is likely t o aggravate the formation of triiodide. ACKNOWLEDGMENT
The author is indebted to the Research Gorp* for the purchase Of the Beckman DU spectrophotometer and to E. I. du Pont de Nemours & Go., Inc. for the grant to the department, with part of which the silica cuvettes used in the investigation were purchased.
LITERATURE CITED
( I ) Allen, T. L., Keefer, R. M., J . .4m. Chem. SOC.77, 2957 (1955). ( 2 ) Awtrey, A. D., Connick, R. E., Ibid., 73, 1842 (1951). ( 3 ) Ibid., p. 4546. (4) Bell, R. P., Gelles, E., J . Chem. SOC. 1951, 2734. (5) Bower, J. G., Scott, R. L., J. Am. Chem. SOC.75, 3583 (1953). (6) Custer, J., Natelson, S., ANAL. CHEM.21, 1005 (1949). (7) Good, M. L.. Edwards. R. R., J.
lnprg. and Nuclear Chem. 2, 196 (1956). ( 8 ) Katzin, L. I., J . Chem. Phys. 2 1 , 490 (1953). ( 9 ) Latimer, W. M., “Oxidation Potentials,” 2nd ed., p. 63, PrenticeHall, New York, 1952. (10) Murray, H. D., J. Chem. SOC.1925, 882. ( 1 1 ) MGeFs, 0. E., Kennedy, J. W., ,I 9 m . Chem. SOC.72, 897 (1950).
RECEIVED for review October 17, 1956. Accepted January 16, 1957.
Application of Thermistor Bridge Method to Determination of Water in Solids R. M. ENGELBRECHT and SAM DREXLER Research Department, lion Oil Division, Monsanto Chemical Co., El Dorado, Ark.
b The thermistor bridge method has been applied to the determination of
E
moisture in ammonium nitrate.
a
040
--
5
D
investigation of the determination of moisture in ammonium nitrate ( I ) , a procedure was developed which uses the thermistor bridge-calcium hydride method ( 2 ) . It is believed that the method described here could be used to determine the free water content, as distinguished from the water of hydration or crystallization, of numerous materials. A preliminary study of the removal of moisture from ammonium nitrate with a stream of dry nitrogen mas made to determine the feasibility of the method. The results shown in Figures 1 and 2 were obtained by passing dry nitrogen a t room temperature for 10 minutes through a Schwartz tube containing the sample into a weighed Schlvartz tube containing phosphorus pentoxide. The difference between the initial and final weighing of the phosphorus pentoxide tube, divided by the sample weight, was calculated as the
d -o-
D
2 2
-
0
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0 3 0 ~
,
--
-
---
a/--
U
URING
.
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0
0
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P
020.
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-
:=I
moisture content. These results were plotted against the moisture values obtained by the Karl Fischer titration. Moisture is not completely removed by the dry nitrogen method. However, the amount removed in 10 minutes is indicative of the moisture content of the sample; this is established from the linear
ii B
C
D
D -
Time study of
relationship, shown in Figure 1, between the two methods. The dotted lines are placed 0.05 unit on either side of the calibration line; all points are within these limits. Figure 2 gives the results of a time study which determined the 10-minute gas flow period. A differentiation may be made a t the 4-, 6,and
n
- C
Figure 2.
dry nitrogen method
-
- NITROGEN SUPPLY
- MERCJRY SAFETY - FLOW M E T E R - D R Y I N G COLUMN
VALVE
E - SCHWARTZ TUBE FOR SAMPLE F THERMISTOR BRIDGE REACTION VESSEL
-
Figure 3.
%
MOISTURE
(KARL FISCHER)
Figure 1. Linear relationship between Karl Fischer and dry nitrogen methods
1 100
Reaction train
ANALYTICAL CHEMISTRY
Figure 4. Calibration curve for thermistor bridge
0
01
0.2 %
03
0.4
MOISTURE
0.5
0.6
10-minute levels relative to the moisture content of the sample. EXPERIMENTAL M E T H O D A N D RESULTS
Figure 3 s h o w the reaction train used for the preliminary experiments and for the thermistor bridge-calcium hydride method. The Schwartz tube with the phosphorus pentoxide was replaced with a thermistor cell. The cell and measuring circuit were like those described by Harris and Nash ( 2 ) . Commercial tank nitrogen, dried with Drierite, was used throughout. A uniform flow rate was used for all experiments; this should be adjusted so that it is rapid enough for quick removal of moisture, but not so rapid as to disrupt the calcium hydride charge in the reaction chamber.
The bridge circuit is balanced initially by passing the dry nitrogen gas through the thermistor vessel a t ambient temperature. The resistance of the decade box is recorded as the initial reading when the galvanometer is at zero. For determination of moisture in ammonium nitrate, the nitrogen is passed first through the test sample and then through the thermistor vessel. The maximum deviation in resistance from the initial decade box setting is recorded. For the work reported, this maximum deviation is related to the moisture content of the ammonium nitrate. Figure 4 shows the calibration curve obtained with the thermistor bridge data for the determination of moisture in ammonium nitrate. The moisture values for the test samples were de-
termined by the Karl Fischer titration. All points are within 0.05 unit, as denoted by the dashed line. The sensitivity of the method is good; for a 0.1% change in moisture content there is about a 110-ohm change in resistance. The time for an analysis is from 6 to 10 minutes, depending on when the maximum change in resistance takes place. The apparatus is easily assembled and cost of equipment is nominal. LITERATURE CITED
( I ) Engelbrecht, R. M., Drexler, Sam, McCov. F. A.. J . Aar. Food ChenL. 4,
786"(1956). '
(2) Harris, F. E., Nash, L. K., ANAL. CHEM.23, 736 (1951).
RECEIVEDfor review October 8, 1956. Accepted January 14,1957.
Spectrophotometric Determination of Boron in High-Temperature Alloys by Quinalizarin Method A. H. JONES Research Staff, General Motors Corp., Detroit, Mich. Boron in high-temperature aHoys can b e determined spectrophotometrically in the range from 0.01 to 0.1 0% by using the characteristic color of the boron-quinalizarin complex in strong No separations are sulfuric acid. necessary, as extraneous absorption due to colored ions is compensated. Titanium interference, which was revealed b y this investigation, might prove serious a t very low levels of boron concentration, but can b e corrected if the titanium content of the alloy is known. Only concentrated sulfuric acid is used to obtain proper acid concentration. Titration and subsequent adjustment of the concentration are not necessary.
B
has been determined in aluminum-silicon alloys (4)and soils and plants (1) by visual comparison of the color formed when quinalizarin and boron react in strong sulfuric acid. Photometric measurement has been applied to the estimation of boron in plant tissue ( 2 ) and corrosion-resistant steels ( 5 ) , also with quinalizarin as the reagent. In the last instance, iron was removed from a solution of the sample by means of sodium hydroxide precipitation. In this investigation an attempt was made t o adapt the reaction to the determination of boron in high-temperature alloys in the range of 0.01 to 0.10% by using the objective spectrophotometric approach. This might permit ORON
accurate measurement of the colored complex in the presence of highly colored ions such as those formed by chromium, nickel, and cobalt, and thus eliminate the need for their removal. Smith ( 4 ) states that none of the common metals spoil the test, and Berger and Truog (1) state that the only known substance that is similar to boric acid in causing a color change with quinalizarin is germanic acid. The method of Berger and Truog was applied t o low alloy steels with no separations (3). Complete solution of the sample is accomplished by fusing fine chips with sodium peroxide in an iron crucible and acidifying a water leach of the melt with sulfuric acid. EXPERIMENTAL
Special Apparatus. Beakers, storage bottles, Erlenmeyer flasks, and condensers made of boron-free glass are available commercially, and are recommended for use wherever possible. The Erlenmeyer flasks and reflux condensers should be equipped mith ground-glass joints. Glass-stoppered, 2-ounce bottles made of soft glass are used for color development. The Beckman Model DU spectrophotometer with 5-cm. cells was used for this investigation. Reagents. Sodium peroxide, reagent grade. Sulfuric acid, c.P., spwific gravity, 1.84. (Some brands of sulfuric acid give a very high blank and should not be used. Those from Du Pont
and Bakm BE Adamson are satisfactory.) Sodium sulfite, c.P., anhydrous. Quinalizarin stock solution. Dissolve 120.0 mg. of quinalizarin in 1 liter of sulfuric acid. This solution is stable indefinitely if kept free from water. Quinalizarin reagent solution. Dilute 25.00 ml. of the stock solution to 500 ml. nith sulfuric acid and mix. Standard boron solution. Dissolve 285.8 mg. of boric acid in water and dilute to 500 ml.; contains 100.0 y of boron per ml. Standard titanium solution. Transfer 1.657 grams of titanium dioxide (KBS standard sample 154a, dried a t 105' C. for 2 hours) to a 500-ml. Erlenmeyer flask, add 10 grams of ammonium sulfate and 22.0 ml. of sulfuric acid, and heat until all the titanium dioxide is dissolved. Cool and rapidly pour the solution into 450 ml. of cool water which is vigorously stirred. Rinse the flask with sulfuric acid (5 to 95). Transfer the solution to a 500-ml. volumetric flask, cool to room temperature, dilute to volume, and mix. This solution contains 2.00 mg. of titanium per ml. Calibration Solutions. Transfer 140 ml. of water t o each of five 200-ml. volumetric flasks. Immerse the flasks in cold water t o prevent breakage due t o thermal shock, add 40.0 ml. of sulfuric acid with swirling and cool to room temperature. For evaluation of the titanium interference, pipet 50.00 ml. of standard titanium solution into each of five 200-ml. volumetric flasks. Add 90 ml. of water and mix by sm-irling. VOL. 29, NO. 7, JULY 1957
1101
