IN D U S T R IA L aiENGINEERING C H E M IS T R Y
V o l. 31, C o n s e c u ti v e N o . 19
ANALYTICAL EDITION
21,000 Copies of This Issue Printed
Issu ed M ay 15, 1939
H a r r iso n E . H o w e , E d ito r
Vol. 11, N o. 5
D e t e r m i n a t i o n o f I o d i n e i n S o d i u m T e t r a i o d o p h e n o l - p h t h a l e i n . Albert Q . Butler and Robert A. B urdett 2 3 7 D e t e r m i n a t i o n o f D i s s o l v e d O x y g e n i n A q u e o u s
S o l u t i o n s ...G. A . Perley 240
M e a s u r e m e n t o f P l a s t i c P r o p e r t i e s o f B i t u m i n o u s C o a l s ... R . E. Brewer and J. E. Triff 242
Si m p l e Vi b r a t o r...
... Joseph F. Vincent and Morton M. Spruiell 247
C o m p o s i t i o n o f H i g h - S o l v e n c y H y d r o c a r b o n T h i n k e r s ...E. II. McArdle, J. C .
Moore, H. D. Terrell, E. C. Haines, and Cooperators 248
M o d i f i e d B e i l s t e i n T e s t f o r H a l o g e n s i n V o l a t i l e O r g a n i c C o m p o u n d s ...Wm. L. Ruigh 250
S e p a r a t i o n a n d D e t e r m i n a t i o n o f C o p p e r a n d N i c k e l b y S a l i c y l a l d o x i m e . L. P. Biefeld and D . E. Howe 251
D e t e r m i n a t i o n o f I r o n i n T u n g s t e n a n d T u n g s t i c A c i d ...M . L. Holt and Donald Swalheim 254
De t e r m i n a t i o n o f Ca r o t e n e i n Si l a g e. Im p r o v e d Me t h o d...
. . D. M. Hegsted, J. W. Porter, and W. H. Peterson 256
Br o m i d e Co n t e n t o f Fr u i t s a n d Ve g e t a b l e s Fo l l o w i n g Fu m i g a t i o n w i t h Me t h y l Br o m i d e...
... II. C. Dudley 259
Hy d r o g e n- Io n Ac t i v i t y a n d Bu f f e r Ca p a c i t y o f Na t u r a l a n d Tr e a t e d Wa t e r s...
... A. P. Black and Edward Bartow 261
M e a s u r i n g O x i d a t i o n o f L u b r i c a n t s . V. R. Damerell 265
R a p i d P o t e n t i o m e t r i c D e t e r m i n a t i o n o f Z i n c . . . ...D . G. Sturges 267
T e t r a p h e n y l a r s o n i u m C h l o r i d e a s A n a l y t i c a l R e a g e n t . . H obart H. Willard and George M . Smith 2 6 9 C o l o r i m e t r i c D e t e r m i n a t i o n o f M a n g a n e s e w i t h
P e r i o d a t e ...J . p . Mehlig 2 7 4 Se p a r a t i o n a n d De t e r m i n a t i o n o f Al u m i n u m a n d
Be r y l l i u m Us i n g Ta n n i n...
... M. L . Nichols and John M. Schempf 2 7 8 Ac t i v a t e d Sl u d g e— Mi l o r g a n i t e...
... C. J. Rehling and E . Truog 2 8 1 L a b o r a t o r y C o l u m n s f o r C l o s e F r a c t i o n a t i o n .
C o n i c a l T y p e o f S t e d m a n P a c k i n g . . L . B. Bragg 2 8 3 A n t i f o a m i n g D e v i c e s ... Robert Schnurmann 2 8 7 Gl a s s He l i c e s f o r Pa c k in g La b o r a t o r y Fr a c t i o n a t
i n g Co l u m n s ...
. . . . Robert W. Price and William C. M cDerm ott 2 8 9 Se m i a u t o m a t i c, Mu l t i p l e, El e c t r o m e t r i c Ti t r a t i o n
Ap p a r a t u s...
... Maurice E . Stansby and G. A. Fitzgerald 2 9 0 C o r r e s p o n d e n c e : 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 n E N O L IN D O P H E N O L F O R A S C O R B IC AciD T lT R A T I O N . ... O . H . Keys 2 9 3 Mi c r o c h e m i s t r y :
Q u a l i t a t i v e S e p a r a t i o n s o n M i c r o S c a l e . . . .
. . . . Beri S . Alstodt and A. A. Benedetti-Pichler 2 9 4 P r e c l S u l f u r C o m b u s t i o n o f M e t a l l i c C o m p o u n d s
... Joseph F. Alicino 2 9 8 Mo d e r n La b o r a t o r i e s: Re s e a r c h La b o r a t o r y' o f
N a t i o n a l L e a d C o m p a n y — T i t a n i u m D i v i s i o n . . .
... Walter W. Plechner and Sandford S. Cole 2 9 9
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4 INDUSTRIAL AND E N G IN E ER IN G CHEM ISTRY VOL. 11, NO. 5
MAY 15, 1939 ANALYTICAL ED ITIO N 5
Reliable PRIMARY STANDARDS
f o r R e s e a r c h a n d C o n tr o l L a b o r a t o r ie s
Since Prim ary Standards are the starting point for accuracy in many analytical determinations, they m ust pass rigorous and extremely accurate tests. The care taken by M allinckrodt chemists in controlling these im portant chemicals has make Mallinckrodt Prim ary Standards the choice of many laboratories.
Refined to m eet predetermined purity specifications, these as well as all other Mallinckrodt Analytical Reagents are unvarying in their composition and reaction.
R e p re se n ta tive P rim a ry S ta n d a r d s b y M a l l i n c k r o d t
ACID BENZOIC IRO N W IR E
ACID OXALIC POTASSIUM ACID PHTHALATE
ARSENIC T R IO X ID E SODIUM OXALATE
M allinckrodt manufactures nearly 500 chemi
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lytical Reagents and Laboratory Chemi
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ST. L O U IS , M O . P H IL A D E L P H IA N E W Y O R K , N. Y .
6 IND U STR IA L AND E N G IN E E R IN G CHEM ISTRY VOL. 11, NO. 5
D E T E R M I N A T I O N S
RUBB ER
SOLVENTS STEEl
for the determination of Sulfur in all its forms, Baker and Adamson has developed
a complete line of the necessary reagent chemicals. Their high degree of a ccu racy makes possible results that are within the narrow limits permitted by to d a y ’s rigid specifications.
--- B & A R E A G E N T S F O R CO DE
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1689 Easchka's Mixture, Reagent 2448 Zinc O xid e Powder, Reagent G r.
2227 Sodium Carbo nate, Anhydrous, Reagent, A .C .S . 1121 Nitric Acid, Fuming, Reagent G r.
2255 Sodium H ydroxide Pellets, Reagent, A .C .S . 2105 Potassium Chrom ate, Cryst., Reagent, A .C .S . 1554 Carbon Tetrachloride, Reagent, A .C .S . 1472 Bromine, Reagent, A .C .S .
S U L F U R D E T E R M I N A T I O N --- CODE
N O .
2122 Potassium N itrate, Cryst., Reagent, A .C .S . 2099 Potassium Bromide, Reagent, A .C .S . 2272 Sodium Peroxide Powder, Reagent, A .C .S . 2118 Potassium H ydroxide, Reagent, A .C .S . 2202 Sodium Bicarbonate Powder, Reagent, A .C .S . 2429 Zinc M etal, G ra n u lar, Reagent
1917 Magnesium O xid e Powder, Special Low Sulfur, A .C .S.
1408 Barium Chloride, C rystal, Reagent, A .C .S . also C. P. Acids and Ammonia
S E T T I N G T H E P A C E I N C H E M I C A L P U R I T Y S I N C E 1 8 8 2 T J . y -
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B a k e r & A d a m s o n
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A t l a n t a • B a l t i m o r e • B o s t o n • B u f f a l o • C a m d e n ( N . J . ) • C h a r l o t t e ( N . C .) • C h i c a g o • C l e v e l a n d • D e n v e r ■ H o u s t o n • K a n s a s C ity L o s A n g e l e s * M ilw a u k e e • M in n e a p o l i s • M o n t e z u m a ( G a .I • P i t t s b u r g h • P r o v i d e n c e I R . I .) • S a n F r a n c i s c o • S t . L o u i s * U t i c a ( N . Y .) W e n a t c h e e ( W a s h . ) • Y a k i m a ( W a s h . ) • I n C a n a d a : T h e N i c h o l s C h e m i c a l C o m p a n y , L i m i t e d • M o n t r e a l * T o r o n t o • V a n c o u v e r C O A l
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MAY 15, 1939 ANALYTICAL E D IT IO N
KIMBLE GLASS C O M P A N Y v i n e l a n d , n . j .
N E W Y O R K •• C H I C A G O •• P H I L A D E L P H I A • • D E T R O I T •• B O S T O N
BLUE L I N E
Alm ost two d eca d es ago, the Kimble G lass C om pany m ade this prom ise to sc ie n c e land industry: a p le d g e to d esign 'an d produce the finest q u al
it y of G radiiatedl Laboratory;'.Glassware that A m erican craftsm anship cbidd fcdjridkte, That this proiiuse h a s B een fulfilled is e v id e n c e d by the fact that today Kim ble BLUE LINE < « £ > R E T E ST E D -the PIONEER of color-calib rated volum etric glassw are • • and Kim ble <>3,MAX> P recision W are — are A m erica's u n deniable standards of ACCURACY and RELI
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T H E P I O N E E R O F C O L O R E D C A L I B R A T I O N S
The V is i bl e G u a r a n t e e o f I n v i s i b l e Q u a l i t y
8 INDUSTRIAL AND E N G IN E E R IN G CHEM ISTRY VOL. 11, NO. 5
T h e r e sh o u ld b e n o th in g “ s h o d d y ” ab ou t p y r o m e t e r a c c u r a c y . Y o u w a n t it “ a ll w o o l and a y a rd w id e .” . . . T h is m e a n s th a t if y o u a r e u s in g C h r o m e l- A lu m e l c o u p le s , y o u sh o u ld a lso b e u sin g C h r o m e l- A lu m e l le a d s. R e m e m b e r that “ c o m p e n sa tin g ” le a d s c o m p e n sa te o v e r a n a rro w lo w te m p e r a tu r e ran ge. T h e ju n ctio n of
th e c o u p le s and th e lea d s o fte n g e ts v e r y h ot. A n d in that c a se a se r io u s error is apt to b e c r e a te d . Y o u a v o id all that c h a n ce, b y u s in g C h r o m e l - A l u m e l l e a d s w it h C h r o m e l-A lu m e l c o u p le s . F o r th e n , th e r e is n o th in g to c o m p e n s a te . G e t th e w h o le sto r y in F o ld e r C -A . . . . H o s k in s M a n u factu rin g C o m p a n y , D e tr o it, M ich ig a n .
C H R O M E L - A L U M E L
"ALL WOOL..
MAY 15, 1939 ANALYTICAL E D ITIO N 9
I T T O
T„
L IM E A L O N E proves the worth o f any test tube. T im e alone determines its econom y. T im e alone indicates w hat brand it pays to specify.
And tim e has proved the savings possible through standardization on Pyrex brand te st tubes. T oday their econom y is gener
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M ade of Pyrex brand Balanced Glass,
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Their wall thickness is more uniform.
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Translated into use and into dollars, all these qualities mean a better, longer la st
ing, more econom ical tube. T h at is why, for year-in and year-out savings, it pays to standardize on Pyrex brand test tubes.
“ P Y R E X 1* is a registered trade-m ark a n d in d ica te s m a n u fa c tu re b y
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10 INDUSTRIAL AND E N G IN E E R IN G CHEM ISTRY VOL. 11, NO. 5
A N E W S E R I E S OF
W ATER BATHS OF M O N E L M ETAL
W I T H R EMOVABLE T O P PL AT E O F MO NE L ME T AL OR COO R S P ORC E LAI N
ARTHUR H. T H O M A S CO M PANY
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9903. W ATER BATH , M onel M etal, A .H .T . Code Co. Specification, for G as H eatin g.
Outside dimensions 14J^ inches square x 5J^2 inches deep, on Monel metal legs 9 inches high. With removable top complete with four sets of concen
tric rings of Monel metal inches diameter. Body is reinforced a t cor
ners by extensions of the legs welded to the side walls, and is provided with flame guards 234 inches deep. With nickel plated stopcock to draw off water and constant water level a t
tachment, but without b u rn e r.. .3 4 .5 0 Pfuur 9903-A. Ditto, but with top plate and four sets of
concentric rings of Coors porcelain in
stead of Monel metal top and rings.
W ithout burner...48.75 Pfuva
9904. W ATER BATH , M on el M etal, A .H .T . Co. Specification, Steam H ea te d . Identical with N o . 9903 but on S c inch legs and with heavy, nickel plated copper steam coil with J-g-inch i.p.
threads. W ith Monel metal top plate and concentric rings, but without steam valves or flame guards...38.50 Pfuvp 9904-A. D itto, but with top plate and four sets of
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9905. W ATER BA TH , M onel M etal, A .H .T . Code Co. Specification, Electric, identical or with 9903, i.e. with Monel metal top and concentric rings, b u t 3J4 inches deep and with annular electric heating element controlled by three-heat switch. The interior is unobstructed as the heater is clamped beneath the bath. Using 5 quarts of water, a tem
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INDUSTRIAL »„a ENGINEERING CHEMISTRY
ANALYTICAL EDITION ♦ H a rriso n E. H o w e , E d ito r
D eterm ination o f Iodine in Sodium T etraiod op h en olp h th alein
A L B E R T Q . B U T L E R a n d R O B E R T A . B U R D E T T M a l l i n c k r o d t C h e m i c a l W o r k s , S t . L o u is , M o .
T h e io d in e a ssa y o f s o d iu m te tr a io d o - p h e n o lp h t h a le in w a s s tu d ie d w it h t h e o b j e c t o f p r o d u c in g a m e t h o d w h ic h (1) w o u ld e n s u r e a c o m p le t e d e c o m p o s it io n o f th e o r
g a n ic m a t t e r in t h e s a m p le , (2) w o u ld give a n a c c u r a te d e t e r m in a t io n o f t h e io d in e , a n d (3) w o u ld b e r a p id a n d s u it a b le fo r a r o u t in e p r o c e d u r e .
I n t h e p e r m a n g a n a t e - s i l v e r n i t r a t e m e t h o d w h ic h w as d e v e lo p e d , th e o r g a n ic m a t t e r is c o m p le t e ly d e str o y e d b y m e a n s o f a lk a lin e p e r m a n g a n a te a n d t h e io d id e is a c c u r a te ly d e te r m in e d a r g e n tim e tr ic a lly u s in g a n a d s o r p tio n in d ic a t o r . T h e p r o c ess is s im p le a n d r a p id , a c o m p le te a n a ly s is r e q u ir in g a b o u t 1.5 h o u r s .
T
H E m ethod for th e determ ination of iodine in sodium tetraiodophenolphthalein (soluble iodophthalein, TJ. S. P.X I) described in this pap er is based upon a stu d y of various existing m ethods, supplem ented by certain new features m ade possible through recent developm ents in analytical chemistry.
In brief, a m ethod is proposed in which th e organic m a tte r in th e sodium tetraiodophenolphthalein is decomposed w ith alkaline potassium perm anganate, and after acidification th e excess perm anganate is reduced w ith sodium bisulfite. T he iodide is titra te d w ith silver n itra te and th e end point is detected b y m eans of an adsorption indicator such as diiodo- fluorescein.
The quantitative determination of iodine contained in organic compounds has received considerable attention in recent years, and its determination in sodium tetraiodophenolphthalein has been described by several investigators. Delbridge (4) proposed a method in which the sample was subjected to a combustion with lime, and after acidification was titrated with silver nitrate and thiocyanate according to the Volhard (12) method. Seeker and Mathewson (11) described a method in which the organic m atter was destroyed with acid potassium permanganate, the excess permanganate was reduced with sulfur dioxide, and the iodide was precipitated and weighed as silver halide.
Leclercq (7) recently reviewed the determination of iodine in organic compounds and included a study of the methods for iodine in sodium tetraiodophenolphthalein (§). He compared, among others, a so-called “ international method” with the classical methods of Carius (3) and Raubigny and Chavanne (2), and with the official U. S. P. X I method. As a result of his study, Leclercq favored the international method as most prac
tical and effective for sodium tetraiodophenolphthalein. In the international method, the sample is intimately mixed with an alkaline oxidizing mixture consisting of potassium carbonate, sodium carbonate, and potassium nitrate. The mass is heated to fusion in a nickel crucible, the melt is extracted with hot water, and the solution is treated with sodium hypochlorite to ensure complete conversion of the iodine to iodate. Excess chlorine is removed by boiling, the solution is neutralized, and after addi
tion of potassium iodide the liberated iodine is titrated with thiosulfate. Leclercq also described a method in which an alkaline permanganate oxidation of the sample was followed by treatm ent with alcohol, and after addition of potassium iodide the liberated iodine was titrated with thiosulfate.
T he official m ethod for sodium tetraiodophenolphthalein (9) consists essentially in a fusion of the sam ple (as te tra iodophenolphthalein) w ith sodium carbonate, followed by extraction and acidification of th e residue and subsequent titra tio n w ith potassium iodate according to th e m ethod of Andrews (1). T his is n o t a rapid m ethod, and furtherm ore it is subject to several inherent errors which combine to give a low value for iodine. Free iodine is lost b y volatilization and th e sodium tetraiodophenolphthalein is n o t com pletely decomposed during th e sodium carbonate fusion. T he iodine lost during th e fusion process was found to am ount to as m uch as 1 per cent of th e w eight of th e sample. T he iodine left in the mass in th e form of undecomposed sam ple varied in quan tity , probably depending on th e tem perature and length of tim e of the fusion. T his iodine was found to am o u n t to ab o u t 3 per cent.
In order to establish th e fact th a t free iodine is lost during th e fusion process in th e U. S. P. X I m ethod, and th a t th e fu
sion mass contains undecomposed m aterial, th e following experim ents were carried out:
A large porcelain crucible was inverted over the crucible cover
ing the fusion mixture, but an air space of several millimeters was allowed between the crucibles. A porcelain tube was sealed to the upper crucible through a hole bored in the bottom. This tube was in turn attached to a Pyrex glass tube leading into a bulb which could be chilled in ice. Fusion was carried out in the regular manner over a Bunsen flame with the crucible heated to a dull red. During the fusion a very slow stream of air (one to two bubbles per second) was aspirated through the system leading to the chilled tube and the free iodine lost from the fusion mass 237
238 INDUSTRIAL AND E N G IN E E R IN G CHEM ISTRY VOL. 11, NO. 5 was collected in this tube. A t the conclusion of the fusion proc
ess the Pyrex tube was removed and washed with a solution of potassium iodide. The solution containing the iodine was then titrated with sodium thiosulfate and the value for the recovered iodine calculated.
The experiment was completed by the regular U. S. P. X I procedure and the percentage of iodine in the sample calculated.
In addition, th a t portion of the fusion mass which was insoluble in the extraction process, and thus collected on the filter paper during the filtration, was analyzed for iodine according to the permanganate-silver nitrate method described in detail below.
T a b l e I. S o d i u m T e t r a i o d o p h e n o l p h t h a l e i n S a m p l e A-l
Io d in e
%
F o u n d in te tra io d o p h e n o lp h th a le in b y U . S. P . X I m e th o d 5 6 .3 3
R ecovered (v olatilized d u rin g fusion) 0 .7 5
R eco v ered from fusion residue 3 .2 7
T o ta l iodine found 6 0 .3 5
S am e sam p le b y p roposed m e th o d 6 0 .5 9
I t was shown b y these experim ents th a t iodine was lost during th e fusion process, and th a t th e U. S. P. X I fusion pro
cedure does n o t com pletely decompose th e sample. The experim ents were carried o u t on a single sam ple of te tra iodophenolphthalein precipitated and separated according to th e U. S. P. X I m ethod, and th e n divided into tw o parts.
One portion was trea ted b y th e regular U. S. P. procedure;
th e o ther portion was analyzed b y th e perm anganate-silver n itra te m ethod described in this paper. T he results given in T able I show th a t th e iodine found b y th e U. S. P. X I m ethod when added to th e iodine volatilized during fusion and to th e undecomposed iodine gave a to ta l iodine very nearly th e sam e as th e q u a n tity found b y direct analysis of th e second portion b y th e proposed nerm anganate-silver n itra te m ethod.
Ta b l e I I . De t e r m i n a t i o n o f Io d i n e i n So d i u m TETRAIODO
PHENOLPHTHALEIN
KIO»
%
54.3 1 I b y K M nC V I b y KMnO<- I b y K M nOi-
Sam ple AkN Oi K IO s Sam ple A gN O i
% % %
A-2 5 3 .4 2 B -l
A-3 ss'.V o“ B-2 54 .’21“
A -4 5 3 .7 8 “ B-3 54.51b
A -5 5 3 .5 1 “ B-4 5 4 .4 0 “
A-6 5 3 .5 4 b B-5 54.4 8 b
A-7 53.6Gb B-6 54.33b
A-8 5 3 .6 6 b B-7 5 4 .5 0 “
A v. 53 .6 4 B-8 5 4 ,3 0 b .'
A v. 54.3 9
“ E o sin ind icato r.
b D iiodofluorescein in d icato r.
e 5 % chlorine, as so d iu m chloride, was a d d ed to th is sam ple th e analysis.
Five analyses by th e U. S. P. X I m ethod gave results all more th a n 3 p er cent lower th a n th e values obtained by th e per
m anganate-silver n itra te m ethod, and, furtherm ore, the five analyses varied between them selves by as m uch as 3 per cent (Table II).
P r e lim in a r y D e v e lo p m e n t o f M e th o d A n a tte m p t was m ade to develop a procedure which would give m ore reliable results th a n th e U . S. P. X I m ethod, and a t th e same tim e would be more rapid and suitable for routine analysis. Before this w as fully developed, th e perm an- ganate-iodate m ethod was tested. An alkaline solution of th e sodium tetraiodophenolphthalein sam ple was treated w ith a sa tu ra te d solution of potassium perm anganate, the solution was acidified, and th e excess perm anganate w as re
duced w ith sulfurous acid. An ad ju stm en t was m ade w ith 0.02 N potassium perm anganate to th e poin t where th e clear solution showed th e first trace of yellow color. T he solution was m ade strongly acid w ith hydrochloric acid and th e titra tion was carried o u t w ith potassium iodate as in th e U . S. P.
X I m ethod.
T his procedure gave fairly consistent results, considerably higher th a n b y th e U. S. P., b ut, as shown in T ables I I and III, slightly lower th a n the values obtained b y th e perm an
ganate-silver n itra te m ethod. T he m ethod was rapid and was used successfully in th e au th o rs’ analytical laboratory for m ore th a n a year, b u t had certain features which were n o t altogether satisfactory.
T h e alkaline perm anganate tre a tm e n t was found very convenient for th e destruction of organic m a tte r in th e sample, and m ore satisfactory th a n th e various d ry m ethods now in use. Leclercq (7) suggested th e use of solid alkaline perm an
ganate. H is procedure also called for boiling th e alkaline perm anganate solution, and he reported th a t this caused a loss of iodine. T he authors found th a t th e oxidation was com plete and no appreciable iodine was lost w hen an excess of a satu rated solution of p erm anganate was added to a solu
tion of th e sam ple, and th e resulting solution was digested on a steam b a th for ab o u t 45 m inutes.
T a b l e I II. D e t e r m i n a t i o n o f T e t r a i o d o p h e n o l p h t h a l e i n a n d I o d i n e i n T e t r a i o d o p h e n o l p h t h a l e i n
T e traio d o p h en o l
p h th a le in Io d in e in T etraio d o p h e n o lp h th a le in b y U. S. P . B y U . S. P . B y K M n O t- B y K M n O t-
Sam ple X I X I A gN O i K IO i
% % % %
A -l 5 6 .3 3 “.b 6 0 .59b, c
A-9 86'.35 5 3 .9 4
A-10 8 0 .3 2 5 7 .1 2
A - l l 8 6 .2 1 5 6 .5 2
A-12 8 5 .7 5
A-13 60.'24
A-14 6 0 .1 8
A-15 86! 23 55.'43<i 6CK56* 6 0 .4 5
A -16 8 6 .9 5 60.5 0 *
A v. 8 6 .3 0 5 5 .8 7 6 0 .5 5 6 0 .2 9
“ Loss of iod in e d u rin g fusion d e te rm in e d as 0.75% . b R ep o rte d in T a b le I.
c D iiodofluorescein used as in d ic a to r.
d Loss of iodine d u rin g fusion d e te rm in e d as 0 .6 8 % . e E o sin used as in d icato r.
T he Andrews iodate titra tio n (1) offers an accurate end poin t b u t is n o t particularly satisfactory for a routine analysis, because th e operations of shaking and subsequent w aiting for equilibrium are tim e-consum ing. T here is also a safety hazard involved, in th a t th e flask nearly filled w ith con
ce ntrated acid m ust be shaken vigorously. F or these reasons a m ethod involving a direct titra tio n appeared to offer dis
tin c t advantages. F ajans and Wolff (5) suggested th e use of an adsorption indicator in th e silver n itra te titra tio n of iodide, and K olthoff (6) recommended eosin and diiodo- fluorescein as indicators for titra tio n of iodine in th e presence of chlorine. I t was found possible to m ake use of th is titra tion in th e determ ination of iodine in sodium tetraiodo
phenolphthalein. A fter th e oxidation of th e sam ple w ith alkaline perm anganate, th e excess perm anganate was re
duced w ith sodium bisulfite in place of th e sulfurous acid used in th e perm anganate-iodate m ethod, and either eosin or diiodofluorescein was found to be a suitable indicator.
However, diiodofluorescein is recommended, since it produces a sharper end p o in t in th is p articu la r case.
P r o c e d u r e fo r P e r m a n g a n a t e - S ilv e r N it r a t e M e th o d
Weigh accurately approximately 0.2 gram of sodium tetra
iodophenolphthalein or tetraiodophenolphthalein into a 500-ml.
Erlenmeyer flask and add 15 ml. of 5 per cent sodium hydroxide solution. Place the flask on a steam bath, and when the sample is completely dissolved, add 25 ml. of a saturated solution of potassium permanganate. Wash down the sides of the flask and let the solution digest on a steam bath for about 45 minutes, swirling the solution in the flask a t about 5- or 10-minute inter
vals. Remove the flask from the steam bath, cool under the tap to room temperature, and add 75 ml. of distilled water and 10 ml. of dilute sulfuric acid. Add slowly from a buret a con
centrated solution of sodium bisulfite until the solution in the flask becomes colorless. Finally add 2 ml. of glacial acetic acid, one 1.25-cm. (0.5-inch) cube of ammonium carbonate, and 1 ml.
of a 0.5 per cent solution (in 70 per cent ethyl alcohol) of diiodo
fluorescein indicator. T itrate the solution in diffuse light with
MAY 15, 1939 ANALYTICAL E D IT IO N 239 0.1 N silver nitrate until the color changes from a brownish red
to a bluish red color. [In case eosin indicator is used, add 20 drops of a 0.1 per cent solution (in 70 per cent ethyl alcohol) of the dye and titrate to the appearance of a pink color. ] The results obtained by this method on two different samples of sodium tetraiodophenolplithalein are shown in Table II.
In th e U . S. P . X I procedure for sodium tetraiodophenol- phthalein, the iodine determ ination is carried o u t on th e pre
cipitated and dried tetraiodophenolphthalein. In T able I I I is shown a series of com parative analyses on th e te tra iodophenolphthalein produced from portions of sodium tetraiodophenolphthalein sam ple A. T he q u a n tity of te tra iodophenolphthalein found in several analyses has also been tabulated. I n analysis A-15, com parative results for iodine b y three m ethods based on an identical sam ple of te tra iodophenolphthalein are shown.
C h e c k b y P r e g l C o m b u s tio n M ic r o m e th o d T he P regl (10) com bustion m icrom ethod was utilized as a check on th e results obtained b y th e perm anganate-silver n itra te m ethod. T he Pregl m ethod was applied on a semi
m icro scale, and th e iodine was determ ined both by weighing as silver halide and titra tin g w ith silver n itra te using an ad
sorption indicator. T he double m icroanalysis served as a check on b o th th e iodide content of th e sam ple and th e titra tion m ethod itself. If there was an appreciable q u a n tity of chloride in th e sample, th e gravim etric m ethod alone would be inadequate, b u t th e titra tio n m ethod should n o t be in
fluenced b y th e presence of chloride.
Ta b l e I V . Io d i n e i n So d i u m Te t r a i o d o p h e n o l p h t h a l e i n b y Mi c r o m e t h o d s
W t. of W t. of P p t. or I b y G ra v i- I b y V olu
Sam ple Sam ple Vol. of A gN O j m e tric m etric
M g. M g. % %
A-17 3 1 .0 1 2 3 .2 2 5 3 .8 2
A-18 2 0 .0 2 14.6 2 5 3 .8 8
A-19 18.15 1 3 .2 7 5 3 .8 0
A-20 3 0 .2 1 2 1 .7 6 5 3 .8 2
M l.
A-21 2 8 .1 0 1.1 9 2 53.84«
A-22 3 0 .8 2 1 .3 0 8 53.8 6 ^
A-23 2 0 .7 7 0 .8 8 2 5 3 .8 9 “
M g . A v. 5 3 .8 3 5 3 .8 6
B-9 8 .9 2 6 .4 9 5 4 .3 6
B-10 2 0 .7 8 15 .2 3 54 .4 1
B - l l 13.21 9 .6 1 5 4 .3 8
M l.
B-12 64 .1 4 2.7 5 0 54 .4 2 «
B-13 26 .8 3 1.151 54.44«
B-14 2 0 .3 7 0 .8 7 5 54.51&
B-15 2 3 .2 8 1.0 0 0 54.511-
A v. 5 4 .3 8 5 4 .4 7
« E o sin in d ic a to r.
b D iiodofluorescein in d ic a to r.
Samples for the microanalyses were weighed on an assay balance sensitive to 0.01 mg., and the titrations were made with a microburet graduated to 0.02 ml. About 25 mg. of sodium tetraiodophenolphthalein were weighed into a platinum boat of about 3 X 4 X 12 mm. The boat with sample was introduced into a combustion tube constructed according to Pregl, and con
taining a glass spiral for the absorbent. The sample was burned in a slow stream of oxygen and the liberated iodine was absorbed in a saturated solution of sodium carbonate containing a few drops of sodium bisulfite solution. Oxygen was passed through the tube for about 30 minutes after the combustion was com
pleted. When the tube was cool it was rinsed out with water.
The excess of reducing agent was removed from the solution by the addition of a few drops of 27 per cent hydrogen peroxide. A mixture of silver nitrate and nitric acid was used to precipitate the silver halide and the precipitate was filtered on a platinum Gooch crucible having a very fine, dense platinum-sponge mat.
The crucible and precipitate were dried in an oven a t 250° C., cooled, and weighed as silver iodide. All details were carried out according to Pregl except in the use of the platinum-sponge crucible.
The procedure for the volumetric micromethod was carried out exactly as in the gravimetric micromethod up to the point where the combustion process was completed. The combustion
tube was rinsed out, and the solution was made acid with acetic acid and titrated with 0.1 N silver nitrate using an adsorption indicator. Both diiodofluorescein and eosin were used in these analyses. The results by microanalysis are shown in Table IV.
Ta b l e V . Co m p a r i s o n o f Av e r a g e Re s u l t s Io d in e F o u n d
Sam p le A S am p le B
% %
S em im icrom ethod
K M n O i-A g N O j m e th o d 5 3 .8 4 ^ 0 .0 3
5 3 .6 4 0 .0 8 5 4 .4 3 =*= 0 .0 5 5 4 .3 9 =*= 0 .0 9
T he tw o m icrom ethods gave fairly consistent results and agreed reasonably well w ith each other. T h e results obtained by th e m icrom ethods were slightly higher th a n , b u t still in close agreem ent w ith, th e results b y th e p erm a n g a n a te - silver n itra te m ethod (Table V).
D is c u s s io n
T he perm anganate-silver n itra te m ethod is suitable for routine analysis of sodium tetraiodophenolphthalein. T he sam ple is weighed directly into th e flask and oxidation and titra tio n are carried o u t in th e sam e flask w ith no transfers involved. If th e sam ple has n o t been com pletely decom
posed b y th e perm anganate treatm en t, this fact can easily be observed by th e appearance of th e solution after th e excess perm anganate has been reduced. T he silver n itra te titra tio n is rapid and th e end poin t is easily detected. A single analysis can be carried out in ab o u t 1.5 hours, and i t is possible to com plete ten or more analyses in one day.
T he U. S. P. X I procedure for sodium tetraiodophenol
phthalein calls for th e determ ination of tetraiodophenol
phthalein, followed b y an iodine assay on th e dried sam ple of tetraiodophenolphthalein. T he results of this determ ination are n o t particularly concordant, as can be seen by T able I I I . If th e sam ple of sodium tetraiodophenolphthalein contains soluble iodide, it will n o t be detected by th e present U. S. P.
X I procedure. T he control analysis of sodium tetraiodo
phenolphthalein could be very satisfactorily effected b y m eans of an iodine determ ination on th e original sample, supple
m ented by a te s t for soluble iodide. T his procedure would elim inate th e present unreliable and tim e-consum ing de
term ination of tetraiodophenolphthalein. T he soluble iodide could be determ ined b y dissolving a sam ple in w ater, pre
cipitating th e tetraiodophenolphthalein w ith acetic acid, and filtering. T he filtrate and washings could be titra te d w ith 0.1 N silver n itra te using diiodofluorescein as indicator.
T he end poin t w ith th is indicator is sharp and reliable for sm all quantities of iodide in th e presence of as m uch as 5 per cent of chloride. Samples A and B showed 0.29 an d 0.26 per cent of titra ta b le iodide, respectively.
A c k n o w le d g m e n t
T he authors wish to express th eir appreciation to H . V.
F a rr and M elvin A. T horpe for th eir cooperation an d interest in th is sodium tetraiodophenolphthalein assay investigation.
L ite r a tu r e C ite d
(1) Andrews, L. W„ J . A m Chem. Soc., 25, 756 (1903).
(2) Baubigny and Chavanne, Compt. rend., 136, 1198 (1903).
(3) Carius, L., A n n . Chem. Pharrn., 116, 1 (I860).
(4) Delbridge, T . G„ A m . Chem. J ., 41, 397 (1909).
(5) Fajans and Wolff, Z . anorg. allgem. Chem., 137, 221 (1924).
(6) Kolthoff, I. M „ Z. anal. Chem., 70, 395 (1927); 71, 235 (1927).
(7) Leclercq, L., J . pharm. belg., 17, 837 (1935).
(8) Leclercq and Clossot, Ibid., 20, 233, 253 (1938).
(9) Pharmacopoeia of the United States, X I, p. 196 (1936).
(10) Pregl, F., “Quantitative Organic Microanalysis” , 2nd English ed., p. 130, Philadelphia, P. Blakiston’s Son & Co., 1930.
(11) Seeker and Mathewson, Chem. News, 103, 61 (1911).
(12) Volhard, J., J . prakt. Chem., 117, 217 (1874).
D eterm ination o f D issolved O xygen in A queous Solutions
G . A . P E R L E Y
L e e d s & N o r t h r u p C o ., P h i l a d e l p h i a , P e n n a .
T
H E W inkler m ethod is recognized as reliable except w here very sm all q uantities of dissolved oxygen are involved. T hree types of errors m ay arise w hen applying this m ethod to th e estim ation of traces of dissolved oxygen in w ater: (1) Im purities in th e w ater such as nitrites, sulfites, iron ions, and organic m a tte r m ay cause inaccuracies; (2) the correction for th e dissolved oxygen added in th e reagents m ay introduce uncertainties; (3) th e dependence of th e titra tio n end p o int of th e iodine upon th e n a tu re of th e starch and upon th e tem p eratu re introduces other uncertainties.
T h eriau lt (8) has discussed th e determ ination of dissolved oxygen by th e W inkler m ethod; an excellent bibliography on th e determ ination of dissolved oxygen in w ater by all m ethods has been presented by Schw artz (0); and th e problem as applied to boiler feed w ater has been considered b y W hite, Leland, and B u tto n (10). W ith such excellent reviews available, it seems unnecessary to discuss th e earlier work.
Our problem involves the analyses of power p la n t w aters, p articularly where th e oxygen concentrations are less th a n 0.5 ml. per liter. W hen the au th o r had occasion to calibrate in d u strial dissolved oxygen recorders, th e serious lim itations of th e starch-iodide titra tio n end point becam e app aren t. T he sam pling m ethod suggested b y Sw artz and G urney (7) was adopted in an effort to correct for th e errors from im purities and from th e oxygen added in th e reagents. W hen th e work was sta rted , th e au th o r did n o t have available th e sam pling procedure of W hite, Leland, and B u tto n (10), who collected th e dissolved oxygen in th e distillate from th e sam ple in an effort to elim inate th e nonvolatile substances which affect th e accuracy. T h ey used essentially th e a u th o r’s titra tio n m ethod (3).
I o d o m e tr y b y E le c tr o m c tr ic M e th o d s W illard and Fenwick (11) and Van N am e and Fenwick (9) suggested a bim etallic electrode system for use in th e electro
m etric titra tio n of iodine. Foulk and Bowden (1) modified th e previous bim etallic electrode titra tio n and described a
“ dead-stop end p o in t” m ethod for iodom etry. Hewson and Rees (2) applied the above m ethod to th e determ ination of iodine liberated b y th e W inkler reagents.
A consideration of the electrom etric determ ination of iodine in solution leads to th e following:
I , + 2S20j ;=± S<08 + 2 1 - or I2 + 2 (e) — 21—
w hich is a case of th e general class Oxidant + (e) ^ reductant
Kolthoff U) showed th a t th e po ten tial of th e iodine elec
tro d e a t 25° C. is represented by th e equation:
A ccording to Jones and K ap la n (3), w hen using a sa tu ra te d iodine electrode, we have a t 25° C.
E = 0.5362 - 0.059 log [ I“ ]
Kolthoff (4) pointed o u t th a t th e p o tential of th e iodine electrode depends upon the iodide concentration.
Kolthoff and F urm an (6) considered th a t th e thiosulfate- te tra th io n a te electrode is irreversible.
T he p latinum -saturated calomel electrode is one of th e m ost satisfactory for electrom etric oxidation-reduction system s.
I t seemed th a t th e electrom etric m ethod should be p a r
ticularly applicable to th e determ ination in question.
M e th o d o f A n a ly sis
S a m p l i n g . All oxygen m u st be rem oved from th e sam pling system before sam pling is begun.
W hen th e w ater is a t elevated tem peratures and pressures, it is necessary to avoid flashing of th e sam ple. T he flow to the sam pling bottles should be controlled b y adjusting a valve on th e discharge side of an adequate cooling coil.
T he tem p eratu re of th e w ate r a t th e sam pling tim e should be slightly below th a t of th e room tem perature. T he tem p era tu re of th e sam ple b o ttle should n o t be allowed to de
crease 1° C. betw een th e tim e of sam pling an d th e tim e of analysis. Hence, th e tem p eratu re a t th e sam pling p o in t preferably should n o t exceed 30° C. (86° F .).
Three samples are collected in scries in sampling bottles equipped with rubber stoppers and with inlet and outlet tubes.
The sampling bottles should be slightly oversize and should have narrow mouths designed to accommodate ground-glass stoppers.
The end of the glass stoppers should be ground to a semiconical shape to prevent trapping of air bubbles when replacing stoppers.
No trace of a gas bubble can be tolerated in the top of the sam
pling bottles. Two 250-ml. samples and one 500-ml. sample should be taken.
The water sample should enter one of the 250-ml. bottles through a tube extending to the bottom. The sample overflows through an outlet tube a t the top into the 500-ml. bottle intake tube. This overflows into the second 250-ml. bottle. McLean sampling tubes may be used in place of the bottles. Glass-to- glass b u tt connections should be provided for all connections.
Rubber tubing is used merely to hold the connections in place.
At least seven times the total volume of the three sampling bottles should be withdrawn before the sampling is stopped.
R e a g e n t s . T he following stock reagents are desirable:
0.1 molar stock sodium thiosulfate solution, 24.82 grams of NasSjOa.SHaO per liter (stored in a brown bottle protected by a soda-lime tube). A 0.01 molar sodium thiosulfate solution is made up from the above solution and standardized each day by means of a 0.01 molar potassium biiodate solution.
0.01 molar stock potassium biiodate solution, 0.3250 gram of KIOj.HIOs per liter.
Manganous chloride solution, 412 grams of MnCl2.4H20 dis
solved in distilled water and made up to 1 liter.
Alkaline-iodide reagent, 700 grams of potassium hydroxide and 150 grams of potassium iodide per liter. The reagent should be free from carbonates, as manganese carbonate does not react with dissolved oxygen. A paraffined glass stopper should be used in the bottle.
Concentrated sulfuric acid of specific gravity 1.84, diluted with an equal volume of water.
P r o c e d u r e . T he 500-ml. sam ple and one of th e 250-ml.
sam ples are trea ted as follows:
Remove the rubber stopper with inlet and outlet tubes. By means of separate pipets rapidly add 2 ml. of the alkaline reagent, and then 2 ml. of the manganous chloride reagent. Both re
agents sink to the bottom of the bottle without excessive air contamination when the tip of the pipet is held below the sur
face of the sample. Rapidly insert the glass stopper. The slightly air contaminated upper portion of the sample is elimi
MAY 15, 1939 ANALYTICAL EDITION 241 nated by the overflow when the glass stopper is replaced. Shake
thoroughly for 2 minutes and let stand until the precipitate settles three quarters of the height of the sampling bottle. Remove stopper, add 2 ml. of sulfuric acid reagent, replace stopper, and shake thoroughly until the precipitate dissolves.
Iodide solutions are slowly oxidized by air. Accordingly, the glass stopper should not be removed from the sample bottles until all is prepared for the subsequent titration. The titration should be easily completed in less than 5 minutes; hence the error due to the liberation of iodine by air oxidation is very small.
Measure out exactly 250 ml. of the sample from the 250-ml.
bottle. Add exactly 250 ml. of untreated water from the other 250-ml. bottle. Then add 0.5 ml. of 0.01 N potassium biiodate solution from a pipet. The addition of the standard biiodate solution serves as a check on the titration, particularly when small traces of oxygen are involved in the analysis. Proceed to titrate electrometrically with 0.01 N sodium thiosulfate, using a certi
fied buret with a special small tip to give not over 0.02 ml. per drop. Measure out exactly 500 ml. of the sample from the 500- ml. bottle, add potassium biiodate solution in the exact amount used in the 250-ml. sample, and titrate as in the previous case.
The oxygen content for a 250-ml. sample is determined by the difference between the 500-ml. and the 250-ml. sample.
(1 ml. of 0.01 N Na2S20 3 is equivalent to 0.0612 ml. of oxygen a t 25° C. and 760 mm.)
As an optional procedure, a titration with 0.01 N potassium biiodate solution may be found to give slightly greater accuracy.
If this method is used, a known excess of 0.01 N sodium thio
sulfate should be added.
E le c tr o m e tr ic T it r a t io n
A 1 X 1 cm. sheet of p latinum provided w ith a suitable lead wire is used as th e indicator electrode, and a saturated calom el-saturated potassium chloride system is used as the reference electrode. T he tw o electrodes are m ounted in an 800-ml. beaker. S tirring should continue during th e entire titra tio n . A m echanical stirre r is desirable. A portable potentiom eter w ith a range of 0 to 1100 millivolts is used to ob tain th e e. m . f. per ml. of thiosulfate relationship.
I t is n o t necessary to m ake a com plete titra tio n , since the significant a b ru p t e. m. f. change is easily detected. The
stan d ard thiosulfate solution m ay be added rapidly u n til th e e. m .f. is approxim ately 0.3100 volt, and th e titra tio n then continued drop by drop un til th e end point is reached. T he end poin t occurs betw een 0.290 and 0.260 volt, depending upon th e n atu re of th e solution, th e p H of th e solution, and th e concentration of th e iodide present. In any instance, a t th e exact end poin t one drop of 0.01 N thiosulfate solution results in an a b ru p t drop of over 30 millivolts. T he au th o r has found th a t th e end poin t for th e average high-purity w ater involved in power p la n t boiler practice occurs a t an e. m. f. value of 0.2900 v o lt for tem peratures between 15° and 30° C.
As th e end p o in t is approached in iodine solutions, th e e. m. f. tends to d rift slowly to a higher voltage value im m ediately after th e addition of thiosulfate. A t th e end poin t there is no tendency to drift. W ith an excess of thio
sulfate, there is a tendency for th e e. m . f . to d rift to lower voltage values. As a m a tte r of fact, th e use of a properly sensitive galvanom eter is all th a t is required to d ete c t th e end point by the d rift m ethod; however, th is is m ore critical to operate th a n th e above potentiom eter m ethod.
Figure 1 shows a portable u n it which th e au th o r used to carry o u t dissolved oxygen tests in the field. Provision has been m ade for all th e necessary pipets, buret, electrodes, sample bottles, beaker, and m echanical stirring equipm ent.
An antim ony electrode is also included so th a t w hen used w ith a suitable portable potentiom eter, it is also possible to obtain pH m easurem ents.
I n flu e n c e o f V a rio u s Io n s
T he norm al variations in th e concentration of sulfate and chloride ions have little influence on th e end point. T he iodide-ion concentration changes th e e. m . f. value of th e in
flection point, y e t th e same thiosulfate end p o int results, ir
respective of th e iodide concentration. T he inflection point of the curve for th e e. m . f. per ml. of thiosulfate occurs a t a lower voltage for high iodide concen
tratio n s th a n for low iodide con
centrations. T his is co n stan t for th e a u th o r’s procedure and hence does n o t involve an y error.
T he hydrogen-ion concentration m ust be controlled w ithin lim its.
T he a u th o r’s m ethod is sufficiently standardized so th a t th e hydrogen- ion concentration is held w ithin th e desired lim its. M ore thiosul
fate is required to reduce all of the iodine to iodide as th e concentra
tion of hydrogen ion is increased.
T he m ore nearly th e solution is held to 7.0 pH , th e less is th e effect upon th e thiosulfate end point.
Fi g u r e 1. Po r t a b l e Un i t
P r e c is io n o f t h e M e th o d T he high sensitivity of th e change a t th e end point is no te
w orthy. One drop of thiosulfate from a specially small b u ret tip , which has been found to be equiva
le n t to 0.02 ml., results in a 30- m illivolt change. T h u s th e au th o r was able to detect th e presence of 0.0000016 gram of oxygen in th e 250-ml. sample. T his is roughly 0.0064 p a rt b y w eight of
242 IND U STR IA L AND E N G IN E E R IN G CHEM ISTRY VOL. 11, NO. 5 oxygen per million p a rts b y w eight of w ater (1 p a r t in ab o u t
156,000,000).
T ests indicate th a t th e lim it of error of th e titra tio n is
±0.001 ml. of oxygen a t 25° C. and 760 mm.
A d v a n ta g e s o f t h e M e th o d
T he au th o r has used this equipm ent extensively in con
nection w ith power p la n t te sts and has found th e following advantages in m aking dissolved oxygen determ inations:
T he use of th e simplified electrom etric titra tio n procedure elim inates th e tem perature, starch quality, and personal equation errors of th e starch-iodide m ethod.
T he analysis is based upon a difference determ ination w hereby th e influence of dissolved oxygen in th e reagents, small ionic variations of foreign substances, secondary re
actions, loss of dissolved oxygen by displacem ent, possible
contam ination of th e sam ple b y air w hen th e reagents are added, and tem p eratu re variations are minimized.
T he com plete equipm ent can be m ade in portable form.
L ite r a tu r e C ite d
(1) Foulk and Bowden, J . A m . Chem. Soc., 48, 2045 (1926).
(2) Hewson and Rees, J . Soc. Chem. In d ., 54, 254t (1935).
(3) Jones and Kaplan, J . A m . Chem. Soc., 50, 2066 (1928).
(4) KolthofT, Rec. Irav. chim., 41, 172 (1922).
(5) Kolthoff and Furman, ‘‘Potentiometric Titrations”, 2nd ed., p.
69, New York, John Wiley & Sons, 1931.
(6) Schwartz, M. C., Louisiana State Univ., U niv. Studies No. 21 (1935).
(7) Swartz and Gurney, Proc. A m . Soc. Testing M aterials, 34, 796 (1934).
(8) Theriault, E. J., Pub. Health B ull. 151; Suppl. 90 (1925).
(9) Van Name and Fenwick, J . A m . Chem. Soc., 47, 9, 19 (1925).
(10) White, Leland, and Button, Proc. A m . Soc. Testing M aterials, 36, 697 (1936).
(11) Willard and Fenwick, J . A m . Chem. Soc., 44, 2504, 2516 (1922).
M easurem ent o f P lastic Properties o f B itu m inou s Coals
C om p arison o f G ieseler and D a v is P la sto m eter an d A gd e-D am m D ila to m eter M ethods
R . E . B R E W E R AND J . E . T R I F F , C e n t r a l E x p e r i m e n t S t a t i o n , B u r e a u o f M i n e s , P i t t s b u r g h , P e n n a .
T
H E torsional principle— th a t is, th e m easurem ent of resistance to shear caused by m ovem ent of a stirring device w ithin the heated coal charge— was first applied in 1931 b y D avis (6) to th e determ ination of th e “ p lastic”properties of bitum inous coking coals. Since then, this general principle has been em ployed in various form s of other instrum ents (9-13). A lthough th e la ter designs of th e D avis plastom eter have incorporated a few m inor changes to ensure sm oothness in operation and im prove general appearance, th e original instrum ent, after m ore th a n seven years of continued use, has proved satisfactory. I t has been found, however, th a t th e procedure (5-8) gives m ore uniform te st results when modified (3), especially by th e use of a larger sam ple of representative coal and b y operation of th e re to rt a t a slower speed of rotation, and th a t “m inor lim itations lie in th e difficulties of determ ining accurately small changes during th e period of greatest fluidity and extrem ely high resistances, above 63.4 kg.-cm. (55 pound-inches) shown by certain coals.” These difficulties have been overcome b y th e use of tension springs w ith a sensitivity of less th a n 0.23 kg.-cm.
(0.2 pound-inch), during th e period of greatest fluidity, which perm it accurate m easurem ents of resistances up to 149.8 kg.-cm. (130 pound-inches).
In th e D avis plastom eter m ethod (5) th e coal charge as a whole is rotated and stirred; th e pro p erty m easured is th e resistance to shear of th e p artly fused coal adhering to the inner periphery of th e reto rt. In th e Gieseler plastom eter m ethod (9) th e coal is static a t th e sta rt, and la ter stirring is proportional to the fluidity of th e coal. Accordingly, w ith increase in fluidity of the heated coal are noted (a) a decrease in resistance, or torque, m easured in kilogram-centimeters, in th e D avis ro ta ry retort, and (b) an increase of th e ra te of ro tatio n of th e stirring shaft in th e Gieseler sta tio n a ry retort.
In (a) th e resistance is created by th e m ovem ent of th e coal in the re to rt against th e rabble arm s on th e inside shaft, which is prevented from free ro tatio n by th e tension springs; in (6) th e ro tation of th e stirring shaft is caused b y application of a co nstant force on th e loading pan.
Gieseler (9) criticized th e m ethod of D avis (S) because the coal is heated under conditions corresponding to those of a ro tary reto rt, perm ittin g volatile m a tte r and ta r to escape more freely th a n in a coke oven. Gieseler (9) m ade th e broad assertion th a t all m ethods for th e determ ination of plasticity in which th e coal is n o t prevented from expanding are unsatisfactory, quoting a sta te m en t from D avies and M o tt (4) th a t a “ coal which is free to expand loses volatile m a tte r readily and plasticity ends a t a com paratively low tem perature.” D avies and M o tt (4) showed, however, th a t th e tem perature of solidification, term ed by them th e “ end of plasticity ” , is higher th a n th e tem perature of final expansion as determ ined b y th e Sheffield laboratory coking te st on a num ber of th e b e tte r coking coals.
A t th e beginning of th e solidification of a m elted coal mass into semicoke a coal rapidly loses its fluidity. A t th is stage the Gieseler in stru m en t n atu ra lly shows w ith increasing tem perature less and less m ovem ent of th e stirring shaft per unit of tim e, and as semicoke form ation proceeds th is move
m en t falls off rapidly to zero. T he ap p aren t discrepancy in the in terp retatio n of th e “ end of p lasticity ” is, therefore, purely one of definition. T he tem p eratu re lim its of the plastic range for th e D avis plastom eter te st are defined as the difference betw een th e tem perature a t which resistance develops and th a t a t which resistance ends. T his la tte r tem p eratu re is some degrees higher, th e m agnitude varying w ith different coals, th a n th a t of m axim um resistance or solidification, which, in tu rn , is higher th a n th e tem perature
