INDUSTRIAL a n d ENGINEERING CHEMISTRY
A N A L Y T IC A L E D I T I O N
H A R R IS O N E. HOWE, E D I T O R p I S S U E D A P R I L 15, 1940 » V O L . 12, NO. 4 » C O N S E C U T I V E NO. 8
Se p a r a t i o na n d De t e r m i n a t i o no f Is o m e r i c Me n t h o l s
R. T. Hall, J. H. Holcomb, Jr., and D. B. Griffin 187
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 P r l m a r y M o n o n i t u o - p a r a f f i n s . . Eugene W . Scott and Joseph F. Treon 1S9 Id e n t i f i c a t i o n o f Pa r a f f i n s...
Aristid V. Grosse, E. J. Rosenbaum, and H. F. Jacobson 191
A c c e l e r a t e d S u b l i m a t i o n ...A . J. Bailey 194 J
Qu a n t i t a t i v e Sp e c t i i o c h e m i c a l An a l y s i sb y Me a s u r e m e n t o f Re l a t i v e In t e n s i t i e s...
E. K. Jaycox and A. E. Ruohle 195
Co m p a r i n g Re l a t i v e Ef f e c t i v e n e s s o f Wa t e r- Re p e l l i n g a n d Re t a r d i n g So l u t i o n s i n Wo o d . . .
Ernest E. Hubert
De t e r m i n a t i o no f Or g a n i c Ph o s p h o r u si n So i l s . . .
R. W. Pearson
R a p i d Q u a l i t a t i v e T e s t f o r A l c o h o l i c H y d r o x y l G r o u p ...F. R . Duke and G . Frederick Smith
Ri b o f l a v i n Co n t e n t o f Ye a s t s De t e r m i n e d Ph o t o m e t r i c a l l y a n d Bi o l o g i c a l l y...
A. E. Schumacher and G. F. Heuser
De t e r m i n a t i o n o f Ro t e n o n e i n De r r i s Ro o t . . . .
Th. M. Meijer and D. R. Koolhaas
St a r c h- Io d i d e Me t h o d o f Oz o n e An a l y s i s...
Clark E. Thorp
De t e r m i n i n g Em u l s i f y i n g Ef f i c i e n c i e s...
Leonard II. Cohan and Norman Hackerman 197
1 9 8
201
2 0 3
2 0 5
2 0 9
210
J
R o u t i n e D e t e r m i n a t i o n o f E q u i v a l e n t A c i d i t y o r B a s i c i t y o f F e r t i l i z e r s ... E . W. Constable 2 1 4 Ap p a r a t u s f o r Co n t i n u o u s Au t o m a t ic Me a s u r e m e n t
o f Ev o l v e d Ga s...
M. L. Crossley, R. H. Kienle, and C. II. Benbrook 2 1 6 Ne u t r a l We d g e Ab r i d g e d Sp e c t r o p h o t o m e t e r . . .
Paul A. Clifford and Brooks A. Brice 2 1 8 I I e a t C o n t r o l U n i t s ...John A. R i d d i c k 2 2 2 Re m o v a l o f Ad h e r e d Ru b b e r St o p p e r s... 2 2 4
Ne w De v e l o p m e n t i n Th e r m i o n i c Re l a y s...
Howard M. Waddle and Walter Saeman 2 2 5 Mi c r o c h e m i s t r y :
F r i e d r i c h E m i c i i ...A. A. Benedetti-Picliler 2 2 6 De t e r m i n a t i o n o f Al u m i n u m b y Ph o t o m e t r i c
Fl u o r e s c e n c e Me a s u r e m e n t...
Charles E. White and C. S. Lowe 2 2 9 Co l o r i m e t r i c Mi c r o d e t e r m i n a t i o n o f Ma g n e s i u m
C. P. Sideris 2 3 2 Li m i t s o f Id e n t i f i c a t i o n o f Si m p l e Co n f i r m a t o r y
Te s t s ...
A. A. Benedetti-Pichler and Julian R. Rachele 2 3 3 De t e r m i n a t i o no f So d i u mi n Bi o l o g i c a l Fl u i d s . .
M. C. Darnell, Jr., and B. S. Walker 2 4 2 G a s - V o l u m e t r i c S e m i m i c r o d e t e i i m i n a t i o n o f C a r
b o n ...E. Berl and W. Koerber 2 4 5 Mo d e r n La b o r a t o r i e s :
R e s e a r c h a n d D e v e l o p m e n t O r g a n i z a t i o n o f G e n e r a l F o o d s C o r p o r a t i o n . Thomas M. Rector 2 4 7
T h e A m erican C h em ical Society assum es no re sp o n sib ility for th e s ta te m e n ts an d opinions a d v an ced b y c o n trib u to rs to its p u b lic a tio n s.
22,900 copies of th is issue p rin te d . C o p y rig h t 1940 b y A m erican C hem ical Society.
P u b l i c a t i o n O ffic e : E a s t o n , P c n n a . E d i t o r i a l O ffic e : R o o m 7 0 6 , M ills B u i l d i n g , W a s h in g t o n , D . C .
T e l e p h o n e : N a t i o n a l 0 8 48. C a b l e : J i e c h e m ( W a s h in g to n )
P u b lish e d b y th e A m erican C hem ical Society, P u b lic a tio n Office, 2 0 th &
N o rth a m p to n S ts., E a s to n , P e n n a . E n te re d as second-class m a tte r a t th e P o s t Office a t E a s to n , P e n n a ., u n d e r th e A ct of M arch 3, 1879, as 24 tim e s a y e a r . In d u s tria l E d itio n m o n th ly on th e 1st; A n a ly tic al E d itio n m o n th ly on th e 15th. A c ce p ta n c e fo r m ailin g a t special r a te of p o stag e p ro v id ed for in S ectio n 1103, A c t of O cto b er 3, 1917, a u th o riz e d J u ly 13, 1918.
A n n u a l su b sc rip tio n ra te , In d u s t r i a l Ed i t i o n an d An a l y t i c a l Ed i t i o n
so ld o n ly as a u n it, $4.00. F o reig n p o stag e to c o u n tries n o t in th e P a n
A d v e r t is i n g D e p a r t m e n t : 332 W e st 4 2 n d S t r e e t , N e w Y o r k , N . Y . T e l e p h o n e : B r y a n t 9-4430
A m erican U n io n , $2.25; C a n a d ia n p o stag e, $0.75. Single copies: In d u s tria l E d itio n , $0.75; A n a ly tic al E d itio n , SO.50. Special ra te s t o m em bers.
N o claim s can b e allow ed fo r copies of jo u rn a ls lo s t in th e m ails unless su ch claim s a re receiv ed w ith in 60 d a y s of th e d a te of issue, a n d n o claim s will b e allow ed for issues lo st as a re s u lt of insu fficien t n o tice of c h an g e of a d d ress. (T en d a y s ’ a d v an c e n o tice re q u ire d .) “ M issin g fro m files"
c a n n o t b e acc e p te d as th e reaso n fo r h o n o rin g a claim . C h arle s L . P a rso n s, B usiness M an a g e r, M ills B u ild in g , W ash in g to n , D . C ., U . S. A.
4 INDUSTRIAL AND ENGINEERING CHEMISTRY VOL. 12, NO. 4
i m h i h n t ;
B>A WILL IBP YOU SI1VE PHUIEMS SIKH AS IS
*7he Pn&ldetn,
p a r t o n e : c h e m ic a l “ X ” is a n in o r g a n ic r e a g e n t, at p r e s e n t a v a ila b le o n ly at c o m p a r a tiv e ly h ig h c o st b e c a u se o f its lim ite d u se.P A R T T W O : A ssu m e th e u se o f “ X ” in th e la b o r a to r y d e m o n stra tes it to b e a “ k e y ” c h e m ic a l f o r a c o n te m p la te d p r o c e ss.
F u r th e r e x p e r im e n ta tio n in th e p ilo t p la n t is n e c e ssa r y . I f s u c c e s s fu l th e r e , fu ll-sc a le p la n t o p e r a tio n w ill b e c a lled fo r .
T H E Q U E S T IO N O F C O S T A N D A V A IL A B IL IT Y O F C H E M IC A L “ X ” IN S U F F I C I E N T Q U A N T IT IE S I S A F A C T O R T O B E C O N S ID E R E D E A R L Y I N Y O U R E X P E R I M E N T S .
Soiutixut:
T h e m a tte r o f p r o d u c in g “ s p e c ia l in o r g a n ic s ” in q u a n titie s su ffic ie n t fo r p ilo t o r a c tu a l p la n t o p e r a tio n is a fie ld in w h ic h th e B & A o r g a n iz a tio n h a s p r o v e d u n u s u a lly a d e p t— in h e lp in g o th e r s to so lv e th e ir p r o b le m s w ith th e a id o f th e B & A p la n t a n d its tr a in e d p e r so n n e l.
Y our re s e a rc h a n d d e v e lo p m e n t p ro g ra m s m a y t u r n u p p ro b le m s such as th is. W h e n th e y do, le t ’s ta lk th e m ov er— in s tric te s t con fid en ce, of course. Y O U p re s e n t th e p ro b le m . W E w ill b rin g to b e a r u p o n i t th e 58 y e a rs of B &A’s c u m u la tiv e e x p e rie n c e in p ro d u c in g fine a n d re a g e n t g ra d e ch em icals to h e lp y o u find th e answ er. We c o rd ia lly so lic it y o u r in q u irie 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 O
B a k e r ^ A d a m s o n
D iv isio n of G E N E R A L C H E M I C A L C O M P A N Y , 4 0 Re ct o r St., N e w York C . H
Atlanta • Baltimore • Boston • Buffalo • Charlotte IN . C .I * Chicago • Cleveland * Denver ‘ Houston • Kansas City • Los Angeles Milwaukee • Minneapolis • Montezuma (G a.I • Philadelphia • Pittsburgh • Providence tR . I.) • San Francisco • S t . Louis • Utica (N .Y .l Wenatchee (W ash.I • Yakim a (W ash.) • In Canada: The Nichols Chemical Company, Lim ited • Montreal • Toronto • Vancouver
APRIL 15, 1940 ANALYTICAL EDITION 5
IT’S THE
LONG-RUN COST
THAT COUNTS!
W h e n yo u b u y a H o sk in s com bustion fu r n a c e , y o u ’ll find It la sts so lo n g t h a t its m a in te n a n c e co st p e r y e a r a p p ro a c h e s a fig u re t h a t ’s t r iv ia l. N o t o n ly is y o u r s e n s e o f th rift s a tis fie d — y o u r p e rfo rm a n c e r e q u ire m e n ts a r e a lso fu lly m e t. . . . H o sk in s M an u factu rin g C o ., D e tro it, M ich ig an .
E L E C T R IC H EA T T R E A T IN G F U R N A C E S • • H E A T I N G E L E M E N T A L L O Y S • • T H E R M O C O U P L E A N D LEAD W IRE » • PYROM ETERS • • W ELD IN G W IR E • • HEAT RESISTANT C A ST IN G S • • EN AM ELIN G FIXTURES • • SPA RK PLUG ELECTRODE W IRE ♦ • SP EC IA L A L LO Y S O F N ICKEL • • P RO TECTIO N TUBES
H O S K I N S P R O D U C T S
[Right) O p e ra te s d ire c tly on the lin o w ith o u t t ra n s fo rm e r . T e m p e ra tu re is c o n tro lle d b y rh e o sta t.
Th e fo rm e r 5 " O .D . o f the c a s e is n o w 7 " , w ith c o rre sp o n d in g in c re a s e in h e a t- in s u la t io n .
A t 2 0 0 0 ° F .,fo r m e r c a s e te m p e ra tu re o f 3 9 3 ° is n o w 1 3 5 ° c o o le r. H o ld in g w a tt a g e h a s b ee n re d u c e d 1 4 % .
H e a tin g u n it , a s in g le C h ro m e l c o il, th a t v e r y e a s ily Is w ra p p e d a ro u n d the g ro o v e d tu b e .
A g iv e n fu r n a c e b u ilt fo r on e g iv e n v o lta g e p e rm its a h e a v ie r C h ro m e l u n it th a t la s t s lo n g e r.
R e co m m e n d e d m a x im u m o p e ra t- in g te m p e ra tu re is 1 8 0 0 ° F . fo r F D ; a n d 2 0 0 0 ° F . fo r FH (b e lo w ).
H o sk in s c o m b u stio n fu r n a c e s a re c h e a p e r in the lo n g r u n . S e nd fo r d e s c rip tiv e fo ld e r .
(L e ft) To a p p ly a C hrom el unit in the FD furnace is as e a s y as w rappin g a rope around a stick.
(Right) T yp e F H - 3 0 3 - A ; o p e ra te s on A .C . only through a transform er. H e a v y
> C hrom el unit, g o o d fo r 2 0 0 0 ° F .
6 INDUSTRIAL AND ENGINEERING CHEMISTRY VOL. 12, NO. 4
PRECISION SCIENTIFIC COMPANY
Designers and Builders of Modem Laboratory Equipment
1730-54 NORTH SPBINGFIELD AVE.. CHICAGO. ILLINOIS. U. S. A.
FLOOR MODEL
PRECISION-FREAS
CONSTANT TEMPERATURE CABINETS
-ADJUSTABLE EXf
M E C H A N IC A L C O N V E C T IO N
DIFFUSER WALLS
A motor-driven centrifugal turbo-blower creates a forced circulation o f heated air, con
trolled for uniform heat d is
tribution throughout the work
ing chamber. H eat transfer is accelerated fo r high thermal efficien cy. Loading capacity is greater, and drying speed considerably faster than with gravity convection models.
6 LA5 3 WOOL INSULATION
TURBO-BLOWER
BALL BEARING MOTOR
IDEAL FOR THE CROWDED LAB WHERE SPACE is a t a PREMIUM
ADJUSTABLE AIR INTAKE
MECHANICAL CONVECTION MODELS
M o d e l N o . C A B IN E T S I Z E
W id th Depth H e ig h t
Temperature Range
F lo o r space, 2 3 " x 2 2 O v e ra ll height 5 2 "
Sin gle Door
W x i r x i r
F lo o r Space 3 0 " x 2 7 O v e ra ll H e ig h t 5 8 '
Sin g le D oor
& e * u ê N & iu ß u lle iittA { J io ii ß u J d c iA & i
305 310
37"x 19'x 25"
F lo o r space 4 9 " x 2 7 O v e ra ll height 6 4 "
D o u b le D oor A n 8-page illustrated treatise on heat transfer discussing important
factors t o consider when selecting constant temperature laboratory equipment.
A 16-page presentation o f features and advantages o ffered by gravity and mechanical convection cabinets, with listings and specifications.
n ü i i i
APRIL 15, 1940 ANALYTICAL EDITION 7
A sk you r la b oratory su p p ly d e a le r or se n d for la b o ra to ry fu rn ace b u lletins.
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
LABORATORY FURNACES MULTIPLE UNIT ELECTRIC EXCLUSIVELY
R E C . U . S . P A T . O F F .
M I L W A U K E E , W I S C O N S I N Like m any of the outstanding
university laboratories in the country, L e h ig h University u ses Multiple Unit laboratory furnaces to carry on metallur
gical study and research.
8 INDUSTRIAL AND ENGINEERING CHEMISTRY VOL. 12, NO. 4
C E N C O -C O O L E Y I N D E X E R F U R N A C E
E v e r y
C A F C r r r u u o c i c b n i l e b t ! l e
H E A R T H R O TATES
13645
N o m o re singed h a n d s a n d sc ra m b le d crucibles to rem o v e crucibles fro m th is fu rn a c e . A n y cru cib le in th e h e a tin g c h a m b e r ca n b e b ro u g h t to th e d o o r b y tu rn in g th e n u m b e re d in d ex in g w heel. T h e m uffle is cy lin d rical a n d th e circ u la r h e a r th r o ta te s w ith th e tu rn in g o f th e in d ex er w heel. T h is design n o t o n ly elim in ates aw k w ard n ess in h a n d lin g w o rk to a n d fro m th e h e a tin g c h am b er, b u t gives m o re u n ifo rm te m p e ra tu re d is
tr ib u tio n a n d 2 0 % g re a te r cru cib le c a p a c ity t h a n t h a t o f u su a l m uffle fu rn aces o f co rresp o n d in g dim ensions.
T h e p y ro m e te r th e rm o c o u p le e n te rs th e c h a m b e r ab o v e th e c e n te r o f th e h e a rth , a n d , w hen ex a c t d e te rm in a tio n s o f te c h n ic a l c h a ra c te ristic s o f m a te ria ls u n d e r te m p e ra tu re a re to b e m ad e, th e th e rm o co u p le can be low ered u n til in in tim a te c o n ta c t w ith th e w o rk to
re g iste r its e x a c t te m p e ra tu re a t all tim es. T h e p y ro m e te r h a s a d o u b le scale c a lib ra te d to 1100°
C e n tig ra d e a n d 2000° F a h re n h e it.
F o r 115 v o lts, A .C . o r D .C ., w ith a po w er con
su m p tio n o f a p p ro x im a te ly 1300 w a tts . D im e n sions, o v e r a ll: H e ig h t, 15 in ch es; w id th , 183/ 4 in ch es; d e p th , 1 6 y 2 inches. M uffle sp ace:
H e ig h t, 3 in ch es; d ia m e te r, 7 inches. W id th of d o o r, 4V2 inches.
13645
C E N C O -C O O L E Y I N D E X E R F U R N A C E w it h R h e o s t a t a n d P y r o m e te r
$127.50
I n t e r i o r V ie w o f N o . 13645 F u r n a c e
S C I E N T I F I C INSTRUMENTS
New York • Boston •
(M D
C H I C A G O
LABO RATO RY A P P A R A T U S
Toronto • Los Angeles
APRIL 15,1940 ANALYTICAL EDITION 9
SODIUM OXALATE Primary Standard
NsjCjO«
A N A L Y T IC A L r e a g e n t
f O I S O N v
OCHROM c h e m ic a l r
“OWUtAL Bmw'** ^
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. Louis • Chicago • Philadelphia • New York
PRECISION
i n t h e L A B O R A T O R Y
A ccurately m easuring laboratory app aratu s is of little value in analytical procedure unless th e chemicals employed are free from im purities giving rise to erroneous results. M allinckrodt A nalytical Reagents—each scrupulously refined to m eet predeterm ined sta n d ards of p u rity —are especially designed to facilitate analytical p re
cision. Chemists can depend upon M allinckrodt A. R. Chemicals because th ey conform to A. C. S. specifications.
S en d for new catalogue o f a n a ly tic a l re a g e n ts a n d o th e r c h e m icals fo r la b o r a to r y u se. I t c o n ta in s d e sc rip tio n s o f c h e m i
cals s u ita b le fo r e v e ry ty p e o f a n a ly tic a l w o rk . . . g ra v i
m e tric , g a so m e tric , co lo rim e tric o r titr im e tr ic .
10 INDUSTRIAL AND ENGINEERING CHEMISTRY VOL. 12, NO. 4
A .H .T . C O . S P E C I F I C A T I O N
ELECTROANALYSIS APPARATUS
F O R T H E Q U A N T I T A T I V E A N A L Y S I S O F M E T A L S , A L L O Y S O R M A T T E S
4785-L
ELECTRO A N A LY SIS A P P A R A T U S, S in gle U nit, A .H .T . Co. Specification, fo r th e q u a n tita tiv e a n a ly sis of m e ta ls , allo y s o r m a tte s . A n asse m b ly w h ich p ro v id e s m a x im u m flex ib ility a n d g re a te s t p o ssib le p ro te c tio n fro m acid fu m es fo r th e e le c tric al c o n tro l p a rts .
C o n sistin g of a p o w er u n it fo r s u p p ly in g c o n tro lle d low v o lta g e d ire c t c u rre n t, fro m a 110-volt, 60-cycle, sin g le p h a se , a lte r n a tin g c u rre n t c irc u it, c o n n e c te d w ith a s e p a ra te e le c tro d e s u p p o r t w ith b a se a n d sw in g -o u t b e a k e r shelf of C oors p o rc e la in , a n d v a ria b le sp eed e lectric s tir r e r fo r r o ta tin g a glass s tirrin g ro d or one of th e electro d es.
The power unit is enclosed in a ventilated sheet metal micro tests when used with cells of the Clark-Hermance type, case with overall dimensions 12 inches high X 7 inches wide The electrode support consists of an acid-proof Coors X 6 inches deep, mounted on rubber feet and with slotted porcelain base 81/» X 61/« inches with 20 X 'A-inch rod of openings in the back for hanging on the wall. It contains aluminum alloy with “Alumilite” finish; beaker shelf of a dry disk rectifier and a variable transformer for delivering Coors porcelain on swinging arm; non-corrosive electrode stepless direct current up to 5 amperes, and an outlet for clamp with adjustable aluminum binding posts and clamp connection to stirring motor. On the front face are mounted holder; and electric stirrer consisting of brushless, shaded the transformer dial, a voltmeter, range 0 to 10 volts in pole motor totally enclosed in acid-resisting housing with 0.1 divisions, an ammeter, range 0 to 5 amperes in 0.1 divi- aluminum supporting rod and with rheostat, and two alumi- sions, a replaceable safety fuse and switches for the stirrer, num chucks, one attached to the motor for holding the spe- the electrolytic current and for changing the polarity of the cial glass stirring rod which rotates inside a platinum elec- electrodes, and binding posts for connecting the electrode trode, and a smaller chuck for insertion in the motor chuck leads. The power unit is suitable for macro determinations to take electrode stems up to B&S gauge-16 wire when ro- and because of its wide range of control, is also suitable for tating electrode is used.
4785-L. Electroanalysis Apparatus, as above described, complete as shown in illustration, with power unit and electrode support for stationary or rotating electrodes, insulated lead wires with terminals, Pyrex beaker 180 ml, two extra fuses, cord and plug, and directions for operation but without platinum electrodes. For 110 volts, 60 cycles, single phase, a. c... 97.25 Code W ord... Exulk
4785-N . E lectro ly tic P o w e r U n it, on ly , as su p p lie d w ith a b o v e. C o m p le te w ith tw o e x tra fuses, co rd a n d plu g , b u t w ith o u t c o n n ec tin g cords for electro d es. F o r 110 v o lts, 60 cycles, single p h a se a. c... 70.00 C ode W o r d ... E x u m i 4 7 8 5 -P . E lectro ly tic S u p p o rt, on ly , as s u p p lie d w ith a b o v e. C o m p le te w ith C oors p o rcelain base a n d s w in g o u t b e a k e r shelf, non-co rro siv e
e lectro d e c lam p , c la m p h o ld e r a n d stirrin g m o to r w ith tw o chucks, glass s tirrin g ro d a n d rh e o s ta t, b u t w ith o u t p la tin u m electrodes, b e a k e r or c o n n ec tin g le a d s ... 26.75 C ode W o rd ... E x u n f N O T E — N o. 8307 a n d 8308 P la tin u m E lec tro d e s, as lis te d on page 660 of o u r catalo g u e , a re s u ita b le fo r u se w ith a b o v e. W e also offer a
special a n o d e, w eig h t 8.5 g ram s, a n d tw o sp ecial e lectro d es, 6.5 a n d 8 g ram s resp ectiv ely , fo r th e sam e p u rp o se.
More detailed information sent upon request.
A R TH U R H. T H O M A S C O M P A N Y
R E T A 1L— W H O L E S A LE— E X PO R T
LA B O R A TO R Y A P PA R A TU S A N D REAG ENTS
W E S T W A S H IN G T O N S Q U A R E , P H I L A D E L P H I A , U.S.A.
C ab le A ddress, “ B a la n c e ,” 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
Separation and Determ ination o f Isom eric Menthols
R . T . H A L L 1, J . I I . H O L C O M B , J R ., AND D . B . G R I F F I N , S w a n n & C o m p a n y , B i r m i n g h a m , A la .
D
U R IN G the past several years the authors have analyzed numerous samples of menthol, mixtures of menthols, and mixtures of menthol with other terpene alcohols. In some cases the usual methods for the determination of menthol have been found satisfactory, b u t in many instances they do not give correct results, particularly when dealing with mixtures of isomeric menthols. The purpose of this work is to study the application of various methods of analysis to the separation and determination of menthol and to indicate cer
tain necessary modifications.
The structural formula for menthol as established by Semmler, Beckman, and others (8) is shown in Figure 1. I t is apparent th a t menthol is capable of existing in eight opti
cally active forms. Six of the eight have been isolated and identified, as shown in Table I.
T a b l e I. M e n t h o l S t e r e o i s o m e r s
M eltin g Specific B oiling P o in t
S tereo iso m er (7) P o in t R o ta tio n (760 M m .)
0 C. „ 3 5 a D ° C.
¿-M enthol 43 - 4 9 . 5 216
d -M e n th o l 43 + 50 .1 216
¿ -N eom enthol L iquid - 1 9 . G 212
d -N e o m e n th o l - 1 7 + 19 .6 212
¿-Iso m en th o l 8 0 .5 - 2 4 . 1 218
d -Iso m e n th o l 8 5 .0 + 2 6 .3 218
r
U
r
Stereoisomers containing two or more asymmetric carbon atoms may differ in their physical properties. Further, al
though they undergo similar reactions, the difference in rates of reaction may be marked, as shown by this study.
U ntil a few years ago the industry ob
tained all its “menthol U. S. P .” from Japan, where it occurs naturally in oil of peppermint, Mentha arvensis. /-Menthol in the pure state is the U. S. P. material.
In recent years, however, m any synthetic menthols have appeared on the market.
They have consisted of varied mixtures of the other stereoiso
mers along w ith some of the U. S. P. product. The number and proportion of isomers in any mixture of menthols is de
pendent on the method of synthesis. When d-citronella (4) obtained from citronella oil is used as the starting material, a m ixture of three isomers—d-neomenthol, d-isomenthol, and
1 P re s e n t a d d ress, H ercu les P o w d er C o m p a n y , W ilm in g to n , D el.
Fi g u r e 1
/-menthol—is obtained. The large proportion of /-menthol present in this particular mixture makes possible its separa
tion on a commercial scale. The chief interest of the authors has been in the analytical reactions of these three stereo
isomers. The physical constants of the various menthols studied were determined as shown in Table II.
T a b l e I I . P h y s i c a l C o n s t a n t s o p M e n t h o l s M eltin g Specific R e fra c tiv e B oiling
P o in t P o in t R o ta tio n In d e x (760 M m .)
° C. D3 „ 2 ° n D ° C.
/-M e n th o l OJ. S.
d -N eo m en tlio l P .) 43 - 5 0 . 0 1.4600 216
- 1 7 + 19 .7 1.4 6 0 0 212
d -Iso m en th o l 83 + 2 5 . 5 1.4600 218
M ixture® 15 - 2 .8 5 1.4 6 0 0 214
a T h e m ix tu re co n sisted of a p p ro x im a te ly 3 5 % ¿-m enthol, 4 0 % d-neo- îe n th o l, a n d 2 5 % d -isom enthol.
The (¿-neomenthol was obtained by separating it from an isomeric mixture which had been enriched in this lower-boiling material by careful fractional distillation in a 240-cm. (8-foot) laboratory fractionating unit. The final purification was ef
fected by preparation of the d-neomenthol acetate (9) ester and subsequent hydrolysis of the recrystallized product.
The d-isomenthol was prepared by separating it from a mix
ture which had been enriched in this higher-boiling material by careful fractionating as in the previous case. Final purifi
cation was achieved through repeated alcohol recrystalliza
tions. Although it is evident th a t the d-isomenthol was slightly impure, the /-menthol and d-neomenthol were pure, as shown by comparison w ith Table I.
D is c u s s io n o f M e th o d s
M ost methods for the determination of total menthol {1, 5) involve acetylation followed by hydrolysis of the acety- lated product w ith an excess of standard alcoholic potassium hydroxide. However, saponification by the use of potassium hydroxide in diethylene glycol (6) is an improvement for the reaction and can be carried out in one fourth to one fifth of the time. Preliminary studies indicated th a t the rates of both the acetylation and hydrolysis varied for different isomers of menthol. However, an acetylation time of 2 hours was found to be sufficient for complete reaction in all instances— in fact, 1 hour sufficed for all except the (/-neomenthol. The low results obtained for some of the isomers were found w ithout exception to be due to a too short hydrolysis time. Therefore, 187
188 INDUSTRIAL AND ENGINEERING CHEMISTRY VOL. 12. NO. 4 in the authors’ study the aeetylations were done in a 2-hour
period, and only the time of hydrolysis was varied.
A p p a r a t u s a n d R e a g e n t s . The pieces of equipment neces
sary are 125-ml. conical Pyrex flasks, burets, pipets, and reflux condensers. The reagents are alcoholic potassium hydroxide (approximately 0.5 N) and 0.5 N aqueous hydrochloric acid.
Tne acid is standardized against the potassium hydroxide which in turn is standardized against benzoic acid (Primary Standard 39c, National Bureau of Standards). In applying the methods of Redemann and Lucas (6) conical Pyrex flasks fitted with 90- cm. (3-foot) air condensers instead of glass stoppers were used, since it was found that 15 minutes or more of gentle refluxing were required for complete hydrolysis of some of the samples.
P r o c e d u r e s . For the acetylation, 20 grams of the menthol were introduced into an acetylation flask along with 25 ml. of acetic anhydride (c. p. grade), and 5 grams of c. p . anhydrous sodium acetate. The mixture was refluxed gently for 2 hours.
One hundred milliliters of distilled water were added, the mixture was heated on a steam bath for 30 minutes to destroy excess ace
tic anhydride, and the aqueous layer was drawn off. The oil layer was washed twice with 10 per cent sodium bicarbonate solution and three times with distilled water until the last wash
ings were neutral. In the past high results have been reported (S) because of failure completely to remove the excess acetic an
hydride. The use of the bicarbonate washes very effectively eliminates this source of error. Finally the material was dried over anhydrous sodium sulfate and filtered.
For the hydrolyses, 1.0 gram of the ester was weighed and trans
ferred to conical Pyrex flasks equipped with water-cooled con
densers. Twenty-five milliliters of 0.5 N alcoholic potassium hydroxide were added and the solutions were brought to refluxing temperature. Determinations were made in triplicate and a blank was run with each set.
T a b l e III. S a p o n i f i c a t i o n w i t h A l c o h o l i c P o t a s s i u m Hy d r o x i d e
Sam ple
E s te r H y d ro ly sis
T im e //o u r*
T o ta l M en th o l
%
A verage M e n th o l
%
C o rre
sp o n d in g E s te r V alue
M ea n E a te r V alue
¿-M enthol 0 .5 9 9 .7
9 9 .7
9 9 .7 9 9 .7
2 8 2 .4 2 8 2 .5 2 8 2 .4 2 8 2 .4
Z-M enthol 1 .0 1 0 0 .5
10 0 .0
10 0 .0 1 0 0 .2 2 8 4 .2
28 3 .1
2 8 3 .2 2 8 3 .5
d -Iso m e n th o l 0 .5
9 8 .4 9 S .7
9 8 .4 9 8 .5
2 7 9 .5 2 7 9 .5 2 8 0 .2 2 7 9 .8
d -Iso m e n th o l 1 .0
9 9 .8 9 9 .9
1 0 0 .4 1 0 0 .0 2 8 2 .5 2 8 2 .7 2 8 4 .0 2 8 3 .0
d -N e o m e n th o l 1 .0 0 8 .9
0 9 .2
0 8 .4 0 8 .8
2 0 9 .0 2 0 9 .7 2 0 7 .8
2 0 8 .8
d -N eo m en th o l 2 .0
8 8 .9 8 8 .0 8 8 .5
8 8 .7 2 5 7 .7 2 5 7 .1
2 5 0 .8 2 5 7 .2
d -N eo m en th o l 3 .5 ° 9 9 .9
1 0 0 .2 1 0 0 .4
1 0 0 .2 2 8 2 .9 2 8 3 .0 2 8 4 .0 2 8 3 .5
M ix tu re 2 .0 9 3 .0
9 2 .9
9 3 .4 9 3 .1 2 0 7 .3
2 0 7 .1
2 0 7 .8 2 0 7 .4
M ix tu re 3 .5 «
1 0 0 .2 100.4
1 0 0 .2 100 .3
2 8 3 .0 2 8 4 .0 2 8 3 .0
2 8 3 .7
* N o t oom plete a t e n d of 3 hou rs.
The results are shown in Table III. Values are given in terms of total menthol calculated according to the usual formula for ester-free materials (3) and also in terms of the corresponding ester value. The results obtained when the diethylene glycol reagent (6) was used are shown in Table IV.
Inspection of Table I I I indicates th a t the hydrolysis of the esters of Z-menthol and d-isomenthol is practically complete within 30 minutes and is definitely finished a t the end of 1 hour, b u t the d-neoester requires 3.5 hours for complete hydrolysis. A t the end of 1 hour only 68 per cent “total menthol” is obtained for m aterial th a t is really pure d-neo- menthol, as is shown by the result obtained on the same ma
terial when hydrolysis time was 3.5 hours. Low results were
obtained also on the mixture a t the end of 1- and 2-hour periods. Although the error is less here than in the case of d- neomenthol, the time required for complete saponification is essentially the same.
T a b l e IV. S a p o n i f i c a t i o n w i t h P o t a s s i u m H y d r o x i d e i n D i e t h y l e n e G l y c o l
Sam ple
E s te r H y d ro ly sis
T im e M in .
T o ta l M e n th o l
%
A verage M e n th o l
%
C orre
sp o n d in g E s te r V alue
M ea n E s te r V alue
¡-M en th o l 5
9 8 .5 9 9 .0
9 9 .5 9 9 .0 2 7 9 .5
2 8 0 .9 2 8 2 .1 2 8 0 .6
i-M e n th o l 15 9 9 .8
100.1
100.1 9 9 .9 2 8 2 .5
2 8 3 .3
2 8 3 .3 2 8 3 .0
d -iso m e n th o l 5
9 9 .5 9 9 .1
9 9 .2 9 9 .2 2 8 2 .2
2 8 1 .0 2 8 1 .3 2 8 1 .5 d -Iso m e n th o l 15
1 0 0 .2 9 9 .5
1 0 0 .2 9 9 .9 2 8 3 .6 2 8 1 .8 2 8 3 .6 2 8 3 .0
d -N e o m e n th o l 15
9 9 .5 9 9 .3
9 9 .4 9 9 .4 28 2 .1
2 8 1 .6 2 8 1 .9 2 8 1 .9
d -N eo m en th o l 30 9 9 .7
9 9 .7
1 0 0 .3 9 9 .8 2 8 2 .5
2 8 2 .5 2 8 3 .7 2 8 2 .9 Isom eric
m ix tu re 15 9 8 .4
9 8 .5
9 8 .5 9 8 .5 2 7 9 .7
2 7 9 .8 2 7 9 .8 2 7 9 .8
Isom erio
m ix tu re 30
10 0 .4 100.3
10 0 .0 1 0 0 .2 2 8 4 .0 2 8 3 .7 2 8 3 .1 2 8 3 .6
By the use of the diethylene glycol solution of potassium hydroxide, all the hydrolysis times are greatly reduced, and the precision of the results is equally as good. Again, the d-neomenthol and the isomeric mixture require the longer time. However, all the results indicate the definite advantage of using the diethylene glycol as a hydrolyzing medium instead of the usual alcoholic solution.
S u m m a r y
A comparison has been made of the value of alcoholic po
tassium hydroxide and of potassium hydroxide in diethylene glycol for the saponification of isomeric m enthyl acetates.
In the case of the acetate of d-neomenthol and of mixtures containing it, it has been found necessary greatly to increase the time usually specified for hydrolysis, since the d-neoester hydrolyzes so much more slowly than other menthol esters.
A method for separating d-neo- and d-isomenthol from an isomeric mixture of menthols has also been described. The method of Redemann and Lucas (6) for rapid hydrolysis of esters has been satisfactorily applied to the m enthol esters.
A c k n o w le d g m e n t
The authors wish to thank Swann & Company for their kind permission in allowing this article to be published.
L ite r a tu r e C ite d
(1) Assoc. Official Agr. C hem ., “ Official an d T en tativ o M ethods of A nalysis” , 4 th ed., p. 571 (1935).
(2) E lliot, F . L., J . Assoc. Official Agr. Chem., 13, 333 (1930).
(3) G ildem eister an d H offm an, “ T h e V olatile Oils” , 2nd ed.t New Y ork, Jo h n W iley & Sons, 1933.
(4) Glass, H . B., an d Bliss, A. R ., D rug Cosmetic Industry, 44, 289- 91 (M arch, 1939).
(5) Griffin, R . C., “ T echnical M ethods of A nalysis” , N ew Y ork, M cG raw -H ill B ook Co., 1927.
(6) R edem ann, C . E . , and L ucas, H . J., I n d . E n q . C h e m ., A nal. E d ., 9, 521 (1937).
(7) Schimm el & Co., “ A nnual R e p o rt on E ssential Oils an d S y n th etic P erfum es” , 1933.
(8) Simonsen, “ T he T erp en es” , C am bridge U niversity Press, 1931.
(9) Zeitschel, O., and Schm idt, H ., Ber., 59, 2301 (1920).
Colorimetric D eterm ination of Prim ary Mononitroparaffins
EUGENE W. SCOTT A N D JO SEPH F. TREON
K etterin g L aboratory, University of C in cin n ati, C in cin n ati, Ohio
R e a g e n ts
« 200- Sodium hydroxide, 20 per cent, hydrochloric acid (concen-
trated diluted 1 to 7), 10 per cent ferric chloride, and a standard •= . solution of nitroethane containing 1 mg. per ml. g 180'
o
P r o c e d u r e g l60.
An aliquot of the sample containing 1 to 20 mg. of nitroethane .2 in 1 to 15 ml. is neutralized and treated with 1.5 ml. of sodium ¿j hydroxide in a 25-ml. volumetric flask. After standing for 15 1 minutes the solution is acidified with 6.0 ml. of hydrochloric acid, il and 0.5 ml. of ferric chloride is added immediately. A standard 3 solution containing approximately the same amount of nitro- -5 '20- ethane is treated similarly. After standing for 15 minutes the 2 solutions are diluted to the mark and compared in a colorimeter
equipped with a 1.58-cm. (0.625-inch) Wratten filter No. 65A in 100- B glass (Eastman Kodak Co.).
T
H E recent work of Hass and his associates ([4) on the nitration of paraffins in the vapor phase has made the mononitroparaffins and their derivatives commercially available. In the course of studies on the toxicity of certain of these compounds carried out a t this laboratory, a method for the determ ination of primary mononitroparaffins in air was developed, and was later modified for analysis of biological materials.
The determination of these compounds in mixtures with air was first attem pted by reduction of the nitro compound and determ ination of the amine formed. Air samples con
taining nitroethane were absorbed in dilute sodium hy
droxide and this solution was added to reduction mixtures of sulfuric acid w ith iron, tin, and zinc. Q uantitative yields of ethylamine were not obtained under these conditions, al
though aqueous solutions of nitroethane were reduced, with yields of from 95 to 97 per cent. I t was observed th a t when one of the alkaline samples was added to an excess of hydro
chloric acid containing ferric chloride, a pink color was formed. This color reaction was made the basis of a satis
factory method of determining nitroethane and further ex
periments with reduction methods were abandoned.
The method adopted consisted of adding an excess of hydro
chloric acid to an alkaline solution of nitroethane, this being followed immediately by the addition of ferric chloride.
W hen the final pH was between 1.25 and 1.30, a reddish brown color was formed which rapidly changed to deep red.
After a study of the factors which influenced the intensity and stability of the color, a procedure was adopted which gave reproducible results w ith amounts as low as 0.5 mg. in 25 ml.
S t u d y o f t h e R e a c tio n
The final pH of this solution was found to be 1.25 to 1.30, which was the optimum for the greatest intensity and sta
bility. Solutions which contained more acid faded gradu
ally, while those which had a higher pH failed to give the change from the original brownish red to a deep red. The am ount of acid necessary to obtain a pH of 1.25 to 1.30 was determined each time fresh solutions of hydrochloric acid and sodium hydroxide were prepared. W ith larger amounts of nitroethane (15 to 20 mg.) it was necessary to use the indi
cated am ount of ferric chloride, b u t w ith very small quantities of nitroethane it was desirable to reduce the ferric chloride
20+-
l - . l - I- I. | 1 1 1 1
4 0 0 5 0 0
Wavelengths ( mp)
concentration in order to lessen its color interference. The color was always developed a t room tem perature. When the colored solution was heated it lost color rapidly. N itro
ethane solutions which had not been made alkaline did not react with ferric chloride, and alkaline solutions after the addition of acid lost their ability to react if they were allowed to stand for a short time.
The evidence points convincingly to the theory th a t only the aci form of the nitro compound reacts w ith ferric chloride.
By analogy to similar structures such as those of phenols, enols, and aliphatic acids which also give colors w ith ferric chloride, it might also be assumed th a t the ferric chloride
320-
3 0 0 -
2 8 0
260-
240-
220-
60-
4 0 '
Fi g u r e 1
189
190 INDUSTRIAL AND ENGINEERING CHEMISTRY VOL. 12, NO. 4
Concentration (Mg. per 2 5 ml.) Fi g u r e 2
combines w ith the hydroxyl group formed by the shift of a proton from the adjacent carbon atom to an oxygen atom a t
tached to the nitrogen.
Stable colored complexes with ferric chloride were also formed by 1-nitropropane and 1-nitrobutane and these colors were used to determine these substances in the same manner.
Ferric chloride reacted w ith 2-nitropropane and 2-nitrobutane to give colors, b u t they faded rapidly. N itrom ethane did not react and was determined by means of the color which it formed w ith vanillin and ammonia (2, 3).
In the case of nitroethane the colored complex was iso
lated in an impure state by mixing relatively large amounts of nitroethane and ferric chloride and evaporating a t room tem perature in a vacuum desiccator. This complex could not be purified for analysis, however, because of its instability.
The colors given by the prim ary nitro compounds and ferric chloride were examined in a photoelectric spectrophotometer and the absorption curves of the complexes in the range of 420 to 690 m/i were obtained by determining the density of the solutions a t 10 m u intervals.
The curves shown in Figure 1 were obtained by plotting wave lengths against the molecular extinction coefficient, E = D /Cl, where D is the observed density, I is the length of the cell in centimeters, and C the molar concentration of the absorbing material. The latter value was assumed to be the same as the concentration of the nitro compound used. This assumption was sufficiently correct for the authors’ purpose—
namely, comparison of the absorption of the three nitro com
pounds on an equivalent basis—b u t the true values of E may vary somewhat from these figures.
The absorption of all three compounds a t their maxima was examined over two ranges of concentration with the use of a 1.25-cm. (0.5-inch) and a 5-cm. (2-inch) cell. When density was plotted against concentration the resultant curves were in straight lines, which indicates th a t in these ranges the absorption followed the law of Lambert-Beer. The re
sults are given in Figures 2 and 3.
A p p lic a t io n o f M e th o d
The method as given above was first used to determine the am ount of nitroethane in air samples taken from a cage into which a constant stream of air and nitroethane was flowing.
The latter was forced by means of a special plunger geared to a synchronous motor into a stream of air which vaporized the nitroethane. The air flow was measured with a rotam eter (1). The air samples were taken from the cage by means of large evacuated bulbs and the nitroethane was removed by shaking the sample w ith alkali placed in a smaller bulb con
nected to the large bulb by a stopcock. In one experiment in which a mixture calculated to contain 0.05 per cent of nitro
ethane was used daily for 23 days, the results obtained on 23 samples taken 2 hours after the sta rt varied from 0.043 to 0.055 per cent with a mean value of 0.0485 =*= 0.0004 per cent.
O 0.5 1.0 1.5 2 0 2.5 3.0 35 4.0
Concentration ( Mg. per 25 ml) Fi g u r e 3
The method with slight modifications has also been applied to the determination of nitroethane in tissues and in m ost instances the recovery of added nitroethane has been b etter than 95 per cent.
S u m m a r y
A simple colorimetric method has been described for the determ ination of the prim ary mononitroparaffins w ith the exception of nitromethane. The absorption curves of the colored complexes of nitroethane, 1-nitropropane, and 1- nitrobutane w ith ferric chloride in acid solution have been determined. A study of the reaction indicates th a t these complexes are formed only by the aci forms of the nitro com
pounds.
L it e r a tu r e C ite d
(1) M achle, W . F ., Scott, E. AV., and T reon, J. F ., J . Ind. Huo- Toxicol., 21, 72 (1939).
(2) M achle, W. F ., Scott, E. W , and T reon, J. F ., in press.
(3) M anzoff, C. D „ /?. Nahr.-Genussm., 27, 469 (1914).
(4) Seigle, L. W ., and H ass, H . B „ I n d . E n g . Cu em., 31, 648 (1939).
Pr e s e n t e d b efore th e D iv isio n of P h y sic a l a n d In o rg an ic C h e m istry a t th e 9 8 th M ee tin g of th e A m erican C h em ical Society, B o sto n , M ass.
Identification o f Paraffins
A nalysis o f P arafiin ic M ixtures by M eans o f R am an Spectra
A R I S T I D V . G R O S S E , E . J . R O S E N B A U M , A N D H . F . J A C O B S O N , U n i v e r s a l O il P r o d u c t s C o ., R i v e r s id e , 111., a n d U n i v e r s i ty o f C h ic a g o , C h ic a g o , 111.
A n a p p lic a t io n o f R a m a n s p e c tr a t o t h e id e n t if ic a t io n a n d a p p r o x im a te ly q u a n t it a t iv e a n a ly s is o f in d iv id u a l p a r a ffin s, u p t o a n d in c lu d in g o c t a n e s , in
p a r a ffin ic m ix tu r e s is d e sc r ib e d .
I
N VIEW of the recent accomplishment of a catalytic formation of paraffins by direct addition of olefins to paraffins using metal halide [boron fluoride (14), aluminum chloride (IS, 16), etc.] or sulfuric acid (1), etc., catalysts, methods for identifying these compounds have become of increasing value. Of practical importance is the alkylation of isobutane with ethylene, propylene, or the butylenes leading, respec
tively, to isomeric hexanes, heptanes, or octanes. Further
more, the accomplishment of catalytic cyclization of para- fins to aromatics (12), as well as a number of other reactions (11,18), requires a knowledge of the composition of the initial paraffinic material. And last, b u t not least, the possibility of identifying paraffins allows also determination of the carbon skeleton of any aliphatic unsaturated hydrocarbon after its catalytic hydrogenation.
The method herein described is based on the determination of the Ram an spectrum of a narrow-boiling cut. [The use of Ram an spectra as an analytical tool has been considered by a number of workers including Crigler and Goulieau (5 ,7).]
This paper is limited to the analysis of mixtures containing paraffins with less than nine carbon atoms; the identification of nonanes and higher paraffins will remain a problem of the future, since less than half of the 35 possible isomeric nonanes are known a t present. The identification of the Ci to C.|
paraffins is so simply solved by methods of gas analysis and low-temperature distillation th a t Raman analysis is unneces
sary. The same really applies to the three pentanes, which represent a borderline case. However, they are included in this investigation, together with the five possible isomeric hexanes, nine heptanes, and eighteen octanes.
M e th o d o f A n a ly s is
The Ram an spectra of the isomeric pentanes, hexanes, heptanes, and octanes are widely different, as illustrated for
the hexanes and heptanes in Figures 1 and 2. The spectra of all possible isomeric pentanes, hexanes, and heptanes have been measured and previously described (17, 18, 20, 21).
The octanes will be reported in the near future.
For qualitative analysis the method consists in matching the Raman spectrum of a chemically treated narrow-boiling still cut, prepared as described below, with the characteristic lines of pure isomers. The lines attributed to stretching and bending of the C—II bonds (around 3000 and 1450 cm .-1, respectively) are unsuited for this purpose, as they are nearly identical in all paraffins. Figure 3 illustrates the actual procedure. Here the unknown sample boiling in the range of 79° to 81° C. a t 760 mm. is compared with the spec
trum of pure 2,4- and 2,2-dimethylpentane (boiling point 80.8° and 79.1°) and 2,2,3-trimethylbutane (boiling point 80.8°). The coincidence of all the intense characteristic lines in the spectrum of the unknown is evidence of the pres
ence of each of these heptanes.
The over-all intensity of the spectra of the individual iso
mers depends on their structure: Branched isomers, such as 2,2,4-trimethylpentane, show more intense spectra for equal lengths of exposure than linear isomers like n-octane. For this reason one can detect substantially smaller quantities of a branched isomer than of a straight-chain compound.
All the work which has been done so far on the relation be
tween the concentration of a substance and the intensity of its Ram an lines indicates clearly a direct proportionality (2, 5, 7), except in those cases where intermolecular forces play an im portant role. This exception does not apply to mixtures of paraffins, which are practically perfect solutions.
The question of quantitative analysis is then reduced to the problem of determining the relative intensities of Ram an lines. The most complete way of doing this involves adding a small am ount of a good scatterer (such as carbon tetra-
Fi g t j r e 1. Ra m a n Sp e c t r a o f He x a n e s
192 INDUSTRIAL AND ENGINEERING CHEMISTRY VOL. 12, NO. 4
chloride) as an internal standard, microphotometering the spectrum, and determining the blackening curve for the par
ticular plate used. However, these rather elaborate measures are rendered largely futile by the existence of a continuous background to the spectrum. This continuum is not un
common and is frequently very difficult to clear up. For
tunately, for m any purposes it is necessary only to have the fraction of each component in a sample known to within 5 to 10 per cent. This degree of accuracy can be reached for m any binary and ternary mixtures by a simple visual estim ate by a trained observer, and all the analyses quoted in this paper were made in this way.
C h e m ic a l a n d P h y s ic a l P r e p a r a tio n o f S a m p le The method is limited to the Ram an analysis of paraf- finic mixtures th a t are practically free from naphthenes or
tC tt
0 W
00 00
cycloparaffins. The determination of the latter in the pres
ence of paraffins and vice versa, which will allow the identifica
tion of the carbon skeleton of any possible type of hydrocar
bons, will be reserved for a subsequent publication.
M ixtures obtained by catalytic alkylation are usually free from naphthenes and this fact simplifies the identification to a great extent. However, if naphthenes are suspected, any doubts m ay be dispelled by a hydrogen-carbon determ ination of a narrow-boiling cut by means of an accurate organic combustion analysis (19). The hydrogen-carbon ratio of all naphthenes is 2.000 and substantially lowers the corresponding ratio of pentanes (2.400), hexanes (2.333), heptanes (2.286), or octanes (2.250). The specific refraction of the sample may also, w ith due caution (8), be used to check for naphthenes.
The aromatics and olefins can be conveniently eliminated by concentrated sulfuric acid treatm ent or by sulfur dioxide
w tc r
*«i s
a to b-
CO o
1 2
8 i
Fi g u r e 3 . Il l u s t r a t i o n o f Me t h o d o f An a l y s i s 1. P u r e 2 ,4 -d im e th y lp e n ta n e 3. P u re 2 ,2 -d im e th y lp e n ta n e 2 . U n k n o w n sam p le 4. P u re 2 ,2 ,3 -d im eth y lb u tan e
