Measuring temperature without a thermometer

If you need to measure the temperature of something, chances are you’ll come up with a half-dozen ways to do it, almost all of which will require the use of some kind of thermometer, thermistor, thermocouple, or other thermocouple device. But what if you need to measure something really hot, hot enough to destroy your instrument? How would you then get the job done?

If you find yourself in this incredible situation, relax – (Anthony Francis-Jones) has explained it all to you. is a calorimetric method for measuring high temperatures. The principle is simple; Instead of directly measuring the temperature of a flame, use it to heat something of known mass and composition and then plunge that object into water. If you know the amount of water and its temperature before and after, you can calculate how much energy was in the object. From this, you can work backwards and calculate the temperature that the object would have to be at to have that amount of energy.

To demonstrate in the video below, (F.J.) hung a steel ball on a chain into the flame of a Bunsen burner and dipped it in 150 ml of room temperature water. After a nice long toast, the ball went into the drink, raising the temperature by 27 degrees. Knowing the specific heat capacity of water and steel, as well as the mass of each, he calculated and concluded that the flame temperature was about 600°C. This is by a wide margin; Typical ratings for a natural gas burner are in the 1500°C range.

We suspect that the main source of error here is that the ball and flame did not come to equilibrium, but no matter – this is mainly intended to demonstrate calorimetry. This may remind you of the bomb calorimetry experiments in your high school physics lab, which can also be used to study the efficiency of human digestionif you like that kind of stuff.