Method

frorn -15.4' up to 181.6' in the neighborhood of the critical point; two independent observations in the neighborhood of zero gave values as follows: ...
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T H E DEYSITIES O F SOLUTIONS OF ALUXtINIUM CHLORIDE I N LIQUID PHOSGENE BY ALBERT F. 0 . GERMANN

In a study undertaken in this laboratory on the conductivity of phosgene solutions of aluminium chloride, it was found necessary to know the densities of these solutions, in order to convert the percentage concentrations given by the method used to molecular concentrations. The literature seems to contain no data on the density of phosgene solutions. The density of liquid phosgene itself has been determined by several investigators. Emmerling and Lengyell give the density at 0' as 1.432; at 18.6'~ 1.392. BeckmannZ gives the value 1.42 at 8.2'. Paternb and Maezucchelli3 determined the density of liquid phosgene frorn -15.4' up to 181.6' in the neighborhood of the critical point; two independent observations in the neighborhood of zero gave values as follows: at 0.07'~ 1.4269; at O.OI', 1.4272; they found that the equation D,= 1.4264-0.002326 t agreed very well with their observations at other temperatures up to 15') the maximum deviation amounting to only seven units in the fourth decimal place. Finally, Atkinson, Heycock and Pope4 have made a series of determinatione of the density of liquid phosgene at four temperatures, ranging from - 104' to 49.9'; at 0 ' ; two measurements made with the same weight thermometer gave values 1.436 and 1.433 for the density by a method involving absorption of the phosgene by concentrated sodium hydroxide, and titration of the excess of sodium hydroxide.

Method The form of apparatus used in the present determination is shown in Fig. I , in which the lower bulb A was calibrated at both 0' and 25' to various FIG.I points on the stem cf the graduated capillary tube: since the preparation of the solutions of aluminium chloride had to take place within the instrument, the graduated capillary tube was surmounted by a 'Ann. Suppl. 7, 106 ( 1 8 7 ~ ) . * Z. anorg. Chcm. 5 5 , 371 (1907). 3 Gaxz. 5 0 , 30 (1920). 4 J. Chem. SOC. 117, 1410 ( 1 9 2 ~ ) .

DENSITIES O F PHOSGEXE SOLUTIONS

I39

bulb B, of somewhat larger capacity than A, to the top of which was fused a stop-cock and flat joint D, and to the side a filling tube C, large enough to admit a small weighing tube capable of holding, about 1 gram of anhydrous aluminium chloride; after introducing a weighed sample of the salt, C was sealed off, and the tube was evacuated and weighed. Pure phosgene was then distilled in, condensing it in B with liquid ammonia applied with a swab, until all of the aluminium chloride was dissolved; condensation was continued in A, until the bulb was perhaps half full; then the solution was boiled off for several minutes, to drive off any foreign gases and more phosgene distilled in until the meniscuc stood at some point on the capillary a t 0'. To permit the establishment of thermal and pressure equilibrium in the tube, the latter was immersed in a thermostat a t the requisite temperature until the position of the meniscus remained constant for a t least a half hour; then a reading of the volume was made, and the tube was carefully weighed. Fur the density of the solution a t the higher temperature the amount of phosgene was adjusted t o bring the meniscus on the scale a t 25') and observations made as before. Two dilatometers were prepared and calibrated for the measurements, the bulb h being constructed with heavy malls, to resist deformation under pressure-the maximum t o be withstood being less than one atmosphere excess pressure. Calibration gave the following values for the two tubes, designated dilatometer S (the one shown in the figure) the graduated capillary of which was 4 cm. long, and dilatometer L, the graduated capillary of which was 13 cm. long. Freshly distilled mercury was used for the calibrations. The volumes are given when bulb A was filled up t o the indicated graduation mark : Dilatometer

L L L

L L S S S S

S

Meniscus 27.14 cm. 26.80 15.39 27.74 16.35 5.30 2.00

3.70 4.40 6 . IO

Volume Temperature 7.4630 cc. 7.4739 7.8304 7.4401 7.7950 6.2579 6.2916 6.2745 6.2632 6.2461

The volume of bulb B, with the filling tube C I . cm. lon was 15.7 in dilatometer L, and 14.9 in dilatometer S. The aluminium chloride used was the same sample used by Germann and McIntyrel, for the determination of the vapor tensions of these solutions, and the phosgene was purified in the same way. J. Phys. Chem. 29, 102 (1925).

.

140

ALBERT F. 0. GERMhNN

Calculation of Results The total weight of phosgene in the dilatometer during a measurement had to be corrected for the weight of vapor filling bulb B; this could be accurately estimated, since the vapor tension of the solution was known from the work of Germann and McIntyre, and the volume of the vapor was known. proper correction being made for the length of the filling tube C during each measurement. A direct measurement under the conditions of the experiment gave as the weight of saturated phosgene vapor at 2 j", 8.18 mg. per cc.;

FIG.2

and a t oo, 3.65 ing. per cc. These values were used as the basis of the calculations of the vapor correction. The volume of liquid was read from a graph, drawn to large scale, and the percentage concentration and density followed directly from the figures thus obtained. Results oo

Table I contains the results obtained for the density of pure phosgene at and at 2 5 O , while Table I1 contains the results obtained for the solutions:

TABLEI Dilatometer

Density at o0

L L S S L

I . 4263

Density at 2 j" I

I . 4287 1.4273 1.4275 I . 4278

I . 3691

1'3693 I . 3680 I . 3681

Average

I

.4275

I . 3685

.3678

These values check those obtained by Paternb and Mazzucchelli very closely, though with phosgene made by the same method as that used by Atkinson, Heycock and Pope.

141

DESSITIES O F FHOSGEXE SOLCTIOR-S

The mean coefficient of cubical expansion between oo and 2 s o is found to be 1.4275-1.3685 I

=o. 001725

.3685X25

TABLEI1 Dilatometei

q AlClS

L L S S L I, S S L

2.97 2.99 5.72 5.96

Temperature

I, L L

O0

I . 4422

25O

I . 3861

1.45'73

O0

25'

9.70

Density

I . 4009 I . 4758

O0

9.77 20.89

2.5'

21.55 30.38 30.50 46.33 4 6 . 53

2 So

,4215 ,5303 I ,4825 I . 5760 I . 5283 I ' 6473 I . 6089 I

O0

I

O0

2 So O0

2 jo

Figure 2 contains the density curves as given by plotting the values obtained, and s h o w the excellent concordance of the results obtained with the two dilatometers. From the curves drawn on a large scale, the densities a t intervals cf 5y0 were obtained; these, with the corresponding molar concentrations have been recorded in Table 111.

TABLEI11 Density at oo

1.4275 1.4530 I . 4782 I . 5027 I .5270

1.5505 1.5741 1,5972 I . 6194 I . 6416 I . 6632 .....

I

Mol. conc. at o o

Density at 25' I ,3685

0.545 I.

IO8

I . 689 2.289 2.906

3.540 4.191

4.856 5.538 6 ' 234 I

.

.

t

.

,3966 ,4225 1 ' 4483 1.4740

0.523 I ,066 I . 629

I . 5000

2.811 3,431

I

I

1.525; I .5512 1.5765 1.6018 I . 6272 I . 6526

2,210

4,070 4.727 5.403

5,099 6.814

Acknowledgment I wish to express my thanks t o the Chemical Warfare Service for supplying the phosgene necessary for this investigation. Stanford Uninersit y , Calijornia.