Annual Report 1961 - BEEP

-- 86 --5. CHEMICAL CONTROL NOTES(a). FLRTlIER STUDIES ON THE USE OF THE REFRACTOMETERFOR ROUTINE CHEMICAL CONTROLF. LE OUEN & M. RANDABELFollowing the preliminary work carried outby LAMUSSE (1960). it was decided to studymarc thoroughly the use of the refractometerinstead of hydrometers for the routine chemicalcontrol of sugar factories. The original projectwas to carry out parallel controls with therefractometer and the hydrometers in threefactories over the whole of the 1961 crushingseason. Unfortunately the Bausch and Lambprecision refractometcrs were not received untilthe early days of November when the crushingseason was nearly completed. Hence it waspossible to carry out parallel controls for onlyone week at Factory A, two weeks at Factory Band four weeks at Factory C.Comparisons were made during theseperiods with first expressed juice, mixed JUiceand final molasses, The analytical methods usedfor the dcnsimctric Brix and sucrose determinationswere the standard ones followed inMauritius for routine chemical control. Forthe determination of refractometer Brixes andcorresponding sucrose determinations in molasses,the methods adopted were those used in Hawaiiand described in the Official Methods of theHawaiian Sugar Technologists for Routine Controlof Cane Sugar Factories, The Hawaiian methodof determining sucrose in juices differs verylittle from that used in Mauritius sinee in thecase of juices no dilution is necessary. Itwas therefore deemed preferable for the purposeof the experiment to use the latter methodwhich involves the removal of excess leadwith potassium oxalate.The results of these analyses are publishedin Table 40 from which it may be seen thatthe refractometer Brix is usually lower than thedensimetric Brix and hence the sucrose valuecalculated from the pol reading and the refractometerBrix is usually slightly larger than theTable 40.Comparison of Brix, Sucrose and Purity Values obtained with densimetric and refractometer controls.First Expressed Juice Mixed Juice Final MolassesFACTORY A B C A B C A B CPER[OD [ week 2 weeks 3~ weeks 1 week 2 weeks 4 weeks week 2 weeks 4 weeksNo. of samples for Brix 45 137 329 45 137 368 9 11 18Range of differences in Brix(Rcf-Dens) ... -0.02 to -10.38 to -;-2.[4 to -0.02 to -0-0.80to +1.51 to -3.3 to -6.2 to -3.1 to-0.91 -0.85 -2.09 -0.87 -0.98 -1.84 -8.0 -8.5 -10.7Mean dcnsimctric Brix: 20.35 20.!7 21.03 14.85 14.22 15.7[ 96.0 96.1 97.0Mean refractometer Brix 19.98 19.97 20.53 14.56 14.02 15.46 88.85 88.17 89.61No. of samples for Sucrose~~ gm. 6- 12- 23- 6- 12- 23- 9 ][ 18Range of differences inSucrose /~ gm (Rcf-Dens) 0.02 to 0.00 to 0.02 to O.O! to 0.01 to 0.00 to -0.20 to -[.48 to -1.90 to0.04 0.03 0,07 0.Q3 0.02 0.04 -1.80 -1 1.66 -;-2.][Mean dcnsimetric Sucrose/~ gm 17.92 18.01 18.42 12.88 12.41 13.40 31.20 34.62 34.85Mean refractometer Sucrose0() gm [7.95 18.03 18.45 12.89 12.42 [3.41 30.37 34.21 34.87Range of differences inPurity (Ref-Dcns.) 1.5 to 0.6 to 0.9 to 1.5 to I.l to 0.4 to 0.6to 1.4 to -0.1 to2.[ 1.6 3.0 2.1 2.1 3.5 2.7 4.8 6.0Mean densimctric purity 88.1 89.3 87.6 86.7 87.3 85.3 32.5 36.0 35.9Mean refractometer purity 89.8 90.3 87.9 88.5 88.6 86.8 34.2 38.8 38.9-Composite samples.