Diaphragm

(a) In telephones and microphones a disc of iron thrown into motion by sound waves or by electric impulses, according to whether it acts as the diaphragm of a transmitter or receiver. It is generally a plate of japanned iron such as used in making ferrotype photographs. (See Telephone and Microphone.) (b) A porous diaphragm is often used in electric decomposition cells and in batteries. The porous cup represents the latter use. [Transcriber's note: Japanned--covered with heavy black lacquer, like enamel paint.] 183  STANDARD ELECTRICAL DICTIONARY.