Double-pan balance

Corrections required when weighing volumetric flasks are somewhat different than straight volumetric readings. Both single- and double-pan balances have four common parameters which can affect the accurate weighing of liquids, but the single-pan balance has one separate parameter of its own. The common parameters are water density, glass expansion, and the buoyancy effect. 

In a double-pan balance, the pull of gravity on the mass of an object placed in one pan causes the pan to rotate downward. To balance the rotation, an equal downward pull must be exerted on the opposite pan, as in a seesaw. You can produce this pull by placing calibrated masses on the opposite pan. When the two pulls are balanced, the masses in each pan are equal. ... 

Two instruments used to determine mass are the double-pan balance and a triple-beam balance. How each functions is illustrated in Figure 2. You can read how an electronic balance functions in How it Works in Chapter 12. 

You wiU use either an electronic balance or a mechanical single-pan balance (if you have a double-pan balance, your instructor will provide instructions on its use). The electronic balance is set to zero using the zero (tare) control bar or button before weighing an unknown object. For mechanical balances, the zero point is determined before weighing. 

Double- and single-pan and electronic balances are frequently used in the clinical laboratory. 

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