IN D U S T R IA L andENGINEERING C H E M IS T R Y
V ol. 30, Consecutive N o. 47
H a r r is o n E. H o w e , E d ito r
ANALYTICAL EDITION
20,100 Copies of This Issue Printed
December 15, 1938
Vol. 10, No. 12
An a l y s i s o f Su g a r Mi x t u r e s Co n t a i n i n g De x t r o s e,
Le v u l o s e, Ma l t o s e, a n d La c t o s e...
...F. W . Zerban and Louis Sattler 669
Li q u i d- Li q u i d Ex t r a c t i o n i n Se p a r a t i o n o f Pe t r o
l e u m Ac i d s...Henry G. Schutze, Walter A. Quebedeaux, and H . L. Lochte 675
Pr e p a r a t i o no f I Iy d r i o d i c Ac i d Su i t a b l e f o r Al k o x y l
a n d Fr i e d r i c h- Kj e l d a h l Ni t r o g e n De t e r m i n a t i o n s
... E. P. Clark 677
De t e r m i n i n g Se d i m e n t Co n t e n t o f Fu e l Oi l . . . .
...S. H . Hulse and H . L. Thwaites 67S
Pl a s t o m e t r y o f Sy n t h e t i c Re s i n s...
...R. Houwink and Ph. N . Heinze 680
Ti t r i m e t r i c St e p i n De t e r m i n i n g Ro t e n o n e . . . .
... Howard A. Jones 684
Si m p l e Me l t i n g Po i n t Ou t f i t...Jesse Werner 685
D e t e r m i n a t i o n o f O r g a n i c S u l f u r w i t h S p e c i a l R e f
e r e n c e TO SuLFON E S A N D SULFOXIDES . G. H . Young 6 8 6
S t a n d a r d i z a t i o n o f 2 , 6 - D i c h l o r o p h e n o l i n d o p h e n o l
w i t h F e r r o u s C o m p o u n d s ...
...A. J. Lorenz and L. J. Arnold 687
D e t e r m i n a t i o n o f S u l f u r i n S u r f a c e - A c t i v e A g e n t s
... Ralph Hart 6 8 8
S u l f a m i c A c i d a s S t a n d a r d o f R e f e r e n c e i n A c i d i m e -
t r y . . . . M . Josetta Butler, G. Frederick Smith, and L. F. Audrieth 690
Pr e c i p i t a t i o n o f Ni c k e l .a n d Co b a l t Su l f i d e s i n
Cr y s t a l l i n e St a t e... E . A. Ostroumov 693
Se p a r a t i o n o f Co b a l t a n d Ni c k e l f r o m Ma n g a n e s e
. E . A. Ostroumov and G. S. Maslenikova 695
Ne w Ca t a l y s t f o r De t e r m i n a t i o n o f Ni t r o g e n b y
Kj e l d a h l Me t h o d R. B. Bradstreet 696
De t e r m i n a t i o n o f Pa l l a d i u m b y Me a n so f Po t a s s i u m
Io d i d e...F. E . Beamish and J. Dale 697
De t e r m i n a t i o n o f Fr e e So d i u m Cy a n i d e a n d Am
m o n i a i n Br a s s Pl a t i n g So l u t i o n s...
... Samuel Heiman and Wallace M . M cN abb 698
De t e r m i n a t i o n o f Di s s o l v e d Ox y g e n ...
. C. C. Ruchhoft, W . Allan Moore, and O. R. Placak 701
De t e r m i n a t i o n o f Fr e e Su l f u r i n Fe r t i l i z e r s . . .
F. B. Carpenter 703
Mo d e r n La b o r a t o r i e s
Mi c r o c h e m i c a l La b o r a t o r y o f Ab b o t t La b o r a
t o r i e s ... E . F. Shelberg 704
Au t h o r In d e x... 7 0 7
S u b j e c t I n d e x ...7 1 1
T h e American Chemical Society assumes no responsibility for the statem ents and opinions advanced b y contributors to its publications.
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4 INDUSTRIAL AND ENGINEERING CHEMISTRY VOL. 10, NO. 12
It has been estimated that 60,000,000 people will visit the New York W orld’s Fair in 1939- Many o f those who choose to reach the Fair grounds via motor vehicle from Manhattan and the Bronx, will drive over the spacious Triborough Bridge, an outstanding example o f modern engineering achievement.
Representing an expenditure o f $63,000,000 for land and labor, iron, steel, concrete, cement, lighting, and other equipment, there was another item which played an equally
important, though less spectacular part in the successful completion o f this enormous project. We refer, o f course, to the reagent chemicals which were used by research chem
ists for the analysis and testing o f basic materials used in the work o f construction.
In such exacting laboratory work, Merck Reagent Chem
icals are used by exacting chemists because their purity and dependability ensure uniformly satisfactory results. A catalog will be mailed on request.
M E R C K & C O . I N C .
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DECEM BER 15, 1938 ANALYTICAL EDITION 5
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♦Lubricants are necessary on ordinary ground glass join ts to facilitate rotating one portion o f the connection and to prevent sticking. “ N o Lub” join ts are processed with a material (patent pending) which allows their use even under extreme conditions without sticking. There is no surfacing material on “ N o Lub” parts to wear off, and service tests show that im provem ent o f lubricating quality takes place during use. These join ts are n ot affected b y chemicals which do not attack the glass itself. N o fouling o f burette columns as no lubricant is used.
All interchangeable join ts are constructed in strict accordance with the requirements o f the National Bureau o f Standards specifications.
M ark you r orders “ N o Lub” and all ground join ts and stopcocks o f P yrex glass or lime glass will be processed “ N o Lub” at no increase in cost. A t the same time we are reducing prices on ground glass join ts and apparatus equipped with join ts below those listed in our catalog GG5-38.
D O Y O U H A V E O U R L A T E S T C A T A L O G G G 5 -3 8
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6 INDUSTRIAL AND ENGINEERING CHEM ISTRY VOL. 10, NO. 12
Especially Suited to
Eleetrom etrle Measurements
P O T A S S I U M P H O S P H A T E M O N O B A S I C A. R.
S O D I U M P H O S P H A T E D I B A S I C A N H Y D R O U S A. R.
(b y M allinckrodt)
These two salts are especialy refined for use in buffer solutions for hydrogen- iori determinations. The Potassium salt meets both A.C.S. and Sorenson specifi
cations. The Sodium salt, being anhy
drous, should be used in correspond
ingly smaller amounts than the salt described by Sorenson which is a two- water salt. Also refined to predetermined standards of purity are the buffer salts, Potassium Acid Phthalate A. R. Primary Standard and Acid Boric A. R. Crystals.
Other Reliable Mallinchrodt Reagents for Electrom etric Titrations
CHEMICAL WORKS
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A M M O N IU M P E R S U L F A T E A . R . P O T A S S IU M C H L O R ID E A . R . M E R C U R O U S CH L O R ID E A . R . P O T A S S IU M D IC H R O M A T E A . R . M E R C U R Y A . R . P O T A S S IU M P E R M A N G A N A T E A .R . P L A T IN U M CH L O R ID E A . R . SIL V E R N IT R A T E A . R .
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m ined m a xim u m lim its o f im purities for these and nearly 500 other reagents and laboratory chemicals.
DECEM BER 15, 1938 ANALYTICAL EDITION 7
Why Use
There are a n u m b e r of reasons w h y C h e m ists in all lines of I n du stry specify W H A T M A N F ilter Papers and refuse to accept a n y s u b s titu tio n . T h e y have fo u n d W H A T M A N F ilter Papers u n ifo rm in rapid ity and retentiven ess. T h ey kn ow th a t th e low ash w eight show n on th e box represents th e a ctu a l ash th ey w ill find w h en th ey use th e paper. T h e y like th e n ea t, efficient p a ck in g , th e w rapping of th e acid w ashed grades in c ello p h an e to resist d u st and fu m e s.
T h e y kn ow th a t th ey can o b ta in W H A T M A N F ilter Papers p r o m p tly , since all recognized dealers carry stocks for im m e d ia te delivery and th ese sto ck s are a u g m e n te d by a large stock in our N ew Y o r k w are
h ou se.
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CO., INC.7-11 SPRUCE ST., NEW YORK, N. Y.
INDUSTRIAL AND ENGINEERING CHEM ISTRY VOL. 10, NO. 12
IN A NEW CONSTANT TEMPERATURE DRYING OVEN
Low first cost, economy of operation, simplicity of control, wide range of temperature settings, beauty and utility combine to make the new Cenco-deKhotinsky Oven a desirable and inexpensive addition to the equipment of any laboratory requiring a space in which accurate tem
perature control is achieved.
Its temperature range is from that of the room to approximately 2 1 0 degrees centigrade above surrounding temperature. It can therefore be used as an incubator, a drying oven, a sterilizer, or as a baking oven for varnishes, lacquers and japans, as well as for curing synthetic resins.
Temperature constancy and uniformity in the oven chamber are ex
cellent. Departure from average temperature at any point in the operating range is within one degree centigrade. The temperature control unit, which is of utmost simplicity', is independent, both struc
turally and functionally, of the oven chamber; but the expansible element is located wholly within the chamber, with the result that it responds quickly to temperature changes. No relay is employed.
The heating current is turned on and off automatically by means of a snap-action control switch.
The oven chamber is so well insulated that at maximum temperature the input is only 400 watts— about 4 0 % less than that required for an electric toaster or flatiron. The heating units operate considerably below incandescence, and are not exposed to the air in the oven cham
ber; and the switching and control mechanisms are entirely removed from the chamber. Without change in heating units, the oven may be operated on either 115 or 230 volts A.C., merely by throwing a switch.
The external housing is made of metal and finished with aluminum
"shrivel” finish. The design is modern, with chromium-plated hinges
and latch. •
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DECEM BER 15, 1938 ANALYTICAL EDITION 9
NORTON
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W here furnaces of this design are applicable Alundum Cores give excellent results. M ade of electrically fused alumina, they are extremely refractory and can operate at any temperature which would be demanded. In addition, they are chem ically inert and extremely resistant to wear.
A t the left is a drawing of a pot furnace utiliz
ing an internally wound A lundum Core. The furnace is simple in design and can be easily constructed in the laboratory.
N O R T O N C O M P A N Y , W O R C E S T E R , M A S S .
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10 INDUSTRIAL AND ENGINEERING CHEMISTRY VOL. 10, NO. 12
POLARIM ETERS, HALF SH AD E, Duboscq. T h e double field is divided vertically, and the polar
izers are o f the Jellet-C orn u -D u b oscq typ e, which are adjustable for sensitivity, i.e., with variable half
shade angle w hich perm its m ore or less polarization with reference to the greater or less absorption o f the solution under investigation. T h e y have adjustm ent for zero, and m irror for illum ination o f scales.
C om pensationus b y rotation o f the analyzer. T h e scales read in angular degrees and they, together with the half shade system s are adjusted for the D sodium line 5892A. These instrum ents are, therefore, n ot recom m ended for use w ith sources o f light o f other w avelengths such, for example, as that o f the M ercu ry V apor lam p, i.e. 5461A, and can not be used with p olych rom a tic light. T h e troughs were heretofore m ade to take on ly French tubes o f 41.5 m m diam eter, b u t are now m ade specially for us with troughs to take tubes of 29 to 30 m m diam eter, such as are now in m ore general use.
8341. Polarimeter, Half Shade, Duboscq, as above described, for tubes up to 200 mm long, and with scale reading by vernier to 2 minutes, i.e. 1 /3 0 ° of arc. W ith one each 100 and 200 mm tubes and Sodium Lamp for gas, as a source of mono
chromatic light. On tripod base, in case with lock and key ... 260.25 Code W ord... Myzdl 8343. Polarimeter, Half Shade, Duboscq Precision Model, as above described, for tubes up to 500 mm long, and with scale
on divided circle 27 cm diameter, reading by vernier to 1 /1 0 0 ° of arc. This instrument was used by M M . Mascart and Bdnart for the official determination of the present French normal weight, 16.29 grams. See Annales de Chimie et Physique, 1899. W ith one each 100, 200 and 400 mm tubes and Sodium Lamp for gas. On tripod base with leveling screws, in case with lock and k e y ... 459.75 Code W o rd ... Naamo
T h ese two Polarim eters, together w ith th e N o. 8356 D uboscq Sacch arim eter listed on page 6 6 6 o f our current catalogue, are m ad e specially for us by th e original French m an u factu re r, and have been sold by us w ith u n i
versal satisfaction to the purchasers for over tw enty years.
ARTHUR H. TH O M A S COMPANY
R E T A I L — W H O L E S A L E — E X P O R T
LABORATORY APPARATUS AND REAGENTS
W E S T W A SH IN G TO N S Q U A R E P H IL A D E L P H IA , U .S.A .
Cable Address, “ B alance,” Philadelphia
D U B O S C Q
HALF SHADE P O LA R IM E T E R S
I N O U R S T O C K F O R I M M E D I A T E S H IP M E N T
INDUSTRIAL »»a ENGINEERING CHEMISTRY
A N A LYTIC A L EDITION ♦ Harrison E. H ow e, Editor
Analysis of Sugar Mixtures
Containing Dextrose, Levulose, Maltose, and Lactose
F . W . Z E R B À N a n d L O U IS S A T T L E R New Y o rk Sugar Trade Laboratory, New Y o rk , N . Y .
D
URING the past few years methods for the determination of dextrose and levulose in sugar products have been studied in this laboratory. A procedure applicable to raw cane sugars has been published (17, 18), and likewise one for cane molasses (5). Some food products also contain mal
tose and lactose, and the investigation has been extended to include these sugars as well. Sucrose can be estimated in the presence of the other four sugars by means of invertase, and for this reason only the four reducing sugars are considered in this article.
With such complex sugar mixtures it is usually necessary to resort to combined methods, as has been pointed out by Browne (2, 8), because there are few reactions which permit the quantitative separation of one sugar from all the others.
Selective fermentation with specific organisms has been em
ployed successfully by a number of investigators, but the necessary pure cultures are not always readily available, they require painstaking technique in their propagation and applica
tion, and in the usual chemical laboratory used for sugar analysis it is difficult to prevent contamination.
Chemical methods have lately become available for the selective determination of levulose and of monosaccharides, and have been applied to the analysis of sugar mixtures. This suggested their possible use in the analysis of mixtures of the four sugars in question.
Principle o f the M ethod
The determination of four sugars by combined methods re
quires four equations. In the absence of salts and organic impurities the total solids or the polarization may serve as criteria, but such cases are rare in practice, and it is generally necessary to depend on methods that are less affected by ac
companying impurities. Lactose is the only sugar among the four that can be determined independently. It may either be oxidized to mucic acid and weighed in this form, or else the other three sugars may be removed by fermentation with yeast, and the residual lactose estimated by any suitable method. The dextrose and levulose may be determined by combining Jackson and Mathews’ modification of the Nijns method (8) for the selective determination of levulose with the method of Steinhoff (14) for the selective determination of monosaccharides in the presence of disaccharides by means of a modified Barfoed reagent. The total reducing sugars are found with Fehling solution.
If G = mg. of dextrose (glucose) F = mg. of levulose (fructose) M = mg. of maltose hydrate L = mg. of lactose hydrate
R\ — mg. of apparent levulose by the method of Jackson and Mathews
i?2 = mg. of dextrose plus levulose, expressed as levulose, by the .copper acetate method of Steinhoff
R3 = mg. of total reducing sugars, expressed as dextrose, by Fehling solution
then
L is determined separately (1)
Rx = 0.0806 G + F (2)
R2 — aG -f- F (3)
R , = G + bF + cM + dL (4) The factor 0.0806 in .Equation 2 is the reducing ratio of dextrose to levulose (12.4 mg. of dextrose have the same reduc
ing power as 1 mg. of levulose). Factor a is the reducing ratio of dextrose to levulose in Steinhoff’s acetate method, and b, c, and d are the reducing ratios of levulose, maltose, and lac
tose, respectively, to dextrose for Fehling solution. The values of a, b, c, and d vary with the concentration, and are found from tables.
By solving Equations 2 and 3 for G and F, we find r, Ri — Ri
~ a — 0.0806 and
F = R t - aG L, G, and F being known, Equation 4 gives
M = R , — (G + bF + dL) c
If the disaccharides had no reducing effect whatever on the reagents employed for the determination of the monosac
charides, as claimed by the original authors of the methods, the procedure and the calculation of the results would be simple. But it has been found that both maltose and lactose have a slight reducing effect on the Jackson and Mathews reagent, as well as on the Steinhoff copper acetate reagent.
This subject, and the procedure for applying the necessary corrections are discussed below.
D eterm ination o f Lactose
The writers first tried the mucic acid method of Tollens.
Kent, and Creydt (4, 9), as modified by van der Haar (6), The method lacks precision, as stated by van der Haar him
669
670 INDUSTRIAL AND ENGINEERING CHEMISTRY VOL. 10. NO. 12 self, differences of as much as 8 mg. of mucic acid being some
times obtained in duplicate determinations. It is not very- accurate either and usually gives low results in the presence of other sugars or nonsugars. The galactose, found from van der Haar’s Table I and multiplied by 2, should give lactose hydrate, but experiments by the writers with known sugar mixtures have given an average factor of 2.2. With low percentages of lactose in the mixture the method gives fairly satisfactory results, sufficiently exact for practical purposes but it is not recommended.
The method finally adopted is a modified form of the fer
mentation procedure of Hoffman, Schweitzer, and Dalby (7).
The sample is placed in a 500-ml. volumetric flask, and a thin suspension of a mixture containing 35 grams of compressed bakers’ yeast, 0.5 gram of ammonium sulfate, and 0.2 gram of sodium bisulfite in water is added. The mixture in the flask is further diluted with water to a volume of about 400 ml. The flask is closed with a stopper provided with a delivery tube, the outer end of which is immersed I cm. below the surface of water in a beaker. The flask is placed in a water bath or thermostat kept at 30° C ., and it is shaken from time to time.
After standing a minimum of 4 hours, 15 ml. of a 20 per cent solution of neutral lead acetate are added, and the volume is made up to the mark at 20° C. Next, 1 gram of Filter-Cel is added, and the contents of the flask are thoroughly shaken and filtered through a folded quantitative filter paper. The first, turbid portion of the filtrate is discarded, and exactly 2 0 0 ml.
of the clear filtrate are collected in a dry volumetric flask cali
brated for 200- and 220-ml. contents. To the 200-ml. solution 15 ml. of a phosphate-oxalate solution are added, prepared by dissolving 7 grams of disodium phosphate (NaiHPOj. 12H20 ) and 3 grams of potassium oxalate (K2C20 < . H.O) to 100 ml.
The flask is made up to the 220-ml. mark at 20° C., 0.5 gram of Filter-Cel is added, and the contents are shaken vigorously.
The solution is filtered through a quantitative filter paper, and the clear filtrate is collected for the sugar determination. Lactose can be determined by any of the standard methods, such as the Munson and Walker method used by the writers.
The fermentation method should be carried out with a reliable brand of yeast, and its fermenting power should be checked by appropriate tests. Blank tests run with a good yeast usually yield very low reduction values, and the results are not trustworthy for corrections. It is a much better practice to use pure lactose for the purpose. It is therefore recommended to run parallel determinations with lactose alone, or with a known sugar mixture approximating that of the sample.
To give an example, 1.056 grams of lactose were treated in the 500-ml. flask. After the fermentation, 200 ml. of the filtrate, containing 0.4224 gram of lactose, were made up to 220 ml., and of the final filtrate 50 ml., containing 96 mg. of lactose, were used for the sugar determination. Found, 0.1622 and 0.1601 gram of cupric oxide; average, 0.1612 gram of cupric oxide, corresponding to 128.8 mg. of copper and 97.5 mg. of lactose hydrate. In another experiment a mixture of 1.056 grams of lactose, 0.704 gram each of maltose and dextrose, and 0.176 gram of levulose was similarly treated, and there was obtained 0.1626 and 0.1621, an average of 0.1624 gram of cupric oxide, corre
sponding to 98.2 mg. of lactose hydrate. The higher result is due in part to the volume occupied by the yeast and the lead precipitates in the flasks, and in the second case possibly to un
fermented reducing substances. A corresponding correction must be applied to the result obtained upon the sample analyzed.
Determ ination o f the Apparent Levulose This is carried out according to the directions of Jackson and Mathews (S). It has been found by the writers that both majtose and lactose reduce the copper carbonate reagent.
The reducing effect is smaller than that of dextrose, but much larger than that of sucrose. It varies not only with the con
centration of these sugars alone, being relatively greater for higher concentrations of them, but also with the concentration of dextrose and levulose present in mixtures, the reducing power also increasing with the total sugar concentration. The variations are small, however, and for practical purposes
average figures may be used to correct for the reducing effect of maltose and lactose. An average of 26.0 mg. of maltose hydrate and 25.6 mg. of lactose hydrate was found to be equivalent to 1 mg. of levulose.
D eterm ination o f Dextrose Plus Levulose The reduction method of Steinhoff has been retained with only slight changes, but the estimation of the reduced copper had to be modified. Steinhoff acidifies the reaction mixture while it is still hot, and immediately adds standard iodine solution. After cooling, the excess iodine is titrated back with standard thiosulfate. This procedure leads to uncertain results because the iodine added to the hot solution is partly volatilized. The writers have therefore adopted the iodo- metric method of Shaffer and Hartmann (12), modifying it to suit the particular conditions.
The following reagents are used:
Sodium acetate solution, prepared by dissolving 500 grams of the crystallized salt (C H3C O O N a . 3H20 ) in about 800 ml. of hot water, cooling, and making up to 1 liter.
Sulfuric acid, about 2 N, prepared by diluting 57 ml. of con
centrated acid to 1 liter.
Potassium iodide-iodate solution, prepared by dissolving 5.4 grams of potassium iodate and 60 grams of potassium iodide to a total volume of 1 liter. The solution is made alkaline by adding 0.25 gram of sodium hydroxide dissolved in a little water before completing the volume.
Saturated solution of potassium oxalate, prepared by dis
solving 165 grams of the hydrated salt (K2C ;0 4. H20 ) in 500 ml.
of hot water, and cooling to room temperature.
0.1 N thiosulfate solution, exactly standardized by iodo- metric determination with potassium dichromate.
Soxhlet copper sulfate solution (Fehling I), prepared according to the directions of the Association of Official Agricultural Chemists (I).
Ta b l e I. Co p p e r Ac e t a t e Re a g e n t
(M illigram s of dextrose or levulose corresponding to varying volum es of 0.1 N thiosulfate solution; reducing ratios for varying proportions between
levulose and dextrose)
Th io D ex Levu 100 levulose
---IVCUULIllg
75 levulose 50 levulose 25 levulose sulfate trose lose 0 dextrose 25 dextrose 50 dextrose 75 dextrose
M l. M g . M g .
1 5 . 0 3 . 2 0 .6 4 0 0 .5 5 6 0 .8 2 9 0 .8 5 2
2 7 . 0 5 . 8 0 .8 2 9 0 .8 0 3 0 .9 3 3 0 .9 5 6
3 9 . 0 8 . 3 0 .9 2 2 0 .9 5 2 0 .9 7 6 1 .0 0 0
4 1 1 .1 1 0 .7 0 .9 6 4 1 .0 0 0 0 .9 8 1 1 .0 1 3
5 1 3 .3 1 2 .9 0 .9 7 0 0 .9 8 0 0 .9 5 5 1 .0 1 0
6 1 5 .5 1 4 .9 0 .9 6 1 0 .9 5 3 0 .9 3 0 0 .9 8 4
7 1 7 .8 1 6 .8 0 .9 4 4 0 .9 1 4 0 .9 0 5 0 .9 5 7
8 2 0 .3 1 8 .6 0 .9 1 6 0 .8 9 7 0 .8 8 0 0 .9 3 1
9 2 2 .9 2 0 .3 0 .8 8 6 0 .8 7 0 0 .8 5 5 0 .9 0 6
10 2 5 .7 2 2 .1 0 .8 6 0 0 .8 4 5 0 .8 3 0 0 .8 8 0
11 2 8 .7 2 3 .9 0 .8 3 3 0 .8 1 9 0 .8 0 5 0 .8 5 3
12 3 1 .8 2 5 .7 0 .8 0 8 0 .7 9 3 0 .7 8 0 0 .8 2 5
13 3 5 .4 2 7 .7 0 .7 8 2 0 .7 6 7 0 .7 5 5 0 .7 9 7
14 3 9 .0 2 9 .4 0 .7 5 4 0 .7 4 7 0 .7 3 0 0 .7 6 9
15 4 3 .3 3 1 .4 0 .7 2 6 0 .7 1 5 0 .7 0 6 0 .7 4 0
16 4 7 .9 3 3 . 6 0 .7 0 1 0 .6 8 8 0 .6 8 1 0 .7 1 1
17 5 3 .3 3 5 . 8 0 .6 7 2 0 .6 6 6 0 .6 5 6 0 .6 8 1
18 5 9 .5 3 8 .4 0 .6 4 5 0 .6 4 0 0 .6 3 1 0 .6 5 1
19 6 6 .6 4 0 .9 0 .6 1 2 0 .5 9 5 0 .6 0 5 0 .6 2 1
20 7 4 . 6 4 3 . 8 0 .5 8 7 0 .5 8 3 0 .5 8 1 0 .5 9 3
21 8 4 .1 4 6 .9 0 .5 5 8 0 .5 5 5 0 .5 5 5 0 .5 6 4
22 9 5 .0 5 0 .5 0 .5 3 2 0 .5 3 0 0 .5 2 9 0 .5 3 6
Ten milliliters of the copper sulfate solution and 20 ml. of the sodium acetate solution are pipetted into a 250-cc. wide
mouthed Erlenmeyer flask, and a measured amount of the sugar solution is added. The quantity of sugar solution must be such that the thiosulfate corresponding to the copper re
duced is within the limits of Table I, and that the thiosulfate corresponding to the copper reduced from Fehling solution by the same quantity of sugar solution is within the limits of Table II. A fewr preliminary experiments are usually neces
sary to ascertain the optimum amount for both determina
tions.
After the sugar solution has been added, the volume is com
pleted to a total of 50 ml. by the addition of water. After
DECEM BER 15, 1938 ANALYTICAL EDITION 671 thorough mixing, the Erlenmeyer is closed with a rubber stopper
provided with a Bunsen valve, to prevent reoxidation of the reduced copper. The solution is placed in a briskly boiling water bath, the stop watch started, and the flask removed from the bath after exactly 20 minutes. It is then quickly cooled to room temperature under a water tap. During this time the Bunsen valve must be vented from time to time to prevent boiling caused by the vacuum. After cooling, 25 ml. of the iodide-iodate solution are carefully added from a pipet and mixed with the solution by gentle shaking. Then 40 ml. of the 2 Ar sulfuric acid are run in rapidly from a measuring cylinder, the flask being rotated to wash down the inside wall. This is followed by the addition of 2 0 ml. of the potassium oxalate solution from a measuring cylinder. The contents of the flask are well mixed until the precipitate is completely dissolved, and the excess iodine is titrated with the standard thiosulfate.
A blank is run with water instead of sugar solution. The difference between the thiosulfate titer of the blank and that of the sample is a direct measure of the cuprous oxide precipitated.
Ta b l e II. Co p p e r Ta r t r a t e Re a g e n t
(M illigram s of dextrose corresponding to varying volum es of thiosulfate solution, and reducing ratios of levulose, maltose, and lactose, with respect
to dextrose)
Thiosulfate 7?j,
Dextrose Levulose, b
-R ed ucing R atios
M altose hydrate, c
Lactose hydrate, d M l.
1
M g .
2 . 2 0 .6 4 8 0 .3 9 4 0 .4 9 9
2 5 . 3 0 .8 1 5 0 .4 8 1 0 .6 1 6
3 8 . 5 0 .8 6 8 0 .5 0 8 0 .6 5 3
4 1 1 .6 0 .8 9 3 0 .5 2 1 0 .6 6 9
5 1 4 .8 0 .9 0 7 0 .5 2 8 0 .6 7 8
6 1 8 .0 0 .9 1 4 0 .5 3 2 0 .6 8 3
7 2 1 .2 0 .9 1 8 0 .5 3 5 0 .6 8 5
8 2 4 .4 0 .9 2 1 0 .5 3 7 0 .6 8 6
9 2 7 .6 0 .9 2 2 0 .5 3 8 0 .6 8 9
10 3 0 . 8 0 .9 2 2 0 .5 3 8 0 .6 8 5
11 3 4 . 0 0 .9 2 1 0 .5 3 8 0 .6 8 4
12 3 7 .2 0 .9 2 0 0 .5 3 8 0 .6 8 3
13 4 0 .5 0 .9 1 8 0 .5 3 7 0 .6 8 1
14 4 3 .7 0 .9 1 7 0 .5 3 7 0 .6 7 9
15 4 7 . 0 0 .9 1 4 0 .5 3 6 0 .6 7 7
16 5 0 .2 0 .9 1 2 0 .5 3 6 0 .6 7 5
17 5 3 .5 0 .9 1 0 0 .5 3 6 0 .6 7 2
18 5 6 . 8 0 .9 0 7 0 .5 3 4 0 .6 7 0
19 6 0 .0 0 .9 0 4 0 .5 3 3 0 .6 6 8
20 6 3 .3 0 .8 9 5 0 .5 3 1 0 .6 6 5
21 6 7 .1 0 .8 9 7 0 .5 3 4 0 .6 6 8
22 7 1 .3 0 .9 0 1 0 .5 4 0 0 .6 7 3
23 7 5 . 5 0 .9 0 5 0 .5 4 5 0 .6 7 8
24 8 0 .0 0 .9 1 0 0 .5 5 1 0 .6 8 5
25 8 5 .1 0 .9 1 5 0 .5 6 1 0 .6 9 5
Results of duplicate determinations usually check within 0.1 to 0.2 ml. of thiosulfate. But larger discrepancies occur occasionally, due to the following causes:
Differences in buret drainage, because of the relatively larger amounts of thiosulfate run out and the greater speed of their removal in blank determinations, may cause an error amounting to 0.15 ml.
A difference of one drop in the quantity of the iodide-iodate solution pipetted out causes an error of as much as 0.15 ml. of thiosulfate, and for this reason the emptying of the pipet must be carefully standardized.
The end point, determined with starch solution, while sharp, is affected by light conditions. It is best to use a daylight lamp, and to prepare a blank solution of the copper reagent for com
parison.
The precipitate must be completely dissolved before the titration with thiosulfate. Without this precaution there may be fading of the end point, indicating incomplete solution.
The boiling water in the bath causes a certain amount of agita
tion of the contents of the flasks, and variations in this factor affect the results. The water must be boiling briskly in all parts of the bath. It may be preferable to use a constant- temperature bath kept at 100° C. by the use of a higher boiling liquid, and to agitate the flasks mechanically.
If the Erlenmeyer flasks are not thoroughly clean, the copper precipitate tends to creep up on the walls. To prevent this, the flasks should be cleaned regularly with chromic acid mixture.
The reducing effect of dextrose and levulose, obtained from the National Bureau of Standards, and of mixtures of the two, on the copper acetate reagent was determined, and the results are shown in Table I, which gives the milligrams of
dextrose or levulose equivalent to the number of milliliters of thiosulfate found, and also the values of the factor a in Equation 3, for varying proportions between the two sugars.
D eterm ination o f T otal Reducing Sugars In this determination, 10 ml. of Soxhlet copper sulfate solution (Fehling I) and 10 ml. of alkaline tartrate solution (Fehling II), both prepared according to the directions of the Association of Official Agricultural Chemists (1), arc mixed in a 250-cc., wide-mouthed Erlenmeyer flask. The same quantity of sugar solution as was used in the determination of dextrose plus levulose is added, the volume is made up to a total of 50 ml., and the analysis is carried out exactly as described for that determination, except that only 25 ml. of the 2 N sulfuric acid are used instead of 40 ml.
The reducing effect on the copper tartrate reagent has been measured for dextrose, levulose, maltose, and lactose. The results are shown in Table II, which gives the milligrams of dextrose corresponding to varying milliliters of 0.1 A thiosul
fate solution, and the values of the factors b, c, and d (reducing ratios of levulose, maltose hydrate, and lactose hydrate with respect to dextrose) in Equation 4. These reducing ratios are very close to those for the Munson and Walker method, as would be expected.
Reducing Power o f M ixtures o f Sugars Two hypotheses have been used to account for the com
bined reducing effect of sugars present in mixtures. One of these assumes that the reducing effect is an additive prop
erty— for example, the copper reduced by a mixture of a mg.
of dextrose and b mg. of levulose is expected to be the sum of the copper reduced by a mg. of dextrose and b mg. of levulose, each present alone. Schwartz (11) found, however, that the reducing power of mixtures is governed by a rule analogous to that observed by Yosburgh (16) for the specific rotation of sugar mixtures. This rule states that the specific rotations in a mixture of two sugars are equal to the specific rotations which each sugar would have if present at the total sugar concentration. Similarly, the amount of copper reduced by a mg. of invert sugar is the sum of one-half of the copper re
duced by a mg. of dextrose and one-half of the copper reduced by a mg. of levulose. This “ fractional proportionality” rule is illustrated by the following example from the reduction tables of Quisumbing and Thomas (10):
Copper
•. ' M g .
200 m g. of invert sugar alone 3 7 2 .1
100 m g. of dextrose alone reduce ' 2 0 1 .2
100 m g. of levulose alone reduce 1 8 5 .0
200 m g. of invert sugar, according to the simple additive ---
rule, would reduce 3 8 6 .2
200 m g. of dextrose reduce 3 8 6 .0
200 mg. of levulose reduce 3 6 0 .0
One-half of copper reduced b y 200 mg. of dextrose equals 1 9 3 .0 One-half of copper reduced by 200 m g. of levulose equals 1 8 0 .3 200 m g. of invert sugar, according to the fractional pro- ---
portionality rule, would reduce 3 7 3 .3
The last figure checks within 1.1 mg. with the copper actu
ally found, while the simple additivity rule gives 14.1 mg. of copper too much.
Analogously, the amount of copper reduced by a mixture of 50 mg. of dextrose and 150 mg. of levulose equals the sum of one-quarter of the. copper reduced by 200 mg. of dextrose and three-quarters of the copper reduced by 200 mg. of levulose.
The simple additivity rule has been found to give correct results, within the limits of error, in those cases where the re
ducing effect of one sugar is very small with respect to that of another, as, for instance, for mixtures of levulose and dextrose analyzed by the method of Jackson and Mathews. The frac
