682 INXES: THE INFLUENCE OF TEMPERATURE ON

LtXXII.-The ln,ucnce of Temperatum on Association in Benzene Solution, and the Vulue of the Molecular Rise of Boiling Point for Benzene at Different Temperatures.

By WILLIAM Ross I m E s , M.Sc. (Vict.), Ph.D. (Heidelberg).

~UBSTANCES containing hydroxyl groups give, as is well known, ab- normal molecular weights in hydrocarbon solutions by both the cryoscopic and ebullioscopic methods. A large number of hydroxyl compounds have been investigated in benzene by Beckmann, Auwers, Paternb, and others, and it has been shown that they may be divided into two classes according to their behaviour with increasing con- centration : carboxylic acids and oximes have in general the normal molecular weight in dilute solution ; as the concentration is increased, the molecular weight increases, at first rapidly, then more slowly, until it reaches double the normal value ; further increase of concentration affects the value but little, Alcohols and phenols also give the normal

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ASSOCIATION IN BENZZNE SOLUTION. 683

molecular weight in dilute solutions, but the molecular weight found increases regularly with thc concentration and does not seem to reach a limit. The behaviour of acids and oximes with increasing concen- tration is qualitatively similar t o that of an associating gas such as NO, when its pressure is increased, and in some cases the association follows Guldberg and Waage's law with sufficient closeness, in others the agreement is not satisfactory. It is generally assumed that the apparent increase in molecular weight in the case of the alcohols and phenols is due also to association taking place with increasing con- centration.

Although the influence of concentration on association has been largely investigated, the effect of temperature has not, as yet, been measured. Molecular weight determinations have been carried out with a few substances by both the boiling and freezing point methods in benzene solution, and it might be assumed that the difference between the values found is due to the difference of temperature. It has yet t o be shown that the increase in cryoscopic molecular weight is not due, in part, to separation of dissolved substance with the solid benzene. Until this has been done, it is not justifiable to compare the results of the two methods in the case of the alcohols and phenols. As most of the acids give almost the same molecular weight over a considerable range of concentration, the results obtained in this way with them are more trustworthy.

Several methods might be used to determine the influence of tem- perature on association in solution, the most promising being the variation of vapouy pressure with temperature, and the boiling point method at different pressures. The latter method was chosen in the present research, partly because it has been more fully worked out, and partly to elucidate some other points about the boiling point method.

The value of the molecular rise of boiling point may be calculated i n a number of ways. Arrhenius has shown that it may be calculated from the heat of vaporisstion, 1 0 0 ~ ~ RT2//1;, where R is the gas constant, L the heat of vaporisation of one gram of the solvent, and T the absolute temperature, The total heat of vaporisation of benzene has been determined by Regnault (Memoires de E'Iststitut, 26, SSl), and Schiff (Annulen, 1888, 244, 344) has determined the specific heat at different temperatures. The heat of vaporisation of benzene was calculated by means of their formulae a t intervals of lo", and the values so obtained substituted in van't Hoff's equation.

By means of the latent heat equation, we can substitute L in 1007 = RT2/L ; we thus obtain 1007 = Mp/(dp/dt) (Nernst and Roloff, geit. physikal. Chem., 1893, 11, 24).

The same formula may be derived from the lowering of vapour

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684 INNES: THE INFLUENCE OF TEMPERATURE ON

pressure equation, p -p' /p = n / N (Ostwald, Grundviss, 203, 1899 edition). The equation, 1007 = Mp/(dp/dt), enables us to calculate the molecular rise of boiling point from the rate of change of vapour pressure with temperature, provided the substance has the normal molecular weight in the state of vapour at the boiling point, and the method is quite independent of the state of association of the liquid solvent.

The molecular rise of boiling point at atmospheric pressure has been determined in this way for a large number of solvents by Beck- mann and Fuchs (Zeit. physikal. Chem., 1895, 18, 492). The results obtained show a satisfactory agreement with those obtained by the direct method. In the present case, the value of the molecular r k e of boiling point

has been calculated from Ramsay and Young's determinations of the vapour pressure of benzene at different temperatures (Ramsag and Young, Phil. Mag., 1887, [v], 23, 6 1 ; Young, Trans,, 1899, 55, 501). The results so obtained are compared with those of determina- tions of the rise of boiling point, using phenanthrene, benzophenone, and in three cases benzil as dissolved substances, at pressures ranging from 31 to 109 cm. The pressures were chosen 50 as to give differences of about 10' in the boiling point of the benzene.

Determinations were also carried out a t various pressures with typical abnormal substances. The substances chosen had to be solids, as it would be exceedingly difficult to introduce a liquid into the apparatus without disturbing the pressure ; it was also necessary that they should be easily soluble and have very little vapour pressure a t the highest temperature used, Benzoic acid, o-bromobenzoic acid, P-benzilmonoxime, and dimethyl tartrate were the substances used. The value of the results with benzoic acid may be partly vitiated by its volatility.

The Method.

In order to carry out the experiments, it was necessary to maintain a very constant pressure in the boiling point apparatus for a consider- able time.

The arrangement of the apparatus,* for pressures less than the atmospheric and its method of working will be readily understood on reference to Fig. 1.

The Beckmann apparatus is seen to the right ; both the boiling point tube and the vapour mantle are connected to the large bottle, B, and the pressure in the apparatus may be found by reading the manometer,

* An apparatus for maintairiing a constant pressure near that of the atmosphere, similar in principle t o that used, has been described by A. Smit [(Zeit. physikal. Chem., 1900, 33, 38).

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ASSOCIATION IN BENZENE SOLUTION. 685

H, and subtracting from the barometric height. The whole apparatus is connected with a water vacuum pump. N is a drying tube contain- ing calcium chloride. The syphon barometer tube, U, has a platinum wire fused through a t K and is connected to the pump through the

I---- - t ap t . The tube 1; has a platinum wire fused through its lower end, 20, electrical connection is made with the copper wire lead by a little mercury. Imagine the apparatus to be working and the tap to be open, the pressure in the apparatus falls and the mercury in the right

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686 INNES: THE INFLUENCE OF TEMPERATURE ON

hand limb of U rises until it touches the platinum wire at tu; the circuit of the relay, R, is then complete and the arm, a, is raised, this breaks the circuit of the magnet, M, and the tap t is closed by the spring 8’. Owing to leakage in the apparatus, the pressure gradually rises and the mercury falls until the contact at w is broken ; the arm, a, then falls, completing the circuit of M, and the tap is opened. The pump was worked at its full power i n all the experiments. To prevent too great a rush of air when the tap opened, a capillary tube, c, was placed between the pump and apparatus, and a final adjustment given to the rate at which the air was pumped out by the screw clip, d. It is evident that when the tap opens the pressure in Ufalls much more rapidly than in the bottle, 3, consequently the mercury rises and the tap is closed before the pressure in 13’ has time to fall much; the mercury in U then falls almost to its original height owing t o equal- isation of pressure in U and B’. The large bottle, B, was connected to B‘ by a capillary tube (c’). The pressure in B, therefore, only follows the changes in B’ slowly; i t is obvious tha t if the pressure in B’ varies rapidly by small amounts about a mean pressure, the pressure in B will be practically constant and will be the mean pressure in B’. The natural leakage in the apparatus was not sufficient to keep the tap opening and shutting quickly enough to give the most constant pres- sures; the whole apparatus was so tight that , working a t 109 cm., the pressure only fell 2 cm. in a n hour with the tap closed. A small flask, F, containing a little sulphuric acid was therefore connected to B’, and a stream of air, which could be regixlated by means of a screw clip, allowed to bubble through the acid at a convenient rate. Wi th the tap opening 20 to 30 times per minute, no motion at all could be observed, even with a magnifying telescope, in the mercury manometer, H ; using a water manometer for pressures near the atmospheric, only a slight motion, about 1/5 mm., was visible. To alter the pressure, the tube, L, is raised or lowered to the necessary amount. The tube slides in a piece of rubber pressure tubing and can easily be adjusted with sufficient accuracy in the required position. The surface of the mercury a t Wwas covered with a little alcohol,

The magnet, M, was kindly designed for me by Dr. D. K. Morris so as to give as equal a pull as possible over a considerable range. A n iron plug (y) was connected to the keeper and this moved in the core of the magnet. The bottom and sides of the magnet were encased in iron. An ordinary glass tap was used for t, this was fitted, a t a suit- able angle, with a brass arm held on by plaster of paris.

The Beckmann boiling point apparatus was arranged in the usual way. A metal vapour jacket was used ; this was about one-third filled with benzene. The boiling point tube and condenser were made in one piece, and the mouth of the boiling tube contracted so that a small

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ASSOCIATION IN BENZENE SOLUTION. 687

copk could be used. It, is of course, most important that there should be no leak in the boiling tube, as benzene would be swept out of it by the escaping air. A rubber stopper could not be used to hold the thermometer, aB it was liable to absorb considerable quantities of behzene : a good, well softened cork was found to be perfectly tight. The loss of benzene after 3 or 4 hours seldom exceeded 0.1, and never 0 9 gram. The liquid in the boiling tube boiled quietly both under reduced and increased pressure, even the platinum wire usually fused through the bottom of the boiling tube was unnecessary. The beads were placed in the tube in the way described by the author (Trans., 1901, 79, 261), and platinum clippings placed over them. The plati- num cylinder was not used as the boiling temperatures were not high enough to make its use of advantage. The space between the boiling tube and vapour jacket was packed a t top and bottom with asbestos paper. A gas regulator was used to keep the gas pressure constant. The flames were protected from draught by pieces of zinc fitting closely to the Beckmann stand, and the whole apparatus was surrounded by a zinc screen as high as the top of the boiling tube. An electrical tapper was used to tap the thermometer.

I n the experiments at increased pressure, the capillary (c) was con- nected to a large metal reservoir into which air was forced by a large bicycle pump. A mercury manometer was in connection with the reservoir. The flask 3' was removed, and the delivery tube from B' joined to a tube drawn out to a point and dipping into water. The rate at which the air escaped could then be readily regulated by a screw clip. The relay was cut out and the leads from U connected directly to the large battery and M. It will be seen that the tap now opens when the pressure falls below that fixed upon and closes when it rises above it, The tap t was held in by a spring which pressed gently against it. It was found that more satisfactory results were obtained if the pressure in the air reservoir was kept considerably above that in the apparatus j an excess pressure of a t least one-fourth of an atmosphere was used.

I n the earlier experiments the pressure was allowed to vary con- siderably. In series (16) the pressure in the reservoir changed by about an atmosphere from time to time. I n the other series a t 79 cm, the variation was about one-fourth of an atmosphere. The experiments a t 109 cm, were all carried out with a pressure in the reservoir which did not vary more than 2 cm. about the mean, and the thermometer read- ings were taken when the mercury in the manometer stood in the mean position. It will be seen that very concordant results were obtained, however much the pressure changed ; the only reason for giving more attention to the pressure in the later experiments was tha t i t seemed safer t o work under as constant conditions as possible,

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688 INNES: THE INFLUENCE OF TEMPERATURE ON

After the liquid had boiled about an hour, the temperature be- came as constant as it is at atmospheric pressure under favourable conditions.

When the temperature had become constant, the clip d' was closed, the tube Sremoved, and the weighed pastille placed in it, The tube was then replaced, the clip removed, and X pushed well down into the rubber tube ; on tapping gently, the substance fell into the boiling tube. The tube was then partly withdrawn and the clip replaced, when everything was ready for the addition of the next portion of substance. Working a t increased pressures, the rubber tube was wired to X before the clip was opened, otherwise there was danger of X being blown out. As the rubber tube is fully distended in this case, the substance falls in without difficulty.

The benzene used in the experiments was carefully purified and was dried over sodium. The substances, with two exceptions, were purchased from Kahlbaum, and were pure. The P-benzilmonoxime was made according to Meyer and Auwers' instructions, and melted at 113' to 114'. The dimethyl tartrate mas prepared by Frankland and Aston's method, and purified by distillation and precipitation from benzene by light petroleum,

The determinations at about 80' were carried out under atmospheric pressure.

Determination of the Molecular Rise of Boiling Point at DtJ'erent Temperatures.

Column 1 gives the number of the series. Column 2 ,,

Column 3 ,, the corresponding temperature. Column 4 ,, the weight of solvent. Column 5 ,, the weight of aubstance. Column 6 ,, the observed rise of boiling point. Column 7 ,, Column 8 ,, 1/100 gram-molecules of substance per 100 grama

Column 9 ,, the molecular rise of boiling point.

the pressure in cm. at which the experiments were carried out.

grams of substance per 100 grams of solvent.

of solvent.

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ASSOCIATION IN BENZENE SOLUTION. 689

- 9.

18-4 18.7 19'6 19.2 18.4

19.0 --

21'3 21.3 20 9 20 % 20.1

TABLE I. - 1.

- 8.

__-

0.754 1.95 4 *45 6.88 9'47

Mean

0.863 2.00 3 -61 5 65 7.05

Mean

0.705 2 17 4 *21 5.73 8.61

Mean,

0.683 1.32 2 '46 4.13 6.16 8.83

Mean.

0'611 0.99 1.68 2.53 3.72 5 '24

Mean.

2. 3. I 4. ! 5. I 6. I 7.

Diphenykamine, C,,H,,N = 169.

24'4

31.1

31.7

31-0

35 *8

48 .o 21'55 0.2698 0'6984 1,592 2.458 3'384

0-139 0.365 0.840 1 '270 1.678

1-28 3.29 7'53

11.62 16-0

Phenanthvene, C,,K,, =: I 78.

53.7

54.3

20.18

19-81

0.3040 0.706 1'270 1 -989 3'127

0.2424 0.751 1.455 1.977 2-973

0.184 0'427 0'755 1.165 1'789

0.147 0.465 0.875 1.175 1-71?

1.54 3.57 6'42

10'06 15.8

1-25 3.87 7'49

10.19 1 5 3 2

21.0

20.9 21.4 20.8 20 *5 19.9

20'9

19.8 20 *4 20.5 20'2 20.0 19.6

20-2 --

21 -0 21 *3 21 '2 21-1 20 '8 20-3

21'0 --

Benxophenone, C13H,00 = 182.

21 '31 092600 0.501 0-936 1-573 2.345 3.360

0.135 0.268 0.505 0.835 1.232 1.733

1 '24 2.40 4 -48 'I *52

11.21 16.07

B e n d , C,,HIoO, = 2 10.

57.6 22'19 0'2794 0.454 0.771 1.157 1'702 2.401

0.128 0.211 0.357 0.534 0.774 1.063

1 -28 2.08 3-53 5.30 7 '81

11-03

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690

72.8

1.

6

7

8

9

19 22'19

INNES: TEE INFLUENCE OF TEMPERATURE ON

2.

4 3 5

43-5

43.48

43.3

60.3

TABLE I. (continued).

8.

63 '3

63.3

63.3

83 *1

24-13

24.99

Fhenanthene.

0.2320 0.5180 1'661 2'314 3'474 4.516

0.2240 0.4968 0.9260 1'546 2.477

0.135 0.284 0.895 1.239 1.785 2.275

0.112 0.258 0.472 0.787 1 *240

Benaophes . x e .

22 *7

21 $3

0.2450 0.5804 1 '1 60 1.919 2.974 3.847

0.2914 0.7286 1.4308 2.163 3 *226

0-128 0.303 0,604 0.973 1.490 1.912

0.170 0.406 0.793 1-171 1'703

Phenantlri*ene.

0.2490 0.608 1.217 2.162 3'247 4.224

0.159 0.371 0.742 1 '289 1.878 2'404

0'982 2 *19 7 -03 9 -79

14-70 19'11

0.910 2 '02 3.76 6 *29

10.07

1.08 2-56 5-11 8.45

13'10 16'94

1'37 3 '43 6 '94

10'16 15.18

1.14 2.79 5'58 9 -92

14'89 19'38

0.551 1 *23 3.95 5.50 8'26

10.74

Mean..

0 512 1.13 2'11 3'53 5 *65

Mean..

0.593 1'40 2.81 4-64 7 '20 9-31

Mean..

0'754 1.89 3'71 5 '47 8-35

Mean..

0'642 1-57 3'14 5 5 7 8.37

10.89

Mean.

9.

24-5 22 -5 22.7 22.5 21'6 21.2

22.6

21.9 22.7 22 3 22 *3 21 '9

22-22

--

--

21.6 21'6 21.5 21 -0 20.7 20.5

21.40

22'6 21 -5 21 '4 21 '4 20'4

21'72

--

--

24.8 23.7 23'7 23'1 22'4 22'1

23.5

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ASSOCIATlON IN BENZENE SOLUTION. 691

TABLE I. (continued).

2. _-

61.28

61 -3

75.7

75 *3

I 4. ~ 5. 6. 8. 9. 1.

_-__

11

12

13

14

-

Yhenunthrene (continued).

0.575 1'25 2'39 3.89 5-61 7 *58

Mean.. ,

0-807 1-74 2 *98 4.91 6.87

Mean..

0'481 1'00 1-40 3.05 4.25 6.73

Mean..

0'91 2.06 3'11 4.26 13-87

Mean..

23.8 23.7 23'6 23.6 23 *3 22.9

73-2

73'8

80'2

22'19 0.2230 0'4970 0.929 1.507 2.175 2-940

0.137 0.304 0'573 0.917 1.304 1.738

1.02 2 -28 4.26 6'91 9.98

13.49

1-47 3.18 5'42 8'93

12'49

23'6

21 -6 23 .O 22-8 23.0 22-8

Bennophenone.

22.19 0.3202 0.6920 1.182 1.946 2.723

0.174 0'401 0.681 1.130 1 *563

22-95

23 -5 25.0 25.4 25% 25.0 24.5

25 -25 --

24-7 23 *7 23.7 23.9 23.6

f

22-19 0.1866 0.3884 0.6824 1'184 1.648 2.610

0.856 1'78 3-13 5.43 7'56

11'97

0.113 0.250 0.447 0.782 1.062 1.647

Benxophenone.

80.0 22'19 0.3614 0.8166 1.2330 1.688

0.225 0.490 0.740 1.019 1'622

1-66 3-75 5 '66 7.75

12.50

23'8

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692

1. -

1 5

16

17

18

INNBS: THE INFLUENCE OF TEMPERATURE ON

TABLE I. (continued).

2

75.5

79.7

79.2

79 '2

80.1

82.4

82'0

82 *O

22-19

Benxil.

0.2556 0.5626 0.960 1.767 2.975 4,354

0.124 0.282 0.493 0'902 1'479 3 '1 26

22'19

22.19

Phenant hi*ene.

0.1836 0.3978 0'742 1.060 1'660 2.251

0'2094 0'4496 0.857 1-446 2.213 3.046 4.231

0.123 0.257 0.476 0'691 1'056 1.415

0.133 0.285 0.550 0.925 1 *370 1.894 2'541

Benzophenone.

22.19 0.2290 0'4706 0.767 1.165 1 *672 2.488 3'327

0'135 0.273 0'446 0'669 0.967 1.403 1.894

1 *17 2.58 4.41 8'11

13'6 20 .o

0,843 1 '83 3.40 4 '86 7.62

10.33

0-959 2 -06 3.94 6'64

10.16 13.98 19 '4

1 -05 2.16 3 -52 5 -35 7.67

11.4 15.3

8.

0.558 1 '23 2'10 3 '86 6'50 9.49

Mean ...

0'474 1.03 1.91 2.73 4'28 5.80

Mean ... 0.538 1.16 2'21 3'73 5.70 7-85

10'9

Mean..,

0 5 7 7 1'19 1'93 2-94 4'22 6.27 8 '39

Mean..

--

9.

22.2 22-9 23 *5 23.4 22.7 22 '4

23-3 -___

25'9 25.0 24'9 25 '3 24 -7 24'4

25 '0

24 *7 24'6 24 *9 24.8 24'0 24 '1 2 3 3

24.8

--

---

23 '4 23'0 23-1 22'8 22-9 22'4 22'6

23.0

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1.

19

20

21

-

2

108'2

109 .0

109.0

ASSOCIATION IN BENZENE SOLUTION.

3.

92 8

93.1

93.1

TABLE I. (continued),

693

Phenanthrenc.

22-19 0 '2800 0.5670 1'001 1.531 2'268 3.167 4.271

0.199 0.402 0.708 1.070 1'565 2'138 2.819

22.19

22.19

Benxophenone.

0.2956 0.6452 1.076 1.599 2.169 2'871

Benzil.

0.3026 0.613 0 ,998 1 '548 2,556 3.613

0.197 0.427 0.717 1'073 1'405 1'843

0.184 0.359 0.579 0 876 1'403 1'940

1'28 2.60 4.59 7.03

10 '4 14.5 '19'6

1'36 2.96 4 '94 7 . 3 4 9.95

13 '2

1.39 2-81 4,58 7.10

11.7 16.6

8.

0.722 1 4 6 2.58 3.95 5.85 8.17

11 '0

Mean..

0.745 1 *63 2.71 4.03 5 '47 7 '24

Mean..

0'661 1 '34 2.18 3'38 5.58 7'90

Mean..

9.

27'6 27 .t5 27'4 2 7 ' 1 26'8 26 '2 25 '6

2 7 . 3

26 '4 26.3 26 '1 2 6 , 6 25.7 25.5

26'1

27'8 26.3 26'6 25 '9 25 '1 24'6

26.2

The values of the molecular rise of boiling point given in the pre- ceding tables, as well as the molecular weights to be given subsequently, are all calculated with 0.4 gram less solvent than mas actually taken, to allow for the solvent adhering to the upper parts of the tube and for tha t in the state of vapour.

Three series of determinations were carried out with diphenylamine at 48". Two of these gave values for T which rose o r fell considerably with the concentration. The pump could only further reduce the pressure slowly, this may perhaps account for the error. All the experiments carried out, with the exception of the above-mentioned

VOL. LXXXI. 3 A

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694 INNES: THE INFLUENCE OF TEMPERATURE ON

series, and of two in which the tap failed to act for lack of sufficient grease, are given in the above tables.

On examination of the numbers, i t will be noted that for concentra- tions of less than 6/100 gram-molecules per 100 grams of solvent, the

FIG. 2. -Pli.cnanth rem.

Eiindrcdth-grant molcculcs pcr 100 grants of benzene.

values for These values were used for calcu- lating the mean molecular rise, and the first determination was not included in the mean if the rise of boiling point was less tha t 0.1.

The agreement in the double series carried out with phenanthrene and benzophenone is most satisfactory. The mean values for T never

change but little.

FIG. S.--Bc7tzophenonc.

E I-

9 10 ll

differ by more than 0.3, and for solutions of similar concentration the agreement for single determinations is, in many cases, within 0.1.

The regularity of the results obtained a t different temperatures is well shown by the curves got by plotting r against the concentration

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ASSOCIATIOX I N BENZENE SOLUTION. 695

I 21'1 22.5 24.4 26 .j 25.8

expressed in 1/100 gram-molecules of substance per 100 grams of solvent (Figs. 2 and 3). The curves are practically parallel ; those for phenan threne show a slight but distinct downward tendency, whilst the benzophsnone curves are almost horizontal.

The variation of T with temperature is shown clearly by plotting the values of T fo r each substance at different temperatures against the temperature. Tho curve for 7, calculated This is done in Fig. 4.

F I G . 4.

Tempcrnt i t re.

from the latent heat (calculated A) and from Ramsay and Young's determinations of the vapour pressures (calculated B), are also given. Below is a table of the dctta from which these were calculated :

TABLE 11.

50" 60 70 80 90

100'4 98 3 98.0 93.7 91 ' 2

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696 I N N E S : T H E I N F L U E N C E O F TEMPERATURE ON

I I cm.

Temperature - 1 Pressure in

40" 50 60 70 80 90

100 110

18 '02 26-83 38'85 54'82 75-50

100.8 133'5 173.9

TABLE I1 (continued).

dpldt.

0.881 1 *202 1 5 9 6 2.068 2.530 3.27 4 '04

Mean I I pressure.

22-42 I 32.84 1 46-83 65.16 88.1 ~

117'1 153.7

19.85 21-31 22'89 24-58 27'17 27'96 29.68

Mean Values of the Jfolecular Rise of Boiling Point at Diferent Temperat uves.

i Calculated A . . . . . . ~

Calculated B .. ... Phenanthrene . . . . . I Benzophenone . . . . . . ~

Benzil . . . . . . . . . . . . . . General mean for: phenanthrene and1 benzophenone . . . j

54". ~___--

21.6 21 *05 21 -0 20.17 -

20.6

58". I I

! 22.2 21 -6 - -

21 .o I 1

-

63". ' 73".

I 23.0 ! 25.0

22.4 23'55 21.6 22-95

22.4 , 24.25

- , -

22.0 23'26

80"

26.5 25'5 25.25 23.8 23 -3

24 *1 -

93".

29.5 27 '8 27 '3 26 '4 26.2

26.9

The molecular rise of boiling point, calculated from the variation of vapour pressure with temperature, forms, when plotted against the temperature, a very regular curve from -5" to +145", the values increasing somewhat more rapidly than the temperature. The only value which does not lie well on the curve is t,hat a t 85". This deviation is accounted for by the fact tha t the vapour pressures below and above 80" were determined in t w o separate researches (by Ramsay and Young, and Young respectively). I n Young's paper, the vapour pressures calculated by means of Biot's formula and constants calculated from his own measurements are given. The calculated vapour pressuro a t 80' is smaller than t h a t found by direct experiment, and is larger at 90' ; although the differences are small, dp/dt is decreased considerably. If T be calculated from the pressures given by Biot's formula for 80" and go", the value obtained falls well on the curve. This is shown by the dotted portion of the curve.

The molecular rise found at the various temperatures using phenan- threne as dissolved substance, agree closely with those calculated from the vapour pressure, the greatest difference being a little more than 2 per cent. The molecular rise with benzophenone is considerably smaller

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ASSOCIATION I N BENZENE SOLUTION. 697

than with phenanthrene. If smoothed curves be drawn, it will be seen tha t the difference is nearly the same at the different temperatures and amounts to about 0.8. It is well known that different values are obtained for the molecular rise at atmospheric pressure according to the substance dissolved, even though the substances cannot be con- sidered ns abnormal in the ordinary sense. That this difference is not due to association in the case of benzophenone is shown by the fact! tha t the molecular rise does not decrease with concentration. I t is interesting tha t the two closely related substances, benzophenone and benzii, give curves which agree closely with one another.

The molecular rise calculated from the heat of vaporisation is greater than that calculated from the variation of vapour pressure with tem- perature. The molecular rise found by direct experiment agrees much better with tha t calculated in t'he latter manner : a result which was hardly to be expected,

A bn ornza I Xu bstan ces . Columns 1 to 8 have the same meaning as in Table I (p. 688),

column 9 gives the molecular weight found. The molecular weights are calculated with the mean molecular rise for phenanthrene and benzophenone :

TAnm 111. - 1.

22

63

24

- 2.

31'0

43 -3

61 '3

; Benxoic Acid , C,H,O, = 122.

53 *i

63 -1

73.2

24'21

22.19

22.19

0.151 6 0.3373 0.5636 1.2550 1.616 2.262 3.001

0'1210 0 '291 0 0.5294 0.926 1.501 2.2724

0.1806 0.3680 0.6402 0.905 1.324 1.813 2.527 3 *285

0.059 0,135 0.213 0.460 0.585 0'825 1.083

0.066 0.143 0.254 0.416 0.655 0-984

0.106 0.20'2 0.333 0.465 0,660 0.889 1 *208 1 a538

0.637 1-42 2.37 5.27 6 .78 9.50

12'iiO

0.555 1.33 2 *43 4-25 ii *89

10.42

0.829 1'69 2.94 4.15 6-07 8 -32

11 60 15'1

8.

0 '529 1-16 1.94 4'32 5'56 7.78

10'33

0'455 1-09 1 -99 3-48 5 *65 8.54

(J-679 1-38 2.41 3 -40 4-98 6 *82 9 5 0

12.36

- 9.

229 223 236 243 248 245 247

185 205 210 225 231 233

182 194 205 207 214 218 223 228

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698

1.

25

26

INNES: THE INFLUENCE OF TEMPERATURE ON

TABLE 111. (contimed).

2.

75.6

109'0

Benxoic Acid, C7H,0, = 122 (continued ).

80.1

93.1

22.19

22.19

-

0.3430 0.7016 1'026 2.391 2.052 2.836 4.287 5'924

0.2894 0.5898 0'948 1 '426 2,196 3.252 4'947 -

0'209 0 403 0'563 0'743 1.070 1.441 2 *088 2'823

0.181 0'359 0'560 0'809 1'199 1 *706 2,436 -

1 -57 3 -22 4'71 6.38 9 '42

13.0 19.7 27'2

1'33 2.71 4-35 6.54

10.08 14.9 22-7 -

8.

1-29 2 '64 3-86 5 -23 7 *72

10.7 16'1 22 -3

1'09 2.22 3.57 5-36 8'26

12-24 18.61 -

-- -

9.

181 192 201 20 6 211 217 226 231

194 200 206 215 223 232 247 -

Bertsoic Acid, The results obtained are graphically expressed in Fig. 5. The tem-

The curve for perature a t which each series was carried out is shown.

FIG. 5.-&?nZO?k acid, C,H,O,. Mol. wt. =122.

Hundredth-gram molecules per 100 grams of solvent.

benzoic acid in benzene (Beckmann, Zeit. physikal. Clem., 1888, 2, 729) is also given. The freezing point of benzene is 5.4'. The values obtained by the boiling point method at 5 4 O agree closely with those by the Freezing point method. The curve at 63" lies much lower than

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ASSOCIATION I N BENZENE SOLUTION. 690

tha t at 54", the difference being greatest in dilute solution, the differ- ence between the curves decreases up to 80'. The 93" curve lies higher than tha t for 80'. The agreement in the molecular weights at 5.4" and 54Odoes not necessarily show tha t there is no change of association between these temperatures. I t is well known tha t benzoic acid volatilises considerably a t temperatures below looo, and it boils at 134" under 1 2 mm. pressure. If the benzoic acid had a vapour pressure of between 3 and 4 mm. in a solution containing 6/100 gram-mole- cule per 100 grams benzene, this would raise the apparent molecular weight about 10 per cent,, tha t is, more than 20 units. The apparent decreasing effect of change of tompsrature on the association as the temperature rises may be due t o increase of vapour pressure of the benzoic acid with temperature, and the f a c t tha t higher values were obtained at 93' than at 80" might be due to tho same cause.

Although the unknown influence of the vapour pressure detracts con- siderably from the value of the results with benzoic acid, i t may safely be said that increase of temperature brings about a decrease of associa- tion between 54" and 80', since the change of vapour pressure of the benzoic acid would tend t o bring the molecular weights a t dift'erent temperatures nearer together :

TABLE IV,

1. 2.

22

23

24

35.8

75.35

109 '0

o-Bromobenxoic A c i d , C7H50,Br = 201.

57'8

80.0

93 -1

22'1 9

22.19

22'19

0.3872 0.885 1'341 1,314

0.5388 1 ' 0 7 4 1.599 2.382 3.176 4.225

0,3732 0-682 1.216 1.786 2.600 3.748 5'056 6,775

0-1 24 0.262 0.382 0'521

0.1 93 0.364 0.529 0'768 0.989 1.278

G.167 0.288 0 *47 5 0'668 0.910 1.268 1.650 2.158

17s 4 - 0 6 6.15 8 7 8

2.47 4 '93 7-34

10.7 14 '6 19'4

1 .71 3'13 5.58 8'20

11.93 17.2 23.2 31.1

8.

0'884 2'02 3-06 4'37

1 .23 2.45 3 -65 5.44 7.25 9-64

0.851 1'56 2.78 4.08 5 -93 8.56

11'54 15.5

9.

307 332 345 361*

307 325 333 346 354 364

271 288 311 32.5 348 360 373 382

* The substance apparently dissolved completely, but further addition of sub- stance caused no increase of boiling point.

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700 INNES : THE INFLUENCE OF TEMPERATURE ON

I

5. 1 6. 1 7. 1 8. I 1 I

3. ' 4.

o-B~omobertxoic Acid.

Three series of determinations were made with this substance at 58', SO', and 93' respectively. The o-brornobenzoic acid mas not sufficiently soluble to make a series of determinations at the freezing point. From the curves (Fig. 6), it will be seen tha t the molecular

9.

FIG. 6. -0-Bromobenzoic acid, C,H,O,Br. Mol. wt. = 201.

57.8 21'96

%undredth-gram molectslcs per 100 grains of benzene.

0.3852 0 185 0.750 0'320 1.115 0.441 1-575 0-591 2.033 0.716 2.643 0.880

weight at 80' is, for similar concentrations, considerably smaller than at 58', and the difference increases with the concentration. I n dilute solutions, the 93' curve lies considerably below t h a t for SOo, with increasing concentration, the curves approach one another and finally become practically parallel :

TABLE V. - 1.

25

- 2.

35.8

I I I , p-Benzilrnonoxi.me, C1,H,,O2N = 225. !

I

1 * i 9 3 '48 5 -17 7'31 9.43

12'26

0.794 1 -55 2'30 3'24 4'19 5 -45

23 1 259 280 295 314 332

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ASSOCIATION IN BENZENE SOLUTION. 701

1.

'Lo

2;

2.

S:.0 22.19 0 1680 0.339 0.520 0.897 1'427 2.019

93 1 22.19 , 0,3670 I 0.718

1'034 1'610

, 2.097 2.700

0.072 0.151 0.233 0.359 0.593 0-812

0.1 80 0,350 0'488 0.7 23 0'896 1.097

0.762 1.56 2 *39 4.12 6.55 9.26

1 *68 3.30 4 '74 7.39 9'54

12'39

8.

0.339 0.692 1.06 1 *83 2 '91 4 '12

0,748 1'46 2'11 3'28 4'21 5.51

9.

249 243 242 350 261 269

249 25 I 259 a73 261 301

P- Bendmonoxime.

Determinations were carried out a t 5S0, 80°, and 93'. I n the table of curves, the molecular weights found by the freezing point method in benzene (Auwers, Zed. physikal. Chem., 1893, 12, 701) and in naph- thalene (Innes, Inaug. Biss. HeidelbeTg, 1896) are also given. De- terminations with more concentrated solutions in benzene could not be carried out a t the freezing point, because of the small solubility of the substance. /3-Benzilmonoxime crystallises with benzene of crys- tallisation, the formula of the compound is 2C,,Hl10,N,C,H,. The abnormality in benzene might be considered to be due to the formation, in part, of this compound, It is impossible to decide in the present state of our knowledge whether this is really the case; i t seems more probable, however, t ha t the combination with the solvent does not affect the molecular weight to an appreciable extent in this instance.

From the curves (Fig. 7, p. 703), it will be seen that the association of /3-benzilmonoxime decreases considerably with rise of temperature up to SOo, the association then seems to increase, the 93' curve lying somewhat higher than that for SOo; the greatest difference is about 4 per cent. :

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702

1.

28

29

30

31

32

INNES: THE INFLUENCE OF TEMPERATURE ON

- 2.

31.0

43-3

61'28

73 *5

109.0

TABLE VI.

3. 4. ~ _ _ _

5. 6. 7. I

___--I-

Dimethyl Turtrute, CGH,,OG = 178.

53.7

63.1

73'2

79'2

93.1

24'74

22.19

22-19

22.19

22.19

0,3196 0.8606 1.470 2.@57 2.898 4.000

0.1704 0 *4402 0.816 1 *355 2.086 2.917 3,932 5 '1 22

0.2966 0 '6744 1 '207 1.836 2.894 4.134 5.213 6.283

0.2670 0.5528 0.990 1.662

3.919 5.025

0.4280 0.8590 1-459 2.002 3.103 4-170

2.528

0.147 0,337 0,520 0.662 0-821 1 *ooo

0.083 0,214 0.367 0.556 0.764 0.957 1.156 1.344

0.162 0.339 0-567 0.794 1.091 1.371 1 -57 1 1.751

0.159 0.301 0 5 0 0 0.751 1.029 1.371 1.592

0.266 0.492 0.780 0.997 1.351 1.613

Dime thyl 2'urtrat e.

1.31 3.53 6.04 E -45

11.91 16-43

0.984 2.02 3 *74 6 *22 9 *57

13.39 18-04 23.51

1 -36 3.09 5-54 7-51 1; *84 16.90 21-31 25 *69

1 -23 2.54 4.54 7.63

11.60 18.0 23 -1

1-96 3-94 6 '69 9-18

14.24 19-14

8.

0.74 1.99 3 -39 4 -75 6.69 9'23

0.553 1'13 2*10 3 '49 5 '38 7 $2

10.14 13'20

0.962 1-74 3 *11 4 *22 6 *65 9.50

11.98 14.44

0'69 1 '42 2.55 4-38 6 -51

11.2 14.35

1.10 2.215 3.76 5.16 8 *oo

10.75

9.

186 218 242 266 302 342

207 208 225 246 276 3 07 343 385

195 212 227 247 283 322 354 383

185 202 218 244 271 315 348

198 215 230 247 282 318

W i t h increasing dilution the molecular weight of dimethyl tar t ra te tends towards the same value a t the various temperatures, the mole- cular weight found being in every case near the normal (Fig. 8, p. 705). I n more concentrated solution the molecular weight decreases with rise of temperature between 54" and 79", the decrease increasing with t h e

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ASSOCIATION IN BENZENE SOLUTION. 703

temperature. The molecular weight at 93" is lower than that at '79" in solutions of moderate concentration, but the curves cross at a concentration of 8*7/100 mols. The curves are all slightly concave downwards, with the exception of that at 93O, which is almost straight.

FIG. 7. -fi-BenxiZmonoxime.

360

340

320

$ 300 -3 4 8 N

G

360

340

t I

6 320b 1 2 3 4 5

Hundredth-gram molecules per 100 grams of benzene.

The degree of concavity increases with the temperature up to 794 An attempt was made to carry out a series of determinations of the molecular weight by the freezing point method. Only one determina- tion could be made; at higher concentrations the substance sometimes separated out :

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704 INNES: THE INFLUENCE O F TEMPERATURE ON

10.0 1 0.197

lf7q*eexi*ng Point Method.

..

0.189 1.9'7 1'11 271

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ASSOCIATION I N BENZENE SOLUTION. 705

The heats of dissociation ( Q ) of P-benzilmonoxime, benzoic acid, and o-bromobenzoic acid from double to single molecules were calculated by means of the equation

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706 ASSOCIATION IN BENZENE SOLUTION.

in which V2 is the volume occupied by one gram-molecule of the sub- stance calculated as double molecules, at the temperature T2

P was taken as the volume of benzene in litres in which one gram-molecule of the substance, calculated as double mole- cules, was dissolved, and Vl as equal to Vz.

x was calculated by a slight modification of the equation used o calculate the degree of dissociation of a gas from its

density. x=- . M is the molecular weight of the

double molecule, m the molecular weight found.

,,

,,

M - m m

The following data were used :

1 .73 356 264 0'258 0'704 278 331 13 264 249 0'704 0.807 331 353 14

2.00 332 318 0'211 0.264 331 353 12.3 3.00 220 195 0.117 0'251 336 353 8.18

3'bO 344 328 0'169 0.232 331 353 8.18

- &.

14600 19900

7500 5300

23000

The heat of dissociation of gaseous N,O, (tl = 2 6 * 7 O , t , = 11 1 *3O) is 12,900 calories ; that of iodine vapour, 28,500 cal, ; acetic acid, 20,000 cal., and dimethyl ether hydrochloride, 8600 cal. It thus appears that the heat of dissociation of a substance in solution is of the same order as that usual for a vapour. The above result adds another instance to the many already known of the close analogy between the behaviour of a substance in solution and in the state of vapour.

The above experiments were carried out in the Chemical Laboratories of the University of Birmingham. I should like to take this oppor- tunity of thanking Professor Percy Frankland for his kindness in supplying most of the apparatus required for the experiments.

UNIVERSITY COLLEGE, LIVERPOOL.

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