The Advantages of Controlled Atmospheres for Arc Spectroscopy

Effective spectrochemical analysis depends upon three components of the apparatus. Two of them, the detector (including such elements as plates and photocells), and the light disperser (including prisms, gratings, and now echelles) are relatively well understood and perfected. The third and most significant of the three, the light source, has proved a more difficult problem. One line of attack used fairly recently, however, has been on the atmosphere around the arc. Air, the usual medium, has one major failing, namely, the interference of the cyanogen bands accompanying the reaction between atmospheric nitrogen and the electrode carbon. Other gases used in place of air not only overcome this disadvantage, but provide several additional advantages which may prove to be as important as they were unexpected. The reasons for these gains are still not understood, and painstaking trial-and-error selection of the best medium for a particular analysis is still necessary. Nevertheless the gains realized from operating a source in artificial atmospheres are frequently great enough to justify each analyst in trying all available gases for his own peculiar circumstances, problems, and apparatus. In addition to the control of source environment by varying the gas around the arc another approach to the problem is possible: that of varying the pattern of the gas flow around the arc.