BY J.
H. PETTIT
I. Minimum Boiling-points I n the general discussion of s!.steiiis iiiade u p of t n o 1.olatilr coiiiponents, Rancroft' iiiakes tlie follon-ing statement : ' * If two consoliite liqiiids ha\-e the same 1-apor-pressure at a gi\.en teiiiperature, some iiiixture of tlie two must have either a iiiaxiiiiiitii or a niiniiiiuni vapor-pressure at that temperature unless all coiiceiitratioris have the same value. If a t other teniperatures tlie isotheriii~lcurve has neither a iiiasiniiiiii nor iiiiiiiiiiuiii, it is possible to pass by change of temperature from a s!.stetii liehaI.ini,. i n one \\-a!. to a s!.steni belia\.iiig in another. T h i s would preve.;t an!- deductions from the form of the pix+ sure c u n - e a t one teiiiperature to that at another. T/ic( z / f c r i ! ( T t i x is t h n f n i l coiisoliltc, liqiiids v i t l i iiitcr.ic(.tiii.l alcohol and ether (Table 11) is arranged in a manner similar to the first. In this case also tlie pressures vary but little from the nieari [ d u e of 738.7, but ne\.ertlieless tlie correction has been applied here also.
T;IBLEJ I B Pt
.\lco1101 Ether
B Pt
Bar ~
~~
~~~~~~
64.90" 64.94' 60.62 S j . 0 1 j . o 7 3 5 . 3 56.30 j6.31 65.3 34.7,;39.347.20 ' 4 7 . 1 8 59 4 40.6 j 3 S . S 44.00 44.00 j2.5
hol ~
1Oo.0 0 . 0 l j 3 7 . S 92.2
-11~0-
corr ~~~~
j , S j j 8 . 1 60.60
47.5 739.8 42.92 4 2 . 9 2
Ether
Bar
B Pt
B I't corr
~
51.1
48.9
738.6
42.jO' 42.jC)"
42.3 15.4 8.8
83.6 91.2
0.0
100.0
738.8 738 S 738.8 738 Y 7?9,1
39 90 39.90
22.9
57.7 77.1
j 6 . 6 j 36.65 3.5 65 35.65 34.70 34.70 34.20 3 4 . 2 1
The curl-e DEF in Fig. I expresses tlie resiilts gii.en i n the preceding table. It possesses neither iiiasiinuin nor miniinuin. T h e results obtained for acetone and methyl alcoliol are premitetl in Table 111 wliich is arranged in the usual manner. I n this case also, it is possible to correct to the inearl barometric pressiire, h i t as tlie table is to be used later in the deteriiiinatioii of \.apor compositions, it has been reduced to the standard pressure of 760 iniii. T h e corrections have been taken froin 1,andolt and Rornstein's Tabellell (p. 191) which gi\-es the value of 0.037" ;is corresponding to i riini increase of pressiire for alcohol het:n-een the pressures of 730 and 760 iiiin, wliile for acetone tlie saine \-slue is 0.039'. For all inistiires mean 1-alues lia\-e been nssiirned depending on tlie proportions of eacli present. 17aliies o?itained in this way m a y not be rigidl!. accurate, biit in tlie absence of more reliable data ma!- be assumed as very nearl!. correct.
TABLE 111 hlco- .ice1101 tone
Bar
B Pt
H Pt corr
Alco1101
Acetone
R I't Bar
R Pt
corr
7 2 9 7 j6.50 5 7 . 6 5 j29.4 55.50 56 68 728 9 jj.10 j6.29 728.9 54.90 j 6 09
728.9 54.80j j . 9 9 7 2 8 9 54.90 56.09 7 2 8 4 j j . 4 0 56.62
354
J. H. Pettrt
T h e curve G H K which gives the representation of these results is slio\t.n i n Fig. 2. A minimum boiiing-point occiirs a t a temperature of j 5.93" a t a pressure of 760 inm,the composition of the solution being approximately 13.j percent alcohol and 86.j percent acetone. In testing the conformity to the theory of the results which have so far been given in connection with boiling-point deterniinations, it will be well to refer to a paper which gives a very fair sunimar~.of s-aporpressure deteriniliatiom up to the year I 894. I n this paper the author' has gathered the most satisfactor;\-iiieasiireiiients of vapor pressures of cliff erent componnds with the idea of finding what vapor-pressure cnrves intersect. T h e difficulty of access to this paper, tlie fact that it has been o\.erlooked by a t least one scientist, aiid its m e for further reference, make excuse for its insertion completely iinnecessary. T h e paper proceeds as follon-s : I shall limit myself to merely recalling tlie measurements of Sa,jotscliewskyz \\.hose cur\-es do not intersect and proceed a t once to those of Kamsaj-, Young and Thoiiiasj which are more interesting from a double standpoint - tlie boiling-points of the liquids examined are much closer to each other, and the accuracy of the iiieasureiiients is of a verJ- high order. In the following table will be found non-associated liquids arranged in the order of rising boiling-pointsl if we regard these & h
( $
-
Guye. ;\rch. de Geiieve. ( 3 ) 31, 164 , 1S94). Sajotschewsky. Beihliitter. 3, 741 i r S 7 9 ) . (I These iiieasureitieiits have heeii puhtisheci i n articles written b y Ranisay anrl Young. Young, atit1 Young and Tho11ias. Recapitulation of the results ohtained ma\- he found ill the two articles : S . Young. Phil. J h g . [ j ] 34, 5 1 2 (1892), and S . Young and Thomas. Jour. C h r m . Soc. 63, r z j 9 (1Sg3 I .
A l f i J 2 imL 112 BOil'i?Zg-/Oi?Z iS a?Zd bh/O J'
3 j ,j
('0 J 1 1 ~ 0 S tlolls 2
boiling-points a5 taken under a presstire of 760 nini of mercury *is a matter of fact the determination of the molecular neight in the state of liquid has not been made for all the compounds, bnt according to all analogy it is almost certain that all the bodies mentioned in this table are not polymerized in the liquid state, a t least not to an appreciable extent. I' -
I 2
3 4 5
6
' I
6 9 IO I1 I2
'3 '1 15 16 17 I8
19
~______~~_ Methyl formate Ethyl ether Carbon bisulfid Ethyl formate Methyl acetate Carbon tetrachlorid Ethyl acetate 11et h y 1 pro pion at e R enz en e Propyl formate Fluor benzene hlethyl isobutyrate E t 11y 1 propionate Propyl acetate Methyl butyrate T i n tetrachlorid C11 1o rbe n zeii e Brombetizene Iodbenzene
~
P = 760
ZOO
mm
mm
P = 40tm P nini
31.8 34.5
81.0 91.6
IO. I
46.2
IO7.j
20.8 23.5
54.3
79.7 80.3
112.4 I14 3 114.3 13s.; 141.0 146.0
80.9
143.S
$0. j
1.6
57.3 76.8
--
38.7
41.6 43.9 42.4 45.0 47.3
I /.I
8j.I
jj.0
61.6 63.6 64.3 73.0 80.0
92.3
99.0 101.6 IO2.j
114.2 131.9
I IO. I
I 56.0
'39.2
188.6
Ij0.S
157 3
164.3 167.1 16s.; 1h6.0 206. c, 23 .o 2 72.;
~
2jotxi
mrii I
I7j O 189.1 202.j 210.s 210 j 2jY j
2404 244 7 2j8.8 2jo.6 263.0 26j.6 272.3 Ljj.7
278 jog
j I
.... . ...
,...
" By following these columns from top to bottom, it ma\ be readily seen that the temperatures of ebullition under tlie pressiires of 2 0 0 , 4000 and 25000 inn1 of mercury, increase graduall! in exactly the same manner as those gix-en for the pressure of 760 nim, which determined the foregoing arrangement ; the only exceptions are the fatty ether< whose boiling-points lie close to those of benzene and carbon tetrachlorid, for which the vapor-tension curves cut a t a few tenths of a degree below the pressure of 760 mm. These exceptions are possibly attributable to tlie fact that some ethers begin to decoiiipose \\hen the? are heated to high temperatures : this fact has been announced by
__ Battelh.
Atti. . \ c a d . Sci. Toritio,
( 2 )
42.
356
f,H. I%.iiii
Sadesjdine' aiid has been confirmed bJ. Young aiid Thoinas.' T h e general statement may therefore be made that non-associated liquids gil-e vapor-tension curves which do not intersect. " In addition to the preceding results, there are now to be gil-en the boiling-points of bodies made u p of poljmerized moleciiles, under tlie extreme range of 2 0 0 and 25000 iiiiii. p 200 ~:~ 2jO3O -~
~
~~
~ ~ ~ _ _ _ _ _
~
~
_
_
I{-a t er 66. j 239.9 51et 11 y 1 alcohol 34.5 191.0 I Ethyl alcohol 48.1 206.2 Propyl alcohol 67 237 Acetic acid 79.7 2S2. j From these data, i t follows that at the pressure of 2 0 0 miii tlie \.apor-teiision curl-e of water passes betn.een those of iiietlij.1 1)utJ-rate (64.3' 1 and tin tetrachlorid (73.0' ) ; a t the pressure of 25000 111111 it passes betweell those of ethyl acetate ( 240.4" and niethJ.1 acetate j 2 1 0 . 7 ' ) ; this curl-e should therefore cnt tlie cur\-es of all tlie intermediate bodies bearing the numbers 6 to I 5. AAccorcling to its boiliiig--point under the pressure of 2 0 0 iiiiii, methyl alcoliol slioulcl lie placed betn-een iiiethj.1 acetate and carbon tetrachlorid ; while under the pressure of 25000 mi11 the boiling-poitit of inetliJ.1 alcohol lies het\veeii those of etliJ.1 ether and carbon bisiilfid : the 1-apor-tension curl-e of this alcohol ciits therefore those of the four intermediate bodies, nietli!.l acetate, ethyl formate, carbon bisulficl and ethlj. etli er. 13). analogous reasoning it might be reall!. pro\.ed that tlie curl-e for etlij-1 alcohol cuts tlie ciirl-es of liqtiid Sos. 4,5) 6, 7 . 8,9, IO, and 1 1 ; propJ.1 alcohol the cui-1-es, Kos. 6, 7 , S, 9, IO, 11, 12, 1 3 ~ 14,and 1 5 : acetic acid o n 1 ~one - ciir\-f9S o . 16." Up to the present there ha\-e been observed tniiiiinum boiling-points with the following pairs of coriipletel>- miscible suhstances : nietli>.l alcohol n.itli carbon t e t r n c h l o r i d , ~ acetone,' 5
1
L h
~~
' Saclesjdiiie. ?
'
Repertoriuiii tier PliJ-sik, 1-01, 2 3 . Y o u n g and Tlioiiiiis. loc. cit. Thorpe. Jour, Cheni. SOC.35, 54; I 15;s)'. . 3, 31; ( is99 :. Haywood. Jour, P l i ~ - sCheiti. This paper.
_
L1fi72iui11u1
Bo2'liiigy.kiiuf.sniiri 1 kpor C;iiujositioiis
3j 7
cliloroforiii,' * iiieth!-l acetate' aiid iiietli!.l cyanide ; 7 eth!-1 alcohol with carboii bisulfitl,+cliloroforiii,i benzene ;> water and iiietli!.l c!-aiiide' : all!.l alcohol and water : 7 triiiieth!.l carbinol and tvater ; 7 acetoiie with carlion tetraclilorid : I etli!-l acetate ant1 carbon hisulfid ;4 water with but!.ric :icid"or propj.1 a l c o l ~ o l . Of ~ these, the (lata collected b!. C;ii!.e show that tlie curve for methyl alcohol cuts tlie correspoiidiiig presslire ciir1.e for iiieth)-l acetate ; that the cur\-e for ethJ-1 alcohol cuts the vapor-pressure curve for benzene, while water atid propyl alcohol also linr-e pressure curves it-liicli intersect. Siiice oiil!. three of tlie sisteeii cases eiiiuiierated are substantiated h!- the data here presented, it is iiecessar!. to siiliiiiit the theory to a iiiore careful test. There has accortlingl>. been gatliered from the iiiost a\-ailable soiirce - iiiaiiily Laiiclolt aiitl IZoriisteiii's Tabelleii -- tlie data from which coiiclusioiis ma!- lie drawn as to the iiitersectioii or noli-iiitersectioii of each pair of curt-es. In the follon-iiig table there are given in the first t\vo coluiiiiis the substances n-liich are beiiig esaiiiiiietl : in the third coliiiiiii the apprc~siiiiateteiiiperatiire, in the foiirtli the approsiinate pressiire, at the poiiit of intersection of the ixpor-pressiii-e ciir\.es : in the fifth coliiiiiii tlie iiaiiie of the obsei-1-er n-lio e s ariiiiied tlie pressures of die liquid tlciioted i i i the first coliiniii, n-liile the sixth holds the iiaiiie oi the observer wlio esniiiiiietl tlie substance iiaiiied i l l the second colniiiii.
TABLE I
111 I\Y 1-1 Teiiip of Pressure Ohyerver Observer inter- of interof first of secc)iitI section section subbt-iiice subsmice
I1
Pairs of substances
Methyl alcohol Carboii tetrachlorid I-+.jL i o i i i m ~ 7 0 u i i g X70uiig Methyl alcohol Aicetone I ~ ~ j600 O Regiiault Regnault Alethy1 alcohol Chloroform (IoI.
