British Abstracts: Pure chemistry and physiology. ser. A

ation number six for tervalent ruthenium in its chlorosalts (cf. Briggs, A., 1925, ii, 703; Charonnat, ibid., 586). The salts [RuCl]M,,H2O, where M-K and NH, were prepared by saturating with hydrogen chloride a cooled 10% solution of the salt [RuCl (H2O)]M2. The potassium salt forms orthorhombic plates which lose their water at 120°. Howe's method of preparing the salts [RuCl5(H2O)]M2 was found to yield the salt [RuCl]Na,,12H2O when M-Na, which crystallised from acid-free solutions in soluble, efflorescent, dark red, rhombohedric crystals. The water of crystallisation is lost at 130°. Five ruthenium chloro-salts are thus known, completely analogous to the corresponding iridium and rhodium salts in which the metals have almost certainly a co-ordination number of six. Dark red, deliquescent needles of the acid RuCl3,HC1,2H2O were also prepared; this substance is considered to be [RuCl(Ĥ2O)2]H rather than [RuCl]H,2H,O, because no salt of the latter constitution is known. S. K. TWEEDY.

Properties of active hydrogen. K. F. BONHOEFFER (Z. Elektrochem., 1925, 31, 521-522).Monatomic hydrogen can be produced, by means of suitable apparatus, in a concentration of approximately 20%. Its life is about sec., as measured by chemical methods. Towards elements, oxides, and reducible organic compounds it is very active, but it does not react with nitrogen to form ammonia. The blue glow which active hydrogen emits on contact with mercury contains, in addition to mercury hydride bands, a resonance line at 2537 Å., which requires 112,000 cal. for excitation and for which no simple explanation is apparent. W. A. CASPARI.

Preparation of an ash-free wood charcoal. L. H. REYERSON (Ind. Eng. Chem., 1925, 17, 1114).See B., 1925, 979.

Hydrogen electrode electrode for flowing liquids. A. H. W. ATEN and P. H. J. VAN GINNEKEN (Rec. trav. chim., 1925, 44, 1012-1038).-See B., 1925, 1014.

Colorimetric pH test of water or unbuffered solutions. H. T. STERN (J. Biol. Chem., 1925, 65, 677-681). In order to convert bromothymol-blue into a suitable indicator for unbuffered solutions in the region of the neutral point, it is necessary to adjust the indicator to a pure dark green colour by the addition of alkali; such adjusted solutions are not stable, and a neutral solution of p-nitrophenol forms a more satisfactory indicator, being also apparently not affected by atmospheric carbon dioxide. C. R. HARINGTON.

Volumetric determination of soluble sulphates by means of barium chloride and potassium stearate. H. ATKINSON (Analyst, 1925, 50, 590600).-Barium chloride solution reacts with the alkaline (to B.D.H. universal indicator) solution of potassium stearate to form a neutral solution when the whole of the stearate is precipitated, and it is therefore possible to determine sulphates volumetrically under certain conditions. A comparison of the solution of unknown concentration with a standard solution of approximately the same concentration is necessary because the end-point of the titration is reached before the theoretical quantity of barium chloride has been added, and this discrepancy is constant for equal concentrations. In order to obtain a sharp end-point, the concentration of the solution should be of the order of 0.05N or less, and the barium chloride solution should be added in excess and titrated back with standard potassium stearate solution. Aluminium, zinc, calcium, and magnesium are quantitatively precipitated by the potassium stearate solution, but their presence is not a serious drawback. The standard potassium stearate solution is prepared by adding 22-23 c.c. of 0.5N-alcoholic potassium hydroxide solution and 100 c.c. of neutral 95% alcohol to 3 g. of pure stearic acid, and boiling. A few drops of phenolphthalein are added and either more alcoholic potassium hydroxide solution or stearic acid, until the pink colour is just discharged. The solution is made up to 450 c.c. with neutral alcohol, and 50 c.c. of distilled water are added, the flask corked, and the liquid cooled. This solution is standardised against 0-IN-barium chloride solution, of which 5.5 c.c. in 50-60 c.c. of water are used, and 25 c.c. of the stearate solution are added, or more, until the end-point is passed at the development of a greenish-blue colour. Barium chloride solution is again added until the true yellowish-green endpoint is reached. The limit of error of this method is of the order of 1 drop of 0.01N-solution.

D. G. HEWER.

Splash-head for Kjeldahl apparatus. H. LOWE (Analyst, 1925, 50, 605).—The tube from the tap funnel passes through the centre of the bulb of the splash-head. The whole is sealed together and requires only one hole in the cork of the digestiondistilling flask. D. G. HEWER.

Determination of nitrogen by Acél's method. F. HIMMERICH (Biochem. Z., 1925, 160, 105–112).— A number of modifications and improvements of Acél's method are suggested (cf. A., 1922, ii, 225). P. W. CLUTTERBUCK.

Determination of arsenic. I. BANG (Biochem. Z., 1925, 161, 195–209).—The material is incinerated with sulphuric acid and nitric acid is dropped in from a special container. After driving off excess of the latter, reduction is effected by ferrous ammonium sulphate in the presence of potassium bromide and chloride, followed by distillation into sodium hydroxide. To the distillate are added sodium hydrogen carbonate and a crystal of potassium iodide and the solution is titrated with 0.005N-iodine.

C. RIMINGTON.

Azido-dithiocarbonic acid. II. Determination of the azido-dithiocarbonate radical. A. W. BROWNE and G. B. L. SMITH (J. Amer. Chem. Soc., 1925, 47, 2698-2702). The azido-dithiocarbonate radical resembles the halogenoid radicals and may be determined by titration of the free acid with alkali, by precipitating and weighing the silver salt, by converting this into silver chloride and weighing, by titrating with silver nitrate solution by Gay-Lussac's or by Volhard's method, or by titration with alcoholic iodine. These all give slightly low results, the best being Volhard's method.

A. GEAKE.

Micro-determination of sodium. E. TSCHOPP (Helv. Chim. Acta, 1925, 8, 893-900; cf. A., 1921, ii, 655; 1924, ii, 123, 413, 500).-Volumetric, colorimetric, and electrolytic methods for micro- and semimicro-analysis of biochemical products are described in detail. The complex sodium cæsium bismuth nitrite, 6NaNO,,9CsÑO,,5Bi(NO2)3, may be precipitated under suitable conditions. A solution of the complex on electrolysis deposits the bismuth quantitatively at the cathode. R. A. MORTON.

Electrometric study of the separation of silver iodide, bromide, and chloride. H. T. S. BRITTON (Analyst, 1925, 50, 601-604). Since the solubility products of the iodide, bromide, and chloride of silver are of the order 10-16, 10-13, and 10-10, electrometric titrations of ammoniacal solutions of the three halides with silver nitrate solutions, in which the concentrations of the ammonia and silver nitrate are suitably varied, enable the continuous change in silver-ion concentration to be made sufficiently gradual to permit of the complete precipitation of one halide before the separation of the next begins. A silver electrode placed in the beaker containing the ammoniacal halide solution was connected through a salt bridge of saturated potassium nitrate solution with a normal calomel electrode. The E.M.F. of this combination were measured after the addition of each amount of silver nitrate. Using 3.37N-ammonia solution and 0.5N-silver nitrate solution, the bromide and chloride were separated quantitatively from the bromide, but not the iodide. With 0-1N-silver nitrate solution and (i) 18N-, (ii) 8N-, and (iii) 4Nammonia solution it was possible with (i) and (ii) completely to separate the silver iodide (by filtration through a Gooch crucible), but not with (iii). The experiments are illustrated by means of curves. The following mean values at 18° were found, [Ag.][I'] = 7 x 10-17; [Ag.][Br'] = 2.8 x 10-13; [Ag•][CI′]=1·8 × 10-10

D. G. HEWER.

Micro-determination of calcium and magnesium in organic liquids. L. CONDORELLI (Rend. Accad. Sci. Fis. Mat. Napoli, 1925, [iii], 31, 73—83). -When precipitated from an albuminous solution, calcium oxalate is included in a gelatinous envelope which resists the action of water and should be washed with dilute ammonia solution. The micro-methods developed by the author for determining calcium and magnesium in organic liquids are as follows: 1 c.c. of the blood or other liquid is evaporated to dryness and ashed in a platinum crucible. The ash is dissolved in 0.5 c.c. of N-hydrochloric acid and the solution transferred, by means of a thin pipette bent at right angles, to a 12 c.c. centrifuge tube, the crucible being washed successively with 0-5 c.c. of the acid, and 0.5 c.c. of water, and twice with 0.5 c.c. of 3% oxalic centrifuge tube. After addition of a drop of methylacid solution, and the wash liquors also placed in the red solution, the tube is immersed in a boiling waterN-ammonia solution from a micro-burette. Next bath and the solution neutralised by slow addition of

1 c.c. of ammonium chloride solution and 1 c.c. of

9% ammonium oxalate solution are added and the liquid is stirred well with a small glass rod, which is then washed into the tube with sufficient water to bring the total volume to 6 c.c. After 24 hrs., the liquid is centrifuged for 20 min., the clear solution being pipetted into a dry test-tube and replaced by 5 c.c. of water, which is removed after a brief centrifuging; this operation is repeated with two further quantities of water. Five c.c. of N-sulphuric acid are then added and, with the tube immersed in a boiling waterbath, the solution is titrated with 0.01N- or 0.005Npermanganate. With a liquid such as blood which contains iron, care must be taken that this is not precipitated with the calcium. To this end, the acid with which the ash is treated is introduced into the bottom of the centrifuge tube and centrifuged rapidly for 1-2 min., the clear liquid being then pipetted off into the precipitation tube; each of the washing liquids is treated similarly, the subsequent operations being as described above.

In an aliquot part of the liquid decanted from the calcium precipitate, the magnesium is precipitated as magnesium ammonium phosphate by addition of 1 c.c. of 2.5% ammonium phosphate solution and 2 c.c. of 10% ammonia solution. After 24 hrs., the crystalline precipitate is washed with three separate quantities of 5 c.c. of 10% ammonia, which are pipetted off after centrifugation. About 3 c.c. of the last wash water are neutralised with dilute sulphuric acid and treated with 1 c.c. of molybdic acid solution (50 g. of pure ammonium molybdate dissolved in 1000 c.c. of cold N-sulphuric acid) and 2 c.c. of quinol solution (20 g. dissolved in 1000 c.c. of water and 1 c.c. of concentrated sulphuric acid added); if no blue or green colour develops in 5 min., the washing is complete. The precipitate is then dissolved in 1 c.c. of N-sulphuric acid, which, together with five or six quantities of 1 c.c. of wash water, is transferred to a 25 c.c. flask, the whole being treated with 1 c.c. of the molybdic acid solution and 2 c.c. of the quinol solution, and, after 5 min., with 10 c.c. of a solution prepared by filtering a mixture of 2000 c.c. of 20% sodium carbonate solution with 500 c.c. of 15% sodium

phosgeno-aluminates "[chloroaluminates] have been prepared by allowing carbonyl chloride and aluminium chloride to react in a sealed tube with metallic chlorides. The solution was decanted and fractionally crystallised from carbonyl chloride. The vapourpressure curves at 25° have been determined and are discussed in the systems formed by the chloroaluminates of barium, strontium, and sodium, respectively, with carbonyl chloride. The data also are tabulated. The m. p. of the salts BaAlCl, CaAlCl, SrAlCl ̧, and NaAICI, are 295°, 280° (with loss of aluminium chloride), 325, and 155-5°, respectively; the solubilities in carbonyl chloride (omitting the calcium salt), 52.5%, 52-3%, 36.5% at 25°. Compounds of the following composition have been identified : 3BaAl C1,8COCL; BaAl2CI, COCl2; 5SrAl,CI,9COCI; and SrAlCl ̧,COCl2. The sodium salt forms no such compound at 25°. "Calculations of mol. wt. from the lowering of the vapour pressure indicate 15-20 atoms of metal in the strontium and sodium compounds. L. S. THEOBALD.

Solid hydrides of arsenic, antimony, and bismuth. E. J. WEEKS and J. G. F. DRUCE (Rec. trav. chim., 1925, 44, 970-974; cf. A., 1925, ii, 700).-Amorphous arsenic dihydride, As,H,, is formed as a brown powder when a solution of alkali hydroxide is electrolysed with an arsenic cathode and a platinum anode, the electrodes being separated by a porous pot. It is also produced when a solution of arsenic trichloride in dilute hydrochloric acid is added to an ethereal solution of stannous chloride; 2AsCl2+4SnCl2+2HCl=As2H2+4SnCl4. Solid antimony dihydride is similarly prepared by electrolysis, and also by the reduction of antimony salts by zinc in acid solution. Solid bismuth dihydride, BiH, is prepared by adding a solution of bismuth trichloride in hydrochloric acid to a mixture of zinc and acid while the latter is evolving hydrogen. It is a grey powder which decomposes when heated in a vacuum, and reacts violently with fused potassium nitrate. W. HUME-ROTHERY.

Hydrates and hydrogels. IX. Silicic acid. R. WILLSTÄTTER, H. KRAUB, and K. LOBINGER (Ber., 1925, 58, [B], 2462—2466; cf. Mylius and Groschuff, A., 1906, ii, 160).-Solutions of monosilicic acid are not suitably prepared by the interaction of sodium silicate and hydrochloric acid, since the subsequent dialysis is too slow and is accompanied by great loss. It is preferable to add silicon tetrachloride slowly to a well-stirred mixture of ice and water or to pass the vapours from the boiling chloride by a rapid current of air into water at 0° to -3°. The bulk of the hydrochloric acid is immediately removed by precipitation with silver oxide at 0°, whereby about 10% of the silicic acid passes to the precipitate. Very cautious addition Very cautious addition of the final quantities of silver oxide permits the removal of 99% of the hydrochloric acid, but the remainder cannot easily be eliminated in this manner owing to the solvent action of silicic acid on silver oxide; it is removed by dialysis. Solutions of a-silicic acid, free from chloride, can be rapidly concentrated at 15° in the high-vacuum distillation

apparatus until they contain 5-7% SiO2; they are completely transparent and mobile. Rapid evaporation without gelatinisation has not been effected with solutions containing more than 7-10% SiO.. Precipitation of gels from these solutions is best effected by ammonia and much ammonium chloride. The water content of the gels which have been treated with acetone never exceeds 22% (calculated on SiO2) and generally lies between the values required for HSiO and HSiO. Dialysis experiments establish the existence of at least two forms of a-silicic acid, one of which readily, the other slowly, passes through a diaphragm. They are regarded as monosilicic acid and oligosilicic acids formed from a few molecules of the former; in contrast with them are the polysilicic acids of the ẞ series formed by further condensation. The latter acids readily precipitate egg-albumin, whereas the former do not. It is remarkable that a-silicic acid is somewhat volatile with steam. H. WREN.

Bismuth nitrates. M. PICON (Bull. Soc. chim., 1925, [iv], 37, 1365–1375).-The water content of basic bismuth nitrates cannot be accurately determined from the loss of weight at 110°, but only by decomposition by heat in the presence of copper, and absorption of the water formed. The nitrate content is not accurately determined by boiling with sodium hydroxide or by the oxalic acid method, but results correct to 1% are obtained by boiling with a ferrous salt solution in an atmosphere of carbon dioxide, followed by titration with permanganate. The effect of conditions of formation on the composition of the medicinal compounds is determined. When the salts concerned are kept in a vacuum at 15° in the presence of phosphoric oxide, the following changes take place: (1) Bi(NO3)3,5H2O →→ Bi2(NO3)6,3H2O ; (2) Bi(OH)2(NO3)(NO,BiO)12,5H2O; (3) (NO3)18B20021,7H2O (NO3)18 Bi2002,6H2O; (4) (NO3)10B112013,SHO (NO3)10B112013,4H2O. The action of heat on these salts is complex and pure bismuth trioxide is not obtained below 425°. W. HUME-ROTHERY.

SOACH

Additive compounds of hydrogen chloride and sulphates of the heavy metals. F. EPHRAIM (Ber., 1925, 58, [B], 2262-2267).-Attempts to prepare anhydrous "chloro-acids" by the action of dry hydrogen chloride on lead, silver, cadmium, nickel, cuprous, cupric, mercurous, or mercuric chloride over a wide temperature interval were unsuccessful. On the other hand, hydrogen chloride readily combines with certain metallic sulphates, yielding compounds of the type [XSH H2 or [ Cl2 or [X2C) Addition of (2HCl) hydrogen chloride occurs readily with the sulphates of metals of which the chlorides do not readily evolve hydrogen chloride when treated with concentrated sulphuric acid, and the temperature at which evolution of the gas commences is very approximately the dissociation temperature of the complex. The evolution of hydrogen chloride from sulphuric acid and a chloride appears, therefore, not to be an ionic reaction. The additive products generally lose about 1-5HCI at the temperature of dissociation, whereas the

remainder is evolved only at a gradually increasing temperature; the production of additive compounds containing 0.5HCl is not definitely established. The following compounds are incidentally described and the temperatures of dissociation for the mean pressure of 713 mm. are recorded: PbS04,2HCI (32°); CdSO4,2HCl (128-135°); CuSO4,2HCl (83°); HgSO4,2HC1; Ag2SO4,2HCl, which does not exhibit a definite temperature of dissociation, but yields a series of solid solutions when heated until it ultimately becomes converted into a mixture of silver chloride and silver hydrogen sulphate. Zinc sulphate and hydrogen chloride appear to yield only a series of solid solutions; the temperature of dissociation of the adduct lies below that of the customary freezing

mixture.

H. WREN.

Conditions underlying the attack of hydrogen chloride and ammonium halide on metals.

K. A. HOFMANN and F. HARTMANN (Ber., 1925, 58, [B], 2466-2475; cf. A., 1925, ii, 685). The greater readiness with which copper is attacked by ammonium chloride vapour than by hydrogen chloride is explicable on thermochemical grounds, but the magnitude of the superiority of the former over the latter can be accounted for only if the much greater adsorption of ammonium chloride vapour is taken into account. In every case, the evolution of hydrogen from ammonium chloride is preceded by vaporisation of the latter and adsorption of the vapour. The previous view (loc. cit.) that copper reacts with undissociated ammonium chloride molecules is therefore abandoned in favour of the hypothesis that the reactive system is an adsorbate, Cu... NH,,HCl. All those conditions which increase the adsorption of hydrogen chloride or of hydrogen chloride and ammonia within the temperature range 270-330° facilitate the reaction, which yields hydrogen in a remarkable manner. Thus the presence of carbon dioxide increases the yield of hydrogen from copper gauze of limited surface, whilst aniline hydrochloride and, in particular, dimethylaniline hydrochloride are more active than ammonium chloride, since the bases are less readily carried away by the gases than ammonia. Under like conditions, hydrogen chloride gives only a very small yield of hydrogen, which, somewhat unexpectedly, is lowered by the presence of water vapour. The reaction is not facilitated by mixing the hydrogen chloride with methyl alcohol, ethyl alcohol, ether, or diphenylamine. The activity of hydrogen chloride can be increased, not only by the presence of substances which facilitate adsorption, but also by increase of the adsorbing surface, which is most readily effected by substituting copper powder for the gauze. Under these conditions, the difference between the activity of ammonium chloride vapour and hydrogen chloride may be reduced to such an extent that the ratio of the amounts of hydrogen evolved is only 1.8: 1 (instead of 140: 1); this order of magnitude is in agreement with that expected on thermochemical grounds. The superiority of ammonium chloride vapour over hydrogen chloride in chemical activity towards copper depends therefore mainly on its much greater adsorption, and is more pronounced as the surface of the copper is reduced. The decom

position of ammonium chloride vapour by tin is much less marked than by copper, since tin has but little affinity for ammonia.

If the conditions are sufficiently favourable for adsorption the chemical energy of the system is a measure of the extent of the change. Thus, ammonium bromide gives 1.7 times as much hydrogen with copper powder as does ammonium chloride, whilst ammonium iodide and copper gauze yield 2-6 times the amount of hydrogen obtained with ammonium chloride; these amounts agree with those expected from the heats of formation of cuprous bromide and cuprous iodide. H. WREN.

COPAUX and C. MATIGNON (Bull. Soc. chim., 1925, Different states of beryllium oxide. H. [iv], 37, 1359-1365).-See A., 1925, ii, 1192.

Occurrence of

dvi-manganese (atomic number 75) in manganese salts. V. DOLEJŠEK and J. HEYROVSKÝ (Nature, 1925, 116, 782-783).— An examination of the polarograph curves obtained in investigations of the electrolytic deposition potentials of manganous solutions, particularly when prepared from potassium permanganate, reveals humps which cannot be due to the presence of zinc, nickel, cobalt, or iron, but may be due to that of ekamanganese (atomic number 43) and dvi-manganese ("rhenium," atomic number 75). Manganese amalgam in contact with platinum foil was immersed for several days in a nearly saturated solution of manganous sulphate, the deposit removed from the platinum with concentrated hydrochloric acid, and, after dilution, neutralisation with sodium carbonate, and acidification with acetic acid, the solution was treated with hydrogen sulphide; the solution then contains manganese with about 2% of dvi-manganese. One of the humps is due to the element 75, but it could not be determined whether the other is caused by the element 43. Concentrated acidic solutions containing the element 75 are green, and the dry green chloride becomes black on keeping. Neutral solutions yield a yellowish-brown precipitate, probably by oxidation. Apparently higher valency compounds of the element 75 are more stable than those of manganese. Provisional spectroscopic results were obtained as follows: La1, 1430X., LB1, 1235-3X., LB2, 1204-3X., Ly1, 1059 X., the copper KB line being used as reference. The results of Noddack, Tacke, and Berg (Naturwiss., 1925, 26, 567) are inconclusive, their observed lines agreeing better with those of thallium than those of the element 75. A. A. ELDRIDGE.

Occurrence of dvi-manganese (atomic number 75) in manganese salts. A. N. CAMPBELL (Nature, 1925, 116, 866).-The second hump in the potential-current curve obtained by Dolejšek and Heyrovský (preceding abstract), and ascribed by them to the discharge of dvi-manganese, may represent the potential of incipient discharge of hydrogen. A. A. ELDRIDGE.

Complex compounds of ruthenium chlorides. R. CHARONNAT (Compt. rend., 1925, 181, 866-867).— Observations are recorded confirming the co-ordin

ation number six for tervalent ruthenium in its chlorosalts (cf. Briggs, A., 1925, ii, 703; Charonnat, ibid., 586). The salts [RuCl]M, H2O, where M-K and NH, were prepared by saturating with hydrogen chloride a cooled 10% solution of the salt [RuCl5(H2O)]M2. The potassium salt forms orthorhombic plates which lose their water at 120°. Howe's method of preparing the salts [RuCl, (H2O)]M2 was found to yield the salt [RuCl]Na,,12H2O when M-Na, which crystallised from acid-free solutions in soluble, efflorescent, dark red, rhombohedric crystals. The water of crystallisation is lost at 130°. Five ruthenium chloro-salts are thus known, completely analogous to the corresponding iridium and rhodium salts in which the metals have almost certainly a co-ordination number of six. Dark red, deliquescent needles of the acid RuCl,,HC1,2H2O were also prepared; this substance is considered to be [RuCl(H2O),]H rather than [RuCI,JH,2H2O, because no salt of the latter constitution is known.

S. K. TWEEDY.

Preparation of an ash-free wood charcoal. L. H. REYERSON (Ind. Eng. Chem., 1925, 17, 1114).See B., 1925, 979.

Hydrogen electrode for flowing liquids. A. H. W. ATEN and P. H. J. VAN GINNEKEN (Rec. trav. chim., 1925, 44, 1012-1038).-See B., 1925, 1014.

Use of the Lehmann micro-electrode. G. E. VLADIMIROV and M. J. GALVIALO (Biochem. Z., 1925, 160, 101-104).-Lehmann's micro-electrode gives good results in the case of liquids free from carbon dioxide. In presence of carbon dioxide, the method is inferior to others in both accuracy and rapidity. The method is especially applicable to very viscous liquids, jellies, and tissues.

P. W. CLUTTERBUCK.

Argentometric titration of iodides. I. M. KOLTHOFF (Pharm. Weekblad, 1925, 62, 1309— 1312; cf. A., 1921, ii, 517).—In slightly alkaline solutions, iodides may be titrated with silver nitrate solution, after addition of a trace of iodate, with very fair accuracy even in presence of large quantities of bromides or chlorides. A suitable degree of alkalinity is obtained by the addition of ammonium carbonate. In 0.1N-solutions the results are about 0.6% too low. S. I. LEVY.

Volumetric determination of soluble sulphates by means of barium chloride and potassium stearate. H. ATKINSON (Analyst, 1925, 50, 590600).-Barium chloride solution reacts with the alkaline (to B.D.H. universal indicator) solution of potassium stearate to form a neutral solution when the whole of the stearate is precipitated, and it is therefore possible to determine sulphates volumetrically under certain conditions. A comparison of the solution of unknown concentration with a standard solution of approximately the same concentration is necessary because the end-point of the titration is reached before the theoretical quantity of barium chloride has been added, and this discrepancy is constant for equal concentrations. In order to obtain a sharp end-point, the concentration of the solution should be of the order of 0.05N or less, and the barium chloride solution should be added in excess and titrated back with standard potassium stearate solution. Aluminium, zinc, calcium, and magnesium are quantitatively precipitated by the potassium stearate solution, but their presence is not a serious drawback. The standard potassium stearate solution is prepared by adding 22-23 c.c. of 0-5N-alcoholic potassium hydroxide solution and 100 c.c. of neutral 95% alcohol to 3 g. of pure stearic acid, and boiling. A few drops of phenolphthalein are added and either more alcoholic potassium hydroxide solution or stearic acid, until the pink colour is just discharged. The solution is made up to 450 c.c. with neutral alcohol, and 50 c.c. of distilled water are added, the flask corked, and the liquid cooled. This solution is standardised against 0-IN-barium chloride solution, of which 5.5 c.c. in 50-60 c.c. of water are used, and 25 c.c. of the stearate solution are added, or more, until the end-point is passed at the development of a greenish-blue colour. Barium chloride solution is again added until the true yellowish-green endpoint is reached. The limit of error of this method is of the order of 1 drop of 0·01N-solution.

D. G. HEWER.

Splash-head for Kjeldahl apparatus. H. LOWE (Analyst, 1925, 50, 605).-The tube from the tap funnel passes through the centre of the bulb of the splash-head. The whole is sealed together and requires only one hole in the cork of the digestiondistilling flask. D. G. HEWER.

Determination of nitrogen by Acél's method. F. HIMMERICH (Biochem. Z., 1925, 160, 105-112).— A number of modifications and improvements of Acél's method are suggested (cf. A., 1922, ii, 225). P. W. CLUTTERBUCK.

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