Question

Information in the table showing the properties of substances used for manometers. To measure the pressure between 0-0.3 atmosphere with a feeling of 2mm / 0.2 torr With temperatures between -10 and 40 degrees Celsius, what kind of substance is suitable for The invention of the said meter Liquid Properties 2 3 18.6 -40 -40 290 240 70 Melting Point, °C Boiling Point, °C Density at 20 °C, g/cm Vapor Pressure at 50°C, mmHg 1.261 0.959 1.27 0.0025 0.1 0.0015

Answer 1

Answer: As the temperature is to be measured between -10^oC and 40^oC, so the melting point of the substance should be less than -10^oC and boiling point should be greater than 40^oC. So, either substance 2 or 3 will be the most suitable one.

Now, as it is supposed to measure pressure between 2mmHg and 0.2mmHg( one torr = one mmHg), so the vapour pressure of the substance should be lower than both these values.Vapour pressure of substance 3 is less than 0.2mmHg .

Hence, substance 3 would be the most suitable substance to be used in the manometer.