Density Determination Kit Helps in Accurate Analysis

These density determination kits work on the buoyancy method, based on Archimedes’ Principle and recognized for a high degree of accuracy. As an example, 10 cm³ glass plummet is used for measuring the density liquids, giving a resolution of 0.0001 g/cm³.  The density is determined from the weight of the plummet in air and its weight in the liquid being measured.

For solids, the density is the ratio of the object’s weight in air and its volume.  Volume is determined by the buoyancy of the sample when immersed in a liquid, the density of which is known.

Both methods of calculating density involve the use of formulas programmed into the balances and presented with the instruction manuals.

Preparing the Analytical Balance for Measuring Density

Instruction manuals for setting up a density determination kit may vary depending on the analytical balance and density determination kit used, so this information is somewhat generalized.

Kits typically consist of a weighing platform with a vertical rack to support a sample dish for weighing in air and a suspended mesh sample holder for weighing in liquid, a platform to support the furnished glass beaker, its thermometer and holder, and a glass plummet of known volume and weight.

First turn off the analytical balance and disconnect it from its power source.  Open the balance door and remove the grading ring, the weighing plate and its support, putting these components in a safe place.

Carefully position the weighing platform and vertical rack assembly in the weighing area of the analytical balance.  Next center the glass beaker platform over the weighing platform.  The glass beaker platform is equipped with feet that rest on the analytical balance in such a way that they do not touch weighing platform.  This is very important.

Place the glass beaker on its platform.  Install the weighing platform assembly (the sample dish for weighing in air and suspended mesh sample holder for weighing in liquid) by lifting it up and over the beaker rim and sliding it into the support grooves on the vertical rack.  Put the thermometer in the beaker.

Reconnect the analytical balance to its power supply.  Density calculations for liquids and solids can then be conducted by following the instructions that accompany the kit.

Important Cautions

Extreme care must be taken when measuring the density of solids and liquids.

For example, air bubbles as small as 1 mm³ will have an effect when measuring small specimens by increasing buoyancy by approximately 1mg resulting in an error of 2 digits.  Bubbles must be removed by gently swirling the liquid or by using a fine brush.  Bubbles must not be on the sample, on the immersed sample support screen, on the plummet.  Always wear gloves because finger marks contain oil that will create bubbles on immersed equipment.

The temperature of the fluid used in density determination affects the density of the fluid and must be factored in as an error of 1˚C can result in an inaccurate fourth decimal place. Density tables are available for fluids at 1˚C temperature intervals.

Surface tension can impair repeatability of density tests especially for small samples.  The remedy is to add a few drops of dishwasher detergent or another surfactant.  The impact of this on the density of the water can be ignored.

Remember:

• Several density measurements must be made to form a reproducible mean value
• Carefully clean the equipment on a regular basis
• Dry the equipment after each measurement, avoid a static charge by using a cotton cloth
• Contact the weighing experts at Tovatech for additional tips on density determination

What procedures are in place in your organization to determine the density of liquids and solids?   What type of equipment do you use?