Determination of Traces of Nitrogen in Refractory Metals and Alloys by Hydrofluoric Acid-Phosphoric Acid-Potassium Dichromate Decomposition and Indophenol Photometry Silve Kallmann, Everett W. Hobart, Hans K. Oberthin, and Walter C. Brienza, Jr. Ledoux & Co., Teaneck, N . J . 07666 The most exasperating obstacles for determining traces of nitrogen in refractory metals and alloys are the inability to dissolve appropriate weights of solid pieces of metal and relatively high blanks. Potassium dichromate, in conjunction with phosphoric and hydrofluoric acids, was found to be an effective combination for the rapid dissolution of up to 5-gram pieces of various refractory metals. Potassium dichromate can be prepared by purification of potassium chromate from an alkaline medium sothat blanks generally are below 0.5 pg of nitrogen.
THEDETERMINATIONof a few parts per million of nitrogen in refractory metals and alloys has been a challenge to analytical chemists for many years. Vacuum fusion methods have been applied t o determining nitrogen in the
