(2) Manufacturing process: add some colored water into the jar, match a rubber stopper, and insert a thin glass tube with one end closed on the rubber stopper. Heat the closed end of the thin glass tube to make the air in the glass tube escape, and quickly plug the bottle mouth with a rubber stopper. A simple thermometer was made by ourselves.

(3) Experiment and conclusion: Put the self-made thermometer (jar) into hot water, carefully observe the position of the water column in the thin tube, and then put it into cold water to observe the position of the water column. When put into hot water, the colored water column in the thin tube rises; When put into cold water, the colored water column in the thin tube drops.

(4) Phenomenon explanation: The above phenomenon is caused by the law of liquid expanding with heat and contracting with cold.