Commission Regulation (EEC) No 000/90 (repealed)Dangos y teitl llawn

4. REFERENCE METHOD U.K.

4.1. Apparatus: U.K.

Normal laboratory equipment, and in particular:

4.1.1. A Pyrex pycnometer(1), of approximately 100 ml capacity, with a removable ground-glass jointed thermometer calibrated in tenths of a degree from 10 to 30 °C (Figure 1). The thermometer must be standardized. U.K.

The pycnometer has a side tube 25 mm in length and 1 mm (maximum) in internal diameter, ending in a conical ground joint. This side tube may be capped by a ‘reservoir stopper’ consisting of a conical ground-glass joint tube and terminating in a drawn-out section. This stopper serves as an expansion chamber.

The two ground joints of the apparatus should be prepared with great care.

4.1.2. A tare bottle, consisting of a vessel with the same outside volume (to within at least 1 ml) as the pycnometer and with a mass equal to the mass of the pycnometer filled with a liquid of specific gravity 1,01 (sodium chloride solution 2,0 % m/v). U.K.

A thermally insulated container, exactly fitting the body of the pycnometer.

4.1.3. A twin-pan balance with a range of at least 300 g and a sensitivity of 0,1 mg, U.K.

or

a single-pan balance with a range of at least 200 g and a sensitivity of 0,1 mg.

4.2. Calibration of pycnometer U.K.

Calibration of the pycnometer involves a determination of the following quantities:

• tare of the empty pycnometer,

• volume of the pycnometer at 20 °C,

• mass of the water-filled pycnometer at 20 °C.

4.2.1. Method using a twin-pan balance U.K.

Place the tare bottle on the left-hand pan of the balance and the clean and dry pycnometer, fitted with its ‘reservoir stopper’, on the right-hand pan. Add weights to the pan holding the pycnometer and record the weight required to establish equilibrium: let it be p grams.

Carefully fill the pycnometer with distilled water at the ambient temperature and fit the thermometer; carefully wipe the pycnometer dry and place it in the thermally insulated container. Mix it by inverting the container until the temperature reading on the thermometer is constant. Accurately adjust the level to the upper rim of the side tube. Wipe the side tube dry and put the reservoir stopper on; read the temperature t °C carefully, possibly correcting it for the inaccuracy in the temperature scale. Weigh the water-filled pycnometer against the tare and record the weight p′ in grams required to establish equilibrium.

Calculation (2) : U.K.

Taring of empty pycnometer:

tare of empty pycnometer = p + m,

where m

=

mass of air contained in the pycnometer,

m

=

0,0012 (p − p′).

Volume at 20 °C:

V _20 °C = (p + m − p′) · F_t ,

where F_t

=

a factor taken from Table I for the temperature t °C.

V _20 °C should be known to within ± 0,001 ml.

Mass of water at 20 °C:

M _20 °C = 0,998203 V _20 °C,

where 0,998203 is the density of water at 20 °C.

4.2.2. Method using a single-pan balance U.K.

Determine:

• the mass of the clean and dry pycnometer: let this be P,

• the mass of the pycnometer filled with water at t °C, following the procedure described in 4.2.1 above: let this be P ₁,

• the mass of the tare: T ₀.

Calculation(2): U.K.

Taring of empty pycnometer:

tare of empty pycnometer = P − m,

where m

=

mass of air contained in the pycnometer,

m

=

0,0012 (P ₁ − P).

Volume at 20 °C:

V _20 °C = [P ₁ − (P − m)] × F_t

where F_t

=

a factor taken from Table I for the temperature t °C.

The volume at 20 °C should be known to within ± 0,001 ml.

Mass of water at 20 °C:

M _20 °C = 0,998203 V _20 °C,

where 0,998203 is the density of water at 20 °C.

4.3. Method of measurement(2) U.K.

4.3.1. Method using twin-pan balance U.K.

Fill the pycnometer with the prepared test sample, following the procedure described in 4.2.1 above.

Let p″ be the weight in grams required to establish equilibrium at t °C.

Mass of liquid contained in the pycnometer = p + m − p″.

Apparent density at t °C:

Calculate the density at 20 °C using one of the correction tables given later, in accordance with the nature of the liquid being measured: dry wine (Table II), natural or concentrated must (Table III), sweet wine (Table IV).

The 20 °C/20 °C specific gravity of the wine is calculated by dividing its density at 20 °C by 0,998203.

4.3.2. Method using a single-pan balance(3) U.K.

Weigh the tare bottle and let its mass be T.

Calculate dT = T ₁ − T ₀.

Mass of the empty pycnometer at the time of measurement = P − m + dT.

Weigh the pycnometer filled with the prepared test sample, following the procedure described in 4.2.1 above. Let its mass at t °C be P ₂.

Mass of liquid contained in pycnometer at t °C = P ₂ − (P − m + dT)

Apparent density at t °C:

Calculate the density at 20 °C of the liquid under test (dry wine, natural or concentrated must, or sweet wine) as indicated in 4.3.1 above.

The 20 °C/20 °C specific gravity is calculated by dividing the density at 20 °C by 0,998203.

4.3.3. The repeatability of the density measurements U.K.

• for dry and semi-sweet wines: r = 0,00010,

• and for sweet wines: r = 0,00018.

4.3.4. The reproducibility of the density measurements: U.K.

• for dry and semi-sweet wines: R = 0,00037,

• and for sweet wines: R = 0,00045.

(1)

Any pycnometer with equivalent characteristics may be used.

(2)

A numeric example is given in section 6 of this chapter.

(3)

A numeric example is given in section 6 of this chapter.