Table 24

A = Ethylene dichloride ; B = Benzene ; c = 1.134 ; Temperature =49.99° ; PA/PB at 50° = 1135

Molecular

. percentage of

A in liquid.

Vapour pressures.

Molecular percentage of A in vapour.

Observed.

Calculated.

A.

Observed.

Calculated.

A.

0.0

268.0

268.0

0.0

...

7.16

265.5

265.7

+ 0.2

...

...

...

7.07

265.8

265.8

0.0

...

.....

...

15.00

263.3

263 2

-0.1

11.52

13.47

+ 1.95

15 00

263.8

263.2

-0.6

12.72

13.47

+ 0.75

29.27

258.8

258.7

-0.1

26.38

26.73

+ 0.35

29.27

259.3

258.7

-0.6

27.06

26.73

-0.35

29.79

259.0

258.5

-0.5

27.22

27.23

+ 0.01

41.56

254.7

254.8

+ 0.1

38.72

38.68

- 0.04

41.65

255.0

254.8

-0.2

38.90

38.63

-0.27

52.15

251.3

251.4

+ 0.1

49.00

49.01

+ 0.01

52.34

252 0

251.4

-0.6

49.42

49.20

-0.22

65.66

247.3

247.1

-0.2

62.66

62.77

+ 0.11

65.66

247.4

247.1

-0.3

6261

62.77

+ 0.16

75.42

244.1

244.0

-0.1

72.96

73.02

+ 0.06

75.42

243.9

244.0

+ 0.1

73.07

73.02

-0.05

92.06

238.7

238.7

0.0

91.00

91.09

+ 0.09

91.89

238.3

238.8

+ 0.5

90.72

90.90

+ 0.18

100.0

236.2

236.2

0.0

..

...

...

With the exception of the first two percentages the agreement is good, and in the case of these two it will be seen that the percentage of A in the liquid is the same, while the observed percentages of A in the vapour differ by 1.2. It seems clear that little weight can be attached to the first two observations in this series.

For this pair of liquids the constant c has almost exactly the same value, 1.134, as the ratio of the vapour pressures, 1.135.

Linebarger's Results

It is unfortunate that the method employed by Linebarger 1 - passing a known volume of air through the mixture at constant temperature - did not give more trustworthy results, for he examined some mixtures of fairly closely related substances. It may be well to give the results obtained with one pair of liquids, chlorobenzene and benzene, for Linebarger found that there was no appreciable heat change on mixing these substances in several different proportions.

Table 25

A = Chlorobenzene ; B = Benzene ; c = 7.3 ; t = 34.8° ; PA/PB = 7.16 at 34.8°

Molecular percentage of

A in liquid.

Vapour pressures.

Molecular percentage of A in vapour.

Observed.

Calculated.

A.

Observed.

Calculated.

A.

15.18

126.3

126.4

+ 0.1

1.33

2.39

+ 1.06

29.08

107.9

109.0

+1.1

6.11

5.30

-0.81

65.06

63.6

64.0

+ 0.4

19.37

20.32

+ 0.95

79.21

47.0

46.3

- 0.7

35.15

34.29

-0.86

Here the difference between c and PB/PA is probably within the limits of experimental error, but the number of observations is too small, and the errors are too large to allow- of the definite statement that c is quite constant.