BY J 0 € I S Tl-AU)IIEI.I,
T h e object of tliii investigation vas to deterniiiie. as far as possible, the wa). in n-liicli acetic acid cliaiig-es the iiiutual solnhilities of lieiizene aiitl lvater ; i n other words, to stitd!- the (listrihntioii ratio of acetjc acid in benzene and \ v a t u as solx.eiits. There were t v o reasoiis for taking acetic acid as the consolute liciiiid. I t coiilcl he deteriiiiiied 11)- titration ant1 TT-right, [,eon aiicl Tlioiiipsoo"' had a'lreatlj- st d i e d a siiiiilar s>.steiii in v.liicli cliloroforiii replaced the benzene. T h e acetic acid \\'aspurified li!. crj-stallizaticm till a fractioii melting at I 6" was obtaiiied. Titratioii with deciiioriiial potash' slio\ved this to contain only 0.3 percent of water. a11 aiiioiiiit \vliicli \vonld correspo.id to 0.015 cc in j cc of acetic acid ;ind which falls nitliin the limit of esperiiiieiital error. T h e biirette in n-liicli tlie acid \vas measured n coiinected ivitli :I resen-oir coiitaiiiiiig tlie acid, aiid all air that cntered tlie burette or the reservoir passed tlirougli calciuiii chloride tubes. T h e lxiizene !\-as first liented \\.it11 coiiceiitrated siilpliiiric acitl and then distilled. T h e distillate n-as treated nitli iiietallic sxliuiii aiitl redistilled, going m'er \i-itliiii half a degree. Soiiie portioiis of tlie benzene used were freed aliiiost eiitirelj. from thiophene :~iid a i i ~ other . siilxtaiices v;liicli lilackcii concentrated siilpliiiric acid. Other portions n-ere not piirifiecl so carefull!. ; hiit I coiild detect 110 tliffereiice in iiij- experinleiits. T h e water \vas ohtainetl adcliiix alkalilie permanganate solution to tlie distilled \vater of the laborator>-and redistilliiig, rejecting the first aiid last por-
tioiis. T h e burettes \rere calibrated against a 2 cc pipette which had been staiidarclized with iiierciir!.. Tlie burettes could be read to 0 . 0 2 cc. Tlie iiieasiireiiieiits were niacle i i i tlie usual \va!. 1 1 ~ .adding var!.iiig amounts of benzene or Ivater to 5 cc acetic acid and then rniiniiig in the \\-ater or lmizeiie til! satiiratioii \\-as reached. T h e experiiiieiital error seems to be ahout three percent. It \vas holiecl that the results could he represented h!. one or tivo exponential forniulas of tlie general form - 1 1 " : coiist, where s aiid 1'refer to the aiiioiiiits of heiizene and ivnter in a coiistaiit yiiaiitity of acetic acid. In case tu-o ciirT.es were iiecessar!-, it n-as expected that tlie point of intersection n-ould correspond exa d > -Tritli the point at n.liic!i the tn-o solution pliases beconie identical. Sotliiiig of the sort n-ac: fouiid. There is no discontinuit!- n-hen the saturated solution cliaiiges froiii being the denser- to beiiig the less dense pliase. Allso vlieii tlie data are plotted 011 lo:,.arithniic coordinates, the resulting- curl-e is a n-a\.!. oiie. TVitli tlie isotheriii for 2 j " , one niiglit easilJ- consider the curve as iiear1)- straig-lit if oiie omitted soiiie of the middle portions. T h i s \\-ill be seeii iiiore clearl!- if we esaiiiine the esperiiiieiital data given in Table I. Tlie results ha\-e been recalculated into g-aiiis and represeiit grains of benzene and of water in 5 . 2 j g acetic acid. In the table are also :,.i\-eii the calculated \-slues, assuiiiiiig that the miioniits of lieiizeiie and n-ater \-ar!. accorcliiig to the forinnla .q~;2.54. where .I- refers to the henzeiie and 1' to the ivater. T'ntler " calc " are the \-slues obtaiiietl when one suhstitiites in the foi-iiiula the foiuicl 1-alnes for one of the components aiid solves for tlie other. Tlie absolnte difference betn-een tlie calciilated and the found \ d u e s \vi11 be less if oiie solI.es for the coiiiponeiit preseiit in lesser aiiiouiits, aiicl for this reas011 the water \ d u e s are takeii for coinparison in the first part of the talile and the lmizeiie \-slues in tlie last part. Tlie bracketed \-aliies are those of the consoliite point or tlie point n-liere tlie two licliiitl pliases 1,ecoiiie identical. 7
Table I Temp.
For iiiula -T
g benzene ; y
:
-11found J'
calc
-
2j"
-TJ:= collst = 2 . 54
g water per
const
j . 2j
g acetic acid
x calc x found .76
0.24
0.2';
2.07
1.89
I
0.42
0.44 0.46
2 42 2 30
I .Ol
0.S8
0.90
0.so
0.51 0.59 0.63
0.51
2.j6
0.40
0.jj
2.79 2 f q
0.32
0.39 0.29
0.72
o 70 0.7j
2.bj
o.17
2.62 2.75 2.61
0.14
0.44
0.761 0.Sj 0.99
0.62
0.81
0.58
1
'
0.23
0.11
0
og
0.21 0.1s 0.1j
3'
const
I .22 I.% 2.00
2.37
S.43
2
4.0 j.o
2.32
j.0
3.14 2.94 2.97
6 .0
0.13
s.0
0.I I
9.0
2.22
2.26
47
2.34
2.64
If one coiilcl eliminate tlie tliree solutions in u-liicli tliere are 1.76, 0.88 and 0.8 g r a m s of benzene! tlie other figures might easily seem to come within the limits of experimental error. T h i s is not a possilhility hecanse these deteriiiiiiatioiis can he iiiade with great accuracj- and the inapplicabilitj- of tlie formula beconies more el-ident n-lien we coiisitler the isotlieriii for 35 ', Plotted on l o p - i t h i i i i c coordinate paper, the general foriii of tlie ciir1.e is approxiiliate1:- that of a straight line, one-half of which has heen displaced to :I certain extent tlioiiKli still keeping approximatel!, parallel nit11 tlie other half. Sirice iieitlier line is reall!. straight. tlie ci1rT-e may be describecl more accuratelJ- as half way bet\s-eeii tlic: letter S and ail integral sign.' Under these circuiiistances it is not possible to make even the approxiiiiate calculation in Table I and tlie data are therefore given in Table I1 n-ithout coiiiiiient. Tlie coilstant cjti;iiitit!- of acetic acid in each case is 5.25 g and the data for the consolute point are iiiarked b y a square bracket. ~~
\\-as not
Special experiments sho~\-e(l that tlie iiiiscil)ility of hciizeiie and {rater of importance.
236 Table I1 Temp. 3 j 3 x -= g benzene : j '
g water per
:
3'
.I~
a-
,
~~~
I j.60 13.20
s.s
6.16
0.29
0.3j
h.96 3.j 2
0.46
2.64 1.76
0.62
j.28
j 2j
"7'
0.851 0.91 I O j
I ,SO I . j0
g acetic acid -2' 1.12
0.55 0. j0 0.20 0.20
0.79 , 4.4 In order to constl-nct the isotherms, using a triangular diagram, it is tiecessar? to make the siiiii of the three components constant. This calculation lias heen made and the figures are given iii Table 111, the \ d u e s lieiiig graiiis per linndred grain\ of solution atid the coiisolute poiiit being iiiarked b) a q u a r t . bracket.
Table I11 Concentrations expressed in grains per hundred grains Temp. -Acid 22.7 36.3
Temp. 3 j "
25'
Benzene \I-ater 76.2 1.1 60,s
n'ater I
2.9
.s
38.j
jS. I
3.4
3.3 6.3
41 .o
jj.0
4.0
j.6
43.6
51.3 47.2 42.3 39.6 36.5 25,s
j .I
8.41
5.7
9.4
11.0
21.j 11.0
14.7
6;. 1 64.3 65.0 64.9
23.4
CO.4
10.0
2j.0
52.0
$3.
44.0
47.1
j0.7 rj2.S
54.7 59.2 63.8 65.6 65 .o j7.0 5.5.0
4.3 3.1
7.0 7.61 8 .j
j0.2
2.0
1
45.9
1.6
1
42.I
1.4 '
30.0 36.6
0.7
1.0 1
I
41.9
47.8 j2.j
j6.j 60.0
62.;
11.8
iiiterpolatioii and extrapolation aloiig tlir isotherm it is possible, withoiit difficnlty, to deterniiiie the coordinates of a solution coiitaiiiiiig ;my particular percentage of acetic acid. T h e n e s t poiiit \\'a!< to cleteriiiine the tie-lines. Measured anioniits of acetic acid, benzene aiid water were allowed to s t a d i n the constant teinpc:ratui-e bath at 25' until the two liquid layers were in equilibriuin. Portions of each l a ~ w were piI)etted off and the acetic acid deterinined b y titration. I n the fonr sets of figures enclosed in brackets in Table IT*, the coinposition of each of the lower or a.queoiis layers was obtained b y drawing-tlie tie-line from the poiiit in the diagram gi\.eii IIJ- the composition of the upper Iaj.er throiigh the poiiit representin:,. tlie c o i n p s i tioii of tlie origiiial inistiire and noting where i t cut the c1in.e. L-iider tlie cii-ciimstai-ices, tliis is the most accurate inethod for a reference to Tahle 11' will sho\v that a very slight difference in tlie percentage of the acid corresponds to great variations in the rel:iti\.e ainouiits of hi-nzene and water. This n;ethod of procedure is jnstifiecl bj. tlie fact that, in each of the cases in which both layers were aiial;,-zed. the tie-line passed accuratelj. throu:,.li the poiiit of total conipositioii. T h e data for the isotherm a t 2 jL are gi\.eii iii Table 11.. Table IT Temp. 2 j " Cotice 11t ra t i o n s iz x pres s ed i 11 g ra ni s per h u n clr e d g r a ni s
9.4
CI.
IS
16.j
c,,
I
0 . 1j
28.2
0 .j 3
02 j
3; 7 43.9 48.3
0.S.F I .j
49.5
1.93
53 2 61.4 64. j
2.72
0 0 2
o 06
1
0.34 0.42 0 43 0. jI
0.79 1.04 1.10 2.13
2.44 j.6
7.6
I I
'
~
6jo 66 0 6j.0 60.0 j2.8
I
.s2
6 .I 9.2 10.0
,
13.8 17.8 29.0 39.6
TYOpoints are Ter! noticeable in this table. T h e amount of acetic acid in tlie aqueous la? er passes through a iiiaximum. -1similar phenoiiienon has already been noted by S. F. Taylor1 with alcohol, benzene and n ater. T h e iiiore striking feature is that, just before the consolute point is reached, there is not only iiiore benzene than water iii both la! ers ; but there is a great deal iiiore beiueiie than nater. &Isthere is no real justification for coiiipai-ing grams of beiueiie with grains of water, the data have beeii recalculated and are given in Table >.\ the values being reacting \T eights per liunclred reacting \\ eights in tlie solution. Table V Teiiip. 2 j ' Conceiitrations expieised i n reacting R eights Fer hundred Upper layer Lower layer -Acid Benzene TT'ater Acid Benzene Water 3 02 060 0.04 96 91 99 3 [ 0 09 I
68
9S.06
0
26
j.61
00s
0.19 n.2;.
s SI
0.j1
0.6j 0.69 1.03 2.65
445 4.93 7.38 IO.0j
1S.74 2S.08
9431 s9 2 2 81.23 80.14 76.96 76.43 72.66 62.12
55.09 53.41 46.79 42.17 30.82 23.85
Both of the salient points of the preceding table remain though tlie excess of heiizeiie in the aqueous la\-er is decreased enorlllousl~. I t has been slionn b!- S. F. Ta!.lor that a formula of the general form zq :-.-:coiist, expressed the clistribntion of alcohol between benzene mid u-ater.' In this foriiiula zr represented ~~~
' Jour. I'li~-s.Chem. I, 465 '' Ibirl. I, 471 (rS9;).
rS97 I .
t h e aiiiount of alcohol in the beiizeiie phase referred to a ~011stant qiiantitj- of benzene, n-hile zz 1-epreseiited the aiiiount of alcohol in tlie aqueous phase referred to a constant quantitj- of \rater. Tliis general formula coiiltl iiot he expected to app1~. absolutelJ- to the (list>-ibiitionof acetic acid betn-een benzene and \rater because it has l)eeii found, i n this in\-estigatioii, that the course of the isotherm cannot lie represented the theoretical forinnla. I t was quits coiicei\-ahle liowe\.ei- that tlie distribution of acetic acid betwee1:i benzene and water might lie represented n-itli tlie smie degree of approrimation as v a s ~iossihlewith the isotheriii itself. Tlie calculation lias heen macle aiicl tlie 1-esiilts are given in Table T-1. Tlie foriiiiila nscd is z2i’irl.:- IO, n h e r e ,: denotes grams of acetic acid per gram of benzene in the less dense phase. and zz p a i i i s of acetic acid per gram of water in the iiiore deiise phase. t-iider c d c ” are given the ~-aliiesfor acetic acid per liiuidred grnnis of solutioii, in the less dense 11liase. \rliicli correspond to tlie found ” percentag-es of acetic acid in the iiioi-e deiise phase. Table T Y Tenip. 2 j‘ Forniula zi!i‘, -const : IO i:, :,q acid in benzene layex- per g henzenc z, -~ g acid in aqueous layer per g water Colicexitratioxi expressed i n grains per h u n d r e d g r a m s L 6
Acid i n upper layer calc found
0.49 1.14 SI 4.92 6.94 s.71 9.06 2
I I .1
19.4 25.6 2’7.2
3 2 .j $3.
I
46.0 52.4
-1cid i n Ion-er layer ccmst
It will be noticed that tlie agreeiiieiit between theory and esperiiiieiit is pretty fair except just a t the iiiaxiiiiiiiii for acetic acid where a very slight error makes a x-erl- iarge difference. -4 r-ariation of oiie percent in tlie coinposition of the aqiieous laj.er rvould account for the variation of twenty percent in the coiistant. I n the most dilute solution E-iven in Table 1-1there is ahoiit twenty times as iiiiicli acetic acid in oiie hundred grams of the aqueous Ia!-er as in a coi-respoiidiiig \\-eight of tlie beiizeiie phase. Two other determinations were made rvith more dilute solutions. Iii tlie oiie case (I.j cc of acid \\-asadded to I O cc beiizeiie aiid I O cc water ; in the second case O. I cc of acid was taken. The analyses of the npper and lou-er layers were approximate oiil!., or\-iiig to tlie small qiiaiitity of acid. These iiieasurenieiits were made in order to see rvlietlier the ratio of the acid in benzene to tlie acid in n-ater n-oultl reach an>- definite liniit. In tlie first esperiiiieiit the ratio n-as I : 40 : in the second I : j6. TL-Iiile these two estiriiations rvere only approxiinate, as has been said, the!- were siifficientl!- accurate to siiorv that there is 110 apparent limiting ratio. These results are in accordance qiialitativelj- and quantitatively nit11 tlie dieor\- of ?;ernst,’ according to \\-liicli relati\.ely iiiore aiicl iiiore of the acetic acid should pass into tlie acineous phase as the solution becomes more dilute.
Table 1-11 T e m p . 3j’ Concentrations expressed i n g r a m s per hundred grams I-pper layer Lon.er layer Xcid Benzene Il‘ater Xcid Benzene Il‘ater 1.24 98.68 0.0s 16 4 0.62 82.98 5.; 93.97 0.
