Industrial and Engineering Chemistry : analytical edition, Vol. 15, No. 11

INDUSTRIAL ^{a n d} ENGINEERING CHEMISTRY

ANALYTICAL EDITION

W A L T E R J. M U R P H Y , E D I T O R O I S S U E D N O V E M B E R 17, 1943 • V O L . 15, N O . 11 • C O N S E C U T I V E N O . 22 Editorial A ssistant: G . G l a d t s G o r d o n M anuscript A ssistant: S t e l l a A n d e r s o n M ake-up A ssistant: C h a r l o t t e C . S a y r e

B. L . C l a r k e

T . R . C u n n i n g h a m

Advisory Board G. E . F . L u n d e l l M . G. M e l l o n

R . H . M ü l l e r

H . H . W i l l a r d

Because of the high value of this com prehensive article as a work of reference, a special arrange­

ment has been made to have it republished in permanent b o o k form instead of the usual stand­

ard reprint. In addition to the material here presented, the b ou nd reprints will also contain a bibliograph y of the literature of infrared spectroscopy consist­

ing of some 2 0 0 0 items. The b ib liog rap h y was omitted here because of space limitations.

The b o o k can be obtained for pro bably $ 2 .2 5 from R einhold Publishing Corp., 3 3 0 W e st 4 2 n d St., N e w Y o rk 18, N . V.

Book R e v i e w s ... 7 1 0 Infrared S p e c tro s co p y . In dustrial A p p l i c a t i o n s ...

R. B. Barnes, Urner Liddel, and V. Z . W illiam s 6 5 9

H e rsch e l’s Draw ing of the A p p a ra tu s U sed in the D iscove ry of Infrared

Radiation

This drawing appeared in a paper by Sir Frederick William Herscnel in 1800 and is copied from the

"Philosophical Transactions" of that year.

The spectrum of sunlight produced by a prism was allowed to fall on a table. The tempera­

ture rise produced by radiation beyond the red was measured by one thermometer while the other two were used as controls.

T h e A m erican C h em ical S o c ie ty assu m es no re s p o n sib ility fo r th e s ta t e m e n ts a n d o p in io n s a d v a n c e d b y c o n trib u to rs to its p u b lic a tio n s.

28,500 copies of th is issue p rin te d . C o p y rig h t 1943 b y A m erican C h em ical Society.

P u b lish e d b y th e A m erican C hem ical S o ciety a t E a s to n , P e n n a . E d i­

to ria l Office: 1155 1 6 th S tr e e t, N . W ., W ash in g to n 6, D . C .; telep h o n e, R ep u b lic 5301; cab le, Jiec h e m (W a sh in g to n ). B usiness Office: A m e ric a n C hem ical Society, 1155 16th S tr e e t, N . W .f W a s h in g to n 6, D . C . A d v e rtis ­ ing Office: 332 W e st 42 n d S tr e e t, N ew Y o rk 18, N . Y .; te le p h o n e, B ry a n t 9-4430.

E n te r e 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 c t of M arch 3, 1879, as 24 tim es a y e ar— I n d u s tr ia 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 15 th . A ccep tan ce for m ailing a t sp ecial r a te of p o sta g e p ro v id e d for in S ectio n 1103, A c t of O c to b er 3, 1917, a u th o riz e d J u ly 13, 1918.

R e m itta n c e s a n d o rd e rs fo r s u b sc rip tio n s a n d fo r single copies, n o tices of ch an g es of a d d re ss a n d new p ro fessio n al c o n n ectio n s, a n d claim s fo r m issing n u m b e rs sh o u ld b e s e n t to th e A m erican C hem ical S ociety , 1155 I 6 th S tre e t, N . W ., W a s h in g to n C, D . C . C h an g e s of ad d re ss for th e I n d u s tria l E d itio n m u st b e receiv ed on or b efo re th e 18th of th e p reced in g m o n th a n d for th e

A n a ly tic a l E d itio n n o t la te r th a n th e 3 0 th of th e p re c ed in g m o n th . C laim s fo r m issing n u m b e rs will n o t be allow ed (1) if receiv ed m o re th a n 60 d a y s fro m d a te of issue (ow ing to th e h a z a rd s of w a rtim e d e liv e ry , no claim s c an be ho n o red fro m s u b sc rib e rs o u tsid e of N o rth A m erica), (2) if loss was d u e to fa ilu re of n o tice of c h an g e of a d d re ss to be re c eiv ed b efo re th e d a te s specified in th e p re c ed in g sen te n c e , or (3) if th e re a so n fo r claim is “ m issing fro m files’*.

A n n u a l su b sc rip tio n — In d u s tria l E d itio n a n d A n a ly tic a l E d itio n sold . o n ly as a u n it, m em b ers $3.00, n o n m e m b e rs $4.00. P o sta g e to c o u n trie s n o t in tn e P a n -A m e ric a n U n io n $2.25; C a n a d ia n p o stag e S0.75. Single copies—

c u rre n t issues, In d u s tria l E d itio n $0.75, A n a ly tic al E d itio n $0.50; b a ck n u m b e rs, In d u s tria l E d itio n $0.80, A n a ly tic a l E d itio n p rices on re q u e st;

special ra te s to m em bers.

T h e A m erican C h em ical S ociety also p u b lish e s Chem ical a n d E ngineering N ew s, Chemical A bstracts, a n d J o u rn a l o f the A m erica n C hem ical Society.

R a te s on re q u e st.

fears

^ y V la d e r s o f c f m e (C e n tr ifu g e s f o r Q l lo r e ill a n ^ f f o r h j

Q/e<

I NTE RNAT I ONAL E Q U I P M E N T COMPANY

B O S T O N ,M A S S A C H U S E T T S

Precision Performance

Trained to International’s rigid standards, Molander may be fairly considered represent­

ative of American machinists at their best.

Look at his face, his posture, his hands! They speak the language of precision in a day when precision is the mother tongue of mechanical perfection. In many widely separated

fields of scientific and industrial opera­

tions Precision Performance is daily accounting for the phenomenal success

of America’s production line in the Fight for Free­

dom. To insure th at this production meets impor­

tant specifications, thousands of laboratory con­

trol tests are required daily. To develop new weap­

ons and devices of unequalled efficiency for our fighting men, monthsand even years of painstaking scientific research are necessary. Inter­

national Centrifuges—precision made

— are helping the scientist make these

outstanding contributions to victory.

N ovem ber 15, 1943 A N A L Y T I C A L E D I T I O N

THE EMIL GREINER COMPANY

161 SIXTH AVENUE NEW YO R K 13, N. Y.

Manufacturers of Precision Hydrometers, Thermometers, Scientific Glassware, Constant Temperature Equipment a n d Apparatus fo r Petroleum, General, Industrial atid Research Laboratories. Dealers in a Complete Line of Laboratory Apparatus, Chemical Reagents a n d Supplies Used in the Testing of Materials.

Some Special E. G. Co.-Built Apparatus

^ y i s

demands of quality of materials grow w ith experience from war-time conditions, specialized control apparatus to test them in the laboratory must be available. These instruments subject the product to the tough conditions of actual use under accelerated and controlled conditions.

Illustrated are:

1. British A ir Ministry Oxidation Unit for evaluating quality of aviation engine lubricants.

2. Constant Temperature Bath for use in above or below room temperatures to condition samples before test

3. U. S. Navy Work Factor Machine to determine deterioration of lubricants under an accelerated endurance test

Various other instruments of this type, as well as numerous special test assemblies, have been built singly or In quantity.

While undertaking special products of this type, our regular service of supplying government, industrial and inspec­

tion laboratories with usual requirements of standard fixed or expendable equipment has been carried on in spite of unusual demand and obstacles resulting from war-time conditions.

4.

5.

6.

MacCoull-Ryder Machine for evaluating quality of aviation engine lubricants through determination of corrosion rate of bearings. Information on re­

sistance of various bearing alloys due to corrosion can also be obtained.

Special Digestion Apparatus under conditions of controlled temperature and vacuum.

U. S. Navy Heat Fouling Unit to rate the stability of fuel oils and their tendency to form sludge, either in storage or in use.

MEETING YOUR NEEDS

c o m b u s t i o n b o a t s

Cenco Combustion Boats are made from an improved . /

ceramic mixture extremely dense in composition and

highly refractory — will withstand temperatures up to

2700 degrees

No. 26278C Cenco "Barge” is wide for larger samples. t( i l |K A It is an excellent replacement for nickel "barges” .

Size: 3-7/8 x 3 /4 x 5/16 inches. Price: 15p each; ^ — ■muniMiiin i , s

$6.50 per 50. J26278D^Boot with No. 26279A Cover

No. 26278D Combustion Boat is thin for quick heating and deep for repeated samples. Size: 3-7/8 x 1/2 x

1/4 inches. Price: $4.50 per box of 100; $35.00 per 1000.

I C E N C O - L A P P F U N N E L S

i Cenco-Lapp Buechners are separable for easy clean- ^ ^ B f l l

■ ing and low for table top use. Ground annular rims ^ ^ H | | ;!||IJ8

■ between both parts provide a seal to permit vacuum a O f

■ filtrations. No. 18598C Funnel, 3 gal. capacity, meas- ^ ^ B K

V ••

■ ures 11-3/4 inches inside diameter by 9-1/8 inches in ^ ---

B height and sells for $36.00. For a heavy, rapid filter R paper proper for this funnel, specify No. 13260, 29

B cm. % $1.35 per box of 100. 18598

| N E W S A F E T Y S I P H O N S

ff|§§[ Cenco Safety Siphons eliminate hazards in trans- 'Vi ’M d V\W^

| B ferring dangerous solutions from carboys. No pressure

is placed on the container. The flow of liquid is con- 1111

tinuous and instantly controlled. The siphon is self- s. 7~|] |88fj H H priming and fabricated from Saran tubing — highly / U 'VS! g r a H B resistant to most acids and alkalies. No. 10007 Safety H B B B 9 H \ I ^ B

H Siphon sells for $15.00. Another Safety Siphon, espe- B B B cially constructed for transferring hydrofluoric acid, is f | | | j l K | [J

W m m listed as No. 10008 at $17.00. jj f# ctN scl |1§$

| C E N C O - C A R R D E S I C C A T O R S 8

® These heavy molded glass Scheibler type desiccators ^ B g p | j> ^ ~ p M are provided with a new style cover to reduce the pos- K§7 I | \\ p |||

sibility of its breakage during handling or transporting. ^ B B l i I III \\^_

s ^ B l ^ H The safety feature of the cover is contained in three ^ B l f r S r

j l B B equally spaced lugs placed on its underside to prevent I |r^ \ \ sliding too far in any direction. A small wedge-shaped B

/ // K^Tvlf

groove extending partially across the ground surface of [l (j| _ ) p the cover will relieve any reduced pressure developed ■ f lB B F BIIIB,BaEi^ ^ S ^ S ^

—- isA within the desiccator when the cover is moved slightly. B B B

“ 1 l Y T l B No. 14545A, 100 mm. diam eter... Each, $3.00.

I pjl jl No. 14545C, 150 mm. diam eter... Each, $4.00

sci.ca. '■

i'ÂÎaKSHŒflô!

1 4 5 4 5

Ä S

C H IC A G O , IL L . 1700 Irvin g Pork Rood

Lokeview Station S C I E N T I F I C

I N S T R U M E N T S

L A B O R A T O R Y A P P A R A T U S

N e w Y o r k » .Boston • C H I C A G O Toronto • S in Francisco

MULTIPLE

L A B O R A T O R Y F U R N A C E S A R E S T A N D A R D

IN MO S T

L A B O R A T O R I E S

S 3 H ^ f l D J U T Y E I L I E ( 3 I T E S I <5 © @ E 3 I ? Ä B J i r

N ovem ber 15 1943

tu a y/ec/i.

âP uu/ne

ÜPitncefcti

ttfc/tff/

TRADE MARK

LABORATORY FURNACES MULTIPLE UNIT ELECTRIC EXCLUSIVELY

R F C . U. S. PAT. O F F

M I L W A U K E E ,

I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y Vol. 15, No. 11

f y a it e s i a t a l l p n e A A u si& i —

T h e re is a s im p le m o d ic u m of c o m m o n s e n s e in th is m a tte r of the sp e e d of p u m p in g a t r e d u c e d p r e s s u r e s . T h e p u m p th a t h a s a la r g e r free-air c a p a c ity a n d a b e tte r u ltim a te v a c u u m —

will pump faster at all pressures

Welch DUO-SEAL VACUUM PUMPS

have a pumping speed

of 14.9 Liters Per Minute at 1 Micron

w hen the pump is running at 3 0 4 R.P.M.

2 4 .2 Liters Per Minute at 1 Micron

w hen the pump is running at 5 2 8 R.P.M.

G U A R A N T E E D V A C U U M —

.05 Micron (.00005 mm Hg.)

FREE A IR C A P A C IT Y —

33.4 Liters Per Minute

O P T I M U M O P E R A T IN G SPEED

300 Revolutions Per Minute No.

• E L E C T R O N IC S

• F R E E Z IN G

• D IS T IL L A T IO N S

• D R Y IN G

O IL R E Q U IR E D

T his va lu a b le B o o k le t FREE.

Write fo r Y our Copy.

I t s 32 p a g e s t e l l a ll a b o u t W e lc h D u o - S e a l P u m p s a n d V a c u u m T e c h n iq u e .

650 ml. Duo-Seal Oil

DUO-SEAL PUMP, Motor Driven. Vacuum to less than .05 micron and free air capacity of 33.4 liters per m inute... $140.00.

Also supplied with a larger motor giving 57 liters free air capacity per minute and a vacuum of 0.1 micron . . . . ... $155.00.

Order notv. Prompt shipment assured.

W . M. WELCH SCIENTIFIC COMPANY

1518 Sedgwick Street

Established. 1880

Chicago 10 , Illinois, U .S.A .

N ovem ber 15, 1943 A N A L Y T I C A L E D I T I O N 9

H

s is —an im portant contribution to war industry—is n o w available. T h e d evelop m en t o f the G-E M o d el CA-6 beryllium w in d o w x-ray tube for use in th e G-E M od els X R D -1 and X R D -2 U n its perm its registration o f patterns w ith exposure tim es w hich are from three to tw enty tim es faster than was p ossib le previously.

Today, w ith G -E X -R ay Diffraction U nits, 15 to 30 m inute exposures have replaced the four to eight hour tests w hich w ere formerly routine in diffrac­

tion studies o f steel. Corresponding r e d u ctio n s in ex p o su re tim e s have materially speeded up the control o f alum inum and m agnesium refinement.

M odern, progressive analytical labora­

tories have found in the G -E X-Ray Diffraction U n its an exceedingly satis­

factory m eth od o f quantitative and qual­

itative analysis. T h e diffraction m ethod is ideal for the analysis o f solid com ­ pounds, for exam ple, because it pro­

vides inform ation n ot obtainable by con ven tional analysis w hich generally identifies elem ents present rather than com pounds.

An interesting new b ook let w hich de­

scribes and illustrates G-E Equipm ent for X -R ay Diffraction w ill so o n be available. T o make sure that you receive your copy, address your request to D e ­ partment NN411.

GENERAŁ @ ELECTRIC X-RAY CORPORATION

2 0 1 2 J A C K S O N 1 1 V D . C H IC A O O . I L L ., U . S . A .

Z ' e j f T Z uif —f a S , U fa % o**cfy

10 I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y Vol. 15, No. 11

A P P L I E D R E S E A R C H 4 3 3 6 .S A N , F E R N A N D O RD

N H---— —

L A B O R A T O R I E S , G L E N D A L E , CALIF,

R. L.

N T R O L

H A R R Y ... W. D f f T T Ü T ^ 9330 ROSELAW N AVE., DETROIT,....

Q U

P

MULTISOURCE EXCITATION UNIT FOR SPECTROGRAPHIC ANALYSIS

The ARL-DIETERT Multisource Unit is another outstanding advancement in the field of spectro- graphic equipment.

This new unit combines the sensitiveness of the arc with the accuracy of the spark. Thus, it materially improves the accuracy and widens the range of the spectrometric analysis of all mate­

rials. Improvement in accuracy is obtained be­

cause the electrical constants of inductance, ca­

pacitance, and resistance may be closely selected

and controlled over extremely wide ranges.

This means that the excitation conditions are precisely reproducible and selectable so as to produce either very arc-like or spark-like spectra depending on the requirements of the material under test.

A constant check on the fine reproducibility of the discharge is afforded by the oscillograph incor­

porated in the unit.

Write for complete details on the Multisource Unit.

Novem ber 15, 1943 A N A L Y T I C A L E D I T I O N 11

Construction

• R ugged. H e a v y s h e e t m e ta l h o u sin g encloses co u rses of selected h ig h te m p e ra tu re in s u la tin g slab s a n d re f r a c ­ to ry b rick .

• V ertical lift m e c h a n ism ra ise s d o o r so t h a t h o t sid e is alw ay s facin g aw a y fro m o p e ra to r.

• A c o n v e n ie n t led g e is re v e a le d w h e n d o o r is open.

• H eav y ro d ty p e lo w v o ltag e n ic k e l c h ro m iu m elem en ts.

E x c e lle n t fo r te m p e ra tu re s u p to 200(TF. L ong life, few re p la c e m e n ts.

• B u ilt- in tr a n s fo r m e r p ro v id e s re d u c e d voltage.

O p e r a t io n

• L in d b e rg I n p u t C o n tro l a c c u ra te ly p ro v id e s “ste p le ss”

a p p o rtio n in g of h e a t.

• In d ic a tin g p y ro m e te r re g iste rs th e te m p e ra tu re th r o u g h ­ o u t th e ra n g e of fu r n a c e ap p licatio n s.

• In d e x p o in te r o n p y ro m e te r g ives v is u a l ch e c k on f u r ­ n a c e control.

• S ig n al lig h t show s w h e n fu rn a c e is in o p eratio n .

Two S i z e s

• T e m p e r a tu re ra n g e u p to 2000°F m ax im u m .

C H A M B E R S I Z E S

B -2 4V2" w id e x 10" d eep x 4" h ig h B -6 7 % " w id e x 14" d eep x 5% " h ig h

O th e r “p e rfo rm a n c e p lu s ” e q u ip m e n t a r e th e C o m b u stio n T u b e a n d C ru c ib le ty p e fu rn a c e s as w e ll as th e c o rro sio n re s istin g H o t P la te s, a ll a v a ila b le in c o n v e n ie n t la b o ra to ry sizes. S ee y o u r u s u a l la b o ra to ry e q u ip m e n t d e a le r—he w ill g lad ly give y o u f u r th e r in fo rm a tio n a n d p rices.

L /

W ell-kn ow n Throughout the W o rld as the Leaders in D e v e l­

opin g a n d M anufacturing Industrial H eat Treating Equipment

L I N D B E R G E N G I N E E R I N G C O M P A N Y

2 4 5 0 W E S T H U B B A R D S T R E E T , C H I C A G O 12, I L L I N O I S Wh e n i t ’s a q u e stio n of p e rfo rm a n c e , d is c rim in a tin g la b o ra ­

to ry te c h n ic ia n s w ill w a n t to b e n e fit b y th e re s u lts o b ta in ­ a b le w ith th e n e w L in d b e rg B o x T y p e L a b o ra to ry F u rn a c e . A sh d e te rm in a tio n s, fusions, ig n itio n s, d ry in g p re c ip ita te s, h e a t tre a tin g sm a ll p a r ts a n d m a n y o th e r o p eratio n s, a re efficiently a n d a c c u ra te ly h a n d le d b y th is sin g le u n it.

C a re fu l d esig n a n d d u ra b le c o n stru c tio n , as w e ll as a p ­ p ea ra n c e , ad d th a t c e rta in “p lu s ” fo r w h ic h a ll L in d b e rg e q u ip m e n t is w id e ly k n o w n . L e t’s lo o k o v e r th e s e im ­ p o rta n t fe a tu re s.

A p p e a r a n c e

• S tre a m lin e d a n d clea n . A d d s to m o d e rn la b o ra to ry sta n d a rd s.

S O L D E X C L U S I V E L Y T H R O U G H L A B O R A T O R Y E Q U I P M E N T D E A L E R S

12 I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y Vol. 15, No. 11

IN THE M ARCH TO VICTORY

lOtli Exposition of Chemical Industries, Madison Square Garden. New York, December 6-11

The platinum metals are playing a p art in the war effort of trem endous im portance

— a vital role no other group of metals can fill.

At the 19th Exposition of Chemical Industries, Madison Square Garden, New Y ork, December 6-11, we shall he able to show you som ething of what we are

doing in the conversion of these metals to the needs of war.

. - The science of electronics is the m odern magic. You will he interested in / 8ee*n S bow platinum goes to m ake the fuhes that m ake the magic a reality.

’y You have read of our p aratroops landing behind the enemy lines; we can sh ° 'v y0« platinum alloy spinnerettes by m eans of which the

yarn fo r the sliroud-lines of th eir parachutes is made. T he nerve n centres of the magnetos and other electrical installations in air- If planes and PT boats are the contacts and collector rings such as f j we will show you. Platinum catalysts, used fo r such divergent If products as explosives and fo r hydrogenation in the manulac- f i tu re of vitamins are other instances where nothing else serves H — J l as well as the platinum metals. These are hut a few items of / _* g |____________ interest; there will he many more.

~"7 And you will want to ask questions. We will have repre- I sentatives in attendance able to give you whatever in f or

B mation you may need.

| D on't fail to stop at o u r Booths 118-120 when you are

§ at l^le Exposition. We will do o u r best to m ake your _____ _________ v isiflte th in te re stin g and profitable.

B A K E R & CO., INC.

1 13 A sto r | t » X o w a r k . S . X . J .

BOOTHS N os. 1 1 8 -1 2 0 M ad ison S q u a r e G a rd en , N ew Y o r k

N ovem ber 15, 1943 A N A L Y T I C A L E D I T I O N 13

HELLIGE, ^{I n c}

N e w York

COLORIMETER

The outstanding features o f this instrument are — C u p s and plungers face the o p e ra ­ tor ‘ A l l operations are made in a com fortable sitting p o si­

tion • D ee p black scales in illuminated white fields p er­

mit easy readings o f liquid depths-* O b s e r v a t io n s are m a d e in u n ifo rm a rtific ia l light, rectified b y a Co rn in g D aylite glass.

A limited num ber o f these colorimeters will be avail­

able in N ovem ber.

P ro c e s s C o n t r o l

- R e f r a c t i v e I n d e x

B e lo w : T h e Spencer R e fracto m eter w ith o u t A m ici prism s for use w ith m o n o c h ro m a tic lig h t.

In creasin gly, in d u strial lab oratories are u sin g refractive in dex m easurem ents to con trol processes. T h is procedure is recom m ended w h ere accurate results are needed q u ic k ly , w h e re sm all sam ples are an ad van tage.

R efractom eters m ay n o w be ob tain ed w it h o u t com p en satin g prism s for use w it h m on och rom atic lig h t . T h ese in­

strum ents are m ore precise, esp e cia lly for d ispersion d eterm in ation s, and e lim ­ in ate on e o f th e m an ip u la tio n s in ­ v o lv e d in ta k in g readings.

I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y Vol. 15, No. 11

Instrum ents are a v a ila b le for essen tial use.

Spencer

S C I E N T I F I C I N S T R U M E N T D I V I S I O N O F

A M E R I C A N O P T I C A L C O M P A N Y

Novem ber 15, 1943 A N A L Y T I C A L E D I T I O N 15

Sele cting the b acte ria th a t will con vert corn into b u tylen e glyc o l a t a U. S. D ep a rtm e n t o f A gricul­

ture la b o ra to ry . Butylene glycol is con ve rte d into bu tadie ne , from w hich synthetic ru b b e r is m ade.

A n o th e r e x am p le of vita l w a r p ro ce sse s in which Kim ble L a b o ­ ra to ry G la ssw a re is se rvin g.

KIMBLE LABORATORY GLASSWARE a n a ly sis an d co n tr o l. U sin g sta n d a rd w ill serve y o u w h erever y o u r p r e se n t ite m s w h ere p o ssib le m a y be im p o r - v ita l p r o d u c tio n d e p e n d s o n resea rch , t a n t in m in im iz in g d e la y s.

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K I M B L E L A B O R A T O R Y G L A S S W A R E

16 I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y Vol. 15, No. 11

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18 I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y Vol. 15, No. 11

A .H .T . C O . S P E C I F I C A T I O N

ABDERHALDEN VACUUM DRYING APPARATUS

4739-R , Fig. 2 Sh ow ing d e sic c a n t c h a m b e r d e ta c h e d su p p o rte d in m id -a ir for refillin g , etc. a n d

VACUUM DRYING APPARATUS, Abderhalden Im­

proved, A.H.T. Co. Specification.

C onsisting of D rying A p p aratu s of P yrex glass w ith dry in g cham bcr A, approxim ately 250 m m long X 26 m m m inim um inside diam eter, w ith by-pass, an d connected by ground jo in t w ith pistol-shaped dcsic- ca n t cham ber B; com plete w ith W est ty p e reflux condenser of P yrex glass an d E rlenm eyer flask, 300 m l capacity, w ith in terchangeable T joints th ro u g h o u t; m ounted on corrosion-resistant su p p o rt w ith special Spring-G rip C lam ps an d M icro B urner.

T h e by-pass for condensate resu lts in greater tem p e ra tu re u niform ity th a n w as possible in th e original execution. T e m p e ra tu re range is lim ited only by th e n um ber an d v a rie ty of co n sta n t boiling liquids w hich are available.

T h e use of th e Spring-G rip C lam p m ounted on slotted b a r w ith ad ju stab le holder p erm its d etac h m en t an d su p p o rt of th e desiccant cham ber in m id-air as shown in Fig. 2, th ereb y offering th e adv an tag es of convenient filling an d refilling of th e cham ber, of avoiding dam age from scratching or breakage w hich m ig h t re su lt from placing it on th e w ork table, and of u n d istu rb ed access to th e dry in g cham ber for delicate m anipulations. D eh y d rite, D rierite o r A nhydrone arc sug­

gested for use in th e desiccant cham ber.

See II. K . A lber, "H ygroscopic S ubstances in M icroanalysis,” M ikrochemie vercinigt m il M ikrochim icd Acta, Band X X V , Ilc ft 1-4 (1988), p. 47.

4739-R . V acu u m D ry in g A p p a ra tu s, A b d e rh a ld e n Im p ro v ed , A .H .T . Co. S p ecificatio n , as a b o v e describ ed , c o m p lete o u tfit as sh o w n in illu s tra tio n , i.e. d ry in g c h a m b e r A, d e sic c a n t c h a m b e r B, co n d en ser a n d E rle n m e y e r flask of P y rex glass w ith in te rc h a n g e a b le T / S jo in ts th ro u g h o u t, m o u n te d on s u p p o rt w ith base of C oors p o rcelain , w ith n ecessary S p rin g -G rip clam p s a n d holders, C h ro m el w ire gauze, a n d m icro b u rn e r fo r use on artificial gases u p to 600 B .T .U .; w ith 4739-W A b d e rh a ld en W eighing T u b e S u p p o rt, b u t w ith o u t w eighing tu b e s or ru b b e r c o n n ectio n s fo r b u rn e r or c o n d e n se r... $60.75

4739-R , Fig. 1

4739-W . W eig h in g T u b e S u p p o rt, A lb er, of a lu m in u m , for d ry in g h y g ro sco p ic a n d v o la tile m icro sam p les, e v a p o ra tio n of liq u id s, m o istu ro d e te rm in a tio n s , etc. T a k e s tw o w eighing tu b e s su ch as 997 7 -F or 9977-K . G ro u n d glass c a p of A lb er w eighing tu b e c an be re m o v ed a n d re sea te d in situ w ith o u t diffi­

c u lty . O verall d im en sio n s 6 % inches lo n g X l* /u in c h w ide X M in c h h ig h ... $6.50 9977-F . M icro W eig h in g T u b e , A lb er, w ith g ro u n d glass cap,

fo r d ry in g , h a n d lin g a n d w eighing hy g ro sco p ic or

v o la tile s u b sta n c e s. C h a m b e r 30 m m long X 5 m m in sid e d ia m e te r, to ta l le n g th 150 m m , w eig h t 1.5 to 2 g ra m s; in a cc o rd a n c e w ith sp ecificatio n s of A .C .S.

... $1.30 9 977-K . M icro W eig h in g T u b e , L ieb a n d K ra in ic k , w ith o u t

glass sto p p e r. C h a m b e r 25 m m long X 4.5 m m in sid e d ia m e te r, to ta l le n g th 155 m m , w eig h t 1.0 to 1.5 g ra m s; in acco rd a n c e w ith A .C .S . sp ecifications.

See H . Lieb a n d H . G . K ra in ic k , ATikrochemie, Vol. 9 (1931), p. 3 6 7 ... $.50

ARTHUR H. THOMAS COMPANY

R E T A I L — W H O L E S A L E — E X P O R T

L A B O R A T O R Y A P P A R A T U S A N D R E A G E N T S

W E S T W A S H I N G T O N S Q U A R E , P H I L A D E L P H I A 5, U. S. A.

Cable Address, “ Balance,” Philadelphia

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 BY 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 • W A L T E R J . M U R P H Y , E D I T O R

INFRARED SPECTROSCOPY Industrial Applications

R. Bowling Barnes, Urner Liddel1, and V. Z. Williams

ST AM FORD RESEARCH LA BO R A T O RIE S, A M E R IC A N C Y A N A M ID C O M P A N Y , STA M FO R D , C O N N .

Infrared spectroscopy has proved a powerful tool in solving problems of organic chemistry and finds a w idening field in industry. The theory of infra­

red absorption and its relation to m olecular struc­

ture are discussed to provide the essential back­

ground for detailed descriptions o f techniques

useful in analysis. Finally a library of 36 3 representative spectrographs of organic com­

pounds taken in the rock salt region of the infra­

red spectrum is presented for comparison with those obtained from unknow n com pounds under investigation.

T

trib u tio n s of physicists to th e chem ical in d u stry . M any im p o rta n t problem s, w hich h a d previously been atta c k e d solely b y chem ical m ethods, are now being stu d ied an d solved by th e m ethods of both physics an d chem istry o r by th e tools of physics alone. P hysical in stru m en ts in increasing v ariety — am ong th em op tical an d electron m icroscopes, m ass spectrom ­ eters, Geiger counters, polarographs, colorim eters, an d optical spectrom eters of m a n y kinds— are proving m ore useful every d ay as th e ir p o ten tialities an d capabilities are te ste d an d proved.

T h e approach of th e p h y sicist to a problem is in h eren tly dif­

feren t from t h a t of th e chem ist. T h e physicist concentrates upon th e physical ch aracteristics of th e m aterial itself, its a b ­ sorption spectrum , x-ray diffraction p a tte rn , exact m ass, elec­

tronic configuration an d properties, w hereas th e chem ist studies th e m aterial in reaction w ith o th e r substances. F ro m these re­

actions th e chem ist deduces a w ealth of inform ation relatin g to th e original m aterial in question. H is a p p a ra tu s in general is relatively sim ple. On th e o th er hand, th e physicist m ay require e lab o rate a p p a ra tu s of special design, b u t once th is a p p a ra tu s is constructed, its applications are versatile and th e p h y sicist’s m ethods becom e d irect, accu rate, rapid, and usually require only sm all sam ples. F o rtu n a te ly , th e results o b tain ed from these tw o m ethods of approach su p p lem en t each o th er a n d suffice in m ost cases to furnish th e desired inform ation.

W h eth er o r n o t one agrees th a t th is is “ a physicist's w ar” , cer­

ta in ly it is a tim e w hen physical in stru m en ts are of enorm ous 1 Absent on leave.

usefulness. D evices capable of a u to m a tic op eratio n h ave al­

read y proved th e ir m erit in p ractically every field of endeavor.

I n th e chem ical ind u stry , to d a y m ore th a n ever before, is the need for speed an d accuracy keenly felt. T h e urgency of th e de­

m an d s for m ultiplied p roduction an d th e strin g e n t shortage of m anpow er have necessitated ab b rev iatio n of th e usual sequence from th e research lab o rato ry th ro u g h th e pilot p la n t to th e final production. S h o rt cuts m u s t be ta k e n an d som etim es the pilot- p la n t stag e m u s t be elim inated entirely. T h e p roduction engi­

neer m u s t h ave im m ediate an d continuous checks on th e q u ality of his p ro d u c t in order to d u p licate efficiently the results of th e re­

search laboratory. D elay in o b tain in g an aly tical resu lts quickly m ig h t lead to th e w aste of large q u an tities of valuable raw m ate­

rials and products. H ere th e saving of tim e by th e p h y sicist’s m ethods is proving invaluable. B u t here, too, th e problem s of th e in d u strial physicist are g re a tly m ultiplied. H e m u st n o t only a d a p t his tools o r in stru m en ts to solve specific problem s un d er ideal conditions in th e research la b o rato ry , b u t he m u st also m odify th e m to function dep en d ab ly u n d er conditions of production analysis an d control.

A ty p ical application of physics on a w idening scale in industry is infrared spectroscopy. One of th e first in d u strial infrared spectrom eters w as co n stru cted in th is lab o rato ry in th e la tte r p a r t of 1936. N um erous applications of th is in s tru m e n t have been em in en tly successful a n d h av e becom e fam iliar to a large num ber of chem ists. D aily, th is tool is perform ing analyses im ­ possible b y an y o th e r m ethod. M ore com m on analyses are being com pleted in a few m in u tes w hich previously required hours.

6S9

660 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 V o l.-15, No. 11 In te re s t in th e p o ten tialities of th is physical tool has becom e so

w idespread th a t in frared spectrom eters m ay now be found in th e laboratories of a n im pressive list of A m erican com panies, an d th e tim e will soon arriv e w hen such in stru m en ts will be sta n d a rd e q u ip m e n t in m ost lab o rato ries a n d plants.

T h e underlying basis of applied infrared spectroscopy is the fa c t t h a t practically all organic substances possess selective a b ­ so rp tio n a t certain frequencies in th e in frared po rtio n of th e elec­

trom agnetic spectrum . E xperim entally, as will be show n be­

low, a sp ectro m eter is used to determ ine th e p er cen t tran sm is­

sion o r ab so rp tio n of th e sam ple a t a series of narrow frequency intervals th ro u g h o u t a chosen p a r t of th e spectrum . A p lo t of these transm ission or absorption values versus frequency or w ave-length u n its co n stitu tes an in frared sp ectru m , w hich is c h aracteristic of th e sam ple being stu d ied an d w hich m ay be used to describe th e sam ple in m uch th e sam e m an n er as boiling point, refractive index value, o r m elting p o in t. B ecause th e in­

div id u al absorption b an d s of w hich such sp ectru m is composed arise from th e m u tu a l m otion of th e atom s w ith in th e molecule, these spectral ch aracteristics b e a r a d irect relationship to the atom ic m asses, th e m olecular configuration in space, a n d the b inding forces p resen t.

A pplications of in frared spectroscopy can be divided into tw o general categories, q u alitativ e an d q u a n tita tiv e .

Q U A L I T A T I V E A P P L I C A T I O N S O F I N F R A R E D S P E C T R O S C O P Y

(a ) "F in g e rp rin tin g " of com poun ds

T he in frared ab sorption spectrum of a given com pound is a unique fingerprint w hich can n o t be d u p licated by an y o th er com­

pound. T h is ch aracteristic is invaluable in identifying u n ­ know ns. Once a large lib ra ry of ab sorption curves for know n com pounds has been am assed, freq u en tly only m in u tes are re­

quired to m a tc h th e ab sorption sp ectru m of an unknow n w ith one of th e know n curves. E v en in cases w here no satisfacto ry m atch is found, assurance t h a t th e unknow n is n o t one of a list of know n com pounds is useful inform ation.

Since th e sam ples required are sm all a n d are in no w ay d am ­ aged o r harm ed, th is m eth o d of analysis is p a rtic u la rly useful in connection w ith chem ical research where lim ited am ounts of m aterial are available.

(b ) Recognitio n of specific chemical bonds, linkages, or groups

C om parisons of sp ectra of large num bers of pu re com pounds have show n t h a t ab sorption bands occurring a t certain frequen­

cies can be correlated w ith certain bonds o r atom ic groups w ithin th e molecule. F o r exam ple, a glance a t a n absorption spectrum gives an indication of th e presence o r absence of such groups as O—H , N —H , C = N , C==0, C H S, etc. O bserved absorption characteristic of h y d ro carb o n u n sa tu ra tio n can be ascribed to e ith e r alip h atic o r aro m atic stru ctu res. M ore p articu larly , the position of th e ab sorption b a n d of a carbonyl group in general in­

d icates w h eth er i t form s p a r t of a n an h y d rid e, ester, ketone, al­

dehyde, o r acid. T h e ap pearance of th e “m e th y l b a n d ” dis­

tinguishes betw een th e term in al m eth y l groups o f a stra ig h t chain a n d a n isopropyl o r te r tia ry b u ty l group. A lthough all the s tru c tu ra l u n its of a sam ple m ay n o t be determ ined in this m anner, a t le a st a considerable n u m b er of th e m ore com m on ones can be identified.

(c) G ross structural features

T h e ap p earance an d analysis of th e ab so rp tio n sp ectru m can often be used to determ ine o r verify th e sp a tia l configuration of th e atom s w ith in a molecule. E xam ples are cis-trans or ortho-, m eta-, a n d para-isom erism , th e p la n a rity of th e aro m atic ring, keto-enol tau to m erism , hydrogen bonding, etc.

(cf) Q ualitative analysis of mixtures

E x ccp t in special cases of strong interm olecular interaction, the ab sorption sp ectru m of a m ixture is eq u iv alen t to a simple superposition of th e sp e c tra of its individual com ponents. H ence it is possible, b y com paring th e spectrum of a m ix tu re w ith the lib rary of sp e c tra of pu re com pounds, to determ ine n o t only the com ponents b u t also th eir relative concentrations.

Q U A N T I T A T I V E A P P L I C A T I O N S O F I N F R A R E D S P E C T R O S C O P Y

(a ) A n a ly s is

A m ixture of m aterials can be analyzed quickly a n d accurately so long as th e com ponents p resen t in th e m ix tu re are know n.

F ro m a stu d y of th e sp e c tra of th e know n com pounds, it is usually possible to find a frequency a t w hich only one com ponent possesses stro n g absorption. B y se ttin g th e sp ectro m eter a t th is p a rtic u la r frequency an d com paring th e ab so rp tio n of an un­

know n w ith t h a t of know n prep ared sta n d a rd s, th e a m o u n t of th e p a rtic u la r com ponent in th e unknow n can be determ ined. U su­

ally a n o th e r ch aracteristic frequency can be found for each of th e o th e r com ponents. T h is rap id m ethod, modified su itab ly to m e e t existing conditions, h as been applied w ith a n accuracy of 1 p er cent or b e tte r to a g reat v a rie ty of m ixtures from simple ones of tw o hydrocarbon com ponents to complex m ixtures con­

tain in g up to six terpenes. I t is p articu larly useful for analyzing close boiling isomeric m ixtures for, as m entioned above, th e ab­

sorp tio n sp e c tra are functions of geom etrical configuration and are n o t related to boiling points. A ch aracteristic curve of a b ­ sorption versus concentration show s th e m eth o d to be p a rtic u ­ larly accu rate for m easuring sm all am o u n ts of im purities, such as w ater in oils, oxidation p roducts, etc.

(b) M easurem ents of reaction rates

T h e principle outlined above can be used for m easuring rates of reaction o r polym erization as a function of tem p eratu re, pres­

sure, o r th e c a ta ly st used. Sam ples m ay be ta k e n from th e re­

a ctio n cham ber a t su itab le tim e intervals, a n d th e am o u n ts of th e re a c ta n ts consum ed a n d new p ro d u cts form ed quickly d eter­

m ined. Since th e a m o u n t of sam ple required is so sm all (less th a n 1 gram ) its rem oval from th e reactin g m ass has a negli­

gible effect on th e reaction.

(c) Determ ination of therm odynam ic data

A know ledge of th e exact values of th e in frared absorption fre­

quencies provides p a r t of th e inform ation needed for a m a th e ­ m a tic a l calculation of th e th erm o d y n am ic co n stan ts of th e m a te ­ rial.

(cf) Process analysis and control

T h e an aly tical m eth o d s described can be used in th e p la n t as well as in th e research lab o rato ry . Small, s tu rd y spectrom eters w hich can be s e t a t fixed frequencies have been co n stru cted for such w ork. F req u en tly , such control analyses m ay be m ade from a by-pass in th e p ro d u ctio n line to give a continuous record of th e co n cen tratio n of one com ponent as a function of tim e. T h e o u tp u t of th ese spectrom eters is a n electrical cu rren t, w hich m ay be used to provide a u to m a tic control th ro u g h su itab le relays.

T he basic m eth o d s described in th is p a p e r h ave been in use in th ese lab o rato ries since 1937, an d are considered to be especially valuable in th e p resen t em ergency. T h is p ap er provides w ork­

ing descriptions of th e various experim ental techniques involved an d a brief discussion of th e th eo retical basis of in frared spec­

troscopy. W ith in th e scope of a single paper, how ever, no a t ­ te m p t can be m ade to p resen t a com plete su rv ey of th is field, nor to describe each of th e m a n y ty p es of in stru m en ts now in use.

R a th e r, th e co n te n t is restricted to a discussion of th e applica­

N ovem ber 15, 1943 A N A L Y T I C A L E D I T I O N 661 tions m ad e in th is lab o rato ry . O bviously, one of th e fundam en­

ta l requirem ents for th e successful application of infrared spec­

troscopy is a knowledge of th e ab so rp tio n sp e c tra of a large n u m ­ ber of pu re com pounds. A ccordingly a lib ra ry of 363sp ectra has been included.

E X P E R I M E N T A L E Q U I P M E N T A N D T E C H N I Q U E

A g rap h of th e com plete electrom agnetic sp ectru m is given in F igure 1. T h ro u g h o u t th e sp ectru m th e fu n d am en tal relation­

ship holds: \v — c, w here X is th e w a v e le n g th of th e rad iatio n , v is th e frequency of v ib ratio n , a n d c is a universal co n stan t, th e velocity of light. Because of th e various in teractio n s of electro­

m agnetic ra d ia tio n w ith m a tte r, each p o rtio n of th e spectrum is of in te re st an d value to th e in d u strial physicist.

T h e in frared p o rtio n of th e sp ectru m extends from th e long w ave-length lim it of sen sitiv ity of th e h u m an eye to th e region of u ltra sh o rt radio w aves— t h a t is, from a b o u t 7500A. (0.75^m)

to a b o u t 350,000A. (350m). T h e u n its m ost often used in desig­

n atin g po rtio n s of th e infrared sp ectru m are : w ave-length unit, m icron o r ^m ( 1m = 1 0 , 0 0 0 Á. = 1 0 “ ‘ cm .); an d so- called frequency u nit, w ave n u m b er or cm .-1 [1 cm .-1 = 1/X (cm .)].

T h e various subdivisions of th e in frared sp ectru m are shown in F igure 1 w ith d o tte d lines a n d are described above th e g rap h . W ithin very approxim ate lim its these are : th e p h o to ­ graphic region from 0.75^mto 1.3^m; th e overtone region from 1.3^m to 2.5m! th e fu n d am en tal v ib ratio n region from 2.5mto a b o u t 25m; an d th e ro ta tio n a l region from 25m to 350m. A lthough each is im p o rta n t a n d capable of yielding m uch valuable inform a­

tion, p rim ary in te re st centers in th e fu n d am en tal v ib ratio n re­

gion. B ecause of th e lim itatio n s of rad iatio n sources an d prism m aterials, a portion of th is range, from 2.5^m(4000cm .-1 ) to 15^m (667 cm .-1 ), has been m o st thoroughly investigated.

T h e infrared sp ectro m eter used in w ork in th is field consists essentially of: (1) a source em ittin g a continuous range of wave lengths desired; (2) a dispersing m ean s2 to spread o u t th is ra d ia ­ tion in ord er to provide narrow w ave-length bands a t accurately know n w ave-length positions; (3) a m eans for interposing a sam ple of su itab le thickness into th e p a th for th is rad iatio n ; an d (4) a d e te c to r an d am plifier to m easure accu rately th e in­

te n s ity of ra d ia tio n in each narrow band. In d icativ e of th e diffi­

culties of in frared technique is th e fa c t t h a t no stan d ard iz ed re­

search spectrom eters are available to d ay . I n other, branches of spectroscopy, it is cu sto m ary to m en tio n a m edium H ilger, a large B ausch & Lom b q u a rtz spectrograph, o r a G eneral Elec­

tric recording sp ectro p h o to m eter a n d le t a reference to th e lite ra ­ tu re suffice as a description of th e in stru m en t. I n c o n tra st to this, th e various in frared laboratories use in stru m en ts con­

stru c te d according to th e in d iv id u al ideas, designs, an d dem ands of each in v estig ato r. U n fo rtu n ately , th is p ap er can n o t include descriptions of all th e various types of in stru m en ts in use, n o r can i t single o u t a n y one as being th e best. H ow ever, a discus­

sion is given of th e sp ectro m eter w hich was used in o b tain in g th e ab so rp tio n sp e c tra given below.

T H E S P E C T R O M E T E R

A schem atic draw ing of th e optical p a th of th e sp ectro m e ter is show n in F ig u re 2. T h e source is an electrically h e a te d com m er­

2 T h o d isp e rsin g m e d iu m m a y b e e ith e r a g ra tin g o r a p ris m . A g ra tin g p ro v id e s g r e a te r d isp ersio n b u t its use in v o lv es m o re e x p e rim e n ta l diffi­

c u ltie s b e ca u se of th e n e ce ssity of e lim in a tin g h ig h e r o rd e r r a d ia tio n . F o r th is re a so n p rism s a r e m o re g e n e ra lly used in in d u s tria l s p ec tro sc o p y . A lis t of p rism m a te ria ls to g e th e r w ith th e ir lo n g w av e-len g th tra n sm issio n cutoffs is ■ g iv en (glass 1.5/i, q u a r tz 3/i, lith iu m fluoride 5/i, flu o rite 9/¿, so d iu m ch lo rid e 15/i, a n d p o ta ss iu m b ro m id e 25/i). Id e a lly , b e s t d isp ersio n is o b ta in e d b y u sin g one m a te ria l u p to its cu to ff a n d th e n sw itch in g to th e n e x t m a te ria l. F o r a sin g le p ris m in s tru m e n t, ro c k s a lt is m o st g e n erally used b e ca u se i t p ro v id e s th e b e s t c o m b in a tio n of d isp ersio n a n d accessible region.

cial G lobar (a silicon carbide rod) h aving a pow er consum ption of a b o u t 400 w a tts a t 115 v o lts controlled b y a voltage regulator.

T h e G lobar is th in n ed in th o c en tral section in o rd er to raise th e in te n sity of ra d ia tio n from th e a c tu a l source area. T h e rad ia­

tio n from th is source is reflected by th e plane m irror, M i, to the spherical m irror, M 2, w hich focuses th e beam a t th e position m arked “ cell” . T h e sam ple is in tro d u ced here by m eans of an electrically d riv en w ay w ith th ree sto p positions so t h a t a sh u tte r, ab sorption cell, or a control cell can be placed in th e sam e posi­

tio n in th e light p a th . T h e ra d ia tio n tra n sm itte d th ro u g h th e cell is th e n focused b y M t on th e en tra n c e s lit a t S . S is a double slit h aving a com m on cen te r a n d tw o m ovable o u te r jaw s.

T h e en tran ce slit is curv ed to com pensate for th e im age c u rv a­

tu r e introduced b y th e prism s. T h e ra d ia tio n from S en te rs the sp ectro m eter p ro p er th ro u g h a slo t in th e plane m irror, M t, is ren d ered parallel b y th e spherical m irror, M \, w hose focal length is 40 cm . T he beam of ra d ia tio n is given its first dispersion on passing th ro u g h th e tw o prism s, a n d is th e n reflected back th ro u g h th e prism s by th e plane L ittro w m irror, Me, for a second dispersion. T h e dispersed beam trav erses th e p a th from P i to M s to M t, th ro u g h th e slo t in M i, a n d passes o u t th ro u g h th e exit s lit a t S . T ho m echanical w id th s of th e tw o slits control the w id th of th e sp e c tra l b an d an d th e w ave length or frequency of th e b a n d cen te r is determ ined by th e ro ta tio n a l settin g of th e L ittro w m irror, M 6. T h e narrow b an d of energy em erging from S is th e n reflected a t a sm all angle by th e plane m irror, M i, to th e elliptical m irror, M%, w hich focuses a greatly reduced im age of th e ex it slit, S , o n to a com pensated, v acuum therm ocouple.

T h e en tire in stru m e n t, except for th e source an d th e ab sorption cell, is housed in a n a irtig h t alum inum case whose in terio r is freed of w a te r v ap o r an d carbon dioxide. F o r th is purpose, air purified over large q u a n titie s of phosphorus pentoxide an d soda lim e is supplied a t in terv als b y a circulating system . T h e ra d ia ­ tio n from th e source en te rs a n d leaves th e sp ectro m e ter case th ro u g h rock s a lt w indow s.

J"rrT— — r—

NUCLEAR

RAYS X-RA y IH.TFAVKX.ET ! ! WRARCO ! RA040

J* ia n* too* ooo* ip n u a i mi in

KfiOO A MX>M

Fi g u r e 1. Gr a p h o f t h e El e c t r o m a g n e t i c Sp e c t r u m

Since these in frared rad iatio n s can n o t be photographed and th ere is no photoelectric elem ent sensitive to th is p a r t of th e spec­

tru m , th e d e te c to r m u s t of necessity be som e ty p e of therm osensi­

tive elem ent, such as a therm ocouple, bolom eter, o r radiom eter.

T h e order of m ag n itu d e of th e energies involved illu strates the difficulties encountered in in frared spectroscopy, a n d accounts for th e slow progress in th is field as com pared w ith o th e r branches of spectroscopy. T h e average energy in th e dispersed beam pro­

duces a voltage a t th e therm ocouple of a b o u t 1 m icrovolt (10~‘

v o lt).3 Since th e therm oelectric coefficient of th e elem ents u sed is of th e order of 100 m icrovolts p er degree centigrade, this rep resen ts a te m p e ra tu re difference betw een h o t a n d cold ju n c ­ tions of th e therm ocouple of roughly 0.01 ° C. Since, as will be seen later, it is necessary for p ractical purposes t h a t energies of th is order of m ag n itu d e be m easured w ith a n accuracy of 0.5 per cent, th e lim it of erro r m u s t be n o t g re a te r th a n 5 X 10-5 ° C. Sm all changes in am b ien t te m p e ra tu re are m inim ized by using a tw o ju n ctio n couple connected in series opposition, only

J E le c tro n ic a m p lific a tio n of th is o u tp u t is d ifficu lt b e ca u se of th e low re s ista n c e (10-20fi) a n d th e slow p e rio d (one second) of th e a v e ra g e th e rm o - couple.