摘要:

318 ANDERSON AND LEDERER : THE. QUANTITATIVE ESTIMATION [Vol. 75 The Quantitative Estimation of 1-Methyl- 5-Amino Acridine BY J. R. A. ANDERSON AND M. LEDERER SYNOPSIS-BY double decomposition between aqueous solutions of l-methyl- 5-amino-acridine and picric acid, a yel1,ow insoluble precipitate, C20H,,N,0,, is formed quantitatively. The compound is only sparingly soluble in many common organic solvents, and melts at 274" C. Aqueous solutions of l-methyl-5-amino-acridine and picrolonic acid react quantitatively to give a yellow precipitate, C,H,,N,O,, which is only sparingly soluble in water and in many common organic solvents. It melts at 296" to 298" C. with decomposition. Both picric and picrolonic acids may be used as reagents for the gravi- metric estimation of 1-methyl-5-amino-acridine and its salts, and are quantitative even in the presence of glucose or sodium chloride.THE chemotherapeutic properties of 1-methyl-6-amino-acridine were discussed by Albert, and his co-workers1 A method for its synthesis was reported by Albert and Gledhill,2 and the pharmaceutical properties of its hydrochloride were discussed by Falk and Lederer.3 Pedley4 has described a method of assay of the closely related 5-amino-acridine which utilises the insolubility of the dichromate, and Hall and Powell" utilised the insolubility of the ferro- cyanides of euflavine , acriflavine and proflavine for their determination. Bolliger6 has estimated proflavine, etc. by precipitation of the picrate at 0" C. and back-titration of the ,excess picric acid with methylene blue.DISCUSSION In this paper two methods for the quantitative estimation of l-methyl-5-amino-acridine, in its salts and in solution, are described. The methods described by Pedley4 and Hall and Powell" for the estimation of 5-amino-acridine hydrochloride were considered unsatisfactory for 1-methyl-5-amino-acridine and its salts. In the first method the dichromate of l-methyl- 5-amino-acridine is too soluble, and in the second" the procedure is rather tedious. The volumetric method recommended by Bolliger6 i.s not readily applied to dilute solutions. It was found, however, that the picrate of l-methyl-5-amino-acridine precipitates quantitatively under controlled conditions and can be weighed after drying at 105" C. A guide to the identification of the picrate is provided by the melting-point (which is accompanied by slight decomposition). The compound formed has the composition C2,H,,NS07.Picrolonic acid (1-~-nitrophenyl-3-methyl-4-nitro-5-pyrazolone) has been estimated by Bolliger7 98 by titration with standard solution of methylene blue in a manner similar to that employed for the estimation of picric acid.6 Schiedwitzg has described its determination by converting it to its acridine salt, which has a low solubility and a high molecular weight. It was found that l-methyl-5-amino-acridine hydrochloride reacted with picrolonic acid to yield a yellow insoluble precipitate; hence it was decided to investigate the use of picrolonic acid as a reagent for the quantitative determination of :l-methyl-5-amino-acridine and its salts. In the case of l-methyl-5-amino-acridine hydrochloride monohydrate, the precipitate obtained may be weighed after drying at 130" C., and the melting-point, 296" to 298" C.(accompanied by slight decomposition), may be determined. The compound has the composition C,,H,,N,O,. The reactions of l-methyl-5-amino-acridine with picric acid and with picrolonic acid are presumably molecular. OH I 1-Methyl-S-amino-acridine No, Picric acidJune, 19501 OF 1 -METHYL-&AMI NO-ACRIDINE 319 According to Welcher,l0 three possible tautomeric structures have been assigned to picrolonic acid, which may be shown as follows- HO 0 I 0 Picrolonic acid Structures (I) and (111) account for the acid properties of the picrolonic acid molecule, although structure (I), containing the acid-form of the nitro group, seems the more probable.PICRIC ACID METHOD Dissolve a sample containing 0.1 g. of I-methyl-5-amino-acridine or its salts in 100 ml. of water. If the insoluble free base is to be analysed, it will be found to dissolve freely in a buffer solution consisting of 260 g. of sodium acetate and 280 g. of 30 per cent. acetic acid per litre. Add 5 ml. of the acetate buffer and heat the solution until nearly boiling. Then add 15 ml. of a saturated solution of picric acid in water (100 per cent. excess) with constant stirring. Transfer the precipitate to a sintered porcelain crucible and wash with ice-cold distilled water (approximately 50 ml.). Bring the crucible to constant weight at 105" C. and weigh as l-methyl-5-amino-acridine mono- picrate, a yellow crystalline powder, melting-point 274" C.(uncorrected under slight decom- position). EXPERIMENTAL- A sample of pure l-methyl-5-amino-acridine was prepared, and it gave an equivalent weight of 208.2 by addition of excess of 0.1 N hydrochloric acid and back-titration with 0.1 N sodium hydroxide, corresponding to 99.9 per cent. of the base. This sample was used to determine the conditions for a suitable analysis, and the results are shown in Table I, using the method described above. A sample of the hydrochloride was then prepared (moisture content 12.90 per cent.), which gave on analysis 73.9 per cent. of l-methyl-&amino- acridine by the picric acid method, thus showing that this sample was the dihydrate of the hydrochloride. Glucose and sodium chloride were added to the solution for analysis and neither substance affected the results to any extent. The loss due to excessive washing of the precipitate was also investigated, and it was found that 100ml.of water, on being poured over the precipitate, dissolved 1.8 mg., corresponding to about 0-5 per cent. of the total. The picrate was soluble in pyridine, somewhat so in alcohols, acetone and ethyl acetate, but only slightly soluble in most other common organic solvents. Details of results are given in Table I. Then leave the mixture at 0" C. for 3 hours. TABLE I RECOVERY OF 1-METHYL-5-AMINO-ACRIDINE BY PICRIC ACID METHOD Weight taken, g. 0-4000 0~1000 O*lOOo 0.1OOo 0-1000 0~1OOo Volume of solution, ml. 100 100 100 200 100 100 Volume of saturated picric acid added, ml.50 15 15 15 15 15 Temperature for complete precipitation, Time of standing Recovery, ca. 15 A few minutes 99.4 ca. 15 18 hours 99-36 0 1 hour 99.0 0 18 hours 100-5 0 3 hours 99.0 O c. % ca. 15 A few minutes 98.4320 ANDERSON AND LEDERER Pol. 75 PICROLONIC ACID METHOD Dissolve 0.1 g. of l-methyl-5-amino-acridi1ie hydrochloride monohydrate in 50 ml. distilled water, boil the solution and add 40 ml. of 0.01 N picrolonic acid, prepared as described by Dworzak and Reich-Rohnvig,ll from a burette, dropwise and with constant stirring to the boiling solution. Then run in a further 40 nil. of 0.01 N picrolonic acid, giving 100 per cent. excess of precipitant. Allow the mixture to stand for at least 1 hour, and then cool to about 15" to 20" C., and transfer to a sintered crucible and wash with cold distilled water (approximately 60 ml.).Bring the crucible to constant weight at 130" C. and weigh as l-methyl-5-amino-acridine mono-picrolonate, a yellowish crystalline powder. EXPERIMENTAL- Samples of pure l-methyl-5-amino-acridine hydrochloride monohydrate weighing 0.1 g. (6-80 per cent. water of hydration; melting-point of free base, 196" to 197" C. (corrected)) were treated with 0.01 N picrolonic acid by the method described above. A 100 per cent. excess of picrolonic acid was found to be sufficient for complete precipitation. The precipitates formed were dried over sulphuric acid in a vacuum desiccator, an average yield of 100.3 per cent. of the monohydrated salt being obtained. Subsequent drying of a number of precipitates' for about 2 hours at 130" C.gave the anhydrous salt, the yield of this being 99.7 to 100.1 per cent. of the theoretical yield. The addition of glucose or of sodium chloride to the solution being analysed had no serious effect on the results obtained. The anhydrous l-methyl-5- amino-acridine mono-picrolonate showed only slight solubility in water and in many common organic solvents. It was soluble in pyridine and somewhat so in alcohols, acetone and ethyl acetate. It was found to have a melting-point of 296" to 298" C. (accompanied by decom- position). The analytical data is summarised in Table 11. TABLE 111 RECOVERY OF 1-METHYL-5-AMINO-ACRIDIlQE HYDROCHLORIDE MONOHYDRATE BY PICROLONIC ACID METHOD Weight taken, €5 0*1000 0~1000 0~1000 0~1000 0*1000 0~1000 0*1000 0~1000 Volume of solution, ml.50 50 50 50 100 100 100 100 0.01 N picrolonic acid added, ml. 120 120 80 80 80 80 80 80 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. Temperature for complete precipitation, O c. 16 16 18 18 20 18 19 16 Weight of Time of glucose standing added, g* 18 hours - 3 hours - 3 hours - 1 hour - 1 hour 6 2 hours - 1.5 hours 1 6 days - REFERENCES Weight of sodium chloride added, g. - - - - - 0.9 0.9 0.9 Recovery, 99.7 99.7 100- 1 99.7 99.1 100.1 99.9 99.8 % Albert, A., Rubbo, S. D., Goldacre, R. J., Dave:y, M. E., and Stone, J. D., Brit. J . Exper. Path., Albert, A., and Gledhill, W., Pharm. J., 1945, 154, 127. Falk, J. E., and Lederer, M., Ibid., 1945, 155, 208. Pedley, E., Ibid., 1945, 155, 148. Hill, G. F., and Powell, A. D., Quart. J . Pharin. Pharmacol., 1933, 6, 389. Bolliger, A., Ibid., 1940, 13, 1-6. -, Aust. J . Exp. Biol. Med. Sci., 1935, 13, 75. Schiedwitz, H., 2. physiol. Chem., 1933, 214, 177-8. Welcher, G., "Organic Analytical Reagents," Vol. IV, D. Van Nostrand Company Inc., New Dworzak, R., and Reich-Rohrwig, W., 2. anal. Chem., 1931, 86, 98-113. 1945, 26, 160. -, J . PVOC. ROY. SOC. N.S.W., 1934, 68, 197. York, 1948, p. 40. CHEMISTRY DEPARTMENT SYDNEY TECHNICAL COLLEGE SYDNEY, N.S.W., AUSTRALIA August, 1949

ISSN:0003-2654    

DOI:10.1039/AN9507500318

出版商:RSC    

年代:1950

数据来源: RSC

摘要:

June, 19501 BACON 321 The Photometric Determination of Phosphorus in Low-Alloy Steels BY A. BACON SYNoPsIs-Although methods utilising the molybdate reaction and stannous chloride or sodium sulphite as the reducing agent have been described by previous workers, concordant results were not obtained when attempts were made to apply the technique as described. It was thought that incomplete reduction was the reason for this failure, and this paper describes the effect of residual ferric iron on the reduction of phosphomolybdate, both by stannous chloride and by ferrous sulphate. The production of ferrous sulphate by the reduction of ferric iron with sulphurous acid is studied and some details of the fundamental reagent con- centrations are also given. From the results of these experiments a method has been devised which, if carefully controlled, gives results reproducible within f0.001 per cent.of phosphorus. The values obtained by this method are slightly lower than those obtained by a referee gravimetric method, and calibration using steels analysed by the referee method is recommended. A DIRECT method for the determination of phosphorus in steel has been described,l in which the phosphorus is converted to phosphomolybdate , followed by reduction to molybdenum blue by means of stannous chloride. Attempts to apply the method proved unsatisfactory and some of the fundamental conditions were therefore studied in order to evolve a satisfactory procedure. Preliminary experiments were conducted in order to determine the effect of variations in the molybdate concentration and in acidity on the production of the yellow phospho- molybdate.These effects were studied on the Spekker absorptiometer, measurements being made in the violet waveband where the yellow phosphomolybdate exerts maximum absorp- tion. As high concentrations of ammonium molybdate resulted in the formation of a yellow precipitate, presumably ammonium phosphomolybdate, the curves shown in Fig. 1 were produced using sodium molybdate. These results show that the optimum acidity, and also the acidity range over which maximum colour develops, increase with the sodium molybdate concentration. Readings showed the absorption of the solutions to be constant over a period of 30 minutes. Substitution of ammonium molybdate at a concentration of 5 g.per litre for the same concentration of sodium molybdate had little effect on the readings obtained, and the absorp- tion was almost constant over a period of 30 minutes. At a concentration of log. of ammonium molybdate per litre, however, precipitation occurred within 10 minutes over an acidity range of 0.2 to 0.3 N sulphuric acid. The poor sensitivity and the resulting high concentrations of ferric salts, which absorb strongly in the violet waveband, prohibit the application of this method to the analysis of steels. STANNOUS CHLORIDE REDUCTION Previous work2 on the determination of silicon by the formation of a silicomolybdate and subsequent reduction with stannous chloride has shown that the background colour is dependent on the concentrations of the three reagents, sulphuric acid, sodium (or ammonium) molybdate and stannous chloride.The effect of stannous chloride is shown in Fig. 2, where it can be seen that there is a critical acidity below which excessive reduction of the molybdic acid occurs. This critical acidity increases with the molybdate and stannous chloride con- centrations, and although a stannous chloride concentration of 0.001 N was chosen for further experiments, acidities lower than 0-5 N sulphuric acid could not be studied when using a concentration of 5 g . of ammonium molybdate per litre. By reference to Fig. 1 it can be seen that the region of maximum formation of phosphomolybdate, as indicated by the absorption in the violet waveband, cannot be studied using stannous chloride. When the formation of silicomolybdate was studied, the solution was strongly acidified after silico- molybdate formation and before addition of the stannous chloride.It was not possible to do this with phosphomolybdate because decomposition occurred immediately.322 BACON THE PHOTOMETRIC DETERMINATION [vol. 75 500. MOLY6. SODo MOLYB. SOO. MOLYB. SOD. MOLYB. I I $4- 5 10 20 30 I I I I I I I I 4CM. CELLS VIOLET FILTERSl 1 5 MIN. READINGS I WIW ACIDITY-H,SO, Fig. 1. Formation of yellow phospho- The effect of molybdate con- molybdate. centrations on the acidity range I -0 0 8 0 6 0 2 0 4 ~ 0 4000 5000 6000 A 7000 WAVELENGTH Fig. 3. Transmission curve for molybdenum blue ACIDITY-!+,SO, Fig. 2. Effect of stannous chloride on the background colour U z W cz w U Y n n Z 4 08 0 6 0 z - n 0.4 0 2 0 0 0 5 1.0 N I 5 ;5 d I I I ACIDITY---H,SO, Fig.4. Effect of acidity on the reduction by stannous chlorideJune, 19501 OF PHOSPHORUS IN LOW ALLOY STEELS 323 ABSORPTION BY THE MOLYBDENUM-BLUE COMPOUND- Although the maximum absorption by the reduced phosphomolybdate occurs in the red waveband, it was found more convenient to use yellow filters in conjunction with the mercury- vapour light source. The transmission curve shown in Fig. 3 illustrates the relative sensitivity in the yellow and red wavebands, and it should be noted that the background also shows maximum absorption in the red waveband. The transmission graph was obtained by plotting the Spekker readings against the wavelengths of maximum transmission of the colour filters, a tungsten-filament lamp being used as the source of illumination.THE EFFECT OF ACIDITY ON THE REDUCTION BY STANNOUS CHLORIDE- The effect of acidity on the production of the molybdenum-blue colour was studied in a series of experiments using concentrations of 5 g . of sodium molybdate per litre, 0.001 N stannous chloride, 0-0006g. of phosphorus per litre, and various acidities in the range 0.5 to 1.2 N sulphuric acid. The molybdate was added to the acid solution containing phosphorus and then the stannous chloride was added with agitation of the solution. The results are shown in Fig. 4 (curve A), together with those for a similar series without the phosphorus (curve B), and the difference between the absorptions is shown in curve C. It can be seen that below 0.6 N sulphuric acid excessive reduction of molvbdic acid occurs and that the maximum absorptioi attributable to the phosphorus is a&ained at approximately 0.7 N sulphuric acid.THE EFFECT OF CONCENTRATION OF MOLYBDATE ON THE ACIDITY RANGE- On increasing the strength of the sodium molybdate to 10 g. per litre, excessive reduction of molybdic acid occurred at acidities below 0.75 N sulphuric acid, and the optimum acidity was increased to 0.9 N sulphuric acid. Substitution of ammonium molybdate, 5 g. per litre, for the sodium salt did not result in any material change in the position of the curves shown in Fig. 4. THE STABILITY OF THE MOLYBDENUM-BLUE COMPOUND- Readings taken after the solutions had stood for 30 minutes showed that the background colour was stable at acidities greater than 0.6 N sulphuric acid.The solutions containing phosphorus showed a loss in absorption equivalent to 0.05 in drum reading over the acidity range of 0.7 to 1.0 N , while at 1-2 N sulphuric acid an increase in absorption occurred equivalent to 0.12 in drum reading. THE EFFECT OF THE STANNOUS CHLORIDE CONCENTRATION- In order to study the effect of the stannous chloride, a series of experiments was conducted using concentrations of 5 g. of ammonium molybdate per litre, 1.0 N sulphuric acid, 0-0006 g. of phosphorus per litre, and various concentrations of stannous chloride in the range 0-0o02 to 0-010 N . The series was then repeated without the phosphorus. The results are shown in Fig. 5. It can be seen that maximum sensitivity occurs at 0.0005 N stannous chloride.Below O~OOO2 N , reduction of the phosphomolybdate is incomplete, and increasing the strength of the stannous chloride above 0.0005 N tends to reduce the sensitivity (curve C), because the background absorption increases more rapidly than that due to phosphorus. It was noted that decreasing the stannous chloride below 0.001 N did not result in any decrease in the background absorption. This residual colour is due to small amounts of phosphorus present as impurities in the reagents used. On the assumption that all of the impurity is in the sulphuric acid, the residual colour is equivalent to approximately 2p.p.m. (w/v) of phosphorus in the concentrated acid. A series of experiments similar to those used to construct Fig. 5 was conducted at an acidity of 0.8 N sulphuric acid instead of 1.0 N .The results obtained at this acidity are shown in Fig. 6, and by comparing the two figures it can be seen that the sensitivity at 0.001 N stannous chloride is practically unchanged. However, the background colour is much more sensitive to variations of the stannous chloride concentration and the sensitivity, as shown by the differences in the drum readings, increases with the stannous chloride concentration. THE EFFECT OF FERRIC SULPHATE ON THE STANNOUS CHLORIDE REDUCTION- The effect of ferric sulphate on the reduction of the phosphomolybdate by stannous chloride was studied in a series of experiments using concentrations of 5g. of ammonium324 BACON : THE PHOTOMETRIC DETERMINATION [Vol. 75 01 I I I 0 0 005 0.010 N STANNOUS CHLORIDE Fig.5. sensitivity Effect of stannous chloride on the (Sulphuric acid, 1.0 N ) YELLOW FILTERS. 5 M\Nl READlNqS. 0 0.0 I 0.02 N FERRIC SULPHATE Fig. 7. Effect of ferric sulphate on the reduction of phosphomolybdate by stannous chloride I ZCM. C€LCS YELLOW FILTERS. I 0 0 00s 0 010 STANNOUS CHLORIDE Effect of stannous chloride on the (Sulphuric acid, 0.8 iV) Fig. 6. sensitivity I STANNOUS CHLORIDE Fig. 8. Effect of stannous chloride on the sensitivity in the presence of ferric sulphateJune, 19501 OF PHOSPHORUS IN LOW ALLOY STEELS 325 molybdate per litre, 0.8 N sulphuric acid, 0.001 N stannous chloride and 0.0006 g. of phosphorus per litre and the iron content was varied over the range 0 to 0.02 N by means of a ferric sulphate solution. A second series was conducted without the phosphorus.The results given in Fig. 7, curves A and A’, show that the background colour and the colour associated with the phosphorus are seriously affected by quite low concentrations of ferric sulphate. Repeating the experiments at two further concentrations of stannous chloride, 0.002 and 0.005 N , yielded curves B, B’ and C, C’, from which it is evident that the sudden change in slope of the curves occurs when the iron concentration is approximately equal to that of the stannous chloride. At a concentration of 0.02 N ferric iron, increasing the stannous chloride over the range 0.001 to 0.005 N had little effect on the background colour. Appreci- able changes occur, however, in the solutions containing phosphorus, and a series of experiments was conducted to determine the stannous chloride concentration necessary to ensure maximum absorption when the solution contained approximately 0.010 and 0-020 N ferric sulphate.The results are given in Fig. 8 and show that as the concentration of the stannous chloride increases, the absorption of the solutions containing phosphorus increases, then remains constant for a period, and then suddenly increases, this sudden increase occurring when the stannous chloride concentration exceeds that of the ferric iron and coinciding with a similar rapid increase in absorption by those solutions not containing phosphorus. The values plotted in Fig. 8 are the average of a large number of determinations, for the readings obtained were not reproducible.Such factors as speed of addition of the reducing agent, temperature of the solution, agitation, and preparation of stannous chloride were all found to affect the partition of the stannous chloride between the ferric salt and the phosphomolybdate ; the graphs showing the effect of ferric iron must, therefore, be interpreted generally. THE STABILITY OF THE MOLYBDENUM-BLUE COMPOUND IN THE PRESENCE OF FERRIC A typical time-curve for a solution containing a concentration of stannous chloride less than that of the ferric iron is shown in Fig. 9. During the first few minutes, rapid forma- tion of molybdenum blue occurs, but as reduction of the ferric iron proceeds, with a subsequent reduction in the stannous chloride concentration, the formation of molybdenum blue slows down and finally, when the whole of the stannous chloride has been removed by the ferric iron, a sudden drop in absorption occurs, most probably because the residual ferric salt attacks the molybdenum-blue compound.After attaining the new level of absorption, the solution fades slowly. The time-curve shown in Fig. 10 is for a solution containing a stannous chloride concentration larger than that required to reduce completely the ferric iron present. In the early stages, a considerable concentration of stannous chloride is present, and this results in the formation of deep and erratic background colours. The development of colour due to phosphorus progresses to a maximum in concordance with removal of ‘ferric iron, with excess of stannous chloride always present.The results obtained from over 300 tests, covering a wide range of solution conditions, were not sufficiently reproducible to offer any hope of a satisfactory method of determining phosphorus in the presence of ferric salts. FERROUS SULPHATE REDUCTION Preliminary tests showed that the phosphomolybdate could be reduced by ferrous sulphate ; the sensitivity, however, is considerably less than that attained when using stannous chloride. As with stannous chloride, the background colour was found to be dependent on the concentrations of the three reagents sulphuric acid, ammonium (or sodium) molybdate and ferrous sulphate. This is shown in Fig. 11, and it can be seen that there is a critical acidity below which excessive reduction of the molybdic acid occurs.With ferrous sulphate this acidity is less critically dependent on the concentrations of reducing agent and molybdate than with stannous chloride, and comparatively high concentrations of ferrous sulphate produce only slight background colours. The acidity below which excessive reduction of molybdic acid occurs even in the presence of 0.4 N ferrous sulphate is in the region of 0-3 to 0.4 N sulphuric acid. Substitution of ferrous sulphate for stannous chloride does not result in any material change in the transmission curve of the molybdenum-blue colour. THE EFFECT OF ACIDITY ON THE REDUCTION BY FERROUS SULPHATE- The effect of acidity on the production of the molybdenum-blue colour was studied in a series of experiments using concentrations of 5 g. of sodium molybdate per litre, 0.004 g.SULPHATE-326 BACON : THE PHOTOMETRIC DETERMINATION [vol. 75 A A' O i I I I 1 0 10 20 30 TIME (MINUTES) Fig. 9. Time - absorption curve. Stannous chloride less than ferric iron concentration 1 0 u a ru d 5 06 d z a 0.8 n 0 4 0 2 LLOW FILTER TIME (MINUTES) Time - absorption curve. Fig. 10. Stannous chloride greater than ferric iron concentration ACIDITY-ti,SO, Fig. 11. Effect of ferrous sulphate on the background colour ACIDITY--H ,SO, Fig. 12. Effect of acidity on the reduc- tion by ferrous sulphateJune, 19501 OF PHOSPHORUS IN LOW ALLOY STEELS 327 of phosphorus per litre, 0.02 N ferrous sulphate and various acidities in the range 0.1 to 1-5 N sulphuric acid. The results are shown in Fig. 12, curve A, together with those for a similar series conducted without phosphorus, curve B.The difference in absorption between A and B is shown in curve C. From these curves it can be seen that, under these conditions, maximum sensitivity is attained at 0.6 N sulphuric acid, and that the absorption by those solutions containing phosphorus decreases rapidly at acidities above 0.75 N sulphuric acid. At acidities greater than 0-3 N sulphuric acid, the background absorption is slight. THE EFFECT OF CONCENTRATION OF MOLYBDATE ON THE ACIDITY RANGE- Substitution of ammonium molybdate, 5 g. per litre, for the sodium salt had little effect on the values obtained, the curves being similar in shape but with a slight displacement towards the higher acidities. Increasing the concentration of the sodium molybdate to log.per litre resulted in excessive blanks occurring at acidities below 0.5 N sulphuric acid. The difference curve was similar in shape and magnitude, but the peak occurred in the region of 0.8 to 1.0 N sulphuric acid. THE STABILITY OF THE MOLYBDENUM-BLUE COMPOUND- Readings taken after 30 minutes showed the background colour to be stable at acidities greater than 0.25 N sulphuric acid. The solutions containing phosphorus were stable up to 0.75 N sulphuric acid. Above this value the solutions showed an appreciable increase in absorption during a period of 30 minutes. THE EFFECT OF THE FERROUS SULPHATE CONCENTRATION- It can be seen from Fig. 13 that the background colour is proportional to theconcentra- tion of ferrous sulphate. It can also be seen that a stage is reached where any further addition of ferrous sulphate does not produce an increase in absorption by the solution containing phosphorus. At a concentration of 0.004 g.of phosphorus per litre, maximum sensitivity, as shown by curve C , is attained at a ferrous sulphate concentration of 0-05 N . A further series of experiments showed that 0.016 g. of phosphorus per litre required a concentration of 0.15 N ferrous sulphate to attain maximum sensitivity. It was also deduced from these experiments that when sufficient ferrous sulphate was present to ensure maximum sensitivity, the absorption produced was proportional to the phosphorus content. It is evident from these results that the values shown in Fig. 12 were obtained at a ferrous sulphate concentration that was insufficient to ensure maximum colour from the phosphorus.When these experi- ments were repeated at a concentration of 0.1 N ferrous sulphate, the shape and position of the curves were not affected by the values obtained. The maximum sensitivity, as indicated by the peak of the difference curve, was slightly increased to a difference of 0.62 in drum reading. THE EFFECT OF FERRIC SULPHATE ON THE FERROUS SULPHATE REDUCTION- In order to study the effect of ferric sulphate on the reduction of the phosphomolybdate by ferrous sulphate, a series of experiments was conducted using concentrations of 5g. of ammonium molybdate per litre, 0.8 N sulphuric acid, 0.02 N ferrous sulphate and O W 4 g. of phosphorus per litre. The ferric iron content was varied over the range 0 to 0-012 N by means of a ferric sulphate solution.The series was repeated omitting the phosphorus. Three further series were conducted at ferrous sulphate concentrations of 0.10, 0-20 and 0.4 N , and the results are shown in Fig. 14. A study of this figure shows that the absorption due to phosphorus is considerably reduced by the introduction of ferric sulphate, and that the effect is minimised by increasing the concentration of the ferrous sulphate. The back- ground colour is unaffected by the ferric salt. From Fig. 14 conditions can be derived such that a range of 0 to 0.5 per cent. of phosphorus in steel can be directly determined in the presence of the ferric iron; but for a more limited phosphorus range, employing a larger weight of sample, the ferric iron must be reduced prior to coloration.THE STABILITY OF THE MOLYBDEN.UM-BLUE COMPOUND IN THE PRESENCE OF FERRIC SULPHATE- Readings taken over a period of 40 minutes during the determination of the values used in the construction of the curves shown in Fig. 14 showed that the background colour328 BACON THE PHOT0MET:RIC DETERMINATION [Vol. 75 0 2- 2 t M . CELLS. YELLOW FILTERS: 5 MIN. REAOINqS. 1 A P 0.004 gle 6 P NIL t C DIFFERENCES. n Z 4 0 6 0.4 0 2 0 0 0 1 0 2 03 N FERROUS SULPHATE Fig. 13. The effect of ferrous sulphate on the sensitivity FERRIC IRON 0*058"1. VOLUME 0.25 N SULPHUROUS AClO 0-50 N SULPHUROUS AClO 1.0 N SULPHUROUS AC\O Fig. 15. Reduction of 0.06 g. of ferric iron by sulphurous acid Fig. 14. The effect of ferric sulphate on the reduction of phosphomolybdate by ferrous sulphate ACIDITY-H,SO, Fig.16. Reduction of 0.26g. of ferric iron by sulphurous acidJune, 19501 OF PHOSPHORUS IN LOW ALLOY STEELS 329 was stable. The solutions containing phosphorus, however, deepened slightly to a maximum absorption at 20 minutes, both in the presence and in the absence of iron. This is not un- expected, for it can be seen from Fig. 12 that the acidity at 0.8N sulphuric acid is slightly greater than the optimum. REDUCTION OF THE FERRIC IRON BY SULPHUROUS ACID For the experiments on the reduction of ferric sulphate by sulphurous acid, a solution of ferric sulphate was prepared and the iron content determined by reduction with stannous chloride and then titrating with standard potassium dichromate using sodium diphenylamine sulphonate as internal indicator.The acidity of the ferric sulphate solution was determined by adding an excess of standard alkali and titrating back with standard acid using phenol- phthalein as indicator. The sulphuric acid generated during the reduction was taken into hccount during the construction of the graphs. Thus for zero acidity, before adding the sulphurous acid, an alkali addition was made which neutralised the free sulphuric acid, the acid associated with the ferric sulphate and the sulphuric acid generated during reduction. Solutions of sodium sulphite prepared from various samples of the salt were so variable and weak that recourse was had to a saturated solution of sulphur dioxide in water as the reducing agent. The solution was standardised against potassium permanganate, and the strength so found was regularly between 2.0 and 2.5 N . Preliminah tests showed that immersion in boiling water for at least 30 minutes was necessary for the completion of the reduction by the sulphur dioxide.Heating rapidly to boiling-point, however, resulted in the sulphur dioxide being evolved too quickly. Experiments showed that by heating slowly so that 5 minutes elapsed before the appearance of gas bubbles, efficient reduction by the sulphurous acid occurred. The introduction of a short period, about 2 minutes, of boiling resulted in a slightly better reduction, presumably because of a rise in pH as the sulphur dioxide was evolved. Tests showed that increasing the heating period and a variation of 1 minute in the boiling period had little effect on the residual ferric iron.All the experiments on the reduction by sulphurous acid, described below, were therefore conducted by using gentle heating for 5 minutes followed by boiling for 2 minutes. The residual ferric iron was determined by a thiocyanate absorptiometric method. APPLICATION TO THE STANNOUS CHLORIDE METHOD- It can be calculated from Fig. 6 that, using a sample weight of 0.05 g. and a volume of 50 ml. for coloration, the range covered by the use of 4-cm. cells and yellow filters would be from 0 to 0-06 per cent. of phosphorus in the absence of ferric iron. Bty reference to Fig. 7 it can be deduced that the introduction of 0.0001 g. of ferric iron results in a change in absorp- tion of 1 per cent. The prior reduction of the ferric salt by sulphurous acid should, therefore, ensure a difference of less than f0.0001 g.between the ferric iron in the test solution and the ferric iron content of the solutions used to determine the calibration points, if an accuracy of 4 1 per cent. is to be attained. Experiments, using 0.05 g. of ferric iron, were conducted, therefore, to determine the optimum conditions for the reduction by sulphurous acid. The results are given in Fig. 15 and show that maximum reduction is obtained over an acidity range of 0 to 0.1 N . Over this range, as reduction occurs, the acid is associated with the iron as ferrous sulphate. At higher acidities, the free acid causes a rapid fall in pH which prevents reduction of the ferric salt by sulphurous acid.At low concentrations of sulphurous acid, and in the presence of only small amounts of free acid, the precipitated ferric hydrate fails to re-dissolve. APPLICATION TO THE FERROUS SULPHATE METHOD- It can be calculated from Fig. 13 that, using a 0.25-g. sample and a volume of 50 ml. for coloration, the range of phosphorus contents that can be determined by the use of 4-cm. cells and yellow filters would be 0 to 0.065 per cent. of phosphorus in the absence of ferric iron. By reference to Fig. 14, it may be deduced that the introduction of 0*0007 g. of ferric iron results in a change in absorption of 1 per cent. The prior reduction of the ferric salt by sulphurous acid should therefore ensure a difference of less than =tO.O007 g. between the ferric iron in the test solution and the ferric iron contents of the solutions used in the determination of the calibration points, if an accuracy of f l per cent.is to be attained. Experiments, using 0.25 g. of ferric iron, were, therefore, conducted to determine the optimum conditions for the reduction by sulphurous acid. The results are given in Fig. 16 and are330 BACON : THE PHOTOMETRIC DETERMINATION [Vol. 75 similar to those obtained using 0.05 g. of ferric iron. At the lower sulphurous acid concentra- tion of 0.5 N , the ferric hydrate fails to re-dissolve at acidities of less than 0-15 N sulphuric acid. Maximum reduction is attained over an acidity range of 0 to 0.2 N sulphuric acid; the increase in the acidity range is caused by the higher concentration of ferrous sulphate.CHOICE OF REDUCING AGENT- The values in Figs. 15 and 16 were obtained by using pure ferric sulphate, and further experiments were carried out to determine the residual ferric iron after a sulphurous acid reduction on solutions prepared from standard steels. For these experiments, the steels were dissolved in dilute nitric acid, which was su’bsequently removed by fuming with sulphuric acid. Suitable conditions were deduced from Figs. 15 and 16 to ensure maximum reduction by the sulphurous acid, and the results are shown in Table I. TABLE 1 SULPHUROUS ACID REDUCTION USING STANDARD STEELS Residual ferric iron after treatment of Sample 0.05-g. sample, 0.25-g. sample. Residual ferric iron after treatment of €5 g . Electrolytically pure iron . . 0*00007 0.000 12 B.C.S.218 .. .. .. 0.000 145 0.000385 B.C.S. 225 . . .. .. 0-000146 0.00030 Although the residual ferric iron is greater for the B.C.S. samples than for the electro- lytically pure samples, the difference is sufficiently small to permit the use of either reducing agent in the development of the phosphorus colour. It has already been shown that the stannous chloride method is more sensitive to changes in the concentrations of the reducing agent and ferric iron, and changes in acidity; these changes appear to be some of the reasons why such poor reproduction was attained during attempts to evolve a method based on the stannous chloride reduction after a preliminary reduction of the ferric iron by sulphurous acid. The background colours were difficult tcl reproduce and apparently depended on the order of addition of the reagents, the speed at which the reducing agent was added and the temperature of the solution.The results obtained were unsatisfactory, and therefore attention has been confined to the use of ferrous sulphate in the development of a method for deter- mining phosphorus in steel. APPLICATION OF THE FERROUS SULPHATE METHOD TO THE DETERMINATION OF PHOSPHORUS IN STEEL FUMING WITH SULPHURIC ACID TO REMOVE NITRIC ACID- Several 0.25-g. samples of pbre iron were dissolved in dilute nitric acid, 2.5 ml. of 10 N sulphuric acid were added, and the solutions were fumed for various times and subsequently reduced by sulphurous acid after neutralising with 6 ml. of 4 N caustic soda. The residual ferric iron was determined by thiocyanate, and the results, given in Table 11, indicate that a fuming period of 5 minutes is sufficient.TABLE I1 THE EFFECT OF THE FUMING PERIOD ON THE AMOUNT OF FERRIC IRON Samples of pure iron weighing 0.25 g. Fuming period, minutes . . 0.5 1 2 5 20 REMAINING AFTER REDUCTION BY SULPHUROUS ACID Residual ferric iron, g. . . . . 0*00050 0.00036 0.00042 0*00020 0.00025 A similar series of experiments was conduicted to determine the quantity of sulphuric acid lost during fuming in a covered beaker for 5 minutes. The samples used were 0.25 g. of pure iron, and 25 ml. of N sulphuric acid were added. After fuming, the sulphuric acid that remained was determined by titration, anLd 20.4, 22.0, 19.5 and 19.5 ml. were found. These results show that an average loss of 5 ml.of N sulphuric acid occurs. That phosphorus was not lost during this fuming period was proved by adding phosphorus both before and after fuming ; the readings obtained were identical.June, 19501 OF PHOSPHORUS IN LOW ALLOY STEELS 331 FINAL ACIDITY FOR PRODUCTION OF MAXIMUM SENSITIVITY- After reduction, the addition of 3 ml. of 10 N sulphuric acid in conjunction with that introduced by the ferrous sulphate reagent ensures an acidity of 0.7 N in a final bulk of 50 ml., and this can be seen from Fig. 12 to give the maximum sensitivity when buffered by 5 g . of ammonium molybdate per litre. STABILITY TESTS TO ESTABLISH THE STANDING PERIOD- Readings taken at intervals over a period of 1 hour showed that maximum colour was only just developed in 5 minutes, and as the absorption remained constant for a further 55 minutes, a standing period of 10 minutes was chosen.METHOD FOR THE DETERMINATION OF PHOSPHORUS IN STEEL SOLUTIONS- Ferrous sulphate solation-Make a 14 per cent. solution by dissolving 14 g. of pure ferrous sulphate in approximately 80 ml. of water containing 5 ml. of 10 N sulphuric acid, and then dilute to 100ml. Reference solution-Dissolve 1.28 g. of pure ferrous sulphate in 5 ml. of dilute nitric acid, sp.gr. 1.2, add 1-6ml. of 10N sulphuric acid and treat according to the procedure given below. PROCEDURE- Add 2-5 ml. of 10 N sulphuric acid and a few drops of hydrochloric acid to prevent spurting; boil down and fume for 5 minutes. A 100-ml. beaker is recommended and the cover should not be removed during fuming.Cool, add 10ml. of water and digest on a hot-plate to a clear solution. Cool and add 6 ml. of 4 N sodium hydroxide, agitating the solution. Add 25 ml. of water saturated with sulphur dioxide (the solution should be between 2.0 and 2.5 N ) . Heat slowly on the hot-plate, allowing at least ti minutes to elapse before the evolution of gas bubbles, and then boil for 2 minutes. Add 3 ml. of 10 N sulphuric acid and boil down to 30 ml. Coo1,'add 5 ml. of 5 per cent. ammonium molybdate solution while agitating the solution, followed by 10ml. of the 14 per cent. solution of ferrous sulphate. Transfer to a 50-ml. graduated flask, dilute to the mark, and allow the solution to stand for 10 minutes. The temperature of the solution should be within f 2 " C. of the calibration temperature.Read the absorption on the Spekker using 4-cm. cells, yellow filters and a setting water - water of 1.0. Derive the differences with respect to the reference solution and convert them to the phosphorus content by reference to the calibration curve. CALIBRATION- (NH,),HPO,, in water and dilute to exactly 1 litre. Dissolve 0.25 g. of steel in 5 ml. of dilute nitric acid, spgr. 1.2. Phosphorus solution-Dissolve 0.4260 g. of di-ammonium hydrogen phosphate, 1 ml. = 0.0001 g. of phosphorus. Dissolve several 0.25-g. samples of pure iron in 5ml. of dilute nitric acid and add incremental amounts of phosphorus as shown below- Phosphorus solution, ml. . . .. 0 0-5 1.0 1.5 Phosphorus, per cent. . . . . .. 0 0.02 0-04 0.06 Proceed as described in the method, derive differences with respect to the zero calibration- point and construct a calibration graph by plotting these differences against the phosphorus added.RELATING THE DIFFERENCES OBTAINED BY THE METHOD TO THE CALIBRATION SYSTEM- The readings obtained on a calibration series using pure iron are given in Table 111, and differences are shown derived with respect to (a) the water reading of the cell and (b) the reading of the zero calibrating solution.332 BACON : THE PHOTOMETRIC DETERMINATION Wol. 75 TABLE: I11 CALIBRATION SERIES USING PURE IRON Cell reading for water only = 1-00 (a) Differences with ( b ) Differences with respect respect to readings of to readings of zero Drum reading cell containing water phosphorus solution Phosphorus, , - - * - , t--*-> 7 7 0.80 0.805 0.20 0.195 0 0 % 0 0.02 0-475 0.475 0.525 0.525 0.325 0.330 0.04 0.16 0-155 0.84 0-845 0.84 0-65 0.06 0*05* 0.045* 1.15 1.155 0.95 0-96 * Reading obtained using W/W = 1.20 Construction of a calibration graph from the first series (a) of differences results in a calibration curve which intersects the ordinate at an absorption value equivalent to 0.20 difference in drum reading.This absorption is produced by (a) the background absorption, (b) the phosphorus in the pure iron, (c) the phosphorus in the reagents, and any change in these factors results in a different calibration curve. In the case of a steel sample, when differences are derived with respect to the water reading of the cell, the absorption is due to (a) the background absorption, (b) the phosphorus in the reagents, (c) the inherent colour of the solution, (d) the phosphorus content of the steel.It can be seen that the phosphorus content derived from the calibration graph would be in error if the background absorption or the phosphorus in the reagents was different from that used in calibration. It would also be in error to the extent of the phosphorus content of the pure iron and the absorption due to the inherent colour of the solution (alloying elements). The system is similar in principle to that employing direct readings and no advantage is gained by deriving differences with respect to the water reading of the cell. Construction of a calibration graph from t'he second series (b) of differences results in a calibration curve which passes through the origin.The position of this curve is not affected by the background absorption, the phosphoru:; content of the pure iron or the phosphorus content of the reagents, provided they are constant for the calibration series. In the case of the steel samples, however, differences must be derived such that the value obtained for the absorption is due only to the phosphorus content of the steel. This can only be attained if the reference solution compensates for all abscrptions other than that due to the phosphorus content of the steel. Any reagent which is introduced into the reference solution but not into the sample solution must be free from phosphorus, or the equivalent phosphorus content must be determined and a correction applied. DETERMINATION OF THE SUBSIDIARY ABSORPTIONS Where this is not possible, corrections must be applied.PHOSPHORUS INTRODUCED WITH THE IRON- A calibration graph was prepared by substituting the corresponding quantity of ferrous sulphate for the pure iron used when constructing Table 111. Allowance was made for the acid radicle introduced, and the values obtained are given in Table IV. The slope of the calibration curve is the $;me in both instances, but the difference in absorption between the corresponding calibration points is 0.07 drum difference, equivalent to 0.004 per cent. of phosphorus. This corresponds to the difference in phosphorus content of the two sources of the iron. In order to determine the phosphorus content of the ferrous sulphate, 28 g. were dissolved in water, 5 mg.of ferric iron and 2 drops of ammonia were added and the solution was boiled and filtered. The precipitate was redissolved and a phosphorus determination conductedJune, 19501 OF PHOSPHORUS IN LOW ALLOY STEELS 333 as in the method for steel. A control was conducted simultaneously and the difference in absorption read on the calibration graph as the equivalent phosphorus percentage. This value was 0.0105 per cent. of phosphorus, and thus the equivalent phosphorus percentage introduced into the solution by 1.28 g. of ferrous sulphate is of the order of 04005 per cent. of phosphorus. As previously stated, when the calibration curve is constructed from the differences derived with respect to the zero phosphorus solution. the position of the curve is unaffected whether pure iron or ferrous sulphate is used.It is preferable, however, to use ferrous sulphate to produce the reference solution in order to minimise the correction which must be applied. It must be emphasised that, in the ferrous sulphate method, the base metal after reduction becomes a reagent and affects the background colour. It cannot be omitted from the reference solution because it accounts for approximately half the con- centration of reducing agent. TABLE IV CALIBRATION SERIES USING FERROUS SULPHATE Cell reading €or water only = 1.00 (a) Differences with (b) Differences with respect respect to readings of to readings of zero Drum reading cell containing water phosphorus solution Phosphorus, r-A-, r 0.87 0.87 0.13 0.13 0 0 % 0 0.02 0.65 0-556 0.45 0-445 0.32 0.316 0.04 0-225 0.230 0.776 0.77 0-645 0.64 0.06 0.12* Q.125* 1.08 1.075 0.95 0.946 * Reading obtained using W/W = 1.20.THE REFERENCE SOLUTION- Experiments were conducted to determine whether the phosphorus colour could be completely inhibited by strong acid, but with samples containing 0.04 per cent. of phosphorus absorptions attributable to the phosphorus were found even at acidities as high as 2 N sulphuric acid. A change in absorption occurs when the solution corresponding to the zero point of the calibration curve is strongly acidified. It can be calculated that some of this change is due to the suppression of the phosphorus colour, but the remainder is due to change in background colour. If, therefore, the sample is strongly acidified and used as a reference solution, no compensation is made for the phosphorus in the reagents, for the change in back- ground colour and for the uninhibited phosphorus colour at the higher phosphorus contents.By deriving differences with respect to a solution prepared under the same conditions as the sample but using 1.28 g. of ferrous sulphate to introduce the iron, compensation is made for the background colour and the phosphorus content of the reagents. Allowance should be made, however, for the small amount of phosphorus introduced into the reference solution by the addition of 1.28g. of ferrous sulphate; absorption due to this is not present in the sample solution. Correction must also be applied for any absorption due to colours inherent in the sample solution and not present in the reference solution.CORRECTION FOR ALLOYING ELEMENTS- For every 1 per cent. of chromium, 04045 per cent. of phosphorus should be deducted from the phosphorus value found by reference to the calibration graph. This correction was derived by adding chromium as a dichromate solution both in the presence and absence of phosphorus prior to reducing with sulphurous acid. Nickel gives an interference absorption equivalent to approximately 0.0002 per cent. of phosphorus for each 1 per cent. of nickel. ARSENIC INTERFERENCE- An interfering absorption was found when arsenic was added just prior to the final coloration. The colour forms slowly and many hours are required for the colour to develop fully. Interference by arsenic does not occur, however, after reduction by sulphurous acid.3 This is shown in Table V.334 BACON THE PHOTOMETRIC DETERMINATION TABLE V INFLUENCE OF ARSENIC [Vol.75 Calibration solution made with pure iron and 0.040 per cent. of phosphorus Arsenic added prior to solution in nitric acid Time, minutes A I \ Arsenic added, 5 10 15 20 30 0.175 0.160 0.160 0.160 0.160 0 0.2 0.165 0.155 0.155 0.160 0.160 0.4 0.165 0.160 0.160 0.160 0.160 0.6 0.175 0-155 0.155 0.155 0.155 % EFFECT OF TEMPERATURE- Table VI shows that variation in temperature has little effect on the final absorption produced after the solution ha.s stood for some time but that it affects the speed of formation of the colour. TABLE VI THE EFFECT OF TEMPERATURE Calibration solution made with pure iron and 0.40 per cent. of phosphorus Time, minutes Tempera- ture, 1 2 3 4 5 6 7 8 9 10 15 20 O c.18.0 0.60 0.40 0.29 0.23 0.20 0.17 0.16 0.145 0.145 0.145 0.145 0-145 21.5 0.35 0.27 0.21 0.18 0.16 --- 0.155 - 0.155 0.155 0.155 0.155 0.16 -- - 25.0 0.18 0.16 0.16 - A \ 0.16 - 0.16 0.16 0.16 VALUES OBTAINED FOR THE PHOSPHORUS CONTENT OF BRITISH CHEMICAL STANDARD STEELS Phosphorus determinations were conducted, using the absorptiometric method as described, on the following standard steels- B.C.S. 218 0-15 per cent. carbon steel . . 0-045 per cent. phosphorus B.C.S. 189 Ni - Cr - Mo steel B . . . . 0-024 per cent. phosphorus B.E.S. 159 Carbon steel F . . .. . . 0.049 per cent. phosphorus B.C.S. 225 Ni - Cr - Mo steel .. . . 0.021 per cent. phosphorus The values given above are the averages of the results submitted by several independent analysts after careful investigation.A study of the literature issued by the Bureau of Analysed Samples Ltd. shows that, with B.C.S. 218, all chemists used the gravimetric method issued by the British Standards In~titution.~ The values obtained by the different analysts were within the range 0-044 to 0.047 per cent. of phosphorus, the average being 0.045 per cent. With B.C.S. 189, various methods were used, the figures submitted ranging between 0.021 and 0.026 per cent. of phosphorus, and with B.C.S. 159, all chemists titrated the phospho- molybdate with standard alkali and acid, the values obtained ranging between 0.046 and 0.051 per cent. of phosphorus. With B.C.S. 225, most chemists used the British Standards Institution m e t h ~ d , ~ but four of the analysts finished volumetrically, the values submitted ranging between 0.020 and 0.023 per cent. of ]phosphorus.RESULTS OBTAINED BY THE ABSORPTIOMETRIC: METHOD- The values obtained by the method described in this paper are given in Table VII, and are 0.002 to 0405 per cent. lower than the standard values. An explanation of this discrepancy has not yet been found. During these analyses a control with a synthetic solution containing 0.040 per cent. of phosphorus was repeatedly conducted, and the value found was a€ways in the range 0.039 to 0.041 per cent. of phosphorus. The di-ammonium hydrogen phosphate solution used for the Cali bration was checked against another solution prepared by using the theoretical amount of sodium ammonium hydrogen phosphate, and the values obtained were identical.June, 19501 OF PHOSPHORUS IN LOW ALLOY STEELS 335 The discrepancy in values can be overcome by preparing the calibration graph using steel samples of which the phosphorus contents have been determined by the B.S.I. method. TABLE VII PERCENTAGE OF PHOSPHORUS FOUND IN B.C.S. SAMPLES BY THE ABSORPTIOMETRIC B.C.S. 218 0,0425 0.0420 0.0420 0.0410 0.0420 0.0410 0-0420 0.0420 0-0425 0.0430 Average 0-0420 METHOD B.C.S. 189 B.C.S. 159 B.C.S. 225 0.01 90 0.0465 0*0200 0*0200 0.0450 0.0185 0.0 195 0.0460 0.0190 0.0190 0.0460 0.0180 0.0185 0.0192 0,0460 0*0190 SUMMARY AND CONCLUSIONS- The stannous chloride method is unsatisfactory for the photometric determination of phosphorus in steel, and a suitable procedure has been developed using ferrous sulphate as reducing agent. The method is suitable for routine batch analysis and, if carefully controlled, the reproducibility is within f0.001 per cent. of phosphorus. The values obtained are slightly lower than those obtained by a reference gravimetric method unless steels analysed by this method are used to construct the calibration graph. Acknowledgment is made to the Chief Scientist, Ministry of Supply, for permission to publish this paper. Reproduced with the permission of the Controller, His Majesty’s Stationery Office. REFERENCES 1. 2. 3. 4. Vaughan, E. I., “Further Advances in the Use of the Spekker Photo-Electric Absorptiometer in Metallurgical Analysis,” Institute of Chemistry Lecture, 1942. Davis, H. C., and Bacon, A., J . SOC. Chem. Ind., 1948, 67, 316-31. Snell, F., and Snell, C., “Colorimetric Methods of Analysis,” Vol. I, D. van Nostrand Co. Inc,, New York, p. 503. British Standard 1121, part 1, 1943. METALLURGY DEPARTMENT ROYAL AIRCRAFT ESTABLISHMENT FARNBOROUGH, HANTS. September, 1949

ISSN:0003-2654    

DOI:10.1039/AN9507500321

出版商:RSC    

年代:1950

数据来源: RSC

摘要:

June, 19501 OF PHOSPHORUS IN LOW ALLOY STEELS 335 THE DETERMINATION OF OXYGEN I N CHROMIUM METAL* HITHERTO the only reliable method for the determination of total oxygen in electrolytic chromium has been considered to be the vacuum fusion method, in which the sample is heated in vacuo with a solution of carbon in molten iron and the evolved gases are subsequently analysed. It has been shown that the simpler method suggested by Adcockl can also give useful results. The sample is annealed in a good vacuum for 2 hours at 800" C . and, after cooling, dissolved in dilute (10 per cent. v/v 1-18 sp.gr.) hydrochloric acid. The oxygen in the insoluble chromic oxide represents the total oxygen in the sample. It should be noted that a sample dissolved as deposited, Le., without annealing, may give very little insoluble oxide in spite of a considerable oxygen content.Low results are also obtained if acid stronger than 10 per cent. v/v is used, presumably owing to the solubility of the chromic oxide. * Communication from the National Physical Laboratory.336 NOTES Results on a few samples by the two methods are given below- Pol. 7 5 1. 2. 3. 4. 5. 1. Oxygen calculated from insoluble Cr,O, Oxygen by A 1 Sample vacuum fusion 10% v/v HCl 5% v/v HC1 % % % Electrolytic, small nodules . . .. 0.48 0.59 0.61 2nd sample do. .. .. .. 0.57 0.58 0.59 3rd sample do. .. .. .. 0-55 0.60 0-58 Electrolytic powder (- 100 mesh) . . 0.28 0-28 0.31 2nd sample do. .. .. .. 0.22 0-23 0.22 REFERENCE Adcock, F., J . Iron and Steel Inst., 1927, 115, 369. H. G.SHORT December, 1949 THE ESTIMATION OF HORSE-FAT IN ADMIXTURE WITH OTHER FATS THE method of Paschkel for the detection of horse-fat in admixture with lard, beef-fat and mutton- fat has been investigated and has been extended to include a number of other fats and oils. The method depends upon the presence in horse-fat of 1 to 2 per cent. of linolenic acid, and its relative scarcity in other animal fats. The linolenic acid is determined as its hexabromide using the method given below which is essentially that described by Paschke. PROCEDURE Heat 10 g. of the fat on a water-bath with 100 ml. of 0.5 N alcoholic potash for half an hour under a reflux condenser. Connect to a distillation apparatus and distil until 80 ml. of distillate (containing most of the alcohol) have been collected. Dilute the hot residue with distilled water and wash into a 1000-ml.separating funnel, using a total amount of 250 ml. of water. Add 15 ml. of 5 N sulphuric acid, 250 ml, of saturated sodium chloride solution and 50ml. of ether. Allow to stand for 10 minutes and then discard the aqueous layer. Wash the ethereal extract (containing the fatty acids), with three 15-ml. washings of saturated sodium chloride solution, and filter it through a filter-paper . Place 5 ml. of the ethereal filtrate into a test tube by means of a pipette, and cool to - 15' C. in an ice - salt mixture. Cool a second test tube containing 5 ml. of pure ether and 0.45 ml. of bromine to the same temperature. Add the cooled ethereal solution of bromine in portions of about 1 ml.to the ethereal fatty acid solution; the temperature must not be allowed to rise above O O C . Keep in the ice - salt mixture for 10 minutes and then keep at 5" to 10" C. for a further 15 to 18 hours. Allow the solution to stand at room temperature for half an hour, in order that any separated free fatty acids may be redissolved, then filter through a porcelain Gooch crucible having a porous base. Transfer any residue remaining in the test tube to the Gooch and wash the sides of the Gooch with total of 10 ml. of ether cooled to - 10" C . The contents of the crucible should remain just covered with liquid until the washing is complete. In order to remove all the fatty acids from the insides of the Gooch it was found necessary to remove the crucible from the adaptor and to pour small portions of the 1Oml.of ether down the sides. Carefully wipe the outside of the crucible, dry (at 100" C. for 1 hour, cool to room temperature, and then wash with a further 5 ml. of ether (at room temperature) to remove any remaining free fatty acids. The hexabromide is less soluble in ether when dry than when freshly precipitated. Dry for a further hour at 100" C., cool and weigh. Shake vigorously for 1 minute. APPLICATION TO PURE FATS All the samples of horse-fat were obtained direct from a horse-slaughterer (each from a different horse), and these and a number of the other fats were rendered down in the laboratory. Table I gives the results expressed as milligrams of bromide yielded by 1 gram of fat. The numbers in brackets represent the number of samples examined in each case.The most interesting feature of these results is the high figure of 191 mg. per g. obtained for horse-fat, compared with the figure of 41-2 mg. per g . reported by Paschke. No explanation has been found for this. The only difference between the original method and the method described The method described above was used to examine a number of pure fats.June, 19501 NOTES TABLE I 337 Insoluble bromide found, mg./g. Sample Horse-fat . . .. .. Beef-fat . . .. .. Mutton-fat . . .. .. Pig-fat . . .. . . Butter-fat . . .. .. Neatsfoot oil . . . . Cod-liver oil * . ,. Arachis oil . . .. .. Almond oil.. .. .. Peach-kernel oil . . .. Sesame oil . . .. .. Olive oil . . .. . . Linseed oil . . .. .. r Average .. . . 191 (10) ... . 1.5 (3) .. . . 5.6 (3) .. . . 3.2 (5) .. . . 3.1 (3) .. . . nil (1) .. . . 450 (2) .. . . 3.0 (1) .. . . nil (1) .. . . nil (1) .. . , 0-5 (1) .. . . 538 (2) .. . . nil (1) Limits ' 177 to 213 1-0 to 1.8 5.0 to 6-2 1.0 to 4-8 2-6 to 3-5 420 to 480 500 to 575 above is that in the latter slightly more ether is used to wash the hexabromide. If anything, this would have been expected to produce slightly lower results than those obtained by Paschke. No proof was given in Paschke's paper that the bromide compound was actually the hexa- bromide of linolenic acid. Arachidonic acid, which has been reported in small quantities in some animal fats,2 gives an octabromide under the same conditions, as do also the highly unsaturated acids of marine animal oils. The two bromides may, however, be distinguished by their melting- points; the hexabromide of linolenic acid melts at 181" C., whereas the octabromide of arachidonic acid does not melt but blackens above a temperature of about 220OC.With the 10 samples of horse-fat examined, all the bromides melted within the range 180' to 183' C., whereas the bromides obtained from the two samples of cod-liver oil did not melt but blackened at 220" to 230" C. APPLICATION TO MIXTURES A number of mixtures of horse-fat with animal and vegetable fats were examined with the The composition of the mixtures was unknown to the analyst at results shown in Table 11. the time of the examination. Mixture I Horse-f at, 12.4 10.0 5.0 10.0 7.5 30.0 10.0 25.0 64-8 % Other fats present pig, mutton beef, mutton beef beef, mutton, pig beef, arachis beef, arachis neatsfoot, almond peach-kernel neatsfoot, almond TABLE I1 Weight of hexabromide, 24.0 21.0 7.0 20.6 14.0 57.0 16.2 39-0 126-0 mg./g* Correction allowed for other fats present, mg.4.0 3.0 1-5 4.0 2.0 2.0 nil nil nil Horse-fat found, 10.5 9.4 2-9 8.7 6.3 28.8 8.5 20-4 66-0 % The results show that the presence of 10 per cent. or more of horse-fat in a mixture can be detected with certainty and the amount estimated with a fair degree of accuracy. Indeed, if the examination of a greater number of samples of beef, mutton and pig fats confirms the limits obtained above for these samples, it would appear possible to detect the presence of as little as 6-0 per cent. of horse-fat in admixture with them. The results given in Table I indicate that of the fats examined only linseed and cod-liver oils would interfere with the estimation of horse-fat.Neither of these is considered to be a likely adulterant, but the latter can be ruled out if the melting-point of the bromide is determined. TWO unknown mixtures (not shown in Table 11) were in fact examined and the hexabromides were found not to melt a t 181" C. but to char at about 220" C., and it was reported that no opinion could be given as to the presence or absence of horse-fat in these based on the test as above reported. It was subsequently learnt that cod-liver oil was present in each of these mixtures. SUMMARY An investigation has been made into the method of Paschke for the determination of horse-fat The method depends upon the presence in horse-fat of 1 to 2 per in admixture with other fats.338 NOTES W O I .76 cent. of linolenic acid and its relative scarcity in most other fats. The linole&c acid is determined as its hexabromide, the results being expressed as mg. of hexabromide yielded by 1 g. of fat. Pure horse-fat has been found to give an average of 191 mg. of hexabromide per g., with limits of 177 to 213 mg. per g. ; this is a much higher figure than that reported by Paschke (41.2 mg.). The method has been used to determine the amount of horse-fat in admixture with other animal fats and with vegetable oils, and has given satisfactory results with mixtures containing as little as 5 to 10 per cent. of horse-fat. Although only one sample of neatsfoot oil has been examined the method would appear to be of use in distinguishing this oil from horse-fat.I wish to express my thanks to Mr. E. T. IlZing, B.Sc., F.R.I.C., for preparing the unknown mixtures, and for his advice throughout this work. REFERENCES 1. 2. Paschke, B., 2. Unlers. Lebensm., 1938, 76, 476-478; Analyst, 1939, 64, 47. Hilditch, T. P., “The Chemical Constitution of Natural Fats,” 2nd Edition, Chapman & Hall, Ltd., London, 1947, p. 432. COUNTY ANALYST’S LABORATORY COUNTY HALL R. A. DALLEY TAUNTON January, 1960 A NEW QUALITATIVE REACTION FOR YOHIMBINE THE important group of alkaloids containing the indole nucleus ranges in complexity from simple substances like hypaphorin, the methylbetaine of tryptophan, to the complicated structures of yohimbine and strychnine. Some of these alkaloids have as parent substance the amino acid, tryptophan; in others a carbazole nucleus is present.Consequently these alkaloids have some analytical reactions in common. The best method to use for their detection varies according to the substance present and is influenced by coiistitutional differences. We find, for example, that with sugars, carbazole does not react, but methyl indolel produces deeply coloured compounds almost instantly. A broader application, as is well known, makes use of dimethylaminobenz- aldehyde, which gives coloured compounds with a series of indole derivatives in presence of mineral acids; these, according to Vois&net,* can be transformed to blue compounds in the presence of weak oxidants like hydrogen peroxide or nitrous acid.We found that yohimbine also gives this very sensitive reaction. When aldehydes under certain conditions react with indole derivatives, a red intermediate is formed which changes to a blue pigment in presence of a weak oxidant. The constitution of the coloured compound is not known, but it can be assumed that its formation is the result of multiple condensation reactions between the aldehyde and the indole compound which lead to more complicated ring structures.8 Amongst the alkaloids that undergo the same type of reaction as tryptophan are ergotamine, ergonovine4 and yohimbine, which latter is in its constitution related to haman and carbazole, but contains one more nitrogen atom in its nucleus. Physostigmine does not react, as position five of the indole nucleus is occupied by a urethane group. PROCEDURE Dissolve a small amount of the alkaloid in about 1 ml. of concentrated hydrochloric acid. Add 4 drops of a 2 per cent. solution of 9-dimethylaminobenzaldehyde in concentrated hydro- chloric acid and warm. Add 2 drops of a 0.05 per cent. solution of sodium nitrite to the colourless test liquid. In the presence of yohimbine, a deep violet-blue ring appears after a short time. On shaking gently the whole_ solution becomes deep blue. One milligram of yohimbine is sufficient to give a distinct reaction. Tablets containing yohimbine can be treated in the same way, with the same result. REFERENCES 1. 2. 3. 4. Malowan, L. S., Biodaimica et Biophysics Acta, 1948, 2, 96. Voistnet, E., Compi!. Rend., 1918, 166, 789. Gilman, H., “Organic Chemistry,” Vol. 11, Wiley & Sons, 1938, p. 941. Malowan, L. S., Ciencia, Mex., 1949, 9, 124. LAWRENCE S. MALOWAN First submitted, A %gust, 1948 Amended, April, 1950 DEPARTMENT OF BIOCHEMISTRY UNIVERSITY OF PANAMA

ISSN:0003-2654    

DOI:10.1039/AN9507500335

出版商:RSC    

年代:1950

数据来源: RSC

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June, 19501 MINISTRY OF FOOD 339 Ministry of Food STATUTORY INSTRUMENTS* 1950.-No. 554. The Milk (Great Britain) (General Licence-No. 2) Order, 1950. Price Id. This Order, which came into operation on the 9th of April, 1950, i s a general authority, during the period April 9th to July lst, 1950, inclusive, for the supply of milk to any manufacturer for use by him in the preparation or manufadure of food. - No. 555. The Use of Milk (Suspension of Restriction) Order, 1950. Price Id. For the fieriod April 9th to July lst, 1950, inclusive, this Order suspends the operation of the Use of Milk (Restriction) Order, 1945 (S.R. G. O., 1945, No, 304), and permits the use of milk, milk powder or condensed milk in the preparation or manufacture of biscuits, bread, buns, pastries, cakes, rolls, scones and other similar articles, ice-cream, soft cheese and curd cheese, sweetmeats (including sugar confectionery and chocolate) and synthetic cream.- No. 589. The Food Standards (Fish Cakes) Order, 1950. Price Id. This Order, which came into operation on the 15th of April, 1950, and which should be read with the Food Standards (General Provisions) Order, 1944, as amended by S.R. 6. O., 1944, Nos. 42 and 654, maintains the standard for fish cakes hitherto prescribed in the Fish Cakes (Maximum Prices) Order, 1943, viz., that not less than 36 per cent. by weight of the fish cake shall consist Proceedings fov infringement may be brought in England and Northern Ireland by a Food and Drugs of Jish. Authority tedhout the consent of the Minister. - No.596. The Soft Drinks (Amendment) Order, 1950. Price 2d. 1. The Soft Drinks Order, 1947, as amended by S.R. & O., 1947, No. 2766, S.I., 1948, No. 1291, and 1949, No. 1378, shall be further amended by substituting for the Schedule thereto the Schedule to this Order. 2. The Soft Drinks (Amendment) Order, 1949, as amended by S.I., 1949, No. 1378, is hereby revoked, but without prejudice to any proceedings in respect of any contravention of the Soft Drinks Order, 1947, as thereby amended. This Order, which came into operation on the 19th of April, 1950, prescribes specifications for the ingredients of all soft drinks containing citrus fruit jwice and barley. These specifccations are the same as those that previously applied to “lemon barley” only. THE SCHEDULE (To be substituted for the Schedule to the Soft Drinks Order, 1947) PROVISIONS AS TO INGREDIENTS NOTE-These provisions do not apply to unsweetened soft drinks, other than soda water, or to fruit juice (as defined in Article 1).PART I Soft drinks suitable for consumption without dilution Minimum quantity of fruit juice (expressed in terms of unconcentrated juice of natural Minimum quantity Maximum quantity strength) of added sugar of saccharin Description of soft drink per 10 gallons per 10 gallons per 10 gallons Non-alcoholic cider and non-alcoholic perry 120 fluid 02. 18 02. 82 grains Any citrus fruit juice and barley drink . . 48 fluid oz. 18 oz. 82 grains Lime juice and soda . . . . .. . . 48 fluid 02. 18 02. 82 grains Any other soft drink containing fruit juice . . 82 grains Non-alcoholic wine . . .. .. .. - 74 Ib. No maximum Indian or quinine tonic-water . , * . 18 02. 82 grains 80 fluid 02. 18 oz. Not less than + grain of quinine (calculated as quinine sulphate B.P.) per pint * Obtainable from H.M. Stationery Office. Italics indicate changed wording.340 BRITISH STANDARDS INSTITUTION [Vol. 75 Soda-water . . .. .. .. . . Not less than 5 grains of sodium bicarbonate per pint Any other soft drink (except those mentioned in Part I1 of this Schedule) . . .. -- 18 02. 82 grains PART 11 Soft drinks intended for mnsunz+tion after dilution Any citrus fruit juice and barley drink . . 14 gallons 7& lb. $ oz. centrate containing citrus fruit juice . . 24 gallons 74 lb. 3 oz. containing any other fruit juice . . . . 1 gallon 74 lb. 3 02. in Part I of this Schedule) .. .. - 7* lb. $ 02. Any other squash, crush, cordial or con- Any squash, crush, cordial or concentrate Any other soft drink (except those mentioned

ISSN:0003-2654    

DOI:10.1039/AN9507500339

出版商:RSC    

年代:1950

数据来源: RSC

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340 BRITISH STANDARDS INSTITUTION [Vol. 75 Crystallographic Data ARMOUR RESEARCH FOUNDATION OF ILLINOIS INSTITUTE OF TECHNOLOGY THE Illinois Institute of Technology, 3300, South Federal Street, Chicago, 16, Illinois, U.S.A., announce that the National Registry of Ran: Crystallographic Data has been established by the Armour Research Foundation of the Institute. The Registry is a public service, available to scientists throughout the world. Dr. Walter C. McCrone, supervisor of the analytical section of the Foundation’s Chemistry and Chemical Engineering Department, is in charge. Acknow- ledgment of persons and laboratories who contribute this information will be included in the files. Due recognition in proportion to the exrent of the contribution will be made, varying from senior authorship to acknowledgment within published papers. The current series of monthly reports on new information in the Registry, appearing in Analytical Chemistry, is an example of the intended use of such data. Persons and organisations may obtain information from the Registry on request by describing an unknown compound crystallographically. If it is listed in the file, the informa- tion will be sent to the enquirer, identifying the compound for him. The system of conventions and nomenclalhire set up after the 1947 New York meeting of the American Chemical Society is used by the Registry. This system was described in Analytical Chemistry, 1948, 20, 274 and abstracted in The A.tzalyst, 1948, 73, 579. Scientists are invited to submit data on new compounds which they identify. t Obtainable from the British Standards Institution, Publications Department, 28. Victoria Street, London, S.W.l.

ISSN:0003-2654    

DOI:10.1039/AN950750340b

出版商:RSC    

年代:1950

数据来源: RSC