Discharge a capacitor by building a simple series circuit on a breadboard connecting the two leads of a capacitor with the two leads of a 1000-ohm resistor. Polarity is not an issue with this circuit as the purpose is to discharge a potentially charged capacitor before handling.
Determine whether the capacitor is the axial lead type by noting its leads. Axial lead type capacitors indicate their polarity differently from radial lead type capacitors. Note whether one end is bare metal and the other end is plastic coated; a bare metal end is usually indicative of the cathode (negative) end of an axial lead type capacitor. Observe the labels printed on the body of the capacitor; a line encircling one end of an axial lead capacitor indicates the negative end. A minus (-) sign may or may not be present. The presence of one or more of these indicators is an adequate check for determining the negative and positive ends (polarity) of a DC capacitor.
Determine whether the capacitor is a radial lead type by noting its leads. Radial lead type capacitors indicate their polarity differently from axial lead type capacitors: a bare metal end on a radial lead type capacitor is not indicative of polarity as it is with an axial lead capacitor. Compare the length of the leads; the longer lead is typically indicative of the anode (positive) lead. Observe with a magnifying glass all markings printed on the body of the capacitor: a stripe along the length of a radial lead capacitor indicates which lead is the negative lead. A minus sign usually accompanies the stripe. The presence of an indicator stripe pointing to a lead -- with or without a minus sign -- is an adequate check for determining the negative and positive ends (polarity) of a DC capacitor.