An Investigation of the Magneto-Optic Method of Chemical Analysis

An apparatus similar to that used by Allison in his magneto-optic method of chemical analysis was set up in an effort to verify the existence of the sharp Allison minima. Many visual observations were made, but only occasionally did readings of possible minima occur in more than random groupings. Where these apparent minima did occur, it was thought that they could be explained as being due to such factors as sticky places on the trolley felt by the hand on the hand wheel control. When a motor control was used on a later apparatus, the distribution of readings of possible minima was no more than a chance distribution. Objective tests were made of the variation of intensity of light with trolley position by a photographic method. In this photographic method the effect of spark fluctuations was eliminated by comparing the intensity of the light passing through the cells with that of a comparison beam direct from the spark. Individual runs by this method showed no minima and were good to three percent. When several runs were averaged, the resultant intensity curve showed no variations greater than one percent. Eye tests showed that the writer could not have detected an intensity change visually of less than three percent on the magneto-optic apparatus. These results indicate that the minima occasionally seen by the writer on his apparatus have no objective reality. A broad minimum of the type described by Slack and by Webb and Morey was obtained by the photographic method for C${\mathrm{S}}_2$.