The determination of potassium oxide in glass
JSGT 1959 V43 T062-T072
Conventional analytical methods for potash in glass, based on gravimetric determination as perchlorate, platinichloride or cobaltinitrite, have various disadvantages. The first two methods usually require lengthy preliminary separations; the variable composition of the cobaltinitrite precipitate precludes its use as a weighing form for large amounts of potash. In previously published work the author has shown that precipitation of potassium as the tetraphenyl boron derivative has advantages over the older methods. The tetraphenyl boron method permits the direct gravimetric determination of potash in glass after decomposition with hydrofluoric and perchloric acids and solution of the residue in a suitable medium. This method has now been in use for three years and has been successfully applied to a variety of glasses. The gravimetric tetraphenylboron determination may be completed in 4 to 5h, representing appreciable saving of time compared with the older methods. Recent work has shown that the determination may be shortened still more by using a volumetric finish. After decomposition of a glass with hydrofluoric and nitric acids, the potassium is precipitated with sodium tetraphenyl boron solution, the amount of tetraphenyl boron in excess of that required to precipitate the potassium being found by titration with mercuric nitrate solution. A limited trial of the volumetric method on four glasses containing 7 to 15% of K2O has given results generally within 0·1% of the gravimetric figure. Duplicate volumetric determinations on one sample can be completed within 2 h.
H. J. Cluley
