ANALYTICAL CHEMISTRY
*
1290
24
Table 11. Rate of Hydrolysis of Methyl Bromide i n 10% Alcoholic Potassium Hydroxide Solution Reaction Time, Minutes 0
2 4 8 16 32 64 96 128 160 192 224
Total MI. 0.1 N AgKOa t o Titrate 0.04 0.24 0.30 0.57 0.96 1.16 1.68 1.70 1.80 1.75 1.76 1.75
Methyl Bromide, Mg. 0.9 2.2 2.8 5.3
PP
9.0
10.9 15.7 15.9 16.9 16.4 16.5 16.4
m
5 PO m P W
6
i
v
Table 111. Rate of Dissipation of Methyl Bromide i n 100Cubic Foot Fumigator Total M1. of 0.1 N Mg. of Methyl Bromide Sampling Time, Hours
AgNOr to Titrate
0 0. os
...
0.5 1 2
4 6
4.25 4.40 3.65 3.47 3.31 3.19
per Liter of Air 24.5 19.9 18.7 17.1 16.1 15.5
$18
16
14.9
14 0
bromide (24.5 mg. per liter) was placed in the fumigator and circulated with an electric fan. Samples were withdrawn by the described method a t 5 minutes, 30 minutes, and 1, 2, 4, and 6 hours. The results, shown in Figure 3, indicate that both adsorption and chemical reaction reduce the concentration of methyl bromide under these conditions; hence the seeming contradiction of Table I. ACKNOWLEDGMENT
The authors wish to thank D. L. Lindgren for suggesting the problem and for certain materials and assistance.
1
2 3 4 TIME, HOURS
5
6
7
Figure 3 LITERATURE CITED
(1) Busby and Drake, IND.ENG.CHEY.,ANAL.ED.,10, 390 (1938). (2) Chisholm and Koblitsky, I b i d . , 16, 638 (1944). (3) Glaser, Deut. 2.ges. gerichtl. M e d . , 12, 470 (1928). (4) Lewis, J. SOC.Chem., Ind., 64, 57 (1945). (5) Quayle, Hilgardia, 3, 220 (1928). (6) Stenger, Shrader, and Beshgetoor, IND. ENG.CHEW,ANAL.ED., 11, 121 (1939).
RECEIVED September 13, 1948.
Improvements in Microaeration Technique for Determination of Kjeldahl Nitrogen HARRY G . DAY, EILEEN BERNSTORF, AND R. T. HILL Indiana University, Bloomington, Ind.
THIS laboratory difficulty was experienced in obtaining I Nsatisfactory nitrogen recoveries with the microaeration method
of Sobel et al. (a). A study of the method has shown that it is re-
from known amounts of ammonium sulfate or from protein-free blood plasma filtrates, even with prolonged aeration a t room temperature or by increasing the aeration rate to the point where
liable and practical if larger amounts of alkali are used and if the aeration is carried out a t approximately 70" C. instead of room temperature as recommended by Sobel et al. In principle the latter is to be expected, because Dillingham ( 1 ) and others have stressed the importance of aeration temperature in analytical Kjeldahl nitrogen macro- and semimicromethods. In order to aerate the Kjeldahl digest at an elevated temperature and trap the displaced ammonia in boric acid a t a lower temperature, it is desirable to use a modified Sobel et al microaeration tube. The authors have constructed tubes similar to those used by Sobel et al., except that the side arm is at an angle of 45' with the inlet of the sealed-in bubbIer of the microaeration tube (Figure 1). The tubes are assembled in zigzag formation in a rack with the digestion tubes inside the bath and the receiving tubes outside the bath. The rack can be easily constructed by making four 90" folds in a rectangular piece of 2-mesh hardcloth cloth, so that the ends of the original rectangle join a t the base to clamp over the side of the bath. Short pieces of rubber tubing are used to complete the glass-to-glass connections between tubes, as in the Sobel method. It was found that nitrogen could not be completely recovered
Figure 1. Setup of Aeration Tubes
1291
V O L U M E 2 1 , NO. 1 0 , O C T O B E R 1 9 4 9
at 70 O C. The nitrogen recovered is approximately equal to the Table I. Comparison of Sobel and Modified Methods in Determination of Blood Plasma Nonprotein Nitrogen
Sample
Sobel Method .4dditional N found after adding more alkali“ and aerating 30 min. a t 70’ C. 25O C.
Nitrogen iound after aerating 30 min. a t Y
44.5 39.7 147.2 129.2 107.9 106.9
Modified Method Nitrogen Additional K found after found after aerating 30 aerating 30 min. a t min. longer 700 c. a t 70° C. Y
Y
Y
45.0 44.5 149.5 149.0 115.2 116.6
0 3.9
1.9 20.3 1.9 10.2
dzerence between the values obtained by the two methods. Various other data agree with the results in Table I. iMODIFIED PROCEDURE
The modified procedure for 10 to 200 micrograms of nitrogen is the same as described by Sobel et al. ( 2 , s )except that the aeration is carried out a t 70” C.; the alkali is prepared by adding 19 ml. of saturated sodium thiosulfate solution to 481 ml. of a saturated solution of sodium hydroxide; to replace water lost by evaporation, thereby avoiding salt precipitation, each digestion tube is rinsed down with 1.4 ml. instead of 1.0 ml. of mater; and 0.7 mi. of the alkali is added to each tube. Aeration is continued for 30 minutes a t the rate of approximately 10 liters per hour.
a Following this, alkali concentration equaled that used in modified method. I _ _
____
ACKNOW LEDGM EYT
_______
loss by foaming was imminent. This was the case even though rapid aeration was continued for as long as 2 hours. The effectiveness of raising the aeration temperature to 70’ is indicated by the data in Table I. The samples used were proteinfree plasma obtained from the blood of normal and adrenalectomized rabbits. Duplicate values agree well and the aeration is complete when the modified method is used. On the contrary, when the Sobel (2) method is used, the duplicate samples do not agree well and additional amounts of nitrogen are found if extra alkali is added and the aeration is continued for 30 minutes more
The research project from which this study arose was supported in part by funds from the Division of Research Grants and Fellowships, U. S. Public Health Service, and from the Graduate School of Indiana University, to R. T. Hill. LITERATURE CITED
(1) Dillingham, F. L., J . Am. Chem. SOC., 36, 1310 (1914). (2) Sobel, A . E., Hirrhman, A., and Besman, L., A N A L . CHEM.,19, 927 (1947). (3) Sobel, A. E., Mayer, -4.M., and Gottfried, S. P., J . B i d . Chem., 156, 355 (1944). RECEIVZD October 18, 1948.
Determination of Tin in Manganese Bronzes GEORGE NORWITZ’, THOMAS F. BOYD, AKD FREDA BACHTIGER Industrial Test Laboratory, Philadelphia Naval Shipyard, Philadelphia 1 2 , Pa.
I Tbronzes, IS stated in the literature that in the analysis of manganese tin cannot be quantitatively precipitated as metastannir acid on account of the interference of iron (8-4). The authors have found that if a 5-gram sample is taken, a good excess of nitric arid is present, and the solution is boiled a t least 0.5 hour, thP interference of iron can be entirely overcome. When the solutions were not boiled but were allowed to stand on a steam bath a t 95” C. for several hours in the usual manner, the recovery of tin was excellent for samples containing over 0,870 tin, but very poor (less than 45% recovery) for samples containing less than 0.5% tin. Inasmuch as over 95% of the manganese bronzes of commerce contain less than 0.5% tin, the importance of the method is readily seen. The procedure, which has now been in use in this laboratory for many months, has given astonishingly accurate and precise results even in the hands of routine operators. The filtrate from the metastannic acid precipitate can be uwd for the determination of copper and lead by diluting t o 200 ml., taking a 100-ml. aliquot, and electrolyzing the copper and lend. The lead dioxide deposit should be dissolved in nitric acid and the lead determined by the sulfate method. Determination of copper by the above procedures is especially advantageous for the analysis of copper in manganese bronzes containing less than 0.5% tin, for any unprecipitated tin would contaminate the copper deposit. PROCEDURE
Dissolve a &gram sample in a covered 600-ml. beaker with 50 ml. of 1 to 1 nitric acid b heating on the steam bath. Boil for a minute or two on the got plate t o drive off the oxides of nitrogen, add 50 ml. of hot water and some paper pulp, and boil for 30 minutes. During the boiling keep the volume between 80 and 100 mi. by the addition of hot water. Filter the solution while hot through an 11-cm. No. 44 Whatman filter paper, con1 Present address, Material Laboratory, New York Naval Shipyard, Brooklyn 9, N. Y.
taining some paper pulp, Swab the beaker and wash the precipitate n-ell with hot 1 nitric acid solution. Transfer the filter paper and precipitate to a 500-ml. Erlenmeyer flask and add 15 ml. of sulfuric acid, 5 ml. of perchloric acid (70%), and 10 ml. of nitric ‘acid. Evaporate to strong fumes of sulfuric acid. Allow to cool, add 200 ml. of water and 75 ml. of hydrochloric acid, and reduce the tin with antimony trichloride and lead in the customary manner (1). RESULTS
The results obtained by the authors on three representative manganese bronzes are shown in Table I.
Table I. Determination of Tin
a
Sample
Sn Present
Sn Found
70
%
62b
% 0.97“
Fe Present
0.82
1
0.27b
2
0.10b
0.97 0.98 0.97 0.27 0.27 0.26 0.10 0.09 0.10
1.32 1.20
National Bureau of Standards certified value. Average of three results by umpire A.S.T.M. method (1).
LITERATURE CITED
(1) Am. SOC.Testing Materials, Philadelphia, Pa., “A.S.T.M. Methods of Chemical Analysis of Metals,” p. 187, 1946. (2) Hillebrand, W. F., and Lundell, G . E. F., “Applied Inorganic Analysis,” p. 236, New York, John Wiley & Sons, 1944. (3) Lundell, G. E. F., and Scherrer, J. A., J . Ind. Eng. Chem., 14, 426-9 (1922).
(4)Scott, W. W., “Standard Methods of Chemical Analysis,” Vol. 11,p. 1353, New York, D. Van Nostrand Co., 1939. RECEIVED July 7, 1948. The opinions expressed in this article are those of the authors and are not to be construed as representing the official views of the Navy Department.
