# Determination of Bulk Density of Powder | Loss on Drying Procedure

This test method applies to the determination of the compacted bulk density of a material and the determination of loss in the drying procedure.

### Principle

A known weight of the sample is placed into a measuring cylinder and placed into a bulk density tapping apparatus. A sample is 'tapped' until the volume occupied by the sample is constant the volume is recorded, and the bulk density is calculated.

### Safety

Observe proper laboratory safety rules, personal protection, and chemical handling procedures at all times.

Read MSDS before handling chemicals and products.

### Apparatus

250 mL measuring cylinder

Bulk density 'tapping' device

Analytical balance

## Procedure

1) Place a clean, dry 250mL measuring cylinder on the balance, and tare the balance.

2) Place a plastic funnel in the top of the cylinder and slowly add the sample through the funnel until there is approximately 200mL of product in the cylinder

3) Place the cylinder into a bulk-density tapping apparatus.

4) Tap the cylinder 60 times by lifting the cylinder to the drop height and releasing it. The cylinder should be rotated a quarter turn on each lift.

5) Read off the exact volume, V1 taken up by the sample.

6) Give the cylinder a further 15 taps and read off the exact volume V2, taken up by the sample.

7) If V2 is not the same volume as V1 then repeat Step vi) until two consecutive equal readings are obtained

8) Record the final tapped volume of the sample (mL).

9) Remove the funnel. Record the sample weight (g).

### Calculating bulk density

Bulk Density (g/mL) = Weight of Sample (g)/Volume of Sample (mL)

Result:

Report the result in g/mL. Compare the result to the specification.

## Determination of loss on drying

This test method applies to any substance which may be dried to a constant weight.

### Principle

The weight lost from the material under a defined set of conditions is both quantitative and reproducible. This loss in weight is designated the Loss on Drying. A known weight of a material is placed in an oven at a specified temperature for a specified time, or dried to a constant weight, to remove all traces of free water in the sample. The sample is then re-weighed to determine the loss in weight as a percentage of the original sample weight.

Safety

Check to ensure that substances being tested do not give off noxious fumes on heating.

Observe normal laboratory safety rules and chemical handling procedures.

Beware of hot apparatus. Use appropriate handling techniques.

### Equipment and Reagents

1) Weighing dishes or crucibles

2) Analytical Balance

3) Drying oven - fan forced variable temperature 40 to 200°C

4) Desiccator

5) Tongs

### Procedure

1) Read the specifications of the material to determine the conditions under which the test is to be conducted. Typically, the sample weight, test temperature and drying time shall be defined for the material.

2) Condition the weighing dishes at the specified drying temperature by placing them in the oven for a minimum of two hours.

3) Cool the weighing dishes in the desiccator for 30 minutes.

4) Weigh a clean and dry weighing dish and note down the weight W1 (g) to 4 decimal places.

5) Weigh accurately into the dish the specified weight of the sample, or if this is not specified approximately 2g, and record the weight as W2 (g)

6) Dry the sample at the specified temperature for the recommended time, or to constant weight if required.

7) Remove and cool in a desiccator for 30 minutes, then reweigh and record the weight after drying as W3 (g).

8) Determine the loss on drying as below.

### Loss on drying formula USP

Loss on Drying (% w/w) = (W2 - W1) - (W3 - W1) x 100/(W2 - W1)

Where :

W1 = Weight of the dish

W2 = Weight of the dish and sample before drying

W3 = Weight of the dish and sample after drying

Reference :

BP, USP, BPC, and other recognized texts for raw materials.

BANTI SINGH

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