Physics. - Isotherms of manatamic substances and their binary mixtures. XXVI. Isotherms of helium at -183.0 and -201.5° C. and prCSSllres of 3 ta 8 atmaspheres. By G . P. NIJHOFF and W. H. KEESOM. (Camm. N0. 188b from the Physical Laboratory at Leiden. )

(Communicated at the meeting of October 29, 1927).

§ I. Introdllction. In a former communication 1) we pointed to the importance of

measurements of gases in slightly compressed states in order to obtain values as exact as possible of the first vi rial coefficients. Especially for helium this is of great importance with a view to thermometry at low temperatures. Moreover, as we then also remarked already, the now examined pressure reg ion for helium with its low critical pressure, is of particular importance, because comparison, by means of the principle of the corresponding states, becomes possible with other gases, for which the equäclull Ol state in the corresponding pressure region has already been exactly examined.

We found it a great difficulty that the divided manometer constructed by us for pressures of I to 4 atmospheres, which, as has also been described in the former paper, must be read with a cathetometer, is not very fit for a fast use, so tha t the measurements with it want comparatively much time. With a view to this we have constructed two closed manometers, which are being shortly described here.

§ 2. The closed manometers M 6 and M 20. These have been arranged in the same way as those described by

KAMEI~L1NGI-I ONN ES and HVNOMAN:!).

The first , destined for pressures between 2 and 6 atmospheres, consists of a glass stem ISO cm long, with a section of about 0.08 cm 2 and a capacity of about 12 cm8 . To this was blown at the upper end a small reservoir of 6 cm8 and at the lower end a reservoir of 18 cm3 • So if we read the top of the mercury meniscus to 1/10 mm, when the mercury du'ring the measurements is standing quite at the up per end in the stem we have still an accuracy of 1/ 7 GOO' whereas at a lower place of the mercury the relative accuracy increases proportionally to the volume.

I) G. P . NljHOFF and W . H. KEESOM, These Proc. 28, 963, 1925, Comm. Leiden NO. 179b.

2) H. KAMERLINGH ONNES and H. H. F. HYNDMAN, These Proc. ., 776, 1902, Comm. Leiden NO. 7Bc.

405

The second manometer in principle quite identical to the first has the following dimensions: large reservoir 51.3 cm3 • stem 7 cm3 with a length of 143 cm. small reservoir 2.9 cm3•

It must still be observed that it did not seem desirabIe to us to join the manometer for the reading of the lowest pressures to the piezometer by means of compressed air as is usually done for the other manometers at Leiden. Piezometer and manometer we re being filled out of the same mercury reservoir and formed a coup Ie of communicating vessels. In order to calculate the pressure in the piezometer. we must of course make corrections for the difference in height of the two mercury columns and for a possible temperature difference of the two water jackets.

§ 3. The measurements and results. The measurements are made in the same way as indicated in our former

communication 1). We were very pleased that. for a great part of these. Prof. BORIS ILIIN

from Moscow was willing to work with us. We have collected the results of these measurements in a separate communication 2). The remaining ones we give in table I. In table 11 the values of BA are given then. which we have calculated Erom our measurements and Erom those of ours and of Professor ILIIN.

Por our calculations we took the value aA = 0.0036618 used until now

TABLE I.

8 P dA O-C(pvA) °C. int. atm.

pVA

- 183.07 3.2279 0.33112 9.74845 +0.00012

4 .0064 .33144 12.088 + 7

5.1853 .33197 15.620 + 4

7.3067 .33277 21.957 - 17

8.1456 .33327 24.141 - 6

- 201.52 2.9347 .26323 11.149 -0.00004

3.5627 .26351 13.520 - 5

6.0023 .29471 22.669 + 5

6.5786 .26478 24.845 - 10

1) G. P. NIJHOPP and W. H. KEESOM. These Proc. 28. 963. 1925. Comm. Leiden NO. 179b. •

2) See the following communicatioD NO. 188e. These Proceedings 31. 408. 1928.

27 Proceedings Royal Acad. Amsterdam. Vol. XXXI.

406

TABLE 11.

Measurements of NIJHOPP. KEESOM and ILIIN

0

I BA · 103

11

0

I BA · 103 O°C. O°C.

- 103 .29 + 0.366 - 235.77 + 0.0295

- li6 .50 + 0 .256 - 2i9 .80 - 0 .0085

- 183.07 + 0. 158 - 252.57 - 0.0100

- 201.52 + 0.120 - 255.8i5 - 0.0237

- 22i . 9i + 0.059 - 258.99 I - 0.03iO

Measurements of BOKS and KAMERLINGH ONNES.

+ 20 + 0.550 - 103.6i + 0 .36i

0 + 0.523 - li202 + 0.270

- 37.iO + 0 .i80 - 183.3i + 0.185

- 70 .30 + 0.i28

Measurements of HOLBORN and OTro.

0 + 0.5282 - 183.0 + 0.1562

- 50 + O.i3H - 208 .0 + 0.0998

100 + 0.3366 - 252.8 - 0.0093

- 150 + 0.2295 - 258.0 - 0.0337

- 183.0 + 0.1537

at Leiden. We have given up the idea of a recalculation according to the determination of the fundamental pressure coefficient of helium by KEESOM and Miss VAN DER HORST 1) since the values of BA wiII only slightly

change. But the values of B = ~: will be changed somewhat. It is also

for this reason that we have preferred to give the values of BA in: this communication. instead of those of B.

At the same time we herewith give the values of BA. which we re calculated by us from the measurements of BOKS and KAMERLINGH ONNES 2) and for comparison the values of BA. reduced to Leiden units. which have been found in Berlin 3).

1) W. H . KEESOM and Miss H. VAN DER HORST. These Proc. 30. 970. 1927. Comm. Leiden NO. 188a. .

2) J. D. A. BOKS and H . KAMERLINGH ONNES. Comm. Leiden NO. 170a. 3) L. HOLBORN and J. Orro. Zs. f. Phys. 30. 320. 1924 and 37. 359. 1926.

407

These different values of BA are represented in fig. 1.

r\ .. _-- +

\ 0.25

1-.- :\ +

:\ -$> I'1UHDrr .. 1((( 'SOM & ILllrt

lIJ HOLBCRM LOTTO Ol . v AC,T 6. KAM(nLIJ'1[:~OI'1I'1L5

À .. PInMIl"" .. BOIl'] &.

X P,llL~tIO~1'f4n'lIIlI.~A"{fII.IIC. .. OMnf ':J - - _. ~_.

\ - +

~\ ---- -

0.20

0.15

+0.10

1\ \

+0.05

1\ 0

\ 1\

.00

_0.09 -160 -1110 -200 -220 -Z60"C

Fig. 1.

Herewith we observe that the German results, as far as the temperatllre region, which still can be reached with liquid oxygen, are lying lower than ours, while at the temperatures of liquid hydrogen, though the dispersion of the Berlin values is larger, the agreement can yet be called very satisfactory.

Besides it is very remarkable that at. lower temperatures the BA -values tend to depend linearly from the temperature and that af ter extrapolation this line passes through va lues found in the liquid helium region.

Finally we thank Miss A. SOLLEWIJN GELPKE for her help as weIl at the measurements, as especially at the calibration of the manometers.

27*