T H E J O LTRiVAL O F IL$TDLTSTRI.4L AA7D EhiGI;\rEERINC CHEA41STRY
5 04
frogs a n d fishes Tartaric acid is much more toxic t h a n Rochelle salts. So far as the writer is aware, no series of systematic observations so extensive as those here recorded have ever been made. Only isolated experiments seem t o have been conducted with no efforts a t comparatil-e results. Our conclusions from these experiments were far different from our expectations in t h e beginning, which opinions mere based on opinions of some eminent men in the field of investigation. The Referee Board of Consulting Scientific Experts, for example, laid great stress on t h e fact t h a t sodium benzoate is not toxic t o frogs as comparative evidence in drawing conclusions as t o its toxicity t o men. Such experiments as these in t h e past have been often relied on a s evidence in court as t o t h e poisonous character of substances used in foods. b u t after studying the d a t a we have accumulated somewhat carefully, the writers have come t o t h e conclusion t h a t experiments of this nature, a t least upon animals so distantly related t o man, do not furnish conclusii-e evidence of the effects of such substances upon the human system. OF SOUTH DAKOTA VERMILLION.S D
L NIVERSITY
THE GRAVIMETRIC DETERMINATION OF REDUCING SUGARS IN CANE PRODUCTS B y GEORGEP. MEADEAND JOSEPH B. HARRIS Received February 10, 1916
The reference books devoted t o sugar analysis all describe the determination of reducing sugars in considerable detail. The detail concerns t h e method of heating, t h e time of boiling, the filtration of t h e cuprous oxide, t h e determination of t h e copper b y a n y of sex-era1 methods. and t h e calculation of results. On t h e other hand, t h e preparation of t h e solution, t h e clarification and removal of excess lead are, as a rule, referred t o very briefly and in the broadest terms: “Clarified if necessary with a minimum of neutral lead acetate solution-deleading b y means of sodium carbonate, sodium sulfate, potassium oxalate or other means.”’ li I n case clarification with lead acetate is used, the excess of lead must be removed; this may be done b y t h e addition of a soluble carbonate, sulfate or oxalate.”z T h e present investigation was undertaken a t t h e suggestion of G. L. Spencer, Chief Chemist of T h e Cuban-American Sugar Company, and carried on under his general direction. The work extended over a period of eighteen months. Failure t o obtain concordant figures from several laboratories on exchange samples of final molasses called attention t o t h e necessity for t h e revision of t h e routine method. The method of precipitation and the determination of t h e copper were under strict specifications in all the laboratories t o which the exchange sample had been sent. so the indication mas t h a t the source of difference lay in t h e preparation of the solution for analysis. 1
I
Browne’s “Handbook of Sugar Analysis,” p. 443. Deerr’s “Cane Sugar,” p. 468.
Vol. 8 , l 7 o . 6
G E N E R A L IIETHOD
Throughout the investigation t h e Meissl and Hiller method was employed; 50 cc. of t h e solution for analysis and j o cc. of mixed Fehling’s solution were heated in a beaker t o the boiling point for 1 minutes, and maintained a t gentle ebullition exactly 2 minutes. X gasoline burner mas the source of heat. At the e n d of t h e boiling period I O O cc. of cold, recently boiled distilled water were added and t h e solution filtered in a n alundum crucible or fused silica Gooch crucible. T h e cuprous oxide was always burned t o cupric oxide in an electric muffle a t full red heat for a t least 3 0 min. Other methods of determining the copper were employed a t times as well, and comparisons are tabulated where this was done. L E A D A C E T A T E soLnTIos-The Iead solution employed was a j6O Brix solution of normal lead acetate, acidified faintly with acetic acid. S A M P L E - F O ~ the first part of t h e work a sample of final molasses of the following analysis was used: Brix 8 7 . 2 , polarization 3 6 . 7 , Clerget number 1 2 . 4 3 , reducing sugars about 1 1 . 0 0 per cent. This was warmed, mixed thoroughly and stored in an air-tight jar. Weights of this molasses were taken so t h a t j o cc. of solution contained I gram of molasses A X O U S T O F L E A D T O B E USED-TO rarious portions of solution containing I gram of molasses t o j o cc. u-ere added lead acetate solution-o. I . 0 . 2 , 0 . 3 , 0 . 4 , etc., cc., respectively, per gram of molasses. The filtrates were tested with HCI. The filtrate from the portion using 0 .j cc. lead solution shoTved a slight precipitate. The portion containing 0 . I cc. lead solution filtered slowly, t h e filtrate showing a precipitate with hydrogen sulfide. This covered the range in which might be included “sufficient lead t o clarify,” as 0 . I cc. showed an excess of lead in t h e filtrate (with hydrogen sulfide). and 0 . j cc. was necessary t o precipitate everything which could be brought down completely with normal lead acetate. The first series of tests was made using 0 . j cc. lead solution per gram of molasses. COUPARISOX
OF
ORDIXARY
DELEADIXG
AGEXTS
AKD
V A R Y I K G AMOUKTS O F LEAD
TABLE I-UTEIGHTS OF CUO F R O M 1 GRAMOF ?*fOLASSES 0.5 cc. Lead Solution per Gram of Molasses, Deleaded, with Various Deleading Agents in Solutions, the Amount Indicated Being per Gram of Molasses Sodium carbonate Potassium oxalate Sodium sulfate 2 cc. 10% solution 2 cc. l0Yc solution 2 cc. saturated solution 0.2517 0.2547 0,2646 0,2500 0 2547 0.264; 0.2549 0.2561 0 2649 0.2525 0 2644 0 2515 0 2605 0 2521 0.2616 I _ _
__
__
A v . , 0.2534 0.2634 0.2522 Spaces separate determinations made on different weighings
T h e carbonate and sulfate check, but t h e oxalate gives weights of CuO I O mg higher. As the deleading agents all gave considerable precipitates with 0 . j cc. of lead solution, a second set of tests mas made using 0 . z j cc. of lead solution per gram, one-half t h e amount used above. This was about the minimum of lead giving a rapid filtration. As sodium sulfate did not form any precipitate with this smaller
T H E J O C R N A L O F I,VDUSTRIAL A S D E S G I X E E R I N G C H E M I S T R Y
June, 1916
amount of lead, its use was discontinued, and a series with dry sodium oxalate was substituted. TABLEII--a’EIGHTS OF CUO F R O M 1 GRAMOF MOLASSES 0 25 cc. of Lead Solution per Gram of Molasses, n i t h Decreased Amounts of Deleading Agents as Shown Sodium carbonate Potassium oxalate Sodium oxalate (dry) 1.5 cc. 10Vc solution 1 cc. 10% solution 0.1 gram 0.2710 0.2703 0.2635 0.2704 0 2709 0.2723 0.2717 0.2658 0.2732 0.2664 0.2689 .. 0.2638 , .
__
__
Av., 0.2657
0.2715
0,2706
T h e d r y sodium oxalate checks t h e potassium oxalate in solution, a n d as before the carbonate figures are much lower t h a n those with oxalates. Comparing t h e average results with 0 . 5 cc. of lead solution per gram a n d with 0 . 2 j cc. lead solution per gram we have : 0.5 cc. lead solution. . , . . . . . , . . . 0.25 cc. lead solution.. , . . . . . . . .
Sodium carbonate 0.2534 0.2657
Potassium oxalate 0.2634 0.2715
T h e smaller amount of lead gives much higher results with both deleading agents. Another comparison of t h e effect of varying the lead, deleading with potassium oxalate gave similar results, as here shown.
It is evident t h a t concordant results can be obtained only when the amount of lead is accurately measured, and when the deleading agent is specified. Pending further work, we adopted t h e use of 0 . 2 5 cc. of lead solution per gram of molasses, as this was t h e minim u m amount of lead giving a rapid filtration, and showing a n appreciable precipitate with t h e deleading agent, remo\-ing t h e excess lead with I cc. of I O per cent potassium oxalate solution, or 0 . I gram of dry sodium oxalate, with kieselguhr added t o aid filtration. The ox’alates were preferred for several reasons. Boerntraeger‘ had raised objections t o carbonate, par;ticularly in excess; Sawyer2 considered t h e oxalate preferable; solutions deleaded with carbonate, on standing a short time, frequently developed a cloud which settles on the glassware; and finally the oxalate gives the higher figures. W E I G H I K G AS C U P R O U S OXIDE-Before igniting t o cupric oside, in most cases t h e cuprous oxide was dried a t 1 0 j O C. and weighed. Several determinations of t h e copper present in t h e precipitates were made b y Low’s modifications of t h e volumetric iodide meth~d.~ T ~ B L E1 7
Cui0 0.2532 0.2522 0,2550 0,2449 0.2548 0,2567
TABLE111-DIFFERENT AMOUXTSOF LEADSOLUTION, DELEADED WITH POTASSIUM OXALATEIN SOLUTION 0.5 cc. lead solution per gram molasses 0.2637 0,2626
__
0.25 cc. lead solution per gram molasses 0.2748 0.2744
Av.,
FILTRATIOX;, a n d a comparison of dry reagents with previous figures with reagents in solution was brought out in the following: TABLE IV-DRY DELEADINC AGEKTS,WITH
A N D WITHOUT KIESELGUHR All with 0.25 cc. Lead Solution per Gram of Molasses 0.15 gram sodium carbonate, 0.1 gram sodium oxalate, dry per gram molasses dry per gram molasses
- No
.
--N O
Kieselguhr 0.2670 0.2652 0.2670 wet reagent,
CuO 0.2732 0.2723 0.2742 0.2642 0.2745 0,2740
-
__
cu (calculated) 0.2183 0.2175 0.2191 0.2111 0.2193 0.2189
0,2245
Cu by
Low’s method 0 2192
__
0.2174
0 2176 0.2184 0.2084 0 2187 0 2184 ~
0.2168
0,2746
T H E E F F E C T O F K I E S E L G U H R AS A N A I D T O
Av. with
cu (calculated) 0,2248 0,2240 0,2264 0.2175 0.2263 0.2279
~
Av., 0.2632
Av.,
505
__
0,2664 0,2657
Kieselguhr 0,2669 0.2642 0.2672
Kieselguhr 0.2748 0.2740
__
.. -
0.2663
0.2744
1
.
.
.
Kieselguhr 0.2743 0.2745 0.2742
0.2743
0.2746
T h e kieselguhr aids filtration a n d does not affect the results. D r y reagents give check figures with t h e same reagents in solution. This tabulation again emphasizes t h e difference between deleading with carbonate and with oxalates. suuMARY-considering now t h e possibilities under the options offered in “sufficient lead t o clarify” a n d “deleading with carbonate, sulfate or oxalate,” t h e following figures are taken from t h e foregoing work: o . , j cc. lead per gram of molasses, deleaded with carbonate; average of five check results, weight CuO 0 . 2 5 3 4 , per cent glucose I O . 64. 0 . 2 5 cc. lead per gram of molasses, deleaded with oxalate; average of seven check results, weight CuO 0 .2744, per cent glucose 1 1 . j 4 , showing a difference of about 8 . 5 per cent on t h e glucose content of t h e molasses, using methods both of which are permissible under the directions a s ordinarily given.
Weighing as cuprous oxide is The checks between t h e copper cupric oxide and as determined show t h e reliability of t h e cupric CLARIFICATIOK
WITH
evidently worthless. as calculated from by Low’s titration, oxide weight.
KIESELGUHR
ONLY,
WITHOUT
THE USE O F L E A D
With solutions which are free from suspended matter it has long been t h e practice with many chemists t o dispense with the use of lead or other clarifying reagents. This practice has been objected t o on t h e ground t h a t there might be copper-reducing substances, other t h a n sugars, present in t h e solutions which would be removed b y t h e use of lead. Noel Deerr4 says: “ W i t h the use of no clarifying agent, bodies other t h a n reducing sugars which act on copper may be present. Zerban and S a q u i n have shown t h a t with cane molasses a little more copper is precipitated with unclarified solutions t h a n with solutions clarified with neutral acetate of lead, and t h e writer is of t h e opinion t h a t results closest t o t h e t r u t h are obtained with the use of this material.” I n the present inT7estigation vie have shown t h a t tests made with neutral lead solution may vary between wide limits depending on t h e amount of lead and t h e class of deleading agent used. It is possible t h a t most of t h e work comparing t h e use of lead and no lead has been done using sodium carbonate t o deZ . angew. Chem.. 1894, 333. J . A m . Chem. Soc., 26, 1631.
1 2
SBrowne’s “Handbook,” p. 41 1. “Cane Sugar,” p 467.
4
T H E J O U R N A L OF I N D U S T R I A L A N D ENGINEERING CHEAfISTRk’
506
lead, which gives much lower figures t h a n t h e oxalate, as we have brought out. T h e second phase of the work took u p the comparison of the lead and oxalate method already developed, as against preparation of t h e solution without t h e use of reagents, using kieselguhr for t h e removal of suspended matter. Experiment showed t h a t t h e addition of a few teaspoonfuls of kieselguhr t o t h e molasses solution, after making t o the mark, gave a solution on filtering which was qflite bright a n d clear. The filtration may also be effected quite as well by adding the kieselguhr t o the filter paper before pouring on the solution X new sample of molasses was used, polarization 34. 24? Clerget number 40.31, reducing sugars about 2 1 . o o per cent. This sample was warmed, mixed a n d stored as before. Amounts were weighed t o give 0 . j g. of molasses per j o cc. of solution. TABLE VI-COMPARISON
BETWEEN A SET OP TESTS CLARIFIEDWITH NORMAL LEAD ACETATE SOLUTIOX 0.25 cc. per Gram of Molasses with 1 cc. of 10 Per Cent Potassium Oxalate Solution per Gram of Molasses, a n d Three Sets of Tests Using Kieselguhr Only, with No Lead or Other Reagent No lead __ Lead and potassium A B C oxalate 0.2517 0.2478 0.2481 0.2517 0.2513 0.2478 0.2500 0.2488 0.2505 0.2486 0.2509 0.2512 0.2491 0.2501 0.2492 0.2500 0.2496 0.2494 0.2494 0,2503 0.2493 .. 0.2492 .. 0.2510
-
----
__
__
___
__
A x , 0.2523
0.2501
0.2499
0.2494
The lead and oxalate gives results higher t h a n the tests where n o lead is used. The three sets using no lead agree well with one another and within themselves. It may be of interest here t o note t h a t Series A and B were filtered through alundum crucibles a n d Series C. through silica Gooch crucibles with porcelain discs. T h e agreement is good. We found t h a t if alundum crucibles were given a proger treatment t h e weight remained practically constant through t h e duration of t h e test. ?rem- crucibles were soaked with nitric acid, washed with hot water, then treated with hot Fehling’s solution and again washed thoroughly and finally ignited a t red heat in a muffle furnace for a t least 30 mins. A%fteruse the copper precipitate was removed with nitric acid, the crucible washed thoroughly with very hot water and the ignition carried o u t as before. Prepared crucibles must be stored i n a desiccator t o avoid absorption of moisture. The greater part of our work was done with alundum, and in t h e numerous instances where comparative tests were made using both Gooches and alundum crucibles, the agreement was always very good. D E T E R M I S I K G T H E B O I L I K G P O I N T W I T H A THERhIOM-
t h e tabulations given so far it will be seen t h a t , almost without exception, there is a maximum variation of 3 mg. of CuO among tests made on t h e same solution. The only phase of t h e precipitation and collection of t h e copper precipitate which seemed capable of causing this variation was t h e determination of the beginning of the 2-minute boiling period. T h e ETER-Tn
YoI. 8, SO.6
usual directions read : ‘LHeat the contents of t h e beaker t o t h e boiling point in 4 minutes and continue t h e heating for exactly 2 minutes, maintaining gentle ebullition.’’ Some directions define t h e beginning of boiling as “full ebullition of the solution.” Frequently t h e solution comes t o a boil all a t once; sometimes it boils locally for a few seconds. To place this part of t h e operation on a definite basis, so as t o limit the variations in check tests, one of us (Harris) suggested t h e use of a thermometer t o determine t h e beginning of boiling. The thermometer was thrust through a hole in a metal disc which served as a cover for the beaker in place of the usual watch glass. T h e lower end of the thermometer reached into the liquid t o within 4 or j mm. of t h e bottom of the beaker. The solution was heated a t such a rate t h a t the thermometer registered 100’ C. in four minutes. The heating was continued for exactly two minutes from this point, a gentle ebullition being maintained as usual. We employed this device in all of our succeeding work, and obtained closer checks t h a n with the old method. K o t only is the two-minute boiling period made more definite b y t h e use of t h e thermometer, b u t i t is much easier t o regulate the pre-heating t o t h e required 4 minutes. Local boiling frequently takes place before 100’ C. is reached, and occasionally full boiling does not begin until after t h a t point is passed. Under a n y circumstances, the 2-minute period was timed from t h e 100’ point. Further work with no lead as compared t o lead and oxalate was carried out t o determine, if possible, t h e reason for t h e higher results obtained where lead and oxalate were used. PRECIPITATED B Y 0.5 G R A MMOLASSES, TESTS WITHOET LEAD With 0.25 cc. Lead Solution and 1 cc. 10 Per Cent Potassium Oxalate per Gram of Molasses; and with 0.25 cc. Lead Solution and 1 g . (Large Excess) of Dry Sodium Oxalate per Gram of Molasses Lead and potassium Lead and sodium X o lead oxalate oxalate 0.2498 0.2515 0,2492 0.2500 0.2509 0.2486 0,2497 0.2528 0.2492 0.2506 0.2514 0.2481 0.2515 0.2527 0.2482 TABLEVII-CCO
___
Av., 0.2487
. -
-__
0,2503
0.2519
As in Table VI, t h e use of lead and oxalate gives higher tests t h a n no lead. The excess of oxalate gives still higher figures. Later work, however, did not bear this o u t . (The difference between the no lead and the lead and oxalate methods is so slight t h a t frequently there is a greater maximum difference within a series t h a n between the averages of two series. Our conclusions are justified by t h e constant tendency of the one method t o give higher figures t h a n t h e other.) TABLEVIII-TESTS WITHOUT LEAD M7ith 0.25 cc. Lead Solution and 1 cc. 10 Per Cent Potassium Oxalate Solution per Gram of Molasses; a n d with No Lead, b u t 1 cc. 10 Per Cent Potassium Oxalate per Gram of Molasses Lead and potassium Potassium oxalate N o lead oxalate b u t no lead 0.2512 0.2501 0.2488 0.2497 0.2505 0,2498 0.2493 0.2521 0.2491 0.2503 0.2522 0.2491 0.2492 0.2511 ~
A v , 0.2492
_-
__
0 2500
0.2512
Again the use of lead and oxalate gives figures higher t h a n t h e tests in which no lead is used (although in
June. 1916
T H E J O U R N A L OF I N D l T 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
this particular case t h e two methods agree more closely t h a n before), but t h e addition of oxalate alone gives results higher t h a n where no reagent is used. T h e indication here is t h a t t h e lead is not t h e disturbing factor. T h e combined precipitates in t h e second set of tests (lead a n d oxalate) were dissolved in nitric acid a n d evaporated with sulfuric acid, b u t showed no 1ead.l T o IOO cc. portions of a solution t o which h a d been added 0 .z j cc. lead solution per gram of molasses, a n d filtered, were added 0 .2 , 0 .j , I and z g. of d r y sodium oxalate. After standing three hours these were filtered a n d tested with hydrogen sulfide. The lead was in direct proportion t o the amount, of oxalate used. I n t h e filtrate from t h e 0 . 2 gram of oxalate only a trace of lead was shown, b u t in t h e filtrate from z grams oxalate the precipitate of lead sulfide was quite appreciable. Treadwell-Hall2 says, “ I n a n excess of alkali oxalate, many of t h e insoluble oxalates dissolved. forming double salts.” T o determine whether increasing t h e oxalate with no lead present would increase t h e results proportionately, a series of tests were made as follows: Four portions of molasses of j g. each were made u p t o 500 cc. with quantities of potassium oxalate in solution as indicated i n t h e tabulation. The lime salts formed a precipitate which was filtered out, using kieselguhr. Tests were r u n in duplicate. After weighing t h e ignited cupric oxide, this was reduced t o metallic copper i n alcohol vapor according t o Mredderburn,3 a n d this copper i n t u r n was dissolved a n d determined by Low’s volumetric iodide method. TABLEIX-TES‘~~USING Eo LEAD,BUT
WITH
INCREASING QUANTITIESOF
POTASSIUMOXALATEIN SOLUTION
0,2467 0.2501 0.2510 0.2499 0,2487 0.2502 0.2500
CU Low’s (calcu- reduced titralated) bv alcohol tion 0.1975 0.1975 0.1977 0.1970 0.1979 0.1974 0.1998 0.1995 0.2018 0.2005 0.2011 0.2012 0.1996 0.2007 0.2208 0.1992 0.1992 0.2005 0,1999 0 , 2 0 0 8 0.2008 0.1997 0.2009 0.2002
0.2500
..
cu
Grams potassium oxalate per 100 cc.
CuO
. . . . . . . . . . . . . . . . . 0.2473
None. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.1................................
........................ ........................ 2.0.. . . . . . . . . With lead a n d oxalate. ..........................
cu
The presence of t h e oxalate gives higher figures t h a n where none is present, b u t increasing t h e amount of oxalate does not increase t h e results. Judging from t h e volumetric copper, t h e greater weight where oxalate is present is due t o copper actually precipit a t e d a n d not t o some extraneous material precipit a t e d with t h e copper. The oxalate without lead gives figures corresponding t o those where lead is used a n d t h e excess removed with oxalate. F r o m t h e figures obtained with lead a n d oxalate, oxalate a n d no lead, and no lead or other reagent, i t seems safe t o say t h a t t h e molasses with which we
507
were dealing contained no non-sugar copper-reducing substance removable by lead. Since t h e oxalate without lead gives just as high figures as t h e lead a n d oxalate together, t h e deleading agent a n d not t h e lead is t h e cause of t h e difference between the no lead method a n d t h e method with lead a n d deleading agent As suggested earlier in this article, t h e probable reason for t h e conclusion t h a t t h e use of lead for clarification was necessary because it removed copper-reducing non-sugars, arose from t h e fact t h a t t h e comparisons with t h e no lead method were made using lead 2nd sodium carbonate, which gives low results. SUM M A R Y
Summarizing t h e work on final molasses without lead we find t h a t : Using kieselguhr bnly, without lead or a n y other reagent, gives a clear filtrate a n d consistent results. The no lead method offers no mechanical difficulties, either in preparing t h e solution for analysis or i n t h e precipitation a n d collection of t h e copper precipitate.1 I t eliminates all chance of t h e gross errors which we have shown t o be possible under t h e options offered as t o t h e q u a n t i t y of lead and class of dele’ading agent. The only objection offered, t h a t there m a y be present copper-reducing non-sugars which make t h e use of lead essential, seems t o be contradicted b y our work with oxalate a n d lead, a n d oxalate alone. Compared with tests made with lead solution a n d deleaded with potassium oxalate, t h e results without 9 lead are slightly lower, I . 5 t o z mg. of CuO. Oxalate alone, without lead, gives figures corresponding t o those with lead a n d oxalate, showing t h a t t h e oxalate is t h e disturbing factor, a n d not t h e lead. C 0 MP A R I S 0 N B E T W E E K V.4 RI 0 US D E I.E AD1 N G A G E NT S-
Oxalic acid has been suggested as a deleading agent, as well as phosphoric acid a n d sodium phosphate. Tests were made with these in comparison with t h e no lead method. I n order t o corroborate t h e earlier work with carbonate a n d oxalate, these reagents were also included in t h e comparison. TABLEX-COMPARISOK BETWEEN h-o LEADMETHODA N D VARIOUSDELEADING AGEKTS
S o lead
0.250i 0.2505 0.2513
.. ..
.4verage,
0 2508
LEADSOLUTION 0 25 C C PER G R A MOF MOLASSES Lead Lekd Lead and 1 cc 10% and 1 5 cc lOy0 and 1 cc lOY-, potassium oxalate sodium carbonate oxalic acid 0,2532 0,2439 0.2538 0,2527 0,2424 0.2531 0.2516 0.2447 0.2545 0.2516 0.2444 0.2541 0.2533 0.2418 0.2540
-
__
___
0 2525
0 2434
0 2540
The carbonate method again gives results much lower t h a n t h e potassium oxalate, and t h e relation between t h e no lead a n d oxalate is as before. T h e oxalic acid results are higher t h a n a n y so far obtained. The high inverting power of oxalic acid ( I S . 7 t o I O O for HC1) is sufficient t o condemn it for routine work. The solution deleaded with carbonate was slightly alkaline b u t showed considerable lead when tested with hydrogen sulfide. T h a t from t h e potassium oxalate showed a trace Of lead. The combined precipitates f r o m t h e tests using potassium oxalate showed no lead when and with sulfuricacid” I
T h e work with no lead covered a period of several months, during which time the molasses sample was not remixed. Stratification and absorption of moisture may account for slight variations between sets of tests b y the same method in the different tables, Each table contains all t h e d a t a for the conclusions drawn from it, a n d comparisons must n o t be made between one method as shown in one table and another method as shown in another. Each table should be considered as dealing with a different sample of molasses. 2 “Analytical Chemistry,” Vol. 1, p. 349. 3 THISJOURNAL, July, 1915. 1
-
1 With some samples of molasses requiring 1 g. for a test i t has since been found t h a t the filtration of the cuprous oxide is somewhat slower than where lead is used.
T H E JOC'RllTdL O F I N D C ' 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
508
TABLE XI-COMPARISON BETWEEN X O LEAD hIETHOD, LEADA X D POTASSIUX OXALATE, LEADAND PHOSPHORIC a C I D , A N D LEAD,.4XD LEAD A X D DISODIUM PHOSPHATE.LEADSOLUTION 0.25 cc. PER GRAM OF MOLASSES Lead and 1 cc. 10% Lead Lead potassium and 0.7 cc. 10% and 3 cc. 10% No lead oxalate phosphoric acid disodium phosphate 0.2483 0.2501 0.2478 0.2488 0.2505 0.2499 0.2482 0.2510 0.2479 0.2477 0.2504 0,2500 0.2471 0.2482 0,2488 0.2504 0,2500 .. .. 0.2474 0.2491 _________ Av., 0.2479 0.2505 0.2479 0.2484 0.2498 0.2497 ~
~
The agreement between no lead, and lead and phosphoric acid is very close. The sodium phosphate results check those with potassium oxalate. T h e solutions deleaded wit,h phosphoric acid and with sodium phosphate were tested with hydrogen sulfide. and neither showed a n y lead whatever. These are the only ckses in which deleaded solutions were found quite free from lead. The results using phosphoric acid t o delead are so good t h a t the method seems worthy of a more extended inrestigation t h a n we have been able t o give i t so far. Since so many of t h e deleading agents failed t o delead completely. we thought it might be of interest t o r u n a few tests using lead without a n y deleading agent, i. e . ; le&ving the excess of lead in the solution. The precipitation showed no abnormality and t h e cuprous oxide was t h e usual color and filtered without difficulty. Tests were made on two separate v-eighings of two different molasses samples.
5'01. 8. NO.6
kieselguhr, with solutions of the strength necessary for the glucose test, the filtration was sufficiently rapid for practical purposes. and the resulting filt r a t e quite clear. X test was made on a raw sugar with fairly high glucose content, comparing t h e no lead method with tlarification with 0 . z j cc. lead solution and I cc. I O per cent potassium oxalate solution per I O g. of sugar. As it has been claimed t h a t weighing as cuprous oxide is sufficiently accurate for raw sugar determinations, t h e precipitates were first dried and weighed and then ignited and reweighed. in order t o obtain some figures on this point. TABLE XIII-5 GRAMS OF R A WSUGAR TO 50 cc. OF SOLUTION A-Clarified with 0.25 cc. Lead Solution and 1 cc. of 10 Per Cent Potassium Oxalate per 10 g. of Sugar Cur0 0.2192 0.2189 0.2212
cu
(calculated) 0.1947 0.1944 0.1965
~
Average.. . . . . . . . . Per cent glucose. , B-Clarified
CuO 0.2342 0.2329 0 2361
.~
0.1953 1.79
CU
(calculated) 0.1874 0.1863 0.1890
__
0.1876 1.69
with Kieselguhr Only, without Lead or Other Reagent cu CU Cu20 (calculated) CuO (calculated) 0.2174 0.1932 0.2328 0.1862 0.2179 0.1936 0.2337 0.1870 0.7195 0 1950 0.2353 0.1882
Average.. . , . . , . . . Per cent glucose. .
__
___.
0.1939 1.79
__
I _
0.18:l 1.68
The difference between t h e no lead. method and t h e lead and oxalate method is so slight as t o be immaterial. The copper b y Cu20 is appreciably higher TABLE XII-TESTS USINGLEADSoLrrIoN, 0.25 cc. P E R G R A MOF ~ I O L A S . S&S, WITHOUT DELEADING REAGENT.N O LEAD AiTD L E A D .4ND t h a n b y CuO,the difference being practically as great, OXALATE FOR COXPARISON calculated t o percentages of glucose content, as in Lead and Lead! without Molasses A S o lead potassium oxalate removing excess t h e case of final molasses. 0.2483 0 2499 0.2448 0.2448 T w o series of tests n-ith kieselguhr using no lead 0.2482 0.2502 0.2459 0.2447 .. .. .. 0.2471 were run on another sugar. N o further comparison 0.2454 0.2448 0.2501 Average.. , , . . . , . 0 2479 with other methods was considered necessary, in 0.3266 0.3267 0.3298 hIolasses B . . . . . . . 0.3282 view of t h e extended work already done with molasses. The lower figures where lead is not removed are TABLE XIV-wElGHTS OF CUO F R O M 5 GRAMSOF SUGAR directly opposite t o what had been expected. A j g of R a w Sugar to 50 cc. of Solution, using Kieselguhr and no Lead T w o Series of Tests on the Same Sugar possible explanation might be t h a t lead salts of re0.2619 0.2619 0.2633 ducing sugars are formed. which the oxalate breaks 0.2615 0.2661 0.2641 u p , b u t which are not broken u p b y the boiling with 0.2657 0,2645 0.2647 0.2656 Fehling's solution. Herein also may lie t h e explana__ 0 ,2643 0.2635 Average., . . . . . . . . tion for the low results obtained with sodium car- Per cent glucose. . I . 9 6 1.96 bonate. The lead salts of reducing sugars may be Minimum per cent glucose in 10 t e s t s . , . . , , , , . . . , 1 . 9 4 Maximum per cent glucose in 10 t e s t s . , , , , , . . . , . , 1 . 9 8 precipitated by t h e alkaline carbonate. s L'31~~ARY-Clarification with kieselguhr only, using REDUCIXG SCGARS Ili R A T V SUGARS no lead. is quite as practicable with raw sugars a s with The percentage of reducing sugars (or "glucose") final molasses: t h e greater density of t h e solution oft'erin raw sugars is so low as a rule t h a t fairly large variaing no difficulty in t h e filtration. The desirability tions in t h e weight of t h e proper precipitate make little apparent difference in the result. On t h e other of having t h e same method for both products is suffih a n d , t h e amount of raw sugar handled. both in t h e cient t o recommend it. Weighing t h e cuprous oxide direct without igniting factory and the refinery, is so much greater t h a n t h e amount of molasses produced t h a t small percentage is no more advisable in t h e case of raw sugars t h a n differences in t h e raw sugar glucose content affect with molasses. ,
t h e "glucose balance " perceptibly. The desirability of using t h e same method for both products is evident. The only difficulty which we thought might be encountered with raw sugar was t h a t of filtering a solution of such density (usually 20 grams t o I O O cc.) without defecation. However. we found on experimenting with several sugars, including molasses sugars and raws which had deteriorated, t h a t with
CONCLUSIOKS
I-Results differ with varying amounts of neutral lead acetate solution. 2-Carbonate, sulfates and oxalates are not interchangeable as deleading agents, oxalates giving results from 4 t o j per cent higher on t h e weight of copper t h a n where either of t h e others is used. 3-Kieselguhr only, without the use of lead or other
June, 1916
T H E JOl.R.V.4L O F I i V D L S T R I A L A A V D E.VGINEERI.VG C H E M I S T R Y
reagent, gives a clear filtrate. hoth mith final molasses a n d ran- sugar, a n d t h e solution offers no mechanical difficulty in t h e precipitation a n d collection of t h e copper precipitate. Without lead t h e results are slightly lower t h a n where lead a n d oxalate are used. 4-The use of a thermometer t o determine t h e beginning of t h e two-minute boiling period reduced t h e variations between tests on t h e same solution. j-Weighing as cuprous oxide gives results about j per cent higher. on t h e weight of copper, t h a n those obtained by igniting t o cupric oxide, whether working with final molasses or r a a sugars. Volumetric iodide determinations of t h e copper check t h e cupric oxide. 6-Cnder strict specifications as to t h e q u a n t i t y and class of reagents, a n y method for t h e preparation of t h e solution for analysis will give results which check within themselves.
509
connections for t h e warm water are illustrated in Fig. I, a n d furrher details of t h e thermo-slide are shown in t h e drawing, Fig. 11. PRocEntinE-The apparatus is arranged as shown in Fig. I , and t h e syphon started. then t h e flow adjusted b y means of t h e pinch-cock so t h a t t h e water will run a t t h e rate of not over I O O cc. :L minute; a second pinch-cock may be used as n total cut-off. The t e m perature in t h e flask is hrouEht t o 60' C . , then t h e heat controlled so t h a t t h e thermometer in t h e flask will indicate a rise of i o every minuie. The water bath (flask) and t h e microscope are placed not over 18 in. a p a r t so t h a t there will be hut little difference in t h e temperatures recorded in t h c flask a n t i in t h e slide. This differencc should not be over 3'. A small quantity of d r y starch is placed on t h e thermo-slide, moistened with :m cscess of \vatcr. and a cover
C E N T R A L CONIROL LIaoHroxv TIIECUBAN-AXEXICANSuc,\r C O X P I N Y C A R D E N I S . ccsn
THE DETERMINATION OF THE GELATINIZING TEMPERATURE OF THE STARCHES FROM THE GRAIN. SORGHUMS BY MEANS OF A THERMO-SLIDE By C. K. FRANCIS .AND 0. C . S M I T H Received January 17. 1916
The usual method for determining t h c gelatinizing temperature of starches requires t h a t small quantities of t h e material be placed i n test tubes immersed in a water b a t h , t h e temperature of which is gradually raised; t h e n portions of t h e starch are removed at intervals for microscopical examination. This has been found a tedious method a n d t h e results not so accurate as desired. The apparatus designed for our work on t h e starches obtained from t h e various grain sorghums permitted direct readings so t h a t a large number of tests were made in a comparatively short time; triplicate determinations checked well within one degree. The thermo-slide, Fig. I , was made in this laboratory and may easily be constructed by any one having a little ability t o handle tools. The material consists of: ( I ) Three pieces of steel j in. long. i3Is in. wide a n d ' i g in. thick. with a central opening ? / g X z 3 V 4 in. cut in each piece. approximately 1 in. from each end and I / d in. from each side; two I;, in. nipples are fitted into t h e steel piece, No. I , t h e holes for these being drilled in. from each e n d ; two openings, ' i d in. wide, are cut in steel piece No. 2 , as indicated in t h e top view in Fig. 11. ( 2 ) Two Elass slides I X 3 in. (3) Six rubber gaskets, X j, cut from "16 in. rubber sheets: two of these gaskets are cut t o match steel plate S o . 2 . The pieces of steel anti ruhber have two ',fa in. holes drilled in each end through which holts pass t o clamp t h e entire system together. T h e J/4 in. piping is connected by means of nipples fitted into t h e top plate. The thermometer is small enough t o fit inside t h e T opposite the exit pipe a n d t h e opening made water-tight by slipping a piece of tubing over t h e thermometer and t h e nipple. The general arrangement of t h e micro-polariscope. t h e thermo-slide a n d
Fm. I
glass placed over it. T h e low power (16 mm.) oh-. jective is adjusted a n d focused, t h e n t h e analyzer p u t in place and turned t o t h e dark field, The water is now turned on a n d t h e temperature noted when all t h e starch granules have lost their polarizing properties. This temperature should not he considered t h e correct one, h u t is t o be used as a guide. The slide is now cleaned and a second portion prepared in t h e same way as has heen descrihed. The water i n t h e flask is heated t o t h e same degree which was recorded for t h e preliminary test; this gives a temperature in t h e thermo-slide about 2-3' below t h a t first found, a n d , consequently, below t h e gelatinization point. The temperature of the water is
