Industrial and Engineering Chemistry : analytical edition, Vol. 6, No. 1

A n a l y t i c a l E d i t i o n V o l . 6 ,

No.

1

J ANUARY

15, 1934

I n d u s t r i a l

AN D E N G I N E E R I N G

C h e m i s t r y

VOL. 26, C O N SECU TIV E NO. 3

Pu b l i s h e d b y t h e Am e r i c a n Ch e m i c a l So c i e t y Ha r r i s o n E . Ho w e, Ed i t o r

Pu b l i c a t i o n Of f i c e: E a s t o n , P a .

Ed i t o r i a l Of f i c e:

R o o m 7 0 6 , M ills B u ild in g , W a s h in g to n , D . C . Te l e p h o n e: N a tio n a l 0848 Ca b l e: J ie c h e m (W a s h in g to n )

Ad v e r t i s i n g De p a r t m e n t: 332 W e s t 4 2 n d S t.,

N ow Y o rk , N . Y . Te l e p h o n e: B r y a n t 9 -4430

C O N T E N T S

20,000 Copies of This Issue Printed Composition of F a tty Acid M ixtures. I I . Robert N . Wenzel 1

E xam ination of the Phenols of a Low -Tem peralure Coal T ar . . . . -S. Caplan, J . Ross, M . G. Sevag, and T . M . Swilz 7 S hort-C ut M ethod of H ydrocarbon Analysis. I I ...

...R . Rosen and A . E . Robertson 12 New V olum etric M ethod for D eterm ination of Sulfate . . .

... V. R. Damerell and H . H. Straler 19 Chemical Exam ination of Trichloroethylene for Anesthesia .

...Herman L. Tschenlke 21 Optical D ensity Color M easurem ent for Petroleum Oils . .

...S. IK. Ferris and J . M . M cllvain 23 Inverted Fractional-D istillation Analysis.

R. A . J . Bosschart 29 Q ualitative M ethod for Selenium in Organic Compounds . .

... M . J . Horn 31 Platinized Silica Gel as a C ataly st in Gas Analysis. I I . . .

... Kenneth A . Kobe and E . Bruce Brookbank 35 Volume of Sugar-Beet M arc and Its Adsorptive Effect . . .

...S . J . Osborn 37 Comparison of E xtraction Form ulas . Carroll IK. Griffin 40 D eterm ination of Small Q uantities of Nitrobenzene in Oils .

. . . . C .E . Anding, Jr., B. Zieber, and W . M . MalUojJ 41 Separation of Gold from T e ll u r iu m ...

. . Victor Lenker, G. B . L. Sm ith, and D. C. Knowles, Jr. 43 I .'etermination of Borate Ion in Ores of Borax . I I .L . Payne 45 D eterm ination of Iron . Gladys Leavell and N . R. E llis 46 D irect D eterm ination of Cliromium and of Vanadium in

S t e e l ...Hobart II. Willard and Philena Young 48

Iodine Value of R ubber and G utta-P ercha H ydrocarbons . ... A . R. Kem p and G. S. Mueller 52 Testing Reclaimed R u b b e r ... H enry F. Palmer 56 New T ype of A ntim ony Electrode for pH M easurem ents . .

. T . R. Ball, Webster B . Schmidt, and K arl S. Bergstresser 60 Colorimetric D eterm ination of F l u o r in e ...

... 0 . M . Sm ith and Harris A . Dutcher 61 D eterm ination of Potash in F e r tiliz e r s ...

... F. B. Carpenter and R. 0 . Powell 62 Use of A "ration in Kjeldabl D is tilla tio n s ...

...W. B . Meldrum, R . Melampy, and IV. D. M yers 63 D eterm ination of Lead as Dilead H ydrogen A rsenate. . . .

...C .L . Dunn and 11. V. Tartar 64 Purification of Substances by E le c tro d ia ly sis...

Albert L. Elder, Russell P. Easton, Harold E . Pletcher, and Floyd C. Peterson 65 New A pparatus for D eterm ination of Size D istribution of

Particles in Fine P o w d e r s ...Robert T. K napp 66 U nitized Gas-Analysis A pparatus . . M aryan P. M aluszak 72 E xtraction of T ricthanolam ine Oleate from Aqueous Solution

... Frank M . B iffen and Foster Dee Snell 78 Glass and Other Electrodes for M easuring pH Values of

Very D ilute Buffers and of Distilled W a t e r ...

. . John 0 . Burton, Harry Matheson, and S . F. Acree 79 An Automatic, Modified Falling-Sphere Viscometer . . . .

...B. A . Jones 80 Cleaning Platinum W ire for Flam e T e s t s ...

Wesley G. I^eighton 84

S u b s c r ip tio n to n o n m e m b e rs , In d u s t r i a la n d En o i n e e r i n o Ch e m i b t r t, $ 7 .50 p e r y e a r. F o re ig n p o s ta g e $ 2.10, e x c e p t to c o u n tr ie s a c c e p tin g m a il a t A m e ric a n d o m e s tic r a te s . T o C a n a d a , 7 0 c e n ts . An a l t t i c a i. Ed i t i o n o n ly , $ 2 .0 0 p e r y e a r, s in g le co p ies 7 5 c e n ts , to m e m b e rs 60 c e n ts . F o r e ig n p o s ta g e , 3 0 c e n ts ; C a n a d a , 10 c e n ts . Ne w s Ed i t i o no n ly , $ 1 .50 p e r y e a r. F o r e ig n p o s ta g e , 6 0 c e n ts ; C a n a d a . 2 0 c e n ts . S u b s c r ip tio n s , c h a n g e s of a d d re s s , a n d c la im s fo r lo s t co p ies s h o u ld b e re fe rre d to C h a r le s L . P a r s o n s , S e c r e ta r y , M ills B u ild in g , W a sh in g to n , D . C . T h e C o u n c il h a s v o te d t h a t n o claim s w ill b e allo w ed fo r c o p ie s of jo u r n a ls lo s t in th e m a ils , u n le ss s u c h c la im s a r e re c e iv e d w ith in 6 0 d a y s of th e d a t e o f is s u e , a n d n o c la im s w ill b e allo w ed fo r is su e s lo s t a s a r e s u lt of in su ffic ie n t n o tic e of c h a n g e of a d d r e s s . (T e n d a y s ' a d v a n c e n o tic e re q u ir e d .) “ M is sin g fro m files” c a n n o t b e a c c e p te d a i th e re a s o n fo r h o n o r in g a c laim . I f c h a n g e o f a d d r e s s im p lie s a c h a n g e of p o s itio n , p le a s e in d ic a te i t s n a tu r e .

T he A m e r i c a n C h e m i c a l S o c i e t y also publishes th e Journal of the American Chemical Society and Chemical Astracts.

4

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i r e T h a t M a d e E l e c t r i c l i e n t P o s s i b l e

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 , P u b l i c a t i o n O f f ic e , 2 0 t h & N o r t h a m p t o n S t s - , E a s t o n , P a .

E n t e r e d a s s e c o n d - c l a s s m a t t e r a t t h e P o s t - O f f i c e a t E a s t o n , P a . , u n d e r t h e a c t o f M a r c h 3 , 1 S 7 9 , a s 4 2 t i m e s a y e a r . I n d u s t r i a l E d i t i o n m o n t h l y o n t h e l « t ; N e w s E d i t i o n o n t h e 1 0 t h a n d 2 0 t h ; A n a l y t i c a l E d i t i o n b i m o n t h l y o n t h e 1 5 t h . A c c e p t a n c e f o r m a i l i n g a t s p e c i a l

r a t e o f p o s t a c e p r o v i d e d f o r i n S e c t i o n 1 1 0 3 . A c t o f O c t o b e r 3 , 1 9 1 7 . a u t h o r i z e d J u l y 1 3 . 1 9 1 8 .

a n a l y t i c a l e D I T I o n

V o l. 6, N o . 1

January 15, 1934 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 5

S IO D ID E

M erck’s

R e a g e n t

M CARBOI

ANHYDROUS

M e rc k ’s

M e t h y l , a1

’a ' \ ' v A . o . s . Sp-<

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IODIDE

Merck Laboratory Chemicals are now packed in amber color glass bottles w ith specially de­

signed, durable, non-metallic screw caps.

These new caps were specially designed to over- come corrosion resulting from unfavorable at­

mospheric conditions and also from vapors which are constantly present in the laboratory.

The large facets on the side o f the cap make it easy to open the bottle.

A special liner, impervious to the chemical, ensures air-tight sealing when the handy cap is replaced.

The cap extends over the lip o f the bottle, thus preventing an accumulation o f dust which is a serious problem that is characteristic of cork- stoppered containers.

These new M erck amber color glass bottles, w ith their black caps and blue and white labels, not only afford maximum protection against light and other deteriorat­

ing agents, b u t will add considerably to the attrac­

tive appearance o f your laboratory or stock room.

Your wholesaler is ready to serve you. A sk him M E R C K & C O .

i n c

.

M anufacturing C hem ists

Rahway, N . J.

• N o n -m e ta llic screw cap

• W ill not corrode

• E asy to open

• Special liner ensures a ir­

tight se alin g

• D ust-proof

• A ttractive a p p e a ra n ce

• A m b e r Color G la ss

MERCK

L A B O R A T O R Y C H E M I C A L S IN NE W C O N T A I N E R S

n o w offer these a d v a n t a g e s

NEW "PRECISION" BURNERS

REACH A NEW PEAK OF EFFICIENCY I ON ANY KIND OF GAS

t u n i o r u n i v e r s a l b l a s t J B U R N E R -—T h i s h a n d y n il p u r p o s e b l a s t b u r n e r w ill g iv e y o u a w id e v a r i e t y o f f la m e s iz e s , s h a p e s a n d t e m p e r a t u r e s f o r g la s s w o r k i n g , h i g h t e m p e r a ­ t u r e m e l t i n g , o t h e r l i a r d - t o - l i e a t l a b o r a t o r y j o b s . C o m e s e q u i p p e d w i t h t h r e e i n t e r ­ c h a n g e a b l e b l a s t n o z z l e s , b l e e d e r v a lv e , a n d a d j u s t a b l e t e l e s c o p i n g s le e v e ; h u s o h a s u n i v e r s a l b a l l j o i n t . P r i c e , $10.00

12130

H

i g h t e m p e r a t u r e B U R N E R — D e v e lo p s a t e m p e r a t u r e o f 3 0 6 0 ° F .—

v e r y e f f i c i e n t o n g a s c o n ­ s u m p t i o n , e a s y t o h a n d l e , a n d r u g g e d l y b u i l t f o r l o n g ­ t i m e u s e . H a s n e e d l e v a lv e g a s c o n t r o l , d o u b l e b a r r e l m i x i n g t u b e , a n d M o n e l m e t a l h e a t i n t e n s i f i e r t o p l } ^ ' d i a m e t e r , t o p r o d u c e a s t a b l e h o m o g e n e o u s f la m e . P r i c e ...$2.00

12098

H

e a v y d u t y b u n ­ s e n B U R N E R — T h e a d j u s t a b l e n e e d l e v a lv e , a c c e s s i b l e b e lo w t h e b a s e , a d u p t s t h i s n e w B u n s e n B u r n e r t o a n y g a s s e r v ic e c o n d i ­ t i o n s . _ E q u i p p e d w i t h fH}* d i a m e t e r m i x i n g t u b e a n d h e a t i n t e n s i ­ fie r t o p .

P r i c e . . . . $ 1 .25 12170

T M P R O V E D M E R E R T Y P E 1 B L A S T B U R N E R — T h e n e w a s p i r a t o r a i r i n l e t e n t r a i n s a i r a t h i g h v e l o c it y , s t e p s u p t e m p e r a ­ t u r e a n d e f f i c ie n c y . W i t h t h i s b u r n e r y o u c a n s a v e a g r e a t d e a l o f t i m e o n a s li d e t e r m i n a t i o n s , i g n i t i o n s , a n d f u s i o n s .

S iz e N o . 2 ...$-1.00 S iz e N o . 4 ...$ 5 .75 W r i t e f o r y o u r

f r e e c o p y o f I U x ll e ti n 3 lK — c o m p l e t e a n d c o m p r e h e n ­ s i v e , d e s c r i b ­ i n g t h e e n t i r e l i n e o f “ P R E ­ C I S I O N ” l a b ­ o r a t o r y b u r n ­ e r s .

W. J. GILMORE DRUG CO

L A B O R A T O R Y A P P A R A T U S CH EM IC ALS

422 B L V D . O F T H E A L L I E S P IT T S B U R G H , PA

U N IF O R M T E M P E R A ­

T U R E for T ests o n H e a tin g Loss

of A sp h a ltic C o m p o u n d s

by A .S.T .M . S ta n d a rd M e th o d D 6 -2 0

A sk fo r—

Strip Folder No. 7F.

(0103

No

T

ESTS for loss on heating of asphaltic compounds by A. S. T . M. Standard Method D6-20 requires a uniform tem perature for five hours within a variable range of one degree Centigrade. The space uniform­

ity of the DcKhotinsky triple wall oven is within a variable of plus or minus three degrees Centi­

grade. Use of the auxiliary ro­

tating shelf reduces the tempera­

ture changcs of the sample to variation no greater than one- half of one degree Centigrade.

No other drying oven on the m arket approaches this perform-

H T'H E Cenco DcKhotinsky I Oocn shown is No. 9830B, 14%" x 12* x 11%" inside dimensions fo r 110 colts, or No. 9831B same fo r 220 colts at S 140.00. The rotating shelf is supplied under our No. 9832A fo r 110 or 220 colts, 60 cycle A C or D C at

$80.00.

9832 S h o w n a s U se d in N o . 98 3 0

S ) € ) I E N T I R I ' C r © O J M r P Ä N T f S Ï P P U È S

A p p a r a t u s KEg.U4wt.qFH C h e m i c a l s

N e w Y o r k - B o s t o n - C H I C A G O - T o r o n t o - L o s A n g e l e s W E DO OUB PART

Jan u ary 15, 1934 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

C O M B IN A T IO N

E X T R A C T I O N

A P P A R A T U S

r i? —

M ~

--- 1

Akr—

1 Hi j ---Ti-Jj—

i

S t

GHJ

T his electrically heated , six -u n it Com bi­

n a tio n Extraction Rack and Bath m ay be used for hea tin g either by radiation or by im m ersion.

A Monel metal pan suspended within the rack, just above the heating units, allows for the heating of flasks by immersion when the pan is filled with water or oil. The en­

tire top of the container may be removed and the pan lifted out if desired.

T h e h e a tin g u n i t s c o n s is t o f a p a ir o f s t r i p h e a te r s , so c o n s tr u c te d a s to in s u re p ra c tic a lly u n lim i te d service. T h e s t r ip h e a te r s a re c o n tro lle d b y a p a ir o f 3 - h e a t sw itc h e s so t h a t t h e u n it s m a y b e u s e d s in g ly o r in v a rio u s c o m b in a tio n s to p e r­

m i t o f o p e r a tio n over a w ide ra n g e o f w a tta g e s . Each of the six circular openings on the top of the con­

tainer is fitted with a Monel Metal flanged ring with Monel metal cover and knob. The removable support rods, both vertical, and horizontal are of stainless steel; special adjus­

table clamps are fitted with spring bronze clips.

D im ensions

Overall le n g th ... . . . . 3 1 "

Overall depth... 6Y>‘

Overall h e ig h t...30"

Height to top of container... 1’

Center distances between openings 5*

Dimensions of Monel Metal pan... 29x4%x3' Diameter of openings... V /i"

7509— C o m b in a tio n E x tra c tio n A p p a ra tu s , 6- unit, 1000 watts for connection to 110 volt lighting circuit. Complete as illustrated (excluding glass­

ware) with 6 ft. of insulated cord and separable plug $100.00 7510— C o m b in a tio n E x tra c tio n A p p a ra tu s . As

above, but 220 volts... 100.00

W ^ill C o r p o r a t io n

Products for E very L a b o r a to r y Guaranteed W ithout R eservation

R o c h e s t e r, ,

ô m n j a m c o r

O r g a n i c S u b s t a n c e s I n t

M I C R O - C H E M I C A L T E S T S

• The use of a chemical microscope in the lab o ­ ratory is dependent upon the w orker’s knowledge of chemical microscopy. O f course it has been used in research for years— but, today, if is being used as an accurate "tim e-saver" in many cases of qualitative and quantitative analyses.

The Spencer Chemical Microscope has been designed specifically for use as a simple polar­

izing microscope in chemical laboratories. Q u al­

itatively it is used to identify inorganic or organic substances by micro-chemical tests or by deter­

minations of optical properties. Q uantitatively it is used in the estimation o f elements in mixtures and the measurement of microscopic materials.

Investigate the use of a Spencer Chemical M icro­

scope in your laboratory. W rite us tod ay for Folder M-44.

S fim œ iïJ Ê B m O o w p w u f,

B U F F A L O N E W Y O R K

--- U S E t h i s C O U P O N --- S P E N C E R L E N S C O M P A N Y

19 D o a t S tre e t, Bu ffa lo , N . Y.

G e n tle m e n : P le a s e send me y o u r F o ld e r M-44 co m p le te ly d e scrib in g the S p e n c e r C h e m ica l M icros cop e a n d its uses.

N A M E.

CO M PANY... ... ... . ADDRESS...

CITY... STATE..

8 A N A L Y T I C A L E D I T I O N Vol. 6, N o. 1

<EXAX>

us* <EXAX>

USA

BLUE

L I N E EXAX CENTRIFUGE TUBES

K

IM B L E B lu e-Lin e E x a x C e n tri­

fu g e T u b e s a re m a d e with the sa m e e x a c tin g c a re a n d high q u a l­

ity of w orkm an sh ip that c h a ra c te r­

ize all K im b le scien tific g la ssw a re . S P E C I A L FEA TU RES

1. Tubes closely sorted to have the maxi­

mum possible w all thickness and still safely hold the capacity.

2. The necks a re re in fo rc e d w ith a machine-tooled finish which is much stronger than the ordinary flare.

3. The tapers on tubes with conical ends are carefully shaped.

4. Calibration lines are acid etched and filled with a durable blue glass en­

amel, fused into the lines.

5. Every tube is retem pered (strain-free) in a special lehr or oven.

6. All tubes are individually inspected to insure freedom from defects and retested to assure accuracy.

Illustrated are the two 100 ml. oil centrifuge tubes required by the Am erican Society for Testing M aterials and the Am erican Petroleum Institute; and also the popular 15 ml.

tube subdivided into 1 /10th ml. dimensions.

In addition to these three centrifuge tubes, we manufacture a complete line for all other purposes.

X X

For accu racy and assurance, standardize on Kimble Blue- Line G lassw are. It is stocked by leading Laboratory Su p­

ply Houses throughout the United States and C anada.

KIMBLE G L A S S CO.

V I N E L A N D , N . J .

N E W Y O R K • P H IL A D E L P H IA • B O S T O N C H IC A G O • D ET RO IT

A N A L Y T I C A L E D I T I O N

I n d u s t r i a l

V o l u m e

6 A N D E N G I N E E R I N G

Ja n u a r y

15,

Number i C h e m i s t r y 1934

Pu b l i s h e d b y t h e Am e r i c a n Ch e m i c a l So c i e t y Ha r r i s o n E . Ho w e, Ed i t o r

Composition of F atty Acid Mixtures

II. A F u rth e r D evelopm ent of th e Tw itchell M ixed-M elting-P oint M ethod for D eterm in atio n of Individual S a tu rate d F a tty Acids

R o b e r t N . W e n z e l , M ellon In stitu te o f In du strial R esearch, P ittsb u rgh , P a.

T

H E a n a ly tic a l m eth o d s u su ally ap p lied to th e testin g of com m ercial fa ts a n d f a t ty acid m ix tu res leave th e q u estio n of th e ir com position, in te rm s of c o n stitu e n t f a t ty acids, larg ely u n d eterm in ed . W here co n tro l of com­

po sitio n is a n im p o rta n t fa c to r in th e success of com m ercial processes, as in th e g ro w th of cry stals in m o lten f a t ty acid m ix tu res, relian ce m u s t th erefo re be placed largely on em ­ pirical fo rm u las fo r th e blending of fa ts of different grades a n d d ifferen t sources. B lending fo rm u las are n o t alw ays d ependable, how ever, because th e raw' m a te ria ls them selves a re u su a lly s u b je c t to considerable v a ria tio n . A gain, in in d u s tria l research , analyses of f a t ty acid m ix tu res are fre­

q u e n tly of service o n ly in so fa r as th e y can be in te rp re te d in te rm s of com position. Such in te rp re ta tio n , b ased solely on r e s u lta n t p ro p ertie s of th e m ix tu re— to ta l u n sa tu ra tio n , acid v alu e, tite r , e tc .—is a t b e st u n c e rta in an d often q u ite m is­

leading. T h e re is n eed th erefo re for m eth o d s t h a t d e te r­

m ine, specifically, th e p ercen tag es of in d iv id u al f a tty acids p resen t.

Th e M i x e d- Me l t i n g- Po i n t Me t h o d

I n view of th is situ a tio n , th e m ixed-m elting-point m eth o d devised b y T w itch ell (11) h as certain ly n o t received th e a tte n tio n t h a t its possibilities w ould seem to m erit.

T h e m e th o d is b ased on th e fa c t t h a t if a sam ple consisting of a m ix tu re of f a t ty acids is a d d ed to a single p u re f a tty a cid o n ly th o se acid s in th e m ix tu re t h a t are n o t identical w ith th e p u re acid so lv en t w ill be effective in low ering its m eltin g p o in t. T w itch ell reasoned th a t, because of th e ir un ifo rm ly hig h m olecular w eights, all th e f a t ty acids should h a v e a p p ro x im a te ly eq u al effect in depressing th e m elting p o in t of a n y so lv e n t. T h u s, if th e so lv en t acid is stearic, th e depression of th e m eltin g p o in t gives a m easure of all acids o th e r th a n ste a ric acid in th e m ix tu re. F ro m th is th e p ercen tag e of ste a ric acid in th e sam ple is read ily cal­

cu lated .

As used b y T w itch ell, th e m eth o d w as su b je c t to serious lim ita tio n s, m a in ly b ecause th e m eltin g -p o in t d eterm in atio n itself w as n o t sufficiently precise to p e rm it th e estab lish m en t of ac c u ra te , specific depression c o n sta n ts fo r th e different in d iv id u a l acids. In ad d itio n , T w itch ell m easured all de­

pressions a t 20 p er ce n t of to t a l so lu te acids. T h is n o t only n ecessita ted a p relim in ary tria l, in each analysis, before

w eighing o u t th e final m ix tu re , b u ty it placed th e m easure­

m e n ts beyond th e stra ig h t-lin e p o rtio n of th e m eltin g -p o in t curve a n d th erefo re ou tsid e th e ran g e in w hich m elting- p o in t d a ta can p ro p e rly be ap p lied .

T h e m e th o d w as la te r used b y M cG reg o r a n d B eal (8), in th e ir s tu d y of th e f a t ty acid s of m en h ad en oil, in essentially th e form in w hich i t w as left b y T w itch ell.

A d is tin c t im p ro v em en t in th e resu lts o b tain ab le b y th e m ixed -m eltin g -p o in t m e th o d is m ad e possible b y a n im ­ p ro v ed m eltin g -p o in t tech n ic h ere described. Specific de­

pression c o n sta n ts h a v e been d eterm in ed b y m easu rem en ts on b in a ry m ix tu re s of p u re acids, including stearic, p alm itic, m y ristic, a n d oleic. I t h as been found t h a t depressions in p alm itic acid a n d in ste a ric acid are a p p a re n tly controlled, as m ig h t be ex pected, b y definite m o lar depression con­

s ta n ts c h a ra c te ristic of th e so lv e n t acid a n d in d ep en d e n t of th e solute. R eliable specific depression c o n sta n ts fo r th e in d iv id u a l solute acid s can th u s be based on th e m o lar con­

s t a n t fo r th e so lv e n t a n d th e m olecular w eig h t of th e solute.

F o r so lutions in m y ristic acid, th e beh av io r of dissolved stearic acid is a p p a re n tly anom alous, giving a m o lar de­

pression c o n sta n t h ig h er th a n t h a t o b ta in e d w hen th e solute acid is p alm itic o r oleic. T h is d e p a rtu re from th e th eo retical h a s n o t b een explained. F o r stearic acid in m y ristic, th e re ­ fore, th e specific depression c o n sta n t d irep tly d eterm in ed m u s t be accep ted . T h e p ro p e r depression c o n s ta n t to use in a n y p a rtic u la r an aly sis is read ily calcu lated from th e specific c o n sta n ts h e re estab lish ed .

T h e m e th o d gives re s u lts only reliab le to w ith in a fewr per cen t, b u t, in sp ite of its lim ited accuracy, is a n ex trem ely v a lu ­ a b le to o l. A s h ere w orked o u t, i t h as p ro v ed v e ry useful in th e in v estig atio n of problem s en co u n te red in th e m an u fac­

tu r e of com m ercial f a t ty acids, p a rtic u la rly in defining th e lim its of to le ra tio n of th e cry stallizin g process to v a ria tio n s in th e com position of th e stock.

Th e Me l t i n g- Po i n t De t e r m i n a t i o n

E v e n in th e case of p u re com pounds, m eltin g p o in ts dep en d largely o n a p p a ra tu s a n d tech n ic. T h u s w idely differing values fo r th e m eltin g p o in t of a n y of th e p u re f a t ty acids w ill be fo u n d in th e lite ra tu re . W ith f a t ty acid m ix tu re s th e re is th e fu r th e r difficulty t h a t h ere w e are dealin g w ith a case of solid solutions. T h e co m p o sitio n -m eltin g -p o in t 1

2 A N A L Y T I C A L E D I T I O N Vol. 6, N o. 1 d ia g ra m for m ix tu res of tw o f a tty acids is n o t a single line,

b u t tw o lines, th e so-called liq u id u s a n d solidus curves. E v e n w ith th e m ain te n a n c e of ideal eq u ilib riu m conditions, m eltin g will s t a r t a t one te m p e ra tu re a n d co n tin u e o v er a considerable ran g e of v alu es; a n d a t a n y te m p e ra tu re w ith in th is range

th e m ix tu re exists as a p e rfe c tly s t a b l e , tw o-phase system .

T h eo retically , b o th th e in itia l an d final te m p e ra tu re s of th is m e l t i n g r a n g e a re c h a racteristic p ro p er­

tie s of th e m ix tu re.

P ra c tic a lly , i t is only th e final p o i n t t h a t can b e d e t e r m i n e d w i t h a n y accuracy.

T h e p o i n t u s u a l l y reco rd ed in m elting- p o in t d eterm in atio n s

— i. e., th e te m p e ra ­ tu r e a t w h ic h clear liq u id first a p p e a r s i n t h e s a m p l e — com es a t n e ith e r th e beginning n o r th e end of th e m eltin g range, b u t d e p e n d s u p o n t h e r a t e a t w h ic h t h e s o l i d s e t t l e s th ro u g h t h e l i q u i d first form ed. I n th e p re s e n t w ork, final te m p e ra tu re s w ere th erefo re used th ro u g h o u t.

M cG regor a n d B eal, as w ell as T w itch ell, allow ed th e m a te ria l in th e m eltin g -p o in t tu b e to sta n d fo r a t le a s t 12 h o u rs to rem ove s tra in before th e m e ltin g p o in t w as ta k e n . T h e n ecessity for th is p re c a u tio n in th e case of fa ts h a s been p o in ted o u t b y L ew kow itsch (7), B loor (2), a n d o th ers.

B u rk s (S) found, how ever, t h a t th e double m eltin g p o in ts exhibited b y recen tly m elted glycerides are n o t en co u n tered in th e case of th e free f a t ty acids.

B u rk s’ o b serv atio n s are confirm ed b y th e follow ing series of m eltin g -p o in t read in g s ta k e n on th e sam e sam ple a fte r ex­

p o sin g th e tu b e to th e v ario u s tr e a tm e n ts in d ic a te d . T h e tw o read in g s reco rd ed in each case w ere ta k e n a t th e first ap p e a r­

ance of clear liquid an d a t th e d isap p earan ce of th e la s t of th e solid.

° c.

I n it ia l m e ltin g p o in t 6 0 .7 6 to 6 1 .0 8

A f te r solidifying: a n d s ta n d i n g 4 3 h o u rs a t ro o m te m p e r a t u r e 6 0 .8 8 to 6 0 .9 3 A f te r s o lid ify in g a n d a g a in s ta n d in g 52 h o u rs a t ro o m te m ­

p e r a t u r e 6 0 .9 0 to 6 1 .1 0

A f te r k e e p in g m e lte d in a n o v en a t 6 5 ° to 7 0 ° C . fo r 17 h o u rs

a n d s ta n d in g a t ro o m te m p e r a t u r e 4 5 m in u te s 6 0 .9 4 to 6 1 .1 4 A f te r co o lin g to , a n d h o ld in g a t 5 5 .5 ° t o 5 7 .5 ° C . fo r 4 h o u rs 6 0 .9 7 to 6 1 .1 4 A f te r p lu n g in g in to ic e w a te r, h o ld in g th e r e 5 m in u te s , a n d

r e p e a tin g th e m e ltin g - p o in t d e t e r m in a tio n a t o n c e 6 0 .7 3 to 6 1 .1 5

I t will b e seen t h a t th e m eltin g p o in t is n o t ap p reciab ly affected b y re p e a te d m elting, long sta n d in g a t ro o m te m p e ra ­ tu r e , long co n tin u ed h e a tin g ju s t above th e m eltin g p o in t, slow solidification ju s t below th e m eltin g p o in t, o r rap id solidification in a n ice b a th . W e m a y th e re fo re conclude t h a t th e re is n o decom position a t th e m eltin g p o in t to necessi­

ta t e a ra p id m eltin g -p o in t d e te rm in a tio n a n d t h a t th e re is n o th in g to be gained b y aging th e sam ple in th e m elting- p o in t tu b e .

B u rk s recom m ended a n ex trem ely slow ra te of h e a tin g designed to sim u la te im m ersion of th e sam ple tu b e for tw o m in u te s in each of a succession of c o n s ta n t-te m p e ra tu re b a th s differing b y on ly 0 .1 ° C . T h is procedure w as a d o p te d in th e

p re se n t w ork because i t m ak es possible a high degree of p reci­

sion in th e m eltin g -p o in t d e te rm in a tio n . T h e a p p a ra tu s used is, in all its essential featu res, id e n tic a l w ith t h a t em ­ ployed b y B u rk s.

I n o rd e r to o b ta in th e sh a rp te m p e ra tu re co n tro l re ­ q u ired , i t is essen tial to use a closed m eltin g -p o in t tu b e im ­ m ersed d ire c tly in th e te m p e ra tu re b a th . T w itchelP s in ­ genious m eth o d of loading a n open tu b e fro m th e m elted m ix tu re, to in su re a tr u e sam ple, an d th e n giving it a sh a rp ja r , so t h a t th e sam ple solidifies as a strin g of sh o rt segm ents, h a s b een re ta in e d , b u t th e tu b e is th e n sealed in th e B unsen flam e. W ith p ro p e r p re c a u tio n s th is can be done w ith o u t in ju rin g th e sam ple.

Ap p a r a t u s

F ig u re 1A is a d iag ram of th e a p p a ra tu s used for th e m e lt­

in g -p o in t d e te rm in a tio n s. A 600-cc. P y re x b e a k e r con­

ta in in g w a te r o r a light, colorless m in eral oil serves as th e h e a tin g b a th . T h e im m ersion h e a te r consists of a spiral coil of resistan ce w ire sh eath ed in a loop of P y rex glass tu b in g . T h e lam p b a n k an d rh e o s ta t connections a re in d icated . T h e b ea k e r is n o t in su lated , as a c c u ra te te m p e ra tu re control d ep en d s u p o n a nice b alan c in g of h e a t in p u t a g a in s t ra d ia ­ tio n , b u t i t m u s t be p ro te c te d from fitful a ir d ra fts. Two m eltin g -p o in t tu b e s are faste n e d to th e th e rm o m e te r b y m ean s of a ru b b e r b a n d . I n ad d itio n , a fo rk m a d e of glass tu b in g , w ith tw o prongs e x ten d in g in to th e b a th p arallel to th e th e rm o m e te r, m ak es i t possible to in tro d u c e six tu b e s a t a tim e. T h e slow ra te of h e a tin g allows am ple tim e for observing a n d recording th e b eh av io r of each sam ple.

T h e m eltin g -p o in t th e rm o m e te rs u sed are of ra n g e s 20°

to 60° C . a n d 4 0° to 8 0° C ., g ra d u a te d in 0 .1 ° u n its an d c a lib ra te d b y com parison w ith th e rm o m e te rs certified b y th e U n ite d S ta te s B u re a u of S ta n d a rd s. A m agnifying a tta c h ­ m e n t p e rm its readings to 0.01 ° C . E m e rg e n t stem te m p e ra ­ tu re s are also recorded.

T h e exact size of th e m eltin g -p o in t tu b e is n o t critical.

T u b e s of inside d ia m e te r such as to accep t a N o. 22 B & S gage w ire b u t n o t a N o. 20 w ire w ere selected. A sm all h a n d lens is u sed to observe th e b eh av io r of sam ples d u rin g m elting.

I t is of course essen tial t h a t th e f a t ty acids be d ry . A c o n v en ie n t device for th o ro u g h a n d ra p id d ry in g of sm all sam ples, also suggested b y B u rk s, is th e v acu u m d ry in g tu b e show n in F ig u re IB . T h e d ry in g ch am b e r is d iv id ed in to u p p e r a n d low er co m p a rtm e n ts b y a screen of h e a v y w ire gauze. S am ples are placed in th e u p p e r c o m p a rtm e n t, pho sp h o ru s pentoxide in th e low er. W a te r circu lated th ro u g h th e ja c k e t is h e a te d in th e u p rig h t tu b e , e ith e r electrically or b y m ean s of a sm all gas flame, a n d th e te m p e ra tu re m ain ­ ta in e d a t a p o in t on ly a few degrees below th e m eltin g p o in t of th e sam ple. T h e tu b e is ev ac u a te d b y m ean s of a n oil p u m p . T h o ro u g h d ry in g is accom plished w ith in 15 o r 20 m in u te s in th is a p p a ra tu s.

Pr o c e d u r e

E a c h an aly sis is ru n in d u p licate, tw o m ix tu re s w ith d efinitely d ifferen t p ro p o rtio n s of sam ple an d p u re acid being p re p a re d . T h e m ix tu re, w eighing u su ally a b o u t 2 gram s, is w eighed o u t in a sm all square-shouldered v ia l of 12 cc.

c a p a c ity (F ig u re 1C) a n d m elted dow n in a n oven a t 100° C.

M ixing is effected b y tiltin g th e v ia l u n til th e liquid reaches th e shoulder, ro ta tin g i t in th is position an d shaking.

T w o open m eltin g -p o in t tu b e s a re th e n d ip p ed in to th e m ix tu re . Follow ing T w itc h e ll’s tech n ic, th e sam ple in each tu b e is b ro k en in to a strin g of sm all uniform segm ents a n d , b y p ro p e r m a n ip u la tio n above th e flam e, th e la s t seg­

m e n t is spaced a b o u t 7 m m . from th e end of th e tu b e . B y

Fi g u r e 1 . Ap p a r a t u s

Jan u ary 15, 1934 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

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a c id a c id

o f Mi x t u r e O le ic

a c id

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To t a l So l u t e Me l t i n q Po i n t

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2 9 5 .0 0 5 .0 0 4 .5 2 6 1 .5 0 o.’s o 1*60 1 .7 7

3 9 0 .0 0 1 0 . 0 0 9 .1 0 6 0 .6 2 1 . 6 8 1 . 6 8 1 .8 4

4 8 5 .0 0 1 5 .0 0 1 3 .7 2 5 9 .7 8 2 .5 2 _{1 . 6 8} 1 .8 4

6 8 0 .0 0 2 0 . 0 0 1 8 .3 8 5 8 .6 2 3 .6 8 1 .8 4 2 . 0 0

6 9 4 .5 1 5.4 0 4 .8 5 6 1 .4 4 0 . 8 6 1 .5 6 1 .7 7

7 8 9 .9 9 1 0 . 0 1 9 .1 7 6 0 .6 3 1 .6 7 1 .6 7 1 .8 2

8 8 4 .9 5 1 5 .0 5 1,3.84 5 9 .7 9 2 .5 1 1 .6 7 1 .8 1

9 7 9 .7 4 2 0 .2 6 1 8 .7 6 5 8 .7 9 3 .5 1 1 .7 3 1 .8 7

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1 1 8 4 .8 1 4 .9 9 1 0 . 2 0 1 3 .9 5 5 9 .7 4 2 .5 6 1 . 6 8 1 .8 3

1 2 8 4 .9 9 1 0 . 0 0 5 .0 1 1 3 .7 7 5 9 .7 9 2 .5 1 1 .6 7 1 .8 2

13 1 0 0 6 9 .1 0

14 5 .0 0 9 5 .0 0 5 .52 6 8 . 2 2 0 . 8 8 1 .7 6 l ! Ś 9

15 1 0 . 0 0 9 0 .0 0 1 0 .9 8 6 7 .3 9 1 .7 1 1 .7 1 1 .5 6

1 0 1 5 .0 0 8 5 .0 0 1 6 .3 9 6 6 .4 4 2 . 6 6 1 .7 7 1 .6 2

17 2 0 . 0 0 8 0 .0 0 2 1 .7 4 6 5 .4 7 3 .6 3 1 .8 2 1 .6 7

18 9 4 .9 1 ¿109 5 .1 3 6 8 .2 6 0 .8 4 1 .6 5 1 .6 4

19 8 9 .5 8 1 0 .4 2 1 0 .5 2 6 7 .4 1 1 .6 9 1 .6 2 1 .6 1

2 0 8 4 .9 6 1 5 .0 4 1 5 .1 8 6 6 .6 2 2 .4 8 1 .6 5 1 .6 4

2 1 8 0 .0 1 1 9 .9 9 2 0 .1 6 6 5 .7 2 3 .3 8 1 .6 9 1 . 6 8

2 2 4 *99 8 9 .7 8 5 .2 3 1 0 .7 4 6 7 .4 0 1 .7 0 1 . 6 6 1 .5 8

23 9 .9 9 8 4 .7 4 5 .2 7 1 6 .2 0 6 6 .4 9 2 .6 1 1 .7 1 1 .6 1

24 4 .9 9 8 4 .8 3 1 0 .1 8 1 5 .7 0 6 6 .5 8 2 .5 2 _{1 . 6 6} 1 .6 1

25 3 0 .0 0 7 0 .0 0 6 3 .2 0

26 4 0 .0 0 6 0 .0 0 6 0 .3 3

27 5 0 .0 0 5 0 .0 0 5 6 .7 1

28 6 0 .0 0 4 0 .0 0 5 6 .2 0

29 7 0 .0 0 3 0 .0 0 5 5 .5 0

careful w arm ing, th e w alls of th e end section are now d rained com pletely in to th e la s t segm ent. T h e tu b e is th e n sealed.

S om etim es sealing th e tu b e affects th e m eltin g p o in t of th e la s t seg m en t, b u t it can h av e no effect, of course, on th e o th ers. All th e segm ents in b o th tu b es, m eltin g sim ul­

ta n e o u sly , give assurance t h a t a hom ogeneous m ix tu re has been o b ta in e d an d t h a t th e re is no irreg u la rity in th e m elting p o in t d u e to accid en tal facto rs. T h e loaded tu b e is shown in F ig u re ID .

I n m eltin g th e sam ple, it is h e a te d ra p id ly to w ith in 1°

of th e a n tic ip a te d m elting p o in t. If th is is n o t know n a p ­ p ro x im ately i t is d eterm in ed b y a rap id p relim in ary m elting.

F ro m th e re on th e procedure is to hold th e te m p e ra tu re c o n sta n t, w ith in a few h u n d re d th s of a degree, for 2 m in u tes a n d th e n allow i t to rise 0.1° d u rin g th e n ex t m in u te, when i t is again held c o n sta n t for 2 m in u tes, an d so

on. T h e te m p e ra tu re a t w hich th e la s t speck of solid m a te ria l in each se p a ra te p o rtio n of th e sam p le d isap p ears is ta k e n as th e m elting p o in t. D u p lic a te d eterm in atio n s should agree w ith in 0.05° C.

through an efficient fractionating column. T he first 40 per cent of the distillate was rejected. T he rem ainder, coming over a t constant tem perature, was treated for recovery of the acids which were then recrystallized from acetone. Preparations having m elting points of 02.0° C. or higher are accepted.

M y r i s t i c A c i d . N utm eg butter, obtained from ground

nutmegs by extraction w ith eth er after a prelim inary alcohol ex­

traction had removed most of the color and th e volatile oil, was saponified and the soap solution acidified to liberate m yristic acid. Recrystallized three times from acetone, the acid melted a t 53.32° C. This product was distilled under reduced pressure and the first and last fractions were rejected. T he rem ainder, again recrystallized from acetone, was recovered in two fractions m elting a t 54.17° and 53.88° C., respectively.

O l e i c A c i d . Preparation of oleic acid of a high degree of pu rity is a m atter of considerable difficulty. I t was required here for th e determ ination of melting-point depression constants, b u t is not required as a reagent in th e mixed-melting-point method.

Pr e p a r a t i o n o f Pu r e Fa t t y Ac i d s

In o rd er to estab lish specific d e p r e s s i o n c o n sta n ts, i t w as n ecessary to h av e sam ples of th e p u re f a t ty acids. In ad d itio n , th e pure s a tu ra te d acids are required as reag en ts in the m ixed-m elting-point m eth o d . T h e acids used w ere p re p a re d as follow s:

S t e a r i c A c i d . The m ethyl esters obtained from commercial double-distilled oleic acid were distilled a t low pressure through a fractionating column. T he first half of the distillate, contain­

ing large am ounts of m ethyl p a l m i t a t e , was rejected. T h e second p o r t i o n , b o i l i n g a t practically c o n s t a n t t e m p e r a t u r e (174° to

178° C. a t 3 mm .) and containing only Cis acids, was hydrogen­

ated in 25-gram quantities in alcoholic solution, using platinic oxide as catalyst (/). T he combined alcoholic solutions were then refluxed 4 hours with 2 M equivalents of potassium hy­

droxide to saponify the esters and the soaps split with hydro­

chloric acid. The recovered acids, washed free of chlorides, were recrystallized once from petroleum ether and repeatedly from acetone until no further increase in melting point resulted.

T he product th u s obtained consists of beautifully white, crys­

talline flakes. Samples of melting point 69.0° C. or higher are accepted for use in the mixed-melting-point method.

P a l m i t i c A c i d . F a tty acids recovered from bayberry wax were converted to their m ethyl esters and distilled a t low pressure

-4, in

F i g u r e 2. M e l t i n g - P o i n t D e p r e s s i o n s s t c a r i c a c i d B , i n p a l m i t i c a c i d C, i n m y r i s t i c a d d

Olive oil fa tty acids were used as the source of oleic acid.

M ost of the saturated acids were removed by T w itchell’s lead soap-alcohol method (10, 12). Removal of m ost of th e linoleic acid was effected by refluxing the u n satu rated acids in alcohol, w ith enough finely ground solid barium hydroxide to convert SO per cent of th e acids to their barium soaps, th u s leaving the linoleic acid, together w ith some oleic, in solution. T his is a modification of the procedures of F arnsteiner (6) and of Lap- worth and Pearson (£?). F o r the final purification from small am ounts of palm itic acid and linoleic acid, fractional crystalliza­

tion of th e lithium soaps according to Scheffers (9) was adopted.

T his m ethod was found more effective in rem oving linoleic acid, however, th an in concentrating palm itic acid in the first fractions.

A N A L Y T I C A L E D I T I O N Vol. 6, N o. 1

Ta b l e I I . Me l t i n g- Po i n t De p r e s s i o n s i n Mi x t u r e s In v o l v i n g My r i s t i c Ac i d

Mi x t u r e

.---W 'e i o h to p Ac i d si n Mi x t d k e---.

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3 4 0 . 3 0 1 6 1 . 7 0 6 2 1 5 . 0 2 1 6 . 5 6 5 9 . 5 3 2 . 9 2 1 . 9 4 1 . 7 6

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4 2 1 . 0 0 0 0 0.00 5 4 . 1 7

4 3 1 . 9 0 1 5 0 .ÎÔ Ô 7 5 . 0 3 4.*50 5 3 . 2 6 0 . 9 1 1 . 8 1 2 .Ö 2

44 1 . 8 0 2 9 0 . 2 0 0 0 9 . 9 9 8 . 9 9 5 2 . 3 5 1 . 8 2 1 . 8 2 2 . 0 2

4 5 1 . 7 5 1 9 0 . 2 5 0 6 1 2 .5 1 1 1 . 3 0 5 1 . 9 5 2 . 2 2 1 . 7 7 1 . 9 6

4 6 1 . 7 0 2 9 0 . 3 0 2 6 1 5 . 0 9 1 3 . 6 6 5 1 . 4 5 2 . 7 2 1 . 8 0 1 . 9 9

4 7 1 .6 0 1 9 0 . 4 0 1 9 2 0 . 0 6 1 8 . 2 6 4 9 . 9 3 4 . 2 4 2 . 1 1 2 . 3 2

4 8 1 . 9 0 0 2 0 . 'i Ô i 8 5 . 0 8 4 . 1 2 5 3 . 1 6 1 . 0 1 1 . 9 9 2 . 4 5

4 9 1 . 8 0 5 7 0 . 2 0 1 4 1 0 . 0 3 8 . 2 2 5 2 . 1 5 2 . 0 2 2 . 0 1 2 . 4 6

5 0 1 . 7 4 9 8 0 . 2 5 0 0 1 2 . 5 0 1 0 . 2 9 5 1 . 6 5 2 . 5 2 2 . 0 2 2 . 4 5

51 1 . 6 9 9 8 ' 0 . 2 9 9 5 1 4 . 9 8 1 2 . 3 9 5 1 . 1 4 3 . 0 3 2 . 0 2 2 . 4 4

5 2 1 . 6 0 0 8 0 . 4 0 2 4 2 0 . 0 9 1 6 . 7 9 4 8 . 2 4 5 . 9 3 2 . 9 5 3 . 5 3

5 3 1 . 9 0 4 4 0 Ü Ô 2 4 5 . 1 0 4 . 1 7 5 3 . 3 6 0 . 8 1 1 . 7 5 1 . 9 4

5 4 1 . 8 0 0 9 0 . 2 0 2 3 1 0 . 1 0 8 . 3 3 5 2 . 4 6 1 . 7 1 1 . 6 9 2 . 0 8

5 5 1 .7 5 8 1 0 . 2 5 1 0 1 2 . 4 9 1 0 . 3 5 5 2 . 0 5 2 . 1 2 1 . 7 0 2 . 0 4

56 1 . 7 0 2 6 0 . 3 0 1 9 1 5 . 0 6 1 2 . 5 4 5 1 . 6 5 2 . 5 2 1 . 6 7 2 . 0 1

5 7 1 . 6 0 3 8 0 . 4 0 2 1 2 0 . 0 5 1 6 . 8 6 5 0 . 6 4 3 . 5 3 1 . 7 6 2 . 1 0

Fractional distillation of the free acid, under reduced pressure and in an atm osphere of nitrogen, w ith rejection of a considerable first fraction, was finally resorted to an d should preferably precede the lithium soap recrystallizations.

In the Scheffers lithium soap procedure, th e successive re-

Km M o l . W t . 1 . 8 2 X 2 5 6 = 4 6 6 1 . 6 1 X 2 8 4 - 4 5 7

A v . 4 6 1 . 5 4 6 1 . 5 / 2 2 8 - 2 . 0 2

crystallizations are made after combining fractions of like iodine value. F or th is purpose Scheffers w ithdraw s sam ples from which he liberates and recovers the free acids for analysis. The lithium soaps, however, can be dried a t 110° C. w ithout change and they are freely soluble in glacial acetic acid. Iodine values can therefore be taken directly on th e lithium soaps, an d much time and labor are thus saved.

The only satisfactory criterion of p u rity in th e final oleic acid is to separate it b y distillation through an efficient column into a number of fractions, all of which agree in iodine value w ith the theoretical. T he product eventually obtained was a sparkling liquid, perfectly colorless an d odorless, w ith an iodine value of 89.6.

De t e r m i n a t i o n o f Sp e c i f i c De p r e s s i o n Co n s t a n t s

D a ta from w hich m e ltin g -p o in t depression c o n sta n ts wrere co m p u ted fo r so lu tio n s in p a lm itic a n d ste a ric acids are given in T a b le I . S im ilar d a ta are given in T a b le I I for m ix tu res inv o lv in g m y ristic acid . T h e calc u lated specific depression c o n sta n ts, K „, h ere defined as th e low ering in degrees C e n tig rad e p e r 10 p e r c e n t b y w eight of solute, an d th e m o lar c o n sta n ts, K m, expressed in degrees C e n ti­

grade p er 10 p e r c e n t m ole fra c tio n of so lu te, a re also ta b u ­ lated.

In sp ectio n of T a b le I show s a t once t h a t for e ith e r so lv en t a single m o lar depression c o n sta n t applies, irrespective of th e so lu te. R e je c tin g th e v alu es fo r 20 p e r c e n t of solute, w hich a re high in e v ery case, n in e v alu es of K „ fo r p alm itic acid av erag e 1.81 w ith a n av erag e d ev iatio n of 0.0 2, a n d n in e values fo r ste a ric acid av erag e 1.61 w ith a n av erag e d ev ia­

tio n also 0.02. D isco u n tin g th e re su lts for on ly 5 p er cen t of solute, since th ese inv o lv e a h ig h er exp erim en tal error, th e accep ted values a re 1.82 a n d 1.61, respectively.

U sing th ese m o lar c o n sta n ts an d th e m olecular w eights of th e so lu te acids, we a rriv e a t th e n u m erical v alu es show n in F ig u res 2A a n d 2B fo r th e resp ectiv e specific depression co n sta n ts. T h e d a ta p o in ts a n d curves show how’ well an d how fa r th e m easu red depressions follow' th ese c o n sta n t slopes.

Since th e m o lar depression c o n sta n ts 1.82 a n d 1.61 for p alm itic a n d ste a ric acids, respectively, are alm o st ex actly in th e in v erse ra tio of th e ir m olecular w eights, i t m ig h t seem reaso n ab le to ex p ect t h a t th e v a lu e of K n fo r m y ristic acid w ould be fo u n d a t a b o u t 2.0 2:

T h is v a lu e is ap p ro x im a te d v e ry closely b y so lutions of p alm itic acid a n d oleic acid in m y ristic , b u t so lu tio n s of ste a ric acid in m y ristic give a h ig h e r v alu e— n am ely , 2.45.

T h e specific depression c o n s ta n ts show n in F ig u re 2C for p a lm itic acid a n d oleic acid w ere d eriv ed from th e m o lar c o n s ta n t 2 .0 2 fo r m y ristic acid a n d th e m olecular w eights of th e so lu te acids. F o r ste a ric acid in m y ristic , th e v a lu e of K * d ire c tly m easu red — n am ely , 2.0 2— is showTi.

Sa m p l e An a l y s i s

T h e m a n n e r of a p p ly in g th e se depression c o n sta n ts in th e d e te rm in a tio n of in d iv id u a l s a tu ra te d acid s is illu s tra te d in th e follow ing exam ple. T h e a n a ly tic a l d a ta are given in T a b le I I I .

Ta b l e I I I . Da t a, Sa m p l e An a l y s i s

Pa l m i t i c St e a r i c My r i s t i c

1 2 3 4 5 6

0 . 1 4 0 4 0 . 1 4 9 6 0 . 1 4 1 2 0 . 1 5 2 2 0 . 1 4 5 7 0 . 1 5 4 2 0 . 8 6 0 0 0 . 8 5 9 0 0 . 8 6 7 8 0 . 8 6 0 3 0 . 8 8 9 0 0 . 8 8 3 7 1 . 0 0 0 4

1 4 . 0 3

1 . 0 0 8 6 1 4 . 8 3

1 . 0 0 9 0 1 3 . 9 9

1 . 0 1 2 5 1 5 . 0 3

1 . 0 3 4 7 1 4 . 0 8

1 . 0 3 7 9 1 4 . 8 6 6 0 . 1 2 6 0 . 0 2 6 7 . 1 8 6 6 . 9 8 5 1 . 4 4 5 1 . 2 4 6 1 . 9 3

1 .8 1 6 1 . 9 3

1 . 9 1 6 9 . 2 1

2 . 0 3 6 9 . 2 1

2 . 2 3 5 3 . 8 8

2 . 4 4 5 3 . 8 8

2 . 6 4 S o lv e n t a c id

M ix tu r e N o . W e ig h t of s a m p le ,

g ra m

W e ig h t of s o lv e n t a c id , g ra m W e ig h t of m ix tu r e ,

g ra m

P e r c e n t s a m p le (a) M e ltin g p o in t of m ix ­

tu r e , ° C . M e ltin g p o in t of s o l­

v e n t a c id , 0 C.

D e p re s s io n , ° C . (L )

T his sam ple was obtained in the commercial processing of tallow fa tty acids. I t is known therefore to be essentially a m ixture of palm itic, stearic, and oleic acids, w ith, possibly, sm aller am ounts of linoleic and m yristic whose net effect on the m elting-point depression rates m ay be neglected. F o r solutions in palm itic acid, the specific depression constants for stearic and oleic are practically identical, th e values found being 1.66 and 1.67. Using the average value 1.665, wre arrive a t th e following results for palm itic acid:

Mi x t c h e 1 Mi x t u r e 2 Av x k a o k

P e r c e n t n o t p a lm itic in m ix tu r e (1 0 L /

1.665) 1 0 . S7 1 1 .4 7

P e r c e n t s a m p le in m ix tu r e (a) 1 4 .0 3 1 4 .8 3 P e r c e n t s a m p le p a lm itic in m ix tu r e (6) 3 .1 6 3 .3 6

P e r c e n t p a lm itic a c id in s a m p le (b/a) 2 2 .5 2 3 .2 2 2 .8

In calculating th e percentage of stearic acid in the sample, th e value of to be used will He between 1.62 for oleic and 1.77 for palm itic a t a figure depending upon the proportions of these