Sources of Error in Absorption Spectroscopy

IN studying the absorption spectra of the vapours of the homologous aldehydes1 a band spectrum was observed in butyric and iso-butyric aldehydes, which was ultimately discovered to be due to benzene. Inquiries showed that the catalyst used in the preparation of the aldehydes had been washed with benzene, thus accounting for the presence of an aromatic impurity which would not normally be expected to occur in aliphatic compounds. The spectrum is, however, so intense that, when the observation tube had been used to secure a comparison spectrum of benzene, it was very difficult to get rid of this spectrum in subsequent exposures.