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This practice describes the photomultiplier properties that are essential to their judicious selection and use of in emission and absorption spectrometry. The properties covered here include structural features, electrical properties, and characteristics involved in precautions and problems. The structural features covered are envelope configurations, window materials, electrical connections, and housing for the external structure, and the photocathode, dynodes and anode, and rigidness of structural components for the internal structure. Electrical properties, on the other hand, incorporate the following: optical-electronic characteristics of the photocathode including spectral response; current amplification including gain per stage, overall gain, gain control (voltage-divider bridge), linearity of response, and anode saturation; signal nature; dark current including cathode size, internal aperture, and refrigeration effects; noise nature including additivity of noise power, signal-to-noise ratio, equivalent noise input; and photomultiplier properties as a component in an electrical circuit including output impedance, response time, and signal gating and integration possibilities. Finally, the characteristics involved in precautions and problems cover fatigue and hysteresis effects, illumination of photocathode, and gas leakage.