Fcb., 1002
3t57
NOTES
M
bcing mo1n.r ratio and T the time of gelation, where a,B, n and m are constants. Their values for 2.4 t h e foiir sets are a = 5 3 , 19.9, 18.6, 10.0; B I* 19.05, 14.2, 17.78,X.l4; IL = 3.4,5.0, 6.9, 6.22 i t ~ d m = 2.01, 2.68, 4.16 and 4.68. The fact that the values of the conrtants are not the same may be due to the varying influcnce of factors like solubility, degree of supersaturation, cxtciit of hydration and ii dilution during gelation. 2 1.2 Acknowledgment.-Thanks are due to Dr. A. It. Y0 Kidwai for providing facilities and to C.S.I.R. E (India) for the award of a fellowship to F.A.S. 5
.m
4E 0.6 A rl
STUDIES ON THE SOL-GEL TRANSFORMATION OF THE FERRO- AND FERRICYANIDES OF SOME METALS. PART IV. VARIATIONS I N VISCOSITY AND HYDROGEN ION CONCENTRATION DURING THE GELATION OF CHROMIC FERROCYANIDE
4
104T . e15
3:s
0’15
50
C*VW ~
1.75
la 225
150 200 250 T, min. Fig. l , - C u r v e la, T us. M ; curve lb, log T us. log M ; curve 2, strength of CrCls us. log ( q t - ~ o ) / v o . 100
setting for the gelation mixturcs of molar ratios 0.50:1,0, 1.O:l.O and 2.0:l.O being 25, 17, 85 minBY WAMDU. MALIKAND FASIH A. SIDDIQI utes, respectively, by Fleming’s method and 120, 28 Chamkal Laboratm‘cs, M w l i m Uniombitu, Aligarh, India and 120 minutes, reapectivcly, by the viscosity Recoined A w a t #Se 1881 method), provided due allowance is given to the disThe conductivity method, which was successfully turbances experienced by the gel-forming mixturc employed’ earlier in studying gelation of Prussian during its movement through the capillary; ( 2 ) and Turnbull’s blues, did not give any useful in- similar types of curves are obtained by the two formation here, and hence the methods based on the methods on plotting the time of setting against the variations in viscosity and pH werc adopted. The molar ratio (Fig. l), confirming thereby the existlatter method was particularly chosen with a view ence of two types of gels in chromic ferrocyanide to ascertain the hydrolytic effects operative during (Part 111); (3) a straight line is obtained on plotting log (qt - qo)/qo (for abrupt change) against the congel formation. centration of chromic chloride (Fig. 1, curve 2 ) Experimental (Crs+ concn. for sets I to VII), which indicates a Viscosity measurements were carried out at 80 0.1’ thixotropic behavior of chromic ferrocyanide gcl (a (Fisher Unitized constant temperature oil-bath) with the help of an Ostwald viscometer after applying a vacuum of 1 linear rclationship log 6 = A - Bc, where 0 is the cm. (manometer tube sirpplicd with koppeos viscometer time of setting and c is the concentration of the u n i t was used for this purpose) a t the head of the viscometer electrolyte and A and B are constants, \va$ found by tube. Beckinan pI-1 meter (model H2) was used for pH Freundlich,2 Schalek and Szegvaria for thc gelation measurements. Seven sets were studied, containing 0.25 M of ferric oxide sol). &FeCys and varying concn. of CrC4 (0.083, 0.125,0.18, The results on p1-E measurcmcnts, besides con0.25,0.375,0.50 and 0.625 M ) in the reaction mixture. Thc results arc summarized in Table I. firming the results on viscometry (the time whcn constancy in pH value is reached being taken as the TABLE I time of setting), throw some light on the nature of Time Value the chromic ferrocyanide gel. As cxpected the interval Change in of for abrupt ’I during (at mixtures containing excess of chromic ions have change in this r)a)/qo a t p H change viscwity r) interval abrupt during lower pH values and those containing excess of Seb Crs+/FeCyd- (min.) (centipoise) change gelation potassium ferrocyanide have highcr pH values. I 0.33:l.O 218-250 0.70-2.4 0.75 4.0-7.25 But with lapse of time the pH of the mixtures havI1 0.5:l.O 120-140 0.95-2.7 0.90 3.8-6.8 ing Cra +/FeCye4>1 continuously decreases, I11 0.75:l.O 72-80 1.15-4.8 1.10 3.6-4.0 while for those having Cr3f/l;rCyb4-
