ICSE Class 9 Answered

Take a hard glass test-tube and drop in it a tiny cube of ice, wrapped in a wire gauze.  Fill 3/4 of the tube with ice cold water and then set up the apparatus as shown in the diagram.

Heat the test-tube near its mouth.  It is observed that in few moments water starts boiling near the top, but the ice at the bottom does not melt.  This experiment shows that water is a poor conductor of heat.