iPad 1158 AM 6 An openend mercury manometer is to be used to

iPad 11:58 AM 6. An open-end mercury manometer is to be used to measure the pressure in an apparatus 5 containing a vapor that reacts with mercury. A 10 cmlayer of silicon oil (SG 0.92) is placed on top of the mercury in the arm attached to the apparatus. Atmospheric pressure is 765 mm Hg. (a) Draw a schematic of the apparatus. A1 (b) If the level of mercury in the open end is 365 mm below the mercury level in the other arm, what is the pressure (mm Hg) in the apparatus?

Solution

SG of mercury = 13.54g/cc. SG of your oil = .92g/cc.
13.54/.92 = 14.717:1.
100mm/14.717 = 6.795mm height difference in mercury, at equal pressure both sides of manometer, to balance the oil. The open end has no oil, so is higher by that much.
365 + 6.795 = 371.795mm. actual difference in height. This is BELOW atmospheric.
765 - 371.795 = 393.205mm.

(c) Its high density makes small manometers. A water manomoeter used to measure barometric pressure would be thirty-some feet long.

Also it has low vapor pressure so it does not evaporate like water would, and its lower freezing point means it won\'t freeze up at 0 deg C.