What is an apparatus in which vapor or gas is formed from a liquid or solid by means of heat or chemical process, as a steam boiler, gas retort, or vessel for generating carbonic acid gas, etc called?

generator — An apparatus in which vapor or gas is formed from a liquid or solid by means of heat or chemical process, as a steam boiler, gas retort, or vessel for generating carbonic acid gas, etc. (Webster's 1913.)

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