) OF CARBONIZED PARTICLES IS NOT COMPLETE AFTER 15 MINUTES , REPEAT THE WASHING OPERATION , EVAPORATION OF THE WATER AND RE-IGNITION .
FOR WINES WITH A HIGH SUGAR CONTENT , ADD IF NECESSARY A FEW DROPS OF PURE VEGETABLE OIL TO THE EXTRACT BEFORE THE FIRST ASHING TO PREVENT EXCESSIVE FOAMING . IN THIS CASE PROLONG THE IGNITION FOR A FURTHER 15 MINUTES .
WEIGH THE DISH AFTER COOLING IT IN A DESICCATOR . THE WEIGHT OF THE ASH IS MULTIPLIED BY 50 AND REPORTED AS GRAMS PER LITRE .
7 . ALKALINITY OF THE ASH
7.1 . DEFINITIONS
TOTAL ALKALINITY OF THE ASH IS DEFINED AS THE SUM OF CATIONS OTHER THAN AMMONIUM COMBINED WITH THE ORGANIC ACIDS OF THE WINE .
PARTIAL ALKALINITY OF THE ASH IS THE ALKALINITY FROM THE CARBONATES , OXIDES AND SILICATES ONLY IN THE ASH .
ALKALINITY PER GRAM OF ASH ( OR ALKALINITY VALUE ) IS CALCULATED BY DIVIDING THE TOTAL ALKALINITY EXPRESSED IN GRAMS OF POTASSIUM CARBONATE BY THE WEIGHT OF THE ASH .
7.2 . PRINCIPLE OF METHODS
( A ) TOTAL ALKALINITY
TREATMENT WITH EXCESS SULPHURIC ACID AND BACK TITRATION OF THE EXCESS USING METHYL ORANGE AS INDICATOR .
( B ) PARTIAL ALKALINITY
TREATMENT WITH EXCESS SULPHURIC ACID AND BACK TITRATION OF THE EXCESS IN THE PRESENCE OF CEROUS IONS TO A PH OF 4.5 .
EXPRESSION OF RESULTS
THE ALKALINITY OF THE ASH IS EXPRESSED EITHER IN MILLIEQUIVALENTS PER LITRE AND DETERMINED TO THE NEAREST 0.5 , OR IN GRAMS OF POTASSIUM CARBONATE PER LITRE .
7.3 . TOTAL ALKALINITY
SINGLE REFERENCE AND USUAL METHOD
PROCEDURE
WEIGH THE ASH AND ADD 10 ML OF 0.1N SULPHURIC ACID AND PLACE THE DISH ON A BOILING WATERBATH FOR 15 MINUTES ; REPEATEDLY RUB THE BOTTOM OF THE DISH WITH A GLASS ROD IN ORDER TO ASSIST DISSOLUTION OF THE LESS READILY SOLUBLE MATERIAL . ADD TWO DROPS OF METHYL ORANGE , ONE PART PER 1 000 , AND TITRATE THE EXCESS SULPHURIC ACID AGAINST 0.1N SODIUM HYDROXIDE UNTIL THE COLOUR OF THE INDICATOR CHANGES TO YELLOW . LET THE VOLUME OF SODIUM HYDROXIDE USED BE N ML .
CALCULATIONS
THE ALKALINITY OF ASH IS EQUAL TO :
- 5 ( 10 - N ) EXPRESSED IN MILLIEQUIVALENTS PER LITRE ,
- 0.345 ( 10 - N ) EXPRESSED IN GRAMS OF POTASSIUM CARBONATE PER LITRE .
THE ALKALINITY OF 1 G OF ASH ( ALKALINITY VALUE ) IS EQUAL TO THE RATIO OF THE POTASSIUM CARBONATE ALKALINITY TO THE WEIGHT OF THE ASH .
7.4 . PARTIAL ALKALINITY
SINGLE REFERENCE AND USUAL METHOD
SOLUTIONS
( A ) MIXED INDICATOR : DISSOLVE 0.04 G OF METHYL ORANGE IN 20 ML OF DISTILLED WATER , AND DISSOLVE 0.2 G OF BROMOCRESOL GREEN AND 0.04 G OF METHYL RED IN 80 ML OF ETHANOL . MIX THE TWO SOLUTIONS . THE COLOUR CHANGE TO GREY TAKES PLACE AT PH 4.5 .
( B ) CERIUM CHLORIDE SOLUTION : DISSOLVE 10 G