INDUSTRIAL A N D ENGINEERING CHEMISTRY
A N A L Y T I C A L E D I T I O N
AiSE?«v'y
H A R R IS O N E. H O W E, E D IT O R • ISSUED F E B R U A R Y 15, 1940 9 V O L. 12, NO. 2 • C O N S E C U T IV E NO. 4
Es t i m a t i o no p Tr a c e s o f Le a d a n d Th a l l i u m i n Ph a r m a c e u t i c a l Ch e m i c a l s...K a r l B a m b a c h 6 3
Pr a c t i c a l Ev a l u a t i o no p Co m m e r c i a l Ru b b e r Ca r b o n Bl a c k sb y X - Ra y Di f f r a c t i o n...
...G e o r g e L . C l a r k a n d H e r b e r t D . R h o d e s 6 6
Wi j s Io d i n e Nu m b e r s f o r Co n j u g a t e d Do u b l e Bo n d s . . W i l l i a m C . F o r b e s a n d H a r v e y A . N e v i l l e 7 2
An a l y s i so f Su l f i t e So l u t i o n s Co n t a i n i n g Se l e n i u m . .R . C . S h a v e r a n d C . R . M c C r o s k y 7 4
An a l y s i s o f Na p h t h e n i c Ac i d s...
...J . R . M . K l o t z a n d E d w i n R . L i t t m a n n 7 6
Co n t i n u o u s La b o r a t o r y Me t h o d f o r Bo d y i n g Oi t i c i c a Oi l. . . V i n c e n t M a r c h e s e , J o s e p h M a t t i e l l o ,
a n d L i n c o l n T . W o r k 7 7
De t e r m i n a t i o n o p Py r e t h r i n I ...
.D . A . H o l a d a y a n d J . J . T . G r a h a m 8 0
An a l y s i s o f Ru b b e r f o r Ce r t a i n Di a r y l a m i n e a n d Ke t o n e- Di a r y l a m i n e An t i o x i d a n t s...
...L . H . H o w l a n d a n d E . J . H a r t 81
So l v e n t Ac t i o n o f Li q u i d Pr o p a n e o n Pe n t a n e- So l u b l e Fr a c t i o n o p Hi g h- Te m p e r a t u r e Bi t u m i n o u s Co a l Ta r ...C . S . K u h n , J r . 8 6
An a l y s i s o f An i l i n e- Wa t e r So l u t i o n s...
... J o h n G r i s w o l d 8 9
Po s s i b l e So u r c e o f Er r o r i n Gr a v i m e t r i c De t e r m i n a t i o n s In v o l v i n g Us e o p Hy d r o g e n Pe r o x i d e Fo l l o w e d b y Ni t r o n...
... R a l p h C . Y o u n g a n d P e t e r M . B e r n a y s 9 0
Co n t i n u o u s Ex t r a c t i o n o p Aq u e o u s So l u t i o n s b y Ac e t o n e- Pe t r o l e u m Et h e r...
...M . W a y m a n a n d G . F . W r i g h t 9 1
Pr o d u c t i o n o f Lo w Te m p e r a t u r e s...
...H e l e n L . W i k o f f , B e n j a m i n R . C o h e n , a n d M o r t o n I . G r o s s m a n 9 2
D e t e r m i n a t i o n o p S m a l l A m o u n t s o f C o p p e r a n d M a n g a n e s e i n D y e s a n d O t h e r O r g a n i c M a t e r i a l s . G . F . Palfrey, R . H. Hobert, A . F . Benning,
and I . W. D obratz 94 S t a b i l i t y o f P e r o x i d i z e d T i t a n i u m S o l u t i o n s . . . .
.Gilbert H . Ayres and Edm ay M. Vienneau 96 E s t i m a t i o n o f S m a l l A m o u n t s o p A r s e n i c i n C o p p e r .
... Bartholow Park 97 Q u a l i t a t i v e T e s t f o r E t h y l V a n i l l i n i n V a n i l l a
E x t r a c t ...Howard W . Chenowetli 98 M e a s u r i n g P e r m e a b i l i t y o p R u b b e r t o V a r i o u s
G a s e s ...A . S . C arptenter and D . F . Twiss 99 Hig h- Te m p e r a t u r e Re s is t a n c e- Ty p e El e c t r ic La b o
r a t o r y Fu r n a c e s...
... Wallace M. Hazel and Wm. J. O’Leary 109 C o m p a c t G a s S a t u r a t o r ...Aaron E . M arkham 112 P r e c i s i o n C r y o s t a t f o r R a n g e—35° t o + 2 5 ° C . . . .
...Edwin E. Roper 113 Ne b u l i z e r f o r In h a l a t i o n Ex p e r i m e n t s...
... Roiland J. M ain 117 M ic r o c h e m is t r y :
Es t im a t io no f Su b m ic r o q u a n t it i e so f Ca l c iu m . . . ... Albert E. Sobel and I. Allan Kaye 118 I m p r o v e d I o d i n e A p p a r a t u s . . . . F . X. Gassner 120 As i i i n Or g a n ic Co m p o u n d s...
. . . . A. R. Norton, G. L. Royer, and R. Koegel 121 Mo d if i c a t io n o p Ra u s c h e r’s Me t h o d f o r De t e r
m in in g Me r c u r y...
. . . .Anthony Shukis, Jr., and Ralph C. Tallnmn 123 M i c r o d e t e r m i n a t i o n o f O r g a n i c C a r b o n b y W e t
M e t h o d . . . . Ed. F . Degering and T . Z Ball 124 F u r n a c e f o r M i c r o - C a r i u s D e t e r m i n a t i o n . . . .
...Julius A. Kuck and Maurice Griffel 125
The American Chemioal Society assumes no responsibility for the statem ents and opinions advanced by contributors to its publications.
24,800 copies of this issue printed. C opyright 1940 by American Chemical Society.
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Published by th e American Chemical Society, Publication Office, 20th &
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4 IN D U STR IA L AND E N G IN E E R IN G CH EM ISTR Y VOL. 12, NO. 2
DRYING PRECIPITATES
F U S I O N S - A S H DETERMINATIONS HEATING M E T A L S • E N A M E L I N G
"C o m p a c t a n d Efficient" w a s the verd ict o f John Strelow , Supt. o f the D a ve n p o rt, Io w a S e w a g e \ T r e a t m e n t D e p a r t m e n t , on the M u ltip le U n it M u ffle Furnace used in their la b o ra to ry fo r the ig n itio n a n d b u r n in g o f s e w a g e solid s. M u n ic ip a l a s w e ll a s In d u stria l L ab o ra to rie s h a v e fo u n d m a n y uses fo r M u ltip le U n it M u ffle Furnaces.
T y p e 6 2 ? M u ltip le Unit M u ffle Furn ace at S e w a g e Treatm ent La b o ra to ry D avenportr Io w a
H E V I D U T Y E L E C T R I C C O M P A N Y
T R A D E M A R K
LABO RATO RY FU RN ACES
MULTIPLE UNIT
ELECTRIC EXCLUSIVELYREG. U. S. PAT. OFF.
M I L W A U K E E , W I S C O N S I N
FEBRU A RY 15, 1940 ANALYTICAL E D IT IO N 5
means
Research in Glass
F o r m e a s u rin g th e ra te o f flow o f g ase s •/
a n d fo r m e a s u rin g vacuum , th e se tw o ...
n e w “ P Y R E X ” b ra n d in s tru m e n ts b rin g
n e w e c o n o m y a n d c o n v e n ie n c e. B o th a re c a re fully fa b ric a te d fro m “ P Y R E X ” b ra n d B a la n c e d G lass, m e c h a n ic ally s tro n g , c h em ically sta b le a n d h e a t re sista n t. B o th , th r o u g h n e w a n d im p ro v e d d e sig n , a re s im p le in c o n s tru c tio n , e a sie r to use, lo n g -liv ed .
T h e New “ P Y R E X ” B ran d F lo w m ete r L ow in p ric e , se lf-c o n ta in e d , th is n e w im p ro v e d F lo w m e te r n e ed s n o e x tra p a rts , re q u ire s n o d is m a n tlin g o r re a s s e m b lin g . Its f s to p p e r has fo u r orifices— Vi> Vz. 1 a n d 2 m m . Y o u m erely tu rn th e s to p p e r to th e d e s ire d orifice. T h e d ire c tio n o f flow is in d ic a te d . S im ple and easy to use th is new , im p ro v e d F lo w m e te r offers re a l value.
T h e New “ P Y R E X ” B ra n d M a n o m e te r T h is M a n o m e te r offers you n ew co n v e n ie n c e in vacuum m e a su re m e n t. O f ru g g e d w a ll c o n s tru c tio n , its sim p le d e sig n m ak es fo r lo w cost.
Its scale r a n g in g fro m o to 16o m m is m a c h in e e n g ra v e d , acid etc h e d , a n d filled w ith easy-to- re a d re d p ig m e n t.-T h e re are tw o types— s tra ig h t sid e a rm a n d “T ” sh a p e d arm . F illin g is q u ic k a n d easy. In s tru c tio n s fu rn ish e d w ith e ach p iece.
B o th o f th e se n e w tim e an d m o n ey sa v in g aids are av ailab le th r o u g h la b o ra to ry su p p ly d e a le rs.
Approx. Approx.
Overall Overall Width Height
mm. mm.
Number and Type
5 9 6 0 F L O W M E T E R Complete
T Stopper 1 5 5 30 5 3 $6 .8 0
6 9 5 0 M A N O M E T E R
Mercury, Improved Type, Complete
f Stopper 2 2 0 4 $4-8 5
6 9 5 2 M A N O M E T E R Mercury, Improved Type,
W ith Tee Connection, Complete
T Stopper 2 2 0 4 S 5 .1 5
Usual quantity discounts apply to original packages and assortm ents
o f 20, 50 and 100 orig in al packages. BUsStW fii i
’P Y R E X " is a registered trade-mark an d indicates manufacture by C O R N I N G , N E W Y O R K C O R N I N G G L A S S W O R K S
6 IN D U STR IA L AND E N G IN E E R IN G CH EM ISTR Y VOL. 12, NO. 2
THE MERCK
INDEX
Is Now Available
An Encyclopedia oí Chemicals and Drugs for the Chemist, Pharmacist, Physician, Dentist & Veterinarian.
Thousands of chemists, pharm acists a n d physicians h a v e been w a itin g for this n e w b ook.
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(P rice in C a n a d a , $3.50)• 1,060 pages—nearly twice the num ber of th e previous editions.
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tions of individual substances.
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tion, “ Chemical, Clinico-Chemical Reactions, T ests and R eagents by the A u th o r’s N am e” which includes more th a n 4,500 num bered T ests, R eac
tions and R eagents.
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ics,” 113 colors are described.
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tion of 187 minerals.
• A nother new section contains form u
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tions, com prising a to ta l of 212 for
m ulas and m ethods of preparation.
• Also Useful Tables, A ntidotes for Poisons, and L ite ra tu re References.
P rin ted in clear ty p e on English finish paper, bound in black semi-flexible im i
ta tio n leather covers and stam ped in gold.
The Fifth Edition of
W h a t Trade a n d P ro fe ssio n a l J o u rn a ls S a y a b o u t The M e rc k In d e x
B rie f e x c e rp ts fro m som e o f th e c u r re n t p u b lic a tio n s w h ich c a rrie d re v ie w s o f T h e M e rc k I n d e x :
“ B y r e a s o n o f t h e w e a lt h o f i n f o r m a t i o n c o n t a i n e d , T h e M e r c k I n d e x w i l l b e c o m e a n i m p o r t a n t p a r t o f e v e r y p h a r m a c e u t i c a l l i b r a r y . " — D ru g T ra d e N ew s.
“ T h i s e n c y c lo p e d ia o f c h e m i c a l s a n d d r u g s r e p r e s e n t s t h e m o s t e x t e n s i v e c o m p i l a t i o n o f t h i s a u t h o r i t a t i v e r e f e r e n c e w o r k t h a t h a s b e e n u n d e r t a k e n s i n c e t h e f ir s t e d i t i o n a p p e a r e d i n 18 8 9 .” —T h e A p o th e c a ry .
“ C o n s i d e r i n g t h e p r ic e o f t h e b o o k , i t s c o n t e n t s a n d i t s i m p o r t a n c e , n o p h y s i c ia n s h o u l d b e w i t h o u t t h i s e x c e ll e n t w o r k . " — T h e N ew Y o rk P h y sic ia n .
“ T h e f i f t h e d i t i o n s h o u l d n o w s u p p l a n t
t h e p r e v i o u s e d i t i o n w h i c h is , o r s h o u l d h a v e b e e n , i n t h e r e f e r e n c e l i b r a r y o f e v e r y p r e s c r i p t i o n r o o m . E v e r y p h a r m a c i s t w i l l f i n d e x t e n s i v e u s e f o r t h i s t h e s a u r u s i n h i s p r o f e s s i o n a l w o r k ; s o p l a c e i t b e s id e y o u r U .S .P ., N .F ., a n d D i s p e n s a t o r y w h e r e i t w i l l b e a v a i l a b l e f o r i n s t a n t r e f e r e n c e — D ru g g is ts C irc u la r.
“ T h e M e r c k I n d e x w i l l b e a v a l u a b l e a d d i t i o n to e v e r y p h a r m a c e u t i c a l l i b r a r y , fo r i t is i n f a c t a c o n d e n s e d , c o m p r e h e n s i v e a n d r e l ia b l e e n c y c l o p e d i a o f c h e m i c a l s a n d d r u g s f o r t h e c h e m i s t , p h a r m a c i s t , p h y s i c i a n a n d t h o s e i n a l l i e d p r o f e s s i o n s
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FEB R U A R Y 15,1940 A NALYTICAL E D IT IO N 7
f a d s a b o u t
THE ELECTRO-CHEMOGRAPH
For Q u a lita tiv e a n d Q u an titativ e A n a ly s e s
T h e ap p licatio n o f th e E le c tro -C h e m o g rap h to specific p ro b lem s p re se n ts a challenge to ev ery research a n d co n tro l la b o ra to ry . I t s use as a su p p le
m e n t to existing m e th o d s o f analysis offers th e p o ssib ility o f e ith e r m ore a c c u ra te o r m ore ra p id d e te rm in a tio n s. T h is is tru e especially w here m a n y d aily d e te rm in a tio n s o f th e sam e c o n s titu e n t, in th e sam e m e d iu m , w a rra n t th e tim e req u ire d to esta b lish th e necessary ro u tin e .
T h e possible field o f ap p lic a tio n a p p e a rs v e ry ex ten siv e, so t h a t com plete fam ilia rity w ith th e m e th o d prom ises to be essen tial in a n y la b o ra to ry w hich expects to keep p ace w ith c h e m istry ’s ra p id d ev elo p m en ts.
M o st effective in th e m e th o d ’s ap p lic a tio n is th e re c e n tly an n o u n ced E le c tro -C h em o g rap h . R e q u irin g no p h o to g ra p h ic process a n d no d a rk room , it offers w ith th e d ro p p in g m e rc u ry electro d e th e a d v a n ta g e s o f a 10"
c h a rt a u to m a tic a lly in k ed b y m ean s o f a p o te n tio m e te r-ty p e M icro m ax R ecorder.
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8 IN D U STR IA L AND E N G IN E E R IN G CH EM ISTR Y VOL. 12, NO. 2
For
A B S O L U T E ACC URACY
. . . begin at the beginning
T he starting point for accuracy in analytical w ork is th e selection of A n alytical R eagen ts w ith a high degree of purity that is depend
able at all tim es. R efined to predetermined, published standards of purity,
MALLINCKRODT
ANALYTICAL REAGENT CHEMICALS
never vary in composition or reaction
The catalog of M allinckrodt A nalytical Reagents and other L aboratory Chemicals lists nearly 500 item s of th e high quality necessary for control and research work. All M allinckrodt A nalytical Reagents are m anufactured to predeterm ined m axim um limits of im purities ; fully complying w ith A.C.S. specifications, where such specifications have been published. Ask your d istributor for a copy of th e new catalog showing these m axim um lim its of impurities.
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NEW YORK, N.
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C H IC A G O M O N T R E A L P H ILA D E LPH IA TO RO NTO
FEB RU A RY 15, 1940 ANALYTICAL E D IT IO N 9
If y o u a n tic ip a te th e p u r c h a s e of g a s b u r n e r s , w e w ill b e g la d to le n d y o u o n e of o u r n e w b u r n e r s for te s tin g w ith y o u r g a s su p p ly .
“ L A B C O N C O ” WIDE RANGE GAS BURNER
W ith S e t-L o c k G a s V a lve A d ju s tm e n t an d R ose F la m e D iffu ser
A n E ffic ie n t an d Flexib le G a s B u rn e r for G e n e ra l U se
T
HE ''L a b c o n c o " G a s B u rn e r w a s d e s ig n e d b y u s fo r u s e o n o u r m o d e rn K je ld a h l n itr o g e n a p p a r a tu s a n d its w id e r a n g e a d ju s tm e n t m a k e s it a lso a d a p ta b le fo r s p e c ific in d iv id u a l u se .6 p o in t ’’R O S E FLA M E" d iffu se r for K je ld a h l D ig e stio n w o rk . 4 p o in t ’’R O SE FL A M E '' d iffu se r for D istillatio n a n d g e n e r a l p u r p o s e w ork.
A DURABLE G A S BURNER . . . IM PR O V ED TYPE DIFFUSER Positive Adjustm ent for both A ir a n d G as . . . Individual Cut-off
A ll B ra ss— F in is h e d in W h ite N ickel
$1.90 each— Less in Quantities
A Compact Laboratory Heater. Dimensions 5"x5"x3?^". M olded from Heat Resisting
Eiectrobestos.
• GREATEST HEAT CONCENTRATION
• SEVEN COIL CURVED CORE PLATE
• INTERLOCKING HEAT-RESISTING ELECTROBESTOS BASE AND TOP
• MONEL METAL TERMINALS
Goldfisch Electric H eaters
FAMOUS FOR UNIFORM HEAT
AND DURABILITY
N
O wide variation of wattage in a battery of Goldfisch Electric Heaters. Each individual heater is tested for wattage, permitting its use in batteries with a variation not to exceed 2 per cent on constant voltage.
Showing interlocking top and bottom, curved' porcelain core plate, seven coil element and easy ,
connection to monel metal terminals.
In u se in m an y laboratories sin ce 1929.
F urnished for 110 or 220 volts, w attages 330 to 750.
Price $5.00 each. Less in q u a n titie s.
Flame spread on 4- point rose diffuser.
5'>.5'x3H' E iectrobestos Gas
Burner H ousing A receptacle for sup
porting the flask and an added efficiency for proper combustion of primary and second
ary air. Developed for battery use of gas burners on Kjeldahl nitrogen apparatus.
$2.00 Each Less in Q u an tities
Standard pipe
thread: length from shoulder of thread
SVs’ .
T h e above ite m s w ere developed for u se on o u r h ig h ly efficient K J E L D A H L N I T R O G E N A P P A R A T U S
r # , Write for catalogue ■ \
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LABORATORY CONSTRUCTION CO., INC.
1 1 1 3 - 1 U 5 H O LM ES STR EET K A N SA S C IT Y , M O ., U . S. A.
10 IN D U STR IA L AND E N G IN E E R IN G CH EM ISTR Y VOL. 12, NO. 2
A. H. T. CO. S P E C I F I C A T I O N
WATER BATHS OF MONEL METAL
W IT H A U T O M A T I C T E M P E R A T U R E C O N T R O L
9923-1 9923-J
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W ith ex p a n sio n tu b e b im e ta llic th e rm o -re g u la to r, th r e e -h e a t sw itch , p ilo t la m p , c o n s ta n t w a te r level a tta c h m e n t a n d n ick el p la te d sto p c o c k fo r d ra w in g off w a te r. T h e rm o -re g u la to r is 3 }4 in c h e s lo n g X J^ -in c h d ia m e te r. I n te r io r of b a th is u n o b s tru c te d ex c e p t fo r th e th e rm o -re g u la to r.
A te m p e r a tu r e of 100°C ca n be re a c h e d on “ H ig h ” in one h o u r. T h e r e g u la to r is v e r y s e n sitiv e a n d m a in ta in s th e b a th te m p e r a tu r e c o n s ta n t to w ith in i 0 .5 °C . M a x im u m p o w e r c o n s u m p tio n 1000 w a tts .
9923-1. W ater Bath, Electric, Monel M etal, as above described, with removable top complete with four sets of concentric rings of Monel m etal 4 u /i« inches diameter, therm ometer — 10 to 110 °C in 1° divisions, therm om eter holder, cord and plug. For use on 110 volts, a.c... (55.00 9923-A. Ditto, b u t for use on 110 volts, d.c... 68.50 9923-B. Ditto, b u t for use on 220 volts, a.c... 65.00 9923-E. W ater Bath, Electric, Monel M etal, identical with 9923-1 b u t with top plate and four sets of concentric
rings of Coors porcelain instead of Monel metal top and rings. F or use on 110 volts, a.c 79.25 9923-F. Ditto, b u t for use on 110 volts, d.c... 82.75 9923-G. Ditto, but for use on 220 volts, a.c... 79.25 9923-J. W ater Bath, Electric, Monel M etal, identical with 9923-1 and 9923-E b ut w ithout top plate or concentric rings. With inside flange Yu-inch wide, approximately Vs-inch below the top. Suitable for A. S T M test D-97-34. F or use on 110 volts, a.c... 53.75 9923-K. Ditto, but for use on 110 volts, d.c... 59 25 9923-L. Ditto, b u t for use on 220 volts, a.c... 53 75
P rices s u b je c t to ch a n g e w ith o u t n o tic e.
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ARTHUR H. THOMAS COMPANY
R E T A IL - W H O L E S A L E — E X P O R T
L A B O R A T O R Y A P P A R A T U S A N D R E A G E N T S
W E S T W A S H IN G T O N S Q UAR E, P H IL A D E L P H I A , U.S.A.
C able A ddress, “ B alan ce,” P h ila d e lp h ia
INDUSTRIAL a n d ENGINEERING CHEMISTRY
A N A L Y T I C A L E D I T I O N
P U B L I S H E D B Y T H E A M E R I C A N C H E M I C A L S O C I E T Y • H A R R I S O N E. H O W E , E D I T O R
Estim ation o f Traces of Lead and Thallium in Pharm aceutical Chemicals
A S im p le D ith iz o n e L im it T est
KARL BAMBACH
K etterin g Laboratory o f Applied P hysiology, U niversity o f C in cin n ati, C in cin n ati, Ohio
T
H E heavy metals test of the United States Pharm acopoeia (15) is intended for use in the detection of lead and other metals in pharmaceutical chemicals. While it is adequate where iron, copper, nickel, bismuth, tin, zinc, and other relatively nontoxic metals are concerned, the results usually cannot be interpreted strictly because (1) the test is n ot specific for any one metal, (2) a significant reagent blank cannot be carried out, and (3) the chemical under test often modifies the color of the solution when it is treated with hydrogen sulfide even though no foreign metals are present.
The lead test in the British Pharmacopoeia of 1932 (4) is an improvement over the test official in this country, b u t it also has several disadvantages in th a t it does not differentiate between lead and bismuth, is difficult or impossible to carry out when the chemical under test im parts even a light color to the solution, and cannot be applied to iron or bismuth salts.
The dithizone method described below overcomes these dis
advantages; it is simple and rapid, is very sensitive in all instances, and is specific for lead and thallium. In prin
ciple, it is based on accepted photometric procedures (2,7,10), b u t it does not require the use of special instrum ents or equipment. I t is not presented as a new analytical method b u t as an application of a known test to pharm aceutical chemicals.
Description o f M ethod
R e a g e n t s . All reagents should be as free from lead as possible. While the method corrects for the lead in th e re
agents, more accurate results will usually be obtained if deleaded reagents are used. Pyrex glassware should be employed ex
clusively and should be cleaned with dilute nitric acid (1 + 1).
Ammonium citrate, potassium cyanide, and hydroxylamine hydrochloride solutions are made and purified (if desired) as previously described (8). Chloroform should be prepared for use and reclaimed as indicated by H ubbard (10). Ammonium hydroxide should be deleaded by distilling the gas into cold double-distilled w ater; it is essential th a t this reagent be sub
stantially lead-free. Reagent-grade nitric acid, which usually contains between 20 and 25 micrograms of lead per liter, can be used without further purification.
Only one dithizone-chloroform solution is necessary (except in the te st for lead in bism uth salts), containing 12 mg. of dithi
zone (diphenylthiocarbazone) per liter. Before use, th e solu
tion should be shaken with about one half its volume of 1 per cent nitric acid and during the analysis it should be dispensed from the same separatory funnel in which it has been mixed with the dilute acid. When not in use the solution should be kept in a wrapped Pyrex bottle in the refrigerator.
P r e p a r a t i o n o f S a m p l e . W ith m ost pure chemicals the sample (usually only a few grams, containing less th an 10 micrograms of lead) is dissolved in a few milliliters of dilute nitric acid (1 + 1), boiled, and cooled. This oxidizes any stannous tin th a t m ay be present. There are a few excep
tions to this general procedure.
1. Aminopyrine and Procaine Hydrochloride. After the sample in the separatory funnel is made alkaline the free base is extracted by shaking with several portions of distilled chloroform and the lead is determined in the aqueous phase remaining.
2. Aspirin, Potassium Bromide, Sodium Iodide, and Zinc Phenolsulfonale. H eated with dilute nitric acid to a brown color, not boiled.
3. Barium Sulfate. Boiled with 10 ml. of 6 per cent acetic acid, cooled, and filtered.
4. Bismuth Subcarbonate. Dissolved in the smallest quantity of concentrated nitric acid (with heat), 20 ml. of water added, then sufficient dilute ammonium hydroxide to make the solution alkaline to methyl red. The supernatant liquid should be yellow in color, although the precipitate may be pink. Phenol red is added; the supernatant liquid m ust be acid to this indicator. The solution is then heated on the w ater bath, cooled, and filtered directly into th e separatory funnel and the residue is washed with water. Ammonium citrate, potassium cyanide, and hydroxylamine hydrochloride solutions are added and the solution is made alkaline to phenol red with ammonium hydroxide. The lead (and most or all of the remaining bismuth) is extracted w ith three 5-ml. portions of a special dithizone solu
tion (30 mg. of dithizone per liter of chloroform), and the com
bined chloroform extract is washed with 50 ml. of water, and drained into another funnel. The water is washed w ith 5 ml. of distilled chloroform, which is added to th e dithizone solution.
T he dithizone solution is then shaken with 20 ml. of 1 per cent nitric acid, drained off, and discarded. Dilute ammonium hy
droxide is added to the aqueous portion until pH 2 is reached (orange color of metacresol purple), and the bismuth is extracted with successive portions of the special dithizone solution until the color of the dithizone remains a pure green. T he dithizone solution is drained off, 5 ml. of distilled chloroform are added to the aqueous portion, and the funnel is shaken. The drop of chloroform floating on top is allowed to evaporate, th e lower layer is drained off completely, and the procedure under the head
ing “ Estim ation of Lead” in the general description of the method is followed, except th a t only 3 ml. of ammonia-cyanide mixture are used.
5. Calcium Hypophosphite, Ferric Glycerophosphate, Hypo- phosphorous Acid, Phosphoric Acid, Sodium Glycerophosphate, and Acid Sodium Phosphate. The lead is extracted w ith dithi
zone imm ediately after the m ixture is made alkaline.
6. Cerium Oxalate and Phenolphthalein. Boiled with dilute nitric acid, cooled, and filtered.
7. Cod Liver Oil. H eated cautiously w ith 5 ml. of concen
trated nitric acid and 10 ml. of w ater; th e aqueous portion is 63
64 IND U STR IA L AND E N G IN E E R IN G CH EM ISTR Y VOL. 12, NÖ. Ź evaporated and the residue ignited a t about 500° C. (incipient
red heat or below). The ash is moistened with concentrated nitric acid and ignited as before; this is repeated until the ash is almost white. The ash is then dissolved in 3 ml. of dilute nitric acid (1 + 1) and the lead determined.
8. Gelatin. Ignited a t about 500° C. (incipient red heat or below), 5 ml. of concentrated nitric acid added, the acid evapo
rated, and the residue ignited as before. Continue as for cod liver oil, beginning with “ The ash is moistened” .
9. Potassium Guaiacolsulfonate and Sodium Phenobarbilal.
The sample is dissolved in water w ithout nitric acid. If the lead is excessively high, tin (stannous) interference may be suspected. In th a t case the 20 ml. of 1 per cent nitric acid containing the lead in the extraction step are boiled with 5 ml.
of dilute nitric acid (1 + 1) and the analysis is repeated, this acid solution being used as the sample.
10. Soap Powder. Dissolved in hot water, 5 ml. of dilute nitric acid (1 + 1) added, and the mixture stirred, cooled, and filtered directly into the separatory funnel. The remaining fa tty acids are extracted by shaking with several portions of distilled chloroform and the lead is determined in the aqueous phase remaining.
11. Sodium Perborate. Heated a t a low tem perature in a crucible until all peroxide oxygen is driven off. The residue is dissolved in water and the dilute nitric acid added.
12. Sodium Thiocyanate and Sodium Thiosulfate. Dissolved in water and dilute nitric acid and heated until all the gas is driven off. Then the solution is filtered directly into the sepa
ratory funnel.
13. Strontium Bromide. Heated with dilute nitric acid to a brown color and transferred to the separatory funnel. Am
monium citrate solution is not added; care is taken to extract the lead with dithizone immediately after the mixture is made alkaline.
Chemical
Acetic acid, c. p.
Alum, ammonium, c. p.
Aluminum sulfate, N. F.
Aminopyrine, U. S. P. (1)°
Ammonium valerate, acid, N. F.
Aspirin, U. S. P. (2) Barium sulfate, U. S. P. (3) Bism uth subcarbonate, U. S. P. | Calcium carbonate, U. S. P.
Calcium chloride, A. R.
Oalcium hypophosphite, N. F. (5 Cerium oxalate, N. F. (6) Cod liver oil, U. S. P. (7) Dextrose, U. S. P.
Ferric chloride solution, U. S. P.
Ferric glycerophosphate, N. F . (I G elatin, U. S. P. (8)
Glycerol, c. p.
H ypophosphorous acid, U. S. P.
Iron and ammonium citrates, U.
Laotic acid, A. It. (85%) Lithium carbonate, N. F.
M anganese citrate, soluble, N . F.
Methonamine, U. S. P.
M ilk of magnesia, U. S. P.
Phosphoric acid, A. R. (5) Phenolphthalein, U. S. r . (6) Potassium bromide, c. p. (2) Potassium carbonate, c. p.
Potassium chlorate, U. S. P.
Potassium guaiacolsulfonate, N.
Potassium hydroxide, A. R.
Potassium nitrate, c. p.
Procaine hydrochloride, U. S. P.
Salicin, N. F.
Soap, powdered, U. S. P. (10) Sodium benzoate, U. S. P.
Sodium borate, A. R.
Sodium cacodylate, U. S. P.
•Sodium glycerophosphate, N. F.
Sodium iodide, c. p. (2)
•’Sodium nitrite, A. R.
Sodium perborate, U. S. P. (11) Sodium phénobarbital, U. S. P. ( Sodium phosphate, acid, A. R. (;
8odium salicylate, U. S. P.
Sodium thiocyanate, N. F. (12) Sodium thiosulfate, U. S. P. (12) S trontium bromide, N. F. (13) T artaric acid, A. R.
Zinc phenolsulfonate, N. F. (2) Zinc sulfate, A. R.
T a b l e I.
Sample Used
Es t im a t io n o f Le a d D ilute
N itric Ammo- Potas- Acid nium sium (1 + 1) C itrate Cyanide
Hydroxyl
amine H ydro
chloride Lead
Found Lead
Grams M l. M l. Ml. Ml. M icro-
orams P . p. m.
3 .0 2 3 1 0 .5 2 0 .7
1.43 3 .5 3 1 0 .5 11 7 .7
0.25 3 3 1 0 .5 8 32
1.0 3 3 1 1 .5 2 2
1.0 2 3 1 0 .5 7 7
2 .0 3 3 1 0 .5 1 0 .5
3 .0 2 3 1 0 .5 2 0 .7
4) 1.0 3 1 0 .5 3 3
2 .0 3 (excess) 3 1 0 .5 1 0 .5
5 .0 3 3 1 0 .5 3 0 .6
) 2.0 3 25 1 0 .5 1 0 .5
0 .04 3 3 1 0 .5 12 300
3 .0 3 3 1 0 .5 3 1
5 .0 3 3 3 0 .5 2 0 .4
0 .1 1 6 6 2 9 90
>) 0 .3 1 25 3 1 8 27
2 .0 3 3 1 0 .5 G 3
15.0 3 3 1 0 .5 8 0 .6
8?P. 5 .00 .5 23 253 101 0 .51 101 200 .2
5 .0 2 3 1 0 .5 1 0 .2
5.0 3 (excess) 3 1 0 .5 3 0 .6
0 .5 3 3 1 0 .5 8 16
4 .05.0 3
3 (excess) 3
3 1 0 .5
0 .5 2
2 0 .5
0 .4
5 .0 2 25 1 0 .5 1 0 .2
2 .0 3 3 1 0 .5 8 4
2 .0 3 3 1 0 .5 4 2
5 .0 3 (excess) 3 1 0 .5 9 1 .8
5 .0 3 1 2 0 .4
F. (9) 2 .0 3 1 0.’5 2 1
5 .0 3 (excess) 3 1 0 .5 1 0 .2
10.0 3 3 1 0 .5 3 0 .3
(1) 3 .0 3 3 1 0 .5 1 0:3
1.0 3 3 1 2 1 1
3 .0 5 3 1 0 .5 9 3
2 .0 3 3 1 0 .5 3 1.5
2 .0 3 3 1 0 .5 7 3 .5
3 .0 3 3 1 0 .5 2 0 .7
(5) 5 .0 3 25 1 0 .5 3 0 .6
10.0 3 3 1 0 .5 3 0 .3
2 .0 7 3 1 0 .5 2 1
2 .0 3 (excess) 3 1 5 2 1
9) 2 .0 3 1 0 .5 2 1
>) 5 .0 2 ’ 25 1 0 .5 1 0 .2
3.0 3 3 1 2 3 1
3 .0 8 3 1 0 .5 1 0 .3
5 .0 8 3 1 0 .5 2 0 .4
3 .0 3 1 0 .5 1 0 .3
5 .0 2 *3 1 0 .5 7 1.4
3 .0 3 3 20 0 .5 3 1
1.0 3 3 25 0 .5 3 3
° Numbers in parentheses refer to paragraphs under “ P reparation of Sam ple”
E x t r a c t i o n o f L e a d . The prepared sample is transferred to a graduated Squibb separatory funnel and th e proper quantities of ammonium citrate, potassium cyanide, and hydroxylamine hydrochloride solutions are added (Table I). The solution is made alkaline to phenol red with distilled ammonium hydroxide and is shaken w ith approximately 5 ml. of dithizone solution.
The extraction is repeated with separate 5-ml. portions until the dithizone solution keeps its original green color; if a sample of the proper size has been chosen the second portion will show the presence of only a trace of lead. The combined dithizone extract is then shaken w ith 20 ml. of 1 per cent nitric acid (1 ml. of re
agent acid per 100 ml.) and the chloroform layer is discarded.
E s t i m a t i o n o f L e a d . Five milliliters, measured accurately, of th e dithizone solution and 4 ml. of ammonia-cyanide mixture (JO) are added to th e funnel containing the lead in 1 per cent nitric acid and the funnel is shaken for 30 seconds. The color of this dithizone extract is compared w ith th a t of a standard, which has been prepared by treating a known am ount of lead in exactly the same way as the m aterial being tested. Usually 10 micro-
f
rams of lead are used in the standard funnel; this will im part a right bluish red color to the dithizone solution. If th e sample contains less than 10 micrograms of lead, the dithizone extract will show a bluer or greener hue than the standard. Several funnels containing graduated quantities of lead can be employed as standards and, with practice, am ounts of lead under 10 micrograms can be estimated with a precision of 1 microgram.
Color comparison may be aided by transferring the dithizone solutions to Nessler tubes, b u t this step may cause contamina
tion. If kept reasonably cool and protected against strong light, these color standards will keep for one day; they can be used for all the analyses run during a day if the reagents em
ployed are substantially lead-free or if the same quantity of each reagent from the same lot is used in each test.
The lead standard can be conveniently made by dissolving a pure lead salt, such as the ni
trate, in 1 per cent nitric acid
— , and diluting the solution with 1
{
>er cent nitric acid until the ead concentration is 1 microgram per milliliter. This solu
tion will keep indefinitely in Pyrex glass.
Lead, thallium, and bismuth are estim ated by the above procedure. In practice, bismuth need not be separated unless the apparent quantity of lead exceeds a reasonable limit. In this case the dithizone solution containing the lead (and bism uth and thallium, if present) in the final step is shaken with another 20-ml. portion of 1 per cent ni
tric acid and th e chloroform layer is discarded. Dilute am
monium hydroxide is added to the 1 per cent nitric acid until pH 2 is reached (orange color of metacresol purple) and the solu
tion is shaken with dithizone solution. A change in color indicates the presence of bis
m uth; a t this point it can be completely extracted with dithi
zone and the lead estim ated by th e addition of ammonia-cyanide mixture (only 3 ml.) and dithi
zone solution as before.
T h r o u g h o u t th e s e s te p s thallium, if present, will follow the lead in the analysis and will be estim ated as lead.
This is not felt to be an ob
jection to the method, since the presence of thallium in pharmaceutical chemicals is a t least as dangerous as th a t of lead and its detection is equally im portant. The test makes it possible to reject a chemical containing an excessive am ount of either or both toxic metals.
FEB R U A R Y 15, 1940 ANALYTICAL E D IT IO N 65 Experim ental R esults
A t least one representative of each type of chemical for which the United States Pharmacopceia or the National Form ulary gives a lead or a heavy metals test was analyzed by this dithizone method. The results indicate th a t the method is applicable to practically all pharmaceutical chemicals. Table I gives the experimental data and indi
cates special sample preparations. The quantities of reagents given are probably not optimum, b u t were satisfactory in practice. A few milliliters of double-distilled w ater (not in
dicated in the table) were used wherever necessary.
T a b l e II. C o m p a r i s o n o f M e t h o d s B y lim it test
P . p. m.
-L ead F o u n d -
Alum, am m onium , c. P.
Glycerol, c . p.
Potassium n itra te , A. R.
Sodium benzoate, U. S. P.
7 .7 0.6 0 .30 . 2
By photom etric method P . p. m.
7 .5 0 .7 0 .37 0 .16
In order to check the results obtained by this method, four of the chemicals were analyzed for lead by a photo
metric procedure (2). The photometric method, of course, gives more accurate results, b u t the lead estimations by the new lim it test are reasonably close to the true values (Table II).
T a b l e I II . C o m p a r i s o n w i t h S p e c t r o g r a p h i c M e t h o d -L ead F o u n d - By lim it te st By spectrograph
P . p. m. P . p. m.
B ism uth subcarbonate, U. S. P.
Cerium oxalate, N. F.
Ferric chloride solution, U. S. P.
3 30090
2 to 3 260 100
An inspection of Table I will show several chemicals th a t seem to have unusually high lead content, so th a t their use for medicinal purposes is unwise. Two of these, together w ith a bismuth salt, were analyzed by the spectrographic method in use in this laboratory (6). The results (Table III) show th a t the high values obtained in the lim it test were not due to some interfering element and th a t the procedure given for lead in bism uth salts is reliable.
D iscussion
The dithizone limit test for lead in pharmaceutical chemi
cals is n o t intended for use when an extremely accurate lead determ ination is required. I t does not take the place of the better titrim etric or photometric dithizone procedures (2, 7, 10,17) b u t is useful primarily when it is necessary to know whether or not the lead content of a sample exceeds a certain given figure. Used in this way, the test can become very valuable as a routine method of ensuring th a t the lead con
tents of chemicals and medicinal preparations do not exceed a governmental or other arbitrary limit.
Precautions necessary in other lead microdeterminations should be observed in this procedure. Contamination with lead from dust in the air should be avoided as much as possible. All filter papers used should be of quantitative grade, acid-washed. I t is n o t usually necessary to tre a t the papers further, although a sheet th a t contains lead will occasionally be found.
Although the dithizone lim it test showed th a t relatively large quantities of lead were present in ferric chloride solu
tion, U. S. P., ferric glycerophosphate, N. F., and cerium oxalate, N. F., the official tests gave negative results in each
instance. In addition, when as much as 0.5 mg. of lead was added to 2 ml. of ferric chloride solution, U. S. P., the official lead test still indicated th a t no lead was present. When a similar sample, also contaminated w ith an additional 0.5 mg. of lead, was treated as described in the official monograph (the iron precipitated w ith ammonium hydroxide and filtered), the filtrate proved to be lead-free when tested by dithizone.
This indicates th a t the lead present is removed during the preparation of the sample by the official m ethod; these con
clusions can also be applied to other iron salts.
I t is apparent, therefore, th a t undesirable quantities of lead m ay be present in medicinal preparations and remain undetected by the present official tests. The lead content of the sample of iron and ammonium citrates, U. S. P., was 20 p. p. m. (the United States Pharmacopceia does not give a test for lead or heavy m etals in this chemical) and the average dose is 2 grams. This means th a t a person taking three doses per day would receive 0.12 mg. of lead from this source alone, or almost one half as much lead as from an average d ay’s food (5, 11). I t is conceivable th a t some lots of iron and ammonium citrates m ight contain more lead than the particular sample tested; in addition, quantities greater than the equivalent of three doses of this chemical are often taken in a day, especially when it is used in beef, wine, and iron preparations. Therefore it is probable th a t for m any people the normal daily intake of lead m ay be significantly aug
mented by lead contamination of certain medicines.
Low results m ay also be secured by the official m ethod of sample preparation in the case of gelatin, the ashed residue of which is tested. No statem ent regarding the ashing tem perature is made, although it has been shown th a t serious losses of lead occur if organic m atter is ashed a t tem pera
tures above 500° G., especially if the q uantity of ash is small (1, 3, 8, 9). The analyst is alm ost certain to ash the sample a t the full heat of the Bunsen flame, or to use a burner giving even more heat, and under these conditions much of the lead in the gelatin would be driven off.
T he official test for lead in bism uth subcarbonate depends upon the precipitation of lead sulfate in a volume of 10 ml., corresponding to a sample weight of 0.5 gram. I t has been reported th a t 10 ml. of w ater will dissolve from 400 to 770 micrograms of lead sulfate a t ordinary tem peratures (13), corresponding to about 270 to 530 micrograms of lead.
Therefore, assuming th a t the solubility of lead sulfate in w ater is not depressed m aterially by a slight excess of sul
furic acid and the bism uth salts present, several hundred parts of lead per million parts of sample m ay escape detection by the official test. One average dose (1 gram) of bism uth sub
carbonate, then, could contain 0.5 mg. of lead, or alm ost twice the am ount of lead in an average day’s food, though the official test would still be negative.
T a b l e IV. D e t e r m i n a t i o n o p L e a d i n B i s m u t h S a l t Q uantity of Bism uth Subcarbonate Lead A dded Lead Found
Oram Micrograms M icrooramt
1 0 3
5 8
10 12 ♦
In working out the dithizone test for lead in bism uth salts, several methods of removing the bismuth were tried (12,
14
,16). All, except the one finally adopted, either failed to re
move enough of the bism uth or removed practically all of the lead with the bism uth. This was probably due to the very small quantity of the lead in relation to the am ount of bis
m uth present. As far as can be ascertained, the method given here is the only one reported by which as little as one p art of lead in one million parts of a bism uth salt can be
