Why are liquid and gases preferred to solids in making thermometer ?
Liquids and gases move more in length when contained in a volume than a solid. Plus the liquid can be contained in a glass tube and temperature can be displayed with no moving parts, hence cheap and reliable. The liquid in a mercury or colored alcohol tube is in a very thin capillary and moves in the tube with little friction. It just simple hydraulics. The liquid reservoir is the bulb at the bottom of the thermometer. All that volume is heated by the temperature change and the expansion or contraction of that bulb volume can be multiplied by going up the super thin capillary of the thermometer. So if the volume expands in the bulb by a 1/8 th of a mL that translates into a movement up the capillary of maybe an inch which would show for example a 20 F temp change. You can’t use hydraulics on a solid. If the metal expands it only expands at the source and you can’t visually see the movement. Because of the mobility of the liquid and gas , the thinner you make the display tube, the more
