148
R.
D. TOLD .4XD If. J. RELDhZ1-h;
(26) SHEPPARD, Y. E., , ~ X DGEDDES,A. L.: J. Chem. Phys. 13,63 (1918). (27) STAUFF,J . : 2. physik. Chem. A183, 55 (1938). (28) TARTAR, H. V., A N D CADLE,R. D.: J. Phys. Chem. 43, 1173 (1939). (29) WRIGHT,K. A., AND TART.4R, H. v.: J. -4m. Chem. sot. 61,544 (1939). K. 9., ABBOTT, A. D., SIVERTZ, V., AKD TARTAR, H. V.: J. Am. Chcm. SOC. (30) WRIGHT, 61, 549 (1939).
ELECTRICAL CONDUCTIVITY O F CRYSTALLINE AND LIQUID-CRYSTALLIKE SOAP-WATER SYSTEMS' R. D. VOLD AND M. J. HELDMrlW Department of Chemistry, University of Southern California, Los dngeles 7, Caltfornia Receaved August 26, 1947
The present study was undertaken with a twofold objective: first, to detesmine phase boundaries in soap systems in regions of composition and temperature where other methods have failed, and second, LO learn more about the nature of the various phases and the changes occurring a t the observed transitions. Phase changes can be deduced from changes in slope of the resistancetemperature curves, while the absolute values of the conductance, both A.C. and D.c., and their dependence on temperature and frequency help t o distinguish between dipole oscillation, surface conductivity, and ionic or micellar migration as the mechanism of the process. In some instances these data can also be used to deduce possible internal structures of the different phases. Preliminary experiments were carried out with anhydrous sodium palmitate. Systems of anhydrous and hydrous sodium stearate up to 12.8 weight per cent water were then investigated lvith varying thermal and pressure treatment before and during measurement. Specific conductances of two of the liquid-crystalline phases-soapboiler's neat and middle soap-\\-ere also determined. Previous attempts t o study the electrical properties of solid and semisolid soap systems haye been few and relatirely unsuccessful. Fischer and Hooker (9) determined the change in conductivity rcsulting from \\-hat we now ~ O T toV be the separation of solid soap from solution, although they believed that it was due t o inversion of an eniulsion or solution. Bhatnagar and Prasad ( 2 ) s t u d i d the conductivity of "molten" alkali metal soaps at 182-20i"C., but did not estahlish sufficiently the purity a i d moisture content or' their qamples, nor nerc the questions of adequate clectrodc contact and possible chemical decomposition carefully considered. In the present investigation great pains were takcn t o 1 Presented a t tlic T n e n t ) -hi>t S a t i o n a l Colloid Symposium, mhich was l i ~ ~ !w ~ !t l e r t h e auspices of thc Divisiriii of Co!loicl Cliernistrv of t h c .lmeric i n Chemical S o r i c ~ y.it Pa!o Alto, California, June 18-20,1947. 2 Present address. Depai tiiient of Chemistiy, East 1 x 1 l!~gtbl ~ Junior C olicgt,, Los .ingeles, California.
COXDUCTIVITP O F SOAP-WATER
SYSTEMS
149
establish a Talid experimental technique, and it was shown by comparison with previous literature that sharp changes in the slope of the resistance-temperature curve. could be attrihuted to phase changes in the system.
// \
C'ond iicfizltfg Zwidgc
Conductivities w t w determined n-ith a Khetitstone 1)ritlge which was COIL structed lwgcly from ordinary radio parts3 and is bhonn schematically in figure 1. The potential source for the bridge sou as an audio-frequency oscillator n-ith ~t. range of 20-20,000 cycles, giving a pure wave form and having no frequency 3 F u l l details of circuit diagram and component parts can be found in the doctoral dissertation of 11.J. Heldman, which is on file in the Library of the University of Southern California. The oscillator constructed was similar t o model 200B of the Hewlett Packarc! Co., Palo Alto, California, an instrument now commercially available, b u t not purchasablc s t the time when this investigation was commenced.
150
E. D. TOLD i S D .\I. J. HE1,DXI.L
drift after a hali-hour oi operation -hielectronic nuil-point indicator u - ~ n g3, "magic eye" tube n as constructed, somewhat modified from a previoudy described instrument (11, 131 l modified Wagner shleld (121, made of radio volume controls, was incorporated a. sho\m In fi8ire 1 Resistance arms R1and R? ]\-ere made of carbon resi>tors and values of the ratio, needed in calculations, determined independently of the absolute value? at frequent intervals so as to eliminate error due to change in resistance with time. The observed drift \\as only a few per cent per y a r . Rboxconsisted of a combination of a 0999-ohm 4-decade Leedy b- Sorthrup box and a 2-decade 990,000-ohm bo.; made partly of non-inductive resistors and partly of inductive lO-watt 50,000-ohm resistors. These vere calibrated against known resistance9 on a D.C. bridge. Within the range of 100-100,000 ohms and 100-5000 cycles the precision of measurement was a felv tenths of a per cent. Below 100 ohms the reproducibility v a s within a few ohms, and ~ a . 5also poorer above 100,000 ohms, although still within a fern per cent even at a megohm.
C'o,LdzLctiz?ty cc1l.s
Nost of the measurementh were made in cells construrted of '7-mm. Coining glass tubing 705h.J or '772, into which wer aled respectively Kovar or tungsten wires of 0.05 em. diameter. The electr TTere sealed parallel to each other through the bottom of the tube, about 3-6 mm. apart, and protruding into the tube from 3 t o 9 mm. Since the tubes ~vereorightlly about 15 em. long. they could be opened and rewalctl repeatedly without tlificulty. The wire. IT ere carefully cleaned ( 2 2 ) before iise, and no i-iqible indication of electrode corrosion or sample decomposition TI a s e\ er detected. ('e11 constants were calculated from measured resistances at 2 5 O ( ' . of solutions oi acetic acid of knon-n concentration, using standard 1 aliiez (15) for the equh alent conductivity. During measurement ~ cera1 i cells TT erc siispendrcl I eltically in a e mall air oven, wired vith onr common clcctroclc nith the aclditional lead attached t o ;t terminal strip, thu. permitting easy Suhstitiition of any cell as the iinl~non-n resistance in the bridge. Tcmpeixturr \\-a- tleterininetl hy a calibrated theimometer placed in tlie nic1.t of the group ot cclls, p r e ~ ioiis tests having hlionn no thermal gradients in the o i c n gieater than onc or t u o degrees over t h iange ~ from 20' to 300°C'. For work at temperatuie. 1)clon- 100°('. and v i t h tiiier iainples it 11-3. n c ~ s i r y t o use a different cell in oitlcr to niiiintuin electrode contact and retlucc t h resistance t o menwrable 1 alii+. The rcll iisrtl i- -lion-n in figure 2 , and con-i-tcd essentially of a hollow cylinder sciving as one clectrode, the other electrode Imng a plunger \\-hich wa5 maintained in contact 11-ith the sample by meanq of pic-iirc from a C a n e r pres.. The -amplei u.ed \\-ere generally untler 3 nini. in t h i c k n and t h e soap from vhich they ucrc tormctl 1 not p1:tc~din the cell nntil thc. metal surfaces had been thoroiighly c*lraiied. rinbed I\ith alcohol and ether, and dried at 105'C". The cell was mounted in a itainle--teeI can betnecn tlie jaws of I: ( ' a n e r pr , and maintained :it temperatiire 1)y mean< of dihiityl
151
COSDVCTIYITT OF SO kP--W 4TER bTbTL3I4
phthalate circulated by a imall centrifugal pump from a 2-gallon thermostat. Temperature control within 0.5” was achieved at temperatures from 20” to 100°C., although supplementary cooling by tap IT ater circulating through a copper coil n a c nrceisary at the lon-er temperatures.
Stoa
I
FIG.2. The plunger cell. Tlics diameter of t h e stai~~l(~ss-stetrl c.yli11t1eris 2.5 ill.; tlie rest of the cell is drawn t o scale. Mclt~l,ld5
The sodium palmitate u.ed 71 a- the itlentical pi epaiation employeci in an earlier investigation (29). The sodium rtealate Jvab made t q - neutralizatioll of an alcoholic solution of an unu-ually pure ste:tilc acid i 20) w t h carbollate-free, alcoholic sodium hyclromle 11ith exclu-ion ~i carbon tlio\icle, kpecial care ],ring
152
12. D. VOLD '1ND 31. J. HELDMAN
taken to avoid any esccss of alkali nhich n~ouldhavc resulted in an electrolytic impurity. Great care was taken during the drying of the \vet gel to avoid scorching and decomposition (19). The lwst-quality soap made in this way, given the laboratory designation "sodiiim stearate .I, \vas "used throughout this investigation, TECHSIQCL O F l r l
Ahhydroussodium palmi e, hoclium dearate syste water, and two much more dilute sampleh were studied in the glass cells. Powtlered soap, previously dried at 105"('., vx\ weighed into the cell together with the requihite amount of m t e r with not more than 2 min. expo;.ure to air. Homogenization was achieved by heating in the oven to ahout 300°C. and inverting openctl at the top and a cooling, the tribe fifteen or twenty times. g l : ~ rod inserted which filled mozt of the \.apor space, thu- minimizing change in sample composition at rlevatecl tc.mper:itures. l'he cell u-as then resealed, reheated to 30OoC'., and cooled in tlic o ~ e nto about 50 to GO"('. o\ver the course of an hour. With sodium palmitatc, cell resistance3 iveie meabiired d t e i enough time at e:ich temperature to reach a constant valuc, only a ken- minutes being required. 17alueyfor -odium stearate were determined on continuoiih heating at about 1' per 3-4 min. That thir procedure giveh valid results TV;L\ \liown hy the good ugrecment in transition temperatures obtained from cur1 es (letermined at different rate* of heating, although high r e d t s nere found if the rate exceeded lo per 2 min. At least duplicate run\ Tvere made over the temperature icgion \\here transition< were expected on the h i < of an initial preliminary run. Thr data obtained are - 1 i o ~ nin figure\ 3-15, the ~ e r t i c a l: m o m marking the point. oi phase trnnhition- Itiinh 1)eginning :It clevatecl temperatiires were ii>iidly hturted after tlic >iiniple had lieen held at the temperature in question 01 einight. lYherr trio nunilx>r. are giwn on t h r graph\, the hrht i- the transition tc3nipei ature tin(\ tliv -ccontl i- thr itlentihvxtion nuinher iintkr \~~ltirli the g i en ~ ti*:ui,\itiona p p e m 111 tlie uperwasy and Jvaxy pha >bows that it muit occur close to 16OOC. Point5 33 and 34, although at about this temperature, are marked by the same type of change in the resistance-temperature curve ab iz point 40, which was knoivn to be on the boundary of the joapboiler'i neat phaqe.
160
R. D. TOLD AND &I, J. HELDhL4K
The high resistance of samples with less than 2 per cent water made measurement of resistance impossible for such systems in the region of the subwxy-waxy transition. However, points 14, 15, 23, 24. 26, and 27 are in good agreement with calorimetric data (26), indicating little change in this transition temperature on addition of water, and establish the course of the waxy and subwaxy boundaries in the slightly more hydrous region. The eutectoid between waxy, subwaxy, and soapboiler's neat soap is set a t about 116°C. by points 26 and 31. The chief importance of these results is the demonstration that many of the anhydrous phases of sodium stearate can incorporate only very small amounts of water before undergoing structural rearrangement, as postulated elsewhere in thi.: Journal ( 7 ) ,which result.: in the formation of a different phase. Thus, the conductimetric data, in agrecmrnt with calorimetric rvidence (2G), show that neat and subneat soap can incorporate only 4 and 3 per cent water, respectively, before breaking d o n a to soapboiler's neat soap, whereas previously it had been supposed that 10 per cent water could be incorporated in the homogeneous phase. Similarly, the conductimetric data indicate that waxy soap cannot contain more than 4.5 per cent water nor exi-t as the equilihrium phase below 116"C., as contrasted with literature results, based on very meager vapor-pressure work (17), which shorn a tongue of waxy boap extending down to 100°C. at 15per cent water. I n the case of the more dilute systems (figures 14 and 15) the resistancetemperature curve of the system containing 69.3 per cent water shows an abrupt change of slope at 83'C'., agreeing within 3" with the literature value (18) for the completion of formation of middle soap. The corresponding temperature in the 28.7 per cent system for formation of soapboiler's neat soap was not accurately determined bccausr of some difficulty with that sample at higher temperatures. In both these system< the ciirvr< Ao~\-etlchanges indicative of phase changes occurring below T C . Snfztrc of the pliuse diuyrczm The systems containing 12.S, 28.7. a r i d 09.3 per cent m t e r all show a similar feature in the resistancC--tCmI)~~rr.aturc c'iirvc---;l fairly steep fall of resistance with tmiperature, broken 1)y L: slight increaie I\ it11 the temperature, followed by a, ~ c i yrapid decrease of r tance nith temperat tire- n-hich certainly wggest. that a similar series of phn>c cahanges occur> in :ill thrc emh. The tempemtiires of these changes iii the three s p t c m i :ai(' rci.pwti\ ely dOo. 52", 60°C. and (io", GG", and 72°C. Altfir\t thought tlicsc rllnnge. might 1~ thought to be related to the tenipcmtures of initinl formation of niitldle soap and soapboiler's neat soap. However, the eutectoids due to the coexistence of i-otropic solutioncurd-middle soap and isotropic soliltion-~oapboiler'. ncst-curd phase occur a t 76°C. and 82°C.. respectively (18). Since there is no break in the resistance curve* at these temperatures it can he concluded. in Laccord wit11 other evidence (26,28),that these eutectoids d o not extend into the concentrated region. This certainly suggests the existence of homogeneous phases containing substantial amounts of mater, as contra4cd with the classical picture ot a heterogeneous region with some on^ "curd" phase, containing only w r y little water, in eqidlibriuni with isotropic, solution.
CONDUCTIVITY OF SOAP-WATER SYSTEMS
161
The present data permit some choice to be made between the conflicting views of Buerger, Smith, et al. (4,5 ) and Ferguson and coworkers (8) as to the nature of solid soap. From x-ray work on quenched samples Buerger and coworkers have shown that a given sample may exist a t room temperature in a variety of crystalline forms, depending on the minimum temperature a t which mechanical agitation occurred prior to undisturbed cooling. Even though the critical temperatures determined in this way for the formation of each phase do not necessarily correspond to equilibrium transition temperatures, it may well be that such samples will undergo transitions a t these temperatures on reheating. 4though detailed data have not been published for sodium stearate, it is stated that such a phase map shows two different crystalline forms, delta or alpha, which may be realized below T,, the temperatures of agitation required t o produce these forms being essentially independent of composition. The conductimetric data, although obtained on unagitated systems formed by spontaneous cooling and presumably giving the equilibrium temperatures of phase transitions, are in accord with the concept of two phase boundaries occurring between room temperature and the T , curve, and a t temperatures only slightly dependent on composition. A somewhat similar situation exists in the case of sodium oleate (27), where calorimetric evidence showed the existence of a transition occurring a t constant temperature independent of composition from 15 to 75 per cent water in sodium oleate systems, formed by spontaneous cooling from whatever phase existed a t higher temperatures. This behavior differs from that which would be anticipated on the basis of Ferguson’s concept (8), also based on x-ray examination of samples a t room temperature, that a single phase-in this instance, 0-sodium palmitate-itself containing very little water, exists over the whole composition range at room temperature in equilibrium with isotropic liquid. Ferguson also presents very persuasive evidence that some of the separate phases adduced by Buerger, which he believes to be stoichiometric hydrates, are in reality merely different members of a single solid-solution phase. Severtheless, some such multiplicity of phases as proposed by Buerger, whether they be hydrates or solid solutions, seems to be necessary to explain the conductimetric, calorimetric, and rheological (14, 16) behavior of soap systems. The results obtained with the plunger cell, although limited t o temperatures usually below 80°C. and systems containing less than 4 per cent water, provide further insight into the reversibility of the genotypic (23) and alpha-beta (3, 26) transitions. Calorimetric work (26) in closed cells had shown that a-sodium stearate, prepared by crystallization a t room temperature, underwent a transition a t 52°C. which was apparently irreversible on cooling, jince duplicate runs on samples which had been heated above this temperature failed to show the transition. X-ray investigation (3) showed that this transition was due to decomposition of the hemihydrate (alpha) to a less hydrous form called beta, although there is no agreement as to whether beta is a stoichiometric hydrate or a solictsolution phase (3, 8). On heating the beta form in a sealed tube a t 47°C. in the presence of a drop of water and cooling, it was found (3) that conversion to alpha had taken place. Derpite the fact that the conductimetric qamples had heen
cooled from the melt aborc 300"C., all except that with 0.7 per cent water had an inflection in the resistance~tCmperatiirecurve at 48-52"C., indicative of the presence of at least some a l p h a phase in the initial sample at room temperature, This raises the intere-ting question as to whether alpha may not occur as a stable phase at room temperature in system. containing more water, and prepared by spontaneouq cooling from -oapboiler'- neat or middle soap without agitation. Possibly the concluctimetric tranbition at 50", 52", and 60°C'. in the systems containing respectively 12.5, 28.7, and 69.3 per cent water i:, related to this phase change. .kcording to the phase map ( 5 ) a-sodium stearate should occur over most of the composition range at room temperature, provided the system has been formed on cooling the high-temperature phase with agit a t'ion below some temperature l~elon-Terfollowed by undisturbed cooling. Such an interpretation would again approach the classical view of the nature of the system at room temperature. Although most of the present sy-terns failed to shon- the genotypic transition at 69-73'C. on reheating after having been cooled from the isotropic melt, it did occur in those containing 0.0,3.G, and 4.0 per cent water. Previous calorimetric work (26) had shoivn that beta formed by heating alpha underwent further transition to lambda at about 70°C'. (the genotypic transition), but that this transition was generally missing once the sample had been heated into the subwaxy phase, thi- effect being attrihited to difficulty of reversibility of the lambdahiiperciircl ti ansition. In vie\\ of the concluctimetiic results it must be concluded that under some circumstanw. lambda can be formed on cooling supercurd even though gamma, which doc- not gi\-c the genotypic transition, ~isuallyresults from such treatment. Obvioubly not only the inaunium temperature t o uhich a *ample has heen licated, but al-o the rate 01 cooling, the relati\ e humidity during cooling, and the extent 2nd temperature ot any mechanical agitation during cooling, will be important determinants of \\ hich ot ieveral po--ihle plia3es is act iially present :it room temperat lire. , i / r i c c f ~ r r azmplzcatio/is l
If the cwntluctivity i- duc t o tlipole rotation or o-cillation rather than to migration oi ion-. it ii po--ihlc (10) t o calculate a '*rela\ation time" for re-orimtation of the p:u.ticles from t hr fic~lriciicy range in which the conductivity fall:, oft' m:tiketl!>-. : i d thus mnit~tinic~~ t o tletcrmine the size and shape of the particle. -r:it)ie 3 -llo\vs thc concliict i\ i t > of certain of t h r l soap phase:, a i :I function of frcY~l1c"c.y. so t e m n t k \ aiiution of re4-tance with frequency \\:ai found in t ilc. case ot mixt w e 5 of supc'r\\-n\y m t l -0aphoi1er's neat soap, nor with ,iil)neat \o:ip noi tlic isotropic -elution I-nioitunately, the rang(^ oi t i cquencich a i Ltilable (420-7800 cyclri) i i prcsiimahly too lon- to detect m y such effect, p:irticiilarly since it is known (0) that trequencie- of 0.8-4.0 megncyclc. :ire required to shon- anomalous dispersion in the case oi proteins of moleciilar \\-eight aro~iiicl70,000. Since the aggregate:, in tullinc -oap pha-e. IT of tlw order of the ivave length of visihlc
163
SYSTEMS
COSDUCTIVITY OF SOII'-JY'XTER
light in size, they would have similar particle weights and might be expected t o have relaxation times of similar magnitude. However, it seems unlikely that dipole rotation can account for the conducti\-ities observed in the present ~ o r k , since the values obtained (specific conductance ea. ohms-l) are milch greater ohms-') in cases of dipole rotation (1). than those usually observed (ca. lloreover, a fen. exploratory measurements of D.C. resistance gave rehults substantially the same as the I.C. values. Since the conductivity is sufficiently high to suggest ionic migration as the probable mechanism, it becomes of interest to speculate as to whether either the TABLE 3 Frequency dependence of conductwity of sodaurn stearate-uater samples TEMPERATURE
I
COMPOSITION, PER CENT IV.4IER
'C.
SPECIFIC RESISTANCE
FRE Q K E XC \
0kms
c>cles
14 000
168.5 168.5 168.5
2.0 2.0 2.0
13 800 13,500
420 3500 is00
168.5 168.5 168.5
2.5 2.5 2.5
2,050 2,100 2.050
430 3500 7800
214.0 214.0 214.0
2.0
2.0 2.0
325 325 325
420 3600 7800
214.0 214.0 214.0
2.0 2.0 2.0
250 255 250
3500 7800
240.5 240.5
0.5 0.5
78,000 78,000
420 3500
300.0 300.0 300.0
0.5 0.5 0.5
310 315 315
120 3500 7800
~
~
420
negative ion and negative aggregates or the positive ion or both contribute appreciably to the observed conductivity, and as to whether the medium in n-hich they move is lattice-like or essentially liquid in nature. Presumably the main contribution is made by the sodium ion, since the strong van der V-aals attraction along the length of the hydrocarbon chains tends to keep each negative ion parallel to its neighbors. That the sodium ion alone is responsible for the conductivity is assumed in the following discussion. Examination of the values obtained shows that the conductivity of subneat soap, both anhydrous and containing small amounts of water, increases extremely rapidly with the temperature, while for neat soap the conductivities, though high,
164
H . D. VOLD .LYD 31. J. IIELDXAS
increase much less rapidly. Interpretation of thr>e rehult? according t o the theory of absolute reaction rates leads to some remarkable conclusions. For the morement of ions on a lattice, the cyiiation ciweloped (1) by Eyring and Wynne-,Jones can be used:
Here K is the specific conductancc in absolute units, S is the number of ions per cubic centimeter, %e is the charge on the ion, li ii Planck'q constant, d is the sepaEnergies atrd entropies
abr. ohms-'
per cenl
7.7 3.2
0.0
x
x 1.67 x
cm.-1
10-13 10-14
I
10-15
I
1 . G7 X
0.5
5
--
1.0
I .
i
I
I I
x
lo-"
x x
10-13 10-13
~
1
1.67 Y lo-'? '
2.0
1.4
x
10-13
2.5
oj
TABLE 4 actiantion f o r conductivity in subtieat a n d neat soap
"K.
cal. per mule
527 323 517
3 3
51!1 c503
1 . 2 X lo5
489 473 lb3 4(i3
x
ahs ukms-1 cm.-L
105
1
x
10'26
I
i.1
x
104
I
,
'
I
S
X IO3?
-L
Y 1019
I
I
6.2
x
10'
3.7
x
I
x
10'6
4
x
It15
0 5
1
\
1
2 78 X 2.63 X
i
533 523
10-12
110
1
62
I
__
53i 328
127
~
1
, IO'
~
1.85 x 10-13 1.54 x 10-1z
211
I
I
466
I 1
616
I
-457
0.0
cai./dcg./molc
1
I
,
1.1 x 104
2.x
x
103 I I
__
~
3 G
x
10-8
.1.6
x
10-11 '
1
I
I
2 1
Segut1ve -
ration of potential miiiinin in the direction of motion (lattice points), AX* is the entropy increase in p a A i g from the normal t o the activated Rtate, and AH* is the heat of nctivYtion. identified with tlie activation energy of the ,irrheniu. equation, K = - I P - - ~ ' R ZCalculations , of A , E , anti AS* for subneat and neat soap, based on thi> equation, are given in table 4. T h e number of ions per cubic ccntimeter is taken as 2 X 1021,while cl is asaumed t o be 4 A,, neither of' these values being very critical for the concluqion to be tlra\vn from the enormou; values of A S * which re-tilt. For subneat soap, tlic rapid \-ariation in conductivity with temperature girrs
COSDUCTIVITY O F SOAI’-W.4TER
SYb‘PLMR
165
rise to a very large calculated activation energy. Since, honwer, the conductivity itself is high, the temperature-independent factor A , containing the term cAS*/R , is very large. The values are too large to render the basic picture-that of a semi-rigid lattice at all temperatures within the range of esistence of the phase-at all reasonable. Qualitatively, the results may be interpreted by suppobing that within the subneat soap phase, the structure is changing from latticolike at lower temperatures to a condition of lesser rcgularity at higher temperatures, in which aggregates, still composed of an extensive array of parallel molecules, move freely in a matrix of less ordered structures. This would be the kind of transformation here occurring over a range 30- No(’.which ordinarily accompanies the melting of an ionic crystal at a -ingle temperature, except that the residual order in neat soap extends ovcr it larger number of molecules. Such a postulate might also account for the large discrepancy between the calorimetric and dilatometric value:, for thc transition temperature hetween subneat and neat soap (25’i, since energy ~voultlbe absorbed as soon as degradation of the lattice began while the structural rearrangement giving rise t o the change in volume might not occur until the transformation was complete. \-diw For neat soap, the calculated acti1-ation energy is smaller, arid the correspondingly mailer. In consequence the value of A S * Imomes much more sensitive to the ahsuniptioni made as to the tliutmce hetnwn potential minima (lattice sites). lloscher antl l-old 17) have suggested that the conductivity in this phase is essentially salt-likr. This is based on the observation that, iristeat1 of the enormous values of A6S*for subneat i m p , one haq values of the order of a few calories per degree, suggesting that the activated state is one in which the positive ions are “in transit” between lattice points and more or less randomly distributed, so that Ah’* is of the order of that associated with the order-disortler transition ( 2 R In 2) (21). 111view of the picture now preqented for subneat soap, the degree antl extent of regularity to he associated with the “latticc” itself in neat soap are uncertain, in so far as deductions from the conductivit p data are concerned. Esamination of figures 14 and 15 shoir-s that middle soap and soapboiler’s neat .oap h a w nearly identical values of spccific resistance, which result5 in the equivalent conductivity of middle soap being much larger than that of soapboiler’s neat soap. This result is in accord with the hypothesis (7) that soapboiler’s neat soap has a latticdikc itructure, whereas middle soap is pretiominantly micellar in nature. SUXLMIRT
h technique has been dewlopetl for determination of the electrical conductivity of solid and semi-iolid soap sptems. Rcsistances were determined as a function of temperature for sodium stearate systems containing from 0 to 69 per cent water from room temperature to as high as 300°C. The results obtained permit clerivation of details of the phase diagram in the region of high concentration, and show that none of the anhydrous phases studied can incorporate more than 3 or 4 weight per cent water without transformation to another phase.
166
R . D. VOI,D A S D .\I. J. HELDMAS
I t is concluded that a miiltiplicity of solid phases, rather than equilibrium b e t w e n a single curd phase and isotropic solution, is required to explain the observed properties of the system 11elon- T(,. Interpretation of the temperature coefficient of conductivity of subneat sodium steara’te according t o the theory of absolute reaction rates gives so abnormally l u g e n value for the entropy of formation of the activated state as t o suggest progressive destruction of the “lattice” with rising temperature over the whole range of‘existence of this phase. lTaluesobtained similarly for neat’soap resemhle more closely those for the conductivity of ordinary salts.
REFERESCES (1) BIIRRER, R.&I.: Digusion in and through Solids, pp. 264, 294, 303. The klacmillan Company, S e w Tork (1941). S. S., m n PR.~s.IU, 11.:Kolloid-Z. 34, 193 (1924,. (2, BHATSAGAR, (3) BUERGER, hI. J., SMITH, 1, 13., 1)E BRETTCYILLE, -I.,AND RYER,F. F’.: Proc. ?;ati. .$cad. Sci. I;. S.28, 52G (1942). (4) BCERGER, AI. J., SMITH,L . H . , .\xi) RYER!F. F’.: ,J. .Im.Oil Chem. Soc. 24, 193 (1947). (5) BUERGER, 11. J., SMITH, I,. 13.. RYER,F. T,, ANI) SPIKE,J . E., J R . : Proc. S a t l . .Icad. Sei. L-. S.31, 226 (1945). (6) COHN,E . J . : Chcm. Rev. 24, 217 (1939). (7) DOSCHER, T. 11.,ANI) \ 7 0 ~ , i )It. , D.:
