The positive and the negative corona and electrical precipitation

High-voltage alternating current is rectified by using the Lemp synchronously rotated commutator and the coronas produced by the rectified current are used to cause the removal of suspended matter from gases. The differences between the wattage-volt curves for the positive and negative coronas are discussed. The sparking potential difference between a negative and a positive corona discharging wire and a surrounding earthed cylinder is described and an application is made to the problem of electrical precipitation. The negative corona is found to be much more suitable for this purpose. For the same voltage the positive corona is slightly greater. Increasing the air velocity within small limits does not greatly affect the sparking potential of a positive corona. It increases the sparking potential of the negative corona very appreciably.