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<TDNCAN>
COPPER
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Vol. 1, No. 4 October 15, 1929
Chemical Analysis
YiLbiisnea o y m ejitn en ça n cnemicai ùoeiery
Physical and Mechanical Testing
Edition
POLITECHNIKI
Laborątor^Appliances
2 A N A L Y T IC A L EDITION Vol. 1, No. 4
Solutions
To
Laboratory Filtration Problems
T h e F ish e r C atalog, A n sw ers
W h ic h Grade o f Filter Paper is best suited?
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S C I E N T I F I C C O M P A N Y Laboratory Apparatus and Reagents for Chemistry, Metallurgy, Biology
P I T T S B U R G H , P E N N A .
IN C A N A D A , F IS H E R S C IE N T IF IC C O ., L T D ., 898 S T . J A M E S S T R E E T , M O N T R E A L
Analytical
Ed i t o r i a l Of f i c e:
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Editor: Ha r r i s o n E. Ho w e
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Edition
P u b l i c a t i o n O f f i c e : Easton, Pa.
Ad v e r t i s i n g De p a r t m e n t: 419 Fourth A ve.,
N ew Y ork, N . Y . T e l e p h o n e : Lexington 5608 Associate Editor: E. P . Pa r t r i d g e
(1440 East Eark Place, Ann A rbor, M ich.)
Volume 1 OCTOBER 15, 1929 Number 4
CONTENTS
Volum etric Determ ination of M anganese as D io x id e ... I. M . Koltiioff A N tr-R a iw ii B. Sa n d e ij.
R eaction betw een Lubricating Oils and Phosphorus P en to x id e C. C. Furnas
Quantitative Determ ination of M ercaptans in N aphtha...P. Borgstromand E. Emmett Reid Relation betw een Physical Characteristics and Lubricating Values of Petroleum O ils ... E. D . Ries Determ ination of True Sodium Content of Calcium Carbonate Intended for U se in J. Lawrence Smith M eth od for Alkalies.
Earle R. Ca ley
Calculation of the Com pounds in Portland C em en t R . I-I. Boguk
Determ ination of the Sulfur Content of G ases from Boiler F u rn aces Edmund Taylo r and H . F. Johnstone O ccurrence of Silicates in Natural W a te rs ...O. W . Rees D eterm ination of Silica in the Presen ce of Fluorspar... W . T . Sc h r e n kand W . H. Ode D eterm ination o f Total Carbon in S o ils ... Eric Win ters, Jr., and R . S. Smith
Action of Papain on the Polarization o f G ela tin H . C. Gore
Nature and Constitution of Shellac. II— Potentiom etric Titrations in 95 Per Cent Ethyl A lco h o l...
Wm. How lett Gardn er and Willet F. Whitmore A Com bination E lectrochem ical Sw itch b oa rd ... W . I 'aito u te Munn
Corrosion T esting Apparatus D . F. Othmer
Electrolytic Board for the Determ ination of L e a d O. W . Holmesand D. P. Morgan
Laboratory R ectifying Columns with Non-Siphoning Bubbling-Cap P la te s ... Johan nes H . Bruun Comparison of the Dilution and Absorption M eth od s for the Determ ination of Biochem ical Oxygen D em a n d ...
G. E. Symons w it h A. M . Busw ell Stabilized Starch In dica tor...M . St a r r Nichols An Analysis o f a Peat P r o file ...Re in h ard t Th iessenand R . C. Johnson
Analytical R eactions of Tetraethyl L e a d Graham Edgarand George Ca lin g ae r t
D eterm ination of Inert G as Content of Gas M ixtures b y M ean s of Calcium as an A b sorb en t...
Ma r tin Leath erm an and Ed w ard P. Ba rtlett
D eterm ination of Total M oisture in Carbon B la ck s C. M . Carson
Analyses of Som e Natural Gasoline G ases b efore and after T reatm en t...H. C. Allen
D etection and Determ ination of Carbon D isulfide and Sulfur in F lu id s J. A. Pierce
The Segregation of Analyzed S am ples ... G. Fred e r ic k Sm ith, L. V. Ha r d y, and E . I,. Gard Solubility of Benzidine Sulfate and Benzidine H ydrochloride in H ydrochloric A cid S olu tion s...
Wm. B . Meldrumand Ira G . Ne w lin Determ ination of P h enol in P resen ce of Salicylates E. H . Ham ilto n and C. M . Sm it h Device for M aintaining a Constant R ate of Flow of L iq u ids...John D . Su llivan Buret Clamp and H o ld e r ... .Mario n Ho lling sw orth Author I n d e x ...
S u bject I n d e x ...
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4 A N A L Y T I C A L EDITION Vol. 1, No.
LABORATORY GL A S S W A R E P Y R E X Be a k e r s
Giintn Kcahnt*
G L A S S W A R E l a b o r a t o r y
LABORATORY « * » £ * »
p y r e xf l a s k s t u b u l a t e d ___________
P Y R E X Flasks
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VOLUM ETRICVoiunvrt'k ELukt DkMiUińjf E&»k
G L A S S W A R E
LABORATORY LABORATORY G L A S S W A R E
P Y R E X Ap p a r a t u s . P Y R E X Ap p a r a t u s
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Comp.-
Co r n i n g Cl a s s Wo r k s CoDMIkU N l " YuM . I ' S A
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H IS new P Y R E X L a b o ra to r y G lassw are C a ta lo g illustrates an d lists th e fo llo w in g w ith sizes and p rices:Standard P Y R E X beakers, 6 kinds; flasks, 41 kinds;
tubes in distilling, extraction, filter, melting point and condenser types; condensers of bulb, coil and cylindrical types, the latter with loose or sealed-in inner tubes;
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vacuum and other distilling apparatus; funnels, open and closed; stop-cocks and tubing; graduated beakers, cylinders, etc.; hydrometer jars; percolators; bottles, jars, dishes and trays for all laboratory purposes, etc.
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October 15, 1929 IN D U S T R IA L A N D ENGINEERING CHEM ISTRY 5
How
Cenco DeKhotinsky Ovens are tested for uniformity
A lest cabinet in the Cenco laboratories, equipped w ith a unique self-recording and developing m ultip le lead potcn liom etric sys
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Each o f nine sam ple dishes on each shelf holds its own therm o elem ent and the con
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with a popular oven o f different design.
Identical conditions are carefully held even to environm ental tem perature history and h u m id ity . T his test showed local tem pera
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6 A N A L Y T I C A L EDIT IO N Vol. 1. No. 4
BRO N FEN B R EN N ER
ELECTRO ULTRA-FILTRATIO N APPARATUS
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The high efficiency of this apparatus is due to the following: the dialyzing surfaces arc very large in comparison to the capacity of the apparatus; the permeability of the membranes is easily varied by changing the density of the collodion used in coating the thimbles; the rate of dialysis is speeded up by a continuous removal of the dialysate by a flow of water at each electrode; the constant flow of cold water at the electrodes permits the use of high voltage (110 to 115) without an excessive rise in temperature; the material subjected to dialysis may be kept from becoming concentrated by diluting it during dialysis;
the whole dialyzing chamber is agitated, thus preventing the deposit of solids on the membrane.
See Jacques J. Bronfenbrenner, " A Simple Elcctro-Ultrafilter,” The Journal of General Physiologv, Vol. X , No. 1 (Sep!. 20, 1926), pp. 23-26.
5153. E lectro U ltra-Filtration A ssem bly, Bronfenbrenner, Small M odel, com plete as shown in illustration. W ith Carbon and Copper elec
trodes and with Separatory Funnel not shown in illu stra tion ... $225.00 Code W o r d ... Forwt 5154. D itto, Large M odel. W ith Platinum and copper electrodes... $270.00 C ode W ord ...Fosgtt
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R E T A I L — W H O L E S A L E — E X P O R T
LA B O R A T O R Y A PPA RA TU S AND R EA G EN TS
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Cable Address, “ BALANCE,” Philadelphia
Analytical
^ 1 Kl
Edition
Volume 1 OCTOBER 15, 1929 Number 4
Volum etric Determination of Manganese as D ioxid e 1
W ith Special Reference to Application of Potassium Bromate as Oxidizing Agent
I. M . Kolthoff and Ernest B. Sandell
Un i v e r s i t y o r Mi n n e s o t a, Sc h o o l o r Ch e m i s t r y, Mi n n e a p o l i s, Mi n n.
V
ARIOUS methods for tlie precipitation o f manganese as dioxide and the volumetric determination of this compound have been proposed in the litera
ture. From the p r a c t i c a l point of view the most im
portant procedures are those in which the precipitation of
the dioxide takes place in acid medium; therefore, the writers have studied these more carefully. Oxidation in neutral or alkaline medium by means of bromine, hypobromite, chlorine, hypochlorite, or ferricyanide is unsatisfactory, in general, when iron is present, and even in the absence of iron results tend to be variable (S).
After a preliminary study of the methods in neutral or alkaline solution, the oxidation in acid medium was studied more in detail. In acid solution manganese is oxidized to the dioxide by boiling with ammonium or potassium per
sulfate. Von Knorre (0) has based a determination on this reaction. The precipitated manganese dioxide is collected by filtration, washed and dissolved in ferrous sulfate or hydrogen peroxide, and the excess peroxide is titrated with permanganate. The method docs not give theoretical values;
an empirical factor must be applied. The details of this method will be discussed in the experimental part of this paper. The method has been applied by Lüdert and others (4, 6, 7).
A method that has enjoyed considerably greater popularity than that of von Knorre is the familiar procedure based on the precipitation of manganese dioxide by long boiling with potassium chlorate in strong nitric acid solution. Beilstein and Jawein (I) first made use of this method of precipitation for a gravimetric determination of the element, Ilampe (5) and others based a volumetric estimation on the same reac
tion. Hampe found that potassium bromate could be used in place of the chlorate but preferred the chlorate. As we shall see later, potassium bromate furnishes an excellent reagent for the oxidation of manganese to dioxide even in weakly acid medium.
Persulfate M eth od
The manganous salt used in the determinations to be described was manganous sulfate which had been purified
1 R e c e i v e d M a y 1 8 , 1 9 2 9 .
Th e persulfate m eth od for the oxidation of m a n ganese to m anganese dioxide has been studied and the factors which m ay affect the results have been in vestigated.
Instead of persulfate, the use of potassiu m brom ate is recom m ended as an oxidizing agent. Reproducible results are obtained. T h e brom ate m eth od is suitable for m anganese determ inations in ores and can be applied to the determ ination of m anganese in steel.
by two precipitations with alcohol. It was tested for the presence of foreign cations and anions, and these were fo u n d t o be absent. The s o lu t io n w as a c c u r a t e ly standardized by weighing the manganese as anhydrous sul
fate according to Blum (3).
The average of several sulfur determinations (precipitation as barium sulfate) gave a result 0.2 per cent lower than the accepted value based on the weigh
ing of anhydrous manganous sulfate. The precipitations of manganese dioxide were generally carried out in a volume of 50 cc. in the presence of sulfuric acid. From 3 to 5 grams of pure potassium persulfate were added to the solution and, after boiling for a sufficiently long time to effect complete precipi
tation, the manganese dioxide was filtered off and washed with hot water to remove all oxidizing agent. The manganese dioxide was determined iodometrically. If the solution from which manganese was precipitated contained iron, potassium fluoride was added before titrating to prevent the liberation of iodine by ferric iron, which is always adsorbed in small amounts by manganese dioxide. Obviously, the dioxide could have been dissolved in ferrous sulfate, hydrogen per
oxide, or any other suitable reducing agent, and the excess of the latter titrated with potassium permanganate. The iodometric method was chosen merely for its greater rapidity and convenience.
Manganese in the absence of iron begins to precipitate before the boiling point is reached. The dioxide first separat
ing is brown, but becomes nearly black after boiling for a few minutes,- when precipitation is complete. During the oxidation a trace of permanganate is always formed. The filtrates from the manganese dioxide precipitations made either in the absence or presence of zinc (see Tables I and II) were usually found to contain manganese equivalent to 0.01—
0.03 cc. of 0.1 N permanganate. In filtering through paper, permanganate is partially or completely reduced and the figures given are the amounts of permanganate formed by re-oxidizing with potassium persulfate in the presence of silver nitrate. When iron accompanies manganese, the formation of permanganate is much increased (approximately, tenfold) and varies according to the amounts of iron and manganese present. A high concentration of ferric iron and a low concentration of manganous salt favor the formation
182 A N A L Y T IC A L EDITION Vol. 1, No. 4 of permanganate. Varying the acidity from 0.4 N to 2 N did
not seem to affect the reaction.
T a b le I — O x id a t io n o f M a n g a n e s e w ith P o t a s s iu m P e r s u lfa te in th e A b s e n c e o f Z in c
N o. M n T a k e n Co n d i t i o n s M n F o u n d Er r o r Er r o r
Gram Gram Gram Per cent
1 0.00671 10 cc. 4 N HsSOi;
vol. =* 50 cc.;
boiled 5 min. 0.00638 - 0 .0 0 3 3 - 4 . 9 2 0.00671 10 cc. 4 N HiSOi;
vol. == 50 cc.;
boiled 5 min. 0.00652 - 0 .0 0 1 9 - 2 . 8 3 0.00671 10 cc. 4 N HjSOc
vol. = 50 cc.;
boiled 5 min. 0.00628 - 0 .0 0 4 3 - 6 . 4 4 0.0 2 66 10 cc. 4 N HjSO<;
vol. = 50 cc.;
boiled 5 min. 0.0256 - 0 .0 0 1 0 - 3 . 8
5 0.0671 Neutral soln. 0.0652 - 0 .0 0 1 9 - 2 . 8
6 0.0671 5 cc. 4 N H2SO4;
boiled 5 min. 0.0616 - 0 .0 0 2 5 - 3 . 7 7 0.0671 5 cc. 4 N H2SO4;
boiled 5 min. 0.0645 - 0 .0 0 2 6 - 3 . 9 8 0.0671 5 cc. 4 N HjSO<;
boiled 5 min. 0.0645 - 0 .0 0 2 6 - 3 . 9 9 0.0671 5 cc. 4 N IIiSOj;
boiled 5 min. 0.0646 - 0 .0 0 2 5 - 3 . 7 10 0.0671 5 c c . 4 N HsSOi;
boiled 5 min. 0.0649 - 0 .0 0 2 2 - 3 . 2 11 0.0671 10 cc. 4 N HtSO« 0.0645 - 0 .0 0 2 6 - 3 . 9
’a b le II— O x id a t io n o f M a n g a n e s e w ith P o t a s s iu m P e r s u lfa te ii P re s e n ce o f Z in c S u lfa t e
N o. M n Taken Co n d i t i o n s M n F o u n d Er r o r Er r o r
Gram Gram Gram Per cent
1 0.00671 10 cc. 4 N H2SO4 ; 3 g. Z n S 0 4 .7 H 20 ;
boiled 5 min. 0.00646 -0 .0 0 0 2 5 - 3 . 7 2 0.00671 10 cc. 4 N H2SO4; 3
g. Z n S 0 4 .7 H :0 ;
boiled 5 min. 0.00635 -0 .0 0 0 3 6 - 5 . 4 3 0 .0 2 66 10 cc. 4 N H2SO4; 3
g. Z n S 04.7H 20 ;
boiled 5 min. 0 .0 2 58 -o .o o o s - 3 . 0 4 0 .0671 10 cc. 4 N H2SO4; 3
g. Z n S 0 i.7 H 2 0 ;
boiled 5 min. 0.0651 - 0 .0 0 2 0 - 3 . 0 5 0.0671 Neutral soln.; boiled
5 rain. 0.0 6 55 - 0 .0 0 1 6 - 2 . 4
6 0.0671 Neutral soln.; boiled
5 min. 0.0656 - 0 .0 0 1 5 - 2 . 2
7 0.0671 Neutral soln.; boiled
5 min. 0.0654 - 0 .0 0 1 7 - 2 . 5
8 0 .1 3 30 10 cc. 4 N H 5SO< 0.1315 - 0 .0 0 1 5 - 1 . 1
The presence of iron hinders the precipitation of man
ganese dioxide, but only seriously so when present in a ratio larger than 100 Fe to 1 Mn. When this ratio is not larger than 10 : 1, precipitation is complete within 10 minutes; when it is greater, the time of boiling must be correspondingly increased, and successive portions of persulfate must be added as the reagent decomposes rapidly in hot acid solution.
It may be mentioned that the use of ammonium persulfate instead of potassium persulfate is somewhat dangerous, since after all the persulfate has decomposed the ammonium ions left in solution may reduce the manganese dioxide.
Disc u s s io no f Re s u lt s—-If the precipitation of manganese is made in the absence of zinc salts (Table I), there is a de
viation from the theoretical of about —3.7 per cent for quantities of manganese ranging from 25 to 70 mg.
When a sufficient quantity of zinc ions (from 3 to 5 grams hj-drated zinc sulfate) is present (Table II), results are higher but still are about 3 per cent below the theoretical. The influence of zinc is greater than von Knorre believed it to be.
According to his statement, zinc increases the quantity of manganese found to such a slight degree as to be negligible.
In the presence of iron the values for manganese are about 2.4 [Kir cent low, but are constant over a wide range of iron concentration (0.025 gram to 3.0 gram in 50 cc.). The results obtained by von Knorre are a little less than 1 per cent below the theoretical values. He states that in most cases the same empirical factor can be used in the presence and in the absence of iron. This is not true. From the results of six
teen determinations (Table III) the empirical factor is 1.024 times theoretical when iron is present with the manganese.
The empirical factor (iron being present) according to work done in the Bureau of Standards (S, see also 1) is 1.028 times
the theoretical. Varying the acidity from 0.4 N to 2 N had no appreciable effect on the results.
T a b ic I I I — O x id a t io n o f M a n g a n e s e w ith P o t a s s iu m P e r s u lfa te in P re s e n ce o f Ir o n a s N itr a te o r S u lfa t e
M n Fc M n
N o. Taken Present Conditions Found Error Error
Gram Grams Gram Gram Per cent
1 0.00671 0 .4 10 cc. 4 N II3S04 in 50 cc. v o l.;
boiled 15 min. 0.00654 0.00017 - 2 . 5 2 0.0266 1 .4 10 cc. 4 N II2SO4
in 50 cc. vol.;
boiled 15 min. 0 .0 2 58 - 0 .0 0 0 8 - 3 . 0 3 0.0671 0 .0 2 5 10 cc. 4 N H2SO«
in 50 cc. vol.;
boiled 15 min. 0.0655 - 0 .0 0 1 6 - 2 . 4 4 0.0671 0 .1 2 10 cc. 4 N H2SO«
in 50 cc. vol.;
boiled 15 min. 0.0657 - 0 .0 0 1 4 - 2 . 1 5 0.0671 0 .1 2 10 cc. 4 N HsSOi
in 5 0 cc. vol.;
boiled 15 min. 0.0352 - 0 . 0 0 1 9 - 2 . 8 6 0.0671 0 .1 2 10 cc. 4 N H;SO<
in 50 cc. v o l.;
boiled 15 min. 0.0654 - 0 .0 0 1 7 - 2 . 5 7 0.0671 0 .1 2 10 cc. 4 N H2SO4
in 50 cc. v o l.;
boiled 15 min. 0.0654 - 0 .0 0 1 7 - 2 . 5 S 0.0671 0 .4 10 cc. 4 N H:SOi
in 50 cc. vol.;
boiled 15 min. 0.0657 - 0 . 0 0 1 4 - 2 . 1 9 0.0671 0 .6 10 cc. 4 N H5SO4
in 50 cc. vol.;
boiled 15 min. 0 .0 6 55 - 0 .0 0 1 6 - 2 . 4 10 0 .0671 1.2 10 cc. N H-SOi
in 50 cc. v ol;
boiled 15 min. 0.065S - 0 . 0 0 1 3 - 2 . 0 11 0.0671 2 .4 10 cc. 4 N H2SO4
in 50 cc. vol.;
boiled 15 min. 0 .0 6 50 - 0 .0 0 2 1 - 3 . 1 12 0.0671 2 .4 10 cc. 4 N H2SO4
in 50 cc. vol.;
boiled 15 min. 0.0659 - 0 .0 0 1 2 - 1 . 8 13 0.0671 3 .0 10 cc. 4 N HaSOi
in 50 cc. vol.;
boiled 15 min. 0.0656 - 0 .0 0 1 5 — 2 2 14 0.0671 0 .1 2 5 cc. 4 Ar H7SO4 0.0652 - 0 .0 0 1 9 — 2 ! 8 15 0.0671 0 .1 2 15 cc. 4 N II2SO4 0 .0653 - 0 .0 0 1 8 - 2 . 7 16 0.0671 0 .1 2 25 cc. 4 N H2SO4 0 .0654 - 0 .0 0 1 7 - 2 . 5
The presence of chromium (which during the precipitation of manganese is oxidized to chromic acid) does not lead to high results (Table IV ). Small amounts of tungsten, molybdenum, and phosphoric acid may be present. How
ever, when these occur in large quantities, results are seriously low on account of the incomplete precipitation of manganese, possibly due to the formation of complex trivalent compounds of manganese which are soluble. Cobalt, when it accom
panies iron and manganese, does not lead to high results, even when present in large quantities. Von Knorre found the presence of cobalt to be disturbing, presumably on account of the co-precipitation of cobaltic oxide. Cobalt, when present with manganese in the absence of iron, has a tendency to give high results. The presence of chlorides in small amounts is not detrimental to the determination.
Re c o m m e n d e d Pr o c e d u r e— T o about 50 cc.of solution con
taining 20 to 100 mg. manganese, and at least an equal quantity of iron to maintain the constancy of the empirical factor, suffi
cient sulfuric acid is added to make the acid concentration 0.5 to 1 N . After adding 3 or 4 grams of potassium per
sulfate, the solution is heated to boiling and kept at the boiling point for 10 minutes. If much iron is present more persulfate is added and boiling continued for 10 or 15 minutes more. The mixture is then filtered; if the filtrate is turbid at first it is poured back on the filter. The precipitate is washed with hot water until all persulfate has been removed (test filtrate with potassium iodide and sulfuric acid). The filter paper containing the manganese dioxide is transferred to the flask in which the precipitation was made. The titration is made either iodometrically (with addition of fluoride) or with ferrous sulfate and potassium permanganate.
Empirical factor = 1.024 times theoretical.
In the absence of iron add zinc sulfate. The empirical factor is then 1.030 times theoretical. It appears that the re
sults in the absence of iron are not so reproducible as when it is present.
October 15, 1929 IN D U S T R IA L A N D ENGINEERING CHEMISTRY 183
T a b le IV — O x id a tio n o f M a n g a n e s e w ith P o ta s s iu m P e rs u lfa te in P re se n ce o f I r o n a n d O th e r ]E lem en ts
M n Fe M n
N o. Ta k e n Pr e s e n t Ad d i t i o n Co n d i t i o n s Fo u n d Er r o r Er r o r
Gram Grams Gram Gram Per cent
1 0.0671 0 .6 5 g. ZnSO «.7H jO 10 cc. 4 N HjSC>4; 50 cc. vol.; boiled 5 min. 0.0656 - 0 .0 0 1 5 — 2 2
2 0.0071 1 g. C uS O i.5IIiO 10 cc. 4 N HtSCh; 50 cc. v o l.; boiled 5 min. 0.0658 - 0 .0 0 1 3 — 2 .0
3 0.0671 1 g. CuSCh + 3 g. ZnSO* 10 cc. 4 N HjSCh; 50 cc. vol.; boiled 4 min. 0.0666 - 0 .0 0 0 5 - 0 . 8 4 0.0671 0 .1 g. chrom e alum 10 cc. 4 AT H2SO4; 50 cc. vol.; boiled 5 min. 0 .0643 - 0 .0 0 2 8 - 4 . 2 5 0.0671 0 .1 g. chrom e alum + 3 g. ZnSCh 10 cc. 4 N HjSCh; 50 cc. v o l.; boiled 5 min. 0.0651 - 0 . 0 0 2 0 - 3 . 0 0 0.0671 0 .1 g. chrom e alum + 3 g. ZnSCh 10 cc. 4 N H1SO4; 50 cc. v o l.; boiled 5 min. 0 .0656 - 0 .0 0 1 5 - 2 . 2 7 0.0671 0 .3 5 g. CoS04.7H20 10 cc. 4 N H2SO4; 50 cc. v o l.; boiled 5 min. 0 .0666 - 0 .0 0 0 5 - 0 . 7 8 0.0071 1 .0 g. C0SO4.7H2O 10 cc. 4 N H2SO4; 50 cc. v o l.; boiled 5 min. 0 .0 6 94 + 0 .0 0 2 3 + 3 .4 9 0.0671 0 ! ¿ 0 .3 5 g. CoS04.7H20 10 cc. 4 N II2SO4; 50 cc. v o l.; boiled 5 min. 0.0651 - 0 .0 0 1 7 - 2 . 5 10 0.0671 1 .2 0 .7 g. CoS04.7HïO 10 cc. 4 Ar H2SO4; 50 cc. vol.; boiled 5 min. 0.0652 - 0 .0 0 1 9 - 2 . 8 11 0.0671 1 .2 1 .0 g. CoS04.7HjO 10 cc. 4 N H3SO4; 50 cc. v o l.; boiled 5 min. 0.0661 - 0 . 0 0 1 0 - 1 . 5 12 0.0671 1 . 2 0 .7 g. C0SO4.7H2O 20 cc. II2SO4; 50 cc. vol., boiled 10 min. 0 .0 6 5 9 - 0 . 0 0 1 2 - 1 . 8 13 0.0671 0 .5 1 g. N i(N O j)î.6 H ?0 10 cc. H2SO4; 50 cc. vol., boiled 10 min. 0 .0656 - 0 .0 0 1 5 - 2 . 2 14 0.0071 0 . 6 0 .1 8 g. H 3P 0 4 5 cc. H2SO4; 50 cc. vol., boiled 10 min. 0.0651 - 0 . 0 0 2 0 - 3 . 0
15 0.0071 0 . 6 0 .0 2 g. HjP04 10 cc. H2SO4; 50 cc. vol., boiled 10 min. 0.0656 - 0 .0 0 1 5 - 2 . 3
10 0.0071 0 . 6 0 .0 2 g. H3PO4 10 cc. H2SO4; 50 cc. vol., boiled 10 min. 0 .0657 - 0 .0 0 1 4 - 2 . 1 17 0.0671 0 . 6 0 .0 1 g. HjP04 10 cc. H2SO4; 50 cc. vol., boiled 10 min. 0 .0 6 60 - 0 . 0 0 1 1 - 1 . 6 18 0.0671 0 . 6 0 .0 1 g. H3PO4 10 cc. H2SO4; 50 cc. vol., boiled 10 min. 0.0661 - 0 . 0 0 1 0 - 1 . 5 19 0.0671 0 . 6 0 .0 5 g. NajWCh 10 cc. H2SO4; 50 cc. vol., boiled 10 min. 0.0664 - 0 .0 0 0 7 - 1 . 0 2 0 0.0071 0 . 6 0 .1 0 g. NnaWCh 10 cc. H2SO4; 50 cc. vol., boiled 10 min. 0.0655 - 0 .0 0 1 6 - 2 . 4
21 0.0671 0 . 6 0.10 g. NaiWCh 10 cc. H2SO4; 50 cc. vol., boiled 10 min. 0.0655 - 0 .0 0 1 6 - 2 . 4
2 2 0.0671 0 . 6 0 .0 5 g. ( N H 4 ) i M o 0 4 10 cc. H2SO4; 50 cc. vol., boiled 10 min. 0.0659 - 0 . 0 0 1 2 - 1 . 8 23 0.0671 0 . 6 0 .1 0 g. (NH4)iMo04 10 cc. H2SO4; 50 cc. vol., boiled 10 min. 0 .0 6 60 - 0 . 0 0 1 1 - 1 . 6
Brom ate M ethod
Contrary to the statements of Hampe (5), it was found that manganese could be oxidized completely to the dioxide by boiling for a short time with potassium bromate in dilute acid solution. The bromate used in this manner behaves in practically the same way as potassium persulfate in pre
cipitating manganese dioxide, giving a precipitate of the same appearance and filterability. The reaction takes place in accordance with the following equation:
5M n ++ + 2(B r03) “ + 4H 20 — > 5M nO, + Bra + 8H + As in the persulfate method, traces of permanganate are formed, the amount produced being increased when iron is present. The small error due to the formations of perman
ganate is obviated by the application of the empirical factor.
The use of potassium bromate is preferable to that of potassium persulfate, as it is not easily decomposed by boiling in dilute acid solutions and, therefore, manganese can be precipitated with certainty in the presence of iron. With potassium persulfate the oxidation is effected with greater difficulty on account of the ready decomposability of this reagent, whereas with potassium bromate the results are easily reproducible.
The experimental results given in Tables V to V III were obtained by titrating the manganese dioxide precipitate (produced by boiling with 1 to 2 grams of potassium bromate for 10 to 20 minutes in solutions usually 0.8 N with respect to sulfuric acid) iodometrically, as described under the per
sulfate procedure.
T a b ic V — O x id a t io n o f M a n g a n e s e A b s e n c e o f
w ith P o t a s s iu m B r o m a t e in Z in c
M n M n
NO. Ta k e n Co n d i t i o n s Fo u n d Er r o r Er r o r
Gram Gram Gram P er cent
1 0.00671 10 cc. 4 N H2SO4;
50 cc. vol. 0.00635 - 0 .0 0 0 3 6 - 5 . 4 2 0.00671 10 cc. 4 Ar H2SO4;
50 cc. vol. 0.00638 - 0 .0 0 0 3 3 - 5 . 0 3 0.00671 10 cc. 4 N HiSCh;
50 cc. vol. 0.00636 - 0 .0 0 0 3 5 — 5 .2 4 0.0260 10 cc. 4 N H2SO4;
50 cc. vol. 0.0256 - 0 .0 0 1 0 - 3 . 8 5 0.0266 10 cc. 4 N H îSO<;
50 cc. vol. 0.0257 - 0 .0 0 0 9 - 3 . 4 6 0.0671 10 cc. 4 N H N O3;
50 cc. vol. 0.0649 - 0 .0 0 2 2 - 3 . 3 7 0.0671 10 cc. 4 N HNCh;
50 cc. vol. 0 .0 6 49 - 0 .0 0 2 2 - 3 . 3 8 0 .0671 10 cc. 4 N HNOa;
50 cc. vol. 0 .0651 - 0 . 0 0 2 0 - 3 . 0 9 0 .1 3 30 10 cc. 4 N H N O3;
50 cc. vol. 0 .1282 - 0 .0 0 4 8 - 3 . 6
are still lower, being 5.2 per cent below the theoretical for 0.005 N solutions ( = 7 mg. manganese in 50 cc. of solution).
When sufficient zinc salt is present with the manganese (Table V I), the results arc 2.0 per cent lower than theory demands, and this deviation remains sensibly constant for quantities of manganese ranging from 3 to 130 mg. Quan
tities of manganese as small as 2 to 3 mg. can be determined with an accuracy of about 1 per cent. Factor = 1.020 X theoretical titer.
T a b le V I — O x id a t io n o f M a n g a n e s e w ith P o t a s s iu m B r o m a t e in
• P re s e n ce o f Z in c
De v i a t i o n f r o m
M n M n , Em p i r i c a l
N o. Ta k e n Co n d i t i o n s Fo u n d Er r o r Er r o r Va l u e
Gram Gram Gram P er cent Per cent
1 0.00266 1 cc. 4 V H2SO4: 2
g. ZnSCh.7HaO; - -
vol. = 10 cc. 0.00265 -0 .0 0 0 0 1 - 0 . 4 2 0.00266 1 cc. 4 AT HtSCh; 2
g. Z n S 0 4 .7 H 30 ;
vol. = 10 cc. 0.00264 - 0 .0 0 0 0 2 - 0 . 8 3 0.00266 1 cc. 4 AT HsSCh: 2
g. Z n S 0 4 .7 H 20 ;
vol. = 10 cc. 0.00261 -0 .0 0 0 0 5 - 2 . 0 4 0.00266 1 cc. 4 N HaSCh; 2
g. Z n S 0 < .7 H 20 ;
vol. = 10 cc. 0 .00265 - 0 .0 0 0 0 1 - 0 . 4 5 0.00266 1 cc. 4 N H2SO4; 2
g. Z n S 04.7H 20 ;
vol. = 10 cc. 0.00262 -0 .0 0 0 0 4 - 1 . 5 6 0 .00266 5 cc. 4 N H1SO4;
2 g. ZnSCh; vol.
= 50 cc. 0.00260 -0 .0 0 0 0 6 - 2 . 2 7 0.00266 5 cc. 4 N HiSCh:
2 g. ZnSCh; vol.
= 50 cc. 0.00262 -0 .0 0 0 0 4 - 1 . 5 8 0.00671 10 cc. 4 N H3SO4;
3 g. ZnSO<; vol.
= 50 cc. 0.00648 - 0 00023 - 3 . 4 - 1 . 4 9 0.00671 10 cc. 4 iV H3SO4;
3 g. ZnSO i; vol.
= 50 cc. 0.00656 - 0 .0 0 0 1 5 - 2 . 2 - 0 . 2 10 0.00671 10 cc. 4 N H1SO4;
3 g. ZnS04; vol.
= 50 cc. 0.00654 - 0 .0 0 0 1 7 - 2 . 5 - 0 . 5 11 0.0266 10 cc. 4 N HjSCh;
3 g. ZnSCh; vol.
= 50 cc. 0.0263 - 0 .0 0 0 3 - 1 . 1 + 1.1 12 0 .0266 10 cc. 4 N H:S(>4 ;
3 g. ZnSCh; vol.
= 50 cc. 0 .0 2 60 - 0 .0 0 0 6 - 2 . 3 - 0 . 3 13 0.0671 10 cc. 4 N H2SO4;
3 g. ZnSCh; vol.
= 50 cc. 0 .0 6 60 - 0 .0 0 1 1 - 1 . 6 + 0 . 6 14 0.0071 10 cc. 4 N H2SO4;
3 g. Z11SO4; vol.
= 50 cc. 0.0657 - 0 .0 0 1 4 - 2 . 1 - 0 . 1 15 0 .1 3 30 10 cc. 4 N H2SO4;
3 g. ZnSCU; vol.
= 50 cc. 0.1303 - 0 .0 0 2 7 - 2 . 0 + 0 . 0 16 0 .1 3 30 10 cc. 4 AT H2SO4;
3 g. ZnSCh; vol.
= 50 cc. 0.1311 - 0 .0 0 1 9 - 1 . 4 + 0 . 6 Average - 2 . 0
Disc u s sio no f Re su lt s— The determination o f manganese by oxidation with potassium bromate in the absence of zinc (Table V) and iron gives results which are about 3.4 per cent lower than the theoretical values for quantities of manganese from 25 to 130 mg. For small amounts the values obtained
In the presence of iron (Table V II) the method gives values for manganese which are 1.0 per cent low. The factor, therefore, is 1.010 X theoretical and this value holds for quantities of manganese from 30 to 150 mg. Varying the ratio of iron to manganese from 1 : 1 to 70 : 1 does not affect
