The behaviour of various metals in emission spectrography

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Observations have been made on changes in spectral density caused by variations in electrical parameters using the General Purpose source unit 1 1 Designed by The British Non-Ferrous Metals Research Association. with samples of aluminium, copper, iron, lead, magnesium, nickel, tin, titanium and zinc. Although observed changes were very different for each metal, a broad classification may be made into three groupe, namely (1) aluminium and magnesium, in respect of which only degree of damping has any considerable effect, (2) copper, iron, nickel and titanium with which in general greater density is obtained when the sample is the negative electrode; with these metals greater density is also obtained when the metal forms the positive electrode to an underdamped discharge, and (3) lead, tin and zinc, with which spectral density is consistently greater with negative polarity. By correlating the observations with selected properties of the metals, indications have been obtained that volatilisation of the metal may be influenced by its atomic weight, the stability of its oxide and the direction of the electron stream with respect to the metal, but not to any great extent by melting or boiling point, ionization potential, thermal conductivity or work function. With the second group of metals, it has also been established that when the sample is positive the low voltage discharge conditions the surface in such a way as to render it more amenable to attack by the trigger discharge. Certain conclusions of minor practical importance have been drawn from this work, but the main conclusion is that the influence of electrical parameters cannot be considered independently of the metal under test. At the same time, the observations, although to a large extent unrelated, provide a new outlook on spectral problems and a foundation on which further work can be based.