous sulphate mustbe added if bromides and chlorides are also pre~ent.~'The exact determination of fluorine is a matter of considerabledifficulty and continues to attract attention.The ordinaryBerzelius method depending upon the precipitation of calciumfluoride always gives low results and quantities of the order of0.1% may be missed entirely.For the small amounts found in rocks, the method of G. Steiger,QButilising the bleaching effect of fluorides in acid solution on theyellow colour produced by hydrogen peroxide with titanium sulphate,is well adapted for use. Calibration curves must be constructedfor this method and precautions taken as regards the concentrationof alkali sulphate, acidity, and temperat~re.~~ G. Starck showedthat with soluble fluorides it is possible to utilise the insolubilityof PbFCl for the determination.He found that saturated leadchloride solution effected complete separation from the neutralsolution ; the precipitate was granular and readily filtered andother salts which did not affect lead exerted no influence. Thismethod has been applied to the determination of fluorine in ores oflow or medium fluorine content. The ore is fused with fusionmixture, sulphur is oxidised by sodium peroxide, and the melt isextracted with aqueous sodium carbonate. Some hydrochloric acidis added and the neutralisation is then completed with nitric acid.PbFC1 is precipitated by means of lead acetate containing aceticacid. The precipitate is filtered off, washed, and redissolved innitric acid and the chlorine contained is determined by a suitableD.Dobroserdov andV. Erdmann, Ukraine Chem. J., 1926,2, 16; A., 927.96 K. Kurschner and K. Scharrer, 2. anal. Chem., 1926, 68, 1 ; A.,9 6 P. L. Hibbard, Id. Ens. Chem., 1926, 18, 67, 836; A., 260, 928.9' F. L. Hahn and H. Wolf, Chem.-Zlg., 1926, 50, 674; A., 1220.98 J . Amer. Chem. Soc., 1908, 30, 219.98 H. E. Merwin, Amer. J . IS&., 1909, [ii], 28, 119.490.12. anorg. Chm., 1911, 70, 173; A . , 1911, ii, 436ANALYTICAL CHEMISTRY. 197method. It was found that zinc, sulphates, and phosphates havebut little effect on the result.8A method used by A. Greeff 8 depends upon the fact that theaddition of ferric chloride to a neutral solution of fluoride producesa white or faintly buff-coloured precipitate of M,FeF,. TO theneutral solution of the fluoride, salt and a strong solution of potass-ium thiocyanate are added and the fluid is titrated with ferricchloride solution until a weak yellow colour persists.The end-point is improved by adding sufficient of a mixture of equal partsof alcohol and ether to the aqueous solution and titrating withferric chloride until the red colour persists in the ether layer.4The insolubility of thorium fluoride, ThF4,4H,0, in very dilutenitric acid or in acetic acid 5 provides a method by which as littleas 0.01% of fluorine may be detected. The process consists inadding a slight excess of thorium nitrate to the solution, justacidified with nitric or acetic acid. The precipitate is igniteddirectly to thorium oxide.Phosphates must f i s t be separated inthe usual way, whereas silicofluorides precipitate their fluorinedirectly and can be estimated. I n this process the acidity is bestkept within the limits of 3 / b to 3/50 of acetic acid.6The difficulties of fluorine determination in basic slag due to thepresence of phosphates and vanadium have been surmounted byfusion, extraction of the melt, neutralisation, and treatment withsolid silver sulphate. The last operation and also the atration ofthe precipitated phosphate and vanadate are conducted in thedark. The fluorine is then determined colorimetrically a t 19" to36" by the bleaching effect on an acid solution of titanium sulphatecontaining hydrogen peroxide. Curves are drawn connecting bleach-ing effect with concentration of fluorine, up t o 25 mg.of fl~orine.~This process is clearly applicable to other phosphates.Another colorimetric method for fluorine depends on the bleachingof the blue lake produced by zirconium oxychloride with sodiumalizarinsulphonate in hydrochloric acid. The fluoride, if notalready in solution, is obtained from insoluble fluoride by digestionon a water-bath with 10% zirconium oxychloride solution to whichis added an equal volume of concentrated hydrochloric acid and* F. G. Hawley, Ind. Eng. Chem., 1926, 18, 573; B., 1926, 672.1. See a180 W. D. Treadwell and A. Kohl, Helv. Chim. AcEa, 1926, 8, 600;Ber., 1913, 46, 2511; A., 1913, ii, 97E.A . , 1926, ii, 1197.F. Pisani, Compb. rend., 1916, 162, 791; A., 1916, ii, 393.(I F.A. Gooch and M. Koboyashi, Amar. J . LSci., 1918, [iv], 45, 370; A.,R. G . Warren, C. T. Imminghem, and H. J. Page, J. Agric. Sci., 1925,1918, ii, 177.15, 616198 ANNO& REPORTS ON THE PROGRESS OF CHEMISTRY.1 C.C. of a 0.03% solution of sodium alizarinsulphonate. A similarsolution is prepared without fluoride and both solutions are dilutedto a suitable bulk. Both solutions are then titrated with standardpotassium fluoride until the orange tint is the same. The methodapplies to fluoborates, fluotitanates, fluosilicates, and fluoalumin-atesa8 It is shown that optimum precipitation as, e.g., calciumfluoride occurs in the presence of excess of an alkaline-earth ion ofconcentration 0.027 mol./litre. The addition of a little ferricchloride and some ferrous salt to a fluoride which is to be titratedby using aluminium chloride enables a satisfactory end-point to beobtained in the potentiometric titration.9The azidodithiocarbonate radical, -S*CSN,, resembles the halidesanalytically, Volhard’s method affording the best results.1°A colorimetric method for the determination of minute quantitiesof hydroxylamine, based on the reaction with benzoyl chloridefollowed by addition of ferric chloride, has been described.11Some convenient volumetric process for determining sulphateswould be of great advantage generally.It is found l2 that excessbarium chloride may be titrated with standard potassium stearateand B.D.H. “ universal ” indicator, the solution reacting alkalineas soon as all the barium has been precipitated as stearate.Un-fortunately, the method breaks down in the presence of 1% or moreof neutral salts, which affect the end-point in either direction.13I n a similar process, the excess barium chloride is estimated bytitration with standard potassium chromate until the solutionbecomes alkaline to methyl-red.14 Precipitated benzidine sulphatemay be titrated with sodium hydroxide ; and a modified procedurenecessary in the presence of lead is des~ribed.1~ For the micro-determination of sulphuric acid, it is recommended to bring aboutthe precipitation with barium chloride in the presence of traces ofcolloidal celluloid, which cause rapid flocculation of the bariumsulphate. The method of preparing the celluloid is described andit is stated that adsorption of barium chloride is negligible with thesmall quantities used in micro-analysis.16J. H.de Boer and J. Basart, 2. anorg. Chem., 1926, 126, 213; A., 690.W. D. Treadwell and A. Kohl, HeEv. Chim. Acfa, 1926, 9, 470; A., 701.lo A. W. Browne and G . B. L. Smith, J . Amer. Chem. SOC., 1926, 47, 2898;l1 G. W. Pucher and H. A. Day, J. Amer. Chem. Soc., 1926,48,672; A., 490.l2 H. Atkinson, AnaEyst, 1925, 50, 690; A., 1926, 38; ibid., 1926, 51, 140;A,, 1926, 39.B., 358.Idem, ibid., 1926, 61, S1; A., 261.l4 A. A. B r i d , 2. amrg. Chern., 1926,156, 210; A., 1221.l5 Vlastimii and M. Matula, Chem-Ztg., 1926, 50, 486; A., 928.l8 E. Eigenberger, 2. anal. Chem., 1920, 68, 220; A., 701ANALYTIOAL CHEMISTRY.199Two methods of procedure for the permanganate titration ofhypophosphorous acid and its salts, and the precautions for pre-venting undesirable reduction of the permanganate, have beeninve~3tigated.l~Water Analysis.Free chlorine may be detected and determined in water for drink-ing purposes by means of the red colour developed on treatmentwith acetic acid and then with dimethyl-p-phenylenediamine.The comparison is made with standard iodine solutions treatedsimilarly.l* The sensitivities of the o-tolidine and the starch-iodide test for chlorine have been c0mpared.1~ For the determin-ation of iodides in natural waters, a method depending on oxidationto iodate by means of hypochlorite has been worked out ; additionof potassium iodide to the acid solution then results in the liberationof a quantity of iodine six times as great as that originally presentas iodide.20The somewhat high values found by titration for the carbonicacid concentration of distilled water are due to improperly neutral-ised indicators and to the slowness with which the carbon dioxideescapes into the atmosphere ; the requisite conditions for this deter-mination areThe methods for the determination of dissolved oxygen havebeen critically reviewed ; 23 treatment with ferricyanide, hypo-chlorite, permanganate, carbamide, or azoimide for the purposeof eliminating interfering oxidisable impurities is not consideredto be of general value.A new method is advanced using brominefor the oxidation of interfering substances, the excess being removedby salicylic acid ; Winkler's method, unmodified, is then applied.Apparatus for this determination has been adapted so that onlysmall quantities of water are required.23Methyl-red is not a suitable indicator for ascertaining thehydrogen-ion concentration of waters approaching neutrality ; fordistilled water, the sodium salt of methyl-red or of chlorophenol-red is better, but the most accurate indicator is heptamethoxy-17 D.Koszegi, 2. anal. Chem., 1926, 68, 216; A., 7 0 2 ; I. 11, Kolthoff, ibid.,16 I. &I. Kolthoff, Chein. Weekblad, 1926, 23, 203; B., 517.19 A, M. Buswell and C. S. Bomff, J . Amer. lYuter Works Assoc., 1925, 14.384: B,, 1926, 174.20 H. W. Brubaker, H.S. van Blarcom, end N. H. Walker, J. Amer. Chem.soc., 1926, 48, 1502; B., 630.21 I. RI. Kolthoff, Biochem. Z., 1926, 176, 101; A,, 1116; Chenz. Weekblud,1926, 23, 381 ; A., 1018.2 2 G. Alsterberg, Biocham. Z., 1926, 170, 30; A., 591.28 C. Risch, zbad., 1925, 161, 465; A.. 1926, 140.1926, 6Q, 36; A,, 1018200 ANNUAL REPORTS ON THE PROQRESS OF CHEMISTRY.triphenyl~arbinol.~~ For such unbuffered solutions, bromothymol-blue should be adjusted to a pure dark green colour by addition ofalkali ; since, however, this solution is not stable, a neutral solutionof p-nitrophenol is preferred.25A series of solutions of pE values ranging from 12.5 to 2 andcalibrated by means of the quinhydrone electrode has been preparedin a medium consisting of acetone and water (9 : 1 by volume) ; thecolour changes of a large number of indicators with these solutionsand with water are tabulated.26 Permanent standards preparedfrom potassium chromate and dichromate are recommended forcomparison with nitro- and dinitro-phenols in the determinationof hydrogen-ion c~ncentration.~~ The use of methyl-orange ordimethyl-yellow gives slightly high pE values with the hydrogenphthalate series of solutions, for which bromophenol-blue or methyl-red is better suited; the Sorensen series of citrate solutions arerecommended for use with methyl-orange.28 Standard alkalinebuffers produce with some indicators a salt error which in extremecases may amount to two units as compared with the pH valuesof sodium hydroxide solutions.29Gas Analysis.For the colorimetric determination of free chlorine in air by theuse of o-tolidine, comparison is made with a series of standardsmade by mixing dilute solutions of copper sulphate and potassiumdichromate.30 A study of the concentrations of cuprous chloridenecessary to obtain maximum absorption of carbon monoxideshows that the ammoniacal solutions are more efficient than acidsolutions?l In a review of the various methods for the detectionand determination of carbon monoxide in small concentrations, itis shown that accurate quantitative results are obtained only bycombustion.With practice, however, the time required to producea coloration with ammonium chloropalladite or with ammoniacalsilver nitrate affords a fairly accurate measure of the concentrationof the gas in ahas224 I.M. Kolthoff, Chem. Weekblad, 1926, 22, 690; A,, 1926, 139.26 H. T. Stern, J. BioZ. Chem., 1926, 05, 677; A,, 1926, 38.*a F. M. Cray and G. M. Westrip, Trans. Paraday Soc., 1926, 21, 326; A,,27 A. Janke and S. Kropacay, Biochem. Z., 1928,174, 120; A., 927.28 I. M. Kolthoff, Rec. ~ a v . chim., 1926, 45, 433; A,, 701.29 J. W. MoBain, 0. E. Dubois, and K. G. Hay, J . Gem. Phyaiol., 1926, g,80 L. E. Porter, Ind. Eng. Chem., 1926, 18, 730; A,, 927.81 L. Moser and F. Hanika, 2. anal. Chem., 1926, 67, 448; A,, 376;.s* H. Kast and H. Selle, Qua- u. Wasserfach, 1926, 09, 812; A,, 1018.1926, 374.461; A., 690ANALYTICAL CHEMISTRY. 201Organic Analysis.Quditative.-A large number of qualitative tests for formalde-hyde have been critically examined with the view of ascertainingthose best suited for the detection of small quantities, particularlyin the presence of such substances as acetaldehyde, furfuraldehyde,and carbohydrates.Primary alkyl bromides and iodides are readily converted intothe corresponding mercuric alkyl halides, which are well-definedsubstances suitable for purposes of identification."4 The mono-substituted acetylenes also may be identified by the formation ofcharacteristic mercury derivatives, (CRE3&Hg.363 : 6-Dinitrobanzoyl chloride is particularly suitable as a reagentfor alcohols ; the esters form definite molecular compounds witha-naphthylamine.A number of esters from anthraquinone-p-carboxyl chloride are also describedF6 u-Naphthylcarbimide reactsreadily with primary and secondary alcohols, less readily withtertiary, giving urethane derivatives?' Examination of the pro-ducts of reaction of their toluenesulphonates with ammonia, amines,or hydrazine enables a distinction to be made between primaryalcohols, secondary alcohols, and phenols.38A review of the colorimetric tests for lactic acid depending uponthe formation of acetaldehyde and subsequent reaction with phenolsshows that these are, in general, not very trustworthy.Phloro-glucinol and p-cresol are the most sensitive phenols. Methods forthe isolation and identification of the acid in gastric juices aregi~en.3~ The purple colour of the ferric salicylate complex ischanged by the addition of minute quantities of substances capableof repressing the ferric ion, and a method of testing for the'absenceof citrates or tartrates is based on this effe~t.4~The red colour given by quinine on addition of bromine andphenylhydrazine hydrochloride followed by ammonia is not shownby other common alkaloids.It is inhibited by alkalis, morphine,codeine, and excess of reagent~.~l Either benzidine or citric acid38 T. Sabalitschka and C. Harnisch, Phurm. Zentr., 1926, 67, 289, 309, 324,339, 357, 371, 387; A,, 853.s4 C. S. MarveI, C: G. Gauerke, and E. L. Hill, J . Amer. Chem. ij'oc., 1925,47, 3009; A., 1926, 144.36 J. R. Johnson and W. L. McEwen, ibid., 1926, 48, 469; A., 495.36 T. Reiohstein, Helu. Chint. Actu, 1926, 9, 799, 803; A., 1225.3' V.T. Bickel and H. E. French, J . Amer. Chem. Soo., 1926, 48, 747; A,,I n each case the sensitivity is indicated.33617.K. Freudenberg and H. Hess, Annulen, 1926, 448, 121; A., 935.ID G. Capelli, Ann. Chim. Appl., 1925,16, 53; A., 1926, 632.J. B. Peterson, I d . Eng. Chem., 1926,17, 1146; A., 1926, 84.G. W. Hargreevee, J . Amer. Pharm. A~uoc., 1926, 15, 100; A., 967.0 202 ANNUAL REPORTS ON 'plw PROGRESS OF CHEMISTRY.in sulphuric acid solution gives with morphine and several relatedalkaloids a series of colour changes which may be extended bydilution and addition of ammonia.42 3 : 5-Dinitrobenzoic acid giveswell-defined, crystalline precipitates with some of the principalalkaloids and is recommended as a reagent for their recognition;photomicrographs are appended.@The characteristic colorations given with phosphomolybdic acidfollowed by ammonia constitute a sensitive reaction for distinguish-ing between 0-, m-, and p-dihydroxyphenols.MColour reactions for phenols are obtained by dusting sodiumnitroprusside over the surface of a solution standing over concen-trated sulphuric acid and shaking gently until the surface of contactbecomes coloured.45 a-Naphthylcarbimide reacts readily with hotmonohydric phenols and with aromatic amines, giving urethanesand carbamides, respectively.46Quantitative.-Modifications of the Kjeldahl method for nitrogen,employing copper powder or an iron-copper couple, have beendescribed which give good results with such compounds as phenyl-hydrazine, alkaloids, and pyrazolone ring compouiid~.~~ Othervariations of the method are de~cribed.~sAn apparatus is described for the determination of arsenic andof mercury in organic compounds by treatment in a current ofhydrogen, the elements being weighed as In the absenceof halogens, selenium may be determined in an organic compoundby the ordinary Carius combustion, whereby selenious acid isformed; this is estimated by titration with silver in the presenceof zinc oxide.60In the alkalimetric determination of formaldehyde by means ofsodium sulphite, thymolphthalein is a better indicator, particularlyfor dilute solutions, than phenolphthalein ; still better results areafforded by the latter indicator if the solution be saturated withsodium chloride before titration.51L.Ekkert, Pham. Zentr., 1926, 67, 498; A., 965.4a E. Navmo, Anal. Pis. Quh., 1926, 24, 283; A., 965.44 K. Brauer, Chem.-Ztg., 1926, 50, 663; A., 1036.46 L. Ekkert and L. W. Winkler, Pharm. Zen&., 1926, 07, 566; A,, 1033.46 H. E. FrencF and A. F. Wirtel, J . Amer. Chem. Sot., 1926, 48, 1736;47 K. Kiirschner, 2. anal. Chem., 1926, 08, 209; A., 702; see also K.48 A. C. Andersen and B. M. Jemen, ibid., 1926, 07, 427; A,, 375; A. EIek49 H. ter Meulen, Rec. trav. chim., 1926, 46, 364, 368; A., 490, 492.60 W. E. B r d t and R. E. Lyons, J. AM. Ohem. ism., 1926, 48, 2642; A.,51 IC. TLufel and C. Wagner, 2;. anal. Chem., 1928, 68, 26; A., 635.A,, 830.Kiirschner and K. Scharrer. ibid., p. 1 ; A., 490.and H.Sohotka, J. Amer. Chem. SOC., 1926, 48, 601; A., 632.1266ANALYTICAL CHEMISTRY. 203A convenient table has been constructed showing the relationbetween percentage, density, and freezing point of acetic acid forconcentrations of 90% and upwards; the disturbing effect of pro-pionic acid is discussed.52 A rapid thermometric method forevaluating acetic anhydride depends upon the reaction with aniline,toluene being used as a di1uent.B A gasometric method involvingthe decomposition of anhydrous oxalic acid in dry pyridine byacetic anhydride into carbon monoxide and dioxide has also beendescribed. 54A general method for the determination of the carbonyl groupdepends upon the conversion of the aldehyde or ketone into thecorresponding phenylhydrazone, the excess of phenylhydrazinebeing determined iod~metrically.~~ It is claimed that this methodis better than that of Benedikt and Strache ( A ., 1893, ii, 560),which employs Fehling’s solution. The isopropylidenedioxy-groupmay be determined by hydrolysis with hydrochloric acid; theliberated acetone is determined iod~metrically.~~Dehydration of alcohols may result in the formation of unsatur-ated hydrocarbons or cyclic hydrocarbons. The former may beestimated in the presence of the latter by the action of perbenzoicacid in chloroform solution.57 Dihydroxyacetone boiled withphosphomolybdic acid reduces it 180 times as rapidly as doesdextrose, thus permitting a colorimetric determination of thedihydroxyacetone in the presence of dextrose.58Conditions for the determination of diguanide gravimetrically asthe nickel derivative, Ni(C,H,N,),, have been worked out togetherwith the extra precautions rendered necessary by the presence ofguanylcarbamide.59Arginine in fairly acid solution is precipitated quantitatively byflavianic acid (2 : 4-dinitro-cr-naphthoI-7-sulphonie acid) even inpresence of histidine, and may be determined microchemicallyby this means.g0 The tryptophan content of proteins is readilyand accurately ascertained by means of the reaction with formalde-hyde and sulphuric acid.,1 A number of other papers also deal6* H. D. Richmond and E. H. England, Analyst, 1926, 51, 283; B., 646.68 H. D. Richmond and J. A. Eggleston, ibid., p. 281; B., 646.64 E. L.Whitford, J . Amer. Chern. SOC., 1925, 47, 2939; A., 1926, 189.6 6 E. G . R. Ardagh and J. G. Williams, ibid., p. 2983; Tram. Roy. SOC.I 6 A. Griin and R. Limpacher, Ber., 1926, 59, [B], 695; A., 632.S. Nasletkin and L. Briissoff, J. p . Ohm., 1926, [ii], lla, 169; A., 420.68 W. R. Campbell, J. Biol. Chem., 1926, 67, 69; A., 443.C. D. Carby, Id. Eng. Oh., 1926, 18, 819; A,, 1164.6o A. Kossel and W. Staudt, 2. gAysioE. Chem., 1926,156, 270; A., 967.J. Tillmans and A. Alt, Biochm. Z., 1925, 164, 136; A., 1926, 189Canada, 1926, [GI, 19, 111, 73; A., 1926, 189.0. Fiirth, ibid., 1926, 169, 117; A., 633204 ANNUAL REPORTS ON THE PROGRESS OF CHEMISTRY.with the determination of certain amino-acids.62 The precipitationof proteins, pure or impure, by means of trichloroacetic acid hasbeen investigated from the quantitative aspect.63Aldehyde sugars are completely oxidised t o the correspondingacids in the cold by excess of standard iodine in alkaline solution.642 : 4-Dibromophenylhydrazine furnishes a means of quantitativelyseparating galactose from xylose, , rhamnose, dextrose, lzevulose,maltose, and lactose, but not from arabinose.66Aromatic nitro-compounds may be determined by reduction inthe cold with titanous chloride in the presence of sodium citrate.After a short period, the excess of the reducing agent is estimatedeither potentiometrically by means of iron alum or volumetricallywith thiocyanate as indicator.66 An advantage claimed for thisprocedure is that chlorination of the nitro-compound does notoccur.Nitrobenzene is reduced by titanous chloride in presence ofsodium hydroxide ; the excess of titanous chloride is oxidised in air,and the resultant aniline estimated by the bromide-bromatemethod.67 A gasometric method of estimating primary aromaticamines is based upon diazotisation and decomposition in a nitro-meter of the diazo-compound with acid ferrous sulphate solution ;the nitric oxide formed is removed and the volume of nitrogenthen remaining is found to be equivalent to the amine present.68Aniline and similar aromatic amines may be accurately titratedpotentiometrically with sodium nitrite solution, an average potentialof + 0.58 volt a t the end-point being independent of the amine.6QIn the absence of free mineral acid, benzidine is completely pre-cipitated by mercuric chloride as benzidine mercurichloride ; con-versely, mercury is quantitatively precipitated by excess of benzidineacetate.70The oxidation of quinol by iodine is quantitative only if thehydrogen-ion concentration is less than 10-5N a t the end-point.Methods for the determination by chemical or potentiometric means62 M. T. Hanke, J . Bid. Chem., 1925, 66, 475, 489; A., 1926, 633; J. M.Looney, ibid., 1926, 69, 519; A., 1050; S. L. Jodidi, J . Amw. Chem. Soc.,1926, 48, 751; A., 636; Y. Okuda, J . Dept. Agric. Kyusha Univ., 1925, 1,163; A., 1926, 190.e3 F. B. Seibert, J . Bid. Chem., 1926, 70, 265; A., 1164.64 M. E. Pauchard, J . Pharm. Chim., 1926, 8, 248; A,, 535.'6 E. VotocBk, V.Ettel, and B. Koppovrt, BUZZ. Soc. chim., 1926, [iv], 39,( 0 I. M. Kolthoff and C. Robinson, Rec. Irav. chim., 1926, 45, 169;67 I. M. Kolthoff, Chern. Weekblad. 1925, 22, 558; A., 1926, 84.68 P. Grigorjev, 2. anal. Chem., 1926, 69, 47; A., 1049. *' E. Muller and E. Dachselt, 2. Elektrochem., 1925, 31, 662; A,, 1926, 314.70 W. Herzog, Chern.-Zig., 1926, 60, 642; A,, 1050.278; A., 601.A*, 420ANALYTICAL OHEMISTRY. 206are described, as well as the use of dichromate as the oxidisingagent.7fPhysical Methoh.A study of the absorption spectra of a large number of solutionsof different dyes has demonstrated that the width, B, of the absorp-tion band is connected with the concentration by the expressionB = Aed+y, where d is the thickness of the solution and A and yare constants for absorption bands.72 Absorption-spectra maximahave been listed for the azo-dyes obtained from a number of phenolsby coupling with pnitrobenzenediazonium chloride.73Magnesium electrodes are recommended for the production ofboth arc and spark spectra, since the magnesium lines between7000 and 3500 8.are not numerous and do not mask those of otherelements. 74 Data are given relating to the transmissive propertiesof the various types of spectral fllters employed for visible, ultra-violet, and infra-red radiation.75Details are given for the spectroscopic detection of extremelyminute quantities of mercury in vacuum tubes.76The quantity of ozone present in the atmosphere has been deter-mined by measuring the intensity of a number of Fraunhofer trans-mission lines in the region of the ultra-violet absorption band ofozone a t 3000 to 3300 A.77 Most inorganic substances exhibit nofluorescence or phosphorescence when examined in the ultra-violetlight (from a mercury arc) of wave-lengths 4400 to 2800AL., butmany salts do fluoresce.This test may be used to indicate certainimpurities.78The radio-micrometer has been used to measure the iodine con-tent of starch-iodide.79Small quantities of water may be determined in methyl alcohol,otherwise pure, by measuring the critical solution temperature ofthe sample with hexane.sOA simple X-ray spectrograph of the rotating-crystal type isdescribed,81 and details of a high-vacuum X-ray spectrometer withI.M. Kolthoff, Rec. truv. chim., 1926, 45, 745; A., 1266.J. Sebor, Chem. Listy, 1926, 20, 55, 174; A., 590.73 H. Wales and S. Palkin, J . Ame~. Chem. Soc., 1926, 48, 810; A., 615.E. Dureuil, Compt. rend., 1926, 182, 1020; A., 593.7 6 K. S. Gibson, J . Opt. SOC. Amer., 1926,13, 267; A., 1117.J. J. Manley, PTOC. Physical SOC., 1926, 38, 127; A., 376.7 7 G . M. B. Dobson and D. N. Harrison, Pfoc. Physical SOC., 1925, 38, 74;7 8 R. Robl, 2. angew. Chem., 1926, 39, 608; A., 701.7s J. Field and L. G. M. Baas-Becking, J . Oen. Physiol., 1926, 0,445; A., 590.M. M. Rising and J. S . Hioh, J. Amer. Chem. SOC., 1926, 48, 1929; A.,J. T. Xorton, J . Opt. SOC. Anw., 1926, la, 231; A., 1020.A., 1926, 140.967206 ANNUAL REPORTS ON THE PROQRESS OF CHEMISTRY.rotatory plate-holder end suitable crystal gratings for particularranges of wave-lengths are given.8aElectrochemical Methods.Electrolytic.-Polarisation curves of solutions of metals containingtraces of more noble metals from the electrochemical point of view,obtained with the aid of the dropping mercury cathode, show anumber of undulations the positions and dimensions of which arecharacteristic of the metallic impurities present.Various applic-ations of this process are described, which is sensitive to aboutlo-' g.-equivalent of metal per litre.@Copper free from cadmium may be deposited a t 1 amp. and 4 voltsby electrolysis with a rotating anode of a nitrate solution con-taining nitric, tartaric, and hydrofluoric acids,84 whilst completeseparation from bismuth is obtained by electrolysis a t 60" of asolution of the metals containing phosphoric acid.s5Conditions have been worked out for the electro-deposition ofantimony from hydrochloric acid solution containing hydrazinetmlphate.s6 Tellurium also may be rapidly determined by electro-lysis in a malonic acid solution containing ammonium sulphate andtartrate.8'Potenti0metric.-The reduction of compounds of the platinummetals to the metals by means of titanous chloride in acid solutionhas been followed potentiometricalIy ; very sharp end-points ereobtained with palladium and platinum.S8 Mercuric salts are reducedto metallic mercury by titanous chloride in hot acetic acid solution,containing ammonium chloride and also a bismuth salt 8s carrier.The method may be applied in the presence of arsenious, anti-monious, stannic, lead, cadmium, and bismuth salts and of smallquantities of iron salts.8B Iron may be determined, followingreduction with stannous chloride, in hydrochloric acid solution, bytitration a t 50" with standard potassium bromate in the presenceof cobalt chloride.The amount of bromate used in the oxidationis ascertained from the positions of the two turning points (stannousto stannic and ferrous to ferric) on the titration curve.B0 A similaraa M. Siegbahn and R. Thorreus, J . Opt. Soc. Amer., 1926,13, 236; A., 1020.84 A. Jilek and J. Lukas, ibid., p. 18; A., 262.86 W. Moldenhauer, 2. ungem. Chem., 1926, 39, 464; A., 692.86 A. Schleicher with L.Toussaint and P. H. Troquay, 2. and. Chem.,J. Heyrovskp, Chem. &9ty, 1926, 20, 122; A., 690.1926, 69, 39; A., 1020.J. Lukae and A. Jilek, Chem. Lisly, 1926, 20, 396; A., 1018.88 F. Miiller, 2. anal. Chent., 1926, 69, 167; A., 1222.89 E. Zintl and G. Rienilcker, 2. u w g . Chent., 1926,155, 84; A., 929.90 0. Collenberg and K. Sandved, ibid., 1926,149, 191; A., 1926, 140ANALYTICAL OHEMISTRY. 207method serves for the determination of gold, any aurous chloridepresent being first oxidised by addition of chlorine water; thesolution is then titrated against standard ferrous ~ u l p h a t e . ~ ~If the potentiometric titrations of cerous and cupric ions withpotassium ferrocyanide and of barium, lead, and mercurous ionswith potassium chromate are carried out a t 70" in a 30% ethyl-alcoholic medium, errors due to solubility of the precipitates andt o adsorption of ions thereon are eliminated and the potential a tthe end-point is rendered much sharper and steeper.92By suitable adjustment of conditions, it has been found possibleto effect progressive separation of iodide, bromide, and chloride(as the silver salts) from ammoniacal solution.93 Importantinvestigations and improvements in the potentiometric titrationof halides have also been made and Clark's method lends itself tothe accurate determination of the three halides in mixtures.94A platinum electrode, coated electrolytically with gold, is suitablefor the titration of oxidising acids.The results obtained withchromic, iodic, and periodic acids are described, the E.M.F.beinga linear function of the pE value of the acid, but varying withdifferent acids.95 In the determination of phosphates by titrationwith a uranyl solution in presence of acetic acid, the addition ofquinol or potassium ferrocyanide affords a sharper end-point.Alternatively] using a mercury electrode] titration may be carriedout a t 70" after addition of a known amount of mercurous sulphate,the fall in voltage a t the end-point being very sharp.s6Aromatic nitroso- and nitro-compounds may be titrated directlya t 50-80' with titanous chloride, alcohol being used as solventif necessary. The break in the curve is much more pronounced inpresence of Rochelle salt.97Attention is directed to the advantages of, and methods are givenfor using, the quinhydrone electrode in the measurement of hydrogen-ion concentration, by a number of authors.9sThe potential of a platinum electrode against a solution con-91 E. Miiller and F. Weisbrod, 2. anorg. Chem., 1926, 156, 17; A., 1117.'2 J. A. Athanitsiu, Compt. rend., 1926,182, 619; A., 376; J. Chim. phys.,OS H. T. S. Britton, Analyst, 1925, 50, 601; A., 1926, 39. *' W. Clerk, J . , 1926, 749 ; A., 590 ; E. Lange and E. Schwartz, 2. Elektro.* 5 L. Maleprade, Bull. SOC. chim., 1926, [iv], 39, 325; A., 490.* 6 S. Bodforas, Svensk Kern. T<dskr., 1925, 37, 296; A., 1926, 1018.1926, 23, 601; A., 929.chem., 1926, 32, 240; A,, 701.E. Dachselt, 2. anal. Chem., 1926, 68, 404; A., 1049.W. Ackermann, Collegium, 1926-1927.208; A,, 813; A. Hock, 2. angew.Chem., 1926, 39, 647; A., 701; C. W. 0. Hetteraohij and J. Hudig, Chem.Weekblacl, 1926, 23. 2; A,, 139; 5. B. O'Sullivm, Tram. Paraday Sac., 1925,21, 319; A., 1925, G, 822; L. Smolik, Biachem. Z., 1926, 172, 171; A., 927208 ANNUAL REPORTS ON THE PROGRESS OF CHEMISTRY.taining both ferrous and ferric ions is a function of the ratio of thetwo ions present under limiting conditions of concentration andacidity. If E, is the potential of the electrode against the acidalone and E that of the solution when iron salts are present, thena t 18" we have E = E, + 0.0577 log {[Fe*"]/[Fe"]). Hence the totaliron or the ferrous iron in a solution having been determined,measurement of the potential under standard conditions enablesthe proportion of each of the iron ions to be ascertainedag9 A newmethod for the conductometric analysis of weak acids and baseshas been described,l and also a method, applicable to iodometry,in which a P.D., between two platinum electrodes immersed in thewell-stirred iodine solution, of the same order as the polarisationE.M.F. is maintained.2Simple comparison electrodes for the titration of reducing sub-stances such as arsenious oxide and ferrous and vanadyl salts withpermanganate have been developed and details of the electrodesare furnished.3J. J. Box.B. A. ELLIS.se P. Hirsch and R. Ruter, 2. anal. Chem., 1926, 68, 328; A., 930.P. Hirach, ibid., p. 160; A., 700.C . W. Foulk and A. T. Bawden, J. Amer. Chem. SOC., 1926, 48, 2045; A.,927.a R. Lang, 2. Elektrochem., 1926, 32, 454; A., 1116