O S THE D I E L E C T R I C C O N S T A N T S O F PURE S O L \ 7 E N T SI
BY H E R M A N SCHLUXDT
INTRODUCTION In I 893, Xernst,Zfrom theoretical con5iderations based upon the theory of electrolytic dissociation, deduced his well known rule, that other things being equal, the greater the dielectric constant of a medium, the greater is its dissociating power. I n the same year J. J. Thoiiison3 also pointed out this relation, saying that if we accept the view that the forces between the atoms are electrical in their origin, then the effect of surrounding tlie molecules of a substance by a iiiediuin possessing a very high dielectric const:mt like water, would be to practically dissociate them. ,According to Nernst, proportionality between the dielectric constant and dissociating power need not necessarily exist. T h e experimental facts, he sajs, show beyond a doubt that a inarked parallelism exists between the dissociating power and the dielectric constant of a solvent. Exceptions to the rule, Nernst explains by assuming tlie existence of specific influences of which the association of the ions with the molecules of the solvent is probably of prime importance. T h e existing experimental data, at the time the abox-e relation between the dielectric constant and dissociating power was pointed oiit, accorded well with it ; 4 and subsequent investiga-
’
Extract from the author’s dissertation submitted for t h e Degree of Doctor of Philosoplij- at t h e University of Wisconsin. part of this investigation appeared in \’olume j , p. 157 (1901) of this Journal. T h e present article conipletes the paper as it is printed in full as a Bulletin of t h e University of IVisconsin. Science Series, 1901. ’’ Gott. h-ach. S o . 1 2 ( 1 8 9 3 ) . Also Zeit. pfiys. Chem. 13, 531 (1S94). i Phil. N a g . 36, 320 (iS93j. See Nernst: “Theoretische Cheniie,” p. 365. (Dritte Auflage. ) +
504 tions furnished numerous additioiial examples in its snpport. But exceptions also appeared, which point to a marked specific influence of the solvent. Some of these exceptions are noted and discussed in another part of this article. Since the formulation of the Xernst-Thoinson rule, excellent new methods for determining dielectric coilstants have been devised by T h n ing,I Kernst,' and Drude ; 3 a i d these investigators have measured the dielectric constants of a number of siibstances. T h e pupils of Kernst, and Drude, and others have elaborated, modified, and perfected these respective methods, so that the determination of dielectric constants at ordinary temperatiires is now a comparatively simple operation. During this period the electrical conductivit! of non-aqueous solutions has also received considerable study, and the dissociating power of various solvents which yield conducting solutions has inoreover been investigated by means of cryoscopic and boiling-point determinations. T h e selected examples given in the following table will serve to show that various other solvents besides water possess ionizing pov%'erin a very marked degree. Under V, in the third column, the volnine in liters is given, in which one gram-molecule of substance is dissolved ; and the next column indicates the corresponding molecular conductivity, while the fifth column gives the teinperature at which the iiieasiirenients were made. T h e dielectric constants of the last four aolvents given in the table have, to my knowledge, not been determined before. I n a previous coinmtinication' on this subject, the values obtained for the dielectric constants of the aliphatic nitriles were given, and i t was stated that Drude's I ' second " method was followed in making the measurements. T h e results 11 liich follow were obtained \\it11 the same apparatus. Resides the substituted ammonias, this investigation embraces a number of other orZeit. phys. Chem. 14, 286 (1894). Also P h I s ReLiew, 2 , 35 (1894). Ibid. 14, 6 2 2 (1894). Ibid. 23, 267 (1897). +Jour. Pliys. Cheni. 5 , 157 (1901).
TABLEI. -
1
__
~ ~
f3
Solute
__ Observer -
~
KI
I
2
8 Kohlrnusch'
10.0
I000
Methyl alcohol Formic acid
LiCl
11.7
117.4 I '74
KC1
Liquid amnionia
KBr
Acetone
KI
Li q ui d si11ph u r
I024
301.9 I354 6 j040
~
18 St. v. Las-
144.i
cyiiski" o 1Valdt.n'
11 j 7 . 6
S (C-H; ),I
16
dioxide
Zannino~ichTessariii' 3s Franklin and Kraus'
2j
32 1
128 I024
Benzoni trile
AgSO
Acetonitrile
AgXO,
9.43 151.96 8
2.7
Lincoln'
25
Dutoit and Friderich"
I28
Pyridine
SH,I
Phosphorus oxy S ( C H , ) ,I chloride Arsenic trichloride S( CH,),I
St. Y . Lascynski ant1 Si. v . Gorski!'
79.02 1264.32 204
'
I223 250
Ijoo
j I .4 66.6
25
I~~nlden"'
2j
II-ald~11'"
g a n i c compounds containing nitrogen, and includes most of t h e inorganic solsents i n w h i c h U'aldenxo made electrical coiitluctii.ity measurernents.
' Ivied. A n n .
26, 161 (188j). Ibid. 52, 328 (1894). Zeit. phys. Cheni. 19,2 j 1 (rSg61. ' Anler. Chem. Jour. 23, 288 I, 1900 I . I' Ber. chem. Ges. Berlin, 32, 2S62 I ~ S g g i . Zeit. Elektrochemie, 2, 55 ( 1895 j , Jour. Phys. Cheni. 3, 457 (1899). ' Bull SOC.Chim. Paris, [3] 19, 327 (1S98) !' Zeit. Elektrochemie, 4, 290 (1897). Zeit. anorg. Chem. 25, 209 ~ 1 9 0 0 ) . ''
506 Experimental Results In addition to the nitriles previously measured, the dielectric constants of ethylene cyanide, mandelic nitrile, a- and B-naphthonitriles were measured. E fhylem cyn 12 i& T h e sample of succinic acid nitrile was Scliuchardt's make. I t was treated with fused calcium chloride, filtered, and was twice redistilled under diminished pressnre. Its boiling-point was 168" under a pressure of 2 8 mtn. -4 solid, almost colorless mass was thus obtained which melted at j s o C. Its D.C.' was measured in tlie forin of cell Drude*used for the measurement of substances at higher temperatures. I n making the measurements the cell was kept in an oil-bath, of the form figured by Coolidge,3 attached to the apparatus. T h e temperature of the bath was kept at 60' C during the nieasureinents of the liquid ethylene cyanide. T h e average of three deterininations gave the value 61.2 for the D. C. T h e D. C. of the solid coinponnd was also determined. Four determinations gave an average of 65.3 at 2 3 " C. No sudden change was observed in the L). C. at the nielting-point. T h e absorption of the solid ethylene cyanide wa5 very slight, but the liquid sample did not show quite as well a defined inaxitnnni resotiance, which was found to be due to its greater conductivity. In fact the qualitative measurements of its resistance show that the resistance increases very rapidly as tlie temperature is lowered, but no sudden change in the resistance was observed at the melting-point. a-lVnfilifhonifrilele
Scliuchardt's preparation was redistilled under diminislied pressure. Its melting-point was 37" C, but the substance ma)easily be kept in a liquid state at 20" C provided the solid phase is not present. T h e tollowing 1-alues were found for the D. C. of the liquid sample : I n the $resentation of results this abbreviation is used for dielectric constant.
- See Fig. 7. p. zSg, Zeit. phys. Chetn. \Vied. Ann. 69,
I,
33 (1S99).
23.
Dielectric Coizstnrzts of Firire Soli,eizts
50T
D. C. = 16.0 at 70' C. i L = 17.9at 42' C. := 19.2 at 22'C.
T h e position for maximum resonance was not well defined. 11). efforts to determine the D. C. of the solid sample did not yield satisfactory results. I n solidifying, the mass between the plates of the condenser did not become compact and homogeneous ; air spaces seemed to exist, and a well defined maximum was not observed. T h e value 6.3 at 21" C must therefore be regarded as only approxiinate. ,B-Alkph thoz it?-ilc This sample was also redistilled under diminished pressure. Its boiling-point was 190' under 35 inm of pressure. Its inelting-point was 64" C. I t could not be supercooled. T h e D. C. for the liquid was found to be 16.9 at To", and for the solid the value 4.3 at 2 2 " C was found. Jfafztr'elic m'tm'le T h e preparation from which the sample was obtained showed decided signs of decomposition, being of a dark brown color, and somewhat syrupy. I t was treated with fused calcium chloride for two weeks, was then filtered and distilled under diminished pi-essure. T h e sample thus obtained was redistilled ; its boiling-point was 94" under a pressure of j o mm. X mobile, colorless liquid was thus obtained, whose specific conductivity was found to be 2.2 Y IO-IO reciprocal ohms. Its D. C. was found to be 17.82 at 23". Absorption of about the same order as that of nitrobenzene was observed. Its absorption index wa5 also determined by the method outlined by Drude.' T h e value obtained in this may was 0,045, agreeing very well with that of nitrobenzene, which Drude places at 0.0j. Drude has found that this anomalous absorption is characteristic of compounds containing hydroxyl. The Substituted Ammonias T h e amines whose dielectric constants were measured are enumerated in Table I. T h e samples used were Schuchardt's Zeit. phys. Chern.
23, 2 9 2 - 2 9 7 .
preparations with the exception of the two toluidines and the s),lidiiie, which were of Troiiiiiisdorff’s inatiufacture. Each saiiiple, except metliylaiiiitie, mas deli\-drated with fused potassium hydroxide and then distilled, and in many cases the distillate was again treated with fused potasli arid redistilled. T h e sample of iiietli\-lamine was doubtless iinpure for, iipon eixporation it left a recfidiie, aiid it did not j-ield a well defined position for iiiaxiiiiiini resonance, while with all the other samples well defined maxima were observed. Hence the value found for the L>. C. of niethylaniiiie is cloobtless too high. Tlie third columii in tlie following table gives the boilingpoints of the saiiiples takeii for the measurements, aiid the fourtli column indicates the corresponding haronietric pressure, while the last column g i \ a tlie temperattire at wliicli the dielectric constant was ineasured. TABLEI1 Xa111e
11et11y la mi 11e Et hylamine 15opropylamine Butylamine [ 72 ) Isobutylaniine -%mylamine Dieth ylaniine Dipropylamine Diiiobut>-lamine Trimethylamine Aniline’
6.17~1 5.15 2 0 j.3021
4.43 2 I 4. j 0 2 2 3.5821 2.9022
2 6j22
2.95 4 18.5
7.2
j.9320
5.9 j 2 0 4.9020
5 . 8 20 5.07 2 0 3.55 2 0 Ratz.
Tlie value 7 . 1 j iat 2 1 ” ) was found 1 ) ~ r)rude ; and 7 Zeit. pli!s. Chetti. 19,9 1 (1896).
22
( at
1 5 ” ) by
Dielectric Coizsinnts of Pztw Solvrzfs
509
Miscellaneous Organic Compounds a-Picoliue
T h e sample was Schuchardt's preparation. I t was treated with fused calcium chloride, and redistilled. T h e boiliiig-point of the portion taken for the measureinents was 128.jo-129. j" C at 736 inm of pressure. T h e value foiuid for the D. C. is 9.8 at at 2 0 " C. Pi)o-idiiie T h e sample was E. de Haen's preparation. It was redistilled and the portion distilling between I O ~ . ~ ~ - - I O C~ .under O ~ a pressure of 7.15 111111 was used for the measureinents. I t was a n almost colorless liquid and showed no absorption. T h e x aliie found for its D. C. was 5.8at 2 2 " C. c a r h r i dich loride T h e sainple used mas of Scliiicliardt's make. Its boilingpoint was I 18" at 726. j mni of pressure. T h e Yalue 2.46 was found for its D. C. at 2 1 " C. zV7tm n i e f ha ne Schuchardt's preparation was treated with fiised calcium chloride and redistilled. Its hoiling-point was 99.9" under a pressure of 738.4 iiiiii. T h e dielectric coiistaiit foiind was 40.4 at 19" C. Thwingl gives the value 56.36 a t I j" C. A 7ifitr-oefha Jze Schuchardt's preparation was dehydrated and rectified as in the case of nitroinetliane. Its boiling-point was I 10.5" C iinder a pressure of 738.3 iniii of pressure. T h e value of its D. C. wa5 found to lit 29.5 at 18"C. Lli7efhy1 n 2 tl-nf e The sample of methyl nitrate used for the tneasurements was prepared from Kahlbauin's best ilietlipl alcohol by treating it nit11 nitric acid according to the method of J. Lea." T h e ~
~
-
~
See Beilsteiii. \rO1.
_
' Phys. Review, 2, 35
I., p.
324.
_ ( 1894).
Handbuch der Organischen Chemie."
Third Bdition'
sample was washed with water containing a sinall amount of sodium carbonate, and then with distilled water. I t was dehydrated with fused calcium chloride and finally distilled from a water-bath. Its boiling-point was 64.4" C at j30.2 inm of pressure. T h e value 23.5 was found for its D. C. a t 18" C. S o absorption was observed. EthyZ n i t m f e Schuchardt's preparation was washed witli water containing a trace of sodium carbonate to remove traces of nitric acid and alcohol. I t was then dried with fused calcium chloride and redistilled twice. T h e boiling-point was 86. I " u'nder a pressiire of 729.4 mm. T h e average of three deterininations gave the value 18.3 at 18" C for its D. C. Thrving found the value 17.72 at 15") and Drude found 19.6 for the D. C. of this compound a t
17" C. Propy I $2 itrat e This compound was prepared according to the inethod of n'allach and Scliulze.' T h e propyl alcoliol used for its preparation was redistilled. Its boiling-point was 95.8' under a pressure of 752 inm. T h e saniple of propvl nitrate was dehydrated and rectified as described for i n e t h ~ ~nitrate. l Its boiling-point was 108.5" C under 738.5 mm of pressure. T h e value 13.9 was obtained for its D. C. at 18"C. lsobzi tyI mlrnte Schuchardt's preparation was redistilled. Its boiling-point was I 20.0' under ;38.2 171111 of pressure. One series of measurements was inade which gave the value I 1.7 for its D. C. at 19' C. Iso$t*o$j~I 7 2 i f r i f p A sample of isopropyl nitrite, probably not entirely free from nitrous acid, was measured. T h e value I I . j \\as found for its D. C. at 19' C. E f/yi 2 ZL refha ue T h e sample used for the measurements was kindly furnished by the School of Pharmacy of this University. Its ineltingBer. chern. Ges. Berlin, 14, 422.
Dielectric Constants o f Pzive Sohetzts
jII
point was 48" C. T h e value found for the D. C. of the liquid sample at 60" was 13.6; the solid form gave the value 3. I S at 23' C. A my Zszi@/z;wkzie T h e boiling-point of the sample was 116.5' C under 7 5 2 n1m of pressure. T h e D.C. found was 4.35 a t 2 2 " C. With the exception of the substituted ammonias, the foregoing results are summarized in the following table : T h e third column gives the boiling-points of the samples used for the measurements, and the fourth column indicates the corresponding barometric pressures, while the last column gives the term peratures at which the dielectric constants were measured.
TABLE 111.
______~~Same ~~
~
~
~
Formula
B.P.
P.
___--
D.C ' t o
~
-~
Kitromethatie' CH,NO, 99.9 738.440.4 I9 II0.j 1738.329.5 18 C,H,XO, Nitroethane Methyl nitrate 64.4 730.223.j 1 8 CH,XO, 729.418.3 I 8 C,H,NO, 86.1 Ethyl nitrate' Propyl nitrate '738.j 13.9 18 C,H.NO, 108.j Isobutyl nitrate (CH,),CHCHINO, 1 2 0 . 0 736.211.7 19 Isopropyl nitrite (CH, ),CHXO1 - I I I . ~ 19 ? Ethyl urethane CO( S H , )(OC,H,) - 13 6 60 Ethyl urethane (solid) I -3.18 23 a-Picoline 128.5-129. j 7 3 6 9.8 20 C,H,X.CH,(a) I0j.j-IO7 745 j . 8 20 Piperidine C,H,,E Carbon dichloride c,c4 I I8 726.5 2.46 2 1 Amylsulphydrate C,H,,SH 116 5 752 4.35 2 2 Ethylene cyanide C,H,(CN), 168 28 61.2 60 (solid) '' 65.3 23 a-Xaphthonitrile C,,H,CN(a) 1 - 16.0 7 0 (liquid) " 1 '7.9 42
,
,i
' I
' 8
I '
' I
(solid) '' p-Saphthoiiitrile ClOHiCX(P) " (solid) ' /
' I
Mandelic nitrile
C,H ,CH
-
SO,C1, SOCl, POCl (CK), Br
68.4 76.8
I
1
22
35 33.2 54
21
-
740.2
751.3 739.2
__
I
f3
3 36
-
-
c
-
740 -
750 738
I0j.I
r)
740 1
-
-
___
-
I2
75 18
3.7s 3 2 35
21.
