How to Use a Mercury Thermometer. Part of the series: Child Care & First Aid. To use a mercury thermometer, first shake down the mercury to the end of the thermometer before placing it under the tongue, under the arm or in the rectum, which is ideal for children under 4 years old. Then let the thermometer sit for two minutes to get an accurate temperature. Use a mercury thermometer, washing it thoroughly with soapy water between uses, with expertise from a registered nurse in this free video on first aid. Read more: [ Ссылка ]
