Method to Find Density of Glass by Sink-Float Comparator ASTM C729

Method to Find Density of Glass by Sink-Float Comparator ASTM C729

ASTM C729 measures the density of non-porous solids or glass typically with densities ranging from 1.1 to 3.3 g/cm³. This test is used for comparing the density of the specimen with a standard specimen of known density. ASTM C729 helps measure densities of small specimens of glass by single-tube sink-float apparatus, and density values are in g/cm³.


    ASTM C729 is the most accurate method of finding densities of small-sized specimens of glass. This data holds colossal importance in quality control of production, development, and research on glass samples. This test can also be used for solids with higher densities by adding miscible liquids such as thallium malonate-formate (up to 5.0 g/cm3). The density data obtained has many practical applications in glass manufacturing industries and forensics.

    Test Procedure:

    In ASTM C729, the sample is prepared by cutting in size comparable to the standard glass of known density. A diamond-point marking pencil gives it a proper shape. Acetone or alcohol is used to clean the specimen and is dried by silicone-free lens tissues. The specimen is placed in the solution containing the standard. The solution and the bath temperatures should be 25°C, and they should float. All the thermometers, stoppers, and tubes are kept in the single-tube sink-float apparatus, settling temperature is noted, and the bath temperature is adjusted. As the expansion coefficient of the specimen and the glass standard is lower than the solution, both the sample and the standard sink in the solution. The temperatures at which the standard and model reach the midpoint of the test tube are carefully noted. Using the particular tables, the density of the specimen is calculated.


    The standard deviation (SD) of ASTM C729 is 0.0001 g/cm3. Temperature is set in the range of 25°C to 45°C.


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