[ C O N T R I R U T I O S FROM TIIE D E P A R T M E N T O F C H E M I S T R Y , ~ ~ S I V E R S I TOYF C O N N E C T I C U T ]
Absolute Verdet Constants for Benzene over a Range of Temperatures and Visible Wave Lengths BY
ROBERT1,. C U S T E R '
AND CH.\S.
E.
LYARING
RECEIVED XIAS 1'3, 1!4,52 The purpose of this paper is t o present absolute \'ertlet constants for benzene over a range of temperatures and visible wave lengths. These constants werc olitaitied from experimentally deterniiried values of the magnetic rotation of beiizene arid from precise measurements of the field stretigth of the solenoid emiJllJyed. The uncertainty in the values so obtained \vas found t o IF &O.O:i%. Thew results coristitute t hc, first tli.tcrmiii:itio~i of absolute \.erdet constaiits for this substance
I. Introduction Since its discovery in l S f 3 , the Faraday effect has been widely studied because of its inherent connection with both the universal rnagnetizability of matter and the electromagnetic theory of light. X t present, however, there is still no general theory for liquids and solids. The Larmor-Recyuerel theory,' while derived on a basis independent of the actual origin of niagnetic rotatory polarization, has served to give a general picture of the effect. In its present state, however, it does not account for the teinpvrature dependence, apart from volume effects, of the norrnnl Faraday effect except insofar as it is conditioned by the optical characteristics of the molecule. In connection with this, Schultz3 has pointed out a need for exact and controlled observations of the dependence on temperature 01 magnetic rotatory dispersion of various pure materials on which t o base extensions of present theory. To the same end, Ingersol14 has indicated the necessity for determinatioris of the dependence upor1 wave length of the tciiipwature covllicient of the Faraday effect. In experiments carried out for the purpose of using the results 011 which to base extensions of current theory, benzene has been widely studied. However, no systematic studies of the type indicated by Schutz and by Ingersoll have been done. In addition, no actual absolute Verdet constants are given in the literature for this compound. I n view of its importance as a standard substance, it was felt t h a t such studies should be carried out. I t is the purpose of this paper, therefore, to present absolute Verdet constants for benzene, over a range of temperatures and wave lengths, obtained using a precision Faraday effect apparatus" and expvrin~r.titallytlrtcrniiiid iiiagnetic ficltl strengths.
11. Experimental iremetits was reagent The henzeiir ernployerl in the ni grade, thiopheiie free. I t \vas tiri Li-er PiOj a i i t l distilleti in a 30-plate 01dersh:iw coliimii 1 P d l - . 'I'he middle fraction of this distillatioii, froin which snmplc 1 was obtained, wa< redistilled i i i the s:iiiie crilutnn. Sample 2 R ' ~ S obtained from the r n i t l t l l t ~fr:iction of thi-. di~tillation. Thr criterion of piirity uscil \ v a \ t h e ri.fr:ictivi* iiitlex nie:tsured on a Bausch : i n c l r,oiiiI) pr(~ihi011Al)l)t, refr:ictomcter. At
-
(1: The d a t a ~ ' r e s e n t w l were s u h m i t t e i l in p 3 r t i a l l u i f i l i m r n t c ~ tf h e
25', the two ianiples of benzene differed by only 0.018% ivith the literature values6 a t 589 ni#. hlcnsurernetits of k , the rotation per ampere, were tnadi. i i i he usual way7 over a range of temperatures frotii 5 to BO0 for each of the wave lengths 689, 578, 546 and 436 mhi. Eich valuc for the rotation is an average of thirty-six po1:irinieter readings, eighteen in the positive and eighteen i i i the negative direction of the current flow through thc rii:ignct. Appropriate corrections were made in all the k ~.:iiucs for the rotation due t o the air in the light path and t o tlie rot:ition due t o the end plates in the quartz cell. The v:iriations of the rotation constant, k , for benzene, with teriiperiiture a t the various wave lengths are presented in F i g . I , The complete data niay be found elsewhere.8 \':ilues of the magnetic field strength of the Faraday effect soleiioitl, a t points over a range 11 cm. along the axis UII either side of the center, were obtained from measurements made by a method based upon proton nuclear magnetic resotin~ice.~Four least square equations of field itrviigth as a function of axial position were derived from the t l a t ; i . : ' I The most suit:ible, according t o the Gauss criterion, 1 ~ x 5extrapolated over The 58 cm. length of the Faraday effect cell to obt:iiii LI value of magnetic potential per amIxw over this length. The value so obtained was 2152.6 g:iuss rin. per anipere with an uncertainty of &0.03%. Ikttsities of the benzene samples were determined over a r:inge of temperatures from 8 to DO" in a precision pycnometer \vhow volume had been carefully determined with pure wxter. A11 values were corrected for vapor density and for ~JUO~alley.I n Tahle I are given the density values calcu1:iictl for arbitrary teinperatures front a least squares equat i o n , l i , derived from the data. d = o,!mol'3 - 1.07BBl x IO-"; 8 < t < BO (1) T.iter:itrtre v:ilues of densities of benzenei1 a t the corre-
ABSOLUTEVERDET CONST.\NTS FOR BENZENE
Nuv. 20, 1932
5727
2.25
g 2.20 n
1.30
5
3
1.25
2 8
1.10
.-+g 2.10
2
1.05 1.20 1.05
1.00
43G 546
578 589
0.00
10.00
20.00 30.00 40.00 50.00 60.00 Temperature, "C. of k , the rotation constant for benzene, with temperature.
Fig. 1.-Variation
sponding temperatures are listed for comparison in column 3 of Table I. It is seen that the agreement is excellent.
111. Results Least squares equations for the variation of k, the rotation constant for benzene, as a function of temperature for each of the four wave lengths were derived from the data represented in Fig. 1. These equations are shown in Table 11. TABLE I1
LEAS,.
sQUAREs E~~~~~~~~ OF k FOR BEszEsE FUNCTION OF
x 589
578 540 436
AS A
TEMPERATURE Equation
k = 1,0g912 - 1.68538 k = 1 , 14823 - ,76710
(1) (2)
10-3t
k = 1,31227 - 2.02342 X 10-3t ( 3 ) k = 2.29848 3.57593 X 10-3t ( 4 )
-
,
Values of k for arbitrary temperatures were calculated from the equations in Table 11. These values are shown in Table 111.
Absolute values of the Verdet constants for benzene were calculated from the data in Table I11 from the relation, V = 60 k/2152.6. These, together with specific Verdet constants, V / d , calculated on the basis of the data in Table 111 using the density values of benzene in Table I, and molecular Verdet constants, M V / d , are shown in Table V. The absolute Verdet constants for benzene were calculated with uncertainties of f0.04-O.05%. A value of 3.02 X l o 2 was derived by Richardson12 for this constant a t 559 mp and 20' from his data on the basis of the Verdet constant given by Rodger and Watson for water a t the same wave length and temperature. Since this value would suffer the same precision limitations as t h a t on which it was based, no reliable comparison can be made. These results of determinations of absolute Verdet constants for benzene are the first to have been derived for this substance on the basis of precise values of the magnetic field strength of the solenoid employed in the determinations of its magnetic rota-
TABLE I11 LEASTSQUARES VALUESOF k
BENZENEAS A FUNCTION OF TEMPERATURE
1
10
15
FOR 20
589 578 546
1.0910 1.1394 1.3022
438
2.28UG
1.0826 1.1306 1.2920 2.2627
1.0741 1.1217 1.2819 2.2449
1.0657 1.1129 1.2718 2.2270
Xt-
25
1.0573 1.1040 1.2617 2.2091
30
1.0489 1.0952 1.2516 2.1912
40
1.0320 1.0775 1.2313 2.1554
80
1.0152 1,0599 1.2111 2.1197
60
0.9983 1.0422 1.1909 2.0839
TABLE IV DISPERSIONS,kx/kbss, FOR BENZENEAS
x 678 546 436
5
10
15
20
1.0444 1.1936 2.0904
1.0443 1.1934 2.0001
1.0443 1.1935 2.0900
1.0443 1.1934 2.0897
Values of the dispersions kh/kbbB, calculated from the data in Table I11 are shown in Table IV.
A FUNCTION OF TEMPERATURE 25 30 40 50
1.0442 1.1933 2.0891
tion.
1.0441 1.1932 2.0890
1.0411 1.1931 2.0886
1.0440 1,1930 2.0880
60
1,0440 1.1929 2.0874
Thus, the uncertainties in the constants are
(12) S . S. Richardson, Proc. Roy. Soc. ( L o n d o n ) , 31, 454 (1916).
T A B L E \' ABSULGTF, \.MRDET c O S s l . . l S T S O F 13ESZfi.VL '?unp 1.
A
2
,XI nl@
"C Density
1. X 10' T'/d X 1 0 2
cj0,89474
3.0412 3.0175 2,9940 3.9705 2.9470 2.9233 2.8763 2.8296 2,7826
10 13
3! 2,; 30 40
50 ii0
,88935 ,88397 .8785!) ,87321 ,86783 .85706 ,84629 ,83552
X V/d,.U
2
X 10'
3.3991) 2.6550 3.1759 : 3 . 5495 3.3929 2.6503 3.1512 :i.5133 3,3870 2.6456 3,126(i : i .5371) 3.381C) 2.6409 :3.1090 3.330ti 3,3749 2.6361 3.077:3 :i.5241 3.3688 2.6314 : ~ . 0 3 7 :3.5177 3.3569 2.6213 3.00;15 3.2044 3.3435 2.6116 2.9542 3.4908 3.:3304 2,6011 2.9049 3 ,4767
less than those for any previous \;erdet constants. I t is seen from the data in Table IV that the dispersion for benzene is not constant but decreases slightly with temperature. This behavior is similar to that found previously for the lTlagIletic rotatory dispersion of water above 25'.18 The in Table v show that the molecular Verdet constants, A l ~ b ~ / cdecrease j, with temperature o\.cr the eIltirc range. I ~ i c l l a r d s o n ~ ~ has (13) Chas. E.\\:aring and R r h e r t 1,. C u s t c r . '1 H I S . l o t i ~ x . 74, ~ ~ 2306 , ,' 1'3.3,).
DEPARTMEST OF
ISDUSI'RI.11,
V
3 . 7725 2.i677 2.7627 9 .7577 2.7527 2.7477 2 , it372 2.7267 2.7156
A -. l . $ l i m ~
V X
.M
10' L"iI
X 10:
3.6295 .4.0563 3,1085 0.3568 7 , 104G :S.W19 4.0494 3.1830 6..3069 7.0910 3,5731 4 0431 3,157:j 6,2571 7 . ! ) i 8 4 :3.5449 4,0848 3,151ti 6,2073 7 .(1651 3.5167 4.09i;Y 3,1457 6,1574 7,!1314 3.48% 4.0199 3.1399 6,1076 7 OSTH 3.4321 4.11045 3 . 1279 t j ,0079 7.0099 3.3757 3.9888 3.1156 5,9083 6.9814 3.31'33 3.9727 3,ll):i1 5,8086 6,9381
1
3.549-4 5.5392 5.5289 5 51% 5,507S j.4978 5.4754 3, 5,430t3
suggested that the origin of the temperature dependence of the normal Faraday effect might be in the thermal opposition to the precessioml motion Of finite magnetic nloments, thus, to a mean paramagnetic j'olarization. These results, therefore, might be interpreted in terms of a slight p a r a magnetic polarization in the case of benzene. I t is of interest to note that the temperature coefficient a t 430 nip is approxiniately twice that at 589 1 1 1 ~ . Further extensions of theory would have to account for this behavior. SI IJKR5,
( 1 * l i b. S. Richardson. PI-OLRoy. SOL. Loudoizj, 31, 232 ,d!!Ilii
[ C O S T R I B U T I O N FROM THE
x =x i flLL, 1' x IO' V / d x 102 I
378 r n w
1. X 10: 1"d
C O S S E C I I C [ . I'
C H E M I S T R Y , T H E FACULTY OF E N G I N E E K I S G , K Y O T O r S I V E R b I T Y ,
Kinetics of the Condensation of Melamine with Formaldehyde BY ~ I A s . \ YO~.\n-o ~\ A N D YOSIIIRO OG.~T,\ RECEIVED DECEMBER
26, l!Jjl
The rates of the condensation of melaminc with formaldehyde in aqueous media in thc PH's varying from 3 to 10.6 have been estimated a t 35, 40 and 70' by employing both iodometric a n d sulfite methods. The primary product of the condcnsation, methylolmelamine, was found t o consume iodine like formaldehyde itself, and therefore the result of the iodometric method indicates the amount of formaldehyde together with that of methylol group present, irhile the sulfite method estimates solely formaldehyde unrcacted. From the data obtainctl by thcie two methods, the rates of the fxmation of methylolmelamine, e.g., ( I ) , and methylene-bonded melamines, c . ~ . (, I 1 J , r r e r e determined. There were found evidences that only the formation of methylol conipounds occurs at 35-40" except i n ;iridic solutioii and that the reaction is reversible all through the p H range, its forward rate being proportioual to either [ m e l m ~ ~ n[formaldehyde], c /melamine] [conjugate acid of formaldehyde], or [conjugate base of melamine] [formaldehyde] accordiiig to t h e PH's of the media. The rate of the irteversihlc condensation of methylomelamine with melamine in ricutral and acidic media at 7(Jo, where the hydroxymethylation ( I I i . very rapid, is determined by the condensation step of conjugate acids of li~ethyloltnelamineswith melamine, the rate being expressed as [melamine]* [formaldehyde]. The rate equations based 011the reaction mechanisms which are suggested froiii these results satisfied the relationship bet1veen p€i and the rate co~lstantexperimentally fouud. ,
It has been pointed out that the nature and structure of the melamine-formaldehyde condensate are considerably varied with reactioii conditions, especially molar ratio of reactants, pH and temperature of the solution.' There seems to kit. no
m c s
s
decisive kinetic evidence for this condensation mechanism, although the primary process inay be presumed from the similar reactions such as those Of urea-formaldehyde and aniline-for~naldehycle.' ( 2 ) T S H o d g i n s a n d h I' H o \ r \ l l c i u i ~ r r r i .1rln 1 8 , 431 ( 1 % ? J
ihi
/
3 0 , 10.21 I ' l 3 R
K I
ri I
