651
V O L U M E 20, NO. 7, J U L Y 1 9 4 8 Table 1’. Effect of Temperature of Storage on Ascorbic .4cid Content of Stored Food Slurries Storage Temp.,
F.
Day
70-77
14 45 0 7 14 0 7 14 45
O
2 86 41
- 10
,
8
14 45 77
Ratio of Acid t o Food 4:1 7:l 4:l 7.1 Cucumbers Peppers 7.8 9.5 8.3 1.5 7.8 9.1 6.4 7.8 9.9 9.5
116.9 102.8 112 0 50.7 116.9 100.4 91.0 116.9 106.1 134.1 119.0 116.9 111.0 107.1
126.6 122.8 108.0 126 6 132.0 129.4
7.8 9.1 9.0
8.6 9.6 8.4 4.4 8.6 9.3 6.7 8.6 9.4 9.6 10.9 8.6 8.9 9.3
126.6 138.5 131.0
24.8 24.4 20.8 8.6 24.8 20.8 18.4 24.8 22.5 24.0 24.8 24.8 24.4 23.4
8.9
9.0
iii:s
l28:O
24:6
...
...
...
126.6 136.0 112.0
7;1 Radishes
...
.
.
The effect of storage a t different temperatures upon the ascorbic acid values of radish greens as measured by the dinitrophenylhydrazine reaction is shown in Table V. When samples were stored a t 86” F. for 14 days, there was an 18 to 26% loss of “a8corbic acid,” as measured by the dinitrophenylhydrazine method. -4troom temperature, there was no loss during 14 days’ storage, at 41 O F. no loss during at least 6 weeks’ storage, and a t
-10” F. no loss during at least, 11 weeks’ storage. If accurate estimations of ascorbic acid ill food extract’s are to be made, the influences of time and temperature of storage must be considered. Inasmuch 8s t’he indophenol and diiiitrophenglhydrazine methods agree when used to measure ascorbic acid in groundfresh plant nmterials and diragree more and more during storage after the plant is t,aken from t h ground, t’hese methods should prove usc,ful in checking the fi,cuhness of perishablr vpgetables. LITER.ATURE CITED
(1) Giiild, I,. P., Lorkhart. 1.7. E., and Harris, L i . S.,Scieuce, 107, 236-7 (1948). (‘2,) Harris, L. J., and Olliver. AI.,Biochem. J . , 36, 165-82 (1942). ( 3 ) Herbert. R. IT..Hirst, E. L., Perclval, E. G. V., Reynolds. R. J. W., and Smith, F. F., J . Chkm. SOC.,1933,1270-90. (4) Hochberg, LM., Melnick, D., and Oder, B. I,., ISD. Esc:. CHEM., ANAL.ED.,15, 182-8 (1943). ( 5 ) Loeffler, H. J., and Ponting. J. D.. Ibid., 14, 846 (1943). (6) Penney, J. R., and Zilva, S. S..Biochem. J . , 37, 403-17 (1943). ( 7 ) Ibid., 39, 392-7 (1945). (8) Pijoan, M., and Gerjowich,H. J., Science, 103,202 (1946). EKG.CHEM., AKAL.ED.,15, 389-91 (1943). (9) Ponting, J. D., IND. (10) Roe, J. H., and Oeeterling, M. J., J . Biol. Chem., 152, 511-17 (1944). (11) Tuba, J., Hunter, G., and Steele, H i R., Can. .J. Research, 24B, 37-45 (1946). RECEIVEDSoveniher 24, 1947. Presented in part before t h e Division of Agricultural and Food Chemistry a t the 112th Meeting of the AMERICAN SOCIETY, New York, S . Y . Investigation supported in part by CHEMICAL a grant f r o m the Central American Sritrition Foundation.
Determination of Small Amounts of Ethyl Ether in Ethyl Alcohol W. E. SHAEFER Hercules Experiment S t a t i o n , Hercules Powder Company, K i l m i n g t o n 99. Del. A simple distillation procedure for the determination of 0.0 to 2 . 0 7 ~of ethyl ether in ethyl alcoholis described. Results found after the application of appropriate correction values are accurate within 0.05% of the weight of the sample. The presence of up to 0.5% of benzene in the alcohol does not affect the arctiracy of the results.
I
PI’ THE manufacture of solvent types of smokeless powder dur-
ing World War 11, large quantities of ether-alcohol solutions had to be recovered and separated into their c o m p o n e p by distillation. The recovered alcohol contained 5 to 7% water, 0 to 0.4% benzene, and 0 to 2% ether. For certain operations, it was necessary to use alcohol containing as little ether as possible; hence, an accurate method to determine small amounts of ether in recovered alcohol of the foregoing composition was needed. Binary mixtures of alcohol and ether can be analyzed by the critical miscibility method of Kubias ( 1 ) . The petroleum ether extraction procedure of Rlasson and AIcEwan (9)and the recently published density-refractive index method of Scott (3) are suitable for ternary mixtures of alcohol, ether, and water. None of the foregoing methods, hoIyever, can be used when benzene is present. The distillation method for determining substantial amounts of ether in alcohol, previously described by the author (C), has been modified to make it suitable for the determination of small amounts of ether. Water and 0.5% or less of benzene do not interfere. APPARATUS
The apparatus consists of a 1-liter round-bottomed flask into which a 3-bulb Snyder column is fitted tightly with a rubber
stopper. The outlet of the column is connected to a condenser which is arranged vertically and attached to a suitable receiver The manner of loosely attaching the receiver to a vacuum line, of cooling the lower bulb of the column with an air stream, and of arranging the thermometer to measure the vapor temperature at the top of the column has been described (4). The flask is heated by a hemispherical Glas-Col heating unit controlled by a 5-ampere Variac. PROCEDURE
Place a weighed sample of about 630 ml. (about 500 grams) in the flask, and add about 250 ml. of water and a few particles of Carborundum. In case it is estimated that lesq than 0.2% ether is present, add 2.00 ml. of ether to the sample. This may be readilv accomplished by using a 2-ml. pipet which has just been chilled by rinsing with ether and then blowing air through it for a few seconds. A 2-mI pipet cooled in this manner will deliver 1.38 grams of ether, which will increase the ether content of the standard sample by 0.2S70. The addition of some of the substance being determined in an analytical procedure is always to be deplored, but in this case it is required to make the method function in the very low range of ether content. Attach to the flask a 3-bulb Snyder column bearing a thermometer. IJ‘eigh the system consisting of flask, sample, added water, column, thermometer, and stoppers on a suitably identified cork ring to the nearest 0.1 gram, using a good torsion balance. Place a hemispherical Glas-Col heating mantle in position under the flask, direct a strong jet of air against the base of the column, and
652
ANALYTICAL CHEMISTRY -
flask or by interposing asmall watch glass between the end of the air outlet tube and the column for a few seconds. Lower the heating mantle, disconnect the apparatus, and weigh the system to the n w i est 0.1 gram.
W
I
P O
15 u)
g -020. F
Y
-030.
CALCULATION
U
3 -0 4 0
If no ether \vas added before distillation. the results may be calculated as follow:
Figure 1. C i i n e for Correction Value
--
~-
Table T.
. .-.
Analysis of Ether-Alcohol Solutions of Know-ti Compositions by Proposed Method
Ltiier Present
Ether Found, I-ncorrectrd
Correction Value R e a d from Curve in Figure 1
-0.36 -0.36 -0.22
-0.04 +0.06
$0.08 +0.03 -0.13 -0.34 -0.11 -0.31
Ether Found, Corrected
1.98 1.98 0.99 0.54 0.33 0.24 0.39 0.79 1.48 0.70 1.26
l)lt€er?n,.r~
+0.04
-0.02 -0.04
+0.05 t0.02 +0.01
-0.04 co.01 4-0.04 +0,02 -0.03
lieat the sample rapidly (approximately 10 minutes) to iiicipitBnt boiling. Then lower the heating mantle and decrease its heat until it is just warm enough to permit gentle refluxing of condensed vapor from the lowest bulb of the column. Replace thr heating mantle and allow the distillation to proceed slowly (approximately 0.5 to 5 minutes) until the vapor temperature reaches 52" C. Maintain the vapor temperature at 52" 1 2 ' C until the distillation rate falls below 3 drops er minute and then for an additional 10 minutes. If the initia? rate of distillatioil never exceeds 3 drops per minute in the 50' to 54" C. vapor teniperature range, continue the distillation within this range 20 minutes from the time the vapor temperature first reached 52 O C. Under the foregoing conditions, a small and reasonably constant amount of alcohol, for which a correction can be applied, will be distilled. The distillation temperature is controlled chiefly by adjusting either the Variac or the air jet. It can be raised slightly either by placing a towel around the upper half of the
Loss in w i g h t of syhtem X 100 = % ether, uncorrected \yright sample of alcohol
To the uncorrected per cent etliri ir applied the correction valuta read from a curve similar to Figuie 1 which was constructed from data obtained by the distillation of 500-gram portions of alcohol to m-hich knon-n amounts of ether have been added. The known mixtures were prepared by adding ether from a Smith buret weighed to the nearest 0.01 gram and applying a correction in each case for the 0.02 gram of ether that is lost from such a wpight buret Then the reservoir is removed from its base. If 2.00 nil. of ether were added to the sample prior to the di-tillation, the per cent ether is calculated as described above, a ~ Y I I rection read from the curve in Figure 1 is applied, and from thr, result so obtained 0.28% is deducted to give the rther c o n t m t of the original sample. kPPLICATION OF METHOD
'l'he results found when the foregoing procedure was applied to k ~ i o n nmixtures of ethyl ether in 2B ethvl alcohol, which rontnirts 0.5% hrnz~ne,are shown in Table I. LITERATURE CITED
(1) Kubias, J., C'hem. Obtor., 12, 5-8 (1937). (2) Masson, I., and 1IIc.Ewan. T. L., .J. Sac. Phcm. IILd., 40, 29-32T (1921). (3) Scott, T.A., Jr., J . Phys. Chem., 50, 408 (1946). (4) Bhaefer, \I-.E;. IND. CNG.CHEM.. A N ~ I ,K. n . , 16, 132 (1944). K E C E J V E :February ~ 9, 1947
1,2-CYGLOHEXANEDIONE DlOXlME A Reagent ,for Palladium KOGEH C. VOTER, CHARLES V. BANKS, AND HARVEY DIEHL T h e I n s t i t u t e for I t o m i c Research find t h e D e p a r t m e n t of C h e m i s t r y , Iowa S t a t e College, Ames, Iowu
T
HE preparation of 1,Z-cyclohexanedione dioxinie, nioxime, and its use in the analytical chemistry of nickel have been reported ( 1 , 4). Xioxime also yields an insoluble yellow compound with palladium n-hich can be used for the detection and determination of this metal. This reagent offers several advantages over dimethylglyoxime as a precipitant for palladium. Kioxime is soluble in water, in contrast to dimethylglyoximr which must be made up in alcohol or acetone, and the possibilitv of contamination of the palladium precipitate with excess reagent is eliminated. Palladium nioxime is very insoluble and may be filtered from a hot solution after a brief digestion period, whereaq in many procedures it is recomniendd that the palladium dimethylglyoxime precipitate be allowed to cool and stand for long periods to ensure complete precipitation (2, Thus the
nioxime procedure effects a great saving of time with no sacrifice of accuracv. REAGENTS
An 0.8% aqueous solution of nioxime was used. h standard palladium solution was prepared from commercial palladium chloride. This salt was purified by first precipitating out platinum as ammonium chloroplatinate (9) and then precipitating the palladium as palladium dimethylglyoxime. This complex was destroyed with aqua regia and the solution evaporated to near dryness five times with concentrated hydrochloric acid to eliminate nitrate ions. The palladium content of the diluted palladium chloride solution was determined by precipitating the palladium in weighed amounts of this solution with dimethylglyoxime. These solutions were allowed to stand overnight t o ensure complete precipitation of the palladium dimethylglyoxime.
