ETHANOL INTO THE TWO COLLECTING TUBES SO THAT THE POROUS PARTS OF THE GAS DISPERSION RODS ARE COMPLETELY IMMERSED . COOL THE TWO TUBES EXTERNALLY WITH THE FREEZING MIXTURE . CONNECT THE FLASK TO THE COLLECTING TUBES AND BEGIN TO FLUSH THE APPARATUS WITH NITROGEN AT A RATE OF THREE LITRES PER HOUR . HEAT THE WINE TO 80* C WITH THE HEATING MANTLE , DISTIL AND COLLECT 45 TO 50 ML OF DISTILLATE .
PREPARATION OF THE GAS CHROMATOGRAPH
IT IS RECOMMENDED THAT THE FOLLOWING CONDITIONS ARE USED :
- INJECTOR TEMPERATURE : 200* C ,
- COLUMN TEMPERATURE : 130* C ,
- HELIUM GAS CARRIER FLOW-RATE : 20 ML PER MINUTE .
INTRODUCE WITH A MICROSYRINGE A VOLUME OF THE STANDARD SOLUTION SUCH THAT THE PEAK CORRESPONDING TO THE ALLYL ISOTHIOCYANATE CAN BE EASILY IDENTIFIED ON THE GAS CHROMATOGRAM .
INTRODUCE AN ALIQUOT OF THE DISTILLATE INTO THE CHROMATOGRAPH . CHECK THAT THE RETENTION TIME OF THE PEAK OBTAINED CORRESPONDS WITH THAT OF THE PEAK OF ALLYL ISOTHIOCYANATE .
UNDER THE CONDITIONS DESCRIBED ABOVE , COMPOUNDS NATURALLY PRESENT IN THE WINE WILL NOT PRODUCE INTERFERING PEAKS ON THE CHROMATOGRAM OF THE SAMPLE SOLUTION .
( 1 ) OR GRAMS PER MILLILITRE SINCE 1 ML IS NOW CONSIDERED AS IDENTICAL TO 1 CM .
( 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 ) .
( 3 ) THE CORRECTION FOR THE BUOYANCY OF THE AIR IS THUS MADE ONCE AND FOR ALL .
( 4 ) STRICTLY SPEAKING , IT WOULD BE NECESSARY TO NOTE THE TEMPERATURE OF THE PYCNOMETER AND THE ATMOSPHERIC PRESSURE AND TO CALCULATE THE DENSITY OF THE AIR UNDER THESE CONDITIONS . IN PRACTICE SUCH A CALCULATION WOULD BE NECESSARY ONLY WHEN WORKING AT AN ALTITUDE HIGHER THAN 1 400 M AND AT A TEMPERATURE ABOVE 30* C . A VARIATION OF 10 % IN THE DENSITY OF THE AIR PRODUCES AN ERROR OF 5.10-6 IN THE SPECIFIC GRAVITY OF A WINE DISTILLATE AND A MAXIMUM ERROR OF 0.005 IN THE ALCOHOLIC STRENGTH MEASURED ; THIS IS NEGLIGIBLE .
( 5 ) THE VOLUME SO CALCULATED IS NOT STRICTLY ACCURATE , AS THE BUOYANCY OF THE AIR ON THE WEIGHTS RECORDED HAS NOT BEEN TAKEN INTO ACCOUNT , THESE WEIGHTS GENERALLY NOT BEING CORRECTED FOR THIS BUOYANCY . HOWEVER