[header] How to make a homemade thermometer [title] Make your measuring solution. [step] Fill a measuring cup halfway with water and halfway with rubbing alcohol. Drop four to eight drops of liquid food coloring into the solution and mix gently to combine. 
[substeps] Note that the food coloring does not alter the way that the solution reacts to temperature changes. Its only purpose is to make it easier for you to read the level of the water in the straw when you use your thermometer.