Réaumur used ethanol for his thermometers. Thermometers that use ethanol show the change of temperature better than those using mercury. This is because, when heated, ethanol expands faster than mercury. There is the problem though that the expansion of ethanol is different at different temperatures - it is non-linear. Ethanol has a very low boiling point, which makes thermometers based on it unusable for many applications. Soon, instrument-makers used other liquids, and then chose "80°Ré" as the boiling point of water. 