To liquefy is to turn into a liquid, or to make something turn into one. It works both ways with no change of form: 'the gas liquefies under pressure' (it becomes liquid by itself) and 'they liquefy the gas' (they make it become liquid). The spelling changes as usual: liquefies, liquefied, liquefying. It is a formal, technical-feeling word — science, engineering, and cookbooks. In everyday English people say 'melt' or 'go runny' instead. In a recipe, 'liquefy the mixture' means blend it until it is completely smooth with no lumps, and old blender machines even had a button marked LIQUEFY for the highest speed. The most common form you will see is the past participle used as an adjective: liquefied natural gas, liquefied petroleum gas — LNG and LPG, the gas in the tank under a Taiwanese kitchen counter. Do not confuse it with 'melt'. Melting is going from solid to liquid using heat. Liquefying is the wider word: a gas that is cooled and squeezed into liquid has liquefied, but nobody would say it melted.

液化、使…變成液體。廚房用的桶裝瓦斯 LPG 就是「液化石油氣」。日常講固體變液體還是說「融化 melt」比較自然。