ASTM E126 Inspection, Calibration, and Verification of ASTM Hydrometers

Scope:

ASTM E126 test method describes the principles, apparatus, and procedures for the inspection, calibration, and verification of ASTM glass hydrometers. This test method applies to ASTM hydrometers but can be used for other general hydrometers of the constant-mass, variable-displacement type.

Test Procedure:

In ASTM E126, the hydrometer (Figure 1) is carefully inspected for; cracks, fissures, deep scratches, rough areas, or other obvious damage to the glass. A hydrometer is rejected if any of these defects are present. The hydrometer is checked for strain in the glass, especially at the stem/body junction with the use of a polariscope. A hydrometer is rejected if any of these defects are present. It is particularly important for thermo hydrometers.

The paper scale is inspected within the hydrometer stem. The paper scale is straight and without a twist. The linear dimensions and diameters are checked for compliance with specification requirements by comparing the hydrometer with the appropriate device.

For ASTM E126, the hydrometer is calibrated at a minimum of three calibration points, spaced approximately equally across its range, nominally high, low, and mid-scale. For example, a hydrometer with a range of 9° to 21° API shall be calibrated at (approximately) 10, 15, and 20 API.

Figure 1: A hydrometer

Specimen size:

Hydrometers

Data

The interval between graduations of density and relative density (specific gravity) hydrometers is smaller near the bottom of the scale. As per ASTM E126, the proper spacing shall be obtained from the following formula:

l = L × d₂/d× (d – d₁)/ (d₂ – d₁)

Where:

l = distance from the top line to any line, d, between the top and the bottom,

L = distance between the top and the bottom graduations of the scale,

d₂ = density value, or relative density (specific gravity), of the bottom line, and

d₁ = density value, or relative density (specific gravity), of the top line.

Conclusion:

ASTM E126 test method describes the principles, apparatus, and procedures for the inspection, calibration, and verification of ASTM glass hydrometers.