Dumas Nitrogen Determination on the Decimilligram Scale WOLFGANG J. KIRSTEN and BENJAMIN W. GRUNBAUMl lnrtitute o f M e d i c a l Chemistry, University o f Uppsala, Uppsala, Sweden
A procedure for the determination of nitrogen on the decimilligram scale using volatilization at high ternperature and combustion over nickel oxide is described. Its accuracy, which mainly appears to be determined by the weighing accuracy, is equal to that of the ordinary microproce~ures on the 5-mg. scale. oneoperator can carry Out lo in a '-hour working day. A procedure for the preparation of very pure carbon dioxide is given, and a few important points on the use of nickel oxide are discussed.
out the hack through capillary H (Figure 2), and sweeps out any atmospheric nitrogen which has been absorbed by the grease of joint D during the introduction of the sample. Furnace K (Figure is held at 10500 c. The foot, R, of the nitrometer is made of Lucite and filled with mercury. The nitrometer tubes are made of borosilicate glass and fit into the joints, S , of the foot. Joints A" are lubricated nrith silicone grease. The calibrated capillaries of the nitrometers have a volume of 120 pl. in a length of 300 mm. The funnel, AF, of the nitrometers is made of Lucite and cemented
~~
IRSTEX (2) has described a method for the Duni:Ls derei,mination of nitrogen which involves volatilization of the sample in carbon dioxide a t high temperature using the reactiou C COP 2CO and combustion of the gases ohtained over nickel oxide. The procedure provides for a complete combustion of the Pamples and avoids t,he errors arising from retention of nc-nitrogen in the combustion tube caused by forDat,ion of metaloxygen-nitrogen compounds. [Copper and nickel oxides ohLD tained hy heating their respective nitrates have been investig:itid by x-ray diffraction at the Institute of Chemistry of thip universitJ-. The samples gave exactly the same pattern as the ordinary oxides (9). This fact, together with the facts earlier known concerning these compounds (1, 2, 7 ) , make it probable that the metal-oxygen-nitrogen compounds are oxides in which variable numbers of oxygen atoms have been replaced by nitrogen a.toms.1 The high accuracy and simplicity of the new procedure made it interesting to try its applicability to the determination of nitrogen in very small samples. Figure 1. Setup for nitrogen determination on The original equipment (2) was modified only slightly in the decimilligram scale initial stages of this investigation. The diameters of the tubes .1. Back end of combustion tube, inner diameter G mm., outer 10 111111., wrre ahont half of those previously described. An ultramicro length 180 mm. B . Tube in which sample is yolatilized, diameters as 8 ,length 240 IIIIII. ,,loc~ification of the u-eight nitrometer described by ~ ~ ( , h , C. Side tube where carbon dioxide enters combustion tube, inner diameter 1 mm.. outer 8 nini., length 180 mm. SimollsonJ and Tashinian (') used' When a had Ground joint through which sample is introduced, widest diaineter D. been burned, most of the nitrogen was quickly swept out. Howof ground surface 12.5 m m . . length 20 nim. Score in joint D which a l l o w carbon dioxide t o pass into side tube E . ever, ,vhen blank determinations ~ v e r ecarried out,, blankp , hiah ". Female . ioint- cap joint~ D ~I.on ~ were immediately obtained. These high blanks decreased only F. -.rn G. Side tube on cap very slo~dy,even t,hough the apparatus was not opened after If. Capillary on joint cap F , diameter ea. 0.03 111111. 3lovable split-type furnace, held a t 1050° C., length 70 111111. combustion. When the blank was subtract,ed from the sample Wide part of combustion tube filled with nickel oxide, inner diaiiieter 8 mm., outer 12 mm., length 180 mm. reading, rather low results were obtained. An investigation df. Snlit-tvDe combustion furnace held a t 1000° C:., length 180 inin. showed that the silicone stopcock grease absorbed nitrogen in Split-Gpe heating furnace held a t 130' C . , length ca. 50 m m . 0. Hopcalite length of filling 10 nun. t,he apparatus and released it only very slowly. P. Capillary,' inner diameter 1 mm., outer diameter ea. 0 to 7 111111., length suitable for combustion stand used Vugreased joints and rubber connections have previously Sitrometer tubes, inner dianieter 17 111n 1 , outer 20 niiii., length ( 2 , 4 ) been found still less satisfactory than greased joints, so it 210 mrn. Foot of nitrometer made of Liicite w i q necessary t o reconstruct the apparatus to eliminate all Joints of nitrometer tubes: widest diameter of ground susface 18.8 mm.. length 20 mm. joints or other connections in places where the grease could pick Thin, flexibie copper tubing T. up nitrogen and give it off t o the carbon dioxide which passes into c, Pressure regulator, T-tube type n i t h glass tube connected t o copper tubing T with tapered standard joint lubricated with silicone the nitrometer. grease
+
~
E
''
g; 1'.
AB. AC. AD.
APPARATUS
The apparatus which resulted after some experiments is shown in Figures 1 and 2 and a photograph in Figure 3. The combustion tube consists of the empty parts, A and B (Figure l), divided by t,he side tube, C, and the wide part, L, filled with nickel oxide and held a t 1000" C. by furnace M . The narrower end, 0, is filled with Hopcalite. Capillary P has an inner diameter of 1 mm. and ends right in the joints, S , of the nitrometer tubes, Q. The rate of the carbon dioxide flow in the tube is regulated vith the T-tube type pressure regulator, U , which is filled with mercury, and the capillaq., ilR. A% small part of the carbon dioxide always passes
AE.
Tapered metal joint, widest diameter of gronnd surface 10 inni. Capillary fixed in joint V \\.it11 rubber tubing, diameter ca. 0.05 nini. Leveling bulbs for potassium hydroxide Surgical polyethylene tubing connection to leveling bulbs, inner diameter 3 mm. Canillarv of nitrometer, calibrated t o contain 120 +I. on length of 3'00 mm.
Lucite funnel cemented t o capillary of nitrometer Screws in funnel AF for holding rubber cord A H Rubber cord A K . Rubber stopper cemented into glass tube, A L , \?nth Kronig's glass cement A L , Glass tube A A ! . Ground tapered end of capillary A E AAV. Quartz wool Drying tube containing iodine adsorbed on carbon Rubber tubing holding capillarv H .4 s. Glass tube which prevents orifire of capillary H fro111 being contaminated with grease, etc. A T . Quartz rod
2:; AH.
2;:
___
Present address. Histocheniistry Laboratory, Department of Physiological Cheinistry. University of Minnesota. ;\Iinneapolis, Minn. 1
1806
V O L U M E 27, N O . 11, N O V E M B E R 1 9 5 5
7, Stockholm). It appears probable that the particle size of the nickel oxide is an important factor. The authors attempted in an earlier experiment to use nickel oxide from wire, hut the results were unsatisfactory, probably becauuse nickel, unlike copper, does not allow a free diffusion of oxygen through it, Also, finely divided nickel is pyrophoric, while compact nickel is extremely resistant to oxidation. Precipitated nickel oxide should, therefore, be used for the preparation of the granulated reagent aecording to (e). For the use in the iiltramicroprocedure, a granule size of about 20 to 30 mesh is most satisfactory.
S F & & D
P...
1807
F A R AS
Hopealite. The commercially available product is satisfactory Fine dust should be sieved off. Quartz wool, C.P.
5
Figure 2. Detail of Figure 1 See legend under Figure 1
to the tapered joint, AIM (Figurc 21, of the capillary with plastic cement. AK is rubber stopper which is cemented into the glass tube, AL, with Kranig's glass cement. It is held with the rubber cord, A H . In order to he able to use the two nitrometer tubes alternately, tho Lucite b o t , E, is mounted upon LZ mechanical manipulation device which allows one to raise it, move it sideward, and lower it %gain. The carbon dioxide used comes from B tank. The copper tube, 1' (Figure l ) , is welded to the reducing valve of the tank. Joint V is a long tapared metal joint lubricated with silicone grease. A D are polyethylene tubing connections to the leveling bulbs, AC. REAGENTS
Carbon Dioxide. Royer, Norton, iLnd Foster (8) recommended t,snk carbon dioxide from whith the top half has been hlown off. This method was tested, with irregular results. Experiments revealed that the quality of the remaining gas is unsatisfactory when the first half of the filling is blown off slowly, but that the ooalitv . . is .rood when the filling.is blown off cruiekly. . .. with a fully opeued valve. It appears important to lower the pressure sufficiently over the liquid carbon dioxide so that any entrapped nitrogen greatly expands and is blown off. Much of the remaining liquid is probably precipitated as solid carbon dioxide. I n order to obtain a quick lowering of the pressure and thereby decmai~ethe loss of enrban dioxide, the tube may be cooled to a low temperature hefore the blorvingoff process. T h e following procedure for the preparation of pure carbon dioxideis usedin thislaboratory: The tank containing 10 kg. of liquid m h o n dioxide is plaoed overnight in the freezing room a t -20' C. When it is removed, it is placed upright and the valve is a t once opened fully. The valve is kept open until the sound of the escaping gas indicates that the pressure inside the tank has greatly decreased. The valve is then closed and the gas is ready for use. -4bout 5 kg. of gas have been blown off. The remaining @as is sufficient for about 7 to 10 months of daily use in nitrogen determinations acoording to the procedure (e). No investigation has been made to determine whether satisfactory results could be maintained if less gas were blown off. T h e microbubbles obtained with this gas in the present procedure seem to disappear completely. Even in the ultramieronitrometer no detectable blank is obtained during a single analysis. Nickel Oxide. Approximately 15 setups employing nickel oxide in nitrogen determination are in use in Sweden. Several similar setups are in use in other countries. Most invest,igators report that theRe apparat,us give complete combustion without formation of methane. Parks, Bastin, Aguzi, arid Brooks ( 6 ) report incomplete combustion with a nickel oxide obtained b y oxidation of nickel powder. In this laboratory precipitated nickelous oxide powder has been used for the preparation of the grznulated nickel oxide according to the description given previously (8). Most of the users of the Dumas apparatus in Sweden have used the granulated nickelous oxide prepared in the same manner which is supplied by Nicroma (Klara Viistra Kyrkagata
ire 3.
Equipment for nitrogen determination, with iipulator for nitrometers mounted upon automatic combustion carriage
.ratas is available from Nioroma, Klara. Vastra Kyrkogata 7, Stookholin Swede"
A s s i u m hydroxide, 50% solution. About 2 liters me pred and allowed to stand until any precipitations have settled. pareN The n the potassium hydroxide is filtered through a sintered-glass filtelr. The amount used in every nitrometer is mixed by shaking withI a few drops of isomyl alcohol before it is introduced ( 5 ) . ADJUSTING APPARATUS
The apparatus is assembled as shown in Figures 1, 2,. and 3 . The Hopcalite is introduced into the tube through a long glass tub6> in order to avoid contamination of the other parts of the cambustion tube. The nickel oxide is glowed in a flow of oxygen just before filling it into the tube. The capillaries, A B and H , and the carbon dioxide pressure are adjusted to permit a slow Row back through H. T h e rate of the flow into the nitrometers shotild he adjusted so that the big gas bubbles obtained in an ordinary size combustion begin to decrease markedly 5 minutes after the arrival of furnace K to furnace M , or about 12 minutes after the beginning of the combustion. A combustion, carried out according to the procedure given below, is made to determine the necessary sweeping time. The blank is then determined for the obtained time. In the present work the blank obtained was aero PROCEDURE
The sample is weighed out in a.smsll platinum boat. Joint D is 01iened and the boat is introduced with a glass rod into tube A , abaiIt 3 em. from side tube C. The sample and the glass rod ?emrin there for 5 minutes. The sample is then slowly pushed
ANALYTICAL CHEMISTRY
1808 into the middle of tube B. The glass rod is slowly drawn out and joint D is put on so that the gas passes out through side tube G, for 3 minutes. D is then turned so that the side tube is closed. Gas bubbles should now appear in the nitrometer. If no gas bubbles appear, the carbon dioxide pressure is increased for a moment by raising the leveling bulb of the pressure regulator, U . When the bubbles appear, the ordinary pressure is restored. Furnace K is now drawn over the tube and the motor is switched on. The next sample can now be weighed out. After 30 minutes, joint D is opened, the boat is taken out, and the next sample is introduced. The nitrometer is moved so that the gas passes into the other tube and the gas collected in the nitrometer is moved to a suitable place for reading by loosening stopper A K . If there are several bubbles of gas in the capillary, the leveling bulb of the nitrometer is lowered and potassium hydroxide is allowed to flow doxm by loosening stopper A K . The gas bubbles and the potassium hydroxide move down together and are combined a t the place where capillary A E widens. The leveling bulb is then raised again and the gas bubble is moved back into the capillary for reading. In the few instances when the bubbles do not combine, a small amount of mercury from R can be pipetted into the funnel and drawn down into the capillary. The bubbles will then combine below the mercury. The mercury is then allowed to fall down into the wide part of the nitrometer and the gas bubble is moved up again. There must be sufficient potassium hydroxide in the funnel to fill the capillary after the mercury falls. Care must be taken that no gas bubbles adhere t o the mercury after its introduction into the funnel. Such gas bubbles can be removed with a thin glass rod or a wire. The gas bubble now remains in the nitrometer for 30 minutes to drain. The next combustion is, in the meantime, carried out using the other nitrometer tube. The carbon dioxide bubbles which leave capillary P of the combustion tube do not pass up into the potassium hydroxide one by one, but they are collected below the upper surface of the mercury as a very big bubble which then breaks up and passes into the potassium hydroxide. This avoids all risk of the sticking of nitrogen bubbles to the mercury surface. EXPERIMENTAL RESULTS
A series of analyses was carried out with this procedure. The necessary correction for the film of potassium hydroxide and the necessary waiting time for the drainage were unknown. After
_Table I. Influence of Drainage Time on Volume of h-itrogen Read in Capillary Nitrometer Volume of Nz Read, pl.
Minutes 0 5 10 15 20 25 30 40
g::
9”;;
ig;:
?$”: ;$:!
3.0 3.0
8.9 8.9 8.9 8.9 8.9
26.0 26.0 25.9 25.9
35.8 35.7 35.6 35.5 35.5 35.5
..
3.0
..
..
23.9
..
63.8 63.7 63.6 63.4 63.3 63.3
the combustion, the gas bubble was drawn into the capillary so that the upper meniscus was situated a t the line for 10 A. The position of the lon-er meniscus was then read after several intervals of time. The results of the readings of some analyses, given in Table I, show that small volumes of nitrogen can be read almost inimediately after combustion, while larger volumes require a considerable time for drainage. The 30 minutes for drainage reported abo1.e was chosen as a safe period of time under any circumstances. Analyses have been carried out with up to 0.5 mg. of lauric acid. The analyses gave absolutely no nitrogen reading. It appeared that the most suitable procedure for the correction of the results for all systematical errors was to calculate the nitrogen results obtained without any correction and to cnlculate the average relative deviation according t o the formula: Average % ielative deviation =
( % N found - % N calcd.) X 100 92 N calcd. n in which n is the number of analyses carried out. The result was +2.5%, This average relative deviation contains all systematical errors involved in the method, and it was subtracted from the “volume of nitrogen read” given in Table 11. The values given in the column “volume of nitrogen corrected” were thus obtained. The final results 11-ere then calculated with these values, using the nomograph published h y Koch, Sinionson, and Tashinian (3). The standard deviation of the results is 0.22 absolute %, which is not more than ivhat is considered satisfactory for the ordinary Dumas method on the 5-mg. scale. It appeared interesting to investigate the nature of the empiric correction obtained, 2.5 relative %. The corrections generally appliedin the Dumas micro determination are a constant blank, a correction of 0.3% of the volume read for the w t e r vapor tension over the potassium hydroxide solut’ion ( I O ) and a correction of 0.5% of the volume read for the volume of the potassium hydroxide film on the inner surface of the nitrometer ( I O ) . In the method reported the constant blank is zero. The tension of the water vapor must be the same as in the ordinary micromethod. However, in the ultramicronitrometer used, the ratio
96.9 96.8 96.2 95.7 95.7 95.7
inner glass surface of capillary
R =
volume of capillary
Table 11. dnalyses of Nitrogen-Containing Compounds
NO.
Compound
1
p-Nitrobennoic acid p-Nitrobennoic acid Cyanacetamide 3-Nitrophthalic acid Behenamide Cyanacetamide Cystine Taurine Taurine Taurine p-Nitrobenzoic acid
2 3 4 6 5 7 8 9 11 10
W t . of Sample,
12 dl-Serine 13 4-Amino, 5-bromo, 4-methylpyrimidine 14 Behenamide 1 5 3-Nitrophthalic acid 16 Cyanacetamide 1 7 Cystine 18 p-Nitrobennoic acid 19 Serine 20 Taurine 21 p-h’itrobenmoic acid 22 p-Nitrobenzoic acid Standard deviation, c = 0.22 absolute
~-
y
172 274 106 212 274 94 106 206 136 224 115
Corrected Barometer Reading, Temp., M m . Hg C. 29 754 754 28 754 27 757 28 757 757 29 757 30 757 28 7 59 759
Deriation,
10.7 19.9 13.1
4itrogen Content, % Found Calcd. 3o 8,38 8.32 8.38 32.89 3 3 . 3 3 6.57 6.64 3$!$ 11.39 1 1 . 6 6 10.87 1 1 . 2 0 1 0 . 8 9 11.20
38.7 22.9
32.8 22.3
13.26 13.33 22.58 12.34
-0.07 fO.24
cor-
Read 13,3 20.7 31.6 12.6
rected 13,0 20.2 30.8 12.3
11.0 20.4 13.4
8i:: ‘93:;
759 759
85 178 135 248 362 288 518 175 241
761 761 762 763 763
30 28 31
l&; 40.8 25.8 27.5
39.8 25.1 26.8
763 759
30 29
13.3 18.4
13.0 17.9
~-
gi
::
i::;
3i:,”g
% +O
12
-0
-0.44 -0.07 -0.27 -0.33 -0.31
2i;i lk:i; lk;gi $::!
278 111
Yo.
31 31
Volume of Nitrogen,
!:;:
l:;i
z::
33 31 3 3 . 3 3 11.53 11.66 8.36 8.38
i;:;:
8.42 8.40
8.38 8.38
-0.02 -0.13 -0.02
1;;;:
tO.04
+0.02
is about five times that of an ordinary micronitrometer. A necessary correction of 5 X 0.5% = 2.5% of the volume read should therefore be expected for the volume of the potassium hydroxide film. This givesa total correction of 2.8 relative 7& which agrees very well with the 2.5% experimentally obtained. The difference of 0.3Y0 lies beyond the limits of accuracy with which the theoretical calculation of the correction can be made. It appears therefore, that the correction of 2.5% is also theoretically fully justified. It also appeared interesting to calculate the standard weighing error which would cause the standard deviation of 0.22% obtained for the analyses given in Table 11. The calculationshowed
V O L U M E 2 7 , NO. 11, NOVEMBER 1 9 5 5 that a standard error of 3.5 y in the weight of the samples would cause this deviation. As every sample weight is the difference of two weighings it appears that not even the best tested balances could be expected t o give much better results (11). The Ainsworth balance Model F.D.J. on which the weighings were carried out has been in daily use in the laboratory since 1948. So, if it were assumed that the errors in the determinations were caused by the 11 eighing errors alone-which of course is impossible-the results would still be a good proof of the excellent performance of this balance. The method is so fast and convenient that one operator easily and rvithout having to hurry can carry out 10 complete analyses, including weighing, running the analysis, and calculating the results, in a 7-hour working day. Experiments t o apply the method to the determination of submicrograni amounts of nitrogen b y the use of an ultramicroba1anc.e and finer nitrometers are planned.
1809 with constructional designs, and to E. Sepp for drawing the figures. The work was made possible b y grantsJrom the Swedish Medical Research Council to E. Stenhagen, G. Agren, and IT-.Kirsten. LITERATURE CITED
D u d , Clement, Anal. Chim.Acta, 2, 438 ( 1 9 4 8 ) . Kirsten, W. J., Mikrochemie, 40, 1 2 1 ( 1 9 5 2 ) . (3) Koch, C. W., Simonson, T. K., and Tashinian, V. H., A s ~ L . CHEM.,21, 1133 (1949). (4) Lindner, Josef, “hlikromassnalytische Bestimmung des Kohlenstoffes und Wasserstoffes mit grundlegender Behandlung der Fehlerquellen in der Elementaranalyse,” Verlag Chemie, Berlin, 1935. (5) Pagel, H. .1.,and Oita, I. J.. d s i ~CHEM., . 24, 7 5 6 (1952). 16) Parks, T. D., Bastin, E. L., ..lgaeei, E. J., and Brooks, F. R.,
(1) (2)
I b i d . , 26, 229 (1954). ( T ) Richards, Th. IT., 2. anorg. Chem., 1, 187 (1892). (8) Royer, G. L., Sorton, A. R., and Foster, F.J., IND. ENG.CHEM., ANAL.ED.. 14. 79 (1942). I
_
,
Schonberg, N.E., Soderfors Bruk, private communication. (10) Trautz, 0. P., Mikrochemie. 9, 300 ( 1 9 3 1 ) . (11) Waber, J. T., and Sturdy, G. E., .%SAL. C H m r . , 26, 1177 (1954) (9)
ACKNOW LEDG-M EYT
The authors are very indebted t o E. Stenhagen and G .tgren for their interest in the work, to A. Edenstrom for n-ktance
R E C E I V E for D review October 20, 1954.
Accepted April 23, 1955
Complexometric Determination of Sulfide PEKKA KlVALO Department o f Chemistry, lnstitute o f Technology, Helsinki, Finland
A complexometric method for the determination of sulfide ion is described. The method is hased on the observation that an alkaline sulfide solution added to a neutral or slightly acid solution containing an excess of metal perchlorate gives a stoichiometric precipitate with copper hut not with zinc or cadmium.
T
HE modern volumetric methods of analysis employing ethylenediaminetetraacetic acid [( ethy1enedinitro)tetraacetic acid, EDTA] and related compounds are characterized by a high degree of accuracy and also by the fact’ that the t’iter of the standard solutions is extraordinarily stable. I n seeking a complexometric method for the determination of sulfide ion in which the principle of difference could be used, the following results were discovered. K h e n the alkaline sulfide solution to be analyzed was added to a neutral or slightly acid solution containing an excess of a metal perchlorate, zinc and cadmium gave colloidal precipitates and erroneous results. The cupric ion, on the other hand, gave a stoichiometric precipitat.e of copper sulfide which is knon-n to he extremely slightly soluble ( 2 ) and was easily filterable. The sulfide solution to be analyzed ivas prepared from analytical grade sodiuni sulfide nonahydrate using oxygen-free water, and n-as kept under hydrogen atmosphere. Samples were taken by means of a buret connected to the sulfide flask and the standardization was done iodometrically ( 3 , 4). The titration of the standard solution and the excess of copper was per-
formed according to Flaschka ( 1 ) . The reagent solutions were of the order of 0.05M. Table I lists a few results obtained with the iodometric and the new methods. From the results obtained one can judge that the new method IS as accurate as the classical iodometric one. Hoivever, in addition to the advantages mentioned above, the new method is also characterized by the fact that, in the medium used, the sulfide only will be precipitated as copper sulfide, leaving the sulfite and thiosulfite ions in the filtrate. -4s is knovm, iodine oxidizes all of these ions. -4possible disproportionation of the cupric sulfide into cuprous sulfide and sulfur obviously does not affect the final result. REAGENTS
Disodium salt of EDTA (Compleuon 111),0.05X. Cupric perchlorate, 0.05Alf. .Ammonia, 1-11, hcetate buffei (0.67M acetic acid 0.33.11 sodium acetate), 1.11. Saturated water solution of rniiinide.
+
PROCEDURE
Pipet 25 ml. of the copper solution into a 150-ml. Erlenmeyer flask, rinse it down with little water, and add 15 ml. of the acetate Iiuffer. Add slo~vlythe sodium sulfide solution (10 to 40 ml. of :in approximately 0.02121 solution or equivalent), constantly shaking the flask. Filter off the copper sulfide using a fineporosity (G4) fritted-glass funnel and a 250-ml. suction flask. Wash with 20 to 30 ml. of hot water. h d d a few milliliters of ammonia to the filtrate until the deep blue copper solution is vlear, and dilute to 100 to 120 ml. Add 3 to 6 drops of murexide iiidicator and titrate to a reddish violet color. ACKNOWLEDGMENT
Table I. Standardization of Sodium Sulfide Solution Using Iodometric and Complexometrie 3Iethods (All reagents approximately 0 . 0 5 3 4 ) 12,
hI1. 25 25
25 25 50
Na&,
MI. 10 10 15 20 40
Molarity of NarS Found
0.01710 0.01710 0.01711 0 . 0 1696 O.OlB9G A r . 0.01704
Cu, 111. 25 25 23 25 25
Sa&,
MI. 10 15 20 30 40
The autbor is indebted to Professor Anders Ringboni, Abo ;Ikadenii, Bbo, Finland, for the use of laboratory facilities.
Molarity of Na?S Found 0.01700 0.01696 0.01709 O.Olfi95 0.01700
.Ir.0.01700
LITERATURE CITED (1) (2)
Flaschka, H., Mikrochemie, 39, 38 (1952). Goates, J. R., Gordon, 31. B., and Faux, S.D., J . A m . Chem.
(3) (4)
Kolthoff, I. 31., 2. anal. Chern., 60, 451 (1921). Scott, W. W., ”Standard Methods of Chemical Ana1yi;is.’’ 5th ed., p. 2183, Van Kostrand, Sew York, 1947.
Soc., 74, 835 ( 1 9 5 2 ) .
R E C E I V Efor D reyiew S o v e m b e r 18, 1954.
Accepted M a y 3 1 , 1955,
