. THE THERMOMETER SHOULD BE CAREFULLY CHECKED AND THE TWO GROUND JOINTS OF THE APPARATUS SHOULD BE PREPARED WITH GREAT CARE . THEY MAY BE GREASED LIGHTLY WITH A TRACE OF SILICONE .
A VESSEL OF THE SAME OUTSIDE VOLUME AS THE PYCNOMETER IS USED AS A TARE . IT IS FILLED ALMOST COMPLETELY WITH A SOLUTION OF A METAL SALT SUCH AS SODIUM CHLORIDE , POTASSIUM CHROMATE , ETC . , OF A SPECIFIC GRAVITY SUCH THAT THE MASS OF THIS STANDARD IS EQUAL TO THE MASS OF THE PYCNOMETER FILLED WITH A LIQUID OF DENSITY 1 * 01 ( 2 ) . THIS VESSEL IS SEALED IN A FLAME . ITS OUTSIDE CAPACITY SHOULD BE EQUAL TO THE OUTSIDE CAPACITY OF THE FILLED PYCNOMETER TO WITHIN 1 ML .
TARING OF THE PYCNOMETER
THE EMPTY PYCNOMETER SHALL BE TARED USING A BALANCE WITH A SENSITIVITY OF 0 * 1 MG AND A MAXIMUM RANGE OF AT LEAST 200 G , USING PRECISION WEIGHTS .
( 1 ) OR GRAMS PER MILLILITRE SINCE 1 ML IS NOW CONSIDERED AS IDENTICAL TO 1 CM3 .
( 2 ) THE PYCNOMETER THUS CALIBRATED IS READY FOR MEASURING SPECIFIC GRAVITIES WHICH ARE LESS THAN OR SLIGHTLY GREATER THAN THAT OF WATER , SUCH AS THE SPECIFIC GRAVITIES OF HYDROALCOHOLIC DISTILLATES , OF DRY WINES . FOR THE MEASUREMENT OF LIQUIDS OF A SPECIFIC GRAVITY APPRECIABLY GREATER THAN ONE , SUCH AS SWEET WINES AND MUSTS , THE SAME TARE SHALL BE USED WITH THE ADDITION OF A BRASS WEIGHT OF 20 G . THE VOLUME OF THIS EXTRA LOAD IS SMALL AND THE VARIATIONS IN THE BUOYANCY OF THE AIR ON IT ARE NEGLIGIBLE . IN THE CASE OF THESE LIQUIDS THE DENSITY NEED NOT BE MEASURED WITH THE HIGH ACCURACY NECESSARY FOR HYDROALCOHOLIC DISTILLATES ( MEASUREMENT OF ALCOHOLIC STRENGTH ) .
ADD THE MASS OF AIR CONTAINED IN THE EMPTY AND DRY PYCNOMETER ( 1 ) TO THE WEIGHTS , P , PLACED BESIDE THE PYCNOMETER . THE CORRECTED TARE OF THE EMPTY PYCNOMETER IS THUS OBTAINED .
1 * 2 G PER LITRE MAY BE ASSUMED AS THE DENSITY OF AIR ( 2 ) FOR THE CALCULATION OF THE MASS OF AIR M CONTAINED IN THE PYCNOMETER .
THE MASS OF THE AIR M CONTAINED IN THE APPARATUS IS OBTAINED BY MULTIPLYING THE VOLUME OF THE PYCNOMETER IN MILLILITRES BY 0 * 0012 . AS IT IS NOT NECESSARY TO KNOW M WITH AN ACCURACY GREATER THAN TO THE NEAREST 0 * 5 MG , THIS VOLUME IS NUMERICALLY EQUAL TO P _ P * , P * BEING THE WEIGHT REQUIRED TO BALANCE THE PYCNOMETER FILLED WITH WATER .
TARE THE WATER-FILLED PYCNOMETER AT T C , T BEING THE TEMPERATURE AT WHICH THE OPERATION IS CARRIED OUT AS SHOWN ON THE PYCNOMETER THERMOMETER , MEASURED TO 0 * 02 C , AND P * BEING THE WEIGHT IN GRAMS REQUIRED TO ESTABLISH EQUILIBRIUM .
CALCULATE THE VOLUME OF