0
ld i i
l i m e min Potential
CfiY
Itmc, nr Potential
T 4 0
3 >
3 0
’lime day5 F’otcntial
5
8 !-i 65
11
1;
+I 74
+I 31
4-1 4 5
1:
3
>
+r,i 1
cq2
21 J i
J
It is apparent that the usual potentials acquired by dipping, Or Potentials of either sign Put on by ionized air, all behave in a similar manner.
fCONTRIBUTIOK FROM THE CHEMICAL
Ionium. With xoltage off, the films lose their charge exponentially. The coulombs represented by the area under the automatically registered discharge curve agree n ith Langmuir’s equation which caiculntrs potential resulting from surface charges. The slow leakage of charge from X films left in air can be by the natural elec-
LABORAT ORs
OF S O R THWES? E R S YNIVERSITY]
Magnetic Measurements on Hexaphenyldigermane BY P. W. SELWOOD’
The molecular weight of hexaphenyldigennane has been reported by Morgan and Drew2 as 5G0 to 566 determined ebullioscopically in benzene. They interpret this as evidence for “no recognizable dissociation” although the value obtained is slightly lower than the molecular weight ((306.8) computed for the compound. A sample of this compound was obtained through the courtesy of Professor Warren C. Johnson of the University of Chicago.
Experimental Part Magnetic Measurements.-The magnetic susceptibilities were measured by means of the Gouy balance previously d e ~ c r i b e d . ~The only modifications were (1) the use of a magnetically damped microbalance, and (2) a modified temperature control In previous work the temperature of the sample had been maintained through careful injections of liquid air into a lead block surrounding the samplc. In the present 5%-orkoxygen was liquefied by passing it through a coitdenser surrounded by liquid nitrogen. The oxygen was then allowed to fall, drop by drop, into the lead blocl;. Through control of the ratc of fiow of oxygen into the condenser, a high degree of tenipeiature control W ~ possible F All measurements were referred to freshly boiled distilled water, the specific susceptibility of which was assumed to be -0.7200 X 10-6 a t 20” Preparation of Materials.-Measurements were made on powdered hexaphenyldigermane and on a solution of the digermane in benzene Some rather interesting experiences were encountered in preliminary tests on the powder, and are described
_____
(1) T h e author is indebted to t h e National Research Council for funds for t h e construction of a magnet, and to t h e National Academr of Science.; for a research grant from the Joseph IIenry Fund (2) Morgan and Drew, J Chem Soc , 127, 1760 (1925) ( 3 ) Halier and Selwood Tfirs JOUR\AI., 61, 8 3 11939)
The substance gave evidence of having a magnetic susceptibility markedly dependent on field strength. The at apparent susccptibility varied from +1 45 X l000 oersteds to -0 10 X 1WCa t 11,000 oersteds. This behavior strongly suggested the presence of a ferromagnetic impurity. The digermaiie was therefore recrystalltzcd from benzene, after which the susceptibility became normal, that is, constant, from about 1000 to 17,000 oersteds A small insoluble residue was found to contain a very few almost microscopic specks of some highly magnetic substance, presumably magnetic oxide of iron. These results are illustrated in Fig. 1 in which Aw, the apparent change in weight on application of the field, is plotted against 2, the current through the magnet. While these results h a w no bearing on the main problem, yet they do show the extraordinary sensitivity of the magnetic method for detecting ferromagnetic impurities and the riecesqity E07 excluding ir on-bearing kdboratory dust from wnples under investigation The benzene solution used in this work was prepared by shaking the powdered digermane with redistilled thiophene-free benzene. KO effort was made to exclude air Thc solution was analyzed by evaporating to dryness a t 125” and weighing the tesidue The density was determilied pycnometiically.
Results The susceptibility of the powdered hexaphenyldigermane a t several temperatures is given in Table I. These results follow the relationship x = A (C/T A) where x is the susceptibility, A is the constant diamagnetic part of the susceptibility, C is the Curie constant of the paramagnetic part, T is the absolute temperature, and A is the “molecular field constant.” In the above relationship A == -0.47 X and this is believed
+
+
Nov., 1939
MAGNETIC MEASUREMEN TS ON HEXAPHENYLDIGERMANE
SUSCEPTIBILITY AT
3169
TABLE I FIELDSTRENGTH 13,100
OERSTEDS Susceptibility per gram,
Temp.,
x
OC. 20
x
10s
-0.436 - ,431 - ,423 - .410 - ,390
0
-20 -40 -60 -80
-
,357
to be the magnetic susceptibility of undissociated hexaphenyldigermane. The Curie constant is and A = -150’. 5.0 X The temperature dependence of the measured susceptibility may be interpreted as evidence for slight dissociation or for the presence of a paramagnetic impurity in very small amount. If triphenylgermanium exists, it may be expected to have a molar paramagnetic susceptibility of about 1270 X lone, corresponding to a single unpaired electron spin.* About 1% of dissociation would 0 5 10 15 20 then account for the results. However, this is Amperes. considered improbable because the molecular Fig. 1.-Apparent change in weight, Aw, plotted against current through magnet: field constant, A, would not be expected to apupper curve, original sample; lower, recrysproach - 150’ for such a compound having, as is tallized sample. likely, no orbital contribution to the susceptibility. On the other hand, molecular field constants of A single solution 0.00387 M in digermane was - 150’ are not unusual for such highly paramag- investigated at 25’. Measurements were made netic oxides as might be present as impurities to a t several field strengths. The results are given the extent of a few thousandths of a per cent. in Table 11. Further, if dissociation actually takes place it The susceptibility of the solution, assuming no may be expected to increase sharply with rise in dissociation, may be calculated to be -0.7022 X temperature. The data do not indicate such an using Wiedemann’s law and the observed effect. susceptibility of the solid. On the other hand, The measurements on the powder therefore the susceptibility of the solution, assuming comset an upper limit of 1% as to the extent of dis- plete dissociation, may be calculated to be sociation in the solid. The weight of evidence is -0.7012 X It is therefore evident that that no dissociation takes place. nothing approaching complete dissociation takes Hexaphenyldigermane is not very soluble in place. It is probable that as little as 20% disbenzene a t room temperature. Measurements sociation would have been detected. had therefore to be made as accurately as possible. TABLE I1 0.00387 M soh.
Field strength, oersteds
Pure benzene x x 10’
11,450 16,080 17,100
-0.7024 - ,7027 - ,7019
x x 100 -0.7017 - ,7033 - ,7018
-
-
Averages
--
,7023
,7023
(4) Van Vleck “Electric and Magnetic Susceptibilities,” Oxford Univer\ity Press, New York, N.Y., 1932, p. 274.
Summary Magnetic measurements on hexaphenyldigermane set upper limits of dissociation at 1% in the solid and 20% in a nearly saturated benzene solution a t 25’. It is considered improbable that any dissociation takes place under these conditions. EVANSTON,
ILLINOIS
RECEIVED SEPTEMBER 18, 1939
