volatile substance

例句：

1. 1. The gas was volatile and could be easily ignited.
   这种气体是易燃的，容易点燃。
2. 2.The oil is volatile and needs to be stored under refrigeration.
   这种油是易挥发的，需要储存在冷藏条件下。
3. 3. Volatile compounds are those that can change state or form when exposed to heat or light.
   易挥发化合物是指在受热或光照时可以改变状态或形成的化合物。