DENSITYOF LLQUID TzO
147
The Density of Liquid T,O1
by Maxwell Goldblatt Uniaersity o j Calijornia, Los Alamos Scientific Laboratory, Loe Alamos, NEWMexico (Received August 16, 1988)
~~~
The density of 99.30 mole % TzO was determined from 5 to 54" to h0.01t570 by a magnetic float method. The density of 100% TzO depends on temperature according to D = 1.213124 2.9129 X l O V 4 t -- 1.1954 X 10-5t2 Tj.301 X 10-8t3g./cm.a. The maximum density, 1.21502g . / ~ m .occurred ~, at 13.4 f 0.1". Ptlolar volumes are compared with those of HzO and D20. The concentration of TzOz in 98% TzO was found to be 0.001-0.002 mole/l.
+
+
Introduction Density and thermal expansion measurements on liquid DzO have been made by several workem2 This paper presents data on the density of liquid TzO frorn 5 to 54". A 1-g. sample of 99.30 mole % TzO was used. Due to health hazards a density method had to be used in which the vessel could be filled on a vacuum line and sealed off. Dilatometry was tried but was ditrcarded because gas evolution due to self-radiation caused separation of the liquid in the capillary column. Pressurizing the vessel with Tz gas kept the liquid thread intact for longer periods but gas bubbles still formed. A magnetic float method similar to that of Richards3 was finally adopted.
Experimental Density Apparatus. The essential part of the apparatus (Fig. 1) was a small quartz float containing a rod.of Mumetal. A coil was set just below the bottom of the density vessel. If the current passing through the coil is gradually decreased, the resulting magnetic field falls below a critical value, allowing the float to rise in the liquid. The effective density of the float was thus changed magnetically. The lower limit of measurable density is the density of the float. This was increased magnetically by as much as 1% in this experiment. The density in this 1% range was read from a graph ad density 2's. critical current, determined by calibration with liquids of known density. The coil, a commercial solenoid of 100 ohms, was coated with plastic to prevent shorting in the thermostat. It was fastened to a brass form which also served as a holder for the sample container. Alternating cur-
rent for the coil, taken from a regulated supply (fO.01 %), was determined to better than 0.1% with vacuum thermocouple^.^ Five thermocouples were used to cover a range from 0 to 100 ma. The float, A, was 3 cm. long and was made from 1.5mm. 0.d. thin-walled quartz tubing. The Mumetal rod, 1-mm. 0.d. by 3 mm. long, was waxed in place a t the lower end of the float. The mean density of the float was adjusted by adding or removing quartz with a torch until it just floated in nitrobenzene a t about 22'. The float density was 1.20076 g . / ~ m .a~t 22.40") the temperature of flotation in nitrobenzene. The Pyrex density vessel, fitted with break-seals, was sealed off under vacuum just before the density measurements. The side arm (x) was provided for the freezing and condensation of the TzO. The float section of 8-mm. 0.d. tubing fitted the brass holder tightly. The total volume of the vessel was about 30 ml. Calibrating fluids were placed in the density section of the densirneter with a hypodermic syringe. A water thermostat kept the temperature of the density apparatus constant to .t0.005°. The temperature was measured with a Leeds and Northrup platinum resistance thermometer which had been calibrated by the Xational Bureau of Standards. Calibration. In this application of the electromagnetic densimeter different densities were obtained biy
This work was done under the auspices of the Atomic Energy Commission. (2) I. Kirshenbaum, "Physical Properties of Heavy Water," McGraw-Hill Book Co , Inc., New York, 37. Y., 1951, p. 11. (3) A. R. Richards, Ind. Eng. Chem., Anal. Ed., 1 1 , 44 (1939). (4) F. L. Hermach, I R E Trans., 1-8, 235 (1958). (1)
Volume 68, h'umber 1
January, 1964
MAXWELL GOLDBLATT
148
changing the temperature of standard liquids of known density. Account must be taken of the fact that the TzO and standard are not at thc same temperature for the same critical current. Due to the. variation of the magnetic susceptibility of Alumeta1 with tcmperaturc and dimensional changes in the apparatus with
density between T I and T2 to T 3 . The interpolative corrections amounted to a t most 4 X g . j ~ m .a~t , the highest currents.
10/30
BRASS HOLDER
T,O
OR
CAL I BRAT I NO
I I
I
I
1
I
I
I
I
I
Tht- Journal of I'hysieal Chemistry
l
l
I
I
Figure 1. Densimeter apparatus.
temperature, it is necessary to interpolate to the density of a hypothetical standard which does have the same temperature as the TzO for the measured critical current. Vor this purpose a calibration curve was obtained with each of four standards over the desired density range, approximately 1.20070 to 1.21400 g./ 0111.~. ITor this density range a given standard covered a portion of the temperature range 5 to 54'. A 1.6% (by weight) solution of ethylberizene in nitrobenzene was used from 2 to 1.5'; nitrobenzene from 9.5 to 25.5"; &p'-dichloroethyl cthcr from 24 to &io; and a 13.7% solutio11 of bromolenLeue 111 ilitroherlzene from 41 to 51', The dwsitics of the standards were determined by dilatometry to =t0.0030/0. The dilatorncters were calibrated with conductivity water. The way in which the density-current curves were used is illustrated with the help of Fig. 2, which shows two idealized calibration curves. At temperature T , the measurrd critical current for TzO is i. For this current standard 1 has a density D,and a temperature T1, which is known from its measured density-temperature relationship; similarly for standard 2. For defiriitenrss assume T 2 > TB> Tl. The correct density is then obtained by a linear interpolation of for T L 0 ,D5,
I
CRITICAL COIL CURRENT Figure 2. Idealized calibration curve8.
A standardized procedure was used. The same applied voltage was used to pull the float into position for each measurement. The current in the coil was reduced slowly and uniformly, the same rate of current change in the coil being used for calibration and for measurement. Four to six measurements of the critical current were made for each density determination. Thc sensitivity of the densimeter varied from 5 X g./cm.8 a t low currents, 10--20 ma., to 1 x 10 g,/ ~ r n at . ~the highest currents, 70-80 ma. The long term rcproducibility was * 2 X 10 6 g./cm.3. Temperature cycling of the apparatus did not shift the calihration curves. The error due to the difference in magnetic susceptibilities of the organic density standard and water causes an error of roughly 1 part in lofi. Preparation of Tritium Oxide. Tritium gas was evolved from UT3 arid a sample was analyzed on a Alodel 201 Consolidated-h'ier mass spectrometer. The gas was converted to T20with CuO (3,50'). The tritium gas passed through a palladium valve and contacted the CuO in a mercury-free system. T20 vapor was trapped with liquid nitrogen near the exit of the CuO
DENSITYOF LIQUIDTzO
tube. TzO was then freed of gases, distilled into a storage vessel equipped with stopcock and ground joint, and kept at liquid nitrogen temperature until needed. Two l-g. samples of T20 were prepared. One was used in exploratory work and the other, of better purity, was used in the final density measurements. Analysis of TzO. The isotopic composition of the l-g. sample of T 2 0 was determined by the iron reduotion-mass spectrometer method. The procedure hats been described and tested for absolute accuracy with high purity D,Oe5 Briefly, 10-ml. STP samples of TzO vapor, in equilibrium with liquid TzO a t 20.0’, were reduced with powdered iron (500’), and the resulting Tz was analyzed on the mass spectrometer, previously conditioned with high purity Tz. A correction was made for A N H , the increase in the hydrogen atom fraction of the sample due to pickup of hydrogen in the decomposition system. This was determined5 as with DzO, using 99.0’atom % Tz gas. ANH was 0.0009 :k 0.0004 for TzO (0.0006 f 0.0002 for DzO). In the DzO analysis5 the deuterium content by the iron reduction method was lower by 0.02% than the n.m.r. and density methods (which gave the same analyses). Although this difference is about the limit of error of thle iron reduction method, the tritium atom fraction from the mass spectrometer analysis was increased by 0.0002. A further increase of 0.0009 (A”) was made to give the tritium atom fraction, N,, of the vapor in equilibrium with the original liquid. The corrected values of N , were 0.9922 for each of the two analyses before the density measurements and 0.9924 and 0.9923 for thie two analyses after the measurements (see below), giving N , = 0.9923 (average). The desired tritium atom fraotion of the liquid, N I ,was obtainedBfrom (Ntll - N1)
[N,/(l - N”)l[POH,o/POT,o11’2 (1) P o ~ 2 ~ / isP 1.22 o ~ a2t ~2O.Oo,’ giving N , = 0.9930. The =
estimated uncertainty is f0.0005. Temperature Corrections. The TzO temperature was greater than the bath temperature because of the absorption of self-radiation and heating effects of the coil current. The temperature difference was measured with a differential thermocouple having one junction attached to the float. With 1 g. of 99% TzO in the densimeter and no current in the coil, the temperature difference was 0.48 f 0.01’ (a calculated estimate was in close agreement). The correction for the temperature increase due to coil current was measured as a function of current for TzO and the standards a t 25.0’ and varied from 0.01’a t 25 ma. to 0.04’ at 70 ma. (a.c.). Density Measurements. After two analyses the TzO was transferred to the density vessel. The latter was
149
-
attached to a vacuum system, evacuated, conditioned by exposure to T20vapor, and again evacuated. Tlhe TzO was distilled into the side arm (x) of the density vessel, which was then sealed off. Upon warming to room temperature the T2O was poured into the measurement section, and the vessel was set in its brass holder in the thermostat. Density measurements were first run alternately and repeatedly a t 25.20 and 35.06’ with a reproducibility of =t0.00002 g./cme3a t each temperature. Then measurements were made from 5 to 54’. Densities were then remeasured at 25.20 and 35.06’ and agreed with the initial measurements. The temperature of flotation of the float in TzO, without current, was also determined. After completion of this first density series, the liquid TzO was spilled into the side arm (x), degassed, and analyzed twice. After observation of constant densities for several hours a t 25.20 and 35.06’, a second series of measurements was made from 5 to 54 ’. The 25.20 and 35.06’ points were repeated and agreed with the initial values for this series. On completion of the density measurements the TzO sample was distilled into a storage container through a break-seal. The portion of the vessel above B, Fig. 1, was carefully replaced with a tapered joint and cap. The vessel and float were washed with water and alcohol and dried in uucuo. The complete critical current calibration with nitrobenzene was repeated. The shift from the original calibration was about 2 X 10-5 g./ cma3 throughout the range. This calibration was averaged with the original for evaluation of the T,,O data. An equal shift was assumed for the other standards.
Results Density of TzO. The two series of densities differed by a constant amount, 0.00028 f 0.00001 g . / ~ m . over ~, the temperature range. One-half of this difference, 0.00014 g . / ~ m . ~was , added to the density values of the first series, in which the measurements were more numerous, to give the values in Table I. The total absolute error in a density is about f0.015%. Density values for 100 mole % T20 were calculated using Longworth’sBequation (2). The density of the TzO sample is given by
D = (NIMI 3- NzM,)/’(NiVi
(5)
(6)
(7) (8)
+ N2Vz)
(2)
hl. Goldblatt, and W. XI. Jones, to be published. G. N. Lewis and R. E. Cornish, J . Am. Chem. Soc., 5 5 , 2616 (1933).
W. M. Jones, this laboratory, to be published. L. G. Longworth, J . Am. Chem. SOC.,59, 1483 (1937).
Volume 68, Number 1
January, 1964
MAXWELL GOLDBLATT
150
where M is molecular weight, N is mole fraction, V is molar volume, and subscripts 1 and 2 refer to HzO and TzO, respectively. Using VI = Ml/Dl and V Z =
The average deviation of the corrected experimental densities from ( 5 ) was *0.00003 g./crns3. Densities for pure TzO from (5) are given in Table I1 for 2' intervals.
Table I : Densities of 99.30 hlole yo TzO
Table I1 : Density of Pure T20 Temp.,
Temp., OC.
Density,
OC.
Density, g./cm.l
4.98 5.51 6.49 7.62 8.00 8.60 8.98 9 .63 10.10 10.59 11.66 12.17 12.68 13.09 13 53 13.99 14.70 15.07 15.71 16.06
1,21268 1.21283 1.21302 1.21315 1.21322 1.21328 1.21333 1.21336 1.21343 1.21343 1.21348 1.21351 1.21352 1.21353 1.21352 1.21350 1.21350 1.21349 1,21346 1.21346
16.72 17.91 18.64 19.06 19.54 20.53 21.73 23.09 25.20 28.17 30.10 33.09 35.06 38.07 40,04 43,17 45.13 47.88 49.98 53.04 54.25"
1.21338 1.21333 1.21324 1.21318 1.21313 1.21300 1.21286 1.21257 1.21215 1.21146 1.21096 1.21C08 1.20943 1 ,20833 1,20752 1,20622 1 ,20532 1 .2039!) 1.20293 1.20130 1 ,20069'
g./cm.a
Density determined by temperature of flotation.
Mz/D2, where Dl and and T20, (2) becomes,
are the densities of pure HzO
The physical atomic weightsq of hydrogen and tritium were converted to the chemical scale, giving molecular weights (chemical scale) of 18.01573 and 22.03238 for H20 and TzO. Then, for N z = 0.9930, eq. 3 becomes Dz
=
D 1 - 0.00d764(D - Di)/Di
Temp., OC.
Density, g. /c m .a
Temp.,
Density,
OC.
g ./c in.8
6 8 10 12 14 16 18 20 22 24 26 28 30
1.21445 1.21472 1.21489 1.21499 1.21501 1.21494 1.21480 1.21459 1.21431 1.21396 1.21355 1.21307 1.21254
32 34 36 38 40 42 44 46 48 50 52 54
1.21194 1.21129 1.21059 1,20984 1,20904 1,20820 1.20731 1,20639 1,20543 1,20443 1.20340 1,20234
Maximum Density. Equation 5 gives a maximum density of 1.21502 g./cme3a t 13.4 f 0.1'. Chang and Chien" found the maximum density for 100% DzO td be a t 11.21 f 0.05'. The maximum density of ordinary water occurs a t 3.98'. The maximum differencein densities of TzO and HzO is 0.21692 g . / ~ m and . ~ occurs at about 35'. Relative lllolar Volumes. Molar volumes for pure TzO were calculated at 5' intervals using densities from eq. 5 . Alolar volumes for pure I h O were calculated using the densities of Kirshenbaum12 from 5 to 40' and of Shaten~htein,'~ raised by five parts in 105 to match those of Kirshenbaum, from 45 to 5 5 O . A molecular weight of 20.02838 was used for D2O. Molar volumes of D 2 0 and TzO relative to those of HzO are listed in Table 111. The number of significant figures is given, at least for TzO, only for relative accuracy. Tritium Peroxide Formation. One effect of self: radiation on TzO is the production of T202, which would raise the measured density. Much work has been done
(4) N. A. Lange, "Handbook of Chemistry," Handbook Publishers, Inc., Sandusky, Ohio. 1956, p. 114. (10) "International Critical Tables," Vol. 111. 1st Ed.. McGrawHill Rook Co., New York, N. Y., 1928, p. 25. (11) T. L. Chang and J. Y . Chien, J . Am. Chem. SOC.,63, 1709 (194 1). (12) I. Kirshenbaum, ref. 2, p. 12. (13) A. I . Shatenshtein, et al., "Isotopic W a t e r Analysis," AECTr-4136 (1960); 2nd Ed., 1957, p . 69; available from the Office of Technical Services, Department of Commerce, Washington (9)
The density for HzO was taken from the International Critical Tables.In A least-squares treatment of the 100% TzO densities derived from the data of Table I gave the following temperature dependence.
ll,
+
1.213124 2.9129 X lO-*t 1.1954 X 10-6t2 5.301 X 10-*t3 g./cmea (5)
=
+
The Joicrnal o j Phyaical C h a i a t r y
25, D. C.
151
DENSITY OF LIQUIDTzO
on the radiolysis of water14 but none with the steadystate level of 0-radiation present in 1 of pure TzO, 6 X 10’’ e.v./cc./sec. A measurement was made of the concentration of TzOzin 1 emsaof 98 mole T20 using ultraviolet spectrophotometry.
Table 111 : Relative Molar Volumes of DpOand TzO
5 10
15 20 25 30 35 40 46 50
55
1 ,00555 1 ,00485 1 ,00430 1 ,00393 1 ,00359 1.00329 1 ,00303 1 ,00280 1 ,00265 1 ,00247 1.00235
1,00710 1.00634 1 ,00565 1.00508 1 ,00460 1 ,00420 1 ,00389 1 ,00364 1.00343 1 ,00323
I .(M305
and can be attributed to the difference in the zero-point vibrational energies of the peroxides. The shift of T202from HzOz was estimated to be 560 cm.-’. The T20was distilled into a 0.5-cm. path length rectangular silica cell fitted with stopcock and ground joint. The transmittance measurements were made against ordinary water in a matched cell on a Beckmnn IIU spectrophotometer. Correction for cell fluorescence was made by subtracting the apparent transmission without the beam from the observed transmission. Measurements were started when the sample was 3.5 hr. old and were continued for 4 days. The concentration of T202was constant a t 0.002 f 0.001 mole/l. over this period and from 2200 to 2750 A. This would cause a 0.002% increase in the density of TzO. KO correction was made.
Acknowledgment. The author gratefully acknowledges helpful discussions with Dr. Wesley 11, Jones. He also wishes to thank Mr. R. K. Zeigler for the leastsquares treatment of the density data. A. 0. Al,I,en, “The Radiation Chemistry of Water and Aqueous Solutions, D. Van Nostrand Company, Inc., Princeton, N . J., 1961, pp. 75-98. (16) W. C. Schumb, C. N. Satterfield. and It. L. Wentworth, “Hydrogen Peroxide,” Reinhold Publishing Corporation, New York, N . T., 1956, p. 291. (16) M. K. Phibbs and P. A. GiguBre, Can. J. Chem., 29, 480 (14)
The extinction coefficient curve for TtOz from 2200 to 2750 A. was estimated from values for H20216 and the known shift of the extinction coefficient curve for DzOz relative to H202. According to Phibbs and GiguBrel6 the shift) is about 390 em.-’ toward shorter wave length
(1961).
Volume 68,Number I
Jaauarg, 19R&
