OHAUS PX125D Instruction Manual

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OHAUS PX125D Instruction Manual Manual pdf 17 page image

PX Series Balance EN-15Q = Density of the solidA = Weight of the solid in airB = Weight of the solid in the auxiliary liquidQ0 = Density of the auxiliary liquid at a given temperature (this value depends on the temperature). The densitytable for water is included in Discovery balances.P = Buoyancy of the solid in the auxiliary liquid (corresponds to A-B).Place the solid in the Weighing Pan on the Weigh Below Hook in the liquid as shown. Ensure that there are no airbubbles on the solid to be weighed.Close the draft shield doors and weigh the solid (buoyancy P). The display indicates the density in grams/cc.Solid Density Determinations for items Less Dense Than WaterFor density determination of solids with a density less than 1 g/CM3, the bottom of the Weigh Below Hook forsolids must be used as it holds the solid body below the surface of the auxiliary liquid. If the buoyancy of the solidis greater than the weight of the Weigh Below Hook, the Weigh Below Hook must be weighted by placing anadditional mass on the submerged part of the Weigh Below Hook as shown.Weigh the sample in air first as explained in the previous procedure.After loading the additional mass, tare the balance and start the weighing again. Wait until the balance hasreached stability and note the displayed weight P (buoyancy of the solid).Improving the Accuracy of the Result of Solid DensityThe following tips should help you improve the accuracy of the results in the density determination of solids.TemperatureSolids are generally so insensitive to temperature fluctuations that the corresponding density changes are of noconsequence. However, as work is performed with an auxiliary liquid in the density determination of solids, theirtemperature must be taken into account as the temperature has a greater effect with liquids and causes densitychanges in the order of magnitude 0.I to 1% per °C. This effect is already apparent in the third decimal place of theresult.To obtain accurate results, we recommend that you always take the temperature of the auxiliary liquid into accounton all density determinations.Air Buoyancy1 cm 3 of air weighs approximately 1.2 mg (depending on the physical condition). As a consequence, in theweighing in air, each solid experiences buoyancy of this magnitude (the so-called “air buoyancy”) per cm3 of itsvolume.However, the air buoyancy must be taken into account only when a result is required with an accuracy of 3 to 4