Colloids with amphoteric character

C. Colloids with amphoteric character, which carry both sorts of groups. 

The amphoteric colloids will at very low pH behave practically as " ionised colloids with basic character at high pH just as acid colloids , while in the intermediate region positive and negative charges occur together and just equilibrate one another at the isoelectric point (I. E. P.). 

In addition to dissolving in acids, freshly precipitated niobium pentoxide dissolves in caustic soda and in caustic potash, and hence it appears to possess weakly amphoteric character. Its colloidal state in solution has hitherto prevented any direct determination of its basicity or acidity. According to Weinland and Storz 6 it is comparable to silicic acid, and is more strongly acid than titanic add. That niobic add is a very weak add is shown by the readiness with which the niobates are (a) hydrolysed and (b) decomposed by mineral acids,... 

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