GERXAXIULI. XIXI T H E VhPOR PRESSURE OF GERMBNTUM TETRABROMIDE* BY F. M . BREWER AND L.
Y. DENNIS
Researches upon germanium dibromide which are described in a separate article involved the fractionation of a mixture of germanium bromoform and germanium tetrabromide. Of these two compounds, the tetrabromide had already been prepared and i n ~ e s t i g a t e d ,but ~ nothing was known about its vapor pressure-temperature curve apart from the melting point (26.1') and the boiling point (185.9') given by Dennis and Hance. As a guide t'o the fractionation, the vapor pressure curve was determined for temperatures bet ween zero and the boiling point. Preparation of Germanium Tetrabromide X reflux condenser was sealed to the neck of a round flask of half-liter capacity, the top of the condenser being constricted so that the outlet was about three millimeters wide. An inlet tube to which a separatory funnel could be attached mas also fused to the flask. Five grams of finely divided germanium was placed in the flask, and bromine in excess of the theoretical requirement' for the formation of germanium tetrabromide was run in from the separatory funnel. The mixture was refluxed for four hours, the temperature of the heating bath being held a t 60'. By means of a bath of this temperature and the restricted outlet, evaporation of the bromine was reduced to a minimum. When the germanium had been converted to the tetrabromide, most of the excess bromine was distilled off by heating on a steam bath. The residue was still colored by traces of bromine, which were removed by shaking the product with mercurous chloride. The germanium tetrabromide was then filtered and fractionally distilled. The fractionating column was sealed directly on to the neck of the distilling flask and was filled with glass beads. The main fraction distilled within a range of one degree, and was further purified by crystallization and filtration at about I j o . The melting point of the final product was 26' (uncorr.) Apparatus The principle of the apparatus used for determining the vapor pressure was identical with that described by Laubcngayer and Corey.4 Llodifications were necessary in the construction, however, as germanium tetrabromide is a solid a t ordinary temperatures. The sample bulb and fractionation bulb5 Contribution from the Department of Chemistry, Cornell University. upon part of the thesis presented t o thc Faculty of the Graduate School of Cornell University by Frederick hi. Brewer in partial fulfillment of the requirements for the degree of Doctor of Philosophy. Winkler: J. prakt. Chem., 14, 193 (1887); Dennis and Hance; J. Am. Chem. Soc.,
* This article is based
44. 299, ( 1 9 2 2 ) . 4 5
Laubengayer and Corey: J. Phys. Chem., 30, 1045 (1926). These are marked F and 0 respectively in Fig. 2 of the article by Laubengayarand Corsy.
I102
F. M. BREWER AND L. M. DENNIS
of the original apparatus were discarded and a small distilling flask was attached at B, Fig. I , to the limb of the vapor pressure tube R which was eventually to contain the sample. A vertical side-tube C was sealed into the lower wall of the cohnecting delivery tube, and this served the purpose of a fractionating bulb. The upper end of Q was attached to the main chain as shown in Figure 2 of the article cited.
f
FIG.I
Procedure A small sample of carefully dried crystals of germanium tetrabromide was placed in the distilling flask A , which was then closed with a cork. The flask was immersed in liquid air and the whole apparatus was evacuated. The pressure in the apparatus was less than one millimeter of mercury. The sample was then melted and frozen three or four times at this reduced pressure, to liberate occluded gas. Preliminary runs showed that this precaution was very necessary, since it is difficult to remove the traces of hydrogen bromide resulting from slight hydrolysis by atmospheric moisture. This is unavoidable during the purification of the tetrabromide by freezing, and the transference of the sample t o the distillation flask. The sample was finally distilled into the vapor pressure bulb R , and was frozen by means of liquid air. The residue and the first fraction retained by the side tube C were frozen simultaneously, and the vapor pressure tube was sealed off a t the junction of the delivery tube B. The small differential manometer was then established in Q after which the procedure followed the lines indicated by Laubengayer and Corey. In the preliminary experiments, the heating bath was one of sulphuric acid, but this was replaced for convenience of observation by a water bath for temperatures between zero and 90°, and by an oil bath for temperatures between 80" and the boiling point of germanium tetrabromide. Even the removal of the hydrogen bromide did not prevent the formation a t high temperatures of mercuric bromide, which came from the reduction of the germanium tetrabromide by the mercury of the manometer. The deposit which formed on the surface of the mercury, and on the walls of the manometer prevented accurate checking of the determinations during the cooling
THE VAPOR PRESSVRE OF GERMANIUM TETRABROMIDE
I 103
of samples, as the mercury no longer moved freely in the manometer tube and the meniscus could not clearly be seen. These difficulties entered only a t comparatively high temperatures while the observations are being made a t increasing temperatures, and could be obviated t o a great extent by keeping the external pressure a little in excess of the vapor pressure most of the time.
FIG. 2
The observed values for the vapor pressure were corrected for the vapor pressure of the mercury and mercuric bromide present. The necessary data were obtained from the tables of Landolt-Bornstein-Roth. The following additional corrections were also necessary: ( I ) h calibration correction for the thermometer (2) An exposed stem correction for the thermometer. (3) A brass scale correction for the barometer and manometer. The calibration correction was determined for the thermometer by comparison a t various temperatures with standardized Anschutz thermometerg, and interpolation values were taken from the correction curve so obtained.
I
104
F. M. BREWER AND L. M. DENNIS
Exposed stem corrections were calculated for each reading. used for the barometer scale correction was .00018j - . 0 0 0 0 1 8 ~ I
The formula
+ .000181j
The curve plotted from the corrected temperatures and pressures observed in the two final determinations is given in Fig. 2. The two determiTapor pressure of germanium tetrabrornide. First determination. Temp. "C. (corr.j 4.45
Press. (obs.) rnm.
18.35 23.05 27.8; 32.70 37,60 45.60 4i.65 57.84 68. IO i8.34
88.55 93.65 86.;6
88,84 99.20 104.31 1 0 9 . 44
53 120.84 124.66 129.76 134.89 140.03' 11.4,
145.45 150.14
155.33 160.41 165.55 170.7 1 Iij.10
180.23 182.2;
184.62 185.34 186,37
Corrections applied Scale mm. Hi4
-
-
3.2
-
4. I 4. I
-
-
1.6
7.6
-
10.2
-
11.3
-
17.1
-
24. I 34.6 46.8 j8.8 39.3 46.6 63.4
-0. I
5.1
78.8 91 . o 109.4 131.6 149.6
Press. icnrr.)
HgBr2
-
-
-
I
-0
-
-0.I
-0.2
-0.2
-0. I
-0.2
I
-0.2
-0.3 -0.3 -0.4
-
-0. I
-0.2
-0.
-
-0.2
-0.3 -0.3 -0
__
j
-0.2
-0.3
- 0 .j
-0.6 -0.8 -0 9
17j.j
-0.6
-1.2
-0.8
202.2
-0.7
-0.8 -0.9
5 -1.9 -2.3 -2.8 -3,4 -4.2 -j.o -6. I -7.2
-1.0
235,9 271.8 311.4 361.8 409.8 467.5 533.9 604.8 676. j 70',4
-0.4
--I
-1.0
-1.2
--I
3
-1.j
-1.7 -2.0 - 2 . 2
744.2
-2.3 -2.4
7j8. j
-2.
782.y
-2.6
j
-8.8 -9.4 -10.1
-10.4
- I O .8
-0.2
j
-0.
-1.3 -1.8 -2.5 -3. I -4.0
-5.0 -6.5 -8.3 -10
j
-11.8 -13.4 -13.5 -14.2
mm. 1.6 3.2 4.
I
4.1 5.I 7.6 IO. 2
11.3 '7.1 24.0 34,4 46.5 58.4 39.0 46.3 62.9 78.2 90.0 108.2 130. I 147. 7 172.9 199.0 231.9 266.8 305. I 354. I 400.8
456.0 519.6 587.3 65j.0 677.9 718.3 732. I 755.3
THE VAPOR PRESSURE O F G E R M A S I C M TETRABROMIDE
110;
nations agree entirely above 100'. Below 100' the second falls slightly below the first, but agrees better with the observed freezing point of germanium tetrabromide, 26.1'. The discrepancy between the two curves was probably due to uneven heating of the water bath in the first determination, and the difficulty of adjusting the differential manometer for the very slight changes of pressure recorded near the freezing point. The boiling point derived from the curve plotted in accordance with these determinations falls a t 186.5' which is in good agreement with the value obtained by Dennis and Hance. Vapor pressure of germanium tetrabromide.
Second determination
Corrections applied Temp.
Press. (obs.) mm.
"C .
(corr.)
I8,35 27.85 37.60 47.65 57.84 62.9s 68.10 73 ' 2 0 78.34 83 ' 45
88.55 93.65 100.26 103.82 108.90 113.94 119.00 124.18 129.13 134.23 '39.33 144.43 149.50 154.60 159.71 164.88 170.00
'75.
I5
180.39
3.6 6.9
8.5 10.4 14.7 18.9
Scale mm.
HgBr?
Hg.
-
-
-
22. I
-0.
I
26.1 31.3 39.6 44.0 52.9 66.5 78.4 87.7 106.3 124.6 145.7 169.4 197.3 228.2 266.6 306.3 354.3 402. I 460.5 522.3 594.9 671.3
-0.
I
-0.
I
-
-0.
8.5
-
-0.2
10.4 14.7 18.9 22.0 26.0 31.1 39.4 43 ' 7 52.5 66.0 77.9 86.8
-0.2
105.2
-
I
-0.1
-0. I
-0.2
-0.2
-0.2
-0.2
-0.3 -0.3 -0.4 -0.6
-0.3 -0.3 -0.4
3.6 6.9
-
-0.I
-0.2
Press. (corr.) mm.
-
-
-0,7
-0.3
-0.5
-0.9
-0.
-0.6 -0.7
-1.2
-0.8
-1.4
-1.0
-0.8
-1.8
-0.9
-2.2
-1.3 -1.8
-1.0
-2.8
-2.
-1.1
-3.1 -4.0
-1.7 -1.9
-3.3 -4. I -5.0 -6. I -7.3
-2.2
-8.8
-10.5
-1.3
-1.5
j
j
-5.0
-6.5 -8.3
123,~ 143.8 166.8 194.2 224.3 261.7 300.0 346.8 392 ' 7 449.0
508,0 577.4 649.8
Summary The vapor pressure of germanium tetrabromide has been determined for the temperature range oo to the boiling point. The value of the boiling point of germanium tetrabromide obtained from this determination is 1 8 6 . 5 ~ . Ithaca, New Y o r k .
