INDUSTRIAL a n d ENGINEERING CHEMISTRY
, p ° U r e C :,. /
A N A L Y T I C A L E D I T I O N
HARRISON E. HOW E, E D IT O R » ISSUED OCTOBER 16, 1942
»
VO L. 14, NO. 10 • C O N SEC U TIVE NO. 20D e te rm in in g Oil C o n te n t of P a ra ffin Waxes . . . . Russell Lee and V. A. Kalichevsky 767 L o catio n of E n d P o in t o n C e rta in G ra p h ic a l T it r a
tio n C urves . . . Alois Langer and D. P. Stevenson 770 A lk alim etric S ta n d a r d iz a tio n of Io d in e S o lu tio n s .
F. L. Hahn 773 Lower A lip h a tic A lc o h o ls ...
William Hollyday and D. L. Cottle 774 D e te rm in a tio n of S o y b ean F lo u r in S au sag es a n d
O th e r M e a t P r o d u c t s ... John Bailey 776 D e te rm in a tio n of O lefins in G aseous H y d ro carb o n s
B. R. Stanerson and Harry Levin 782 P h o to m e tr ic D e te rm in a tio n of A ceto n e-In so lu b le
M a te ria l in S o y b e a n O i l ...
Chas. Andrew Murray and E. B. Oberg 78S D e te rm in a tio n of O xide C o p p e r ...
R. S. Young and D. G. M. Graham 787 D e te rm in a tio n of T h ia m in e in V egetables . . . .
James C. Moyer and Donald K. Tressler 788 R o u tin e C o lo rim e tric D e te rm in a tio n of T ita n iu m
in C h ro m iu m S te e ls ... Louis Silverman 791 R em oval of A d so rb e n ts fro m C h ro m a to g ra p h ic
T u b e s ...John Turkevich 792 R apid X -R ay D iffra c tio n M e th o d . . A. T. McCord 793 E lectrical I g n itio n of S p e c tro g ra p h ic A r c ...
Frank G. Brockman and F. P. Hochgesang 796 G ra v im e tric D e te rm in a tio n of A lu m in u m in M ag
n e s iu m A l l o y s ...
V. A. Stenger, W. R. Kramer, and A. W. Beshgetoor 797 S tu d ie s o n C a ro te n o id s . . . Jonathan W. White, Jr.,
Arthur M. Brunson, and F. P. Zscheile 798 A p p a ra tu s fo r Io d o m e tric D e te rm in a tio n of T in . .
William M. Rumberger 801 S ta n d a r d iz a tio n a n d S ta b ility of 0.1 N S o d iu m
T h io su lfa te S o lu tio n s in H o t W e a th e r...
Sigurd O. Rue 802 C arbon D ioxide G e n e r a to r ... J. A. Johnston 805
E x tra c tio n of M etallic C o n s titu e n ts fro m O ils . . .
E. P. Rittershausen and R. J. DeGray 806
E fficient C o lu m n S u ita b le fo r V a c u u m F r a c tio n a tio n S. A. Hall and Samuel Palkin 807 C o n stan t-L ev el Device fo r H o t W a te r B a th s . . . .
B. W. Pocock 811 S im p le T h y ra tr o n C i r c u i t ... Sidney Golden 812 M IC R O C H E M IST R Y :
Q u a lita tiv e A nalysis of M icro g ram S a m p le s . . . A. A. Benedetti-Pichler and Michael Cefola 813 Q u alitativ e a n d Q u a n tita tiv e A nalysis of H y d ro
c a rb o n M ix tu re s by M ean s of T h e ir R a m a n S p e c tra . D. H. Rank, R. W. Scott, and M. R. Fenske 816 S u lfu r in O rg an ic C o m p o u n d s C o n ta in in g N itr o
gen a n d H a lo g e n ...
Edwin L. Brewster and Wm. Rieman, III 820 A d a p ta tio n of I n d ir e c t M e th o d fo r P o ta s s iu m to
P h o to e le c tric C o lo rim e te r . . . . C. P. Sideris 821 Effect of F o rm a ld e h y d e o n V o la tiliz a tio n s of A m
m o n ia , M ono-, D i-, a n d T rim e th y la m in e s . . George J. Benoit, Jr., and Earl R. Norris 823 Im pro v ed P h o to m e tr ic M e th o d fo r A scorbic Acid
Christopher Carruthers 826 E n d P o in t of M ic ro titr a tio n s w ith C olor I n d ic a
to r s . . A. A. Benedetti-Pichler and Sidney Siggia 828 F lu o re sc e n t M icroscope L a m p ...
Louis H. Berkelhamer 833 H e a tin g Device fo r M icro b eak ers, F lask s, a n d
C e n trifu g e T u b e s ... C. R. Noller 834 D e te rm in a tio n of C a rb o n in L o w -C arb o n I r o n a n d
S t e e l ... L. A. Wooten and W. G. G uldner 835 V o lu m etric D e te rm in a tio n of S u lfa te s . S. W. Lee,
J. H. Wallace, Jr., W. C. Hand, and N. B. Hannay 839 A n aly tical Use of S o d iu m R h o d i z o n a t e ...
Fritz Feigl and Hans A. Suter 840
T h e Am erican Chem ical Society assum es no responsibility for the statem en ts and opinions advanced by co ntributors to its publications.
20,200 copies of this issue printed. C o pyright 1942 by American Chem ical Society.
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te le p h o n e : ¡Republic 5301. C ab les J ie c h e m (W a sh in g to n )
Published b y th e A m erican C hem ical Society, Publication Office, 20th &
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J ri Ad EN-0600B(16)
LEEDS &. N O R T H R U P COM PANY, 4920 STENTON AVE., P H IL A ., PA-
LEEDS & N O R T H R U P
M E A S U R I N G I N S T R U M E N T S - T E L E M E T E R S A U T O M A T I C C O N T R O L S - H E A T - T R E A T I N G T U R N A C E S
New Catalog Shows Micromax Recorders and Thermohms
Panel of M icromax Controllers used In our own plant for providing correct hum idity and temperature in manufacture of other L&N instruments. We use hundreds of our own instrum ents in our plant*
th at is one reason for our confidence that they will serve well in our customers’ plants and labs. '
A IR CONDITIONING SER V ES L&N BETTER When Both Temperature and Humidity Are Controlled by tH u M M tftx fk e t it o d s
E le c tric a l cap acito rs a re in one re
spect like m atches, ru b b e r, p ap er, iro n , c ertain food p ro d u c ts an d m an y o th e r th in g s— th ey a re easier to m ake w h e n the w e a th e r is favorable.
A good sp o t fo r a ir c o n d itio n in g ? Y es, b u t n o t fo r th e u su a l “ hum an-com - f o r t” jo b . F o r in c o m fo rt applications, th e te m p e ra tu re an d re la tiv e h u m idity, th o u g h lo w ered , a re n o t u n d e r p a rtic u la rly close c o n tro l, a n d can w a n d e r a ro u n d q u ite a bit. A n d c a p acito r m ak ers do b est w h e n b o th te m p e ra tu re an d re la tive h u m id ity stay p u t. T h e r e is a notice
able difference, fo r exam ple, b etw een the c h aracteristics o f cap acito rs a t relativ e h u m id ities o f 4 0 a n d 45 p e r cen t. W e like h u m id ity to be 4 0 an d te m p e ra tu re 7 7 °, a n d h e re ’s h o w w e c o n tro l o u r Y o rk a ir c o n d itio n e r in o rd e r to m ain tain these v a lu e s:
T w o M ic ro m a x R e c o rd in g C o n tro l
le rs a re used— one fo r re la tiv e h u m id ity ; th e o th e r fo r te m p e ra tu re . T h e h u m id ity c o n tr o lle r o p erates a sp ra y v alv e w h e n h u m id ification is needed a n d a com pres
so r fo r d eh u m id ificatio n . T h e tem p era
tu r e c o n tro lle r o p erates a n electric h e a te r to increase te m p e ra tu re , a n d takes o v er th e o p eratio n o f th e com pressor w hen cooling is req u ired .
I n typical su m m er w e a th e r, w h en the
atm ospheric h u m id ity is high, th e h u m id ity c o n tro lle r o p erates the com pressor fo r dehum idification, an d th e te m p e ra tu r e c o n tro lle r operates a n electric h e a te r to fu rn ish th e necessary rc-h eat.
I n w in te r, w h en atm o sp h eric h u m id ity is lo w , th e h u m id ity c o n tro lle r op er
ates a sp ray v alv e an d th e te m p e ra tu re c o n tr o lle r o p erates th e h e a te r o r th e com pressor as req u ired to m a in ta in th e set te m p e ra tu re .
T h e tw o M ic ro m a x C o n tr o lle r s .a r e e n tire ly in d ep en d e n t o f each o th e r, an d m uch o f th e success of th e C o n tro l is du e to th e fa c t t h a t th ey c o n tin u e to o p erate w h e n e v e r eith e r is needed. E v en m ore o f th e ir success in m a in ta in in g close co n tro l is, how ever, du e to th e accuracy an d m icro-responsiveness o f the C o n tro l, and to th e fa c t th a t it p ro p o rtio n s th e a m o u n t o f c o n tro l action to th e e x te n t an d tim e o f d eviation. T h e re s u lt is an atm o sp h ere w h ic h n ev er in te rfe re s w ith p ro d u c tio n in the least degree — an d heavy p ro d u c tio n o f capacitors, like th a t o f m o st o th e r th in g s, is v ita l th is fall.
F o r a descrip tio n o f th e C o n tro lle rs, see C a ta lo g N -3 3 C o n M ic ro m a x T h e r - T e m p e r a tu r e C o n tro lle rs, an d A -92 o n M ic ro m a x D ire c t-R e a d in g R e la tiv e H u m id ity R ecorders. F o r en g i
n e e rin g service, w rite us fu ll details. '
T h e m ost com plete catalog we have ev er issued o n th e re c o rd in g of resistance- th e rm o m e te r te m p e ra tu re is now ready fo r d is trib u tio n . I t is concerned espe
c ially w ith M ic ro m a x Recorders and T h e rm o h m resistance therm om eters, at te m p e ra tu re s b elo w 20 5 F , but other ap
p licatio n s a re also discussed.
T h e v e ry s lig h t a m o u n t of attention w h ic h th e M i c r o m a x - T h e r m o h m M e th o d o f re c o rd in g needs, is a particu
la rly v a lu a b le c h a ra c te ristic a t present.
I t is e n tire ly d ifferen t, in principle and o p eratio n , fro m expansion-type instru
m e n ts ; it is m o re m ach in e th an instru
m en t. I t has n o je w e lle d b earings; it can be placed a t a n y desired distance from th e te m p e ra tu re m easu red ; both its tem
p e ratu re-sen sitiv e T h e rm o h m and its lead w ires can be replaced w ith o u t affect
ing th e accu racy o r sensitivity. A s many as 16 te m p e ra tu re s can be recorded by the S tr ip - C h a r t M ic ro m a x . T h e re are also R o u n d -C h a rt an d non-recording m odels. I f you use, o r could use, tem- p e r a t u r e - r e c o r d e r s , y o u ’ll w a n t this C a ta lo g . I t ’s N o . N -3 3 C , sent on re
quest.
Relative hum idity is held tig h tly n ear 40% by ustaS a M icrom ax Relative H um idity Recording Con
troller. If tem perature only were controlled* “u‘
m idity would wander by several per cent.
A N A L Y T I C A L E D I T I O N 5
Courtes/ of The Metropolitan Museum of Art.
This recumbent calf was a standard of mass with the ancient Egyptians. It weighed 6 deben, equivalent to 84 grams, made of bronze, with lead contained in the side to bring to weight. This illustration is a replica of one in the New York Metropolitan Museum of A rt. Other Egyptian ani
mal figures were used as weights — bulls, ibices, and hip
popotami.
STANDARDS built BY lab orato ry control FOR laboratory control
Behind every M allinckrodt Analytical R eagent Chemical stan d the guardian scientists who guide th e product through every m anufacturing procedure.
M allinckrodt laboratory men, standardizing these A. R. Chemicals to predeter
mined p u rity levels, know and m eet the problems of the technicians who will use them for accurate gravimetric, gasometric, colorimetric, or titrim etric analysis.
Catalogue of M allinckrodt Analytical Reagents and other laboratory chemicals upon request.
v
A L W A Y S SPEC IFY R E A G E N T S IN M A N U F A C T U R E R 'S O R I G I N A L P A C K A G E S
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
ST. L O U IS C H I C A G O
P H IL A D E L P H IA N E W Y O R K
M O N T R E A L L O S A N G E L E S
I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y Vol. 14, No. 10
Y o u k n o w t h e m . . .
WHATMAN Filter Papers have served the Chemists of America for a quarter of a century. Workers in every type of laboratory have learned, through long experience, the grades best adapted to each determination they make.
Chemists know WHATMAN Filter Papers, there is no need to experiment, no need to waste precious time determining which grade should be used.
WHATMAN Filter Papers are quickly available to every laboratory in the United States from comprehensive stocks of dealers from Coast to Coast. Supplementing these are reserve stocks in New York so that, no matter what emergency confronts you, you can obtain your grade and size of WHATMAN Filter Papers promptly.
H. R EEV E A N G E L & C O ., Inc.
7-11 Spruce St., New York, N . Y .
A N A L Y T I C A L E D I T I O N 7
New Information to Help You Build Labnratory Furnaces
ELECTRIC^
FURNACE Jvt&SED
New and important in fo rm a tio n has been added to this popu
lar manual on the construction of various types of laboratory electric furnaces which can be operated at relatively high temperatures.
Information is provided to help you make the proper selections of refractory shapes and use them to advantage. Detailed methods and design data are presented. All furnace assemblies described have been built and tested under laboratory conditions.
coi»e9) Vab°i a ' Usl to ie<
o tîlecfc10
8 I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y Vol. 14, No. 10
What is the
MOST IMPORTANT PROPERTY
of Glass for Laboratory Use?
Ijl a s s h a s m any p r o p e r t i e s. E a c h is im p o rta n t. A n d e a c h c a n re a d ily be e n h a n c e d in glass fo rm u la e .
S u c c e ss in th e m a n u f a c tu r e o f a n y la b o r a to r y g lass d o es n o t re s t u p o n a p a r tic u la r p r o p e r ty h u t r a t h e r u p o n h o w su c c e s s fu lly th a t p r o p e r ty is c o m b in e d w ith all th e o th e r p ro p e rtie s .
I n 1915 C o rn in g R e s e a rc h d e v elo p e d P y re x b ra n d C h em ical G lass N o. 7 7 4 . I t w as th e n — a n d still is— th e o n ly balanced c h e m ic a l g lass. I n it, th e e s s e n tia l p ro p e r tie s o f c h e m ic a l s ta b ility , m e c h a n ic a l s tr e n g th a n d h e a t re s is ta n c e w e re sc ie n tific a lly co m b in e d . N o o n e p r o p e r ty w as e n h a n c e d a t th e e x p e n se o f a n o th e r . A ll w ere balanced fo r a ll-a ro u n d la b o r a to r y u se .
B u t C o rn in g R e s e a rc h d id n o t s to p th e r e . T h e n e e d fo r sp e c ia l g lasses fo r special u s e s w as re co g n ized . T h r o u g h o u t th e y e a rs th a t fo llo w ed , C o rn in g s c ie n tis ts h a v e d e v elo p e d o v e r 2 5 ,0 0 0 d iffe re n t fo rm u la e .
T y p ic a l o f s u c h sp ecial g lasses is C o rn in g b ra n d A lk a li-R e sista n t G lass N o . 7 28 w h ich is a lso s u ita b le f o r B o ro n d e te r m in a tio n s .
" V y c o r” b ra n d 9 6 % S ilica G lass N o . 7 9 0 is a f u r th e r e x a m p le , sp e c ia lly d ev elo p e d fo r h ig h te m p e r a tu r e re a c tio n s , ra p id c h e m ic a l a n a ly s e s o r e x c e p tio n a lly a c c u ra te w o rk , w ith a lin e a r co efficien t o f e x p a n s io n o f .0 0 0 0 0 0 8 p e r °C.
E a c h o f th e s e g lasses— a n d th e m a n y m o re d e v e lo p e d th r o u g h C o rn in g R e se a rc h em p h asizes C o m in g ’s a b ility to p ro d u c e glass to m e e t a n y la b o r a to r y re q u ir e m e n t.
W h e n c a re fu l a n a ly s is is m ad e o f a n y c o m p a ra tiv e te s t d a ta — w h e n th e t r u e im p o rta n c e o f a n y p ro p e rty is e v a lu a te d — o n ly P y re x b ra n d L a b o ra to ry W a re , fa b r i
c a te d fro m the b a la n c e d glass, c a n tr u ly be called t h e a ll-a ro u n d w are fo r a ll-a ro u n d la b o r a to r y u se.
W h e n y o u b u y la b o r a to r y w a re , eco n o m ize. B en efit fro m B a la n c e . S ta n d a rd iz e o n P y re x b ra n d L a b o ra to ry W a re .
P y re x b ra n d W a re a n d o th e r la b o r a to r y g lassw are, fa b ric a te d fro m sp ecial glasses d e v e lo p e d by C o rn in g R e s e a rc h , a r e a v a ila b le fro m y o u r la b o r a to r y su p p ly d eale r.
PYREX»>»»• LABORATORY WARE
“PYREX” and “ VYCOR” are registered trade-marks and indicate manufacture by I C O R N I N G G L A S S W O R K S • C O R N I N G , N E W Y O R K
October 15, 1942 A N A L Y T I C A L E D I T I O N
H O S K I N S P R O D U C T S
If experience counts for much, then Hoskins Laboratory Furnaces should be pretty good. You see, w e'v e been at it for 35 years. And as you know , the heart of these furnaces is their heating element. In Hoskins Furnaces, this element is m ade of Chrom el— our discovery of w hich in 1906 made possible the developm ent of most all electric furnaces. So, it seems safe to
assume
that our ow n Chromel elements are w ell designed, as are all other parts in a Hoskins Furnace. This results in a reliability of performance that is quite assuring in these hard-driving d ays. For a full description of all Hoskins Furnaces, ask your dealer, or us, for our Catalog-58. . . . Hoskins Manufacturing Co., Detroit, Michigan.This small crucible furnace is our FH-104, g o o d Below is a High
for about 2000“ F„ and useful in melting small Furnace, good for 2300-2400 F. Each bore „ batches of metal; A" x 4" heating chamber. heated independently of the other.
Above is our Combustion Furnace, Type FH-303A, with very heavy insulation. Has a 7 Go. Chromel-A heating coil, that has tough durability and is very easy to renew. Operates only on A.C. Preferred by steel mill labora
tories.
E lE C T R iC H E A T T R E A T IN G F U R N A C E S • • H E A T IN G E lE M E N T A L L O Y S • • T H E R M O C O U P L E A N O l | LEAD W IS E • • PYRO M ETERS • • W ELD IN G W IRE • • HEAT RESISTANT CA S TIN G S • • EN A M ELIN G r t
HX7URES • • SP A R K PLU G ELECTRO DE W IRE • • SP EC IA L A LLO YS O F N IC K EL • • P RO TECTIO N TUBES
10 I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y Vol. 14, No. 10
In Stock f o r I m m e d ia te S h ip m e n t
—CENCO-COOLEY ELECTRIC MUFFLE FURNACE
A very convenient ashing furnace for th e sm all laboratory. Will operate continuously a t tem peratures up to 950° C. and is n o t harm ed during short intervals a t tom peratures n o t exceeding 1050° C.
Overheating is prevented by adju stm en t of th e rheostat. T he pyrom eter is of distinct advantage where it is necessary to a d ju st the tem perature to definite values.
T he furnace is strongly constructed w ith iron end-fram es w ith sup
porting legs cast integral. T he end-pieces are of heavy tran sits and the body shell of sheet steel finished in alum inum bronze. The rectangular muffle is of 5-piece m olded construction w ith parallel 13651A F u r n a c c w ith r h e o s ta t fo r 115 v o lts AC o r D C ...
13652A F u r n a c e w ith r h e o s ta t a n d p y r o m e te r fo r 115 v o lts
grooves in the top and b ottom m em bers in which the heating units are inserted to form the side walls of the muffle. A dditional insula
tion is provided betw een th e muffle and o u ter case of the furnace.
T he hinged door fram e swings from a bracket attach ed to the furnace fram e. T he plug-type door is a thick refractory molding. I t is provided w ith a ‘/«-inch covered peephole and a latch handle.
Dimensions, over all: H eight, 15'/« inches; w idth, 12 inches;
depth, 12'/< inches. T he usable muffle space m easures 3 ’/»
wide, 3 ‘/ i inches deep by 4 inches high. Pow er consum ption, 700 w atts.
... $33.50 AC o r I)C ... $52.00
S C I E N T I F I C INSTRUMENTS
N e w Y o rk • Boston •
Re ç u 3 - P A T . û f f !
C H I C A G O
L A B O R A T O R Y A P P A R A T U S
• Toronto • San Francisco
A N A L Y T I C A L E D I T I O N 11
HERE’S THE
NEW PO RTA BLE G-E X -R A Y
DIFFRACTION UNIT
D esigned expressly to m e e t th e reco g n ized n eed fo r a portable x-ray diffraction apparatus, th e new G -E M o d el X R D-2 U n it p ro v id es full flexibility to expedite back re
flection stress analysis o f larg e beam s, castings, p ipes, an d other types o f co n stru ctio n .
The G -E M o d e l X R D-2 U n it incorporates a single-port beryllium w in d o w diffraction tu b e , d esig n ed fo r con tin u o u s operation, w h ic h p e rm its th e tran sm issio n o f lo n g wave
length x -rad iatio n ; a n d w h e n th e tu b e is o p erated a t lo w kilovoltages, th e ra d ia tio n p ro d u c e d is id eal fo r m icro radiographic in v e s tig a tio n o f th in film s o f m aterials.
T he u n it is p ro v id e d w ith a stan d ard cam era track having
Please send m e com plete details o f the new G-E M odel X R D -2 X-Ray Diffraction Unit.
N am e.
C om pany _____
A ddress_____
GENERAL ELECTRIC
X -R A Y C O R PO R A TIO N
2 0 1 2 J A C K S O N B L V D . C H I C A G O , I I I . , U . * . A .
a base w h ich p e rm its fu ll a d ju stm e n t, in all d irectio n s, to facilitate d ie accurate a lig n m e n t o f th e cam eras w ith th e focal sp o t o f th e x-ray tu b e. A ll o f th e G -E x-ray diffraction cameras can b e used in terch an g eab ly o n e ith e r th e G -E M o d el X R D-1 o r X R D -2 cam era tracks.
T h o ro u g h ly tested by m o re th a n a year’s service in several o f th e n a d o n ’s le a d in g in d u strial lab o rato ries, th e G -E M o d el X R D-2 U n it can b e relied u p o n to m aterially w id en th e scope o f x-ray diffraction analysis. F ull details o f this fast, co n v en ien t, co m p act, p o rta b le diffraction u n it w ill be sen t u p o n re q u e st; ju st fill in th e c o n v e n ie n t c o u p o n an d m ail it, today.
H E V I D U T Y E L E C T R I C C O M P A N Y
LABORATORY FURNACES
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
HEVI DUTY ELECTRIC L A B O R A T O R Y FU R N A C ES
1. M ultiple Uni! Muffle F u rn aces—4 stan d ard sizes—w ith detached rheostat.
2. M ultiple Unit Hot P lates—3 h e a ts —7 stan d ard sizes.
3. M ultiple Unit Muffle F u rn aces with built-in rh eo stat—3 stan d ard sizes.
4. M ultiple Unit Solid Combustion Tube F u rn ace—10 stan d ard sizes.
5. M ultiple Unit Crucible F u rn aces—5 stan d ard sizes.
A s k y o u r l a b o r a t o r y s u p p l y d e a l e r o r
6. Hevi Duty Crucible F u rn a c es—3 stan d ard sizes.
7. M ultiple Unit Hinged Combustion Tube F u rn aces—10 stand
a rd sizes.
8. M ultiple Unit Muffle F u rn a c es—with controlling pyrom eter.
9. M ultiple Unit O rganic Combustion F urnace.
10. M ultiple Unit Muffle F urnaces with transform er a n d rheostat
—2 stan d ard sizes.
s e n d f o r l a b o r a t o r y fu r n a c e b u ll e ti n s
A N A L Y T I C A L E D I T I O N 13
1
A G U A R A N T Y OF Q U A L IT Y
C h e m ic a l e x p e rie n c e o f m an y y e a rs h a s e n a b le d M e r c k & C o . I n c . to p la n , d e s ig n a n d e q u ip th e n e w M e r c k A n a ly tic a l L a b o ra to rie s , w h e re in r i g i d a n d c o n s ta n t c o n tr o l is e x e rc ise d o v er m o r e th a n 1 ,5 0 0 p r o d u c ts b e a r i n g th e M e rc k la b e l. T h e e x te n s iv e fa c ilitie s f o r p r e c is io n a n a l
yses a n d te s tin g in c lu d e n o t o n ly ch e m ic a l m e th o d s , b u t p h y s ic a l a n d o p tic a l p ro c e d u re s as w e ll. B e c a u se o f th e s e m o d e r n c o n tr o l fa c ili
tie s, th o u s a n d s o f in d u s tr ia l c h e m ists, stu d e n ts, a n d r e s e a r c h w o r k e r s u se M e r c k L a b o ra to ry C h e m ic a ls w ith c o m p le te c o n fid e n c e in th e ir p u rity a n d u n ifo rm ity .
FO R V I C T O R Y — B u y War
A P L E D G E O F S E R V I C E
A lth o u g h th e M e r c k fa c to rie s a re n o w o p e r a t
in g o n a 2 4 -h o u r day, 7-day w e e k s c h e d u le in o r d e r to su p p ly th e n e e d s o f o u r a rm e d fo rc e s a n d c iv ilia n p o p u la tio n , it m ay n o t alw ay s be p o s s ib le to su p p ly y o u im m e d ia te ly w ith y o u r c o m p le te re q u ire m e n ts o f M e r c k C h e m ic a ls.
B ut in s p ite o f th e d ifficu lties w h ic h c o n f r o n t u s, w e s h a ll c o n tin u e to d o e v e ry th in g p o s s ib le to serve o u r c u s to m e rs to th e lim it o f o u r a b ility . In fa c in g th e v ita l ta s k a t h a n d , it is o u r h o p e th a t w e m ay c o n tin u e to h av e th e u n d e r s ta n d in g c o o p e r a tio n o f o u r c u s to m e rs , w h ic h h a s h e lp e d us im m e a s u ra b ly in o u r e ffo rts to se rv e th em .
S av in gs B o n d s a n d S t a m p s
- I S m m
M E R C K & C O . I n c . ^ la n u fa c to rin g (ü/em i<iti R A H W A Y , N . J .
New Y ork . N . Y. . P h ila d e lp h ia , Pa. • St. L ouis, Mo. • E lk ton , Va. • C hicago, 111. . L os A n g e le s, Cal.
In C a n a d a : MERCK & CO. L im ited, M ontreal an d T o ro n to
14 I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y Vol. 14, No. 10
BECKMAN PHOTOELE CTRIC
Q U A R T Z S P E C T R O P H O T O M E T E R
A new , self-contained, precision instrum ent with quartz prism, operating on an electronic circuit, for the rapid m easurem ent of percentage transm ission and density.
9101. Beckman Photoelectric Quartz Spectrophotometer
C, Slita w ith precision a d ju stm e n t: D , L ig h t Source; E , C o m p a rtm e n t for G, F ilte r Slide; H , C o m p a rtm e n t fo r A b sorption Cells; J , P h o to tu b e Selector;
A, W avelength Scale; B, B u ilt-in E lectronic In d ic a tin g M eter;
tw o P h o to tu b es: F, H older fo r fo u r 10 m m A bsorption Cells; C.
an d K , Sw itch for checking d a rk cu rren t
QTJARTZ SPEC TR O PH O TO M ETER , Beckm an Photoelectric. A s e l f - c o n t a in e d u n i t w i t h w h ic h a w id e v a r i e t y o f r e s e a r c h a n d c o n t r o l w o r k c a n b e c o n d u c t e d w i t h c o n v e n ie n c e , s p e e d a n d p r e c is io n . C o n s is ti n g o f a q u a r t z m o n o c h r o m a t o r , w i t h l i g h t s o u r c e , h o ld e r f o r a b s o r p t i o n c e lls, t w i n p h o t o t u b e s a n d b u i l t - i n e le c tr o n ic m e t e r f o r t r a n s l a t i n g p h o t o t u b e c u r r e n t s i n t o d i r e c t r e a d i n g s o f p e r c e n t a g e t r a n s m i s s i o n a n d d e n s i ty . S e e C a r y a n d B e c k m a n , “ A Q u a r t z P h o t o e l e c t r i c S p e c t r o p h o t o m e t e r , ” J o u r n a l o f the O ptical S o ciety o f A m e ric a , V ol. S I , N o . 11 (N ovem ber, 1941), p . 682.
Monochromator. Autocollimating type, w ith 30° quartz prism of selected crystal which provides high dispersion in the ultra-violet. W avelength scale approx. 100 cm long, graduated from 200 mmu to 2000 mmu, readable to 0.1 mm u in the ultra-violet and to 1.0 mmu in the red, w ith a scale accuracy of 1 mmu.
Optical parts rigidly m ounted in a massive heat-treated iron block within a dust-proof steel case.
Slits. Protected b y quartz windows, w ith stray light ef
fects reduced to a minimum. Simultaneously and continu
ously adjustable from 0.01 to 2.0 mm by a precision mecha
nism. Slits can n o t be damaged by closing too far. Pull scale reading w ith nominal band width less th a n 2 mmu over all b u t th e extreme ends of th e spectrum.
Electronic Indicating M eter. A built-in potentiom eter and electronic amplifier makes possible direct readings in percentage transmission and density. The switch position
marked “ .1” provides a ten-fold expansion of th e trans
mission scale for more accurate readings on solutions below 10% transmission.
Light Source. A standard 32 c. p. 6-volt, tungsten lamp serves as a light source for the range 320 to 1000 mmu.
F or th e ultra-violet range below 320 mmu a sm all hydrogen discharge tube is offered w ith power supply.
Sample H olders. Absorption cells are accommodated in a rem ovable holder which is inserted in a light-tight com
partm en t and is operated from the front of the instrum ent by means of a sliding rod. Cells and holders are available for 10, 20, 50 and 100 mm liquid lengths.
Phototubes. Two phototubes are furnished in a com part
m ent which adjoins the cells. A sliding rod brings either tube into position and simultaneously switches the electrical connections.
9101. Q uartz S pectrophotom eter, B eckm an Photoelectric, M odel D , R ange 320 to 1000 m illim icrons. C onsisting of m o n o ch ro m ato r w ith q u a rtz prism a n d tw o B li t s , b u ilt-in electronic m eter, 6-volt tu n g sten lam p in d etach ab le housing, one each Cacsium -O xide a n d Blue- Sensitive pho to tu b es, an d holder w ith selected s e t of four Corex glass a b so rp tio n ceils for 10 mm liquid length. W ith d ry cells for o p e ra t
ing th e m eter b u t w ith o u t 6-v o lt Btorage b a tte ry as required fo r operatin g th e tu n g ste n lam p an d electronic tu b e filam en ts...764.00*
9101-B. D itto, M o d el DU, R ange 220 to 1000 m illim icrons, identical w ith above b u t w ith u ltraviolet-sensitive p h o to tu b e in place of th e blue- sensitive tu b e a n d w ith th e add itio n of accessories for far u ltrav io le t consisting of one p air of F used Silica A bsorption Cells for 10 m m liquid len g th , H ydrogen D ischarge Tube, housing for sam e, a n d a pow er su p p ly u n it, 110 volts, 5 0 /6 0 cycles, for m ain tain in g th e discharge a t
co n sta n t in te n s ity ... 1052.00*
* Sub ject to Fed eral Excise T ax
M ore d e ta ile d in fo r m a tio n s e n t u p o n re q u e s t.
A R T H U R H. T H O M A S C O M P A N Y
R E T A IL — W H O LE S A LE — E X P O R T
L A B O R A TO R Y A PPA R A TU S A ND REAG EN TS
W E S T W A S H IN G T O N SQ UARE, P H IL A D E L P H IA , U. S. A.
C a b le A d d re s s , “ B a la n c e ,” P h ila d e lp h i a
INDUSTRIAL a n d ENGINEERING CHEMISTRY
A N A L Y T I C A L E D I T I O N (^ utechnw I
P U B L IS 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
Determining the Oil Content of Paraffin Waxes
R U S S E L L L E E AND V. A. K A LIC H EV SK Y , S oco n y -V acu u m Oil C o m p an y , I n c o r p o ra te d , P n n ls b o ro , N . J .
A
N U M B E R of la b o rato ry m ethods h ave been proposed for th e analysis of oil-wax m ixtures (1 -7 ,1 0 -1 4). Some of these m ethods w ere developed for use on w axy stocks containing large a m o u n ts of oil an d are em ployed chiefly for controlling com m ercial dew axing operations. These are not sufficiently a c c u ra te for th e analysis of waxes containing small am o u n ts of oil. Of th e m ethods which have been proposed fo r th e analysis of b o th scale a n d refined grades of paraffin wax, only th e press m ethod (2) has been used exten
sively in th e p etro leu m in d u stry . T h is is generally recognized to be lacking in a ccu racy an d was abandoned as a ten tativ e standard b y th e A. S. T . M . in 1939. T h e oth er published m ethods for th e analysis of paraffin waxes involve compli
cated procedures o r are lim ited in applicability to waxes of known origin.
T he an a ly tic a l problem is com plicated b y the absence of a sharp line of d em arcatio n betw een “ oil” a n d “ wax” , owing to th e existence of in term ed iate com pounds which m ay be defined as eith er “ oil” o r “ w ax” (8, 9). A n a rb itra ry defini
tion of th e b o u n d a ry line betw een oil an d wax is, th u s, neces
sary in an aly tical m ethods of th is type.
T his p ap er describes a sim ple an d reliable m ethod for the determ ination of oil in scale an d refined paraffin waxes con
taining n o t ov er 10 p e r c e n t b y w eight of oil. T he applica
bility of th e m eth o d to waxes of higher oil co n ten t has n o t y et been fully in vestigated. T h e m ethod is based on the selective sep aratio n of oil an d wax b y solvent extraction
Fi g u r e 2. Pr e c o o l in g Ch a m b e r
* * 1 b ~ 2 " "*1 b 5" s i r
i i*
b *
( .020- ) ;
& s.
G age B r a s s
iF r -
Fi g u r e 1. Co o l iv o Ve s s e l
under carefully specified conditions. “ Oil” is defined in this te s t as th e percentage of solvent-free e x tra c t m inus a correc
tion of 0.15 per cent. T h e 0.15 per c e n t correction fa c to r was developed em pirically on waxes containing know n q u a n titie s of oil and having m elting points betw een 115° F . (46° C.) an d 145° F . (63° C.). F o r w axes m elting outside th is range different facto rs m ay be necessary. T h e resu lts o btained by th is m ethod are u su ally acc u ra te to a b o u t ± 0 .0 5 p er cent on oil-wax m ixtures containing less th a n 1 per cent oil.
T h e m ethod involves dissolving a 25-gram sam ple of w ax in 375 ml. of m ethyl eth y l ketone and chilling th e m ixture to
—25° F . ( —31.7° C .). A portion of th e chilled m ix tu re is filtered by m eans of a n im m ersion-type filter leaf using vacuum . T h e am o u n ts of oil an d solvent in th e filtra te are determ ined b y ev ap o ratio n of th e k etone. As th e proportion of solvent and oil in th e filtrate is th e sam e as t h a t in th e chilled m ixture, th e q u a n tity of oil in th e wax sam ple can be calculated b y sim ple arith m etical rules. T h e filtratio n of only a portion of th e chilled m ixture elim inates th e need of washing th e wax cake w ith chilled solvent, th e re b y ob v iatin g errors due to occlusion of oil by th e wax a n d p e rm ittin g th e use of relatively sim ple a p p a ra tu s an d procedure.
A p p aratu s
T h e a p p a ra tu s consists of th e following item s:
Cooling vessels, V -shaped, of a b o u t 1-liter cap a city an d h aving th e dim ensions show n in F igure 1.
Precooling chamber for filter leaf having the dimensions shown in Figure 2.
767
768 I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y Vol. 14, No. 10
Fi g u r e 3 . Fi l t e r Le a p All p a rts nickel-plated
factory, provided its refractive index a t 68° F. (20° C.) is 1.378
± 0.002 and the residue left on evaporating a 100-ml. sample by the procedure outlined below for evaporating solvent from the filtrate is not more th an 0.002 gram.
P ro ced u re
A representative portion of the -wax sample is melted in a suitable container, using a w ater b ath or oven m aintained at 160° F. (71° C.) to 180° F. (82° C.). T he wax sample should not be held in the molten condition longer th an is necessary for its complete liquefaction. Twenty-five grams (=*=1 cram) of the m olten wax are weighed into a tared 500-ml. Erlenmeyer flask, making weighings to =*=0.2 gram, and 375 ± 5 ml. of methyl ethyl ketone are added to the flask. A water-cooled condenser is attached to the flask and the m ixture is heated on an electric hot plate or steam bath until th e wax is completely dissolved, taking precautions to prevent surging of the solution into the condenser. The flask is then removed from the source of heat and, after boiling has ceased, the condenser is disconnected.
The flask is then weighed to ± 0 .5 gram and quickly stoppered w ith a cork equipped w ith a therm om eter.
T he solution is allowed to cool to about 130° F. (54° C.) but before any wax precipitates it is poured into the V-shaped vessel in the cooling b ath which is m aintained a t —35 ± 5° F. ( — 37 ± 3° C.). T he wax solution is stirred w ith a therm om eter at frequent intervals until th e tem perature reaches —20° F.
( —29° C.) and then continuously until the tem perature reaches - 2 5 ± 0 .5 ° F. ( - 3 1 .7 ± 0.3° C.).
T he filter leaf is removed from the precooling chamber in the cooling b ath and immersed quickly in the chilled mixture. The filter leaf is connected to a 250-ml. Erlenm eyer flask tared to
±0.001 gram and to the vacuum system as shown in Figure 5.
The vacuum should be m aintained between 250 and 600 mm. of mercury gage. A fter about 100 ml. of filtrate have been col
lected in th e flask, the suction is discontinued and the flask dis-
F ilter leaves of the type shown in Figure 3.
The filter medium is No. 8-0 filter canvas tightly fitted to th e leaf. A qualitative grade of filter paper may be used on the circular leaf, provided it is supported by a perforated plate having a free area of not less th an 40 per cent.
Insulating cooling bath large enough to accommodate the desired num ber of cooling vessels and precooling chambers. T he b ath is filled with a suitable liquid such as methyl ethyl ketone which is refrigerated by solid carbon dioxide or brine circulation. T he tem perature of the bath is m aintained a t — 35 ± 5° F. ( —37 ± 3° C.) throughout the test.
Erlenm eyer flasks of 500-ml. capacity for preparation of the wax-solvent mixture.
Erlenm eyer flasks of 250-ml. capacity for collecting the filtrate and evaporating the sol
vent therefrom.
Evaporation assembly as shown in Figure 4.
Jets are provided for delivering a stream of clean, dry air vertically downward into the evaporation flasks. T he inside diam eter of the je t is 3 ± 0.2 mm. and the tip of the je t is 25 ± 5 mm. above the surface of the evapo
rating liquid a t the sta rt of evaporation. Air is supplied a t the rate of 2 to 3 liters per minute per jet. The air is purified by passing it first through a commercial air filter and then through a 30-cm. column of 30- to 60-mesh fuller’s earth. T he cleanliness of th e air is checked periodically by evaporating 100 ml. of methyl ethyl ketone in a w ater b ath which is maintained a t 95 ± 2° F. (35 ± 1° C.). The residue left on evaporation should not exceed 0.002 gram.
Thermom eters of 0° to 300° F. range to meas
ure the tem perature of the wax-solvent solu
tion and therm om eters of —70° to + 7 0 ° F.
ranee to measure the tem peratures of the cool
ing Dath and cooling vessel.
S o lv e n t
M ethyl ethyl ketone is used as the solvent in this test. The commercial grade is satis-
EULLERS EARTH FILTER
COMMERCIAL AIR FILTER
MANIE0LB ( 8 J I T S SHOWN)
. J
Fi g u r e 4 . Ev a p o r a t i o n As s e m b l y
Ta b l e I . An a l y s iso p Kn o w n Oi l- Wa x Mi x t u r e s b y Pr o p o s e d Me t h o d
W ax C om ponent Oil C om ponent Oil C o n te n t
N o. D escription M elting p o in t P our
p o in t S. U. V.
a t 100° F.
Flash p o in t
% b y w t. OI blend
F o u n d b y proposed
m ethod C alcu
lated
1 Deoiled refined
° F.
132.2
0 F . ° F .a
0 .0 0
% by wt.
0 .0 0 0 .0 0
2 wax
131.4 0 .0 0 0 .0 0 0 .0 0
3 124.0 0 .0 0 0.0 5 0 .0 0
4 123.2 0 .0 0 0 .0 0 0 .0 0
5 123.7 0 .0 0 0 .0 8 0 .0 0
5 123.7 i.5 94 ‘.3 32Ö 0 .1 9 0 .1 8 0.1 9
5 123.7 15 9 4 .3 320 0 .3 8 0.3 4 0 .3 8
5 123.7 15 94 .3 320 0 .9 9 0 .8 9 0 .9 9
5 123.7 15 9 4 .3 320 2 .0 9 1.72 2 .0 9
6 Refined wax 131.1 0 .0 0 0 .1 9
O’. 68
6 131.1 0 9 0 .7 0 .4 9 0 .7 5
6 131.1 15 8 6 .8 0.4 1 0 .5 6 0 .6 0
7 123.2 0 .0 0 0.4 1
7 123.2 Î5 8s!s 3 .8 4 4 .0 3 4^25
7 123.2 20 196.0 0 .9 9 1.39 1.40
a P ensky-M artens.
October IS, 1942 A N A L Y T I C A L E D I T I O N
Fi g u r e 5 . Fil t r a t io n As s e m b l y
connected from the filter leaf and vacuum systenri. The outside of the flask is washed w ith acetone, wiped off with a cloth, and
weighed to ±0.2 gram. , ... .
The m ethyl ethyl ketone is evaporated from the filtrate, using the evaporation assembly described above. The flask is eig i to ±0.001 gram after 2 hours’ evaporation and th en alter u.o- hour evaporation periods until the loss between successive weig - ings is not over 0.002 gram. The flask should be rinsed wit acetone to remove water, placed on a paper towel or other w ou ^ to dry for one minute, then placed in a desiccator containing anhydrous calcium chloride a t balance room _ tem perature about 15 m inutes prior to weighing. The time required
evaporation is usually 2.5 hours. ,
The oil content of the wax sample is computed by the following equation:
Oil, % by w t. = 100 X
(weight of oil in filtrate) X (weight of solvent in charge m ix tu r e )________
(weight of wax sample) X (weight of solvent in filtrate)
- 0.15
In performing this test, special c a r e should be exercised keep the equipm ent clean. This applies particularly to filter leaf. T he cleanliness of the filter leaf can be checked y filtering through it about 100 ml. of methyl ethyl k e t o i * ordinary tem peratures and evaporating the filtrate as previ . } outlined. The residue should not exceed 0.00- gram.
Ta b l e I I . In t e r l a b o r a t o r y Re p r o d u c i b i l i t y o p Pr o p o s e d Me t h o d
Oil C o n ten t
L ab o ra- W ax Sam ple to ry A
130-132° F. m . p., refined wax
0 .1 7 0 .1 7 Av. 0 .1 7 128-130° F . m . p.,
refined wax 0 .2 9
0 .2 5 Av. 0.2 7 126-128° F . m . p.,
refined wax 0 .3 0
0 .2 8 Av. 0 .2 9 122-124° F . m . p.,
refined wax
0 .3 4 0 .3 6 Av. 0 .3 5 126-128° F. m. p.,
scale wax 0 .9 5
0.9 1 Av. 0 .9 3 121-123° F . m. p.,
scale wax 1.83
1.8 5 Av. 1.84
Maximum
A verage D eviation L ab o ra- L ab o ra- of th re e from
to ry B to ry C laboratories Average Per cent by weight
0 .1 9
0.21
0 .2 0 0.2 4 0 . 2 2 0.2 3 0 .3 5 0 .3 8 0.3 7 0.41 0.4 1 0.41 0.8 9 0.9 0 0 .9 0 1.72 1.76 1.74
0 .1 8
0.11
0 .1 5 0 .17 0.2 4 0.21 0 .4 0 0 .4 0 0 .4 0 0.4 7 0 .3 9 0.4 3 1.25 1.15 1 .2 0 1.831.89
1.86
0.17
0.2 4
0.3 5
0 .40
1.01
1.81 0.03
0.03
0.06
0.05
0.19
0.07
R e su lts
T he accuracy of th e resu lts o b tain ed in de
term ining th e oil c o n te n t of paraffin w axes by th e described m ethod is illu stra te d b y T ab le I.
These results were o b tain ed on deoiled refined waxes an d know n blends of dew axed oils w ith refined waxes before a n d a fte r deoiling. F o r waxes containing less th a n 1 per cent oil, th e m ethod gives results w hich are u su ally accu rate to ± 0 .0 5 per cent.
T h e in te rla b o ra to ry reproducibility of th e m ethod is d em o n strated b y th e d a ta in T ab le II . E x cep t in one instance, th e resu lts from different laboratories differ from th e average b y less th a n 0.1 per cent.
A com parison of results o b tain ed b y th e pro
posed m ethod a n d th e press m ethod is show n by T ab le I I I . T hese d a ta show t h a t scale an d refined paraffin waxes can be readily differen
tia te d on th e basis of oil contents as d eterm ined by th e proposed m ethod b u t n o t b y th e press m ethod.
T a b l e III. C o m p a r i s o n o f P r e s s a n d P r o p o s e d M e t h o d s Oil C o n ten t
W ax Sample Refined wax
119.6° F . m. p.
123.6° F. m. p.
126.4° F . m. p.
131.0° F. m. p.
Scale wax 118.8° F. ra. p.
123.0° F. m . p.
126.4° F . m. p.
128.2° F . m. p.
• A. S. T. M . D-308-29T (abandoned in 1939).
Press m eth o d “ Proposed (D u re tta cloth) m ethod
% by weight
1.2 0 .4 5
1.3 0 .3 5
1.0 0.2 7
1 .4 0 .1 5
2 .3 3 .7 8
0 .8 2 .9 8
1 .0 0 .8 9
1.1 0.5 2
A c k n o w le d g m e n t
T he a u th o rs wish to express th e ir ap p reciatio n to J . B . R a th e r for perm ission to publish th is article, a n d to th a n k L. C. D rake, T . A. P e try , T . G. R oehner, an d E . L. S m ith of th e Socony-V acuum Oil Co., In c., an d E . L. R u h a n d A.
W illiams of th e S ta n d a rd Oil Co. of N ew Je rse y fo r m an y helpful suggestions in th e developm ent of th is m eth o d .
L ite ra tu re G t e d
(1) Am. Soc. Testing M aterials, Proc., 27, P a rt I, 450-4 (1927);
28, P a rt I, 445-9 (1928).
(2) Ibid., 29, P a rt X, 359-61. 682-6 (1929).
(3) Burch, E. A., Refiner, 17, No. 11, 598-602 (1938).
(4) Diggs, S. H ., and Buchler, C. C ., I n d . E n o . C h e m ., 19, 125-7 (1927).
(5) Hall F. W., and M cCarty, B. Y., Natl. Petroleum News, 29, No. 28, R-15-25 (1937).
(6) Holde, D . (Mueller, Ed.), "Exam ination of Hydrocarbon Oils and Saponifiable F ats and W axes", 2nd ed, pp. 108, 110, New York, John Wiley & Sons, 1922.
(7) Horne, J. W ., and Holliman, W . C., Bur. Mines, Tech. Paper 583 (1938).
(8) Kalichevsky, V. A., “ Modern M ethods of Refining Petroleum Oils” , pp. 30-2, New York, Reinhold Publishing Corp., 1938.
(9) Kalichevsky, V. A., and Lee, R., J . Inst. Petroleum Tech., 24, 59-60 (1938).
(10) M cK itterick, D . S., Henriques, H. J., and Wolfe, H . I., Ibid., 23, 616-41 (1937).
(11) Schwartz, F ., and Huber, H . von, Chem. Rev. Felt u. Harz Ind..
20, 242-4 (1913).
(12) Weld, D . P ., and R ather, J . B., Refiner, 8, 102, 106, 110, 114 (1929).
(13) Wilson, R . E ., and Wilken, R . E., I n d . Eno. C h e m ., 16, 9-12 (1924).
(14) W yant, L. D ., and M arsh, L. G., Bur. Mines, T ech. Paper 368 (1925).
Location of the End Point on Certain Graphical Titration Curves
A LO IS LAN GER AND D. P . ST EV E N SO N , W e s tin g h o u s e R e s e a rc h L a b o ra to rie s , E a s t P it ts b u r g h , P e n n a .
T h e e q u a tio n s for c e r ta in ty p es o f titr a - a n d we h a v e
, . i , . . . 1 — kaA 0 + kjB , (4)
tio n curves are d erived an d p o ssib le m e t h
ods for g ra p h ica lly fin d in g th e e n d p o in t W hen
d escrib ed . T h e p ra ctica l a sp e c ts r e s u ltin g \ , & ^/A o
from llie a n a ly sis are d isc u sse d . we m e (/t0 _ (gi _ p) = g (5)
T h e o r e tic a l
W e will first consider th e sim ple p re c ip ita tio n reaction
A n+ + fl»" = (1)
I n order to keep th e form ulas reaso n ab ly sim ple, we will m ake th e following assu m p tio n s:
(A-+) X (ß»~) á S
I
N T IT R A T IO N S such as p olarom etric (am perom etric) (1 ,6 ), con d u cto m etrie, rad io m etric (Jf), an d o thers, in w hich th e readings of th e en d -p o in t in d ic a to r are pro p o rtio n al to th e co n cen tratio n of ions or m olecules in th e solution, graphical m eth o d s are u su ally m o st convenient for d eterm ining th e equivalence or end p o in t. V arious con stru ctio n s h av e been suggested for finding th e equivalence p o in t from th e titr a tio n curve. Som e of these m ethods, t h a t of M ajer (6), for exam ple, are difficult to a p p ly because th e y require th e a c c u ra te know ledge of c ertain c o n sta n ts w hich áre in m o st cases unknow n. O thers, such as th e ta n g e n t m ethod (Í ) , are u n c e rta in to a p p ly w hen th e so lu b ility of th e p ro d u c t is high o r th e solutions to be titr a te d are d ilu te a n d therefo re th e sh ap e of th e titr a tio n cu rv e s ta r ts to d e v ia te stro n g ly from s tra ig h t lines.
I n th is p ap er a n a tte m p t is m ade to derive th e eq u atio n s for th e ideal titr a tio n cu rv es u n d e r idealized conditions.
A n analysis of th e cu rv e o b tain ed fo r th e en d p o in t in a pre
cip itatio n reactio n in d icated th e co rrelatio n to M a je r’s so lu b ility m ethod, th e ap p ro x im atio n of th e ta n g e n t m ethod, a n d led to a new g rap h ical co n stru ctio n for d eterm in in g th e en d p o in t w hich should suffer from none of th e aforem entioned difficulties if th e specified conditions can be realized.
T he solubility of A B is not changed by either the varying nature of the solution during the titratio n or aging effects.
F urtherm ore,A B is completely dissociated in solution.
T he titratio n is performed a t constant volume, V, or the indicator reading has been corrected for volume increases, and for the background which is always present.
B n~ is added to A n+. I t will be clear from the sym m etry of the equations th a t the results will apply equally well to the opposite assumption.
T he concentrations are such th a t th e activity coefficients may be taken equal to one.
W e le t th e corrected in d icato r reading be i, th e initial a m o u n t of .4 ’*+ in th e solution be *4o, th e a m o u n t of B "- a d d ed be B x, a n d th e q u a n tity of A B th u s form ed be p . If S is th e solubility p ro d u c t of A B , th e condition on th e con
cen tratio n s of A " + an d B"~ is
T h e in d icato r reading will be
i - ka U*+) + h (ii»-)
in w hich th e k's a re p ro p o rtio n ality co n stan ts.
W hen
Bz :£ S /A t, v = 0
— 81
Fi g u r e 1. Ti t r a t i o n Cü r v e s S /A o =» 0 .1 for ail curves
A . ka «* kb = 1
B. ka «■ 0, kb — I
C. k a =* 1, kb “ 0 D . A sym ptotes
a n d
i = ka (/to — p) + k b (Bx — p) (6) Solving E q u atio n 5 for p a n d su b s titu tin g in E q u atio n 6, we o b tain fo r i as a fu n ctio n of B x
. = K _ - h (A# _ B i) + V ( 4 o - Bt y + 4S (7) T h is is th e a n a ly tic expression fo r th e titr a tio n curve (for exam ples, see F ig u res 1 an d 2). B y definition, th e equiva
lence p o in t is given b y Bx = .-10 o r
i =
(A-a+ h) V s
(8)M a je r (5) o b tain ed th e special case for one of th e k ’s equal to zero.
If we tran sp o se th e first m em ber of th e rig h t-h a n d side of E q u a tio n 7 a n d sq u are b o th sides, we o b tain
[» - ka (A 0- B z)1 [i + h (A o -B :) ) = (K + kby S (9)
B , -
Fi g u r e 4 . Ti t r a t i o n Cu r v e s
K = 0 1 i t - I . ifco “ 1. for A . B u B-., a sy m p to tes of A . T is the tan g en t' of A a t & " 0 . E is the equivalence point.
Fi g u r e 2 . Ti t r a t i o n Cu r v e s
fco =■
¡ A t = 0.1 0 - / A t - 0.0 5 C. S/.A« - 0.01
* . «■ *» - 1 for all curves
.1. S / z l o - 0 . 1 0 - 0.001
B . S / A t - 0 .0 5 S/.4» «= 0.000
which is a h y p erb o la w ith th e asy m p to tes i = A'a (/lo — Bx)
i = - h (A. - fl.) (10)
Solving E q u a tio n s 10 we find t h a t th e intersection of the asym ptotes of th e titr a tio n curve occurs a t th e end-point condition.
This resu lt sh ould m ake it possible to use very simple geometric co n stru ctio n s to find th e end p o in t (6). l’rom the theorem (I) th e co n ju g ate diam eters of a hyperbola are also conjugate d iam eters of th e asy m p to tes; it m ay be shown th a t the bisector of a n y p air of parallel chords of th e hyperbola goes th ro u g h th e p o in t defined b y th e intersection of the asym ptotes. T h u s th e problem of determ ining th e end point from th e titr a tio n curve is ju s t t h a t of finding th e point of intersection of th e bisectors of tw o pairs of parallel chords which are n o t m u tu a lly parallel. T h is procedure is illustrated in Figure 3. I t is clear from E q u atio n s 10 t h a t th e m ethod is independent of th e values of k a a n d kb. O r th e theorem (II) th a t on a n y chord th e p arte betw een th e hyperbola and the two asy m p to tes are of equal length, could also be used foi finding th e en d p o in t if th e titra tio n cu rv e an d one asym ptote are know n, since th e second one can easily be constructed.
This procedure is illu stra te d in F igure 5.
In Figures 1 an d 2 are showrn th e various forms th a t the titra tio n curve, E q u a tio n s 4 a n d 7, m ay assum e for p articular values of ka, h , an d S/A<>. A n exam ination of Figure 2 shows t h a t for th e ra tio S / A 0<0.001, th e tan g en ts an d the asym ptotes coincide well. W hen S /A n > 0.001, it would be necessary to ex ten d th e titr a tio n curve to fairly large values of B , to draw a ta n g e n t t h a t w ould a t all closely approxim ate the asy m p to te. I n m an y cases, th e titra tio n of m etallic ions with organic reag en ts, for instance, th is w ould n o t be possible because of th e lim ited solubility of th e reag en t itself. T he
15 2D
*-8*
Fi g u r e 3 . Ti t r a t i o n Cu r v e s
ka «■ 1, kb “ 2, for all curves yt. S / A t = 0 .0 5 B . S / A t - 0.01
C. S / A t = 0 .0 0 0 . L. Parallel chords. M . M id points of chords. E . E quivalence
D o i n t Hi and A1: correspond to E q u a tio n 8. T and T are ta n g e n ts of B. intersecting a t F , which is ab o u t 2 per c en t different from b .
initial ta n g e n t becom es different from th e a sy m p to te a t B , = 0 when S / A 0 <0.001. F ro m th e co n stru ctio n illus
tra te d in F igure 3 i t is clear t h a t only th e easily fo u n d po rtio n of th e titra tio n cu rv e is necessary to enable one to co n stru ct th e tru e end point, th e in tersectio n of th e asy m p to tes.
T he horizontal lines R in F ig u re 3 w hich illu stra te M a jo r’s (6) m ethod of o b tain in g th e end p o in t (E q u atio n 8) will be observed to in tersec t th e titra tio n curve tw ice. Such am -
075 -
