INDUSTRIAL A N D ENGINEERING CHEMISTRY
472 Table
IV.
Analysis of By-product
Vol. 17, No. 8
Oils
Weight of p, Bample
No.
p,p'-DDT Added
1
Grams 0.653 1.230 0,949
2
0.794 1.013 0.691
Weight of Elubstance Uram
CWstalhaatlon Found Corrected p,p'-DDT
1.347 0.770 1.051
Grams 0.981 1.395 1.198
1.206 0.987 1.309
1.008 1.185 0.923
% 26.4 25.1 26.3 Av. 25.9 1.034 19.9 1.213 20.2 0.951 19.9 Av. 20.0
Grams 1.009 1.423 1.226
such "by-product oils" obtained from commercial DDT samples by removal of a large fraction of the p,p' isomer by crystallization from 95% ethanol or hexane are given in Table IV. The validity of the use of such a procedure aa well as the use of the correotion factor of 0.028 gram is substantiated, since good checks were obtained when the percentage of added p,p'-DDT waa varied from 32.6 to 61.5. MODIFIED PROCEDURE FOR USE WITH QUSTS
A wei hed quantity of dust containing 5 to 10 grams of ether-
extracta%le material is placed in a Soxhlet extractor and extracted with ether into a tared flask for 4 hours. The ether is distilled off on a water bath, finally under reduced pressure. The weight of residue is determined. The residue is removed from the f l a k ground in a mortar to ensure representative Sam ling, and analyzed accordin to the general procedure given aiove. A commercial "10%' 8 D T in pyrophyllite dust, when analyzed by this procedure, ave 10.62% of ether-extractable material and 7.87% of p,p'-D%T. TEMPERATURE CONTROL
In order to determine the degree of temperature control necessary for quantitative work, the solubility of p,p'-DDT in 75% ethanol a t various temperatures waa studied. The data presented in Figure 1 indicate that an error of 1"in the range of 20"
0.o[ 0
Figure
I
I
IO
20
I
,
30 40 Temperature 'C.
I
I
50
60
70
I, Solubility of I-Trichloro-9,9-bir(p-chlorophenyl)ethane in 75% Aqueous Ethanol
to 30" C. would give an error of 9 mg. in the procedure, or about of p,p'-DDT. This indicates that somewhat greater accuracy might be obtained by temperature control t o + 0 . l o C.
0.5%
LITERATURE CITED
Annand, J. Econ. Entmol., 37, 125 (1344). Fleck and Preston, Soup Sunit. Chem., 21 (5),111 (1945). Froelicher, Ibid., 20 (7), 115 (1944). Gunther, IND.
[email protected].,ANAL.ED., 17. 149 (1945). . . Hall, Schechter, and Fleck, U. S. Dept. Agr., Bur Entomol Plant Q u a r ~ n t iET-211 ~, (1944). (6) Roark and McIndoo, Ibid., E-631 (1944). (7) Schechter and Haller, J. Am. Chem. Soc., 66,2129 (1944). T H Xwork described in this paper was done under a transfer of funds, recommended by the Committee on Medical Research, from the Office of Scientific Reaearoh and Development to the Bureau of Entomology and Plant Quarantine.
Electrodeposition OF Zinc in Magnesium Alloys Employing Various Buffered Solutions THOMAS F. BOYD, GEORGE NURWITZ,
AND
SIDNEY WEINBERG
Industrial Test Laboratory, United States Navy Yard, Philadelphia, Pa.
Several procedures for the determination of zinc in magnesium alloys were investigated to evaluate their accuracy for routine use. All methods are very rapid and satisfactory. The formic acid method is considered the most suitable for routine use.
R
ECENTLY a rapid method for the determination of zinc in magnesium alloys waa described, in which electrodeposition waa made in ammoniacal medium and tartaric acid and ammonium chloride were employed to keep aluminum and magnesium in solution (9). In connection with this, electrodeposition of zinc in magnesium alloys using other buffer mixtures was subsequently studied, following the procedures given below. The chief purpose of this investigation waa to devise a method most suitable for routine use. Deposition waa made in solutions to which were added, respectively, ammonium hydroxide, sodium hydroxide, citric acid, tartaric acid, and formic acid. Improvements were made upon the previous methods, using weak organic acids (9). An unpublished procedure employing acetic acid was also investigated (1).
The procedure of Winchester and Yntema ( d ) , employing the electrodeposition of zinc from pure salt solutions in an acid sulfate solution, was applied to magnesium alloys, but was found unsuitable since a salting out effect occurred on the cathode, causing very high values. PROCEDURE
I. AMMONIUM HYDROXIDE.Dissolve 0.5 ram of sample in a 300-ml. electrolytic beaker with 40 ml. of tilute sulfuric acid (1 9). Add 2 ml. of tartaric acid solution (25%) and 7 to 8 grams of ammonium sulfate, dilute to 200 ml. with water, and stir to dissolve soluble salts.. Make the solution just ammoniacal, using methyl red aa an indicator, and add 4.0 ml. of ammonium hydroxide (0.90) with stirrin6. Electrolyze for 25 minutes at 2 amperes, agitating the solution gently with a stream of air. (Turn the current on before the beaker is.placed in contact with the electrodes to avoid any solvent action of the ammonium hydroxide on the copper plate of the cathode.) Wash by rapidly lowering the electrolyte and replacing with a beaker of distilled water. Repeat the operation using a second beaker of water. Immerse the cathode in neutral alcohol and place in an oven a t 100' C. until the alcohol has completely evaporated.
+
A N A L Y T I C A L EDITION
August, 1945
473
Remove immediately from the oven to prevent possible oxidaTable Ill. Comparison of Electrolytic with Standard Methods tion of the zinc plate, cool to Zinc, Electrolysis room temperature, and weigh. Zinc Zinc AmmonSodium E i t h e r a copper p l a t e d Alloy Alloying GraviFerroium hyHydrox- Citric Tartaric Formic Acetic platinum gauze cathode ( 5 cm., metric" cyanideb droxide ide acid Type Elements acid acid acid 2 inches, high X 4.4 cm, 1.75 % % % % % % % % inches, in diameter) or a nickel 3.02 265 2.97 3.04 2.84 2.92 3.00 2.95 3% Zn, 6% AI, 2.96 O.2y0 Mn gauze cathode may be used. A 3.00 3.06 3.00 2.82 3.08 2.96 2.96 2:25 260 2.22 2.30 2.22 2.20 2.24 2.24 2.20 2 % Zn 9 % AI. platinum wire spiral should be 2.19 0 2 9 Mn 2.24 2.24 2.20 2.32 used 88 an anode (8). 1.14 1.12 l%'Zno 6 7 Al. 57s 1: i 5 i:is 1.14 1.18 1.18 i:ig 1.18 1.24 1.28 11. SQDIUMH Y D R O X I D E . 0.5%' MZ 1.18 1.08 1.14 1.12 1.20 Dissolve 0.5 gram of sample in Determined as oxide after hydrogen sulfide se arations. b Determined by ritration after hydrogen sulfi& separations. a 300-ml. electrolytic beaker with 40 ml. of dilute sulfuric acid (1 9). Add 5 ml. of tartaric acid solution (25%) and Table IV. Comparison of Results under Routine Conditions 10 to !2 grams of ammonium sulfate, dilute to 150 ml. with water, (Sample No. 70) and stir to dissolve soluble salts. Make the solution just alkaline AmmonSodium with sodium hydroxide solution (15%) using methyl red as an inium Hy- HydroxFormic Formic Acetic droxide ide Acid Acid" Acid4 dicator then add 10 drops in excess. Electrolyze immediately for 25 Ainutes a t 3 amperes and complete 9a. in Procedure I. % % % % % 111. CITRICACID. Dissolve 0.5 gram of sample in a 300-ml. 2.92 3.02 2.84 2.84 3.07 3 . 1 2 3 . 0 8 2 . 8 8 2 . 8 5 3 .02 9). electrolytic beaker with 40 ml. of dilute sulfuric acid (1 2.96 3.06 2.90 2.88 3.05 Add 2 ml. of citric acid solution (25%) and 7 to 8 grams of am2.98 3.02 2.90 2.88 3.02 monium sulfate, dilute to 200 ml. with water, and stir to dissolve 2.96 2.90 2.90 2.98 3.04 2.98 2.90 2.90 3.02 2.96 soluble salts. Make the solution just ammoniacal using methyl 3.00 2 . 9 6 2 . 9 2 3.09 2 . 9 1 red as an indicator, add citric acid solution (25%) until just acid, 3.02 2.96 2.95 3.02 3.01 and add 3 to 4 drops in excess. Electrolyze at 3 amperes for 25 Av. 3.01 3.00 2.90 2.89 3.03 minutes and complete as in Procedure I. Averagedeviation 0.04 0.04 0.02 0.03 0.03 IV. TARTARIC ACID. Proceed exactly aa in Procedure 111, Deviation from accepted value6 f0.07 $0.08 -0.03 -0.04 +0.10 but substituting tartaric acid (25%) for citric acid solution (25%). ACID. Dissolve 0.5 gram of sample in a 300-ml. V. FORMIC Determinations obtained on I-gram samplea. electrolytic beaker,with 40 ml. of dilute sulfuric acid (1 9). b Value 2.93 *0.02% zinc, found by ferrocyanide method. Add 2 ml. of tartaric acid solution (25%) and 7 to 8 grams of ammonium sulfate, dilute to 200 ml. with water, and stir to dissolve soluble salts. Make just ammoniacal using methyl red as an indicator, add formic acid (1 4) until just acid and then 5 to 6 cating magnitudes. The pH of the electrolytes determined bedrops in excess. Electrolyze at 3 amperes for 25 minutes and fore and after electrolysis a t 25" C., employing a Beckman pH complete as in Procedure I. meter, is shown in Table 11. VI. ACETIC ACID. The acetic acid method is similar to Procedure V. Table I11 gives the results obtained by carefully following the respective procedures. RESULTS Table IV compares results under regular routine laboratory In the experiments reported in Table I, the traces of zinc not conditions employing several of the procedures. The citric and deposited on the electrodes during electrolysis were determined tartaric acid methods were not included, as they appeared to offer in the electrolytes by means of dithizone, and in the first wash no advantage over the other organic acid procedures. water: zinc normally lost during the first wash, and loss during the first wash period, allowing 1 second to elapse before bringing DISCUSSION the wash water in contact with the electrodes and one second The authors prefer the use of 0.5 gram of sample as given in with the wash water in contact with the electrodes. This period the written procedures for routine use since more satisfactory reis about 5 times normal. The second washes made with water sults are usually obtained. The amounts of citric and tartaric and alcohol were also tested but less than 0.01 mg. of zinc was acids employed to keep the aluminum and zinc in solution were found in all cases. Because of the low amounts of zinc being kept a t a minimum, aa excessive amounts tended to produce sought, the water was redistilled aa recommended by Prodinger erratic results. If greater amounts of free acid were present in ( 2 ) . While the amounts of zinc found in electrolytes and washes the acid procedures, low results occurred and electrodeposition are somewhat variable, the values in Table I are useful in mdiwas slower. High results have been found upon prolonged electrolysis after electrodeposition of the zinc is completed. It appean that. zinc can be quantitatively electrodeposited Table I. Zinc Remaining in Electrolyte and Dissolved in Wash a wide pH range with acceptable precision. The best results over Water under routine conditions were obtained using the formic acid Zinc Found method (Table IV). The values for the routine acetic acid Procedure Electrolyte Wash water' Wash water6 method are slightly high in comparison with the other procedures. MO. Mo. MO. Ammonia
