The mobility spectrum of spray electrified salt solutions has been investigated with an Erikson mobility tube under conditions of high resolving power. In general there are no charged carriers of mobility greater than 1.7 cm/sec. per volt/cm. At about this value the curves rise sharply, and then level out, approaching a broad maximum in the region between 0.05 and 0.10 cm/sec. per volt/cm, and then very gradually decrease toward zero. Superposed on this "background" striking peaks are observed, indicating groups of unique mobility. For the spraying of distilled water the most prominent peaks occur at mobilities of 1.5 for the negatives and 0.9 for the positives. Carriers of both signs are produced in about equal quantities. For bubbling the negative predominate in the ratio of 2.5 to one, and the prominent peaks occur at 1.5 and 0.3 for the negatives, and 0.9 and 0.4 for the positives. The introduction of salts to the water increases the electrification from spraying up to a concentration of about 1.0×${10}^{-4\mathrm{}}$ normal. At this value the electrification is about double that for distilled water, but at higher concentrations the electrification decreases so that for 0.2 normal it is only 10 percent of that for distilled water. The salt gives rise to very strong peaks at mobility 0.5. Investigations have also been made of the effects on the curves of age of the carriers and humidity of the air. It is concluded that the peaks represent stable groupings, the negative 1.5 group being due to a normal negative ion in moist air coming from an evaporated drop. The 0.5 peaks in the salt curve presumably come from carriers containing electrolytic ions. Probably all of the carriers are singly charged. It is impossible to calculate quantitatively the size of the small carriers in the faster groups from their mobility, but from the value of the potential difference of the double layer, and estimates on salt solutions, it is concluded that the separation of the double layer is 2.0×${10}^{-6\mathrm{}}$ cm corresponding to an extra electronic charge for every 550,000 ${\mathrm{H}}_2$O molecules.

• Received 15 March 1937

DOI:https://doi.org/10.1103/PhysRev.52.184