摘要:

October, 1954; The Determination Of Small Amounts Qf Lithium BY C. F. FOIiSTER A method has been devised for quantitatively separating inicrograni quatititics of lithium from an excess of sodium and potassium salts by precipitating thc lithiiiin potassium ferricyanide ~iexamcth3.lenctetr;tmirie complex from a n ;icetotic - water soliltion. The yellow complex can bc scparated by filtration and weighed, or redissolved in water and the lithium determined absorptiometrically. THE determination of small amounts of lithium by chemical methods is difficult owing to the small number of lithium compounds that are sufficiently insoluble to be of use for its isolation from 1arg-c quantities of other elements. For this reason the most reliable modern methods are physical in character. For example, flame photometry1 and ernission spectrography2 are frequentl;vT used, and polarographic3 and fluorimetric* methods are also used.Refui-e the introduction o f modern pliysical methods of c!iemical analysis, tnost method.- for tlir determination of lithium depended. on the solubility of lithium chloride in various organic solvents and its separation thereby from the comparatively insoluble sodium and potassium sdts. The solvent was tlien renioved by distillation, and the lithium chloride was weighed directly or after conversion to the sulphate. These methods, as well as the recent ion-exchaiige separation,5 perinit reasonable results to be attained ~vlien the amount nf Bitliiuni in the sample is fairly large, and the determination can be performed on the macro630 FORSTER : THE DETERMINATION OF SMALL [Vol.79 scale. They are still useful for effecting a preliminary concentration of small quantities of lithium from much larger quantities of sodium and potassium salts. The amount of sodium and potassium chlorides soluble in the organic solvents used is largely dependent on the amount of water present in the solvent. The complete dehydration of some of the solvents is not easy, as most of them have a considerable affinity for water and some are hygroscopic. Some of the organic liquids that have been used to effect the separation of lithium chloride from other alkali metal chlorides are shown in Table I. TABLE I HISTORICAL SURVEY OF SOLVENTS YJSED FOR THE SEPARATION OF LITHIUM CHLORIDE Solvent Method Date Ethyl ether - ethanol .. .. . . .. Amy1 alcohol . . .. . . .. .. Pyridine . . . . . . .. .. .. isoButanol .. . . .. .. . . n-Butanol - ethyl acetate . . .. . . Dioxan . . . . . . .. .. .. Acetone . . . . .. .. .. .. 2-Ethylhexanol . . .. .. .. .. n-Propanol . . . . .. .. .. Rammelsberg'j Gooch7 Kahlenberg and Krauskopfs Winkle+ Smith and RosslO Sinkall Brown and Reedy12 Caley and Axilrod13 Plyuschev and Shakhno14 1845 1886 1908 1913 1925 1930 1930 1942 1953 In 1929, Moser and Schutt15 made a thorough investigation of the then known methods and declared that most of them were unreliable. They approved Winkler's isobutanol method and improved it by the use of a new technique for drying the solvent with barium oxide. Sinkall and Brown and Reedy12 claimed that sodium and potassium chlorides were nearly insoluble in the completely dry solvents.In 1953, Plyuschev and Shakhno proposed the use of n-propanol saturated with dry hydrogen chloride gas. They found that sodium and potassium chlorides were nearly insoluble in this solvent, but the method was only of use for macro amounts of lithium salts. Among the more novel procedures is one described by Brauner16 in which lithium was precipitated as lithium phosphate, which was centrifuged in a standard capillary tube. The height of the precipitate was used as a measure oE the amount of lithium precipitated. A method for removing the small amounts of potassium and sodium chlorides remaining after a separation with an organic solvent was devised by Caley,17 who precipitated the lithium as stearate and measured the resultant turbidity.By this method he claimed to be able to detect 0.1 mg of lithium in 1 g of mixed chlorides. Various lithium compounds have been proposed as suitable for the precipitation and determination of lithium, and their solubilities are shown in Table 11. TABLE I1 SOLUBILITIES OF VARIOUS LITHIUM COMPOUNDS I N WATER AT 15" c Compound Solubility in 100 ml of water at 15" C, g Lithium carbonate . . .. .. .. .. 1.33 Lithium fluoride .. .. .. .. .. 0.27 Lithium phosphate . . . . . . .. .. 0.04 Lithium arsenate . . . . .. . . . . Very slightly soluble Lithium silicate . . . . . . . . .. Insoluble Lithium stearate .. .. . . . . .. 0.01 Lithium aluminate, 2Li,O.5X1,O3 . . .. . . Insoluble Lithium palmitate . . .. .. . . . .0.01 The use of sodium arsenate was proposed by T. Gaspar,ls who claimed that the resulting precipitate of lithium arsenate could be ignited and weighed. Grothe and Savelsberg19 severely criticised the use of lithium fluoride and lithium phos- phate, and they recommended the use of potassium aluminium sulphate, KAl(SO,),. 12H20, as a precipitant. The resulting lithium compound could then be ignited to lithium aluminate, 2Li20.5A1,0,. In 1938, Korenman and Kursina20 published details of a spot test for the detection of small amounts of lithium in the presence of sodium, potassium, caesium and rubidium.October, 1%4] AMOUN I'S OF LITIlIUM 6 3 I The lithium salt was precipitated from a concentrated aqueous solution by tlie addition of 15 per cent. potassium ferricyanide and 15 per cent.hexamethylenetetramine (hexaminej solutions in water. The formation of characteristic octahedral crystals, visible under the microscope, was indicative of the presence of lithium. Ammonium, potassium, sodium, rubidium and ccesium did not interfere, and as little as 0.6 pg of lithium could lie detected at a concentration of 1 in 50,000. I t involved the use of a ferric periodate complex dissolved in excess of potassium hydroxide, which formed a yellowish- white precipitate with lithium. There was no interference from potassium, sodium, rubidium or caesium. This reaction forms the basis of a method devised by Sande1122 in which the precipitate was removed by filtration, washed with potassium hydroxide solution, then dis- solved in acid and the iron determined.The sodium compound was only sparingly soluble and was co-precipitated, so that it was first necessary to remove most of tlie sodium by extraction of the dry chlorides with ethyl ether - ethanol mixture. Rogers and Caley's method23 was similar, but their periodate complex was of uncertain composition and it had to be precipitated under rigid conditions to ensure uniformity of results. The final determination was made by liberation of the iodine followed by titration with standard sodium thiosulphate. Poluektoff2I described a spot test that was specific for lithium. EXPERIMEYTAL The lithium potassium ferricyanide hexamine complex is extremely soluble in water and in an attempt to precipitate it quantitatively, some method of decreasing this solubility was sought, but this must not cause the precipitation of the reagents.Closely allied to this problem is that of washing the precipitate free frorn the excess of potassium ferricyanide, which is yellow like the lithium complex. This can be done by keeping the volume of the solutions as small as possible and by adding a miscible organic liquid, such as ethanol or acetone, to decrease the solubility of the complex. The reagent was prepared by mixing the solutions described by Korenman and Kursina2" in equal proportions and adding acetone until a slight precipitate was formed. It was also found to be necessary to add acetone to the test solution. This was most conveniently done by evaporating the solution to dryness and dissolving the residue in the minimum amount of the solvent mixture.A similar mixture containing slightly different proportions mas used for washing the precipitate, followed by acetone - water mixture to remove tlie hexainine present in the first washing mixture, if the determination was to be completed by the gravi- metric method. The precipitate can be dried and weighed, or it can be dissolved in water to form a stable yellow solution, the optical density of which can be measured with 3 Spekker absorptionieter. The optical density method is more reliable owin: to the difficulty of removing the excess of hexamine frorn the lithium complex. A colour 20 times as sensitive can be developed from the colourless leuco base of malachite green, which is quantitatively oxidised to the green dye by ferricyanide.This reaction can be used to determine ferricyanide ion provided that no other oxidising agent is present in the solution. METHOD APPAKATCS- Tlzernzostatically controlled water-bath---To maintain reagents and test solutions a t 20" C. EquiZibriz~vz clzamber-This consists of an ordinary glass desiccator containing an acetone - water (I + 1) mixture in place of the normal desiccant. The beakers of test solution are placed in it during the standing period after precipitation so that there is no loss of acetone by evaporation, as this would increase the solubility of the lithium complex. Micro jiltvation apparatzis-This consists of a filter-stick connected by rubber tubing and fine-bore glass tubing to a suction flask or Wtt's filtering apparatus. The rubber connections of the filter-stick should have sufficient flexibility to permit the filter-stick to be lowered on to the surface of the liquid in the beaker and to follow it down as the liquid is removed.If the head of the filter-stick is immersed, the droplets on top of it are not sucked in when the beaker becomes dry and extra washing is required.632 FORSTER: THE DETERMINATION OF SMALL [Vol. 79 REAGENTS- to 100ml. Hexamine solutiow, 30 per cent.-Dissolve 30 g of hexamine in 80 ml of water and dilute Potassium ferricyanide, 15 per cent. sohtion. Ferricyanide reagent-Mix 50 ml of 30 per cent. hexamine solution, 50 ml of water and 100ml of 15 per cent. potassium ferricyanicle solution. Warm the mixture to about 35" C and slowly add 150ml of acetone with stirring. Place the reagent solution in a stoppered bottle and put the bottle in a thermostatically controlled water-bath at 20" C for 24 hours before use so that the solution can reach equilibrium; a small amount of solid will settle on the bottom of the bottle.Solvent solution-Mix 100ml of 30 per cent. hexamine solution, 105 ml of water and 200 ml of acetone and store the solution at 20" C. Washing solution-Mix 100 ml of 30 per cent. hexamine solution with 110 ml of acetone and store the solution at 20" C. Malachite green leuco base-Warm 0.4g of malachite green with granulated zinc and dilute hydrochloric acid until the solution is colourless and then dilute it to 500 ml. Decant the clear solution into a bottle. MACRO PROCEDURE- Concentration of the lithium-(This procedurle is unnecessary if the total alkali salts present are less than 50 mg.) Evaporate the solution containing only chlorides of the alkali- metal group to dryness in a porcelain dish and bake the dish gently to remove ammonium salts.Scrape out the solid into a mortar and crush the aggregates. Transfer it to a Soxhlet thimble that has been dried in an oven at 105" C. Insert a plug of glass-wool into the top of the thimble and return it to the oven for a further half hour. As rapidly as possible insert the thimble into a continuous-extraction apparatus and extract it for 6 hours with 40ml of dry n-propanol. At the end of this time cool the flask and filter the contents through a filter-paper into a clean flask, washing the original flask with dry n-propanol. Remove the solvent by distillation, and transfer the salts to a 10-ml tared beaker with the aid of a few millilitres of distilled water.Evaporate the solution to dryness, cool the residue in a desiccator and weigh it. Precipitation-Dissolve the dry residue in solvent solution at 20" C, using 1 ml of solvent for each 5 mg of solid. When all the residue is dissolved, transfer 1 ml of the solution by pipette to a 5-ml beaker and add 2 ml of ferricyainide reagent. Mix the solution carefully, avoiding wetting or splashing the sides of the beaker. Place lids on the weighing-bottles and maintain them at 20" C for a quarter of an hour. If beakers are used, place them in the equilibrium chamber at 20" C for a quarter of an hour. Filtration-Filter the solution through a No, 3 sintered-glass crucible under suction.Allow the precipitate to drain and, without delay, wash out the beaker with 0.5 ml of solvent solution followed by successive 0 6 m l portions of washing solution delivered from a pipette, pouring each portion through the sinter so that eventually the whole precipitate is transferred to the sinter and washed free from the excess of ferricyanide reagent. Four or five such washes are generally sufficient. Gravimetric determination of the complex-If a gravimetric determination is desired, the precipitate must be further washed with a mixture of acetone containing 6 per cent. of water to remove the hexamine that is present in the normal washing solution. About five 1-ml portions of aqueous acetone are sufficient for this. The crucible is finally washed with pure acetone, dried at 50" C and weighed.For large precipitates 1-ml portions may be used. The weight of precipitate divided by 48.905 = weight of lithium. A bsorptiometric detmnination of the complex-Dissolve the precipitate through the filter into a clean flask with water and dilute the solution to a suitable volume (the use of 100 ml of water for each 1500 pg of lithium ensures a suitable coneentration). Measure the absorp- tion of the solution, making use of the Spekker absorptiometer with a 1-cm cell and Ilford No. 601 violet filters and a water setting of 1.00. Blank determination-As a check on the purity of the reagents, a standard of known lithium content should be tested with each batch of determinations.October, 19541 AMOUNTS O F LITHIUM 633 High results are caused by an excess of acetone in one of the solutions leading to precipitation of the ferricyanide reagent and the co-precipitation of other salts. Low results are usually due to one or more of the following- (i) a rise of temperature during precipitation; (ii) loss of acetone by evaporation causing the water to acetone ratio to be too great; (izi) absorption of water from the atmosphere; and (iv) incomplete drying of the salts when the solution is evaporated to dryness.CaEibration-Accurately measure aliquots of a solution of pure lithium chloride in water Aliquots containing 0, 200, 400, 600, 800, 1000, 1200 and 1400pg of Evaporate the solutions to dryness and proceed as described in the Plot the optical densities into 10-ml beakers.lithium are suitable. method above, using 1 ml of solvent solution and 1 ml of reagent. against concentration of lithium in pg per 100 ml of solution. MICRO PROCEDURE- For the determination of less than 50 pg of lithium, some refinement of the above method is necessary. Precipitation-Transfer the final solution containing the lithium salt, freed from other metals, to a 5-ml beaker or weighing-bottle and evaporate it to dryness. The total residue should not exceed 2000 pg. Add 0.5 ml of reagent from a pipette without splashing the sides of the beaker and place the beaker in the equilibrium chamber at 20" C for 1 hour. Filtration-After applying the suction, gently lower the filter-stick on to the surface of the liquid and continue to remove the liquid until the beaker is dry.Wash the beaker with 0.5 ml of solvent solution followed by three successive 0.5-ml portions of washing solution from a pipette so that all the excess of reagent solution is removed. The final washings should be quite colourless as. they pass through the capillary tube. Replace the receiver by a clean flask. Dissolve the precipitate in a few drops of water and suck the solution through the filter-stick into the flask. Wash the beaker and filter-stick with further small portions of water and suck them through into the flask. Transfer the solution to a 100-ml calibrated flask and add 40 ml of ethanol and 8 ml of malachite green leuco base solution. Dilute the solution to the mark with water and mix it thoroughly. Allow it to stand for 15 minutes before measuring the optical density.Transfer a portion of the solution t o a 2-cm cell and measure its optical density, making use of the Spekker absorptiometer, with an Ilford No. 607 orange filter and a water setting of 1.00. Calibration-With a pipette, place 2 ml of each of the yellow solutions used to calibrate the graph for the macro method and a blank into 100-ml calibrated flasks. To each solution add 40 ml of ethanol and 8 ml of malachite green leuco base solution. Dilute the solution to the mark and mix it. Allow it to stand for 15 minutes and measure the optical densities with a Spekker absorptiometer, Ilford No. 607 orange filters and a water setting of 1.00. Plot the optical densities against concentration of lithium in pg per 100ml of solution.Alternatively a calibration graph can be prepared from a standard solution of potassium ferricyanide on the assumption that 2 atoms of lithium are equivalent to 1 molecule of potassium ferricyanide. RESULTS Dissolve it in 0.2 ml of solvent solution at 20" C. Some typical results are shown in Tables 111, IV, V and VI. INTERFERING RADICLES The heavy metals interfere and must be removed by normal analytical procedures. Calcium can be removed by precipitation as oxalate and magnesium by precipitation with 8-hydroxyquinoline. The use of ammonium phosphate to precipitate magnesium should be avoided as the excess of phosphate is difficult to remove. Calcium and magnesium can be removed simultaneously by precipitation with 8-hydroxyquinoline.24 The alkali metals do not interfere but, if they are present in greater quantities than the limits stated below, they are co-precipitated and lead to high results for lithium.The amounts of alkali metals as chlorides that can be tolerated in 1 ml of solvent solution at 20" C are as follows: potassium, 30 mg; ammonium, 5 mg; sodium, 5 mg; rubidium, 50 mg; and caesium, 30 mg.634 FORSTER: THE DETERMINATION OF SMALL TABLE 1111 [Vol. 79 DETERMINATION OF KNOWN AMOUNTS OF LITHIUM BY THE MACRO METHOD Lithium taken, Pg 50 5 5 60 70 70 83 90 100 100 110 120 130 138 Lithium found, tLg 48 58 5s 65 72 86 88 100 102 115 119 128 145 Error, clg -2 + 3 -2 -5 +2 + 3 -2 Nil + 2 -5 -1 -2 +7 Lithium taken, cL9 150 150 160 1 so 190 220 250 280 3 10 500 1000 1500 2000 1 Lithium found, CLg 150 157 167 178 200 230 257 275 315 488 1010 1515 2000 Error, Pt: Xi1 + 7 ST - 2 + 10 + 10 +7 -5 +5 - 12 + 10 + 15 Nil TABLE IV DETERMINATION OF LITHIUM AFTER SEPARATION FROM A LARGE EXCESS OF SODIUM CHLORIDE BY EXTRACTION WITH %-PROPANOL Lithium taken, Lithium found,* Error, P8 clg Pg 1 g of sodium chloride present- 60 65 +5 90 93 $3 120 124 +4 150 147 -3 180 190 + 10 20 g of sodium chlovide present- 400 415 500 510 600 620 1000 970 2000 1970 + 15 + 10 + 20 - 30 - 30 * Corrected for blank due to impurities in the sodium chloride.TABLE V DETERMINATION OF LITHIUM IN THE PRESENCE OF OTHER SALTS Lithium taken, Lithium found, cLg Pg 4.5 m,g of sodium chloride pesent- 50 47 50 53 60 60 60 65 70 73 80 84 so 79 90 88 100 104 100 104 150 155 200 195 30 mg of potassium chloride pyesent- 500 497 1000 990 Error, cLg -3 +3 Nil +5 + 3 +4 -1 -2 +4 $4 +5 -5 -3 - 10October, 19541 AMOUNTS OF LITHIUM 635 TABLE VI DETEXMITU’ATIOK OF LITHIUM BY THE MICRO METHOD Lithium taken, Lithium found, Error, Pg D 10 15 20 30 40 50 PZ 7 l I 16 20 33 43 49 COMPOSITION OF THE COMPLEX The complex was originally considered to be lithium ferricyanide plus an unknown number of hexamine molecules. However, the graph constructed for the determination of lithium by malachite green based on potassium ferricyanide showed that there were only two lithium atoms equivalent to each molecule of ferricyanide.To establish the probable formula of the complex the following analysis was made. The complex (68,100 pg) made by precipitating 1400 pg of lithium was dissolved in water.Silver sulphate was added to the hot solution to precipitate silver ferricyanide. This was removed by filtration, washed with water, dissolved in concentrated sulphuric acid, and the silver was determined by precipitation as chloride. This showed a ratio of 3Ag to ZLi, which confirmed the result from the calibration graph. Nitrogen was determined in the filtrate from the silver ferricyanide precipitation by means of Nessler’s reagent after distillation, and 9400pg of nitrogen were found. From these results a probable formula for the complex is- Hence 48.905 g of the complex contain 1 g of lithium. 2Li,Fe(CN),.K,Fe(CN),.5 [(CH,),N,.6H20]. Most of this work was carried out at the Admiralty Materials Laboratory, Holton Heath Dorset. 1. 2 . 3. 4. 6. 7 . 8. 9.10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24. 3. REFERENCES Broderick, E. J., and Zack, P. G., A + d . Chem., 1951, 23, 1435. Oplinger, G., I b i d . , 1947, 19, 444. Kolthoff, I. M., I n d . E n g . Chew., A+aal. Ed., 1943, 15, 473. White, C. E., Fletcher, M. H., and Parks, J., AmZ. Chew., 19.51, 23, 478. Sweet, R. C., Riemaii, W., and Beukenkamp, J., Ibid., 1952, 24, 952. Rammelsberg, C., Pagg. Ann., 1845, 66, 79. Gooch, F. A., Pvoc. Aww. Acad. AYts and S c i . , 1886, 22, 177. Kahlenberg, L., and Krauskopf, €7. C., J . A7uzev. Chew. SOC., 1908, 38, 1104. Winkler, S., 2. anal. Cheawz., 1913, 52, 628. Smith, G. F., and Ross, J . F., J . Anzev. Chem. Soc., 1925, 4’7, 774 and 1104. Sinka, A., 2. anal. Chein., 1930, 80, 430. Brown, M. H., and Reedy, J. H., Ind. Evzg. Chew., Anal. Ed., 1930, 2, 304. Caley, I., and Axilrod, G., Ibid., 1942, 14, 242. Plyuschev, V. E., and Shalrhno, I. V., J . rlizal. Chem., U.S.S.R., 1933, 8, 293. Moser, L., and Schutt, K., M h . Che,+z., 1929, 51, 23. Brauner, B., Coll. Czech. Chew. Co:nm., 1930, 2, 442. Caiey, E. R., J . Amer. Chevlz. Sac., 1930, 52, 2764. Gaspar, T., Anal. Fis. Quim., 1932, 30, 406. Grothc, H., and Saveisbcrg, W., Z. a ~ a l . Chew;., 1937, 10, 81. Korenman, I. M., and Kursina, R4. M., J . A$)l. Clzena., U..S.S.R.> 193’7, 10, 1494. Pohektoff, N. S., Mikrocheimie, 1933/34, 14, 265. Sandell, E. B., “Colorimetric Determination of Traces of Metals,” First Edition, Interscience Publishers, New York, 1944, pp. 301 to 304. Rogers, T. B., and Caley, E. R., I n d . Eng. Chem., Anal. E d . , 1943, 15, 209. Silverman, L., and Trego, K., A m l y s f , 1953, 78, 717. CHEMICAL SECTION TEST AND INSPECTION BRANCH POST OFFICE ENGINEERING I)EPARTR.IENT STUDD STREET, ISLINGTON, N. 1

ISSN:0003-2654    

DOI:10.1039/AN9547900629

出版商:RSC    

年代:1954

数据来源: RSC

摘要:

636 BRYSON AND LEKZER-LOWY: THE SEPARATION OF ZINC FROM OTHER [VOl. 79 The Separation of Zinc from Other Elements the Use of Activated Copper BY ALEXANDER BRYSON AKD S. LENZER-LOWY Zinc can be separated from other metals by the addition of activated copper powder to a solution containing cyanide and tartrate. Lead, bismuth, tin, cadmium, silver and mercury are precipitated by the copper, whereas zinc, cobalt, nickel, copper, iron and aluminium remain in solution. Zinc is precipitated from the filtrate by sodium sulphide, and the sulphide is redissolved in acid and determined either volumetrically or gravimetrically. Manganese, if present, is removed before the copper powder is added. The method is applied to the analysis of several ores. A METHOD is presented for the separation of zinc from other elements in alloys such as brasses, bronzes and zinc ores.Activated metallic copper powder is added to a solution of the alloy containing cyanide and tartrate. It displaces lead, bismuth, tin, cadmium, silver and mercury so that only zinc, copper, cobalt, nickel, iron and aluminium remain in the solution. When sodium sulphide and sodium hydroxide are added to this solution, zinc sulphide free from other metallic sulphides is precipitated; the zinc in the precipitate is determined volu- metrically or gravimetrically. Antimony interferes and should be absent except for small amounts. Manganese, if present, is removed as manganese dioxide before the reduction with copper. The only method hitherto described that ensures in two operations a reasonably complete separation of zinc from most other metals consists in precipitating the metals of the copper and arsenic group with hydrogen sulphide in fairly strong acid solutions, and then precipitating zinc after buffering to pH 2 to 3.This method, however, has some undesirable features. Besides requiring large amounts of hydrogen sulphide, it is well established that copper, cadmium and mercury sulphides adsorb considera.ble amounts of zinc su1phide.l ,2 s3 Caldwell and Moyer4 recommend the addition of small amounts of crotonaldehyde to reduce co- precipitation. For routine analysis by the acid ferrocyanide titration, it is usually unnecessary to separate zinc as sulphide, as of the common interfering elements, copper, cadmium, manganese, aluminium and iron, all but cadmium are readily removed.The usual methods of separating these metals, however, lead to unsatisfactory conditions' for the ferrocyanide t i t r a t i ~ n . ~ In the alkaline ferrocyanide method frequently used -in mining laboratories, copper and cadmium must be removed, while ferric ion, if absent, is added together with citrate and ammonium hydroxide. The end-point of the titration with potassium ferrocyanide is indicated by the appearance of Prussian blue on a spot-plate in the presence of acetic acid. The method is very sensitive to operating conditions, but apparently the results are consistent when it is used by experienced workers. The figures for zinc quoted by the laboratories supplying the samples of zinc ore used by us were determined by this method.In a previous papere we described a method for the separation of cadmium and zinc based on the fact that copper will displace cadmium but not zinc from a solution containing cyanide and tartrate. This principle has now been extended, and it has been found that from solutions containing cyanide and tartrate, activated copper will also displace bismuth, tin, lead, mercury and silver, while zinc, cobalt, nickel, antimony, manganese, iron and aluminium remain in solution. When sodium sulphide and sodium hydroxide are added to the solution, zinc sulphide free from all eleirieiits except antimony and manganese is precipitated. Although antimony trisulphide is not precipitated on the addition of sodium sulphide and sodium hydroxide, appreciable amoiints are co-precipitated with zinc sulphide.As it is insoluble in the acid used to dissolve the zinc sulphide, a small amount of antimony trisulphide can be tolerated, but manganese must be removed.October, 19541 ELEMENTS BY THE USE OF ACTIVATED COPPER 637 It is possible to determine approximate values for the standard electrode potentials, Eo’, for the following reactions- Cu + 4CN’ + Cu(CN),”’ + e Zn + 4CN’ + Zn(CN),” + 2e Cd + 4CN’ + Cd(CN),” + 2e Hg + 4CN’ + Hg(CN),” + 2e Ag + 2CN’ + Ag(CN),’ + e Ni + 4CN’ + Ni(CN),” + 2e from the standard electrode potentials of the metals in non-complex forming solutions and the instability constant^^^^ of the complex ions. The calculated values refer to solutions of unit activity for the ions concerned and therefore do not apply to the conditions used in practice.However, they may be taken as indicative of the relative ease of replacement of the metal. Calculated values for Eo’ together with recorded instability constants for the complex ions are as follows- Copper Zinc Cadmium Mercury Silver Nickel Instability constant . . 2 x 10-27” 1.3 x lO-’7t 1.4 x 2.5 x 3.8 x l O - l g t 3 x &’ . . . . 1.09 1.26 0.90 0.37 0.29 1.09 * From Sidgwick.7 t From Latimer.8 f Value from spectropliotometric measurements by B. Morris. These figures indicate that copper should displace silver, mercury and cadmium from a solution containing cyanide. There is little known about the instability constants of cobalt and manganous complex cyanides and the published figures for the Ni(CN),” complex are unreliable owing to the uncertain behaviour of nickel as a metal electrode; but qualitative tests show that these metals are not displaced from solution by activated copper.Cobalt and nickel do not interfere with the precipitation of the zinc sulphide by sodium sulphide from complex cyanide s o l ~ t i o n . ~ Manganese, however, must be removed because it is partly precipitated under these conditions. EXPERIMENTAL Qualitative tests were made initially to determine the metals, other than cadmium, precipitated by copper. This was done by forming the complex cyanide - tartrate of the metal being tested, boiling the solution with copper powder and observing whether or not a deposit appeared on the copper. The filtrate was tested for quantitative removal of the precipitated metal.It was found that bismuth, tin, lead, silver and mercury were precipitated by copper powder, while iron, copper, cobalt, manganese and nickel were converted to stable complex cyanides that remained in solution. Arsenic remained in solution as arsenate and antimony and aluminium as complex tartrates. Only manganese was precipitated by the addition of sodium sulphide, but in presence of zinc and cyanide ions, orange antimony trisulphide was co-precipitated with zinc sulphide and so antimony should be absent except for traces. If manganese is present, it is removed by precipitation as manganese dioxide with hydrogen peroxide from the complex cvanide solution. This method is only suitable with small amounts of manganese, because in the presence of zinc the precipitate may contain manganites.Also, if tartrates are present, the manganese is so strongly complexed that it is not precipitated by hydrogen peroxide, or if partly precipitated, as sometimes happens, it usually redissolves on boiling. Therefore the manganese must be removed before the tartrate is added. If manganese is absent, it has been found preferable to add sodium potassium tartrate to the acid solution after heating to fumes with sulphuric acid rather than after neutralisation of the acid solution with sodium carbonate and addition of potassium cyanide. In this way it is easier to form the soluble complex tartrates, particularly those of metals that do not form complex cyanides. The concentrations of potassium cyanide and sodiuni potassium tartrate for the cadmium - zinc separation6 were found to be suitable for the general separation also.The preparation of an active copper powder is described in the same paper. To determine the efficiency of the method, two sets of quantitative tests were made. In the first series, solutions were prepared containing 1 mg per ml each of arsenic, tin, cadmium, Arsenic was not precipitated under these conditions.638 BRYSON AND LENZER-LOWY: THE SEPARATION OF ZINC FROM OTHER [Vol. 79 bismuth and lead; 25 ml of this mixture were added to various amounts of zinc from 6 to 160 mg. The results were as follows- After separation of the interfering elements, the zinc was determined. Weight of zinc added, mg . . .. . . 166.0 66.4 33.2 6.6 Weight of zinc found, mg . . ... . 165-5 66.0 33.2 6.2 In the first two experiments the zinc was estimated volumetrically and in the last two gravime trically . In a second series of experiments, zinc was s,eparated from mixtures containing various amounts of silver and mercury. The 'zinc was determined volumetrically and the results are shown in Tables I and 11. TABLE I SEPARATION OF ZINC FROM MIXTURES CONTAINING VARIOUS AMOUNTS OF SILVER Weight of silver added, mg . . . . . . 104-0 42.0 104.0 42.0 Weight of zinc added, mg . . .. . . 130.5 1304 65.3 65.3 Weight of zinc found, mg . . .. . . 1:30.0 130.1 65.3 65-3 TABLE 11 SEPARATION OF ZINC FROM MIXTURES CONTAINING VARIOUS AMOUNTS OF MERCURY Weight of mercury added, mg . . 98.0 39.0 98.0 39.0 98.0 39.0 Weight of zinc added, mg. . . . 163.1 163.1 130.5 130.5 65.3 65.3 Weight of zinc found, mg.. . . 162.5 162.6 130.0 130.1 64.9 65.0 The method was then applied to five zinc ores supplied together with their analyses by Broken Hill South Limited and North Broken Hill Limited. The zinc in the ores was determined by separating it as described above a:nd titrating it with potassium ferrocyanide according to the procedure of Richardson and B'ry~on.~ Check analyses on two ores were made by the classical method of removing the copper and arsenic group with hydrogen sulphide from a moderately strong acid solution, followed by the precipitation of the zinc from a solution containing formic acid and sodium formate a t a pH of 2 to 3. The zinc was subsequently determined gravimetrically as zinc pyrophosphate. The results of the analyses are recorded in Table 111.NOTES TO TABLE III- In ores B and D the copper treatment was omitted, as the only interfering metal present in appreciable amounts was lead and this was removed during the initial stages by precipitation with sulphuric acid. In ore C a small amount of free sulphur remained after dissolution in acid. It must be removed by filtration before neutralising with sodium carbonate as it will dissolve in the alkaline solution and precipitate the metals as sulphides. The results by the present method and the check analyses are in satisfactory agreement, but all the figures are lower than those supplied.. These latter, however, were determined by the alkaline ferrocyanide method, which is generally considered to be less accurate than other procedures.METHOD Weigh a sample of ore or alloy containing not more than 200 mg of zinc into a 250-ml conical beaker, dissolve it in 10 ml of aqua regia, cool the solution and add 2 ml of concentrated sulphuric acid. Evaporate the mixture to fumes of sulphur trioxide, cool it and wash the sides of the beaker with 5 to 10 ml of water, and then add 5 g of sodium potassium tartrate and boil for several minutes. Cool the solution and neutralise it by adding small amounts of solid sodium carbonate until effervescence ceases; keep the beaker covered with a watch- glass during the operation. Wash the sides of beaker and add 10 per cent. potassium cyanide solution so that the weight of potassium cyanide is equal to about ten times the weight of metals in the solution.For instance, to 0.3 g of alloy add 30 ml of 10 per cent. potassium cyanide solution. When an unknown ore is analysed, assume a metal content of 50 per cent., e.g., for 0-5 g of ore, add 25 ml of 10 per cent. potassium cyanide solution. Heat the alloy solution, which should have a volume of 70 to 80 ml. Add freshly prepared copper powder6 in small amounts at a time, boiling the solution after each addition until after the last addition it remains red after boiling for several minutes. The reaction takes 15 to 30 minutes, accordingOctober, 19,541 ELENIENTS BY TIIE USE OF ACTIVATED COPPER 639 to the amount of metals to be removed. Separate the copper powder and precipitate by immediate filtration through Whatman No. 30 filter-paper and wash the solid with water.To the filtrate add 20 ml of 5 A’ sodiuni hydroxide, dilute to about 200 ml, heat to boiling and add 25 ml of 40 per cent. sodiuni sulphide solution. Leave the white flocculent zinc sulphide to settic for several hours or overnight. Remove it by filtration through a Whatman No. 42 filter-paper and wash it with 2 per cent. sodium chloride solution. No difficulty should be experienced with the filtration if the filter-paper is carefully fitted to the funnel Sample . . . . SiO,, Ol0 . . . . Fe, oh . . . . .. AlZo,, O G . . .. MnO, 7” . . . . CaO, . . .. .. s, yo . . . . .. so,, 0; . . . . . . Pb, 7o . . . . . . c u , yo . . . . . . As, ?& . . . . . . Sb, yo . . .. .. sn, ,o . . . . . . Ag . . . . . . Insoluble matter, 9, . . Cd? 2: . . . . . .TABLE 111 ANALYSES OF A I3 3.3 32.33 2.5 26.63 s-79 5.70 0.67 3.27 1.96 1-47 0.33 1.75 10-71 0.075 2.66 1.00 22.40 0.09 0.1 8 0.083 0.128 0.40 0.055 0.2 17 - 20 oz 18.8 oz per ton per ton 3 2 - 00 15.90 3 1 * 3 0 - - ZINC ORES C - 13.8 ._ Zinc found by present r51.50 r r l 15.56 8-14 niethod, O/, . . . . 51*41{ 51.30 1 5 . a . 1 ~ 25,53 5.42 8-20[8-30 4 9 * 1 4 { ~ ~ : ~ ~ 151.42 18.14 -- I - 48.64 J 48.95 31.33 Zinc found b~; pyrophospliate 1 4 8 . 7 2 method, O 0 . . Copper treatment . . . . yes no Yes no ye5 Key to zinc ores: -4 South Mine zinc concentrate from Rrolien Hill South Ltd. H South Mine oxitlised crude ore froin Broken Hill South Ltd. C South Mine Conrad ore from Rroken Hill South Ltd. D Flotation lead concentrate from North Broken Hill Ltcl. E Flotation zinc concentrate from Eoi-th Broken IIill Ltd.and washing is carried out as recommended. Of the electrolytes tried, sodium chloride was found to be the most satisfactory for preventing peptisation. Return the zinc sulphide precipitate and filter-paper to the beaker used for precipitation, dissolve it in dilute acid and determine the zinc in the filtrate either volumetrically or gravimetrically. For amounts of lead exceeding 50 mg, it is often more convenient after the evaporation with sulphuric acid and before sodium potassium tartrate is added, to remove the lead sulphate by filtration, as lead sulphate is partly soluble in the tartrate. This also reduces the amount of copper powder required. If manganese is present, it can be removed in the following way.After heating to fumes with sulphuric acid, dilute the residue with a small amount of water and neutralise the acid with solid sodium carbonate, and then add the calculated amount of 10 per cent. potassium cyanide solution and a few millilitres of 30 per cent. hydrogen peroxide and heat slowly to boiling. Continue to boil the solution for several minutes, filter it while hot through a Whatman No. 31 filter-paper and wash the residue with hot water. To the filtrate add sodium potassium tartrate and proceed as above. Sometimes, particularly when much tin or bismuth is present, small amounts of the interfering metals remain in solution and are subsequcntly precipitated by sodium sulphide. On solution of the zinc sulphide in dilute acid, the impurities either remain insoluble or may be precipitated by passing hydrogen sulptiide through the solution.640 HARRISON AND HARVEY : POLAROGRAPHIC DETERMINATION OF [Vol. 70 REFERENCES 1. 2. 3. 4. 5. 6. 7 . 8. 9. Kolthoff, I. M., and Van Dijk, J . C., Chem. Weekbl., 1922, 59, 1351. ~- , Chem. Zentrbl., 1923, 94, [ii], 440. Feigl, F., 2. anal. Chem., 1924, 65, 25. Caldwell, J. li., and Moyer, H. V., J . Amer. Chem. SOC., 1937, 59, 90. Richardson, M. R., and Bryson, A., Analyst, 1953, 78, 241. Bryson, A., and Lenzer-Lowy, S., Ibid., 1953, ’78, 299. Sidgwick, hi. V., “The Chemical Elements and their Compounds,” Clarendon Press, Oxford, 1950, Latimer, W. M., “Oxidation Potentials,” Prentice Hall Inc., New York, 1950, pp. 157, 159, 166, Evans, 13. S., Analyst, 1946, 71, 460. p. 133. 177. DEPARTMENT OF ANALYTICAL CHEMISTRY SCHOOL OF APPLIED CHEMISTRY N.S.W. UNIVERSITY OF TECHNOLOGY SYDNEY, AUSTRALIA First submitted, September 7th, 1953 Amended, April 29th, 1954

ISSN:0003-2654    

DOI:10.1039/AN9547900636

出版商:RSC    

年代:1954

数据来源: RSC

摘要:

640 [Vol. 70 Polarographic Determination of Free Sulphur in Petroleum Fractions BY S. HARRISON A r m D. HARVEY A method is described for the polarographic determination of free sulphur in petroleum fractions. The solvent - electrolyte medium used is a 0.2 M solution of ammonium acetate in glacial acetic acid. A reduction wave of half-wave potential -0.39 volt is produced with a mercury-pool anode. The method is shown to be satisfactory for the direct determination of concentra- tions of free sulphur ranging from 0.5 to 10p.p.m. The non-interference of a number of organic sulphur compounds is demonstrated. OWING to the corrosive effect of free sulphur on engine parts, the careful control of the free sulphur content of petrol and other hydrocarbons is considered essential in their production.Until recently no entirely satisfactory method had been proposed for the analytical determination of free sulphur. Proskel ,2 was the first to publish a polarographic procedure for the determination of sulphur extracted by pyridine from rubber. The polarographic reduction of the sulphur was carried out in an aqueous acetate buffer solution, which was an unsuitable solvent for petroleum fractions. With methanol - pyridine - hydrogen chloride as the electrolyte - solvent, Hall3 reported successful determinations of free sulphur in petrol at concentrations of from 1 to 100p.p.m. In the same year GerbeI"' published details of a polarographic method for determining free sulphur in kerosene and petrol, with a mixture of ethanol and benzene as the solvent and acetic acid - sodium acetate as the electrolyte.A more recent contribution on this topic is a pa-per by Eccleston, Morrison and Smith5 on free sulphur in crude oil. Difficulties of solubility led these workers to use benzene - methanol - pyridine - hydrogen chloride as the solvent - electrolyte medium. Bergman and James,6 who investigated non-aqueous solvent - electrolyte media, reported on the use of glacial acetic acid containing ammonium acetate in polarography. Preliminary investigations indicated that this solvent - electrolyte might be used in the determination of free sulphur in petrol. The method has now been successfully developed and applied to petrols containing as little as 0.5 p.p.m. of free sulphur. We have investigated the possibility that several organic sulphur compounds might interfere in these polarographic procedures, and have concluded that the polarographic method should be of wide application to petroleum products.DISCUSSION AND RESULTS With this method, in which a solution of animonium acetate in acetic acid is used, the solubility of the petrol in the solvent - electrolyte was limited by the concentration of electrolyte in the solvent. The reduction waves were satisfactory in 0.2 M electrolyte solution. The waves became less distinct in more dilute solutions.October, lU54] FREE SULPHUR IS E'ETROLET'M FKXCTIOSS 64 1 i!lien dealing with petrols containing not more than 10 p.p.ni. of free sulphur, a mercury- pool cell was found to be entirely satisfactory. Gerber4 suggested, however, that for higher concentrations of free sulphur (20 p.p.m.), the use of a mercury pool was unsuitable owing to formation of a film of mercury sulphide on it.This determination of free sulphur is based upon the measurement of the diffusion current produced when sulphur is reduced at a dropping-mercury cathode, the reduction occurring at a potential of -0.39 volt. Hall3 suggested that the sulphur was reduced according to the following equation- S + 2H+ + 2e- == H,S 'To establish the reliability of the quantitative determination of free sulphur, a number of standard solutions of sulphur of different types and sources in various solvents 1ver-e prepared, and these standards were checked one against the other. A standard of 10 p.1j.m. of sulphur in the electrolyte - solvent was finally used for calibration.DBTERMINATIOY OF FREE S'C'LPHUR IN SYSTHETIC SOLUTIONS Sulphur added, p.p.m. 0.40 0.50 0.80 1-00 1.80 1.60 2.00 8.00 2.30 Sulphur found, p.p.m. 0.40 0.45 0.80 1-00 1.20 1-60 2.00 1-90 2.40 Sulphur added, p.p.m. 2.80 3.00 3.20 3.60 4.00 5.00 5.00 6.00 Sulphur found, p.p.m. 2.84 2.90 3.20 3-66 4.00 5.05 5.00 6-10 It was observed that a maximum developed in the reduction wave of free sulphur in petrol at concentrations greater than 6 p.p.m. It has not been possible to find a suitable maximum suppressor. Despite its very low solubility in glacial acetic acid, gelatin may be used as a maximum suppressor, but in this application the gelatin was found to give a significant sulphur wave. In the medium used, the half-wave potential of the sulphur wave is -0.39 volt when a mercury-pool anode is used.A number of synthetic samples of petrol containing from 0.4 to 6-0 p.p.m. of free sulphur were examined, and the results are shown in Table I ; the polarograms are shown in Fig. 1. Potential Fig. 1. Polarograms of free sulphur in petrol in glacial acetic acid solvent : curve A, 6-4 p.p.m. cjf sulphur; curve R, 2.4 p.p.m. o f sulphur; and curve C, 3.4 p.p.m. of siilphur Potential Fig. 2. petrol with added sulphur compounds: curve A, 4.4 p.p.m. of sulphur; curve H, 4.4 p.p.m. of sulphur f 100 1i.p.m. c;f thiophene; and curve C, 4.4 p.p.m. o f sulphur -+ 100 p.p.m. of butyl mercaptan Polarograms of free sulphur i n642 HARRISON AND HARVEY POLAROGRAPHIC DETERMINATION OF [Vol. 79 The diffusion currents were plotted against concentration and gave a straight line.The results indicate satisfactory precision. The applicability of the method, however, depends on the non-interference of organic compounds, particularly those containing sulphur. The examination of a number of such compounds was undertaken. Solutions of the compounds at concentrations of 100 to 500 p.p.m. in petrol were examined polarographically to determine whether there were reduction waves at the reduction potential of free sulphur (-0.39 volt). The same solutions were then examined after a standard amount of sulphur (4 P.P.m.) had been added to each; no change in the diffusion current or reduction potential TABLE I1 DETERMINATION OF FREE SULPHUR IN THE PRESENCE OF ADDED SULPHUR- CONTAINING COMPOUNDS Sample* 1 2 3 4 5 6 7 8 9 10 isoPentyl sulphide I added, p.p.m.8-0 8.0 nil nil 8.0 8.0 nil nil nil nil Butyl nercaptan added, p.p.m. 1500 1500 nil nil 1500 1500 nil nil 1000 1000 D iphenyl dphide added, :p . p . m. 1500 1500 nil nil 1500 1500 4000 4000 2000 2000 Sulphur added, p.p.m. 2.00 0.40 0.80 4.00 1-60 2.00 4.00 0.80 nil 10.0 Sulphur found, p.p.m. 1.80 nil 0.65 3-65 1.40 1-85 3-65 0-60 nil 10.0 * Samples 5 and 6 yere made from refined petrol; all other samples were made from crude petrol mixtures. of the sulphur was observed. The effects of the following sulphur compounds were examined: isopentyl disulphide, carbon disulphide, thiophenol, thio+-cresol, dimethylaniline sulphide, isopent yl sulphide, /I-phenyl- p-et hylmercapt opropiophenone, 4-phen ylmercapt o-2-but anone, phenol monosulphide, tetra-ethylthiuram disulphide, thiophene and butyl mercaptan (see Fig.2). It was observed that in the presence of thiophenol and thio-9-cresol the reduction wave of sulphur was shifted to a slightly less negative potential, making measurement of the wave- height slightly less accurate. It should be noted, however, that the proportion of free sulphur to “added impurity” was 1 to 25. Such a high ratio is not likely to be encountered in petroleum fractions. TABLE 111 DETERMINATIONS OF FREE SULPHUR IN PETROLS AND BENZENE Sample . . .. . . Petrol 1 Petrol 2 Petrol 3 Petrol 4 Benzene, Crude Sulphur found, p.p.m. 0-10 0.40 0.50 0.30 nil 1-50 A.R. benzene Hall3 suggested that when a mercaptan was added to a petrol containing free sulphur the sulphur was “consumed,” being converted into disulphide, and that the rate of con- sumption could be followed polarographically. A sample of petrol containing 4 p.p.m.of free sulphur and 100 p.p.m. of added butyl mercaptan was repeatedly examined polaro- graphically over a period of 8 hours. No change in the diffusion current occurred over this period, which indicated the absence of any reaction of free sulphur with the butyl mercaptan. A number of samples were prepared from petrol to which were added large amounts of organic sulphur compounds and small amounts of free sulphur. These samples were examined polarographically for free sulphur, and. the results are shown in Table 11. The method described is of wide applicability to petrol fractions.Many samples of petrol and benzene have been examined and small amounts of free sulphur have been deter- mined. The reagents, glacial acetic acid and ammonium acetate, are easily obtained pure, and the mixture is an ideal solvent for many non-aqueous materials. The sensitivity of the method (0.5 p.p.m.) is such that it is not necessary to make polarograms for solutions containing more than 1 volume of petrol to Some typical results are shown in Table 111.October, 19541 FREE SCLPHUR I N PETROLEUM FRACTIOSS (543 4 volumes of solvent - electrolyte, so difficulties clue to limited miscibility of the hydrocarbons with the solvent - electrolyte do not arise. METHOD APPARATUS- A Tinsley pen-recording industrial polarograph, with mercury-pool cell. Capillary characteristics: drop time, 6.6 seconds in distilled water; rate of mercury flox, 1.8mg per second; height of mercury column, ‘70 cm.REAGENTS- Acetic acid, glacial. Ammonium acetate. Sul;bhaw, sublimed or monoclinic. All reagents were of recognised analytical purity. Samples of sulphur from various sources were used to prepare standard solutions, monoclinic sulphur being the most soluble form. A simple mercury-pool cell was used in this work. It was designed with a mercury trap to ensure an efficient seal to prevent interference from atmospheric oxygen. For purposes of dilution a standard petrol containing less than 0.5 p.p.m. of free sulphur was used throughout the work. The electrolyte - solvent used was 0.2 ammonium acetate in glacial acetic acid. PROCEDURE- Into the flask place 5 nil of petrol sample and make it up to 25 ml with 0.2 114 ammonium acetate in glacial acetic acid.If the sample contains more than 10 p.p.m. of free sulphur, dilute it with a standard petrol of known sulphur content. Transfer the petrol solution to the polarographic cell, lower the anode dome, and bubble nitrogen through the solution for 5 minutes. As it is not certain that all the oxygen is removed when nitrogen is bubbled through the solution, it is important that a standard procedure is adopted. The seal prevents further exposure of the petrol solution to the atmosphere. Lower the anode dome further, until the anode lead is in contact with the mercury pool, and then raise the mercury reservoir to a standard height so that the mercury flows through the cathode capillary at a rate of 1.8 mg per second. Set the sensitivity of the instrument to 1-0pA and the potentiometer panel indicator to 0.0 volt. Adjust the zero in the usual way and switch on the automatic recorder. Switch on the auto-potentiometer and record the polarogram between 0.0 and - 1.2 volts. Finally measure the height of the reduction wave at a potential of -0.39 volt. Prepare the samples for analysis in 25-ml calibrated flasks. REFERENCES 1. Proske, G., Naturwiss., 1946, 33, 220. 2. -__ , Angew. Cheni., 1947, A59, 121; Clzcm. Abstr., 1947, 41, ‘i807B. 3. Hall, M. E., Anal. Chevlz., 1950, 22, 1137. 4. Gerber, M. I., and Shusharina, A. D., Z~LZLY. Aizal. Khinz., 1950, 5, 262; Chem. Abstr., 1950, 44, 5. 6. 1 0 5 9 3 ~ . Eccleston, B. H., Morrison, M., and Smith, H. M., -4naI. Clienz., 1952, 24, 1745. Bergman, I., and James, J. C., Tixans. Fnmday Sot:., 1952, 48, 956. lMPERIAL CHEMICAL INDUSTRIES LIMITED BILLINGHAM, Co. DURHAM

ISSN:0003-2654    

DOI:10.1039/AN9547900640

出版商:RSC    

年代:1954

数据来源: RSC

摘要:

644 LEWIS : POLAROGRAPHIC DETERMINATION OF 2 4: 6-TRINITROTOLUENE [VOl. 79 Polarographic Determination of 2 : 4 : 6-Trinitrotoluene and cycZoTrimethylenetrinitramine in Explosive Mixtures BY D. T. LEWIS A polarographic method is described for the micro-determination of 2 : 4 : 6-trinitrotoluene and cyclotrimethylenetrinitramine. Samples of less than a milligram of explosive are qualitatively identified by observing their characteristic half-wave potentials in an acetone solution of alkaline sulphite. The IlkoviC equation is shown to apply for the quantitative determination of the nitro compounds in such media. THE general composition of explosive mixtures containing ammonium nitrate, barium nitrate, nitrocellulose, pentaerythritol tetranitrate, 2 : 4 : 6-trinitrotoluene, cyclotrimethylenetrinitr- amine, and so on, has been described broadly by Thorpe and White1ey.l No reliable method exists for the accurate micro-determination of some of these con- stituents when present in small samples of mixed explosives, e g ., explosives of the amatol or baratol type. Solvent extraction or titrimetric methods are unduly cumbersome and inaccurate when only milligram quantities of sample are available and this necessitates the use of colorimetric or polarographic methods of analysis. Colorimetric methods for the micro-determination of 2 : 4 : 6-trinitrotoluene are generally based on measurements of the intensity of the red colour that is given by this explosive in certain alkaline solutions (cf. Halfter and Winkler2). The polarographic method has been found to give a reliable quantitative analytical procedure for cyclonite and T.N.T.explosives, and samples weighing about a milligram can be quickly and accurately assayed. But it should be remembered that the errors inherent in such polarographic micro-determinations are generally about 2 per cent. Where macro quantities of explosives are available, the classical methods of gravimetric analysis would be more accurate. Pentaerythritol tetranitrate and nitrocellulose are irreducible at the dropping-mercury cathode, and their presence in the mixtures to be assayed introduces no particular com- plication. The sensitive explosive 2 : 4 : 6-trinitrophenylmethylnitramine does, however, give an ill-defined reduction wave at -0.3 to -0.6 volt with respect to the saturated-calomel electrode, and the presence of this substance would interfere with the polarographic deter- mination of related nitro compounds.Organic nitro derivatives can generally be removed from mixtures containing inorganic nitrates by extraction with suitable solvents. The mechanism of the polarographic reduction of nitro compounds has been studied by several investigators, and an excellent review of these researches has been published by Page,3 who gave a comprehensive bibliography of work on the organic nitro derivatives. Pearson4 has carried out a detailed study of the reduction of nitrobenzenes and nitro- toluenes in aqueous ethanolic solution, and he has postulated that the irreversible reduction of the nitro group in these compounds consists in the reversible deposition of hydrogen ions at the cathode, which is a reaction determining the cathode potential and producing the observed current.Few explosives are satisfactorily soluble in aqueous ethanol, and aqueous acetone is probably the only suitable medium for the polarography of insoluble cyclotrimethylene- trinitramine. The deoxygenation of the acetone solutions by means of a stream of nitrogen gas, with consequent loss of volatile solvent, may be rendered unnecessary by the use of a base solution that is 0.05 M with respect to sodium sulpliite and borax. This procedure avoids the wave due to dissolved oxygen and considerably expedites the routine determinations of numerous small samples. EXPERIMENTAL 2 4 : 6-TRINITROTOLUENE- Pearson’s values for the half-wave potentials of trinitrotoluene in alkaline ethanolic In alkaline acetone solutions of pH 9.98, the reduction solutions have been confirmed.October, 19541 AND CYC~OTRIMETHYLEn'ETRINITRAMINE I N EXPLOSIVE MIXTURES 64.5 potentials at 25" C against the saturated-calomel electrode were markedly increased arid were found to be -0.51, -0.65 and -1.05 volts, respectively, three separate reduction waves being readily discernible, as shown in Fig.1. Maxima were frequently developed at higher reduction potentials and constituted examples of what HeyrovskP5 has called "negative maxima.'' Gelatin, gum arabic and various dyestuffs were tried as suppressors, the results being best with 0.01 per cent. w/v solution of gentian violet or basic fuchsin. These dyes were strongly adsorbed on glass surfaces, but the use of a suppressor when only the first wave of trinitrotoluene was being recorded was considered unnecessary, as this wave appeared to be of a consistentljr stable character.The present analytical method is based on an examination of this first wave, and so no suppressors are used in the quantitative determinations. Cambridge pen-recording and photographic polarographs were used throughout the investigation, the cells being maintained a t 25" + 0.2" C. Drop times were noted at the half-wave potentials, as they were found to vary appreciably with the applied voltage (cf. Lingme and Kolthoff 6 ) . 0 _I -- 0.5 Potential, volts 1.0 Fig. 1. Polarograms o€ T.N.T. and cyclonite: curve -4, 0 . 1 g of T.N.T. per litre; curl-e 13, 0.2 g of cyclonite per litre ILKOI~IC CALIBRATION CURYE FOR 2 : 4 : 6-TIIIKITROTOLCENE- For the preparation of a calibration curve, 2: 4 : 6-trinitrotoluene (setting point 80.7" C) was dissolved in AnalaIZ acetone.Then 0.05 LV sodium sulphite and 04,5 34 borax solutions were prepared, and all solutions were placed in a thermostatically controlled water-bath maintained at 25" C. Just before the polarographic readings were taken, 1 volume of the 2: 4: 6-trinitrotoluene solution was intimately mixed with 2 volumes of the sodium sulphite solution and 2 volumes of the borax solution. Results for the diffusion constant are shown in Table I. DETERIORATIOS OF 2 : 4 : 6-TKIXITROTOLVESE SOLGTIOh S- Alkaline sulphite solutions of 2 : 4 : &trinitrotoluene undergo ;t slow decomposition on standing, and the recorded diffusion currents sliow a small, but progressive, decrease in magnitude. This reaction begins when tlie supporting electrolyte is mixed with the acetone in the range 0.01 to 0.1 g of T.K.T.pcr litre. As a polarographic measurement can readily be made in 10 minutes by the method dcscribed above, the error in observation is less than 2 per cent., and for most purposes it ma>- be regarded as negligible. The decomposition solution of the explosive, and the rate of decomposition is of the same order at concentr a t ' lolls646 LEWIS : POLAROGRAPHIC DETERMINATION OF 2 : 4 6-TRINITROTOLUENE [VOl. 70 is almost certainly due to the sulphite additive and, if the reaction is analysed according t o the unimolecular law, the velocity constant decreases with increasing time, as shown by the results in Table 11.TABLE I ILKOVIC CALIBRATION CURVE FOR 2 : 4 6-TRINITROTOLUENE m = 1.708 mg per second t = 3.22 seconds mW = 1.736 Temperature = 25" C Concentration of 2 :4 :6-trinitrotoluene, g per litre (C) 0.1129 0.0904 0.0600 0.0540 0.0452 0.0225 Current , 4.25 3.44: 2.28 2.05 1-75 0.92: PA TABLE I1 Diffusion constant, 37.8 38-0 38.0 37.9 38.7 40.8 i / C POLAROGRAPHIC DETERMINATION OF THE DETERIORATION OF CONTAINING 0.01608 g OF 2 : 4: 6-TRINITROTOLUENE PER A SOLUTION LITRE Time, Current, Loss, l / t log,, i / ( i - x)* hours PA % 0.00 0.60 - - 0.92 0.53 11.7 0.059 1.59 0.50 16-3 0.049 19.17 0.30 50.0 0.015 43.67 0.00 100.0 - * x = amount of T.N.T. consumed. The alkaline ethanolic solutions of pH = 9.20 that were used by Pearson* have also been examined for this effect, and the decrease in diffusion current was found to be negligible during the first day, but it occurred slowly thereafter. If the explosive mixture can be satisfactorily extracted with ethanol, then the use of an ethanol supporting electrolyte is to be recommended.It is considered, however, that the use of acetone as a solvent consider- ably simplifies the experimental procedure, and that the results are within the polarographic errors of measurement. Typical results for the: recovery of known amounts of explosive are shown in Table 111. The explosive samples were weighed directly on a semimicro balance having a sensitivity of 9 pug per division, then dissolved in 1 ml of cold acetone and intimately mixed with 4 ml of the sulphite - borate base solution.TABLE I11 RECOVERY OF KNOWN MILLIGRAM AMOUNTS OF 2 4: 6-TRINITROTOLUENE (DIFFUSION CONSTANT, i / C = 37.9) T.N.T. T.N.T. Mean T.N.T. used, Current, recovered, recovered, deviation 2.58 19.12 2.522 97.7 2.6 1.78 14.00 1-847 103.8 1.10 8.62 1.137 103.4 0.72 5-39 0-711 98.7 mg PA mg % The average recovery from the four samples was 100.9 per cent., which gave a value of 2.6 per cent. for the relative mean deviation. Quantities of trinitrotoluene outside the range of the average microbalance can be determined quite satisfactorily by making polaro- grams for suitable solutions of small particles of explosives and determining the unknown concentration by interpolation of the Ilkovie calibration curve.October, 19541 AND C~~OTRIMETHYLENETRINITRAMINE IN EXPLOSIVE MIXTURES 64'7 C~CZOTRIMETHYLENETRINITRAMINE (CYCLONITE, HEXOGEN)- No polarographic investigations on this explosive are recorded in the literature. The general chemistry of this substance has been described in detail by Davis,' who recommends acetone as a solvent for its recrystallisation, and this is the solvent used in the present investigation.One of the complications attending the analysis of this trinitramine is its insolubility in common organic solvents. The acetone base solution recommended for T. X.T. is suitable as a supporting electrolyte provided that the concentrations of the explosive are below 0.2 g per litre. Solutions in 50 per cent. acetone and in acetone - dioxan mixtures have been examined, but the inorganic salts tend to crystallise from these solvents.In a 20 per cent. acetone base solution, cyclotrimethylenetrinitramine is reducible at the mercury cathode to give a single, well-defined wave with a half-wave potential of -0.77 volt against the S.C.E. at 25" C. Thereafter, the polarographic curve rises steeply, the molecule being presumably unstable at the higher reduction potentials. The diffusion current is found to vary linearly with concentration, the current magnitude for equivalent concentrations being approximately half that recorded for 2 : 4 : 6-trinitrotoluene at the same drop electrode. Typical results are shown in Table IV. TABLE IV ILKOVIC CALIBRA4TIOS' CURVE FOR CyCzOTRIMETHYLENETRINITRAMISE mW = 1.736 Concentration, g per litre 0.1668 0.1334 0~1001 0.0667 0.0335 0.0167 Current, 3-20 2.55 1.90 1.29 0-71 0.28 P A Diffusion constant, i / C 19.1 8 19-11 18-99 19.34 21.20 16 81) MECHANISM OF THE REDUCTION OF CYCLONITE- In the application of the IlkoviE equation to the determination of the electrode process, the diffusion coefficient, D, of the reducible substance must be known with reasonable accuracy. For the nitrophenols and nitrotoluenes, Pearson suggested that the molecular sizes of these materials were about the same as the benzoate ion, and he used a value for the diffusion coefficient of this ion that is calculable from conductivity data as 8.28 x 10-6 sq.cm per second at 25" C. The Stokes- Einstein8 equation suggests that D is given with fair accuracy by the expression- where Y is the inolecular radius and 7 is the viscosity.This expression has been used extensivelyg to determine the diffusion velocity of large ions at 25" C, and it is stated by Rolthoff and LinganelO in the form- 2.96 ' ''-' sq. cm per second, D = 7VS where I/ is the molar volume of the pure substance in the solid state and D is considered to be at infinite dilution. The viscosity of the 20 per cent. acetone base solution used in this investigation was determined at 25" C by means of a conventional B.S.S. Ostwaldt viscometer and was found to be 1.281 centipoises. Thorpe and Whiteleyll quote a figure of 1.83 g per C.C. for the absolute density of cyclonite, and from these figures the diffusion coefficient at 25" C was computed to be 4.67 x 10-6sq.cm per second. Similarly, Lewis12 gives a figure of 1.65 per g per C.C. for the absolute X-ray density of T.N.T., whence D = 4.48 x 10-6 sq. cm per second for this substance in the present supporting electrolyte solution.648 LEWIS [Vol. 79 Accepting the conventional IlkoviE symbols, values of n, the number of Faradays required per mole of the electrode reaction, are as follows- Substance m%t+ Concentration, Current, n millimoles per litre PA Cyclonite . . .. .. 1.901 0.5403 2.70 2.01 Cyclonite . . .. .. 1.736 0.7512 3.20 1.88 T.N.T. .. .. .. 1.736 0.4973 4.25 3.85 COIIU’CLUSIONS It is apparent that under the stated conditions, cyclonite undergoes a two-electron reduction according to the scheme- 2e + RNO, j- 2H+ = RNO + H,O Similarly, the first polarographic wave for 2 : 4 : 6-trinitrotoluene is due to a hydroxylamine reduction of the following type- 4e + RNO, + 4H+ = RNH-OH + 2H,O The author is indebted to the Division of Atomic Energy, Ministry of Supply, for permission to publish this paper. 2. 3. 4. 5. 6. 7. 8. 9. 10. 1 1 . 12. REFERENCES Thorpe, J . F., and Whiteley, M. A., “Dictionary of Applied Chemistry,” Halfter, G., and Winkler, H., Die. Chemie, 1944, 57, 17/18, 124. Page, J. E., Quart. Rev. Chem. Soc., 1952, 6, 262. Pearson, J., Trans. Faraday Soc., 1948, 44, 683. Heyrovskf, J., Actualite‘s Sci. Ind., 1934, No. 90. Lingane, J. J., and Kolthoff, I. M., J . Amer. Chem. Soc., 1939, 61, 825. Davis, T. L., “Chemistry of Powder and Explosives,” Wiley and Sons, 1943, p. 396. Einstein, A., Ann. Physik., 1906, 19, 371. Friedman, L., and Carpenter, P. G., J . Amer. Chem. Soc., 1939, 61, 1745. Kolthoff, I . M., and Lingane, J. J., “Polarography,” Interscience Publishers Inc., New York, Thorpe, J. F., and Whiteley, M. A., “Dictionary of Applied Chemistry,” Longmans, Green and Lewis, D. T., J . Appl. Chem., 1953, 3, 157. Longmans, Green and Co., London, 1946, Volume IV. 1946, p. 50. Co., 1946, Volume 111, p. 536. ATOMIC WEAPONS RESEARCH ESTABLISHMENT ALDERMASTON, BERKS. May 14th, 1954

ISSN:0003-2654    

DOI:10.1039/AN9547900644

出版商:RSC    

年代:1954

数据来源: RSC

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October, 19541 NOTES 649 THE DETERMINATION OF METALLIC LEAD IN PIGMENTS ALTHOUGH metallic lead has been used in reductors of the Jones type by Cooke, Hazel and McNabbl and by McNabb, Hazel and Dantro,2 the determination of metallic lead by a volumetric reduction method does not appear to have found practical application. Light and Russel3 used a solution of ferric sulphate in diluted sulphuric acid for the assay of aluminium powder. As there was need for a method of determining finely divided lead, it seemed probable to the author that, by the use of a similar but modified reagent, a sufficiently accurate method for technical consultative work might be evolved. METHOD REAGENTS- Ferric sulphate reagent-Heat 250 g of anhydrous ferric sulphate with 135 g of 95 per cent. w/w sulphuric acid and 800 ml of distilled water until the solution is clear and light brown in colour; this usually entails heating for 5 minutes at 80" C. Ferric sulphate - mixed acid reagent-To 300ml of ferric sulphate reagent add 100ml of 32 per cent.w/w hydrochloric acid and 50 ml of 85 per cent. w/w phosphoric acid. Sodium acetate reagent-A saturated solution of sodium acetate containing 1 per cent. v/v of acetic acid. Sodium thiosulphate solution, 0.1 N. Iodine solution, 0.1 N. Potassium permanganate solution, 0- 1 N. Ferrous sulphate solution, 0.1 N. - PROCEDURE FOR METALLIC LEAD- Place a weighed amount of powder or pigment containing approximately 0.2 g of lead in a conical flask and add 45 ml of ferric sulphate - mixed acid reagent. Displace the air from the flask with carbon dioxide, fit a bunsen valve to the flask and heat the contents a t 90" to 95" C for Q to 2 hours.Cool the flask to 20" C, dilute the contents to 200 ml with cold freshly distilled water and titrate with 0.1 N potassium permanganate. Make a blank determination concurrently. 1 ml of 0.1 N potassium permanganate = 0.01036 g of lead. The precision approaches &toe25 per cent., depending on the weight of lead taken. PROCEDURE FOR METALLIC LEAD - RED LEAD MIXTURE- a trace of wetting agent if necessary. until the red lead disappears. the residue, the original flask and the thimble with water. sulphate in the combined filtrate and rinsings with 0.1 N iodine. in a similar manner. Triturate a weighed amount of the powder with 30 ml of the sodium acetate reagent and add Add 50 ml of 0.1 N sodium thiosulphate and stir the mixture Filter the mixture through a No.2 porosity thimble, and wash Titrate the excess of sodium thio- Make a blank determination 1 ml of 0.1 N sodium thiosulphate = 0.0343 g of red lead. Wash the residue, mainly metallic lead, in the thimble with water and then with acetone. Dry it a t 105" C, weigh it and then determine the metallic lead by the procedure described above. PROCEDURE FOR ALUMINIUM AND LEAD IN ADMIXTURE- a t 60" to 70" C for 15 minutes. by filtration on a No. 2 porosity thimble. described above. permanganate. Treat a weighed amount of the powder with the ferric sulphate reagent and heat the mixture Cool the flask to 20" C and separate the lead and insoluble matter Dry the solid, weigh i t and determine the, lead as Dilute the filtrate to a suitable volume and titrate aliquots with 0.1 N potassium 1 ml of 0.1 N potassium permanganate = 0.00090 g of aluminium.It has been found possible to determine the lead remaining in the flask after the titration by adding hydrochloric and phosphoric acids as in the ferric sulphate - mixed acid reagent, and650 NOTES [Vol. 79 then reducing the ferric salt by heating at 90" to 95" C. is present in the pigment, alternative methods of analysis must be used. When lead chromate or zinc chromate PROCEDURE FOR ZINC AND LEAD IN ADMIXTURE-- Treat a weighed amount of the powder (cont:aining about 0.1 g of zinc) with a mixture of 10 ml of the ferric sulphate reagent and 20 ml of 0.1 N potassium permanganate at 20" C for 10 minutes. Separate the lead and insoluble matter by filtration on a No.2 porosity thimble. Dry the solid, weigh it and determine the lead iZS described above. Titrate the filtrate with either 0-1 N potassium permanganate or 0.1 N ferrous sulphate solution, whichever is necessary. 1 ml of 0.1 N potassium permanganate = 0.00327 g of zinc, The zinc should be free from aluminium, iron and magnesium, as these metals would affect the result. RESULTS The results of the determination of lead in various mixtures by the methods described above are shown in Table I. TABLE I DETERMINATION OF LEAD IN VARIOUS MIXTURES Lead taken, g 0.2318 Metallic lead pigment powder (99.1 per cent. cd Pb) Metallic lead powder .. .. . . .. 0-193 White lead . . .. .. ... . .. 0.308 Metallic lead powder .. .. .. .. 0.1672 Red lead . . .. .. .. .. .. 0.318 Sample containing 0.5 per cent. of organic matter-- Metallic lead . . .. . . .. . . .. 0.307 Metallic aluminium . . .. .. .. .. 0.0342 Sample free from organic matter- Metallic lead . . .. * . .. .. .. 0.2975 Metallic aluminium . . .. .. . . .. 0.0326 Metallic zinc . . .. .. .. . . .. 0.0732 Metallic lead . . .. .. .. . . .. 0.2198 Lead found, g 0.230 0.191 0.307 0.166 0.312 0.306 0.0340 0.294 0.0322 0.0730 0.2170 DISCUSSION Sampling requires special care on account of the wide differences in specific gravity and other physical properties of the components of heterogenous mixtures containing metallic powders. It may be necessary to add to the sample a weighed amount of finely divided inert inorganic material of high specific gravity, such as barium sulphate, on which the metallic powders will disperse themselves uniformly.Sometimes the method in which the entire sample is dissolved and aliquots are used for the assay is useful, especially for pigments extracted from paints. The above remarks are more important for samples tha.t are free from organic matter. For samples containing organic matter, it has been found satisfactory to boil the extracted pigments twice with pure dioxan followed by one wash with cold acetone ; great care is then needed when the final sample is prepared. On occasion, heating the sample in a vacuum oven at 250" to 300" C is useful for the removal of organic matter. The author thanks Mr. F. Fancutt for permission to publish this Note and Mr.F. G. Dunkley and Mr. W. J. Hair for helpful advice. REFERENCES 1. 2. 3. Cooke, W. D., Hazel, F., and McNabb, W. M., Anal. Chem., 1950, 22, 664. McNabb, W. M., Hazel, F., and Dantro, H. F., Ibid., 1951, 23, 1325. Light, A. K., and Russell, L. E., Anal. Chem., 1947, 19, 337. BRITISH TRANSPORT COMMISSION (BRITISH CHEMISTRY DIVISION RAILWAYS) RESEARCH DEPARTMENT PROTECTIVE COATINGS LABORATORY LONDON ROAD, DERBY A. WOOLLER First submitted, January 19th, 1954 Amended, April 27th, 1954October, 19541 APPARATUS 651 MANGANESE DIOXIDE - ASBESTOS IN STEEL ANALYSIS IN a combustion train for determining carbon in high-sulphur steel, the disadvantages of an acid silver nitrate solution for absorbing the main bulk of the sulphur oxides, caused by (u) dilution of the chromic acid trap by aqueous vapour and (b) by the necessity for frequent renewal of the silver solution, can be overcome by substituting for it a dry manganese dioxide absorbant. A suitable reagent that does not impede the flow of oxygen can be prepared as follows. Shake 25 g of ignited asbestos fibre with 400 ml of saturated potassium permanganate solution in a 2-litre flask, add 400 ml of saturated manganous sulphate solution and shake the flask thoroughly. Separate the manganese dioxide - asbestos by filtration under slightly diminished pressure, through a 6-inch funnel and filter-cone. Wash the fibre twice with hot water and dry it a t 100" C. A U-tube, 2 inch in diameter and 58 inches high, filled with the reagent and placed in the combustion train immediately in front of the usual chromic acid bubbler, will absorb the bulk of the sulphur oxides from about 1100 g of steel containing sulphur in amounts varying between 0.03 and 0.50 per cent. before the filling needs renewal. THE PARK GATE IRON AND STEEL CO., LTD. ROTHERHAM, Y ORKSHIRE A. P. LUNT November Sth, 1953

ISSN:0003-2654    

DOI:10.1039/AN9547900649

出版商:RSC    

年代:1954

数据来源: RSC

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October, 19541 APPARATUS 651 Apparatus A TWIN-BEAM NULL-POINT FLUORIMETER FOR THE ANALYSIS OF LIQUID SAMPLES (Pwsented at a meeting of the Physical Methods GyouP on Friday, May 28th, 1954) THE instrument described was constructed to measure the fluorescence produced a t an inter- mediate stage in a particular reaction. Peak fluorescence is produced in 30 to 60 seconds after the reaction begins and then it rapidly diminishes in value. The exciting radiation is 3 6 0 0 ~ and the wavelength of the fluorescent light is approximately 4000 A. An attempt was first made to use a Hilger absorptiometer with barrier-layer cells and a fluorimeter attachment to measure the fluorescence developed, but this instrument was insufficiently sensitive. No high-amplification instrument for the measurement of fluorescence was commercially available in this country at the time the investigation of the reaction began, so i t was decided to construct an instrument to make use of a photomultiplier as the light-detecting device. A photomultiplier was chosen rather than a photo-cell and valve amplifier combination, because it offered a much more compact amplification system and a t least as good a signal-to- noise ratio as could be attained when a photo-cell followed by a broad-band amplifier was used.The first instrument made utilised a single light beam and one photomultiplier in which the unknown fluorescent solution was compared with a reference standard. A series of Ayrton shunts were connected as the final dynode load and operated with a Yaxley switch.A suitable shunt was switched into the circuit and the fluorescence value was indicated by the swing on a galvano- meter connected across one arm of the shunt. This instrument was very sensitive to the variations of the input voltage of both the lamp and the photomultiplier. The graph (Fig. 1) shows the magnitude of this error, even when the power supply was regulated through a stabilising transformer. Another disturbing feature of high-amplification single-ended instruments is that it becomes very difficult to remove the final traces of ripple in the power supply by smoothing, and this is indicated by a gentle oscillatory motion of the galvanometer needle when the instrument is used on a lightly shunted range. For these reasons it was decided to build a balanced light fluorimeter, of which the essential parts are described below.SOURCE OF LIGHT- illumination. as the light source, as this gave peak excitation a t the required wavelength. it suffered from several defects, which were as follows- A 12-volt 24-watt bulb having a single vertical spiral filament was used as the source of The single-ended fluorimeter was originally fitted with a mercury-vapour lamp In practice, however, (2) The apparent intensity fluctuated erratically owing to changes of path in the mercury arc. Other types of mercury lamp, in which attempts had been made to confine the arc to a precise path, still suffered from the same fault, although perhaps to a lesser extent.652 APPARA.TUS [Vol. 79 (ii) It generated considerable heat, and thermal effects in the instrument became difficult to obviate.(iii) The intensity of illumination depended cln the length of time the lamp had been in use. (iv) It was necessary to screen the lamp to avoid harmful effects to the operator. (v) The current-limiting choke or resistance was bulky, so the final instrument lacked portability. The small tungsten lamp replaced the mercury-vapour lamp with little loss of sensitivity. No attempt has been made to use a parallel beam of exciting light through the test solution. DETECTOR SYSTEM- Two photomultipliers, one on each side of the lamp, are connected together with the final A galvanometer is joined Under normal conditions a maximum current of 8 pA is permitted dynode load resistors, one of which is variable, i:n a bridge circuit.between the final dynodes. 60 50 40 i 30 2 w 20 10 0 Id5 115 130 140 I50 160 17'0 180 190 200 210 220 230 Supply voltage Fig. 1. Graph to illustrate the error in fluorimetric readings caused by varia- tions in mains voltage: curve A, single photomultiplier, single-beam instrument ; curve B, twin photomultiplier, twin-beam instrument on each photomultiplier final dynode. It seems likely that both photomultipliers are operated under fatigue conditions, and this appears to give more stable long-term operating conditions with only a slight loss of amplification under the conditions of use. (u) The photomultipliers are chosen with low dark-current, high gain and maximum response in the blue spectral region; 25,000-ohm, 11-watt resistors are used in the dynode chain.(b) The variable load resistor is a 25,000-ohm Colvern or Fox helical-wound potentiometer fitted with a slow motion dial graduated in one thousand divisions. This is the final dynode load resistor in the control photoniultiplier circuit. With no light on either photomultiplier and the variable resistance set at maximum value, the apparatus is switched on. Beginning with a 25,000-ohm resistor as the test-photomultiplier final-dynode load resistor, resistances are inserted until the nearest point to current balance is found. If the value of resistance is markedly different from 25,000 ohms, say 15,000 or 35,000 ohms, one of the photo- multipliers should be replaced, the test photomultiplier if the balance is at 15,000 ohms, the control if it is at 35,000 ohms.A Cambridge spot galvanometer, 1-pA full-scale deflection, is used to indicate the null- point. The value of the fixed load resistor is determined experimentally as follows. (c) A shorting switch is fitted to protect the galvanometer. TEST CELLS- An optical-glass cell with internal dimensions of 4.5 cm high, 3.5 cm long and 1.5 cm wide was chosen because it had a capacity of 22 ml and the total amount of solution for examination was 25 ml. Light enters through a narrow face of the cell, and the photomultiplier measuring the developed fluorescence is placed as near as possible to a wide face.October, 19541 APPARATUS 653 A second cell, 3.6 cm high, 1-1 cm long and 1.1 cm wide, holding 2 ml of solution, was obtained, and retained in position in a suitably machined wooden block.FILTERS- (a) Wood’s-glass filters are placed between the test cell and the lamp and between the control photomultiplier and the lamp. Originally, a 7.5 per cent. copper sulphate solution was also used to cut out unwanted red radiation, but it was later omitted without the accuracy of measurement being affected. (b) An Ilford No. 106 filter is inserted between the test cell and the photomultiplier to eliminate stray light reflected or refracted from the test solution. The filters described are used in our particular analytical procedure ; alternative filters may be used in other determinations. (c) A variable-density neutral filter is placed between the control photomultiplier and the light source, and is arranged to be readily adjustable.The range of this filter will determine P = Photomultiplier, type IP28 V, = Half of 6SL7 V, = Rectifying valve VR = 25-kR helical potentiometer V2 --;- 900-V, 100-pA corona stabiliser Fig. 2. Circuit diagram of twin-beam fluorimeter the range of the instrument; the lowest density will give the largest range, say 0 to 100 p g of material, read over 1000 divisions on the graduated potentiometer dial, and the highest density gives the smallest range, say 0 to 10 pg. POWER SUPPL~~--- Many types of power supply have been tried, principally with the single-ended fluorimeter. Large accumulators to supply the lamp current were tried and discarded. In use considerable time was required before they settled down to a reasonably steady e.m.f., and even then the voltage gradually decreased and this necessitated continual adjustment of the fluorimeter against a standard reference solution throughout the day.Bubbles of gas in the cells caused spurious flicks on the galvanometer, and a final objection to the use of accumulators was that they were bulky and troublesome. They proved to have a poor shelf life, they were bulky and they were liable to be highly dangerous to operators. A constant-voltage transformer is used to supply a lamp transformer a t 12 volts and 2 to 3 amps., and a stabilised lOOO-volt, 2 to 3-mA supply. The most successful circuit, with very few components, but having a high ratio of output- to-input stability, makes use of a corona stabiliser controlling a high-gain triode connected as a cathode follower. The power supply to the photomultipliers is controlled by a potentiometer fitted on the fluorimeter panel and connected between the cathode and earth of the cathode follower (see circuit diagram, Fig.2). The instrument is normally used a t 900 volts, and little or no adjustment of the voltage is required under widely different mains input conditions. High-tension batteries to power the photomultipliers were tried. The following system has proved highly satisfactory.654 APPARATUS [Vol. 79 The graph (Fig. 1) shows the remarkable sta.bility of the instrument over a wide range of The apparatus has also been successfully run from a carbon-pile-regulated mains input voltages. rotary convertor, which makes it independent of mains supply. SCREENING- The test cell, photomultipliers and filters are screened to prevent the ingress of stray light.Light falls on the control photomultiplier through a Q-inch diameter hole in the cylindrical screening can and on the test-cell photomultiplier through a series of +-inch x &inch holes cut in the screening boxes. The photomultiplier is arranged so that the maximum photocathode surface is presented to the fluorescent light. Fig. 3. General view of apparatus A light shutter, made from a strip of bakelite in which is cut a suitably placed &-inch x &-inch hole, is fastened to the lid of the test-cell screening box, which is positioned by four vertical rods, and is used to protect the photomultiplier from an excess of light when the test cell is being removed or placed in position. The instrument should be constructed of sheet brass or copper.An aluminium fluorimeter was made, but it was found that control readings depended on the temperature of the laboratory. The apparatus is normally used in a wooden box, open at the front, in order to obviate the effect of draughts and bright sunlight. A general view of the apparatus is shown in Fig. 3.October, 19541 APPARATUS 665 USE OF THE INSTRUMENT- The galvanometer is set to zero and then short-circuited. The fluorimeter is switched on and 5 minutes is allowed for it to warm to operating temperature. At the end of this time a known strength of solution of a fluorescent substance, which should have a similar fluorescent emission to that of the substance under examination, is placed in the cell.The reading should correspond approximately to the maximum expected for the samples under examination. The dial of the helical-wound potentiometer is adjusted to a precise figure (say 900), the galvanometer is switched into the circuit, and the variable-density neutral filter is moved until a null-point is indicated on the galvanometer. The instrument is now ready for use. I t is advisable to check it at intervals throughout the day against the standard solution. Variation seems to be mainly caused by the deposition of a film of moisture on the filters and test cell, and is most noticeable on a cold wet day. Normally, however, little adjustment has to be made. The solution under examination is placed in the cell with the galvanometer short-circuited. The potentiometer is turned to the expected reading, the galvanometer shorting switch is opened, and the dial of the potentiometer is rotated until a null reading is indicated on the galvanometer. The reading on the dial is noted; it corresponds to the fluorescent value of the unknown solution.A reagent blank is placed in the cell and the reading on the dial recorded as described above. A calibration curve is prepared with known weights of the substance under examination, and the amount of the unknown substance is found by referring the reading, corrected for the blank, to the curve. SENSITIVITY- With the appropriate filter combinations, 0.01 pg of riboflavine and sodium naphthionate in 2 ml of solution can be determined, and 0.001 pg of fluorescein can be measured. These values are given with some reserve, as the chemical stability of the compounds at this level of concentra- tion is unknown; but fluorescein, for example, appears to be readily decomposed by light in very dilute alkaline solution.The results for a fluorescent substance having a similar response to sodium naphthionate show a standard deviation of &-2 per cent. on amounts between 0-5 and 40 pg. Reference curves made over 12 months indicate that the long-term stability of the instrument is reasonably satisfactory. The instrument has been in use for about a year, and has been in almost daily use. The advice of Prof. E. J. Bowen, F.R.S., in the early stages of development of the instrument This paper is published by permission of the Chief Scientist, Ministry is gratefully acknowledged.of Supply. CHEMICAL DEFENCE EXPERIMENTAL ESTABLISHMENT J. P. DoWD-kLL MINISTRY OF SUPPLY H. STRETCH PORTON, WILTS. May 5th, 1954 TWO IMPROVED CONTROL SYSTEMS FOR HORIZONTAL MICRO-BURETTES RECENT work in these laboratories has necessitated the use of a simple micro-burette of 1 to 2-ml capacity. Of the many micro-burettes described in the literature, that of Hybbinette and Benedetti-Pichlerl is the simplest, but it has the disadvantage that the jet is difficult to adjust, and cleaning, filling and emptying of the burette are consequently rather tedious. These difficulties were overcome to some extent by Stock and who used a screw-valve device embodying a capillary brake similar to that mentioned by Benedetti-Pichler.3 With a mechanism of this type, efSlux of liquid from the burette continues after the air inlet is closed, and ceases only when the air pressure in the burette is reduced sufficiently to compensate for the hydrostatic head in the jet.Unless the rate of efflux is extremely slow, therefore, the burette is difficult to control. Experience has shown that the permissible rate of efflux is limited more by this factor than by drainage errors, or by the necessity for preventing diffusion of the titrated liquid into the tip of the burette, which is normally immersed. Attention was therefore concentrated on the con- struction of a micro-burette that would combine reasonably rapid delivery with adequate control near the end-point of the titration. Two control systems that have proved satisfactory are shown in Figs.1 and 2.656 APPARATUS [Vol. 79 A S Neoprene Mer b C *cury/ a B t . r . l . r . l . l . , . l . l . , . , , 3 -J.-k-l 0 I 2 Scale, inches Fig. 1 In both systems the main tube of the burette terminates in the mercury trap, C, the purpose of which is described below, and the control valves are connected to a side tube attached at c. In the system of Fig. 1, valve A is similar in principle to that described by Stock and Fill, the open end of the tube being closed by a resilient pad under pressure from the screw. It has been found desirable, however, to fuse the glass housing of the valve to the capillary tube, to have the pad-holder attached to the screw, although not rotated by it, and to replace the rubber pad by one of Neoprene, which has a greater resistance to wear.Valve B is a Screw-operated piston. I t was not found possible to make a mercury-tight joint simply by passing the screw A B / I b C Mercury II II I 2 3 O L J " ' 1 " . 1 ' I " . ' . L " ' 1 Scale, inches u--u a Fig. 2 through a suitably tapped plug into the mercury. 'The end of the screw was therefore turned on a lathe to give a smooth plunger, which was passed through a Neoprene washer in the simple gland assembly shown. It is important that the mercury chamber should be long enough to contain the plunger when it is By tightening the gland nut, the joint was easily made mercury-tight.October, 19541 MINISTRY OF FOOD ti57 screwed up fully. If this is not so, lock-nuts should be fitted, as shown, to limit the travel of the plunger.It does not matter if the plunger emerges from the mercury, as the main purpose of the latter is to provide an air-tight joint. Valve ,4 is conveniently made of brass, but valve B must be made of steel to avoid amalgamation with the mercury. The threaded block containing the screw of xpalve A and the gland box of valve €3 are cemented to the glass tubing with sealing wax. The greater part of the solution used in the titration is added fairly rapidly by manipulation of valve A, but when the end-point is approached this valve is closed and the titration is completed by screwing in the plunger of valve B. This arrangement permits very accurate control, b u t it must be possible to complete the titration within the capacity of the plunger arid the plunqer must be reset before each titration.To overcome this difficulty the simpler but slightly less precise assembly shown in Fig. 2 was devised. Valve B is made of fine capillary tubing, the bore of which is further obstructed by the insertion of a length of platinum wire. This obstruction is adjusted so that, when valve l3 is open, liquid will flow only very slowly out of the burette. There is some risk that foreign matter entering this obstructed tube may choke it completely, and there- fore the wider tube of valve A is made co-axial with it, so that the wire and foreign matter can be ejected by a suitable wire inserted through valve A. In addition, the valve mechanism has been modified. Threaded brass sleeves are cemented over the capillary tubes by means of sealing wax, and they carry threaded brass cups containing the Neoprene closing pads. These cups are easily removed for the purpose of cleaning the capillary tubes. The titration is nearly completed by the use of valve A and is then completed under the more sensitive control of valve B.This is done by closing valve A (Fig. 1) or both valves (Fig. Z), applying gentle suction at a and closing hole b with the finger while the jet is immersed in the appropriate standard solution. This solution then flushes the burette and runs to waste a t n. IVhen the burette is judged to have been flushed sufficiently, valve A is cautiously opened, when the column of liquid breaks at c and the excess runs to waste through the trap. For refilling, it is necessary to close b only until sufficient solution has been drawn into the burette. The constant hydrostatic head characteristic of horizontal burettes ensures that the meniscus of the mercury in C is stable throughout a titration and no errors attributable to movement of the inercury have been detected. R EFEKEN CE s Valve A is similar in function to valve A in Fig. 1. As a result, thc flow stops almost instantaneously when valve B is closed. Thc mercury trap, C, enables the burette to be filled and cleaned rapidly. Hole b is then promptly uncovered and valve A is closed. 1. 2. Stock, J . T., and Fill, M. A., ibfetnllwgin, 1944, 31, 103. 3. T~enedetti-~'ichler, A . A , , 2. a m l . Chew., 1928, 73, 200. Hybbinette, A., and Renedetti-Pichler, A. A., ,42ikvorhenzie, 1942, 30, 15.

ISSN:0003-2654    

DOI:10.1039/AN9547900651

出版商:RSC    

年代:1954

数据来源: RSC

摘要:

October, 19541 MINISTRY OF FOOD Ministry of Food STATI:TOKY IXSTRUMEST* 1954---No. 1089. The Food Standards (Soft Drinks) (Amendment) Order, 1954. Price dd. This Ordev, which came into opevatioia o n August 22nd, 1954, amends the Food Standards (Soft Dviiqks) Order, 1953 (S.I., 1953, No. 1828; Analyst, 1954, 79, 56), by e x t e d i n g the exewptio9a of f r u i t juice f r o m the provisions of the pvincipal order to include undiluted f r u i t jTtirc, with or without added sugav, and anzy such juice in concentrated (or fi.ozen) fomn. FOOD STANDARDS COMMITTEE ANTIOXIDANTS THE Minister of Food has approved for publication a Revised Report, presented to the Food Standards Committee by its Preservatives Sub-committee, making recommendations about the use of antioxidants in foods. Since then the Sub-committee has reviewed representations from trade and other interests and the Revised Report replaces the earlier Report. An earlier report on this subject was published in June, 1953 (see Analyst, 1953, 78, 504). * Obtainable from H.M. Stationery Office. Italics indicate changed wording.658 BOOK REVIEWS [Vol. 79 The present Report proposes that the Public Health (Preservatives, etc., in Food) Regulations should be amended to give effect to the Sub-Committee’s revised recommendations. Any further representations from interested parties should be made to the Assistant Secretary, Food Standards and Labelling Division, Ministry of Food, Great Westminster House, Horseferry Road, London, S.W. 1, before November 30th, 1954. Copies of the report can be obtained from H.M. Stationery Office, price 6d. (plus postage).

ISSN:0003-2654    

DOI:10.1039/AN9547900657

出版商:RSC    

年代:1954

数据来源: RSC

摘要:

BOOK REVIEWS [Vol. 79 Book Reviews METHODS OF BIOCHEMICAL ANALYSIS. Volume I. Edited by DAVID GLICK. Pp. x + 521. This is the first volume of a series intended to provide authoritative information on methods for the determination of enzymes, vitamins, hormones, lipids, carbohydrates, proteins and minerals. The techniques and instruments used in chemical, physical, microbiological and perhaps animal assays will be described, and the Editor is assisted by an Advisory Board of well-known workers, including, from this country, Consden, Marrian and J . K. N. Jones. The declared policy is to give preference to subjects of current importance and to “essentially new approaches which bear promise of great usefulness.” Each chapter is planned not only to include a critical evaluation of previous work but also to “furnish the laboratory worker with the complete information required t o carry out the analysis.The series . . . will become an encyclopaedic treatment of the complete methodology of Biochemical Analysis.” This is an ambitious project, and the 17 articles in the first volume give it a good start. The first chapter (by Chinard and Hellerman) is on the determination of “sulfydryl” groups, and the second chapter (by Bray and Thorpe, of Birmingham) is on the analysis of phenolic compounds; both are clear and balanced accounts. The next two chapters deal with micro- biological assays of antibiotics and of vitamin BIZ. Then comes a concise account (by J. H. Roe) of the chemical determination of ascorbic, dehydroascorbic and diketogulonic acids. Kunkel, under the title zone electrophoresis, deals with preparative electrophoresis, the use of filter-paper, starch blocks and purified cellulose fibres, as well as column electrophoresis.The chromatographic separation of the steroids of the adrenal gland (discussed by Haines and Karnemaat) is topical, and the authors themselves regard the chapter as a review of work in progress rather than a set of definitive procedures. Chromatography is also considered (by L. Hough) in relation to the analysis of mixtures of sugars. Roche and his colleagues discuss the chromatography of 1311-labelled substances for studying the biochemistry of iodine and thyroid hormones. Useful chapters follow on choline, nucleic acids, and raffinose and kestose (the latter by de Whalley and Gross, based on work carried out in this country).Strehler and Totter, of the Oak Ridge Laboratory, describe the determination of ATP and related compounds. Various methods are discussed, but the firefly luminescence system is preferred; it is sensitive and specific and has proved “consistent and reproducible to about 5 per cent. accuracy for as little as 10-10 g of labile ATP phosphorus. Fireflies are available during early summer in the entire eastern United States and because of the economy of the test involved, the collection of a few evenings will be sufficient for a year’s investigation in the average laboratory.” The flies (Photinz~ py~alis) are vacuum dried and stored for use. The assay of catalase and peroxidases is very fully covered in two sections, general assay methods by Maehly and special methods by B.Chance. The in vitro determination of hyaluronidase (Tolksdorf) is followed by ultracentrifugal analysis of serum proteins (de Lalla and Gofman) and the assay of urinary neutral 17-ketosteroids (IJ. L. Engel). * Obtainable from the British Standards Institution, Sales Department, 2, Park Street, London, 1%’. 1. New York and London: Interscience Publishers Inc. 1954. Price $9.50; 75s.October, 19541 BOOK REVIEWS 659 This book is a first rate example of the secondary literature of chemistry that is flourishing in the form of annual series published in the U.S.A. These books are expensive, particularly outside America, and each new series needs to be carefully assessed before a library is advised to add it to the list. This new series will clearly be worth while in libraries serving biochemical laboratories.13. A. MORTON BIOCHEMICAL PREPARATIONS. Volume 111. Editor-in-Chief, E. E. SNELL. Pp. viii -I- 128. 1953. Price 28s. U-ith Volume I11 of the series, “Biochemical Preparations” may well be said to have become an established institution, and biochemists engaged in preparative work can now look fonvard with pleasurable expectation to the publication of each succeeding volume in the certain knowledge that in due course one or other of his tasks will be made easier by the publication of these excellent nionographs on the preparation of substances of biochemical importance. If “Organic Syntheses” has become essential to the organic chemist, how much more so will its counterpart become to his biochemical colleague, in a field in which even greater attention to detail is necessary in order to achieve success and where there appear to be so many different ways of making irrevocable mistakes.In the volume under review, for instance, the preparation of two crystalline enzymes- muscle phosphorylase and ribonuclease-is described. The methods are extremely complicated, and only a detailed monograph compiled and checked by experts would be of any use in such instances. This is just what “Biochemical Preparations” provides. Two other methods, only slightly less complicated, are the preparation of the two coenzymes, di- and bi-phosphopyridine nucleotides, from yeast and liver, respectively. The preparation of two other coenzymes, pyridox- amine phosphate and pyridoxal phosphate, of a group of six organic acids and related compounds that are used as substrates in enzymic reactions, of several amino-acids and of the amino-acid reagent, dinitrofluorobenzene, are described in other monographs. Several of the preparations involve the use of conventional organic chemical reactions : some, such as those already referred to above, involve the extraction of animal tissues: and some of the compounds described are made by microbiological synthesis ; L( -1)- and D( -)-lactic acids, for instance, by the fermentation of glucose with certain Lactobacilli, and L-citrulline by the action of Streptococcus fuecalis on L-arginine.Enzyme reactions are also used : sodium ketoiso- caproate is made from L-leucine by the action of rattlesnake venom, although British biochemists will presumably prefer to make it by the alternative process in which D-amino-acid oxidase from hog kidney is allowed to act on D- or DL-leucine.d-isocitric acid is made by extracting the leaves of a plant belonging to the Crassulaceae, and it is recommended that the leaves be picked early in the afternoon because then their content of other organic acids is a t a minimum. This brief summary will indicate what a wide variety of methods is described by those responsible for the monographs, but it makes no mention of points of detail throughout the book that will be found of great value to those interested in biochemical preparations. Modern bio- chemical techniques are used extensively in those preparations where they are appropriate, for example, in the crystallisation of enzymes and in lyophilisation and ion-exchange chromatography for purification and isolation.As usual, each monograph has a section on properties and purity, and in addition to the use of the more conventional constants for characterisation, such as optical rotation and ultra-violet absorption, reference is made when necessary to appropriate biochemical techniques for assaying the substances made. The printing is up to the usual high standard of the earlier volumes of the series and its counterpart, “Organic Syntheses,” and the binding has been designed t o stand up to the hard wear this book will receive in the laboratory, where it will undoubtedly be kept, STRUCTURE AND MECHANISM IN ORGANIC CHEMISTRY.London: Chapman L9: Hall Ltcl.; New Tork: John Wiley & Sons Inc. F. A. ROBINSON By C. I(. INGOLD, D.Sc., F.R.S. Pp. Some practising analysts may be surprised to see more than a passing reference in this journal to a book on what might appear essentially to be theoretical problems of organic chemistry. But the analyst dealing with organic materials has always been aware of the need to allow adequate time for his reactions to go to completion, and can often base analytical procedures on the different rates a t which components of a mixture react. The increasing use of organic reagents in inorganic analysis as complexing reagents, and in the determination of microgram quantities by solvent extraction or absorptiometry, has provided innumerable examples of procedures in which the speed of formation or decomposition of some intermediate or final product is of vital importance. vii + 828, with many tables.London: G. Bell & Sons Ltd. 1953. Price 77s. Cid.660 PUBLICATIONS RECEIVED [Vol. 79 Such kinetic phenomena have generally been studied only to the extent demanded by the solution of the analytical problem at issue, but there is no question that more detailed studies would strengthen one of the weakest sections of present-day fundamental analytical chemistry and should help to reduce time and effort now spent on purely empirical solutions cf similar problems. Professor Ingold deals first with problems of valency and molecular structure, the types of interactions possible between and within molecules, and their physical properties.After a discussion of the aromatic nucleus and a clear account of ways of formally classifying reagents and reactions, he elaborates his theme with reference in turn to electrophilic and nucleophilic substitutions, olefin-forming eliminations, and saturated-, unsaturated- and aromatic-rearrange- ments. The work concludes with a chapter on addition reactions and their reversal, and a critical account of contemporary acid - base theory, carboxyl reactions and nucleophilic aromatic sub- stitutions. This is a hard book to read and demands the closest attention, but it is packed with authoritative information and shows on every page the impact of a logical and penetrating mind. It is indispensable to anyone seriously studying the kinetics of reactions (inorganic as well as organic) and its perusal cannot fail to stimulate others, even though-and perhaps even because- it makes no direct reference to problems of chemical analysis. H. IRVING INDEX TO THE LITERATURE ON SPECTROCHEMICAL ANALYSIS. Part 111, 1946-50. By B, F. SCRIBNER and W. F. MEGGERS. Pp. iv + 226. Philadelphia, Pa. : American Society for Testing Materials. 1954. Price $4.50. Part I11 closely resembles Part I1 (published in 1947) in form of presentation and contains A The abstracts References to This compilation is more than an index; it is a compre- A.S.T.M. Special Technical Publication No. 41-C. 1264 references with abstracts, listed for each year in alphabetical order of authors’ names. detailed subject index is provided as before, and an author index is now included. are truly informative and of varying length according to the subject-matter. published reviews are given for books. hensive bibliographical survey. D. M. SMITH

ISSN:0003-2654    

DOI:10.1039/AN954790658b

出版商:RSC    

年代:1954

数据来源: RSC

摘要:

660 PUBLICATIONS RECEIVED [Vol. 79 Publications Received REPORTS ON THE PROGRESS OF APPLIED CHEMISTRY. Volume XXXVIII: 1953. Edited by F. CLARK, B.A., B.Sc., A.R.I.C. Pp. 989. London: The Society of Chemical Industry. 1954. Price 60s. By P. ALEXANDER, Ph.D., D.I.C., A.R.C.S., and R. F. HUDSON, Ph.D., D.I.C., A.R.C.S. Pp. x + 404. London: Chapman & Hall Ltd. 1954. Price 45s. THE STRENGTHS OF CHEMICAL BONDS. By 2'. L. COTTRELL. Pp. viii + 310. London: Butter- worths Scientific Publications; New York: Academic Press Inc. 1954. Price 30s. ; $5.50. PETROLEUM MICROBIOLOGY. By E. BEERSTECHER, JUN. Pp. xvi + 375. New York and Amster- dam: Elsevier Publishing Co. Ltd.; London: Cleaver-Hume Press Ltd. 1954. Price 55s. VOLUMETRIC GLASSWARE : SCIENTIFIC ASPECTS OF DESIGN AND ACCURACY. National Physical Laboratory Notes on Applied Science No. 6. London: H.M. Stationery Office. 1954. Price 1s. 6d. BALANCES, WEIGHTS AND PRECISE LABORATORY WEIGHING. National Physical Laboratory Notes on Applied Science No. 7. Pp. vi + 46. London: H.M. Stationery Office. 1954. Price 2s. SIGNIFICANCE OF PROPERTIES OF PETROLEUM PRODUCTS. Pp. iv + 74. London: The Institute of Petroleum. 1954. Price 7s. 6d. WOOL: ITS CHEMISTRY AND PHYSICS. Pp. iv + 21. Edited by G. SELL, F.Inst.Pet.

ISSN:0003-2654    

DOI:10.1039/AN9547900660

出版商:RSC    

年代:1954

数据来源: RSC