Colloid amphoion

Colloid amphoion 4- colloid cation + colloid anion... 

Colloid amphoion + micro cation 4- micro anion... 

We arrive with this at the pronouncement that for the production of the flocculations discussed here the simultaneous presence of complex relations between a colloid amphoion a suitably chosen micro cation and a suitably chosen colloid anion is essential. 

Where we wish to bring about a possible tricomplex flocculation with Ca, i.e. with a strongly polarising cation (since small and in addition divalent), it will be favourable in all respects that the polarisability of the n ative group of the colloid amphoion is large, that of the negative group of the colloid anion small. See p. 418, Fig. 51. 

If one chooses a particular colloid amphoion (for example egg lecithin or isoelectric gelatin) and investigates with the aid of a number of cations and anions in what combinations of the latter ions complex flocculation occurs or not, one obtains a collection of data from which it is immediately clear that specific properties of the ions play a very great part. See Table 1 and 2 (p. 422 and 423). 

Since ammonium molybdate already gives a precipitate with Ba itself in the control experiment, it is not possible to establish whether tricomplex flocculation occurs in the combination colloid amphoion -f- Ba -f paramolybdate. 

At a suitably chosen ratio of colloid amphoion and colloid anion, the added cation brings about tricomplex flocculation from a certain small concentration onwards. On increasing the cation concentration the flocculation increases to a maximum and then decreases again. 

Proteins taking part in the formation of tricomplex colloid systems (see p. 415), act however preferably as amphoions. Therefore the above no longer applies here, for at the most favourable pH, namely the the apparent equivalent weight is... 

Similarly a tricomplex flocculation is a flocculation in which a disperse colloid-rich phase happens to separate out, in which latter phase complex relations are present simultaneously between amphoions, cations and anions. 

The abnormal behaviour of the pho hatides is closely connected with the association character of these colloids. Their negative charge is due to impurities of an acid nature (probably phosphatidic acids) which are tenaciously attached to the actual phosphatide molecules by London — v. d. Waals forces. The relative amount of them compared with the actual phosphatide molecules (amphoion ) determines their colloid equivalent weight, the magnitude of their reversal of charge concentrations with cations and the position of the isoelectric point (see p. 295). 

We already discussed previously (see p. 270, Table 2 p. 274 and 295) that egg lecithin, acting as a negative association colloid, has a very high equivalent weight, the soya bean phosphatide a much lower one. That means that the egg lecithin is much less mixed with acid constituents (for example phosphatidic acid) than the soya bean phosphatide and thus approximates much better to the theoretically pure phosphatide, which must consist exclusively of amphoions. 

It is quite possible that some heavy metal cations, possibly also the UOa ion, attach themselves to a non-ionogenic group of the protein molecule and this combination of amphoion and cation, since it now carries more positive than negative charges, begins to behave as a colloid cation with respect to the anion and then really forms a dicomplex system with it. 

We have as yet discussed tricomplex flocculations in which the amphoion is the association colloid lecithin. It is obvious that the above statements are mutatis mutandis also applicable to a protein as amphoion. 

For a discussion of this sequence we again start from the condition c + d ) a + 6 and since we are working throughout with the same amphoion and the same colloid anion (and these both in the same ratio in addition) a and d are constant. Replacement of the one cation by another only causes each time different values of c and 6. It is therefore the ratios c/6 which will determine the position of a cation in the given sequence. 

---