INDUSTRIAL
and
ENGINEERING
CHEMISTRY ANALYTICAL EDITIORi
+
Harrison E. Howe, Editor
,
Determination of Manganese, Nickel, and Phosphorus in Iron and Steel The Use of Rapid Spectrophotometric Methods W. hl. RIURRAY, JR., AND S. E. Q. ASHLEY, General Electric Company, Pittsfield, Mass.
The authors present methods for the rapid photometric determination of manganese, nickel, and phosphorus in iron and steel. From four to six determinations of any of the elements mentioned may be run with checks in an hour and the speed of single determinations is almost as great as €or a group. No standard solutions are required, and any instrument may be quickly calibrated with two or three determinations within the limits mentioned. The reproducibility of the determinations is high, and judging from the results obtained on Bureau of Standards samples the accuracy is as good or better than is obtained with most routine determinations.
T
H E development in recent years of various types of instruments for the quantitative measurement of the degree of absorption of visible light in solutions has vastly enlarged the domain of chemical colorimetry by substituting accurate absolute measurements for crude comparisons of the color of solutions. Excellent review articles by Mellon (6) and Strafford (Is),describing these instruments and pointing out their advantages, have appeared during the last year. One of the great advantages of a spectrophotometer is that it is a selective instrument and permits the determination by the absorption of a chemical constituent even in the presence of another colored compound which would mask or pervert the color of the solution so much as to make an ordinary color comparison impossible. One very important application of this advantage immediately comes to mind in the rapid analysis of ferrous alloys, and it is this field which the present authors have investigated for spectrophotometric exploitation. Most absorption bands are rather broad, so that for practical purposes it is sufficient to employ an instrument which
isolates the various regions of the spectrum by means of filters transmitting a narrow band of light. Such an instrument is the Zeiss Pulfrich step-photometer which was used in the present investigation. The construction of this instrument is too well known t o warrant description, but may be found in any of the Zeiss Company’s literature (15). ; isurvey of the literature showed that the problem which was undertaken had already been treated in part by other investigators, mostly in Germany, and much of it is too recent to have been tested by other workers. The task a t hand became that of testing some of the methods which have already been developed and improving some of the older methods which have not proved sufficiently reliable by the older colorimetric technic. The methods selected were those for manganese, nickel, and phosphorus, based on requirements of local foundry work as well as their chemical adaptability for the purpose in mind.
Technic All photometric measurements were made with the Zeiss Pulfrich step-photometer. The general technic employed in making the measurements was that described in the directions which accompany the instrument. The extinction, k , was read directly from a calibrated drum on the photometer. The extinction coefficient, K , was then obtained by dividing k by s, the length of the cell used. K = -k B
It is thus possible to cover a wide range of concentrations by using cells from 0.5 t o 5 cm. in length, and have all measurements reduced to the common basis of a I-cm. cell length. Calibration graphs were plotted with per cent of constituent and extinction coefficient, K , as coordinates. The graphs in each case were straight lines, so that a simple equation for the per cent of the constituent X may be derived from the slope of the line. K
% X = -C
The constant c is specific for a given procedure, and once determined will aln-ays hold for that particular method. It has thus been found expedient to use these equations for routine rrork since they are much simpler and less liable t o
INDUSTRIAL AND ENGINEERING CHEMISTRY
2
error in interpretation than calibration graphs. I n some instances graphs will be given as illustration of typical results in the work which is to follow.
Manganese There are many procedures for the colorimetric determination of manganese in iron and steel. hlehlig (6) has studied a spectrophotometric method using a procedure depending upon preliminary precipitation of manganese dioxide and subsequent oxidation of the separated manganese with sodium bismuthate. Muller (9) has pointed out that such separations are probably not necessary and that equations employing the extinction coefficient are very reliable. I n a review of photoelectric colorimetry, hluller (IO) gives a calibration graph for pure permanganate solutions which were oxidized by a periodate procedure, but neither details of the procedure nor applications were given. TABLE I. SPECTROPHOTOMETRIC DETERMINATIOX OF M.kSG.4NESE Sample
(Synthetic and Bureau of Standards samples) Manganese k Cell Length K Found
Manganese Present
%
Cm. 0.10 3.0 0.30 0.31 3 0 0.94 1.0 1 09 1.09 0 5 1.50 0.75 0.5 2.52 1.26 1 0 0.52 0.52 0.5 0.50 0.25 3.0 0 04 0.13 2 30 0.5 1.15 1.54 0.5 0.77 51, 5 5 , 100, 5f are Bureau of Standards samples.
0 0 0 0 1
0 0 0
1
05 15 54 75 26 26 25 02 15
0 77
% 0 0 0 0 1 0 0 0 1 0
04 14 53 75 27 2i 2i 019 13 76
I n the viork described here, the periodate procedure of Willard and Greathouse (14)was used for oxidizing the manganese. This procedure has been noted as a superior means for oxidizing manganese to permanganic acid, but it does not lend itself easily to use in titration methods, as it is not easy to destroy the excess of periodate without destroying the
VOL. 10, NO. 1
permanganate a t the same time. The advantage of the method lies in the rapidity, accuracy, and stability of permanganate, and as no separations are involved, the procedure is very simple. The stability of the permanganate absorption band has been studied many times (7') and it has been found that it does not shift appreciably with changes in concentration or cation. PROCEDURE. Weigh 0.500 gram of the iron or steel sample, and transfer to a 150-ml. beaker. Dissolve in a mixture of 15 ml. of concentrated nitric acid and 25 ml. of viater, heating on a hot plate to hasten solution. When the sample is dissolved, add 20 ml. of water, filter, and wash with small portions of xater. To the clear filtrate add 10 ml. of concentrated sulfuric acid and a small lump of ammonium persulfate. Boil for 10 minutes. Cool slightly, and add 10 ml. of 85 per cent phosphoric acid and approximately 0.5 gram of potassium periodate. Boil for 1 minut'e, and keep hot (90" C.) for 10 minutes. All heating and boiling should be done in an open beaker t o keep the volume down. Cool to room temperature by placing in a pan of cold water, then dilute to exactly 100 ml. in a volumetric flask. The extinction coefficient of t'he clear permanganate solution is t,hen determined, using distilled water as a comparison liquid. The measurement is made with a green filter with mean transmission at 5300 a., since this is in the region of maximum absorption for the permanganate ion (3,4). RESULTS. Calibration graphs prepared from pure manganous sulfate (from c. P. potassium permanganate) and ferric nitrate (from Bureau of Standards ingot iron) solutions gave straight lines passing through the origin. This means that the effect of iron is negligible in the presence of the large excess of phosphoric acid present. The range covered is from 0.01 up to about 1.5 per cent of manganese. The accuracy is of the order of 0.01 per cent of manganese. The calibrat'ion equation derived for this procedure was K yo manganese = (3) 2
The data in Table I are typical and serve to illustrate t'he results obtained by dividing K by the constant 2 as found from the calibration graph and given in the calibration equation (3). This calibration equation applies only to this specific procedure and photometer, but similar equations can be derived for other photometers with only one or two measurements on standard solutions, as the procedure has been found reliable and reproducible.
Kickel
FIGURE1
Rollet (11) studied t'he colorimetric determination of nickel in cobalt salts, nickel steels, and organic matter. The method depends on t,he formation of a soluble nickelic dimethylglyoxinie. It was found that iron hydroxide tends t o drag down sniall amounts of nickel hydroxide in ammonia precipitat,ion, and this was avoided by adding dimethylglyoxime to form the nickel complex before the ammonia is added. Recently Dietrich and Pchmitt (1) have used a modification of this procedure in the development of a rapid photometric method for nickel in iron and steel. It is inferred that iron was separated by ammonia precipitation, although the treatment is not mentioned specifically. The iron must be either removed or held in solution as a complex, since the nickelic complex is formed in alkaline solution. I n the procedure developed in this study, the iron is held in alkaline solution by adding a large excess of citric acid. This alkaline iron citrate solution has a light yellow color. The nickel dimethylglyoxime solution is a deep wine-red color. Absorption curves for these solutions are given in Figure 1. It is obvious that the iron has practically no tbsorption in the visible region of the spectrum above 5000 A. On the other hand t$e nickel shows a plateau in its absorption band near 5300 A. Therefore, if the photometric measuremen$s are made using a filter with mean t'ransmission a t 5300 A., the
JANUARY 15, 1938
ANALYTICAL EDITION
absorption of the iron will be eliminated entirely and a preliminary separation becomes unnecessary. Dietrich and Schmitt (1) found the absorption curve of the nickelic dimethylglyoxime solution to be stable for eight hours. As is evident from Figure 1, such was not found to be the case in this n-ork. The freshly prepared solutions ( p r v e 1) show a n absorption plateau in the region of 5300 A. The first curve taken immediately after mixing the reagents corresponds to the curve given by Dietrich and Schmitt. Curves 2, 3, and 4 show that this plateau rapidly disappears, and after the solution has stood for an hour the absorption curve shows only a single wide and smooth band. These curves were all prepared from pure nickel solutions, but it was found that the same curves were obtained when citric acid was present. Although the Pulfrich photometer used gives only eight points on the curves, their general shape has been confirmed on a General Electric spectrophotometer which automatically records a smoothJine from a monochromator whose slit emits a band only 100 A. in width. The reason for the appearance of this plateau and its rapid change has not been ascertained, but i t has been found to be reproducible and measurements completed within 10 minutes after mixing the reagents give consistent and reliable results. I
I
3
The limit of usefulness of the method for high nickel concentrations is determined by the solubility of the complex. If samples containing over 20 per cent nickel are analyzed by this method, a precipitate forms rather quickly and the results are of no value. It is possible, however, to start with a smaller sample and calculate the results back to the basis of a 0.400-gram sample as used. TABLE11. SPECTROPHOTOMETRIC DETERMINATION Sam(Bureau of Standards samples) ple B. of S. Cell Sickel No. So. Length Iz K Found Cm. % la 107 0.275 0.091 0.83 3.0 b 107 0.275 3.0 0.091 0.83 2a 33a 1.0 0.36 0.36 3.27 b 33s 1.0 0.37 0.37 3.36 3a 32b 0.41 0.14 1.27 3.0 b 32b 0.40 0.13 1.18 3.0 4 101 0 . 9 4 3 0 . 9 4 6 8.60 1.9 5 115 0.87 1 ,i 4 16.83 0.9
OF
NICKEL Nickel Present
% 0.807 0.807 3.24 3.24 1.20 1.20
8.44 16.89
The data in Table I1 show the results obtained on the analysis of Bureau of Standards samples by this method. The agreement is satisfactory for routine foundry analyses, and the time saved by using the photometric method is considerable. The values for the per cent of nickel found were obtained from the calibration equation, which was derived from several values from the calibration graph and was found to be
Phosphorus
0
2
4
6
8
IO
12
14
16
I8
20
% NICKEL
FIGURE 2
PROCEDCRE. Weigh 0.400 gram of the iron or steel and transfer to a 1000-ml. volumetric flask. Add 25 ml. of 1 to 1 nitric acid and warm on a hot plate until the sample is dissolved. (In some cases of difficultly soluble chromium-nickel steels, a mixture of equal parts of nitric and hydrochloric acids may be necessary.) When solution is complete, cool and dilute to 1000 ml. Mix thoroughly and allow to stand for 5 or 10 minutes so that, any graphitic carbon and silica may settle to the bottom. Pipet exactly 25 ml. of t h e clear supernatant solution into a 100-m1. volumetric flask. Then add the following reagents to the small
sample in the order given and xith thorough mixing after each addition: 10 ml. of citric acid solution (10 per cent), 5 ml. of saturated bromine water, 5 ml. of 1 to 1 ammonium hydroxide, and 3 ml. of a 1 per cent solut'ion of dimethylglgoxime in alcohol. Dilute the cont'ents to exactly 100 ml. with distilled water and again mix thoroughly. The solution should be clear and a deep red color. The photometric measurements must be made within 10 minutes after the addition of the reagents. The measurement is made with a green filter with mean transmission at 5300
A.
RESULTS. Pure solutions of iron (from Bureau of Standards sample I l d ) and nickel (from Hilger H. S.brand nickel rod) nitrates were used in preparing the calibration graph which is given in Figure 2. The line is satisfactory, showing a maximum error of about 0.2 per cent nickel in the higher concentrations and about 0.05 per cent nickel in the lower concentrations. The range covered is from 0.5 to 19 per cent nickel.
The determination of phosphorus in iron and steel samples has always been a tedious and time-consuming task. The many methods in use are practically all based on some modification of a method involving preliminary precipitation of ammonium phosphomolybdate. The question always arises as to how complete this precipitation can be made, how definite is the composition of the salt, and how reliable are the subsequent methods of treatment of the salt after i t is obtained. Very good results can be obtained by these standard procedures in the hands of a skilled operator; however, most of them are open to many errors and a quicker and less tedious method is desirable. Of the older colorimetric methods for determining phosphorus in iron and steel, the one worked out by hiisson (8) appeared to be most worth studying. It has been used and found satisfactory by Schroder (12) and Getzov (d), but does not seem to have been given any widespread use. This method depends on the formation of a yellow phosphovanadomolybdate, whose formula is (SHJ3P04 yH4VO3 16hloO3 according to Llisson (8). It n-as found to be a stable complex, showing almost no color change after 14 days' standing. The accuracy claimed for the method was 0.005 per cent of phosphorus in the range 0.04 to 0.1 per cent of phosphorus. All of this work was done using the old method of visual comparison with standard solutions. This method has been studied in the present work with consideration of the effect of concentration of reagents, acid concentration, and temperature a t the time of making the photometric readings. Since the solutions are yellow in color, it is rather difficult to make accurate visual comparison with standard solutions, and slight differences in concentration are not readily detected by the eye alone. The method depends largely on using a n acid concentration which is optimum for color formation, and which is different from that used in the original procedures. The method using this new procedure and using the Pulfrich photometer gives very satisfactory results for the range 0.01 to 1.0 per cent of phosphorus.
IKDUSTRIAL AND ENGINEERIXG CHEMISTRY
4
VOL. 10, NO. 1
With these limitations in mind, the following procedure was devised as being best fitted for the phosphorus determination. PROCEDURE. Dissolve a 0.500-gram sample in 20 ml. of 1 to 2 nitric acid Kith heating. Filter off any silica or graphitic carbon residue, washing Kith small portions of water. Heat the clear solution almost t o boiling, add 5 ml. of 1 per cent potassium permanganate solution and keep the solution just below the boiling point for 10 minutes. Then cool the solution somewhat and add 2 drops of 30 per cent hydrogen peroxide (less than 0.001 per cent phosphorus content). Add exactly 10.0 ml. of ammonium vanadate solution from a pipet. (This solution is prepared by dissolving 2.345 grams of ammonium vanadate in 500 ml. of hot water, adding 20 ml. of 1 to 1 nitric acid, and diluting to 1000 ml.) Heat the sample again to destroy the excess hydrogen peroxide, then place it in a pan of cold water and cool to room temperature. At this point it should be clear and almost colorless. Transfer the solution to a 100-ml. volumetric flask, add 10 ml. of 10 per cent ammonium molybdate solution, and shake thoroughly t o dissolve the precipitate whicb forms momentarily. Dilute to exactly 100 ml. and allow to stand for 10 minutes before making the photometric measurements. The extinction coefficient is measured with a violet filter with mean transmission at 4300 A. A 3.0-em. cell is used for samples containing 0.01 to 0.1 per cent phosphorus, and a 0.50-cm. cell for samples containing 0.1 to 1.0 per cent phosphorus.
10
0 02
0
0 2
004 0 4
0.06 0 6
0.08 0 8
0.10 10
3.00CY
CELI
-a s o c ~CELL
% PHOSPHORUS
FIOURFI 3 Preliminary experiments showed that the acid concentration and the size of sample used in the Misson (8) procedure gave rather erratic results. It was found that the limit of the phosphorus concentration is about 5 mg. per 100 ml. of final volume and higher concentrations tend to give a precipitate. Misson used a 1.0-gram sample of iron, but i t was found that a 0.50-gram sample was sufficient and 5 mg. of phosphorus correspond to 1 per cent of a 0.50-gram sample, thus increasing the range of the method. I n the older procedure the sample was dissolved in 20 ml. of 1 to 1 nitric acid. The complex is rather sensitive to acid concentration above a certain minimum, so that it is advisable to work with as small amount of acid as is feasible. This was found to be 20 ml. of 1 to 2 nitric acid used to dissolve the sample with a final volume of 100 ml. The effect of acid is illustrated in Table 111. As is evident from the data in Table 111,a precipitate forms when the acid concentration is too low. I n the case where 40 ml. of acid were used, the color was very slow in forming and the extinction coefficient tended to drift towards higher values as the solution was allowed to stand. Several experiments of this type proved that a maximum color is developed in solutions which are low in acid content, so that it is desirable to work with the minimum of acid present. This is limited, however, by the requirement that a certain amount must be present to prevent the formation of a precipitate. When readings are taken with the solution a t a temperature of 10" C., the values for the extinction coefficient are low, while if the temperature is very high (50" C , ) ,the extinction coefficient tends to be high. It was found that anywhere in the range 20" to 30" C., the readings were almost identical and temperature is unimportant in this small range which covers the usual room temperature.
RESULTS.Pure solutions of iron nitrate from Bureau of Standards ingot iron and c. P. potassium phosphate were used in the preparation of the calibration graphs, which are given in Figure 3. It was found that the values of K , the extinction coefficient for a 1.0-cm. cell, were not the same when using cells of different lengths on the same solution. The values of K decrease as the cell length is increased from 0.5 to 3.0 cm., and &-henvalues of K are plotted against cell length, a straight line is obtained. However, this is an error of the instrument and not of the method or this particular solution, for similar results were obtained with potassium chromate, picric acid, and ferric chloride solutions. All these solutions show a maximum absorption in the 4300 A. range, so that i t is apparently an effect peculiar to this region which was not observed when working with the nickel and permanganate solutions using the 5300 A. filter. Because of this effect, two calibration curves and equations were prepared, one using a 3-cm. cell for low concentrations and the other using a 0.5-cm. cell for the higher concentrations. The equations derived from the two calibration graphs were: % phosphorus
=
1.g"d 28 for 0.5-em. cell
(5)
%phosphorus
=
- o*22for 3.0-cm. cell 1.50
(6)
The term subtracted from K in the numerator of each equation is the value of K at zero phosphorus concentration. These solutions contain ferric nitrate which shows a small absorption and they also contain a n excess of vanadic acid which also shows a small absorption in the region of measurement. However, this absorption is relatively constant and does not interfere with the measurements. TABLE111. EFFECTOF ACID CONCENTRATION ON EXTINCTION COEFFICIENT OF PHOSPHOVANADOMOLYBDATE SOLUTIONS (Samples oontaining iron with 0.35 per cent of phosphorus, using ta cell of 0.50-om. length in each case) 1 t o 2 HNOi k K
MZ. 15a 20 25 40 4
0 : h
0.45 0.41
0:66 0.94
0.82
Precipitate formed quickly.
The results obtained in the analysis of Bureau of Standards samples by this procedure are given in Table IV. The values for the per cent of phosphorus found were calculated from calibration equations 5 and 6.
ANALYTICAL EDITION
JANUARl 15, 1938 TABLE
Sample
KO.
Iv.
Cell Length
Cm.
DETERMISATION OF PHOSPHORUS
SPECTROPHOTOXETRIC
(Bureau of Standards samples) Phosphorus k K Found
so
Phosphorus Present
70
The results using the Bureau of Standards samples are satisfactory and show a relatively small error. The method has been used on routine work and found to be more reliable than the older phosphomolybdate methods when a n inexperienced operator is using them. The only serious interference with the method is brought about by large amounts of silicon, as in 4 per cent silicon steels. I n such cases, this method will not work, for the formation of yellow silicomolybdic acid vitiates any measurement on the color caused by
5
small amounts of phosphorus. Excepting such cases, the method appears to be very reliable and useful.
Literature Cited ( I ) Dietrich, K., and Schmitt, K., 2. anal. Chem., 109,25 (1937). (2) Getzov, B. B., Zaaodskaya Lab., 4, 349 (1935). (3) Kasline, C. T., and hlellon, M. G., IND. ENQ.CHEM.,Anal. Ed., 8,436 (1936). (4) Landolt-Bomstein, “Physikalische Chemisciie Tabellen,” 5 auflage, Vol. 11, p. 897, Berlin, Julius Springer, 1923. (5) Mehlig, J. P., IND. ESQ. CHEM.,Anal. Ed., 7, 27 (1935). (61 Mellon, M. G., I b i d . , 9, 51 (1937). (7’ Mellor, J. W., “Comprehensive Treatise on Inorganic and Theoretical Chemistry,” Vol. XII, pp. 309-10. New York. Longmans, Green & Co., 1932. (8) Misson, G., Chem.-Zlg., 32,633 (1908). (9) Muller, R. H., ISD.ENG.CHEM.,Anal. Ed., 7, 361 (1935). (IO) Ibid., 7 , 223 (1935). (11) Rollet. A. P., Compt. rend., 183,212 (1936). (12) Schroder. R., Stahl u. Eisen, 38, 316 (1918). (13) Strafford, K., Chem. SOC.Annual Rpts., 33,456 (1937). (14) Willard, H. H., and Greathouse, L. H., J. Am. Chem. Soc., 39, 2366 (1917). (15) Zeiss Mess, 430d/IIIe. See also: Kohlrausch, F., “Praktische Physik,” Leiprig, B. G. Teubner Verlag, 1935; Weigert, P., “Optische Methoden der Chemie,” Leipzig, Akademische Verlagsgosellschaft, 1927. RECEIVED October 28, 1937.
Determination of Pyrethrin I J
In Commercial Insecticides Containing Pyrethrum or Pyrethrum Extract D. A. HOLADAY, Food and Drug Administration, Washington, D. C.
P
YRETHRUM insecticides consist of pyrethrum powder
or mixtures containing it; mineral oil containing pyrethrum extract, a n essential oil or perfume, and frequently other substances such as derris extract or organic thiocyanates; or, in the case of plant sprays, essential oils, a n emulsifier such as soap, a sulfated alcohol or sulfonated oil, pyrethrum extract, derris extract, and a solvent, usually alcohol, acetone, or water. The method proposed by Seil (S) has been largely used for the determination of the pyrethrins in pyrethrum powder. A modification of this method has been used for the determination of pyrethrins in mineral oil-pyrethrum sprays. Graham (I), however, reported a loss of pyrethrin I in the preliminary steam distillation in this method when applied to mineral oil sprays, and Wilcoxon ( d ) , working with purified pyrethrum resins, found that the monocarboxylic acid from the pyrethrin I is not completely recovered after the steam distillation for separating it from the dicarboxylic acid, so that a low value for pyrethrin I is obtained. Wilcoxon determined pyrethrin I in pyrethrum flowers by utilizing the reaction between the monocarboxylic acid and DenigBs’ reagent, by which mercury is reduced, and the determination of the reduced mercury by the iodate method of Jamieson (2). I n the author’s hands this method has given good results on pyrethrum powders, but unsaturated compounds formed by saponification of perfumes, essential oils, or other substances m-hich may be present in many pyrethrum insecticides interfere with the iodate titration by absorption of iodine. By modifying Wilcoxon’s method so as to remove unsaturated organic compounds, a procedure has been developed for the determination of pyrethrin I in many commercial insecticides. This modification has been used on mineral oil sprays containing pyrethrum extract, essential oils, perfumes, derris extract, and organic thiocyanates, and in the analysis of
plant sprays containing essential oils, derris resins, soaps and other spreaders, tobacco extract, alcohol, or acetone. The method depends on the reduction of DenigPs’ reagent by the monocarboxylic acid, precipitation of the reduced mercury as calomel, removal of unsaturated organic compounds with a c e tone and chloroform, and determination of the reduced mercury by titration with iodate solution. The monocarboxylic acid is separated from the dicarboxylic acid by extraction with petroleum ether, in which the free dicarboxylic acid is only slightly soluble. Under the conditions of the determination, the dicarboxylic acid reacts very slowly with DenigBs’ reagent, so no appreciable error is introduced by the small amount present. Experimental I n the experimental work an alcoholic extract of pyrethrum flowers Yas analyzed by Geil’s method and by the proposed method. After analysis by the Seil method the titrated solution was acidified and the monocarboxylic acid was extracted with petroleum ether and determined by treatment with DenigM reagent. These results are given in Table I. Samples were also made up containing the same amount of extract to which were added 5 per cent of pine oil, 4 per cent of oleic acid, and 2 per cent of derris resins. These samples were TABLEI. PYRETHRW I IN ALCOHOLICP Y R E T HEXTRACTS R~ llercury Reduction Method Alcohclic pyrethrum extract Alcoholic extract pine oil, oleic acid, and derris resins
+
Seil Method
llercury Reduction on Titrsted Solution
75 ..
%
%
0.31 0.32
0.27
0.27
0.21 0.20
0.33 0 32
.. ..
..
..
