Double valency rule

We can collect these two rules into the double valency rule, to distinguish it... 

Fig. 11. Double valency rule in the suppression of complex coacervation of 0.01% gelatin and...

Fig. 12 gives similar results with the so-called coacervate volume method. In contrast to the viscosimetric or turbidity method this is a direct method. It is serviceable in sufficiently concentrated colloid mixtures. In it one reads off directly the volume of the separated coacervate in a graduated tube (after sedimentation and coalescence to a homogeneous liquid column). Here also we see that added salts suppress coacerv-ation and that the double valency rule holds. 

If one regards the complex coacervate as a sightly soluble compound of polyvalent colloid ions, one can understand the occurrence of the double valency rule as increase of solubility as a result of the shielding of the colloid cations by the anions of the added salt and of the colloid anions by the cations of the added salt. 

Since this shielding increases with the valency of the shielding ion, the double valency rule follows from this. Indeed in it we always keep the valency of one ion constant (the anion in the valency rule of the cations conversely the cation in that of the anions) and increase the valency of the other ion. ... 

We now turn to another salt rule, the continuous valency rule in which the same salt symbols occur as in the double valency rule, but in which they are arranged in another way. 

If now one investigates the influence of salts of the same valency types as occur in the " double valency rule , the curves for these salts are seen to form a fan in which the salts are always arranged in the same sequence Fig. 14 gives an example for a positively charged coacervate system, but the sequence is the same for an uncharged or a negatively charged system. This is as follows ... 

Although other factors also play a part, this interaction (at least at the optimum mixing proportion) will have the character of a product. The intensity of this interaction will thus only be able to decrease when salts are added. Because of the smallest shielding action of monovalent ions a salt of the type 1—1 (for example KCl) is thus always the least active. Increase of the valency of the cation or of the anion will cause the intensity of the interaction of the two colloid ions to decrease more strongly than 1—1 does. In consequence of this the double valency rule makes its appearance. 

Abscissae salt concentration in m. eq. per 1. The double valency rule makes its appearance in the actual suppressive action. Preceding this in small concentrations a bunching out according to the continuous valency rule (see text). 

To avoid misunderstanding we must add that if on adding small concentrations of salt a bunching according to the continuous valency rule is first produced (such as for example Fig. 15A and C), nevertheless at higher concentrations, at which one is concerned with the real suppression, the curves are arranged according to the double valency rule. 

In 2f, p. 349 we already saw from qualitative experiments that salts in general exert two kinds of action on the one hand a suppressive action in which the so-called double valency rule holds and a displacement of the optimum mixing proportion in which the so-called continuous valency rule holds. 

Only at higher salt concentrations the suppression then (after possibly also passit through a stage of readily visible coacervate drops) proceeds in the usual way accordiiig to the double valency rule. 

Furthermore added indifferent salts suppress the coacervation whereby the so-called double valency rule (see p. 350) again appears ... 

Similar anomalies in the order of the terms of the double valency rule can naturally also occur in the variant micro cation + colloid anion but they then naturally manifest themselves in the rule of the cations. Even a glance at Fig. 37 shows that when we include the auto-suppression of the hexol nitrate in the valency rule of the cations we encounter similar features here 3 — 1 >2 — 1 >1 —1>.6 — 1. 

Finally it appears that salts can also have a suppressive action according to the double valency rule , in which naturally the abbreviations of the series of terms of the cations already discussed in 3c (p. 391) and anomalous sequences of these terms occur. Compare Fig. 43 which relates to the flocculation with 2 m. eq. per 1 Co(NH3)0Cl8 throughout in various acetone concentrations. Here the suppressive actions of the two first terms of the cation series (2 — 1 and 1 — 1) and of the anion series (1 —2 and 1 — 1) have been investigated. 

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