The hydration of a zwitterion, glycine, as a function of pH.

1. The hydration numbers of glycine (concentrations 1--3 M), as a function of concentration, were determined by surface tension measurements, using octan-1-ol as a 'reference' substance. 2. The hydration number of glycine at the isoelectric point decreased from 17.7 to 10.7 upon increasing the concentration from 1 to 3 M. 3. The changes in hydration of glycine as a function of the pH are due to the difference between hydrations of the ionized functional groups (NH+3, COO-) and the added ions (Me+ A-).