,, "V
INDUSTRIAL a n d ENGINEERING CHEMISTRY
A N A L Y T I C A L E D I T I O N
V O L U M E 18, N U M B E R 12 IS S U E D D E C E M B E R 18, 1946 C O N S E C U T IV E N U M B E R 24
Assistant to Ed ito r: N . A . PARKINSON
Manuscript Editing: G . GLADYS GORDON
R. P. CHAPMAN J. R. CHURCHILL B. L. CLARKE
E D IT O R : W A L T E R J, M U R P H Y
Associate Editor: LAWRENCE T. HALLETT Assistant Editors
Manuscript Reviewing: STELLA ANDERSON A dvisory Board
T. R. CUNNINGHAM G. E. F. LUNDELL M. G . MELLON
Contributing Editor: R. H . MÜLLER
M ake-up: CHARLOTTE C . SAYRE
R. H. MULLER B. L. OSER H. H. WILLARD
Quantitative A n alysis of Hydrocarbon Mixtures by M eans of Raman Spectra ... .... ...
E. J . Rosenbaum, C . C . M artin, and J . L. Lauer 731 Operating Characteristics of Sargent M o d el X X V isib le
Recording Polarograph...J . J . Lingane 734 Autom atic Determination of A n ilin e Point of Petroleum
Products...C . W . Brown 739 Automatic-Recording Ultraviolet Photometer for Laboratory
and Field U s e ...I. M . Klotz and Malcolm Dole 741 Quantitative A n aly sis of Isomeric Cresols and Cresol-Phenol
M i x t u r e s ... ....
W . W . Robertson, Nathan Ginsburg, and F. A . Matsen 746 Estimation of Moisture in Solventless Double-Base Powders
John Hardy, W . D. Bonner, J r ., and R. M . Noyes 751 Bromination of Phenols and Phenol A lco h o ls . . . .
I. W . Ruderman 753 Determination of Calcium in Magnetite and Fused Magnesia
W . M . Hazel and W . K. Eglof 759 Effect of Uniform versus Intermittent Product Withdrawal
from Distillation Colum ns... ...
D. M . O ldroyd and L. A . Goldblatt 761 Determination of 1-Trichloro-2,2-bis(p-chlorophenyl)ethane
in D D T Dusts and O i l Solutions . . . . J . B. LaC lair 763 Rapid Electrometric Determination of A lk a lin ity of Sea
Water Using Glass Electrode . . . ...
D. H . Anderson with R. J . Robinson 767 Accelerated O zo n e Weathering Test for R u b b e r...
James Crabtree and A . R. Kemp 76 9 Determination of Relative A c id ity of W ood and Adhesive
J o i n t s F. A . DeMarco and E. A . Smith 775
The American Chemical Society assumes no responsibility for the statements and opinions advanced by contributors to its publications. V ie w s expressed in the editorials are those of the editors and do not necessarily represent the official position of the Americon Chemical Society.
Determination of Dipcntaerythritol in Mixtures of Penta- erythritol and D ip e n tae ryth rito l J . A . W yler 777 Measurement and A n aly sis of Gases in Vacuum-Packed
Food Containers . . . ...L. C . Cartwright 7 7 9 Determination of Egg Y o lk In Egg W h i t e ...
J . H . Cook and V . C . Mehlenbacher 785 Determination of Boric O x id e in G la s s ...
M ax Hollander and William Rieman III 788 p H of W in e s...J . C . M . Fornachon 790 M IC R O C H E M IS T R Y
lodometric Microtitration for Mustard G a s ...
V . E. Kinsey and W . M . G rant 794 Source of Error in G u tzeit M ethod for A rsen ic . . . .
N . I. Goldstone 797 Volum etric Determination..of...Water in Paints and V a r
nishes M . H . Swann 799
N O T E S O N A N A L Y T I C A L P R O C E D U R E S
Precise Low-Pressure Measurements with Thermocouple G a g e ...W . G . Smiley 800 Determination of G o ld with A sco rb ic A c i d ...
E. C . Stathis and H . C . Gatos 801 Preparation of Standard Powders for Reference in Particle-
Size M e a s u r e m e n t ...
E. L. Gooden and R. L. Updike, J r . 802 B O O K R E V I E W ...802 Author Index...803 Subject Index...807 Instrumentation in A n aly sis . . R. H . M 'uller (A d v t. Sect.) 23
W e acknowledge w ith thanks the action of J . T. Baker Chemical C o . In releasing the front cover o f this issue for editorial purpo ses.
Copyright 194 6 by American Chemical Society.
3 7 ,0 0 0 copies of this issue printed.
Published by the American Chemical Society at Easton, Pa. Editorial Head
quarters: 1155 16th Street, N . W ., Washington 6 , D. C .; telephone, Republic 5 301;
cable, Jiechem (Washington). Chicago Editorial Branch: Room 8 1 9 , 25 East Jackson Blvd., Chicago 4 . III.; telephone, Wabash 7 37 6 . Houston Editorial Branch: 413 West Building, Houston 2 , Texas; telephone, Capital 6 5 1 6 . N e w Yo rk Editorial Branch: 6 0 East 42nd Street, N e w York 1 7 , N . Y .; telephone, Murray H ill 2-4662.
San Francisco Editorial Branch: 24 California Street, San Francisco, C a lif.;
telephone. Exbrook 2 89 5 . Business O ffice : American Chemical Society, 1155 16th Street, N . W ., Washington 6 , D. C . Advertising O ffice : 332 West 42nd Street, N e w York 1 8, N . Y .; telephone, Bryant 9 -4430.
Entered as second-class matter at the Post O ffice at Easton, Pa., under the A c t of March 3 , 1 87 9 , as 24 times a year— Industrial Edition monthly on the 1st, Analytical Edition monthly on the 15th. Acceptance for mailing at special rate of postage pro
vided for In Section 1 10 3 , A c t of O ctober 3 , 1 9 1 7 , authorized Ju ly 1 3 , 1918.
Remittances and orders for subscriptions and for single copies, notices of changes of address and new professional connections, and claims for missing numbers should
be sent to the American Chemical Society, 1155 16th Street, N . W ., Washington 6 , i of address for the Industrial Edition must be received on or before the 18th of the preceding month and for the Analytical Edition not later than the 30th of the preceding month. Claims for missing numbers w ill not be allow ed (1 ) if received more than 6 0 days from date of issue Cowing to delivery hazards, no claims can be honored from subscribers in Continental Europe, A sia, or the Pacific Islands other than H a w a ii), (2 ) if loss was due to failure of notice of change of address to be received before the dates specified In the preceding sentence, or (3 ) if the reason for claim is
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Annual subscriptions— Industrial Edition and Analytical Edition sold only as a unit, members $ 3 .0 0 , nonmembers $ 4 .0 0 . Postage to countries not In the Pan- American Union $ 3 .0 0 ; Canadian postage $ 1 .0 0 . Slrjgle copies— current issues, Industrial Edition $ 0 .7 5 , Analytical Edition $ 0 .5 0 ; back numbers. Industrial Edition
$ 0 .8 0 . Analytical Edition prices on request; special rates to members.
The American Chemical Society also publishes Chemical and Engineering News, Chemical Abstracts, and Journ al o f the American Chemical S ociety. Rates on request.
P u r i f y d e f i n e d — n o t t o
" m a x im u m l im lt i" — b ut to t h e d e c im a l b y a c tu a l lot a n a ly s is . T h a t’s th e st o r y of t h e B a k e r 's A n a ly s e d la b e l.
LIME-ALUMINA—LIME-SILICA BALANCE
STARTS IN THE LABORATORY
The cement industry lives largely by its research and control methods. From the first fall of limestone blasted at the quarry’s face, to the final test batches from the filling bins, raw materials are constantly analyzed and finished products are searchingly inspected.
For their routine check on silica in the raws, , many cement companies employ a time- saving m ethod which involves the use of Baker’s Analyzed C.P. Perchloric Acid.
The extremely low content of silica and non-volatile m atter in this acid makes it preferable for many ether tests as well.
Baker’s Analyzed C.P. Ammonium Oxalate is often the chemist’s choice for calcium determination. This reagent is extremely low in non-soluble, non-Volatile and sulphate materials.
Baker’s Analyzed C.P. Chemicals differ from other laboratory chemicals. They have the actual analysis on the label—not mere maximum limits of impurities. This saves the chemist time when making computations.
Baker’s distributors welcome every opportunity to serve the cement industry. "When you order your reagent chemicals from your favorite supplier, be sure to specify Baker s Analyzed.’’
J . T. B a k e r Chem ical Co., Executive Offices and Plant: Phillipsburg, N . J . Branch O ffice s: N e w Y o rk , P h ilad elp h ia, Boston an d C hicago
CHICAGO APPARATUS COMPANY S S S S
D ecem ber, 1946 A N A L Y T I C A L E D I T I O N
BECKMAN pH METER
Laboratory JS/Vodcl C j
This instrum ent is recom m ended for all types of research and precise laboratory pH investigations w here maximum versatility and accuracy are essential. It is also ideal for m easurem ent of oxidation and reduction potentials.
F e a tu r e s in c lu d e :
Continuous indication of circuit unbalance (eliminates the key tapping of ballistic methods).
Built-in tem perature compensation.
Direct millivolt readings for oxidation-reduction measurem ents.
Sealed glass electrodes are small and unusually sturdy; require minimum m aintenance.
Determinations can be m ade on exceedingly small (0.005 ml) samples by the use of the proper electrodes.
Supplied ready for work in cabinet with lock and key, self contained standard cell, electronic tubes and batteries; the 2 1 / / glass-Calomel electrode assembly for pH work on 3 ml samples, buffer solution for standardizing, saturated KC1 solution for the Calomel electrode. C abinet size l l j ^ x 11 x 9 " , net weight 20 lbs.
N o. 75210 B e c k m a n pH M e te r , Laboratory Model G com plete $225.00
Available for Prompt Delivery
O F L A B O R A T O R Y F U R N A C E S
12
T H
Here a re furnaces, the like of which laboratory technicians have never seen— vastly improved in both function and ap p e a ra n ce . Engineered and built by the leaders in developing and manu
facturing industrial heat-treating equipment, they are the last word in efficient and practical lab o rato ry furnaces.
The Lin db erg Box Furnace designed for fast and accurate metallurgical tests and chemical analyses heats up to 2 0 0 0 ° F. Has built-in trans
former; "Stepless” Input Controller and Indicating Pyrometer a re contained in a se p a ra te metal case.
The Lin d b erg P o t-C ru cible Furnace does salt or lead bath immersion tempering, hardening and annealing, cyaniding and aluminum heat- treating. O n the other hand, as a crucible fur
nace, it is used for determining critical points of steel, melting base metals, thermocouple cali
brations and other necessary laboratory o p e ra tions for heats up to 2 0 0 0 ° F.
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. 18, No.
The Lin d b erg Com bustion Tube Furnace is d e signed for fast carbon and sulphur determ ina
tions using the volumetric method of analysis and for gravimetric type analyses for carbon d e terminations of all alloy steels including stainless and heat-resisting steels. Heats up to 2 5 0 0 ° F.
The Lin db erg H ot Plates are for precise, con
trolled all-round laboratory use for tem pera
tures up to 9 5 0 ° F. Built-in input control provides exact tem perature selection.
These furnaces can be secured from your laboratory equipment d ealer. See him to day for full information.
L I NDBE RG E N G I N E E R I N G C OM P AN 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 1 2 , IL L IN O IS
W E L L K N O W N T H R O U G H O U T T H E W O R L D A S L E A D E R S I N D E V E L O P I N G A N D M A N U F A C T U R I N G
I N D U S T R I A L H E A T T R E A T I N G E Q U I P M E N T
As pH problems in p lan t and laboratory grow in num ber and im portance, the M icrom ax family of instrum ents for recording and autom atic control is increasingly depended on to m eet requirem ents, w ith accuracy and de
pendability.
M ost popular Control equipm ent is a S trip -C h art M icrom ax w ith its own electric valve-drive, and w ith glass electrode selected for th e p articu lar situation. This instrum ent requires absolutely m inim um atten tio n , because it has the unique feature of standardizing itself, and its supplies of ch art and ink last for a m onth or more at usual operating speeds. Its wide ch a rt and rectilinear coordinates appeal strongly to the record- m inded engineer.
F or highest visibility, plus a circular ch art, the R ou nd -C h art M icrom ax is used. Its record is outstanding am ong circular charts because its radial lines are perfectly straig h t, and thus really easy to read.
I f you will send a chemical engineering description o f p H conditions in your lab or p lan t, we can probably recomm end specific instrum entation.
O r request C atalog N -9 6 (l), if you prefer.
L E E D S 4 N O R T H R U P COM PAN Y, 4920 STEN TO N A V E., P H IL A ., PA.
LEEDS & N O R TH R U P
^SURING IN STR U M EN TS • T E L E M E T E R S
». Ad XT r\n f f\
AUTO M ATIC CO N TRO LS • H E A T -T R E A T IN G FU RN AC ES
D ecem ber, 1946 A N A L Y T I C A L E D I T I O N
pH INSTRUMENTS
To Match Most Needs
8 I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y Vol. 18, No. 12
PYREX
L*a t.
"Mr. Service of Corning Glass to see you" . .
BACK
FROM THE WARSand back on the job a re most of the C om ing Field Re
search an d Service men. Right now they are undergoing a "refresher course” h e re at the factory brushing up on all the new developments while they w ere away.
Soon, however, they will b e out on the road—calling on users of "Pyrex," "Vycor"
an d "C orning" Laboratory Glassware.
These m en are direct factory representatives. They come to serve—not to sell.
To b ring you news of recent improvements, new discoveries, new methods. To obtain from you your opinion of recen t developments an d how C orning c an m ake them still better.
Each m an is a trained technician. H e speaks your language. H e understands your problems. His work combines both Field Service and Field Research. H e calls on you in your laboratory to determ ine how Corning can serve you better. And, equally important, to gain new ideas, new suggestions from you. For from these first h an d contacts of our field representatives has come th e inspiration—the start—of m uch Corning Research in Glass—research that has constantly im proved laboratory glassware and laboratory technique.
The card of the C orning field contact m an is a card of cooperation. Any time you spend with him will, we know, b e of m utual benefit.
P y r e x is a r e g is te r e d tr a d e m a r k a a d i n d i c a te s m a n u fa c tu r e b y
C O R N I N G G L A S S W O R K S , C O R N I N G , N E W Y O R K
PYREX
F O R A L L - A R O U N D U S E . . . Y E A R ’ R O U N D E C O N O M Ybrand LABORATORY OLA S S WARB
-means---
Research in Glass
D ecem ber, 1946 A N A L Y T I C A L E D I T I O N 9
BURRELL G A S A N A L Y S I S A P P A R A T U S
P ortable Build-Up models are m ounted on a sto u t oak base and m ay be bad w ith or w ithout the carrying case.
For complete information on all types of Burrell Gas A nalysis A pparatus write fo r Catalog 80.
d a 3 2
1 9 4 2 F I F T H A V E N U E P I T T S B U R G H 1 9 , P A .
A FLU E G A S A N A L Y Z E R F O R S T A C K A N A L Y S IS
from Plant Control
. . . to Labora tory Precision
A P P A R A T U S for the analysis o f gases by absorption and combustion m ethods are divided into two general types, laboratory and portable models.
L abo ratory models are more precise while portable models are relatively sm aller, more com pact and sim pler to m anipulate.
The popular Build-U p* frame for both laboratory and portable models comprises standardized parts — clam ps, bases, rods, sup ports—which can be assembled to carry any selection of stan d ard gas analysis glass
ware. T his feature perm its the analyst to choose an ap p aratu s exactly to fit his needs and ju s t as im portant to quickly alter the assem bly should necessity arise.
* T ra d e m a rk reg istered U .S . P a te n t Office.
A L A B O R A T O R Y B U IL D - U P M O D E L F O R P R E C IS IO N A N A L Y S IS
A P O R T A B L E B U IL D - U P M O D E L F O R PLA N T C O N T R O L
H eavy bases in the B uild-U p laboratory models provide stab ility and preclude the necessity of fastening to the bench top. Alum i
num cross tubes are extra long to perm it expansion of the app aratu s if desired. Glass
ware m ay be added or removed w ithout dism antling the frame.
T he Flue Gas A nalyzers are
designed especially for th e
analysis of flue or stack gases,
b u t m ay be used w herever
th re e g a se o u s c o m p o n e n ts
are to be d e te rm in e d by
absorption.
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. 18, No. 12
LABORATORY
Silicone V acuum G rease especially d esigned lor use in high vacuum systems. Of heavy w eight an d w ith exceptional film strength it is further ch aracterized by its h eat stability, low vapor p ressu re and chem ical resistance.
No. 15517 D ow-Corning Silicone V acuum L ubricant
S iz e ... ... A B S iz e tu b e o u n c e s ' ... 2 8 Price, e a c h ... 1.2 5 4 .5 0 No. 27134 G . E. Zahn V iscosim eter convenient for controlling viscosities of paints, varnishes, oils, etc. Capacity, 44 ml. O ri
fice size A recom m ended for solvents, thin oils an d thin m ixtures;
B for o rdinary oil, m ixed paints and lacquers; C for heavy oil an d m ixture paints; D for ex tra heavy m ixtures; an d E for heaviest m ixtures. Price, $ 10.95.
Raney Catalyst is a finely divided alloy of nickel a n d alum inum m ade by a p aten ted process. It is in e rt an d keeps indefinitely until activated. Reactions p ro ceed at norm al pressu res in ordinary laboratory vessels.
No. 23020 Raney C atalyst
Size... A B C Contents, p o u n d s ... 2 4 10 E a c h ..,. ... 3 .7 5 6 .7 5 16.75
"G ear-A ction" Clam ps p rev en t leaky ru b b e r tu b in g connections.
Can be attach ed w ithout rem oving tu b in g . No. 12177 "G ear-A ction" Clam p
S ize... A B For tubing, outside diam. in c h e s ... Y l t° M ’/ « f° l l/w E a c h ... 31 .31 The Tygomatic Pum p dispenses acids w ith ease an d safety from stan d ard 5 pin t a c id bottles. Its resistance to most acids and alkalies is excellent. No. 10006 Tygomatic Pum p—Each $4.00.
No. 18107 Cenco-Frizzell R ubber C rucible H older for holding 25 ml C o o ''h cru cib les an d sim ilar sizes of sintered-glass and o t h e r f ilte r in g c r u c ib le s in a K im b le “ 58” o r a n o r d i n a r y 60 0
f u n n e l . T h e w e t s u r f a c e s of t h e r u b b e r h o ld e r a u t o m a t ic a lly m a k e a t i g h t s e a l a g a i n s t t h e w a ll o f t h e f u n n e l a n d a g a i n s t t h e f ilte r c r u c ib le w h e n s u c t i o n is a p p lie d .
Dimensions: H eight, % inch; diam eter; top, 2 inches, bottom, l j'2 inches; the ce n te r hole tap ers from 1Y inches at the top to inches at the bottom ... Each $ .25.
CENTRAL SCIENTIFIC COMPANY
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 ■
NEW YORK TORONTO CHICAGO BOSTON SAN FRANCISCO
D ecem ber, 1946 A N A L Y T I C A L E D I T I O N
q— 9 o o o <> o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o ~ ô ô o o o c - o o o o o o o o o o o o o o a c
Now G Y C O J a c k e t s protected
um M i AU unim un R& iin
2 S ^ GYCO Jackets now feature a new smooth exterior covering of glass cloth im pregnated with an alum inum vinyl resin, highly resistant to most acids an d laboratory reagents . . . a t no extra cost. Plain glass fabrics used to cover heating jackets have always h ad the disadvantage of bein g soiled easily, and lacked an effective cleaning method. The new GYCO H eating Jackets m ain
tain an attractive ap pearan ce despite frequent handling and long use.
In addition to flask heating jackets, the GYCO line includes jackets m ade to fit bottles, beakers, jars, funnels, B uechner funnels, resin flasks, or special shapes as ordered. GYCO Tubular H eating Jackets (shown at right) for h eating fractionating columns or tubes are available for 25, 37, 51 and 71 mm diam eters, in one an d two foot lengths, and in two styles. O bservation ports feature a built-in Pyrex window, preventing "cold spots” an d possible "flooding.”
W here internal observation is not required, GYCO provides tubular jackets without windows.
For further details, sizes an d prices of GYCO Jackets, write for Bulletin E-100.
Patent A p p lie d for
GYCO
Jackets are distributed exclusively byS C I E N T I F I C G L A S S ™ " uLsDcT E^ r ;
0o o o O O O O O O O O O O o o o o o O O O O O o p 0 0 0 0 0 < > 0 0 0 0 0 <> C><^ C, 0 C> 0 C> o O O O OcTq
o o o < > o o p o o o o o O
OOOOOOOOOOOOOOOOOOO^^^^^^^O0
. . . 7 - g a u g e C h r o m e ! heating unit assures yo u o f long , d e p e n d a b le se rv ic e .
HOSKINS MANUFACTURING CO
4 4 4 5 L A W T O N , DETROIT 8, M IC H IG A N
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. 18, No. 12
. . . T h e y o p e ra te on A .C . through a sm all tra n sfo rm e r.
...T e m p e r a t u re is a c c u ra te ly co ntrolled thru a rh e o sta t.
THESE FH -303-A
COM BUSTION FU R N A C ES CA N BE H EATED FROM
80° TO 2000° F. IN 63 MINUTES
If y o u 're in Ihe market for n ew laborato ry fu rn a ce s, y o u ’re p ro b a b ly loo king for . . . . . . equipm ent that h a s the ab ility to "g et hot" fast and hold constant tem peratures w ith m inim um p o w er consum ption.
w e ll-in su late d fu rn aces to confine Ihe h e a l to the heating cham b er for greater operating econo m y, com fort and safety.
fu rn a ces that w ill give yo u m onth after month of trouble-free perform ance at m inim um m aintenan ce cost.
. . . a n d , important, fu rn a ces equipped w ith lo n g -lastin g C H R O M EL Heating Elem ent W ire.
If these are the q u alities y o u ’ve been looking for in lab o rato ry fu rn a ces, w e invite you to in vestig ate Hoskins com bustion, m uffle a n d crucible type fu rn a ces. Y o u ’ ll find they fit the a b o v e description. Write for C ata lo g 58-R to d ay.
ELEC TR IC HEAT T R EA T IN G EU RN ACES • . P YR O M ET ER S • W ELDING W IRE
S P A R K PLUG ELECTRO DE W IR E
H EATIN G ELEM ENT A LLO Y S • . HEAT RESISTA N T C A STIN G S
S P E C IA L A LLO Y S O f N ICK EL
TH ERM O CO UPLE AND LEAD W IR E . ENA M ELIN G FIX T U R ES •
P RO TECTIO N TUBES
D ecem ber, 1946 A N A L Y T I C A L E D I T I O N 13
R E T E S T I N G
m m
K IM B LE
L A B O R A T O R Y G L A S S W A R E
Careful r e t e s t i n g o f B lu e L ine <TxIT>
a n d P r e c i s i o n
<hobmm>g r a d u a t e d ware m a k e s n o difference in o u t
w a r d a p p e a r a n c e , b u t a d d s t h a t i n v i s i b l e q u a l i t y o f
a s s u r e d a c c u r a c y .
Vol. 18, No. 12
• M o le c u la r a n d A to m ic W e ig h ts.
• C o m p r e h e n s iv e lis tin g o f M ic ro - a n a ly tic a l C h e m ic a ls , A m in o A c id s , a n d V ita m in s .
• C o n ve rsio n r a tio s .
• C h e m ic a l fo r m u la s .
W rite to d a y for you r personal co p y o f th is useful, inform ative catalog.
MERCK
LABORATORY CHEMICALS
MERCK & CO., Inc., RAHWAY, N .J .
. Ä w w i i / i
the 1 9 4 6 Merck Laboratory
Catalog
NOW AVAILABLE UPON REQUEST
Chemists in every field will be interested in these features of the 1946 edition of the Merck Laboratory Chemicals Catalog:
• A l i s t o f M e r c k L a b o r a t o r y C h e m i c a l s — u s e d i n e v e r y b r a n c h o f i n d u s tr y , e d u c a tio n , a n d r e se a r c h .
• M a x im u m i m p u r i ti e s o f M e rc k R e a g e n t C h e m ic a ls , in c lu d in g th o s e w h ic h c o n fo r m to A C S s p e c ific a tio n s .
. • P r o p e r S to r a g e o f F in e C h e m ic a ls .
N a m e ...
(Please ind icate title , if any) C om pany or O rg a n iza tio n ...
M erck & Co., Inc.
M anufacturing C hem ists R ah w ay, N . J.
P lea se send m e a to p y o f th e 1946 M erck L aboratory C hem icals C atalog.
F M -4 0 , Student M icroscope complete with Tilting Fram e, M irror, 5 X and 10X H uygenian eyepiece, convertible achro
m a tic o b je c tiv e le n s a n d h a rd w o o d carrying case.
$ 5 9 .
T h e E m i l G r e i n e r C o m p a n y n o w offers this fine.precision m i c r o sc op e, i n c o r p o r a t i n g the k i n d of f e at u r e s t h a t ar e u su al l y f o u n d in o n l y t he m os t ex pe ns iv e m i c r o scopes at a p r i c e t h a t is w e ll w i t h i n the l i mi t s of s chool a n d col lege budgets.
I n s t r u m e n t s of this t ype a nd w o r k m a n s h i p co u ld n e v e r be sold at this e x t r e m e l y
l o w p r i c e w e r e it n ot f o r t he m a n y n e w m a n u f a c t u r i n g e c o n o m i e s w h i c h w e r e d e v e l o p e d in t he w a r t i m e s p e e d u p .
features t
1. T iltin g frame.
2. Large concave mirror.
3. Full size stage with acid-resistant finish.
4. Rack and pinion coarse adustment and a new type of fine adjustment which elimi
nates all danger of damaging the objective or breaking the slide.
5. Fine optics which include a 5X and 10X Huygenian eyepiece and a convertible achro- inatic objective lens. T h e optical system gives you a great clarity of detail for either low power or high power wor.k ranging from 50X to 260X magnification.
<m> THE EMIL GRE I NE R CO.
1 6 1 S I X T H A V E N U E • N E W Y O R K 1 3 , N. Y.
‘ ' ‘
Franck Offices .* 5709
groves t .,
Oakland, cal.-5 10 9 d is t r ic t b lv d ., lo s A n g e le s,
cal.- 1 1 2
broadway.Cam bridge, m a ss .
D ecem ber, 1946 A N A L Y T I C A L E D I T I O N 15
5 YEARS of planning and engineering has developed this amazingly low-priced
Precision Microscope
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. 18, No. 12
F L A S K P R O TE C TE D by one o r m ore Layers o f glass fabric from d i
rect contact with h eat
ing elem ents. T h u s , no strains a re set u p in the flask wall which are d an gerous in high-vacuum distillation.
C L O S E FIT A R O U N D F L A S K for even heat. M antle contacts flask uniformly.
E X T R A S A F E T Y pro v ed in tests. W ire»
safely covered so inflam
m ab le liq u id s d o n o t b u rn w hen spilled.
N O H O T S P O T S O R C H A R R IN G because h e a t is evenly d i s t r i b u t e d . N o h o t wires to u ch th e flask.
NO EXPOSED HEATER WIRES
H ere is an inside look a t th e safest way to heat flasks and o th er vessels. Glas-Col H eating M antles are constructed o f glass fabric, w ith resistance wires safely covered.
T hese wires are woven thro u g h th e fabric u n d e r one or m ore layers o f p ro tec tin g glass cloth, and th e closely spaced windings at th e b o tto m o f th e h eater are fu rth e r pro tected by being individually covered.
T h i s t y p e o f c o n s t r u c t i o n w a s e v o lv e d b y G l a s - C o l a f t e r e x h a u s t i v e t e s t i n g b y m a n y o t h e r m e t h o d s . I t is t h e s a f e s t i n c a s e o f fla s k b r e a k a g e , a s s h o w n b y a c t u a l t e s t s w i t h in f la m m a b le l i q u i d s .
Glas-Col H eating M antles are available in many shapes an d sizes, to fit columns, fu nn els, an d o th e r special ap p aratu s in addition to flasks o f various constructions.
For com plete inform ation w rite for Bulle
tin 2. Glas-Col A pparatus Com pany, D e p t.
IC , 1700 S. Seventh S t., T erre H au te, In d.
E U S
ECISION
decision Scientific Compan
f y M c c n v e T O O U R N E W H O M E
W e w is h to th a n k o u r m a n y cu sto m e rs/ w h o s e c o n tin u e d u se o f " P re c is io n P ro d u c ts " h a s m a d e th is fin e n e w p la n t p o ssib le . . . o v e r 1 3 0 ,0 0 0 s q . f t . d e v o te d e x c lu - . s iv e ly to th e m a n u f a c t u r e o f S c ie n tific R e s e a rc h a n d P ro d u c tio n C o n tro l E q u ip m e n t. W e s a lu te w it h d e e p p rid e a n d s in c e re a d m ir a t io n e v e r y la b o r a t o r y m a n , fro m d ire c to r to th e n e w e s t t e c h n ic ia n ; th e ir u n tirin g p a tie n c e h a s g iv e n o u r c o u n try th e g re a te s t te c h n o lo g ic a l d e v e lo p m e n ts th e w o r ld h a s e v e r s e e n . A g a in w e s a y —
" T H A N K Y O U " a n d " W E L C O M E T O O U R N E W H O M E '
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. 18, No. 12
IM P R O V E D , A L L - M E T A L M O D E L
N I C H O L S R E F R A C T O M E T E R
For determ in atio n of th e refractive indices of liquids w ithin a w ide ra n g e on th e stag e of a m icroscope
N ichols R efra cto m ete r; only, M ac ro M o d el
C ross-section of N ichols R efra c to m e te r, in d ic a tin g w a ter c irc u la tio n w ith in ja c k e t. P , p rism s; C, c em en t; L , en g ra v ed lin e; a n d T , cover glass
86(54.
N ichols R efra c to m e te r, c o m p lete o u tfit consisting^ of M a c ro M odel a n d accessories, in case
N ichols R e fra c to m e te r, only, M icro M o d el
N IC H O L S R E FR A C T O M E T E R , Im proved M odel, w ith m etal w a te r jack e t. F o r d e te rm in a tio n of th e refractiv e indices of liquids on th e stage of a m icroscope. T h e range for liquids is p ra ctically unlim ited. P o te n tia l accuracy u n d er controlled conditions of te m p e ra tu re an d ligh t is n D = ± 0.0005 and, u n d er usual lab o ra to ry conditions, is nD = ±0.001. See L ym an Nichols, N ational P a in t
Bulletin, Vol. 1 {Feb., 1937), p. 12, and M ar., 1937, p. U ; an d H e rb e rt K . A lber an d Jam es T .B ry an t, Industrial and Engineering Chemistry, A na l. Ed., Vol. 12, N o. 5 {M ay 15, 1940), p. 305.
A determ ination consists of a sim ple m easurem ent u n d er the microscope of th e distance betw een tw o lines an d refer
ence to a calibration graph — prepared in accordance w ith th e m ethod outlined below — w hich p erm its conversion of the distance directly in to n D w ith o u t fu rth e r calculations. T h e two lines observed in th e microscope are refractions of the single line L, 0.0001 inch wide, engraved on th e glass base of the cell b en eath th e prism s a n d are produced because of th e difference betw een the refractive index of the prism s a n d t h a t of th e sam ple placed in the cell.
T he n n of solids can also be determ ined by indirect m ethods as described in the directions for use.
T h e in stru m en t is offered in tw o models, i.e. M acro an d M icro, each having a nickel p lated brass w ater ja c k e t, 76 X 38 X 4-5 mm, to p erm it precise tem p eratu re control a n d tw o cells m arked n o 1-52 and n D 1.72, respectively, to provide for convenient m easurem ent of a wide v a rie ty of liquids. E ach m odel is supplied w ith tw o cover^glasses to pre
v e n t evaporation of liquids w ith high v ap o r pressure.
M acro cells are 11 m m outside d iam eter a n d require 100 to 200 cu. m m (2 to 4 drops) of sam ple; M icro cells are 5 m m outside diam eter an d require only 6 to 8 cu. m m of sam ple, of w hich 5 to 6 cu. m m can be recovered, depending upon th e physical properties of th e liquid.
M ethod of Calibration. T o calib rate th e in stru m e n t in accordance w ith th e individual characteristics of th e cel! and microscope set-up used, th e cell is filled w ith a liquid of know n refractive index, covered w ith a cover glass an d placed under a m icroscope w ith a m agnification of approxim ately 100 X . T hen, using the special eyepiece m icrom eter disc on th e d iap h rag m of th e microscope eyepiece, th e distance betw een th e tw o lines observed is m easured. I his is repeated for each of th e five sta n d a rd liquids supplied w ith th e outfit, an d a graph p repared on cross section p ap er by entering th e refractive indices as o rdinates an d the m easured distances in scale divisions as abscissae. T h e p oints p lo tted for th e sta n d a rd liquids will form a line w hich is nearly stra ig h t an d from w hich observed distances for liquids of u nknow n refractive index can be converted directly into term s of refractive index provided th e conditions of te s t are identical.
8664. R efractom eter, N ichols, Im proved M acro M odel, com plete outfit, as above described, w ith cells 11 m m outside d iam eter w ith tw o cover glasses, eyepiece m icrom eter disc a n d se t of five sta n d a rd liquids, hd 1.4000, 1.4500, 1.5500, 1.6500 an d 1.7000, respectively, in le ath erette velvet-lined case, w ith detailed directions for use. .75.00 8665. D itto, M icro M odel, w ith cells approxim ately 5 m m outside d ia m e te r...93.00
M o r e d e t a i l e d i n f o r m a t i o n s e n t u p o n r e q u e s t .
A R T H U R H. T H O M A S C O M P A N Y
R E T A IL — W H O 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 RE AG EN TS
W E S T W A S H IN G T O N S Q U A R E , P H I L A D E L P H IA 5, P A ., U . S . A .
C able A ddress "B alan ce,” Philadelphia
INDUSTRIAL a n d EN GIN EERIN G CHEMISTRY
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
Q u an titative A n a ly s is of H y d rocarbon M ixtures b y M ea n s of Raman Spectra
E. J. R O S E N B A U M , C . C.
Experimental Division, Sun
T
H E su b ject of hydrocarbon analysis b y physical m ethods has becom e increasingly im p o rta n t in recen t years. Of these m ethods, tw o m ake use of th e fa c t t h a t the set of m olecular v ib ratio n al energy levels is a unique p ro p erty of each com pound.I n th e m ethod of infrared absorption spectra, a beam of continu
ous rad iatio n from a h o t body is passed th ro u g h th e sam ple an d th e tra n sm itte d rad iatio n is exam ined to learn w h a t has been ta k e n o u t of it. T h is inform ation provides th e raw d a ta for th e analysis of th e sam ple. I n th e m ethod of R am an spectra, essen
tia lly m onochrom atic lig h t is se n t in to the sam ple an d th e scattered lig h t is exam ined for lines of modified w ave length.
T h e analysis of th e sam ple is based on th e position an d in ten sity of these modified lines. T h e lite ra tu re on th is su b ject is exten
sive. T he following are ty p ical references: (/, 2, 4, 8).
E ach m ethod has ad v an ta g es an d disadvantages. T he p resen t paper describes th e a u th o rs’ technique for applying R a m a n spec
t r a to th e analysis of certain hydrocarbon m ixtures a n d indicates th e ty p e of results obtained.
T he m ethod described here is n o t p resented as a fully devel
oped m eth o d w hich can be applied w ith sta n d a rd equipm ent d irectly to ro u tin e analysis. H ow ever, i t is a relatively simple procedure w hich leads to useful resu lts w ith liquid hydrocarbon m ixtures.
T h e R am an spectrum of a ty p ical h y drocarbon in th e gasoline range consists of a relatively sm all n u m b er of lines whose sharp
ness depends on th e stru c tu ra l ty p e of th e hydrocarbon. W hen tw o or m ore pure hydrocarbons are mixed, th e R a m a n spectrum of th e m ixture is a superposition of th e sp ectra of th e individual com ponents w ith o u t a n y frequency displacem ent. T h e only ty p e of interference w hich does occur is th e accidental overlapping of lines arising from different com pounds. W ith a sp ectro -.
g rap h of sufficient dispersion, th is is n o t a serious difficulty for m ixtures containing four or five com ponents, an d in alm ost all cases such a m ixture can be analyzed b y use of R am an lines w hich are n o t overlapped. So far as is know n, for co n stan t illum ination of th e sam ple, th e in ten sity of lig h t scattered b y a hydrocarbon in a m ixture is directly proportional to th e concentration of th e hydrocarbon.
M o st R am an sp ectra are accom panied by a n appreciable a m o u n t of background scatterin g , caused eith er by a continuum from th e light sources (m ercury arcs) or b y fluorescence from a m in u te a m o u n t of fluorescent contam ination in th e sam ple.
T h e continuum from th e m ercury arcs can be reduced o r prac
tically elim inated b y th e use of su itab le optical filters, o r b e tte r still, b y a choice of m ercury arc w hich em its relativ ely little con
tinuous rad iatio n . T he fluorescence of th e sam ple can often be g reatly reduced b y a sim ple bulb-to-bulb distillation w ith o u t fractio n atio n , or, in m ore difficult cases, b y a distillation over m etallic sodium . H ow ever, even w hen efforts h av e been m ade to m inim ize th e background, it is usually p resent to som e extent.
M A R T IN , a n d J. L . L A U E R
O il Company, Norwood, Pa.
r ;
T h e only w ay to overcom e th is difficulty is to m ake a suitable correction for th e background w'hen th e spectrum is subjected to q u a n tita tiv e evaluation.
T he m ethod of in te rn a l stan d ard s has been used, in b o th emis
sion an d R am an spectroscopy, to reduce th e effect of v ariatio n s in th e in ten sity of illum inatiqn. A know n q u a n tity of some su it
able substance is added to the sam ple an d th e blackening of th e analysis lines is m easured relativ e to t h a t of th e lines of th e sta n d ard. F o r exam ple, R an k , Scott, a n d F enske (6) have described th e use of 2 cc. of carbon tetrach lo rid e in 25 cc. of sam ple as an in te rn a l sta n d a rd . T h e chief objection to th is procedure is th e undesirable co n tam in atio n of th e sam ple, w hich is often needed for o th er ty p es of work. E v en in m oderately com plicated m ix
tu re s th ere is a considerable p ro b ab ility t h a t th e useful lines of th e in tern al sta n d a rd w ould be overlapped. T h e a u th o rs h ave therefore n o t used in te rn a l stan d ard s.
T h e sta n d a rd procedure of q u a n tita tiv e photographic photom e try involves a calibration of th e photographic m a te ria l used by a graded scries of exposures of know n relative in ten sity on each p late or film. W hen th e resulting spots are m icrophotom etered, th e optical density (defined as th e logarithm of th e ra tio of th e lig h t incident on a sp o t to th e lig h t tra n sm itte d th ro u g h th e spot) can be g raphed as a function of th e logarithm of th e in ten sity of th e lig h t used for th e exposure (for co n stan t exposure tim e).
T h en w hen th e d en sity of a n analysis line is read from th e m i- crophotom etcr curve for a sam ple, th e corresponding in ten sity can be read from Z)-log I curve. T h is procedure is ra th e r tim e- consum ing.
I t has been found possible to evade a g re a t deal of th e aw k
w ardness in h eren t in th e photographic m ethod w ith o u t too m uch loss of accuracy by a sem iem pirical procedure involving a calibration for each system based on a few' m ixtures of known com position m ade u p from com pounds of high p u rity . T h is procedure also m akes i t possible to ta k e in to account th e m u tu a l interference of close-lying R am an lines. Once th e calibration has been carried o ut, th e calculations involved are b rief a n d v ery elem entary.
EXPERIMENTAL
T he R am an spectra described here wrere o b tain ed w ith a S tein- heil spectrograph w ith th re e glass prism s w'hose dispersion varies from 6
A.
per m m . a t 4000 to 2 0A.
p er m m . a t 5000A.
(7). T he spectrograph is enclosed in a th erm o stated plyw ood box. T he lig h t source used for th e earlier p a rt of th is work was th e G E T y p e H -2 m ercury arc. W hen th is arc operates a t its norm al tem p eratu re, i t em its a h eavy continuum , w hich can be reduced by cooling th e arc u n til p a r t of th e m ercury condenses on the walls. How'ever, u n d er these conditions th e light o u tp u t is annoyingly sensitive to sm all changes in th e tem p eratu re of the arc. T h e G eneral E lectric Co. kindly supplied an arc sim ilar to th e H -2 b u t w ith th e m ercury co n ten t reduced to such an ex ten t th a t th e m axim um po ten tial d ro p is 40 volts. T hese arcs, desig- 731732 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. 18, No. 12
Table I. Calibration for A n a ly sis of Four-Component Sample Using Known Mixtures R a m a n
L in e F r e qu ency,
C in .- i
M ix tu re 1 M ix tu re 2
C o m p o u n d It° - I t P Pav. Pe Ri I t P Pav. Pc Ri
818 806 644 744 557 520576
p -E th y lto lu e n e p -E th y lto lu e n e p -E th y lto lu e n e P seu d o cu m en e P seu d o cu m en e m -E tliy lto lu en e M esity len e
0 .5 5 4 0 .5 3 0 0 .4 2 1 1 .3 8 1 .1 3 0 .3 9 8 2 .2 2
0 .5 1 7 0 .5 2 7 0 .3 5 3
0 . 2 Î5 0 .2 7 3
9 3 .3 9 9 .3 8 3 .8
5 4 .0 1 2 .3
9 2 .1
5 4 .0 1 2 .3
58* 1
¿4 ! 1 7 .8
o ’.9 7
1 Ü 4 0 .7 8
0 Ü 3 2 0 .1 1 8 0 .4 5 0 1 .2 0
" 9 .6 1 0 .4 1 1 3 .0 5 4 .0
iô.’o
1 Î 3 .0 5 4 .0
5 .6 63 !9 3 0 .5
0'.56 1 .07 1 .0 2
T o ta ls 15 8 .4 1 0 0 .0 1 7 7 .0 1 0 0 .0
M ix tu re 3 M ix tu re 4
818 806 644 744 557 520 576
p -E th y lto lu e n e p -E th y lto lu e n e p -E th y lto lu e n e P seu d o cu m en e P se u d o cu m e n e m -E th y lto lu e n e M esity len e
0 .5 5 4 0 .5 3 0 0 .4 2 1 1 .3 8 1 .1 3 0 .3 9 8 2 .2 2
0 .0 8 9 0 .0 7 9 0 .0 6 0 0 .4 7 6 0 .3 4 4 2.’ 26
16 .1 14 .9 14 .3 3 4 .5 3 0 .5 lÔ i 6
i ö ' 1 32! 5
1ÔÜ6
iô;
12 Ü 8
68.’
1
Ri
1 .0 1 0 .7 3
1 Ü 3 0 .2 6 5 0 .3 0 6 0 .2 0 5 1 .1 2 1.01 0 .0 8 2
4 7 .8 5 7 .7 4 8 .6 8 0 .8 8 8 .8 2 0 .6
5 Ü 4 8 Ü 8 2 6 ! 6
32! 8 54
1 iàii
Ri
i
.09 o'.90 1 .3 1T o ta ls 149 .2
100.0
1 5 6 .8 100.0Ri Rt Ri Ri Pav.
77-E th y lto lu e n e P seu d o cu m en e w i-E th y lto lu en e M esity len e
0 .9 7 l ‘.i 4 0 .7 8
0 .5 6 1.0 7
1.02
0 .7 3
1.01
1 Ü 3
1.0 9 0 .9 0 1.3 1
0 .7 3
1.02
1 .1 7 0 .9 8 R am an
L in e F re
* q u en cy ,
C m .*» C om p o u n d I t Rav. Ic
818 806 644 744 557 520 576
p -E th y lto lu e n e p -E th y lto lu e n e p -E th y lto lu e n e P seu d o cu m en e P seu d o cu m en e w i-E th y lto lu en e M esity len e
0 .5 5 4 0 .5 3 0 0 .4 2 1 1 .3 8 1 .13 0 .3 9 8
2.22 1.02 1.02 1.02
0 .7 3 0 .7 3 1 .1 7 0 .9 8
0 .5 6 5 0 .5 4 0 0 .4 2 9 0 .8 2 5
1.01
0 .4 6 6 2 .1 7
n ated as T y p e H - l l , are operated w ith the m ercury com pletely vaporized an d consequently are n o t appreciably tem p e ra tu re - sensitive. T h ey have proved to be excellent sources for exciting R am an spectra. Six of them are arranged concentrically a b o u t th e tu b e containing th e sam ple.
F o r m ost of the R am an sp ectra under consideration here, the R am an tu b e h a d a volum e of approxim ately 15 cc.; for th e re
m ainder, th e sam ple volum e w as approxim ately 6 cc. W hen th e a m o u n t of sam ple available perm its, th e use of th e larger size tu b e has tw o ad v an ta g es: th e alignm ent of th e tu b e w ith respect to th e spectrograph is less critical, an d th e spectral lines o btained are longer, which m akes it easier to select th e portion of th e lines suitable for m icrophotom etering.
T he known aro m atic m ixtures for calibration were m ade up from m aterial which w as especially synthesized or purified for th is purpose. T he purities as determ ined b y th e freezing p o in t m ethod were all 98% or b e tte r an d m ost of th em were above 99%
(S). T he usual exposure tim e for arom atic sam ples is 75 m inutes on Ansco Fluorapid film; for paraffinic sam ples th is is increased to 3 hours because paraffins are poorer scatterers th a n arom atics.
A slit w idth of 0.1 mm , is used.
T h e p articu lar R am an lines used for a n analysis are those strong lines w hich have no close neighbors an d w hich show th e least overlapping w ith lines of th e o th e r com pounds present, W hich lines are best often depends on th e com position of th e sam ple. I t is, of course, necessary to use lines w hich are n eith er under- n o r overexposed—i.e., lines whose d en sity lies in th e linear range of th e D -lo g / curve of th e photographic em ulsion.
T he m icrophotom eter curves required are o btained on a Leeds
& N o rth ru p recording m icrophotom eter. T h e optical density of each R a m a n line used for analysis is re a d from th e curve as well as th e d en sity of th e background n ear each line. T he a n ti
lo g arith m of th e background density is su b tra c te d from th a t of th e line d en sity to give a n effective in te n sity of th e R am an line (/.)•
T h e sequence of th o u g h t leading to th e m ethod ad o p ted for obtaining effective in ten sities from th e m icrophotom eter record was as follows:
1. T he exposure of a given line on th e negative is assum ed to be proportional to th e concentration of th e corresponding com
pound in the m ixture w ith co n stan t to ta l illum ination.
2. Along th e linear po rtio n of the characteristic curve (D =
7 log E ), 7, th e gradient, depends only on th e em ulsion an d th e developm ent conditions used.
3. Following Pierce an d N ach trieb (5), it is desirable to m ake th e background correction in term s of E ra th e r th a n D . If 7 = 1, then E = antilog D. Since th e com bination of em ulsion and developm ent conditions used gave a value of n early 1 for 7, th is relation w as th e sim plest one to try . T h e au th o rs have since found th a t even w ith som ew hat different values of 7 they get satisfactory results, presum ably because th e calib ratio n a n d the analysis are carried o u t under th e sam e conditions: A much more rigorous m ethod is th e construction of th e E vs. D curve as Pierce a n d N ach trieb h ave done. In v ieV of o th er possible sources of inaccuracy, it w as n o t considered w orthw hile to a d o p t th e ir procedure.
Table II. A n alysis of Four-Component Mixture R a m a n Line
F req u e n c y ,
C m . -1 C om p o u n d 818
806 p -E th y lto lu e n e p -E th y lto lu e n e 644 p -E th y lto lu e n e 744 Pseu d o cu m en e 557 P seu d o cu m en e 520 ra -E th y lto lu e n e 576 M csity len e
I t P Pav. Pc PknownD e v ia tio n 0 .3 4 8 6 1 .6
0 .3 5 2 6 5 .2 6 1 .8 2 5 .5 25 +Ö*. 5 0 .2 5 1 5 8 .5
0 .5 7 8 5 7 .2 5 9 ’.0 2 4 ’.5 25 — 6 .5 0 .5 0 2 6 0 .9
0 .2 9 0 6 2 .1 62! 1 2 è ’ 25
1 .2 4 4 57 A 57 A 24 25 - 1
If th e exposure conditions a n d th e photographic processing w ere stric tly reproducible a n d th e assum ptions m ade w ere valid, th e effective in te n sity as used here could be expected to be a lin
ea r function of th e concentration, provided th e blackening of th e R a m a n lines is k e p t betw een th e proper lim its. Because th e a c tu a l conditions used are ra th e r fa r from ideal, even w hen an effort is m ade to reach a hig h degree of constancy, use is m ade of a n em pirical averaging process a n d of th e fa c t t h a t in ten sity ratio s are less affected b y v ariatio n s in exposure an d developm ent
