The fact that solid sodium reacts with the moisture in the air to produce a faint glow has been known for years. The color of the light was said to be greenish and its intensity extremely low, although no careful measurements had been made. In this article a method is described for determining its intensity by means of a photoelectric cell. The determination of the spectrum of the light as obtained both by filters and spectrographically is also described. The intensity was found to vary from 3.5 to 10.5 × 10−7 lumens per square inch of sodium surface while the spectrum was found to consist of a band between 5000A and 5300A with a maximum at about 5100A.
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