V O L U M E 25, NO. 5, M A Y 1 9 5 3
837 X-Ray Powder Diffraction ( I )
d, A . Obsd.
B&P (I)
14.5 10.6 9.69 7.79
Au-
thors 14.4 10.5 9.7 7.9
Calcd. I / I i hkl 1 4 . 5 6 80 100 1 0 . 7 0 1 0 001 9.74 80 r o i 7.81 85 101
d, A . Obsd. B&P Au( 1 ) thors Calcd. I / I i 3.48 3.48 3.57 15 3.53 3.50 3.48 3.40 3.41
3.42 3.39
30
221 402
3.32 3.31
5
113
7.29 6.94
7.3 6.9
7.28 6.96
50 200 100 110
. ..
6.4
6.77 6.37
...
20i 50 011
3.31 3.32
6.36
...
6.10
6.1
6.14 5.56
40
lli
3.20
5.37
5.4
5.47 5.43 5.36 5.35
30
2 01 102 210 002
5.15
25 2 1 i
5.14
5.13
...
111
hkl 003 121,203 212 220
z::}
3.22
15
3.0f
5
2 . 8 5 2.85 2 . 6 8 2.70 2.59 2.54
2.54
410
d, A . Obsd. B&P Au(I) thors Calcd. 4,85 4,85
2:;;
4.68
hkl 12 205 300,3oi
3
102
4.44
4.45
4.50 4.48 4.43
30
211 112 012
4.13
4.14
4.15 4.14
50 212 310,3ii
2.17 2.15
4
4.05
4.08 3.96
12 301,302 2 . 0 7 020 2.05
2
3.82
3.91 3.82 3.71
2
4.03
20 20
3.92 3.81
1
I/Ii
4.69
d, A . Obsd. B&P Au(I) thora I/II 2 49 2 . 5 2 5 2 : 43 (plus many 4 other lines 2.37 too faint 2 t o permit 2.32 accurate 4 2.25 measure3 2.22 mentj 3
1 202 20 120 . . . 021,4oi
2
1
1.94 1.88 1.83
5
Optic A4sialAngle (Wratten No. 23 filter; 25" C.). 2Vz = 69.8 i 0.5" (average of 20 direct measurements on a number of different crystals; measurements made with the universal stage Eorrected for refractive index of hemispheres and tilt angle); (0.0' (calculated from refractive indices as listed in preceding paragraph). Optical Axial Plane. I ( O l O ] with X = b and 2 A c = 11.0 & 0.2' in obtuse angle beta. Dispersion. Moderate dispersion of the optic axes with 2V, > 2V,: slight horizontal dispersion of the acute bisectrix with (2, A > TZ. A c ) . Molar Refraction (Wratten No. 23 filter; 25" C,). 4.Vx-NyNz = 1.556; R (observed) = 122.5 for CzsHtoO,N.HzO. Optical Rotation. [ a ]23'0D = $50.9" (c 0.843 in chloroform); [ a ] 2 2 , 6 D = +53.6" (c 1.156 in absolute ethanol); [ a1Y.O = +53.2' (c 2.036 in C.P. methanol) ( 2 ) .
c)
Barnes and Przybylska ( 1 ) state that ELECTRICAL PROPERTIES. the crystals are strongly piezoelectric.
THERarAL DAT.~.The melting point 'of lycoctonine monohydrate as determined on a microscope hot stage is lower than that observed by conventional capillary methods ( 2 ) . Crystals begin t o soften a t about 85" C. and fusion is complete around 107' C. I n this temperature interval the solid and liquid phases coexist. The melt solidifies to a brittle, x-ray and optically amorphous material d.hich, although readily soluble in common polar organic solvents, cannot be recrystallized. A solution of a mixture (produced by partial fusion) of crystalline and amorphous phases yields on evaporation apparently the same phases in the same proportion.
LITERATURE CITED
(1) Barnes, W. H.,and Prsybylska, M., Can. J. Chem., in press
(probably May 1953). (2) Cook, W. B., and Beath, 0. A , , J . A m . Chem. SOC.,74, 1411 (1962). (3) Edwards, 0.E.,and Marion, L., Can. J . Chem., 30, 627 (1952).
Strong Reduction Preliminary to Kjeldahl Digestion in Analysis of Refractory Compounds T SEEMS
paradoxical that the conditions of the Kjeldahl de-
I composition are designed for oxidation when it is desired to reduce nitrogen to ammonia. The usual devices for increasing the effectiveness of the operation include the use of oxidation catalysts, the addition of oxidants, the prolongation of the afterboil or, more recently, the use of higher digestion temperatures (1, 2, 4 ) . Preliminary reduction by familiar agents has a limited applicability in dealing with oxidized-nitrogen compounds, azo compounds, etc., and reduction by hydriodic acid, though open to some uncertainty oBring to the difficulty of expelling free iodine before distillation of ammonia, has been considered useful in the analysis of some refractory types. Certain unsaturated ring systems containing nitrogen are notably stable toward oxidizing agents but become much less stable upon hydrogenation. The work here reported was undertaken to test the hypothesis that initial strong reduction might bring nitrogenous rings, azines, etc., within the scope of the
Kjeldahl procedure or that it might permit shortening of the digestion. Analyses on a semimicro scale ( 3 )were made of nicotinic acid, an azine, and several other compounds, with preliminary reduction follon-ed by digestion as usual. The reducing agents tried are (1) hypophosphorus acid alone and with sulfuric acid, copper sulfate, hydriodic acid, zinc dust, or calcium silicide; (2) chromous chloride or sulfate; (3) sodium and methanol; and (4) electroreduction. Of the agents named, only hypophosphorus acid (alone), sodium and methanol, and electrolysis appear to offer some promise; results by the other agents were unpromising. Catalytic reduction n'as not tried.
Hypophosphorus Acid. During the preliminary heating of sample with 50% aqueous hypophosphorus acid a stream of carbon dioxide was passed into the flask, to avoid flashes of flame or minor explosions (phosphine). Nicotinic acid (X =
.
ANALYTICAL CHEMISTRY
838 11.38%), after 1.5-hour digestions, in 39 trials yielded an average of 10.70y0 of nitrogen (94%), with maximum of 11.39% and minimum of 9.27%. For 6-methoxysalicylaldazine ( N = 8.98%) five trials, involving 2.5-hour digestions, gave an average of 9.03%, with maximum 9.15% and minimum 8.9070. Some of the low results may be attributed to loss caused by irregular but sometimes violent bumping during the reductions. Sodium and Methanol. Nine analyses of nicotinic acid, R-ith 30-minute digestions, yielded results all of wh,ich are acceptable, averaging 11.247, (maximum, 11.487,; minimum, 11,0470); adenine treated in the same way liberated ammonia during reduction. For general use a trap to retain volatilized ammonia would be needed, but a selective determination of nitrogen so liberated and total nitrogen might be possible. Electrolytic Reduction of nicotinic acid, in 80% sulfuric acid, using platinum electrodes and a current of 0.7 ampere a t 4 volts, followed by digestions for 30 to 90 minutes, yielded in three trials one good result (11.41%) and tn-o Ion. results (10.82,10.52).
case of basic stannic sulfate, it is further indicated that the extent of coprecipitation is negligible, once supersaturation is relieved, until one of the ions constituting the carrier has been quantitatively removed from the liquid phase. The complete results of these investigations will be reported to ANALYTICAL CHEMISTRY a t a later date. ACKNOWLEDGMENT
This investigation is supported in part by grants from the Atomic Energy Commission and the Research Corp. LITERATURE CITED
(1) Elving, P. J., and Van Atta, R. E., AXIL. CHEM.,22, 1375 (1950).
Gordon, L., Ibid.,24, 459 (1952). Wagner, W.F., and Wuellner, J. A , Ibid.,24, 1031 (1952). Wahl, A. C., and Bonner, N. A . , "Radioactivity Applied to Chemistry," New York, John Wiley 8r Sons, 1951. (5) Willard, H. H., AXAL.C H E X . , 22, 1372 (1950). (6) Willard, H. H., and Gordon, L., Ibid.,25, l i 0 (1953). (2) (3) (4)
This exploratory study is reported thus incomplete because none of the authors will be able to continue it, and in the hope that someone else may be inclined to do so. Grateful acknowledgment is made to the Committee for the Advancement of Research of the University of Pennsylvania for a grant to support the study, made during the summer of 1951.
DEPARTMEXT OF CHEMISTRY
* SYRACUSE UXIVERSITY S Y R A C U S10, E S . Y.
LITERATURE CITED
LOGISGORDOK CARL.C REIVER HARRY TEICHER
R E C E I V Efor D review March 9, 1953. Accepted April 1, 1953.
(1) Grunbaum, Schaffer,and Kirk, ANAL.C H E X , 2 4 , 1 4 8 7 (1952). ( 2 ) Ogg and Willets, J . Assoc. Ofic.Agr. Chemists, 24, 641 (1941). (3) Wagner, IXD. ENG.CHEM.,S l v . 4 ~ ED., . 12, 771 (1940). (4)
White and Long, ASAL. C H E M . ,23, 363 (1951).
D E P A R T M E OXFTCHEMISTRY ~ N I V E R B I T YOF P E X S S Y L ~ A N I A PHILADELPHIA, PA.
SARAH AI. ROODS DAVIDSCHEIRER E. C. WAGNER
R E C E I V EDecember D 18, 1952. Accepted March 30, 1953.
Coprecipitation from Homogeneous Solution laboratory is utilizing precipitation from homogeneous Tsolution . ( 2 , 6) to study the distribution of foreign ions beHIS
tween the precipitate and liquid phases. Coprecipitation is being studied as a function of the fraction of carrier precipitated; this is similar to the fractional crystallization techniques utilized in studies of the homogeneous and heterogeneous distribution laws as described by Wahl and Bonner (4). This communication describes the preliminary results obtained in the coprecipitation of manganese(I1)by basic stannic sulfate (6) and of strontium by barium sulfate (1, 3). I t has been found, as would be normally expected, that the extent of coprecipitation of manganese( 11) on basic stannic sulfate precipitated by the urea method is increased with increasing rate of precipitation. However, a t a given rate, except in the case of a very slow precipitation rate, much of the foreign ion is coprecipitated during the separation of approximately 25y0 of the total carrier present. Only a negligible amount of the foreign ion is then further coprecipitated as the remainder of the carrier is precipitated up to .the point where approximately 99.9% of the total initially present has been separated. This latter observation is in accord with the Paneth-Fajans-Hahn rule. After complete precipitation has occurred, the adsorption of foreign ions by the carrier becomes appreciable and causes a sharp rise in the total amount of coprecipitation. I n the case of coprecipitation on barium sulfate precipitated a t a slow rate with dimethyl sulfate ( I ) , the quantity of strontium found with the initial fraction of precipitated carrier was sharply reduced Lvhen vigorous stirring was employed. This is not the case with the sulfamic acid procedure (3). These experiments indicate, except possibly in the case of (S), the presence of a supersaturated condition during the early stages of a slow precipitation process, as is provided by the technique of precipitation from homogeneous solution. I n the
Precautions in the Determination of Lead in Biological Material by Diphenylcarbazide SIR: Experience during the past decade Rith the method for determination of lead in body fluids described by Letonoff and Reinhold (1, 2 ) has indicated that occasional analyses were unsatisfactory. K i t h few exceptions, one of three causes has been responsible. Losses of precipitate may result from the use of centrifuge tubes that are asymmetrical or unsuitable for other reasons. However, proper tubes have been made available recently especially for this and similar methods by the Corning Glass Forks. A second cause of low results has been traced to the use of animonium acetate wash solution of pH below 7.0. Elevated content of carbon dioxide in distilled water, carbon dioxide uptake by the wash solution on standing, or excessively acid preparations of ammonium acetate have been responsible. A modified viash solution to replace the 0.470 ammonium acetate solution of the original method is prepared by dissolving sufficient ammonium acetate (of low lead content) to make a solution approximately 1% in water containing 1.5 ml. of 0.1 S ammonium hydroxide per 100 ml. This solution is filtered through Whatman S o . 42 paper, stored in a refrigerator, and used at a temperature of about 10" C. Each tube is nearly filled by using 15 ml. of wash solution. If a refrigerated centrifuge is available, a significant gain in precision is obtained by centrifugation at 5" C. Addition of l5Y0 acetic acid for pH adjustment prior to precipitation seldom is required with chemicals no\T available. The third and most important source of error has been contamination, not so much xith lead from extraneous sources as with chromate residues. Special care should be taken to remove these thoroughly from centrifuge tubes, stirring rods, stoppers, etc., before proceeding 1% ith color development. After the mother liquor from the precipitate has been decanted and dis-
