PROPERTIES OF DIALYSED HYDROUS ALUMINA HYDROSOLS. PART II. TITRATION WITH BASES AND ACIDS

Potentiometric titrations have been carried out with acids and bases. Buffering is maximum at \(p\)H sex with NaOH ; at \(p\)H 11.2 with  NaOH: at \(p\)H 11.0 with Ba(OH)₃. at \(p\)H 10.8 with Ca(OH)_3. A weak inflexion point has been observed at Pa 72'2 and the buffer index wife shows a minimum at this point. The amount of alumina coming into true solution increases with the concentration of alkali and complete solution occurs at the inflexion point at \(p\)H 12.2. Titration of aluminium chloride with NaOH shows an inflexion near \(p\)H 11.0  corresponding to the complete solution of precipitated alumina. The pa at which this inflexion point occurs, however, depends on the age of the precipitate. HCl is totally adsorbed at small concentrations. A strong buffer action indicating true solution is observed at \(p\)H 3.5, 3.4 and 2.8 for acetic, phosphoric, oxalic and sulphuric acids respectively.