Jan., 1912
T H E I O U R N A L OF I A - D U S T R I A L A,YD ENGII\7EERllYG
TEMPERATURE CORRECTIONS IN RAW SUGAR POLARIZATIONS.' B y W.D. HORNE Received November 23, 1911.
I n polarizing raw sugars a t temperatures other than the standard z o o C., errors are introduced t h a t are of serious moment. Much has been written on the subject and temperature corrections have been worked out, but unfortunately they have liot been generally adopted. One of the best methods of effecting the necessary corrections is t h a t described b y Dr. C. A. Browne a t the 7th International Congress of Applied Chemistry, t o be described later; a n d the present paper is t o present results on many hundreds of analyses, which entirely corroborate the reliability of this method of correction. I n the spring of 1909, when the New York Sugar Trade Laboratory was planned, I made some preliminary experiments on temperature corrections in m y own laboratory t o ascertain the relative results of polarizing a t z o o and a t higher temperatures, and later I have made continued close comparisons between the polarizations of the Sugar Trade Laboratory a t 2 0 ' and polarization of the same sugars in other laboratories a t ordinary room temperatures. I n the early experiments it was necessary, for polarizing a t z o o : I , t h a t the solution of the normal weight of sugar should be made u p t o L O O cc. a t 20' C . ; 2 , t h a t i t should be polarized a t z o o C . ; 3, t h a t the polariscope should be a t z o o C. I n order t o accomplish these ends I cooletl the solution of sugar in a flask with a thermometer in ice-water to 2 0 ' C., filling t o the mark with a few drops of water at about this same temperature. The solution was then shaken and filtered a t room temperature, which
CHEMISTRY
polariscope. These caps fit tightly over the ends of the observation tube and each has a glass windowed end and a n annular space inside filled with soda lime, which was found t o be much better for this purpose than calcium chloride or caustic alkali. The polariscope was kept a t z o o C. by enclosing the working parts, including both polarizing and analyzing nichols, in a galvanized iron box covered with a s/,-inch layer of cork board made b y the Armstrong Cork Company, of Pittsburgh, and containing two I/,-inch copper tubes, running along each side of the inside of the box, through which ice-cold water was circulated. It was found advisable t o pass water a t I O C. through this tube a t the rate of I O O cc. per minute, which cooled the polariscope t o 20' C. as shown by a thermometer passing through the box and covering, near the analyzer and compensating quartz wedges. The water issued a t about 13' C. when the temperature of the room was between 23' and 31 ' C. The polariscope was maintained at 2 0 ' C. about an hour before polarizations were made and the observation tube when inserted a t other than 2 0 ' quickly came t o this standard, a change of as much as two degrees taking place in four minutes. Cane sugars polarized at temperatures higher than Z O O C. are subject to a temperature correction, which may be divided into two parts: I , the temperature correction for pure sucrose, given b y the formula P. 2 0 = P . ~ [ I . O o.ooo3(t - z o ) ] and 2 , the temperature correction as applied t o pure levulose, the formula By propbeing P. 2 0 = Pt - 0.00812L(t- 20). er14- applying the combination of these formulas to a raw cane sugar polarized a t temperatures other than z o o , i t is possible t o arrive a t a result very close indeed t o t h a t which would be obtained when polarizing the sugars a t z o o , as may be seen b y the following,set of
.
+
TABLEI .
. At 20. 95.4 At 2 1 c. 95.5 95.5 95.3 At 20 c. 95.3 95.5 95.3 95.2
C:alculated correction for sucrose alone.
Calculated correction for levulose. -0.0330
95.3
Difi. -0.10
95.25 95.2 95.15
4 . 2 5 -0.30 -0.15
10.1572 +0.1571 +0.1570
-0.0279 -0.0279 -0.0279
95,.15 95.4 95.2 95 .O
4 . 1 5 -0.10 -0.10
+ o . 1855 +0.1862 +0.1855 +O. 1856
-0.0330 -0.0330 -0,0330 -0,0330
At 26.5
-0.20
+0.1868
Calculated correction for both levulose and sucrose. +0.1538
Difference of calculated polarization from actual polarization a t Zoo C. +0.0538
+ 0.1293
-0.1207 -0.1708 4.0409
+0.1292 +0.1291 +0.1525
+O. 1532
+0.0025 +0.0532
+0.1525 +0.1526
-0,0476
+0.0525
Average
necessarily warmed i t u p a little, as 'the laboratory was usually above z o o C. This filtrate was put into a tubulated zoo mm. observation tube, containing a centrally located thermometer, a n d immersed in ice-water until the temperature fell a little below z o o C. (about 1 8C~. ) , the tube dried with a towel, two protecting caps containing granular soda lime to prevent condensation of atmospheric moisture on the cold end glasses slipped on, and the whole p u t into the 1 Paper presented a t the meeting of the Association of Official Agricultural Chemists, Washington. November 22. 191 1.
-0.0247
observations, on eight raw sugars, giving the polarizations actually obtained a t z o o C. (the polariscope, the solution and containers all being a t this same degree), as compared with polarizations of the same sugars a t higher degrees, as indicated in Table I . These 9 5 ' sugars were assumed t o contain 1.25 per cent. invert sugar on the average, and having calculated the corrections for the sucrose and levulose separately and having united all these results, it was found t h a t these corrected polarizations were only 0.0247
T H E J O U R N A L OF I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y .
42
polariscopic degrees lower than the polarizations actually made a t z o o C. As the invert-sugar content of these sugars was not definitely known, a further investigation of I z samples of raw sugar was made in which the invertsugar content of each was accurately determined, giving the results shown in Table 11.
Jan., 1912
By use of the formulas above given, the polarizations of all the raw sugars coming t o two technical laboratories have been arranged in groups covering monthly periods, corrected for temperature and compared with the corresponding average polarizations obtained in the Sugar Trade Laboratory, when tested a t z o o C.
TABLE11.
A t 20“. At
28’.
95.1 85.7 94.0 94.1 A t 25’ 93.5 93.3 94.7 94.55 85.8 85.7 94.7 94.6 94.6 94.4 -It 27’ 87.6 87.6 95.3 95.15 94.6 94.4 95.25 86.80 94.25 94.3
Diff -0.15 -0.10 -0.25 -0.20
Calculated correction for sucrose alone +0.2282 CO ,2057 +0.2256 +0.2255
Invert sugar. 1.33 2.50 1.45 1 39
-0.20. -0.15 -0.10 -0.10 -0.20
f 0.I400 +0.1418 +0.1286 + O . 1419 + O ,1416
1.84 0.81 1.77 1.07 1.45
-0.0374 -0,0164 -0.0359 -0,0217 -0.0294
+0.1026
-0.00 -0.15 -0.20
10.1839 + o ,2001 +0.1998
2.15 0.91 1.48
-0.0595 -0 ,0260 -0.0421
f0.1244 +O.li41 +0.1577
Calculated correction for levulose alone. -0.0432 -0.0812 -0,047 1 -0 ,045 1
Combined corrections 0.1850 + O ,1245 4-0.1785 + O . 1807
+
Difference of calculated polarization from polarization a t Zoo. +0.0350
+ 0.0245
-0.0715 -0.0193 -0.0974-0.0246 -0.0073 f 0.0202 -0.0878
+0.1254
f0.0927 0,1202 +0.1122
+
+ 0.1244* f 0,0241 -0.0423
Average -0.0 101 Average without* = -0.0205
Having applied the formulas for correction of sucrose and levulose, the results obtained in the last column show the differences of the polarizations made a t high temperatures and calculated back to 2 o o , from the polarizations actually made a t z o o . The average of 1 2 such determinations gives us a result for the sugars polarized above zoo of only 0 . 0 2 7 3 polariscopic degrees lower than the polarizations actually made a t z o o C. If we omit the tenth sample in the above series, which seems t o be irregular, we find t h a t the average calculated polarization is only 0 . 0 186 polariscopic degrees lower than the polarization actually made a t z o o . These observations are quite in accord with those made by Browne, on mixtures containing known amounts of sucrose and levulose in raw sugars and molasses and reported by him in the article above cited. Date. 191 1 , March -Ipril May June July Aug. Sept
Sucrose cor. +0.0800 + O ,1290
+0.2002 +0.1977 +0.2235 +0.2329 + O . 1359
Laboratory Levulose cor. -0,0140 -0,0236 -0,0303 -0.0575 -0,0576
-0.0634 -0 0373
“4”. Total cor. 0.0660 f0.1054 +0.1699 f O 1402 f0.1659 0.1695 0.1006
+
+ +
The results found are expressed in the following table, which gives in decimal fractions of a single degree polariscopic the variations of my laboratory “A” and laboratory “ B ” results after calculating t o 2 0 ’ C., from the results obtained in the Sugar Trade Laboratory when conducting the whole operation a t z o o C. Thus we see that the average discrepancy in this series of about one thousand samples is.only +0.0148 polariscopic degree, but .that if the levulose correction has not been applied this quantity would be increased t o +0.0499. The levulose correction is thus twice as great as the total experimental error and should b y no means be ignored. The ideal method is, of course, t o conduct the entire operation of polarizing sugars a t z o o , but as this requires a n expensive plant or somewhat increased work and time b y the .method outlined Laboratory “B.”
Diff. from Trade Lab. -0.0070 0.0140 t0.1190 0.0436 0,0273 + O 0625 + o 0047
+
Levulose cor. -0.0059 -0.0036 -0.0180 -0,0355 -0,0550 -0.0344 -0.0520
Total cor. f0.0365 ’ 0.0203 f0.0810 f0.1477 i-0.1793 +0.0833 +0.1146
+ O . 1456
-0,035 1
f0.1135
+
+ + +
Average corrections for both laboratories
I n order to get a further comparison between polarizations made a t zoo C . , and those made a t higher temperatures, and calculated t o zoo C . , I have made monthlj- comparisons between the polarizations of man>- hundreds of samples tested both a t the Sugar Trade Laboratory and a t other laboratories.
Sucrose cor. 0.0424 +0.0239 0.0990 +0.1832 + O ,2373 +0.1177 +0.1666
+
Diff. from
. Trade Lab. -0.0096 0.0200 + O ,0710 +0.0117 -0,0170 +0.0193 -0,0267
+
+ 0.0148
above, cases will arise where a temperature correction will be required. My contention is t h a t if any such correction is t o be applied it should be done in accord with a full appreciation of the significance of levulose as well as of sucrose and thus be made as correct as our present knowledge will allow.
.
