‘42
Vol. 4, No. 1
ANALYTICAL EDITION
writer. and dctermincd by the distillation method. It is tliought, therefore, that tlie results of the direct-titration method arc more nearly correct. Table IV shows results of duplicate boron determinations and results ‘on diflercnt‘sized aliquots of the same water snniplc by the direcetitration method, using 2 grams of mannitol for each 100 cc. of sample. ‘rAnLE
SANPLE
400 11 2731 2831 3931 4231 4731 4831 4931 6031
Iv.
used that is subdividcd into 0.08 cc. and readings estimated to 0.01 cc. Table V shows typical recoveriea of boron when added to a water. All determinations were made on 600 cc. of,ssmple using 10 grams of mannitol. TABLE v.
IhPLICATE DETERMINATIONS OF BORON IN WATlrn SAMPLE8
SAMIV.E
(Comparison of reeulte on diRarerlt ~ N I O I I R ~ofS sample) AM+. OF AMT. OF AUT. OF SAMPLE IlORON SAYPLlE BORON SAMPLE BORON Cc. P. p . m. Cc. P . P. m. Cc. P . P. m, 600 0.83 200 0.84 100 0.82 200 0.72 100 0.72 0.78 500 0.79 600 500 0.75 600 0.74 1.05 600 1.07 600
...
600 600 600
500
1831 1891 433 A 433 A 433 A 433 A 433 A
...
3.06 3.05 3.34 1.21
0.06
250 250 600 225 225
!::2
2’110” :::;”0
6431 6331 91310 600 4.26 ZOO 0 Pacific Ocean at Ventura, Cdit.
3.10 3.06 3.30 1.17
0.68
4.27
225
1.16
:!:g 100
4.27
The smaller samples are about as accurate as the larger ones. This is mainly due to the @eater change Of pH which a given amount of alkali will cause in a sntall sample as compared with a large sample. For small samples, a buret should be
BORONWHENDETEHYINBD DIIIECT-TITRATION METHOD
RECOVERIES OF
IW
---BORON Added
ADDED Found
Rsoovsred
Mo.
Mo.
Mo
0
0.465
0 0.498 2.49 4.98
0.270 0 773 Y 767 6,303 10.270
0.600
0.080 I I
0.06
.
I%ORON
RECOVERED 96 .-
ibik
0:bi)b
ii:2
O:i64 2 488 6.034
09.0 100.9 100.3
I
o.uo1
This report is not intended to be s complete study of the method for determining boron here dcscribed. The procedure has been developed primarily for determining boron in waters, and for waters in this region it is entirely satiefactory. Lack of time prevents further investigation into its possibilities, but no reason for failure on more concentrated aqueous solutions is known.
LITERATURE CITED (1) Wilcox, L. V., IND.ENQ.CHBM.,Anal. Ed., 2, 358-01 (1930).
R E C ~ ~ VJUIY E D 28,1931.
Note on Micro-Dumas Method for Determination of Nitrogen RALPHT . K. CORN WELL,^ National Institute of Health, U.S. Public Health Service, Washinglon,D. C.
I
N ADAPTING the classical Dumas method for the determination of nitrogeu in organic substances to a scale suitable for microanalysis, Pregl originally obtained too large volumes of gas in the micronitrometer (8). This error he showed was caused by the formation of carbon monoxide, “due to a permanent disturbance of the equilibrium between carbon dioxide on the one hand and carbon monoxide and oxygen on the other, caused by the red-hot copper spiral.” Later Pregl (8) improved his method to overcome this error. Experience in teaching Pregl’s method at the University of Pittsburgh, inquiries which have come to this laboratory, and a search of the literature (1, 2, 4-7) all show that high results may still be obtained by this method. Since by using the following very slight modification of Pregl’s method practically theoretical figures have always been obtained, even by beginners, it seemed desirable to publish this note. Furthermore, the time required for the determination is appreciably shortened and no difficulty has been noted in getting “micro-bubbles” a t the end of the ’analysis, The directions given by Pregl (9) are followed exactly through the burning of the sample. The carbon dioxide is then turned on and the stopcock of the micronitrometer adjusted so that “one bubble rises per two seconds.” At the end of 5 minutes (during which time the portion of the tube containing the sample is reheatod), the flame of the long burner is tiirned down slightly (8). During the next 5 minutes the gas is alowIy turned off, 80 that a t the end of 10 minutes from the time of, starting the carbon dioxide, the 1
Prcwnt addreu, &rlrilr Induitriil Corp., Frmlrddnburl, VI.
gas for both burners is turned off completely. After 2 or 3 minutes the stopcock of the micronitrometer can be opened further and the bubbles allowed to rise a8 fast as possible. Here the only precaution necessary is to regulate the speed 80 that the bubbles do not go together and stop at the bottom of the graduated portion of the micronitrometer. In this manner various types of organic substances containing nitrogen have been analyzed successfully in this laboratory. The following are a few illustrations: NITROGEN DETERMINATIONS PER.CENTA0.
No. 1 2 3 4
SUBPRESSTANCE NITROQEH T E U P . luna
Mu.
Cc.
6.734 6.244 3.466 8.b60
0.284 0.261 0.255 0.266
C.
27 28
28 27
FonYuLA OF O F NXTROaBN S U D U T A N CTheory ~ Found
Mm.
760 750 780 757
CsHir01N 6.40 CIHIIOIN 6.40
CitHnOtNt CitHaOtNi
8.08 8.09
11.44 6.43 8.02 8-14
LITERATURE CITED (1) Bock, F., and Beaucourt, K., Mikrochsmie, 6, 69 (1920). (2) Dulmlcy, J. V., Be?., 50, 1710 (1917).
(3) Dubnky, J. V., “Dic Methoden der organieohen Chomie,” 2nd ed., Vol. I, p. 14’4, Houben-Weyl.
(4) Flsrrchontr&ger,B., Mikroahamie, 8, 1 (1930). (6) Halls, F., Zhid., 7, 202 (1029). (6) Hernler, F.,i%fikrochrmhPregl Faahhr., 151 (1929). (7) Lauer, W. M., and Sundls, C. S., Zbid., a35 (192Q). (8) Prod, F., “Quantitative Organic Mimndydr,” PP. 73-8, BlaWaton, 1924. (D) Prod, B.,Ibid., pp. 72-92,
R ~ C ~ I Y Jinurry BD 81, 1Q31. Publlrhed by permidun vf bbr aenrral of the U.8. Publlo H r l t h &rrioa,
l r m
