Text-books, technological treatises, and chemical literature in general have given considerable space in presenting methods and modifications of methods for the estimation of phenol, or carbolic acid. Without exception these methods are instructive and ingenious and more or less accurate. A summary, together with brief criticisms, makes interesting reading. There is some use, practical as well as pedagogical, in making a selection from these methods which will prove appropriate to equipment and abject in view. The determination of choice rests ultimately on three factors: accuracy, time, and economy. The methods may firstly be divided into two groups : gravimetric and volumetric.
Gravimetric Riegler : production of an insoluble diazo-acid, C,H+NO,CeH,OH with para-( Landolt : production of tribromphenol and weighing per se.
{ diazonitraniline, drying at 100" and weighing.
U. S. P. (Koppeschaar).
Roppeschaar, Sutton Modification. Koppeschaar, Sutton Modification, with author's modification. Iodometric method, Messinger and Nortrnann. Schwalbe's Diazo method. Volumetric i j Sodamide Method, S. B. Schryver.
The Landolt method of the volumetric group is not to be considered efficient, in that its operation is tedious and requires too much time with ordinary equipment.