Describe the applications of non-electrical thermometers

Liquid thermometers containing mercury are effective from −39°C to 250°C, while alcohol thermometers are effective from −117°C to 78°C. They are commonly used to measure temperature sublingually, rectally or within limb skin folds (e.g. axilla and groin). These devices are easily portable, cheap to produce and reusable. However, they are fragile and easily broken. In the case of mercury devices there is the added risk of mercury poisoning following damage. They have a slow response time of 2–3 minutes, and there is a risk of cross infection if not disinfected following use.

Liquid crystal thermometers are effective from 0°C to 120°C. Clinically they are used to measure temperature on the skin of the forehead. They are inexpensive, disposable, accurate to within 0.5°C, and have a relatively rapid response time of 1 minute. However, as they are placed on skin they may fail to reflect core temperature accurately in situations of peripheral vasoconstriction. To remain compact for clinical use, individual thermometers tend to only cover a small range of temperatures from 32°C to 40°C and are therefore unsuitable at extremes of physiological temperature.

Bourdon gauge thermometers are effective from −270°C to 1500°C. They are effective over a wide range of temperatures, cheap and robust. However, they are not very accurate and are prone to calibration errors.

Bimetallic strip thermometers are effective from −40°C to 500°C. They are simple, accurate and robust. However, they are relatively insensitive to small temperature changes and are not used to measure temperature in clinical practice. They do serve a role in temperature compensation in devices such as vaporisers.