• Calibrated to measured specific gravity on evenly spaced scales
• Only for liquids heavier than water
• Use baume scale
• Range: 0-70° (Sub-division: 1°)
• Length: 28cm
• Provide a hard plastic case for storage.
Function, Scale Types and Use
A hydrometer is made up of a thin glass or plastic tube sealed at both ends with a graduated or printed scale calibrated to a specific gravity. One end of the tube is bulb shaped and weighted with a ballast of either fine lead shot or steel shot. The ballast causes the instrument to float upright in a liquid like a fishing bobber. A second glass or plastic cylinder, commonly known as a hydrometer jar, is filled with the liquid being measured. The hydrometer is then placed in the hydrometer jar containing the sample liquid. The specific gravity of the sample liquid is indicated when the level of the sample liquid in the jar aligns with a point on the hydrometer scale.
Method of Reading
Fill the hydrometer jar with the sample liquid. Place the hydrometer in the jar and give it a quick twirl to dislodge any air bubbles. Once the hydrometer has settled, take the reading from the appropriate scale. In order for the measurement to be accurate, the sample liquid must be at 20°C. If the liquid is not at 20°C, the measurement should be adjusted.
When reading transparent liquids, the eye should be placed slightly below the plane of the surface of the liquid and then raised slowly until this surface, seen as an ellipse, appears as a straight line. The point at which the line sits on the hydrometer scale should be recorded as the reading of the hydrometer. When a liquid is not sufficiently clear and a reading cannot be made as described above, it will be necessary to read from above the surface and estimate as accurately as possible, the point to which the liquid rises on the hydrometer.
Accuracy depends on three main factors:
1. Cleanliness
2. Temperature
3. Proper Immersion