THE DRY SOLUBLE RESIDUE CONTENT OF A PRODUCT FROM ITS REFRACTIVE INDEX .
IV . APPARATUS
ABBE TYPE REFRACTOMETER
THIS APPARATUS MUST HAVE A SCALE INDICATING THE PERCENTAGE WEIGHT OF SUGAR TO THE NEAREST 0,1 % . IT MUST BE SO CONSTRUCTED THAT SAMPLES CAN BE INTRODUCED EASILY AND QUICKLY . IT MUST BE EASY TO CLEAN .
THE REFRACTOMETER MUST HAVE A THERMOMETER WITH A SCALE EXTENDING FROM AT LEAST + 15 * C TO + 25 * C . IT MUST ALSO HAVE A WATER CIRCULATOR ENABLING MEASUREMENTS TO BE MADE AT A TEMPERATURE OF 20 * C MORE OR LESS 5 * C .
OPERATING INSTRUCTIONS FOR THIS APPARATUS , AND IN PARTICULAR THOSE DEALING WITH CALIBRATION AND LIGHT SOURCE , MUST BE STRICTLY FOLLOWED .
V . METHOD
1 . PREPARATION OF SAMPLE
1.1 . LIQUID AND LIMPID PRODUCTS
MIX CAREFULLY AND PROCEED TO DETERMINATION
1.2 . SEMI-DENSE PRODUCTS , PUREES , FRUIT JUICES WITH MATTER IN SUSPENSION .
CAREFULLY MIX AN AVERAGE LABORATORY SAMPLE AND THEN HOMOGENIZE . STRAIN PART OF THE SAMPLE THROUGH DRY GAUZE FOLDED IN FOUR , REMOVE THE FIRST DROPS AND PROCEED TO DETERMINATION ON THE FILTRATE .
1.3 . DENSE PRODUCTS ( JAMS AND JELLIES )
IF THE HOMOGENIZED PRODUCT CANNOT BE USED DIRECTLY , WEIGH 40 G OF THE PRODUCT TO THE NEAREST 0,01 G IN 250 ML BEAKER AND ADD 100 ML OF DISTILLED WATER .
BOIL GENTLY FOR TWO OR THREE MINUTES , STIRRING WITH A GLASS ROD .
COOL , DECANT CONTENTS OF THE BEAKER INTO A GRADUATED 200 ML FLASK , BRING UP TO THE REQUIRED LEVEL WITH DISTILLED WATER AND MIX CAREFULLY . ALLOW TO STAND FOR 20 MINUTES , THEN STRAIN THROUGH A FOLDED FILTER OR A BUECHNER FUNNEL .
MAKE DETERMINATION IN THE FILTRATE
1.4 . FROZEN PRODUCTS
DEFROST AND REMOVE STONES OR PIPS AND CORES . MIX THE PRODUCT WITH THE LIQUID FORMED DURING DEFROSTING AND PROCEED AS IN 1.2 OR 1.3 .
1.5 . DRY PRODUCTS CONTAINING WHOLE FRUIT OR PIECES OF FRUIT
CUT PART OF THE LABORATORY SAMPLE INTO SMALL PIECES , REMOVE STONES OR PIPS AND CORES AND MIX CAREFULLY .
WEIGH 10 TO 20 G OF THE PRODUCT TO THE NEAREST 0,01 G IN A BEAKER . ADD DISTILLED WATER TO AT LEAST FIVE TIMES THE WEIGHT OF THE PRODUCT . HEAT IN A WATER BATH FOR 30 MINUTES , STIRRING OCCASIONALLY WITH A GLASS ROD . WHEN COOL HOMOGENIZE CONTENTS OF THE BEAKER AND POUR INTO A GRADUATED 100 TO 250 ML MEASURING FLASK ( DEPENDING ON THE SIZE OF THE SAMPLE ) . BRING TO THE REQUIRED LEVEL AND MIX CAREFULLY . AFTER 20 MINUTES FILTER INTO A DRY CONTAINER AND MAKE DETERMINATION ON THE FILTRATE .
2 . DETERMINATION
BRING THE SAMPLE TO THE MEASUREMENT TEMPERATURE ( + 20 * C ) BY IMMERSING THE CONTAINER IN A WATER BATH OF THE REQUIRED TEMPERATURE .
PLACE A SMALL SAMPLE ON THE LOWER PRISM OF