Torbal DK1 Density Determination Guide Bedienungsanleitung PDF herunterladen

Density Determination Guide

The Torbal Density Determination Kit (DDK) is designed to allow Torbal AD Series Precision

Balances to be used to determine the density of solids and fluids using Archimedes principle in a way

that eliminates the need for below the pan weighing. Torbal also makes available an Excel spreadsheet

which makes the calculations required for density determinations. Embedded in this spreadsheet is a

table of water density versus temperature from 15 C to 27 C in 0.1 C increments.

The kit consists of a weighing frame which replaces the weigh pan and adapter, a sinker (the

pan that hold the unknown sample), a 400ml beaker, a frame that supports the weight of the beaker (with

its fluid, bracket, and thermometer) and passes the weight to the frame of the scale (not the weigh

frame). This apparatus will be used to measure the weight of the sample in air, called the dry weight

(Wd), and to determine the weight of the same sample immersed completely in a fluid, called the wet

weight (Ww). The difference between these two (Wd-Ww) is the buoyancy of the sample in the fluid.

It is important to discuss some of the factors which affect the accuracy of density measurements

using this technique:

1. The density of the fluid causing buoyancy changes with temperature.

2. The change in the immersion level of the pan hanging assembly when the sample displaces

fluid.

3. The air buoyancy caused by weighing in air.

4. Liquid adhesion on the suspension wire of the pan hanging assembly.

5. Air bubbles on the surface of the sample.

Item 1. This item is compensated for by the spreadsheet (using a built in table) when the user

enters the fluid temperature to the nearest 0.1 C as measures by the thermometer during the

measurement.

Item 2. This effect can be determined from the ratio of the diameters of the suspension wire and

the beaker. The use of a beaker with a large inner diameter helps to reduce this effect. The

spreadsheet uses a factor determined by the 400ml beaker and the furnished suspension wire. If either

of these is changed in diameter the calculation will be affected.

Item 3. The density of air at sea level, 50% humidity, and 20 C is approximately 0.0012 g/cubic

cm. This can produce a third place error in density measurements and should be compensated for in the

calculation. The spreadsheet uses this 0.0012 g/cubic cm in its calculations in order to correct for air

buoyancy.

Item 4. This effect is largely self canceling since the Sinker (sample holding pan) is immersed for

both dry weight and wet weight measurements and the balance is tared at the beginning of each

measurement. This effect can also be reduced by adding a drop or two of ordinary non-staining

dishwasher detergent to the fluid to minimize the meniscus effect. The spreadsheet ignores this effect.

Item 5. Air bubbles can have a significant effect on density measurements. They can be

brushed off, or the sample can be pre-soaked to eliminate them. The spreadsheet has no way to correct

for this problem, and the user must be diligent in this area.

In its simplest form the equation for density as performed this way is:

D = [ Wd / ( Wd – Ww ) ] x Dw, where Dw = density of water

In its final spreadsheet form it looks like this:

D = [ Wd x (Dw – Dair)] / [ Kimmersion x ( Wd – Ww ) ] + Dair], where Dw is temp corrected

Note: Wd – Ww = Buoyancy (G), its use can simplify the expressions somewhat.

Torbal Density Kit

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Density Determination Guide 1

Inhaltsverzeichnis

Seite 1 - Density Determination Guide

1Density Determination Guide The Torbal Density Determination Kit (DDK) is designed to allow Torbal AD Series Precision Balances to be used to det

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2 MAKING THE MEASUREMENTS Determining the Density (Specific Gravity) of Solids with density >1. Be sure that the sinker and suspension wire h

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31. Enter the two values into the top portion of the spreadsheet where the Sinker volume is calculated, or 2. Use the formula; Volume in cubic cm

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Torbal DK1 Density Determination Guide Bedienungsanleitung

Stöbern Sie online oder laden Sie Bedienungsanleitung nach Ausrüstung Torbal DK1 Density Determination Guide herunter. Torbal DK1 Density Determination Guide User Manual Benutzerhandbuch

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