Atech Center - Hydrometer Procedure

4. At the conclusion of the shaking, place the sedimentation cylinder on a level, firm surface, record the time, and allow the sample to settle. From this point to the completion of the test it is crucial to disturb the sedimentation cylinder as little as possible in order to allow the particles to fall naturally without any undue vibration. The sedimentation cylinder should also be placed in the constant temperature bath or be located in an area where temperature can be controlled for the duration of the test.

Figure 11. Placing the hydrometer into the sample using great care

5. After 120 seconds have elapsed from the cessation of agitation, take the first reading of the sample using the hydrometer 152H (Figure 11).

Some considerations when taking hydrometer readings: lower the hydrometer into the sample slowly, avoid disturbing the sample as much as possible. Do not drop the hydrometer into the cylinder, causing it to bob up and down through the sample. Do not allow the hydrometer to touch the sides of the sedimentation cylinder.

Figure 12. The hydrometer should be stable when readings are taken. Note the meniscus on the stem.

The hydrometer should be placed into the sample several seconds prior to the required reading time in order to take an accurate reading at the prescribed time.

The hydrometer reading should be taken at the top of the meniscus formed by the suspsension around its stem (Figure 12). The temperature of the sample should also be determined and recorded each time a hydrometer reading is taken. Read the scale on hydrometer 152H to the nearest 0.5 g/L.