B " ENDS IN A SMALL SPHERE OF 1 CM DIAMETER WITH 20 HOLES OF 0 * 2 MM DIAMETER . ALTERNATIVELY THE TUBE MAY ALSO END IN A GLASS FRIT PLATE WHICH PRODUCES A LARGE NUMBER OF VERY SMALL BUBBLES THUS ENSURING GOOD CONTACT BETWEEN THE GASEOUS AND LIQUID PHASES .
ENSURE THAT THE GAS FLOW THROUGH THE APPARATUS IS APPROXIMATELY 40 LITRES PER HOUR . THE BOTTLE ON THE RIGHT OF THE ILLUSTRATION IS INTENDED TO RESTRICT THE VACUUM EFFECT OF THE WATER VACUUM PUMP TO 20 TO 30 CM WATER . INSTALL A FLOWMETER WITH SEMI-CAPILLARY TUBE BETWEEN THE BUBBLER AND THE BOTTLE TO REGULATE THE VACUUM .
SOLUTIONS
PHOSPHORIC ACID AT 25 % ( W / V ) .
HYDROGEN PEROXIDE ( AT 0 * 3 VOLUME ) .
INDICATOR REAGENT :
_ METHYL RED 100 MG ,
_ METHYLENE BLUE 50 MG ,
_ ALCOHOL 50 % 100 ML .
SODIUM HYDROXIDE 0 * 01N .
PROCEDURE
MAINTAIN THE WINE AT 20 C IN A FULL AND STOPPERED BOTTLE FOR FOUR DAYS BEFORE THE DETERMINATION OF THE FREE AND COMBINED SULPHUR DIOXIDE . THIS PRECAUTION IS UNNECESSARY IF THE SULPHUR DIOXIDE ONLY IS TO BE MEASURED .
DETERMINATION OF FREE SULPHUR DIOXIDE
INTRODUCE INTO THE 100 ML FLASK " A " OF THE ENTRAINMENT APPARATUS , 10 ML OF WINE AND 5 ML OF 25 % PHOSPHORIC ACID . ASSEMBLE THE APPARATUS IMMEDIATELY . IF A LARGER VOLUME ( 20 OR 50 ML ) OF A WINE OF VERY LOW SULPHUR DIOXIDE CONCENTRATION IS TO BE ANALYZED , USE A FLASK OF 250 ML CAPACITY FOR A .
MAINTAIN FLASK A AT A TEMPERATURE OF 10 C .
PLACE 2 TO 3 ML OF HYDROGEN PEROXIDE AT 0 * 3 VOLUME ( PREVIOUSLY NEUTRALIZED WITH 0 * 01N SODIUM HYDROXIDE ) AND TWO DROPS OF INDICATOR REAGENT INTO THE BUBBLER B .
CONNECT THE BUBBLER TO THE APPARATUS AND BUBBLE AIR ( OR NITROGEN ) THROUGH FOR 12 TO 15 MINUTES . THE FREE SULPHUR DIOXIDE CARRIED OVER IS OXIDIZED TO SULPHURIC ACID . REMOVE THE BUBBLER FROM THE APPARATUS AND TITRATE THE ACID WHICH HAS FORMED AGAINST THE 0 * 01N SODIUM HYDROXIDE SOLUTION .
LET THE NUMBER OF MILLILITRES USED BE N .
DETERMINATION OF COMBINED SULPHUR DIOXIDE
WHEN THE DETERMINATION OF THE FREE SULPHUR DIOXIDE HAS BEEN COMPLETED , AGAIN PLACE 2 TO 3 ML OF NEUTRALIZED HYDROGEN PEROXIDE IN THE BUBBLER B . HEAT THE WINE CONTAINED IN FLASK A TO BOILING POINT WITH A SMALL FLAME OF 4 TO 5 CM HEIGHT WHICH SHOULD DIRECTLY TOUCH THE BASE OF THE FLASK . DO NOT PUT THE FLASK ON A METAL PLATE , BUT ON A DISC PROVIDED WITH A HOLE OF APPROXIMATELY 30 MM DIAMETER TO PREVENT ANY OVERHEATING OF THE EXTRACTIVE MATTER OF THE WINE ON THE WALLS OF THE FLASK .
SIMMER WHILST PASSING A CURRENT OF AIR ( OR NITROGEN ) . WITHIN 12 TO 15 MINUTES