IODIDES OF SOME POLYVALENT METALS
647
THE IODIDES OF SOME POLYVALENT METALS' H. W. FOOTE
AND
MICHAEL FLEISCHER
Department of Chemiutry, Yale University, New Haven, Connecticut Received June M,1939
The methods which have been used in this laboratory to study the addition compounds of alkali iodides and iodine (2, 3) are equally applicable to the study of the iodides of polyvalent metals. From a phase rule standpoint, the relations are the same in both c m s and, furthermore, are not changed if the starting material is a metal rather than an iodide. The study of systems composed of a metal, iodine, and a solvent in which the metal and its iodides are insoluble but which dissolves iodine, is an extraordinarily simple and accurate method of determining the stability conditions of metal iodides. We have studied the iodides of iron, copper, silver, and thallium, a t 6"C., using toluene and benzene as solvents. The experimental procedure and the methods used to purify iodine and the solvents have been described (2, 3). Equilibrium was reached very rapidly in these systems, but a period of 5 days was always allowed before analyzing. As qualitative tests showed that the solid residues were not solvated and that the iodides were insoluble in the solvents used, the composition of the solid residues was calculated from the known original composition and the analytically determined concentration of iodine in the solution after equilibrium had been reached. THE IODIDE OF IRON
The well-known fact that in water solution ferric iodide is unstable and decomposes into the ferrous compound and free iodine does not prove that a solid ferric iodide does not exist and that it could not be prepared in a non-ionizing solvent. It has been shown (4) that when a mixture of iron and iodine is heated to a high temperature, pure ferrous iodide is formed and the exceas iodine is volatilized. Ferric iodide is therefore unstable a t high temperatures, but there has been no systematic study of iron iodides a t low temperatures. The results obtained by us in the systems iron-iodine-toluene and ironiodine-benzene a t 6°C. are summarized in table 1. The iron used was a pure sample of h e l y divided metal which had been prepared from iron carbonyl. We are indebted to Dr. Oskar Baudisch for the gift of this material. This article is baaed upon a thesis presented by Michael Fleischer t o the Faculty of the Graduate School of Yale University in partial fulfillment of the requirements for the degree of Doctor of Philosophy, June, 1933.
648
H. W. FOOTE AND MICHAEL FLEIBCHER
The results in table 1 show clearly that ferrous iodide (iodine content 81.94 per cent) is the only stable binary iodide of iron at 6°C. Ferric iodide can not be prepared at 6°C. or above. As no iodine could be detected in the solution when the solid ,was a mixture of iron and ferrous iodide, the dissociation pressuro of ferrous iodide at 6°C. must be very low. THE IODIDE O F COPPER
Solid cupric iodide has never been prepared, but polyiodides of copper have been reported by Jorgensen (5) and by Walker and Dover (9). A study of the freezing points of mixtures of iodine and cuprous iodide by Kremann and Borjanovics (6) gave no evidence of compound formation, TABLE 1 T h e clystems iron-iodine-toluene and iron-iodine-benzene
1
IODINE I N WLUTION
W A L IODIUli I N P m I D U l i
Toluene; t wdgh; pa cent
weight pa MIL
0.0
~
i
10.46 10.30 ~~~
~
50.00
82’91 90.82
1
I I}
l O L I W PPDIImNT
6°C.
Fe andFe1,
FeI, and 11
~
Benzene: t = 6°C.
8.81 8.81
1
95.44
1)
FeIz and
It
but there has been no systematic study at low temperatures. We have therefore studied the systems copper-iodine-toluene and copper-iodinebenzene at 6°C. Table 2 gives the data obtained for the system with benzene; those for the toluene system are in complete accord and are omitted for brevity. The results show clearly that cuprous iodide (iodine content 66.63 per cent) is the only stable binary copper iodide at 6°C. and that cupric iodide can not be prepared at 6°C. or above. It seems probable that the compounds analyzed by Jorgensen and by Walker and Dover were mechanical mixtures. A s no iodine could be detected in the solution when the solid was a mixture of copper and cuprous iodide, the dissociation pressure of cuprous iodide must be very low at 6°C.
IODIDES O F SOME POLYVALENT METALS
649
THE IODIDE OF SILVER
As it seemed possible that silver might form polyiodides like those of the alkali metals, the systems silver iodide-iodine-toluene and silver iodide-iodine-benzene were studied a t 6°C. Schmidt (8) reported the preparation of silver triiodide, AgIa, by the addition of silver nitrate to a concentrated solution of iodine in potassium iodide. Our results show that he was undoubtedly dealing with a mixture of silver iodide and iodine. The data for the benzene system are given in table 3; those for the toluene system are similar and so are omitted. TABLE 2 The system copper-iodine-benzene at 6°C. IODINE IN BOLUllON
1
TQTAL IODINE IN BEBIDWE
weigh1 pu em1
weigh1 p u cml
0.0
65.00
1
1
OOUW PBEBENT
CuandCuI
3.05 7.79 8*53 8.61
!
69'40 91.57
1)
C U I and I,
TABLE 3 The system silver iodide-iodine-benzene at 6°C. IODINE IN SOLUllON
i
weighlpaernl
1
IODrNE IN PWDUE
weigh1 pucml
SOLIDS PREBENT
1
7.46 8.71 8.68 THE IODIDES O F THALLIUM
Thallous salts are in many ways rather similar to the correspondind salts of the alkali metals. It seemed possible that thallous iodide woulg react with iodine to form polyiodides, so the systems thallous iodideiodine-toluene and thallous iodide-iodine-benzene were studied a t 6°C. While there is considerable evidence for the existence of two higher iodides (7), the only systematic work is that of Abegg and Maitland (l), who used the solubility method with carbon disulfide as solvent a t 25°C. They found the compounds TIIs and Tl& or TlIs.5TlI. Thallous iodide was prepared by mixing equivalent amounts of pure thallous carbonate and potassium iodide solutions, wmhing the precipitate thoroughly, and drying at 105'C. The results obtained are given in table 4.
650
H. W. FOOTE AND MICHAEL FLEISCHER
The average of the four results on the higher iodide is 43.28 per cent available iodine; TlIs requires 43.38 per cent. The lower iodide w ~ t s present in Nos. 3 to 7 and 17 to 22. The composition of the residue shows TABLE 4
The systems thallous iodide-iodine-toluene and thallous iodide-iodine-benzene BIBIAL NO.
eoum P
IODINE IN BOLURON A v A & M ~ ~ I ~ ~ ” , E
Toluene; t = 6’C. weiuht per cent
w&ht p a c a t
1 2
0.043 0.045
2.67 8.66
3 4 5 6 7
0.17 0.74 1.51 1.75 1.81
11.33 11.87 12.28 12.30 12.35
8 9 10
2.29 2.27 2.27
14.91 25.02 39.27
11 12
2.97 9.40
43’47 43.66
] TlI:
13 14
10.17 10.07
49’26 95.14
I)
Tlda and TIIS
TlI: and 11
Benzene; t = 6°C. 15 16
0.038 0.038
17 18 19 2.0 21 22
0.18 0.36 0.75 1.40 1.43 1.57
11.32 11.44
23 24
1.97 1.99
12’27 39.88
25 26
8.27
43.23
8.66 8.60
49’93 94.12
27 28
11’76 11.93 11.95 11.82
3.07
1 I}
TlJs
1
Tlda and TI18
/I
} Tl11 } TlI: and 11
B W ~
651
IODIDES OF SOME POLYVALENT METALS
good agreement with the formula Tl& (available iodine, 11.32 per cent) only when the solution was very low in iodine content (Nos. 3, 17, 18). The other results are all high, the excess iodine in the residue being roughly proportional to the concentration of iodine in the solution. This may be due to adsorption of iodine by the compound. These results confirm the work of Abegg and Maitland (1) a t 25°C. The dissociation pressures of the two compounds a t 6°C. have been calculated by the method previously described (3). The values of C/CO calculated from the results in the two solvent$ are in good agreement. Using the averages of these values, and taking the vapor pressure of iodine at 6°C. to be 0.0546mm.2, the dissociation pressures of TlIa and Tl& are 0.0116 and 0.00022 mm., respectively, a t 6°C. Unfortunately, the work of Abegg and Maitland at 25°C.is given in terms of volumes, and the TABLE 5 Showing the. ratio c/co for both periodides i n benzene and i n toluene
I
WUW P B m M T
IODmIN 8OLURON
I
IODINllN BOLUlrION
1
elm
Benzene; t = 6°C. W&ht
TII, m d In ........................... TlsIs and TlIs . . . . . . . . . . . . . . . . . . . . . . . . TI1 and TIds ........................
pa Mnt
. ,I
6
pa C a t
2.95 (eo)
0.038
0.0118 (e)
Toluene; t = 6°C. TlIs and 1%. . . . . . . . . . . . . . . . . . . . . . . . . . TI& and TlIa . . . . . . . . . . . . . . . . . . . . . . . . TI1 and TlsIa.. ....................
d
8.63 1.98
10.12 2.28 0.044
0.618 (e)
1
i
3.92 (CO) 0.839 (c) 0.016 (e)
0.209 0.00398
~
0.214 0.00407
densities of their solutions are not known, so that dissociation pressures can not be calculated from their data. SUMMARY
The iodides of iron, copper, silver, and thallium have been studied by the solubility method at 6"C.,using toluene and benzene as solvents. Ferric iodide, cupric iodide, and silver triiodide have been found not to exist at this temperature. Thallium forms two higher iodides, TleIs and TlIs. Their dissociation pressures a t 6°C.have been calculated from the solubility results. REFERENCES (1) ABEQQAND MAITLAND:2. anorg. Chem. 49, 341 (1906). (2) FOOTE AND BEADLEY: J. Phys. Chem. 86, 673 (1932).
* By interpolation of the data in the International
Critical Tables.
652
J. E. ARNOLD AND C . F. GOODEVE
(3) FOOTE, BRADLEY, AND FLEISCHER: J. Phys. Chem. 37, 21 (1933). (4) JACKSON AND DERBY:Am. Chern. J. Z4, 16 (1900). (5) JURGENSEN: J. prakt. Chem. 2, 347 (1870). (6) KREMANN AND BORJANOVICS: Monatsh. 36, 923 (1915). (7)MELLOR: Comprehensive Treatise on Theoretical and Inorganic Chemistry, Voi V, p. 460. Longmans, Green and Company, London (1924). (8) SCHMIDT: Z. anorg. Chern. 9, 432 (1895). (9) WALKERAND DOVER:J. Chem. Soo. 87, 1584 (1905).
T H E COEFFICIENT OF THIXOTRCPY OF SUSPENSIONS OF CARBON BLACK I N MINERAL OIL J. E. ARNOLD AND C. F. GOODEVE The Sir William Ramsuy and Ralph Forster Laboratories of Chemistry, University College, London, England Received February 6, 1039 I. INTRODUCTION
It is well known that certain classes of fluids do not obey the ordinary Newtonian laws of flow in that their viscosity is dependent on the rate of shear. Fluids possessing such non-Newtonian viscosi’y a t constant temperature may be divided into three main classes: ( a ) those showing a reversible decrease of viscosity with increasing rate of shesr, a phenomenon which has been called “thixotropy” by Freundlich (1); (5) those showing a reversible increase of viscosity with increasing rate of shear; and (c) those showing irreversible viscosity changes. Colloidal dispersions commonly show non-Newtonian behavior and especially that of type a. Extreme cases of thixotropy are those in which a more or less rigid gel is made fluid by mechanical agitation and again sets to a gel on standing. Goodeve and Whitfield (4) among others (5, 8, 10) have recently shown that if a thixotropic fluid is subjected to a uniform and steady shear rate, u, the apparent viscosity, q , generally follows the empirical equation
.
where qo and e are constants and FT is the force per unit area. If the apparent viscosity is plotted against the reciprocal rate of shear, l/u, a straight line is obtained, the slope of which, e, is called (4)the “co&cient of thixotropy.’’ As deviations from this equation are sometimes found to occur a t low shear rates, the values of the coefficient are taken from the “limiting slope of the apparent viscosity-reciprocal shear rate curve aa the
