Reciprocal germanine number

The reciprocal germanin numbers of clupein were determined at two pH values, at pH 2.1 and pH 11, and were found to be 220 and 261 resp. These pH values were originally chosen as a test of the supposition already made use of in 6b, that the electrophoretic velocity of very dilute sols is an inverse measure of the equivalent weight. Inspecting Fig. 45 (p. 325), we must thus expect that the equivalent weight at pH 2.1 is smaller than at pH 11. The results confirm this assumption. 

If at pH 7— 8 the reciprocal germanin number had been determined, a value very near to 261 would have been obtained (because of the nearly horizontal level of the U-pH curve in Fig. 45 between pH 7—11). 

Takii into account that the reciprocal germanin number is 10—15% smaller than the equivalent weight (see 1 c, p. 269) the (apparent) equivalent weight of clupein at this pH would amount to about 290— 307. 

Now at that pH a reciprocal Na arabinate number of 304 was found, that is, practically the same value as the equivalent weight calculated from the reciprocal germanin-number. 

From this we may conclude, that also quantitatively a charged colloid (here Na arabinate) behaves towards an oppositely charged one (here clupein) in the same way as a large organic ion (here germanin), but with the simplification that the systematic difference between reciprocal anion number and equivalent weight is much smaller (or perhaps absent) if the anion in question is a colloid anion. 

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