Abstract
AbstractTo estimate the impurities in aluminium alloy a d.c. arc is used. An aluminium‐alloy rod, 12 mm. in diameter and faced up on the lathe, is employed as the positive electrode and a graphite rod pointed to 60° as the negative one. Analysed samples and suitable standards are spread over the photographic plate as in spark exposures. They are energized in an arc under defined conditions, i.e. 4‐mm. gap between the electrodes, potential difference 220 v., current 7 amp., etc. Ilford thin‐film half‐tone plates are used and are developed according to the maker's instructions. The spectra registered are then measured and evaluated in a similar manner to that used for the spark spectra; an internal comparison method is used. In arc spectra registered under these conditions the densities of the analysed samples are similar, and on this account the same standards may be used for all unknown samples which pass through the spectroscopic laboratory. This method properly used gives accurate and reproducible results.
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