What is to work so that foaming occurs from too violent ebullition, which causes water to become mixed with, and be carried along with, the steam that is formed; -- said of a steam boiler called?

prime — To work so that foaming occurs from too violent ebullition, which causes water to become mixed with, and be carried along with, the steam that is formed; -- said of a steam boiler. (Webster's 1913.)

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