NOTES
Jan., 1951 A weighed quantity (0.2 9.) of ZnS04.Ti(S01)2 was boiled with distilled water (350 cc.), the metatitanic acid filtered otT and the sp. conductivity in mhos./cm. of the filtrate (made to 100 cc.) was determined by the method of Kohlrausch. This filtrate was again diluted with a n equal volume of distilled water and sp. conductivity measured. This operation was repeated thrice. Similar measurements were made with soutions prepared from the calculated amount of zinc sulfate and sulfuric acid. The values thus obtained which are reported in Table I, are very close t o each other showing thereby that the hydrolysis takes place according to the expression given before and the substance ZnSO4.Ti(SO4)2 behaves as a double sulfate. TABLE I SPECIFICCONDUCTIVITY OF HYDROLYZED SOLUTIONS AND SYNTHETIC SOLUTIONS OF SAME CONCENTRATION Solution
ZnSO4.Ti(SO& ZnS04 H2S04
+
2.2
$ $
3 -? 2.0
-
38 u
.% x
'
Sp. conductivity, mhos. X 10-1
489
1.8
9
5.61 3.05 1.76 0.91 0.48 5.48 2.94 1.67 0.89 0.46
The other compounds of the type RS04.Ti(S04)2were also examined and showed similar behavior.
Acknowledgment.-The author wishes to thank Prof. S. M. Mehta for his interest and encouragement in this work. THEDEPARTMENT OF CHEMISTRY THEROYAL INSTITUTE OF SCIENCE BOMBAY, INDIA RECEIVEDJ u m 6, 1950
1.6 20
40 50 60 70 Temperature, "C. Fig. 1.-Iron silicate gel: velocity-temperature relationships: W, 2.500 ml./s; x, 2.250 ml./s.; Y, 1.250 rnl./s.; 2 , 0.625 ml./s.
M
Elastic Constants of Gelatinous Substances
i
.P
8
BY ARVINDMOHANSRIVASTAVA
2.7 -
30
24
16
8
d
4
2.3
YI
The importance of measurement of elastic con0% h+ stants of gels is threefold, aiz., (1) it provides a * x 1.9 basis for comparison with other substances; (2) it furnishes a criterion for studying the semi-solid nature of gels, and (3) it affords a basis to under1.5 stand the ultimate mechanical behavior of gels. 0.5 1.0 1.5 2.0 2.5 From the knowledge of variation of these quantiFrequency, rnl./s. ties with frequency, temperature and other factors, conclusions may be drawn to elucidate the Fig. 2.-1ron silicate gel: velocity-frequency relationmechanism of gel formation and the internal ship at 30'; 4, 8, 16 and 24 hours. structure of the gel. The method' is an adaptation of the ultrasonic technique developed by Pellam and 2 7 . Galt,2 modified by Teetar3; it is based on the f: theory of Knott.* Ultrasonic waves are gen- X "- X erated by a suitable pulse transmitter, impinged upon a slab of gel, received by a quartz 3 crystal and detected after proper amplifica- 4 $ . tion on a cathode-ray tube. The rotation of the slab in a vertical plane changes the angle -a w of incidence of these waves and in two positions sharp minima in the transmitted inten1. sity are observed due to the total reflection of the two waves set up in the gel. These two waves are due to the resolution of the inci0 4 8 12 16 20 24 dent beam into longitudinal and transverse Time, hours. components. Fig. %-Iron silicate gel showing variation of E with time at From the two *e and Os, the 30': W, 2.500 ml./s.; X, 2.250 ml./s.; Y, 1.250 ml./s.; 2, velocity of the waves V, and V, can be com- 0.625 ml./s. puted. A knowledge of these and the density p of the gel gives the elastic constants from the where u, E , S are the Poisson ratio, Young modurelationships lus and Shear modulus. (1) A. M. Srivastava, Proc. Nat. Acad. Sci., I n d t a , 188, 51 (1949) The values obtained for the various constants (2) J. R. Pellam and J. K. Galt, J. Chcm. PhYs., 14,608 (1946). are plotted in ~ i 1-3.~ The ~ four . frequencies (3) C. E. Teetar, J . Acc. SOC.Am., 18,488 (1946). used were, 0.625, 1250, 2 250 and 2.500 Mc./sec. (4) C.G. Knott, Phil. Mag., 48, 64 (1899).
-
2
2
3
-
Noms
490
Val. 73
sition potentials of zinc halides in methanol solution (to be published a t a later date), we have observed an interesting reaction of iodine in the presence of zinc halide in $3 D methanol and of bromine in methanol so% lution with zinc chloride or bromide, some ;2 qualitative aspects of which we wish to ? report here. If separate solutions of iodine i, and one of the zinc halides be prepared in dry methanol and then mixed, the mixing is followed by a rapid fading of the iodine 0 10 20 30 40 4ti.78. GI.Go. 70 80 90' color until the solution becomes colorless. The rate of fading varies directly as the Angle of incidence. ratio, the period Fig. 4.--Showing the variation of amplitude with angle of incidence: of the order of a few minutes, and all of V, = 1.55 X 10S/sin 8.; V, = 1.55 X lO6/sin 8.. the halides seem to be about equally effecDensity of the iron silicate gel, for which these re- tive. Repetition of the experiments with solutions sults are given, was 1.180 a t 23". Figure 4 containing approximately 0.05% water shows an shows the variation of the amplitude of the trans- induction period of several hours followed by fading mitted rays; the two dips correspond to the Val- a t a considerably reduced rate, the total elapsed ues 6, and 0, in a particular case. Figure 5 is the period to a colorless solution being of the order of oscillogram in which A is the instant of start of the 24 hours or more. Tests with varying amounts of ultrasonic pulse and B the amplitude of the trans- water show that water content apparently controls mitted waves. both length of the induction ueriod and diminution of fadingrate after reaction has started. Aeration and exposure to light seemingly have no effect upon the reaction. Replacement of the zinc halide by A1Br3, aluminum isopropoxide, ZnS04, CdIz, KI, NHICl and HBr appeared to give no reaction, but use of Zn(CH,SO,), produced a partial fading after about one month. Some of these latter systems may have contained small quantities of water which may account for their failure to react rapidly, but such was definitely not the case with NHC1 and HRr. T o obtain a further clue concerning the nature of the reaction, a solution of iodine and zinc chloride was allowed to fade completely. The resulting solution was then electrolyzed without stirring. At from 2 to 3 volts and about 1 milliamp., iodine was regenerated. Increasing the potential to 6 volts caused fading of the iodine color again, beginning at the bottom of the cell; under these conditions zinc simultaneously plated out on the --Showing the amplitudc 01 ihc ti;riwnittcd wave Fig. 6.cathode with evolution of gas. Fading of the 011 the oscillograph. iodine color under such conditions was never Since thcrc is so far no agrccd niechanisiu of gel complete. When the potential was removed gas formation this work has been undertaken to study evolution continued, and in ten to fifteen minutes the problem from a physical standpoint. Details the iodine color had returned to full strength. of this work on iron silicate gels and other gels of Three hours later the solution was again nearly the Weimarn type will appear in forthcoming pub- colorless and gas still was being evolved. On the basis of these observations it appears that the fading lications. My thanks are due to Dr. R. N. Ghosh for help reaction probably involves reduction of the iodine to iodide. Electrolysis oxidizes the iodide first to and guidance in undertaking this work. iodine and then to hypoiodite or sotne higher oxidaDEPARTMENT OF PHYSICS tion state which, in presence of the zinc halide, is UNNERSITYOF ALLAHABAD ALLAXABAD, INDIA RECEIVED MAY22, 1950 unstable and reverts to iodine and then to iodide with the passage of time. The literature appears to be devoid of informaAn Apparent Reduction of Halogens by Zinc tion which provide an explanation of the phenomena described here. Freyz refers to a reaction between Halides in Methanol Solution1 zinc chloride and iodine which occurs in fibers and BY FRANCIS J. Sr1El.L AND IIOWARD K. ZIMMERMAN, JR. may be used for biological staining procedures, In the course of an investigation of the decompo- but no details of the reaction seem to be available. The remarkable specificity of the zinc halides in 4
(I) Bmred up00 rewrreb pcdoormcd under c ~ n t r a c tNo. W30.039~ ~ 3 8 1 8for 4 the U. S. A m y Sigoml Corps.
(2) A Prcy. fohrb. m . , s . E d . . 07, 697-634 (1927).
