INDUSTRIAL ASD ENGINEERING CHEMISTRY
94
temperature. The latter practice will result in the violent evolution of carbon dioxide together with a possible loss of part of the cooling fluid. The same fluid may be used many times by simply adding dry ice whenever a low temperature is desired. If convenient, the solvents may be left in the small Thermos containers which may be closed by corks after the contents have returned to room temperature. When the solvent must be removed from the container, a violent evolution of carbon dioxide together with a possible loss of part of the fluid is likely t o occur if the cold mixture is poured into a bottle or beaker at room temperature.
Conclusions The compounds studied fall into three groups with respect to behavior with dry ice: (1) compounds which crystallize sharply from solutions with carbon dioxide, (2) compounds which thicken and either supercool or fail to crystallize a t all,
VOL. 12, NO. 2
and (3) compounds which neither crystallize nor thicken to any extent. Compounds of the second type are worthless in cooling baths with dry ice. Compounds of the first type will maintain a temperature slightly lower than the initial temperature of crystallization for a few hours if the dry ice is added carefully. Compounds in the third group are merely cooled by the ice and therefore tend to approach -79.5’ C., the melting temperature of solid carbon dioxide. The exact temperature recorded by any member of this group may therefore vary by as much as 4” or 5 O , depending on physical conditions. Table I1 contains final recommendations regarding compounds to be used in producing low temperatures with dry ice.
Literature Cited (1) Brown, J. B., and Stoner, G. G., J . Am. Chem. Soc., 5 9 , 4 (1937). (2) Carbide and Carbon ChemicalsCorp., “Synthetic Organic Chemicals”, table on pp. 6 and 7.
Determination of Small Amounts of Copper and
Manganese In Dyes and Other Organic Materials G. F. PALFREY, R. H. HOBERT, A. F. BENYIYG, AND I. W. DOBRATZ Jackson Laboratory, E. I. du Pont de Nemours & Company, Inc., Wilmington, Del.
T
HE demand for so-called copper- and manganese-free
dyes, intermediates, and rubber chemicals for use in rubber and on fabrics to be rubberized necessitated the development, many years ago, of accurate and sensitive analytical methods for determining traces of these elements. I n the authors’ first methods the organic matter was destroyed by dry-ashing, using a procedure similar to the present A. S. T. M. method D377-37. This ashing procedure was unsatisfactory for most dyes. Copper was subsequently determined colorimetrically by the use of potassium ferrocyanide as indicator and manganese by oxidation to permanganate, using potassium periodate as recommended by Willard and Greathouse (4). During the last 10 years methods have been revised several times as the result of investigations of published methods, private communications (S), and suggestions from several analysts who have used the authors’ methods. T h e following methods, which are believed to contain improvements not published previously, are now used officially in this department for the determination of copper and manganese in dyestuffs, rubber chemicals, and rubber. The organic matter is destroyed by wet oxidation with sulfuric and nitric acids followed, when necessary, by hydrogen peroxide. C o p per is then determined colorimetrically using sodium diethyldithiocarbamate as indicator as recommended by Callan and Henderson (1). Manganese is still determined by oxidation to permanganate. As both copper and manganese are generally required on the same sample, the methods have been combined as far as possible.
Destruction of Organic Matter REAGENTS AND APPARATUS.c . P. concentrated sulfuric acid (sp. gr. = 1.842), c . P. fuming nitric acid, and hydrogen peroxide,
approximately 30 per cent by volume, and essentially free from
copper and manganese.’ A 500-cc. Kjeldahl flask and Kjeldah digestion apparatus. PROCEDURE. Accurately weigh approximately 5 grams of the sample and transfer to a 500-cc. Kjeldahl flask. Add carefully 20 cc. of concentrated sulfuric acid and one or two glass beads, place the flask on a digestion rack, and slowly heat it until the mixture boils. Continue to boil gently until complete charring and disintegration of the organic matter have occurred (about 15 to 20 minutes’ boiling is generally required). As sulfuric acid is consumed in the oxidation, add more in 5-cc. portions, when needed, t o maintain the volume at about 20 cc. When charring is com lete, allow t o cool and add carefully, in small portions, 5 cc. orfuming nitric acid. If a strong reaction occurs, stop the addition and swirl the contents of the flask until the reaction subsides, then carefully continue the addition. Heat the mixture with a low flame until the brown fumes have disappeared, boil vigorously for a few minutes, and then cool. Repeat this process until two successive treatments with the nitric acid produce no decrease in color (three 5-cc. portions of nitric acid are generally sufficient). While agitating, dilute the contents of the flask with 100 cc. of distilled water. Boil the solution down to strong fumes of sulfur trioxide and cool. This hydrolyzes the nitrogyl sulfuric acid and drives off oxides of nitrogen. If a yellow color is present in the solution a t this point it is usually indicative of the presence of either iron or undigested organic matter, and the solution should be treated as follows: Carefully add 5 cc. of hydrogen peroxide. Heat the mixture with a low flame to strong fumes of sulfur trioxide, boil vigorously for a few minutes, then cool. Repeat this process until two successive treatments with hydrogen peroxide produce no decrease in color (two or three 5-cc. portions are generally sufficient). While agitating, dilute the contents of the flask with 100 cc. of distilled water. Boil the solution down to strong fumes of sulfur trioxide and then cool. This will remove any excess hydrogen peroxide. I
1 “Albone C”, lOO-volume, as manufactured b y the R. & H. Chemicah Division, E. I. d u P o n t de Nemours & Company, he., has been found satisfactory.
FEBRU-4RY 15, 1940
ANALYTICAL EDITION
Dilute the solution with 100 cc. of distilled water. If the solution is clear, transfer to a 250-cc. volumetric flask, dilute to volume, and mix well. If the solution contains insoluble matter, heat to a boil and Uter hot, by ravity, through No. 1 Whatman filter aper Wash the filter w& Kith hot distilled water, dilute to vogme in a 250-cc. volumetric flask, and mix well. Aliquots of this solution are used for the determination of copper, and of manganese if it is present in sufficient quantity. Blank determinations using the same quantities of the same reagents should be run simultaneously with each batch of determinations. -411 reagents, including the distilled water used for dilution, should be as free as possible from copper and manganese.
95
When Cadmium I s Present. Cadmium gives a white turbidity with the reagent when present only in traces. When the cadmium content of the aliquot taken for the colorimetric comparison is so small that it cannot be precipitated with hydrogen sulfide in ammoniacal solution, the turbidity produced may be cleared up by using two or three times the usual amount of ammonium hydroxide. When cadmium is present in larger quantities, this method is not applicable and other methods for the determination of copper must be used. CALCULATION. Cc. of standard copper solution %:-0.001 weight of sample in aliquot
- % of copper
Determination of Copper REAGENTS.Ammonium hydroxide solution (sp. gr. 0.880). Sodium diethyldithiocarbamate solution: Dissolve 1.0 gram in 1 liter of copper-free water. Place in an amber bottle and protect from strong light. Standard copper solution. Dissolve 0.3928 gram of c. P. copper sulfate Dentahvdrate (CuSOn.5H20).which contains 0.1000 gram of copier, in 250 cc. of copper-free’water in a volumetric flask. Pi et 25 cc. of this solution into a 1-liter volumetric flask and d i i t e to volume with copper-free water. This final solution is the standard and will contain 0.00001 gram of copper per cc. Gum arabic solution. A 5 per cent solution of gum arabic in distilled water. PROCEDURE. Pipet a suitable aliquot, usually 25 cc., of the solution into a small Erlenmeyer flask or beaker. Drop in a small piece of litmus paper as indicator and make just alkaline with ammonium hydroxide. Add 1 to 2 cc. excess ammonium hydroxide, heat to boiling, and place on a steam bath until coagulation and precipitation of iron hydroxide are complete. If aluminum is known to be present, allow to stand on the steam bath for a t least 1 hour to ensure complete precipitation of aluminum hydroxide. Filter, by gravity, through No. 1 Whatman filter paper, into a 100-cc. Nessler tube, and wash the filter with two or three small portions of hot distilled water. To the solution in the Nessler tube, add 1 cc. of a 5 per cent gum arabic solution, 10 cc. of c. P. ammonium hydroxide, and 10 cc. of sodium diethyl dithiocarbamate solution in the order named. Dilute to the mark and mix well. To a second tube containing a similar aliquot of a blank solution carried through the entire analysis in the same manner as the sample, add equal amounts of the same reagents, dilute to about 90-cc. volume, and mlx. Titrate into the second tube tvith the standard copper solution from a 10-cc. buret (preferably graduated in twentieths of a cubic centimeter) until its color matches that of the sample when diluted to the same volume. Mix m-ell after each addition of copper solution. If the color in the sample tube is too deep for comparison, a smaller aliquot portion of the solution from the acid digestion must be used. If the color in the sample tube is too light for a good comparison, the amount of copper present (on the basis of a 5-gram sample) is below the accuracy of the method. Best results will be obtained when the aliquot contains copper equivalent to 1 to 5 cc. of the standard copper solution. In case the solution in the tube containing the sample is turbid, some interfering substance is present. If one of the following modifications does not remove the turbidity the method is not applicable and a modified or different procedure will be necessary. When Lead I s Present. Add 2 to 5 cc. of 1 per cent ferric chloride to a 25-cc. aliquot of the solution from the acid digestion. Make just alkaline to litmus with ammonium hydroxide, add 1 to 2 cc. excess ammonium hydroxide, and heat as before, to coagulate the precipitate. Filter into a 100-cc. Xessler tube, wash the filter, add the gum arabic, and proceed as above. When Zinc I s Present. Zinc causes a turbidity only when resent in comparatively large amounts. Sometimes this can e! overcome by simply making the solution in the Nessler tube more alkaline n-ith ammonium hydroxide. (Add as much ammonium hydroxide to the known comparison tube. As much as 20 or 30 cc. of ammonium hydroxide may be used.) When this expedient fails, treat a suitable aliquot portion from the volumetric flask as follows: Adjust with ammonia until neutral to litmus, add 5 cc. of concentrated hydrochloric acid, and pass in hydrogen sulfide for 10 minutes. Boil and pass in hydrogen sulfide again for 5 minutes. Filter, but do not wash. Place the filter paper in the original beaker and treat with 10 cc. of 25 per cent sulfuric acid. Boil for a few minutes. Dilute with 25 cc. of water, filter, and wash thoroughly. Neutralize the filtrate with concentrated ammonium hydroxide. Place in a 100-cc. Nessler tube, add the gum arabic. and proceed as above.
Determination of Manganese REAGENTS.C. P. phosphoric acid, 85 per cent. c. P. potassium periodate. Standard manganese solution. Prepare a standard manganese solution by diluting as much standard potassium permanganate as is given by the formula cc. = 4.551/N to 500 cc. in a volumetric flask. (N = normality of the potassium permanganate used.) This solution contains 0.0001 gram of manganese per cc. Do not keep this solution for more than one week. PROCEDURE. Transfer a suitable aliquot, usually the balance of the solution in the 250-cc. volumetric flask, to a 250-cc. beaker and evaporate to about 75-cc. volume. (If the manganese content is very low a separate sample should be used and the whole solution from the acid digestion should be evaporated for the comparison.) Add 10 cc. of 85 per cent c. P. phosphoric acid to decolorize iron if present. Sprinkle in 0.5 gram of potassium periodate and bring the solution to a boil. Cool slightly, sprinkle in another small portion of potassium periodate (about 0.1 gram), and boil again. When the color seems to have developed to a maximum, place the beaker on a steam bath and keep hot for 15 minutes. Should there be any doubt about the completeness of the reaction, add more potassium periodate. After the: sample has stood on the steam bath for 15 minutes remove it and allow it to cool. If the color is too deep for a good comparison, wash into a 250-cc. volumetric flask and dilute to volume with distilled water. Place a suitable aliquot (or the whole sample) in a 100-cc. Nessler tube and dilute to the mark with distilled water. Place a similar aliquot of a blank solution, carried through the entire analysis in the same manner as the sample, in a second tube and dilute almost to the mark. Titrate into this second tube with the standard permanganate solution from a 10-cc. buret (preferably graduated in twentieths of a cubic centimeter) until its color matches that of the sample when diluted to the same volume. Mix the contents of the tube by pouring into a m a l l beaker and stirring, not by shaking in the stoppered tube or by using the hand as a stopper. CALCULATION. Cc. of standard KMn04 solution added~X 0.01 weight of sample in aliquot
% of manganese Applicability and Accuracy These procedures have been checked on samples of azo, sulfur, basic, and vat colors, intermediates, rubber chemicals, and rubber, both as produced and after the addition of known amounts of copper and manganese. Both elements can be determined in these products in the presence of iron, lead, zinc, barium, aluminum, and small amounts of cadmium, and in the presence of each other. The methods may be applied to other materials such as fabrics, pigments, and inorganic chemicals, provided other metals are not present in interfering amounts. The accuracy of both methods is about *5.0 per cent of the amount of metal present. I n sorne cases as little as 0.0002 per cent (0.01 mg.) of copper and 0.0001 per cent (0.005 mg.) of manganese may be detected on 5-gram samples. T h e amount of copper in the solution to be compared should not exceed 0.1 mg. per 100 cc. (10 cc. of the standard copper solution) ; above this concentration the color becomes too intense for satisfactory matching.
INDUSTRIAL AUD ENGIKEERING CHEhIISTRY
96
Discussion I n developing the above inethods the indicators, potassium ferrocyanide and potassium periodate, were fii st tried on aqueous solutions containing kiion n amounts of copper and manganese. Later, sodium diethyldithiocarbainate nab investigated as the indicator for copper and found to be more sensitive. Follon ing the establichineiit of satisfactory indicators the destruction of the organic matter n a s inveqtigated. Obviously, the organic matter niust be completely destroyed without the loss of copper or manganese or the introduction of appreciable amounts of the same or interfering substances. Ignition in porcelain or platinum crucibles had been used and found unsuitable in most cases, owing to the formation of insoluble residues. Aehing in porcelain frequently results in contamination with siliceous matter or losses due t o embedding of part of the copper or manganese. Platinum ware is sometimes attacked and if platinum is dissolved it interferes with the copper determination. Wet digestion with mixed acids is somewhat longer than ashing but gives more accurate results because of the solubilizing action of the acids. An excellent article by Hiltner ( 2 ) emphasizes the benefits of the acid digestion procedure.
Summary Uethods have been described for the determination oi m a l l quantities of copper and manganese in dyes, intet mediates, rubber chemicals, and rubber, which may contain, in addition
T'OL. 12, XO. 2
to copper aiid manganese, iron, lead, zinc, barium, aluminum, and sinal1 amouiit)s of cadmium. Materials containing other metals may require special treatments. Both methods are accurate within * L O per cent of the amount of nietal present. Under best conditions amounts as low as 0.0002 per cent of copper and 0.0001 per cent of manganese may be determined 011 &gram samples.
Acknowledgment ,Ickiio\~letlgriieiitis macle to S.Strafford, of the Imperial Chemical Industries, Dyestuffs Group, Analytical Department, for his technical comments on these methods and to the manageinelit of Imperial Chemical Industries, Dyestuffs Group! for permission to publish information obtained froni their official methods. The authors also wish to express their appreciatioii for the assistance and suggestions contributed by past and present menil,ei~sof the analytical staff of this laboratory.
Literature Cited (1) Callan and Henderson, A n ~ Z y s t 54, , 650 (1929). (2) Hiltner, Vierner, Z . anal. Chem., 110, 241 (1537).
(3) Imperial Chemical Industries, Dyestuffs Group, private ~ 0 1 x 1 munications. (4) Willard and Greathouse, J . Am. Chem. Soc., 39,2306 (1517). C O N T R I B U T ISo. ~ N 44 from t h e Organic Chemicals Department, E. I. i l u Pont de Seiriours & Company, Inc.
Stability of Peroxidized Titanium Solutions GILBERT H. I l H E S ~ N E D D M i Y _\I. \ I E S S E A U Smith College, Northanipton, >lass.
IK
THE colorimetric determination of titanium by the hydrogen peroxide method (4), the color compaiison is usually made by the method of balancing, dilution, or duplication. For the analysis of titanium in bauxite, Gautier ( 1 ) recommended comparison with a series of standards, but indicated that the color was so unstable that renewal of standards was necessary after 8 days. He therefore ( 2 ) proposed the use of helianthin, or methyl orange 111, for the preparation of artificial standards which do not fade. The data presented heren-ith show that the color of titanium by the hydrogen peroxide method is stable over a period of a t least 2 years.
In Sovemher, 1936, standard titanum solution A4was prepared from pure titanium oxide by fusion with potassium pyrosulfate follon-ed by solution in sulfuric acid; the solution v a s standardized gravimetrically. Suitable dilutions were used for the devclopment of the yellow color by hydrogen peroxide. Colorimetric measurements Tvere made with a Toe ( 5 ) photoelectric colorimeter. The second column of Table I gives the per cent of light ahsorption by t,hene solutions. Column three shows the light absorption by the same solutions in November, 1938-that is, after standing for 2 years. During this time the samples were stored in glass-stoppered Pyrex bottles, but no special precautions \yere taken to protect them from light. Column four s h o w the results obtained, also in Sovemher, 1938, on freshly prepared samples made from standard titanium solution B obtained from potassium titanium oxalate by the method of Thornton arid Xoseman (3).
TABLE I. LIGHTABSORPTIONBY PEROXIDIZED TmasIuv SOLCTIOSS
of the instrument-namelv. 0.4 per cent light - absorvtion. At any rate, there is no indication of fading of t'he color. The
I n most cases the readings are within the limit of accuracy
Concenti ation of Ti Mg./l. 4 R
12 16 20 24
2s
32 36 40 48 56 64 72 80
From Standard . 1 Xoveniber, 1936 Xovember, 1938
Froin Standard B, November, 1938
%
70
7c
6.0 8.6 10.8 12.8 14.0 15.2 16.6 17.8 1 8 .. 88 19 21.2 22.8
G.0 9.2 11.6 12.8 14.4 14.8 16.0 17.4 18.G 19.8 20.6 22.6 24.0 25.2 26.2
5.4 8.6 10 G 12.6 14.G 1; 4
23 (i 25.0 20.0
1S:O 21 09 .. 42 22.0 23.6 24.6 25,G ".C
"
I
results indicate that the yellow color of titanium in acid s o h tion of hydrogen peroxide is entirely stable, so t'hat t>heuse of artificial standards for the purpose of obtaining stability is unnecessary.
Literature Cited (1) Gnutier, .I.,Chimiste, 1, 177 (19101. (2) Gautier, :I,, Ibid., 2, 2 (1911); Kec. ycn. chim., 14, 1ti (1911); A m , chim. arial. chim. a p p l . , 12, 135 (1930). (3) Thornton, IV. 31.. and Roseman, R.. A m . J . Sci.. 20, 1-1(I9:N). , Ber., 15, 2593 (1882). ( 5 ) T o e , J. H., and Crumpler. T. B., ISD. ENG.CHEM..Anal Ed.,
7, 28 (19353.
