144
ANALYTICAL CHEMISTRY Table 11. Water Content of Cellophane
Sample
Water,
NO.
%
1
2.70 2.76 2.51 2.71 2.68 2.53 2.53 2.45 7.17 7.12 7.11 6.97
2 3 4 3
6
.\Iean, 7% 2.73
Sample NO.
7
2.61
8
2.60
9
2.49
10
7.14
11
Water,
Mean,
6.04 5.94 7.35 7.47 5.90 6.02 6.83 6.90 6.29 6.35
5.99
75
% 7.41 5.96 G.86
6.32
7.04
Table 111. Comparison of Data Color Comparator Water, Sample No.
1 2 3 4
%
(av. of 4 values) 3.9 6.1
Av. deviation izO.17 0 10.03 0 4v. 1 0 . 0 5
2:;
Electronic Titrator R'ater,
%
av. deviation 14.0 0 11,4 0 11.3
%
(av.of 4 values) 4.0 5.7 5.1 5.1
Av. deviation io.11 10.04 10.08 +0.17 10.10
R
.
av deviation 14.4 12.8 14.1 18.6 15.0
deviation from the mean was 0.1% and in the majoiity of cases measurements within O.O6Q/, of the mean were easily obtainable. I n order to compare the accuracy of measurement possible n-ith the color comparator with that obtainable on a commercially available electronic titrator, specimens of the same cellophane were analyzed on each of these types of instrument. Four separate samples were tested, and four observations were made on each sample using both instruments. It is readily seen from Table I11 that the results when using the comparator were equivalent to those obtained using the electronic titrator. The maximum deviation from the mean for the color comparator of 1 0 . 1 7 % vater and the average deviation from the mean of *0.05'% water or about *1.3% compare favorably with a maximum deviation from the mean of 1 0 . 1 0 % water or &5.0yo for the electronic titrator. Samples 2 and 4 for the color comparator data show zero deviation. This is not usual, but may occur with a small number of samples. I n a majority of analyses, a reproducibility of =k2% can be expected. ACKNOWLEDGMENT
The authors express appreciation to P. 11. Iiampmeger for assistance in preparing this paper, and t o the Olin Mathieson Chemical Corp. for permission to publish. LITERATURE CITED
(1) rllmy, E. G., Griffin, W. C., and Wilcox. C. S., IND. ESG. CHEM., ANAL.ED. 12, 392 (1940). (2) Fischer, E., Angeu. Chem. 64, 592 (19,52). ( 3 ) Frediani, H. A , , ANAL.CHEM.24, 1126-8 (1952). (4) Whittum, J. B., Ibid., 23, 209 (1951). PRESENTED before the Pittsbiirgh Conference on .4nalytical Chemistry and Bpplied Spectroscopy, Pittsburgh, Pa.. 1955.
great value t o the authors. Hon-ever, in the course of the research a t this laborator>- it hrcanie necessary t o determine the free amino nitrogen in wool (B), potato granules (I), and other solid materials such as poultry meat, and feathers. Wool and other fibrous materials could not be introduced int,o the reaction chamber of the Van Si!-ke-Sei11 apparatus. There was great difficulty and loss of many samples in the introduction of potato granulrs and similar materials into the apparatus. There was need for a larger opening into the reaction chamber without alteration of the moothly o p e r a t i n g s t o p c o c k reservoir arrangement of the conventional apparatus. Therefore, the reaction chamber was modified by the use of a S 35/25 ball joint as shown in the diagram. The chamber was constructed t o have the same length, volume, stopcock-reservoir arrangement, and calibration as the conventional apparatus available commercially. The chamber can be mounted with split rubber stoppers in the conventional apparatus by omitting the jacket. Wool and other solid materials could be easily introduced into this modified reaction chamber. Of almost equal importance was the ease with which the apparatus could be cleaned during the analysis of the Eample.
w
OPERATION
The mercury is lowered below the ball joint and the upper section of the chamber is removed. The sample, 5 ml. of Figure 1 distilled n-ater, and 1 ml. of glacial acetic acid are introduced into the lon-er section of the chamber. The ball joint is carefully lubricated. the chamber is assembled to f0rm.a vacuum seal, and the hall joint is secured with a clamp (not shown in Figure 1). T h e standard reaction of the sample with nitrite and the transfer of the reaction gases to the Hempel pipet are carried out as described by Van Slyke (5'). While the nitrogen is in the Hempel pipet the mercury is lowered below the ball joint, the reaction chamber is opened, and the sample residue is removed from the loner section of the chamber by suction. Water is added, and scrubbing with a rubber policeman is applied as needed. The upper section of the chamber can be cleaned in any suitable manner. ;ifter cleaning, the hall joint is lubricated and the reaction chamber is assembled as before. The analysis is completed as descriheti h!- \'an Slyke (3). The discharge tube, A , is included in the modified apparatus, so that it can be used in the manner described by \-an Slyke ( 3 ) for the analysis of samples that do not require opening of the hall joint.
Van Slyke Manometric Apparatus Modified for Determination of Free Amino Nitrogen in Solid Samples Kenneth T. Williams and Marion C. Long, Western Utilization Research Branch, Agricultural Research Service, U. S. Department of Agriculture, Albany 10, Calif.
apparatus described by Van Slyke and h-eill (4)and its use for the determination of amino nitrogen ( 3 )have been of HE
T
LITERATURE CITED
(1) Hendel, C. E., Burr, H. K., and Boggs, 11.l f . , G. S. Dept. -%gr., Western Regional Research Laboratory, Albany, Calif.,
AIC-303, 1951. (2) Jones, W. H., and Lundgren, H. P., Textile Research J . 21, 20-9
(1951). (3) Van Slyke, D. D., Jr., J . Biol. Chem. 83, 42547 (1929). (4) Tan Slyke, D. D., and Seill, J. AI., Ibid.. 61, 523-73 (1924).
