Division C.4 Procedure

The float and measuring cylinder must be cleaned between each measurement with distilled water, dried with soft laboratory paper which does not shed fibres and rinsed with the solution whose density is to be determined. Measurements must be made as soon as the apparatus has reached stability so as to restrict alcohol loss by evaporation.

1. C.4.1.

   Calibration of the balance

   Although balances usually have an internal calibration system, the hydrostatic balance must be capable of calibration with weights checked by an official certifying body.

2. C.4.2.

   Calibration of the float

   1. C.4.2.1.

      Fill the measuring cylinder to the mark with double-distilled water (or water of equivalent purity, e.g. microfiltered water with a conductivity of 18,2 MΩ/cm) at a temperature between 15 and 25 °C but preferably at 20 °C.

   2. C.4.2.2.

      Immerse the float and the thermometer, stir, read off the density of the liquid from the apparatus and, if necessary, correct the reading so that it is equal to that of the water at measurement temperature.

3. C.4.3.

   Control using a water-alcohol solution

   1. C.4.3.1.

      Fill the measuring cylinder to the mark with a water-alcohol mixture of known strength at a temperature between 15 and 25 °C but preferably at 20 °C.

   2. C.4.3.2.

      Immerse the float and the thermometer, stir, read off the density of the liquid (or the alcoholic strength if this is possible) from the apparatus. The alcoholic strength thus established should be equal to the previously determined alcoholic strength.

   Note 2:

   This solution of known alcoholic strength can also be used to calibrate the float instead of double-distilled water.

4. C.4.4.

   Measurement of the density of a distillate (or of its alcoholic strength if the apparatus allows)

   1. C.4.4.1.

      Pour the test sample into the measuring cylinder up to the graduation mark.

   2. C.4.4.2.

      Immerse the float and the thermometer, stir, read off the density of the liquid (or the alcoholic strength if this is possible) from the apparatus. Note the temperature if the density is measured at t °C (ρ_t).

   3. C.4.4.3.

      Correct ρ_t to 20 using the table of densities ρT for water-alcohol mixtures (Table II of Annex II to the OIV's Manual of analysis methods (1994), pp. 17-29).

5. C.4.5.

   Cleaning of float and measuring cylinder

   1. C.4.5.1.

      Immerse the float in the float cleaning solution in the measuring cylinder.

   2. C.4.5.2.

      Allow to soak for one hour spinning the float periodically.

   3. C.4.5.3.

      Rinse with copious amounts of tap water followed by distilled water.

   4. C.4.5.4.

      Dry with soft laboratory paper which does not shed fibres.

      Carry out this procedure when the float is first used and then regularly as required.

6. C.4.6.

   Result

   Using the density ρ₂₀ calculate the real alcoholic strength using the alcoholic strength tables identified below.

   The table giving the value of the alcoholic strength by volume (% vol) at 20 °C as a function of the density at 20 °C of water-alcohol mixtures is the international table adopted by the International Legal Metrology Organisation in its Recommendation No 22.