(Communicated at the meeting of January ).

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Physics. -.. T he variatian at the dielectric canstant at liquid axygen with temperature." By WACLAW WERNER and W. H. KEESOM. (Communication N0. 178c from the physical laboratory at Leiden.

1 Physics. -.. T he variatian at the dielectric canstant at liquid axygen with temperature." By WACLAW WERNER and W. H. KEESOM. (Communication N0. 178c from the physical laboratory at Leiden.) (Communicated at the meeting of January ). ~. ntroductian. The dielectric constant of liquid oxygen has already been investigated by FLEMNG and DEWAR 1). by HASENÖHRL!!) and by BRET and KAMERLNOH ONNES 3). The latter also investigated its variation with temperature. The results differ from each other by 2 %. and this is to be ascribed to the fact that electrostatic methods are less accurate than high frequency methods. such as used R j t-k by BRET and KAMERLNOH ONNES. As however ~Kl the capacity of their connecting wires was not known accurately the absolute values of their provisional re su lts are too small 4). and we thought it desirabe to repeat the measurements with greater accuracy. 2. Methad. We have made use of the method and the apparatus. which we used for the T measurement of the D. C. of liquid and solid hydrogen. From the boiling-point to T = 68.5 we also used the same condenser with a capacity of about 60 cm. (the condenser A). At lower temperatures the liquid cryostat had to be replaced by a hydrogen vapour cryostat. For this a new condenser (condenser B) was constructed according to our ideas by G. J. FLM. to whom s A we ren der our best thanks. This condenser has 3 plates E. Mand. E and 1 were soldered to a copper tube. into which the glass vacuum tube R reaches. The copper tube was narrowed at the Fig. 1. lower end and provided with holes. To 1 was soldered a single glass tube S provided with holes. to which the plate M was fixed. E and. and also the metal cap H were earthed. By means of ) J. A. FLEMNG and J. DEWAR. Proc. Roy. Soc They found at the boijing-point eb = ) F. HASENÖHRL. These Proc Leiden Comm. NO. 52. <B = ) G. BRET and H. KAMERLNGH ONNES. These Proc ; Leiden Comm. NO. 171a. B= i) Compare our communication in these Proc ; Leiden Comm. NO

2 307 the connecting wire D and the movable contact K. which was provided with an elastic silver plate K 2 M could be switched in parallel to the measuring condenser or switched oh. The plates Mand we re also provided with holes. These holes. as wel as the vacuum tube R served for making the entry of liquid during contraction possible. and in order to prevent as much as possible the formation of vacuols on solidification for the measurements in the solid state. The capacity of the condenser was about 21 cm. n the measurements with condenser A the temperature in the condenser vessel as wel as that in the cryostat bath. was calculated from the pressure of the saturated vapour. The temperatures were then calculated from the formula,of CATH-VERSCHAFFEL Tl). For condenser B a platinum wire of 0.05 mmo diameter and ca. 52 Q resistance served as a thermometer. This platinum wire was wounded round the outmost plate of the condenser and insulated from it by means of mica. This thermometer was calibrated with the aid of the platinum thermometer Pt 24 in the hydrogen vapour cryostat. 3. The course of the measllrements. The measurements with the condenser A we re made in the same way as our measurements for hydrogen. As the exchange of the tempel'ature took place slowly. a temperature decrease was of ten observed during the measurement; in such cases the results of the separate measurements we re reduced to a mean temperature and af ter that the average was taken. For the measurement with condenser B this condenser was evacuated. cooled in the vapour cryostat to the right temperature and its capacity measured. Then the condenser was filled with newly condensed oxygen, and brought to the right temperature. The capacity was measured again. The oxygen was taken from a high pressure cylinder. From analysis thc contents of th is cylinder appeared to contain 2.4 % admixtures. mainly nitrogen. As the temperature exchange for this condens er was very slow. the measurements were made during the cooling. The rapidity of cooling was generally 0.01 to 0.04 degree per minute. The case. in which it was greater. is indicated in table 11. The temperature was read oh each 3 or 5 minutes. For a series of 7 to 1 adjustments of the measuring condenser. alternately with or without the experimental condenser. the mean values of capacity and tempera tu re we re calculated. These values are given in Table 11. the necessary correction ( 4) ha ving been applied. Although th is manner of working with a slowly decreasing temperature diminished the accuracy of the measurements somewhat. it. however. made it possible to read more points and so to follow better the course of the D. C. with temperature. 1) P. G. CATH. These Proc Leiden Comm. NO. 152d.

308 4. Calculation and corrections. The value, found for the capacity, was c:orrected for the calibration of the scale. The D. C. was calculated as the ratio between the capacities of the condenser filled and empty.

3 Calculation and corrections. The value, found for the capacity, was c:orrected for the calibration of the scale. The D. C. was calculated as the ratio between the capacities of the condenser filled and empty. This value had still to be corrected for the capacity of the connecting wires. For condenser A the correction was made in the same way as for the measurements with hydrogen, and amounted to to For condenser B the capacity of the wire D was important. This capacity was due chiefly to that part of the wire that was surrounded by the metal tube H. This capacity was measured directly and corresponded to 0.96 scale-divisions. This correction was applied to measurement N0. 12 (boiling-point), which was made in the liquid cryostat. n this measurement the level of the liquid was below the tube H. With all other measurements the liquid was high in the tube R. 50 that the tube H was also filled with the liquid to be investigated. For each temperature the capacities of the condenser consisting of tube H. glass tube and wire in empty and filled state were calculated from the measurements of this condens er and the capacity was subtracted from the measured capacities. The dielectric constants calculated 50, differ from the va lues not corrected by to Accuracy. The accuracy of the measurements with condenser A was of the same order of magnitude as that of the measurements with hydrogen. t was for a capacity measurement 0.15 per mil, and hence was for a determination of the D. C. 0.3 per mil. The mean error of the value of the D. C. at the boiling-point, calculated from th ree measurements, was 0.15 per mil. The measurements with condenser B were e ss accurate, as its capacity was smaller. and 'as at each temperature only one measurement could be made 1). The mean error of a capacity measurement was 1 per mil, hence the determination of the D. C. can be considered as being accurate to 2 per mil. For the measurements with condenser A. the temperature was derived from the pres su re of the cryostat bath. The accuracy of 0.5 mmo of the pressure measurement corresponds to an accuracy of the temperature measurement of ca We are, however, especially for the measurements at the boiling-point, not perfectly certain of the ptirity of the cryostat liquid. Meanwhile the temperature measurement can be considered as being accurate to For condenser B the temperature could be measured to by means of the platinum thermometer. E we take however into account the change of the temperature during the measurement, and the possible errors in the calibration curve, we can con si der the accuracy of the temperature determination for this condenser as also being 0.1 2). ) The measurements Nos. 11 and 12 both consist of 3 separate measurements: thelr accuracy is comparable with the measurements with condenser A. 2) For the inftuence of the oxygen being not perfectly pure see p. 309 note 3.

4 Results. Table contains the results obtained with condenser A. Series was performed with the paper scale, series 11 with the metal scale 1) Series No. 1 Date TABLE. Condenser A Pressure Tem perature Capacty Dielectr. const. e Pi Pe T. T C Co corrected 1 28.m' li V ~ l.i V 8i li Pi and Ti relate to the condenser vessel. pe and Te to the cryostat bath. Table 11 contains the results of the measurements with the condenser B. Table 111 contains the results of the measurements N0. 1, 6 and 12, made under atmospheric pressure. l::,.e represents the correction necessary for the reductio.n of the measurements to the boiling~point of oxygen. T = K 2). 50 the mean value tb = gives the value of the dielectric constant of liquid oxygen at the boij.ing~point 3). ) Comp. our paper about hydrogen, l.c. l) P. G. CATH, l.c. 3) From measurements by Dr. L. EBERT and one of us, shortly to he pubhshed, of the D. C. of liquid nitrogen, we can derlve that the amount of nitrogen, that mlght have been present in the liquid (comp. 3), would make the value of the D. C. somewhat too smal!. but the nfluence of t is less than 1.3 per mil. Some control measurements with pure oxygen confirm our results. These control measurements were made by Dr. EBERT, to whom we render our best thanks.

5 310 [NO. 1 Date TABLE 11. Series. Condenser B. Temperature Capacity Dielectr. const V ' T Co C corr. Remarks in the iquid -cryostat X ' :: partly undercooled solid rapid cooling TABLE \11 NO. T c; 10. ~ <: 1 Ered Average EB = ± Though the measurements we re made with two different condensers. the agreement of the results is satisfactory. The value obtained. is almost

6 311 that of DEW AR 1) (1.493); the difference is less than 1 %, and this is what DEWAR gives as the limit of the accuracy of his measurements. From the values, which LVENO and DEWAR 2) give for the dispersion of light in liquid oxygen, DEWAR 3) calculated for the value of the refractive index for infinitely long waves n", = From th is n;, = ) follows, which agrees very wel with our results for the dielectric constant, indicating that oxygen molecules do not bear electric doublets. Table V contains the values of the D. C. from the 3 observation series. TABLE V. NO. ë- T l,0 P= P PT tabulated after the temperatures, and contains also the va lues of the t function of CLAUSUS-MoSOTT P = and of the product P T. t + e From the boiling-point to 58 K. e has a rectilinear course, see fig. 2. At 55 a small increase begins, which becomes very obvious at 54.4 K. The results, obtained with the two condensers fit very weil onto the same straight line. 1) J. DEWAR l.c. The absolute values of BRET and KAMERLNGH ONNES are too smal owing to the reason mentioned in ; when reduced to the right values. they show the same dependance on the temperature; only the accidental errors are greater. 2) LrvENG and DEWAR. Phil. Mag. (5) 40, 269, ) J. DEWAR, l.c. i) For vibrations with the frequency of the lightwaves, we can take the magnetic permeability as being.

7 312 Accordingly P has an almost constant value, namely P = ); the largest deviations are 0.5 %. This again according to DEBJE'S theory 2) points to the fact that iquid oxygen is to be considered as a iquid free from e1ectric doublets.,,60t ,56t , ~'~ ~-----+~~--~--.. T Fig. 2. This appears still dearer on considering the products P T. Prof. M. WOLFKE was so kind as to calculate from our measurements Nos the constants of DEBJE'S formula: by the method of least squares. He obtained PT=a+bT a = , b = The negative value of a as weil as its small value indicate, that this result for a is cétused by accidental errors, so that a can be considered as being O. from which, as a is proportional to,u 2, it follows again that the molecular electric doublet moment,u = O. The factor bagrees very weil with the optica value of P T calculated from the data of LVENG and DEWAR: n 2-1 T PT= n2+2' e-= The measurements of 25 X (tabe 11) extend to below the melting-point, ) From the measurements of FRTS (Phys. Rev. 23, 345, 1924) t follows that for gazeous oxygen P = ; for oxygen with 2.4% nitrogen P = ) We must bear in mind, however. that the application of DEBJE's theory to iqulds is not quite safe, as n it the mutual actions between the molecules are not taken nto account, cf. SÄNGER, Physlk. Zs. 27, 165, (Note added in the translation).

8 313 and thus also include observations on the solid state. These as wel as further experiments, made by us, leave several points unexplained. The discussion of these results must be delayed till a later publication. Summary. 1. The D. C. of liquid oxygen was measured from the boiling~point to the melting~point. 2. For the D. C. of liquid oxygen at the boiling~point T = K. was found: EB= E-l 1 3. The function of CLAUSUS-MosOTT p:= is constant to E- (! 0.5% from the boiling~point to T = 58. At further cooling P increases from to From the calculation of the coefficients in the formula of DEBJE PT = a + bt follows, that in liquid oxygen the molecules have no own doublet moments.

(Communicated at the meeting of September ).

(Communicated at the meeting of September ). Physics. - "Preliminary measurements of the dielectric constants of liquid and solid nitrogen." By L. EBERT and W. H. KEESOM. (Communication N. 182d from the Physieal Laboratory at Léyden). (Communicated