'■volume 69
No. 814, Pages 1—32 January, 1944
/ ? . ^ 9 C - j r z r . -
T H E A N A L Y S T
The Journal of
The Society of Public Analysts
and other Analytical Chemists
p u b l i c a t i o n C o m m i t t e e
Chairman
: J. R. N I C H O L L S , D.Sc., F.I.C.N. L. A L L P O R T , F.I.C.
F. W . F. A R N A U D , F.I.C.
A. L. B A C H A R A C H , M.A., F.I.C.
R. C. C H I R N S I D E , F.I.C.
H. E. C O X , D.Sc., Ph.D., F.I.C.
B E R N A R D D Y E R , D.Sc., F.I.C.
F. W . E D W A R D S , F.I.C.
B. S. E V A N S , M.B.E., M.C., D.Sc., F.I.C.
E. H I N K S , M.B.E., B.Sc., F.I.C.
Ibon. Secretary:
L. E Y N O N , B.Sc., F.I.C.
7 - 8 , Id o l L a n e , E .C .3
E. B. H U G H E S , D.Sc., F.I.C.
D. W . K E N T - J O N E S , B.Sc., Ph.D., F.I.C.
S. E R N E S T M E L L I N G , F.I.C.
G. W . M O N I E R - W I L L I A M S , O.B.E., M.C., Ph.D., F.I.C.
A. M O R E , I.S.O., A.R.C.S.,
A.R.T.C., F.I.C.
W . H. S I M M O N S , B.Sc., F.I.C.
E R I C V O E L C K E R , A.R.C.S., F.I.C.
K. A. W I L L I A M S , B.Sc., F.I.C.
ibon. measurer:
G. T A Y L O R , F.I.C.
P e e k H ou se, 2 0 , E a s tc h e a p , E ,C .3
JG&itOr:
G. A I N S W O R T H M I T C H E L L , D.Sc,, M.A., F.I.C.T h e C lo se , W eedon, A y lesb u ry , B u c k s .
Secretary auD assistant E&itor
: J. H. l a n e , B.Sc., F.I.C.7 - 8 , Id o l L a n e , E .C .3
H b a t r a c t o r s S. G. C L A R K E , D.Sc., Ph.D., A.I.C.
B. S. C O O P E R , B.Sc., F.Inst.P.
E. B. D A W , B.Sc., A.I.C.
J. G R A N T , Ph.D., M.Sc., F.I.C.
A. O. J O N E S , M.A., F.I.C.
J. W . M A T T H E W S , Ph.D., F.I.C.
E. M . P O P E , B.Sc.
F. A. R O B I N S O N , M.Sc.Tech., F.I.C.
W . R. S C H O E L L E R , Ph.D., F.I.C.
D. R. W O O D , F.I.C.
P u b l i s h e d f o r th e S o c ie t y b y
W . H E F F E R & S O N S LTD., Cambridge, England
I M P O R T A N T N O T I C E T O S U B S C R I B E R S (iO th e r t h a n M e m b e r s o f th e S o c ie t y ) .
A l l S u b s c r i p t i o n s a n d r e n e w a l s t o t h e J o u r n a l s h o u l d b e s e n t t h r o u g h a B o o k s e l l e r o r d i r e c t t o
W . H E F F E R & S O N S L T D . , C A M B R I D G E , E N G L A N D .
P r i c e 3 / 6 ; o r t o S u b s c r i b e r s i n a d v a n c e , p o s t f r e e , 3 5 j - p e r a n n u m .
N . B . — M e m b e r s se n d th e ir s u b s c r ip tio n s to th e H o n . T r e a s u r e r .
En t e r e d a s Se c o n d Cl a s s a t Ne w Yo r k, U.S.A., Po s t Of f i c e Pr i n t e d i n En g l a n d
T H E A N A L Y S T
A N T I - F O A M I N G S P L A S H
H E A D
The persistent frothing met with in the distiila- tionof protein solutions, alcoholic beverages or saponified fats and oils will not impede distilla
tion if the Quickfit Anti- foaming Splash-head is used.
By a reduction of pres
sure in the system, air is drawn through a fine jet in the top of the vapour tube and effec
tively breaks down the most persistent foam, permitting of distilla
tion at norma! rates, yielding an uncontam- inated product.
This apparatus is just one example from the wide range ol Quickfit Laboratory glassware - illustrated in the Quickfit Catalogue.
Apparatus can be supplied ¿n Pyre-.r, Phoenix or fit/sit glass.
M Æ C l a a ù f ô iô
LABORATORY GLASSWARE WITH STANDARD INTERCHANGEABLE GROUND GLASS JOINTS
QUICKFIT & QUARTZ LTD
T R I P L E X W O R K S , K I N G ' S N O R T O N , B I R M I N G H A M
Landen Office; 1 Alternarle Street, WM Phene Regent S17I
. 6VANS
bacteriological
PEPTQI
or6!inl,m*
an d I t co n ta io s Carb° '
b y d r a te . p epi o n « H
p ie te * *
bacteria. dextrose, a sallo®
«iih the addition eVlent ferow
- : s :
- 5 . » « = t r : " - “ " - “ ”" ' “d welchll ¿roopa- u l9 „sad
Z X X S S S — —
r z z z
Xndol test.- —
tntlUS.—
— aTli p o te n t o b ta in e d " 'lt do t h .r this peptnne-
m ed la co n ta in ^ c o a te n t- lt ba» I»« coppe
Bacteriological Peptone (Evans) is issued in 5 and
t6 -o z. amber bottles with bakelite screw caps B I L E S A L T S and o th e r c u ltu r e m e d ia a ls o a v a ila b le . Prices a n d full details will be sent on application to:—
London: H o m e Aiedical Dept., Bartholomew Close, B.C.!
Liverpool: H o m e Aiedical Dept,, Speke, Liverpool, 19
M E D I C A L
€V A N s
R E S E A R C H -M a d e at The Ev a n s Biological Institute, by
E V A N S SONS L E S C H E R A N D WEBB, LTD.
L I V E R P O O L A N D L O N D O N Mjj
T H E A N A L Y S T 111
RAYMOND LABORATORY MILL
F o r r a p i d p o w e r c o m m i n u t i o n o f a w i d e r a n g e o f m a t e r i a l s
T h e n e w R a y m o n d L a b o r a t o r y Mill has a rotor, p o w e r - d r i v e n b y £ H.P. m o t o r at 10,500 r.p.m. S w i n g - o u t h a m m e r s rapidly r e d u c e t o fine p o w d e r coal, limestone, talc, d r y colours, clays, minerals, alum s , etc., etc.
S a m p l e a u tomatically sieved a n d collected.
T u b e t o filter o u t surplus air. H a n d feed b y w o r m a n d s c r e w . E a s y to erect, to r u n a n d to clean.
P le a s e a p p ly f o r d e s c r ip t iv e b o o k le t
CjRIFFINandTATLOCK Etc)
L O N D O N M A N C H E S T E R G L A S G O W E D I N B U R G H Kemble St., W.C.2 19 Cheetham Hill Rd„ 4 45 Renfrew St., C.2 7 Teviot Place, I
Established as Scientific Instrument M akers in 1826
I V T H E A N A L Y S T
REI GATE BRAND
Registered Trade Mark N A T U R A L I S O L A T E S :
E S S E N T I A L O I L S : S Y N T H E T I C S :
F L O W E R O I L S : C i t r a l , E u g e n o l , G e r a n i o l s , l o n o n e s , M e t h y l l o n o n e s ,
H y d r o x y c i t r o n e l l a l S O L E M A N U F A C T U R E R S : —
W H I T E , T O M K I N S & C O U R A G E , L T D R E I G A T E , S U R R E Y
Established 1841 'Phone
Re ¡gate 2242
'Grams Esswhite, Reigate
JUDACTAN
ANALYTICAL REAGENT
W e have m a d e available certain Analytical R e agents with A C T U A L B A T C H A N A L Y S I S con
firmed by I N D E P E N D E N T Analysts of the highest standing: par
ticulars of one example are given.
* Y O U A R E I N V I T E D T O C O M P A R E T H E P U R I T Y W I T H T H A T G U A R A N T E E D B Y A N Y C O M P E T I N G M A K E R .
B O R I C A C I D A . R .
H3BO3 Mol. Wt. 61-84
A C T U A L B A T C H A N A L Y S I S (Not merely maximum impurity values)
Batch No. 12632
Chloride (Cl)... 2-52°1%
Sulphate (SO*)... 0.001%
Heavy Metals (Pb)... 0.0005%
Iron (Fe) ... ... ... 0.0002%
Calcium (Ca)... 0.001%
A rsenic (AS2O3) ... 0 .5 p.p.m .
T h r *b«ve anatysis i« bat«d on th* resulta, not o f o u r ow n C o n tr o l L a b o ra to rie s ilo / it , b u t a tío on th* c o n flrm a to ry A n a ly tic a l C e rtifíc a te Usued by tndependent
Consultante o f in te rn a cio na l repute
T h e G e n e r a l C h e m i c a l & P h a r m a c e u t i c a l C o . , L t d . C h e m i c a l M a n u f a c t u r e r s , J u d e x W o r k s , S u d b u r y , M i d d l e s e x
J ANUARY, 1944 Vol. 69, No, 814
T H E A N A L Y S T
P R O C E E D I N G S O F T H E S O C I E T Y O F P U B L I C A N A L Y S T S
A N D O T H E R A N A L Y T I C A L C H E M I S T S
A J o i n t M e e t in g o f t h e S o c i e t y w i t h t h e F o o d G r o u p o f t h e S o c i e t y o f C h e m ic a l I n d u s t r y w a s h e ld a t 2 . 3 0 p .m . on W e d n e s d a y , D e c e m b e r 1s t, 1 9 4 3, a t t h e L o n d o n S c h o o l o f H y g i e n e a n d T r o p i c a l M e d ic in e , L o n d o n , W . C . l . T h e c h a ir w a s o c c u p ie d b y M r . T h e o d o r e R e n d le , F . I . C . , V ic e - P r e s id e n t . T h e s u b je c t o f t h e m e e t in g w a s “ N u t r i t i o n o f t h e P u b l i c a n d F o o d L e g i s l a t i o n , ” a n d t h e f o llo w in g p a p e r s w e r e p r e s e n te d a n d d is c u s s e d : — " T h e E s s e n t ia l N a t u r a l N u t r i e n t s o f F r e s h a n d M a n u f a c t u r e d F o o d s , ” b y P r o f e s s o r J . C . D r u m m o n d , D . S c . , F . I . C . ; " T h e R o l e o f F o o d L e g i s l a t i o n i n s e c u r in g a d e q u a t e N u t r i t i o n , ” b y H . E . C o x , P h . D . , D .S c .-, F . I . C . ; a n d " T h e P a r t p la y e d b y t h e F o o d S u p p l i e r in S a f e g u a r d in g t h e N u t r i t i v e V a l u e s o f F o o d , ” b y E . B . H u g h e s , D . S c . , F . I . C .
. N E W M E M B E R S
W i l l i a m B r a d l e y , M . S c . , P h . D . ( L o n d . ) ; A r t h u r C a r r o l l , A . M . C . T . , A . I . C . , M . P . S . * ; W i l l i a m B e r n a r d C h a p m a n , A . E C . * ; E d w a r d A l b e r t R o b e r t s ; A l b e r t S c iv e r , B . S c . ( L o n d .) , F . I . C . ; J o h n R o b e r t S t e w a r t , M a j o r , R . A . S . C . , B . S c . ( L e e d s ) ; H a r o l d S y k e s , B . S c . ( L o n d .) * .
D E A T H
W e r e g r e t t o h a v e t o r e c o r d t h e d e a t h o f L e o C o o k s e y . 9
T h e C a li b r a t i o n of F lu o r im e t e r s u s e d fo r E s tim a t in g V i t a m in s , A l k a l o i d s , a n d o th e r S u b s t a n c e s
B y F R A N K W O K E S , B . S c . , Ph.D., F . I . C . , Ph.C., J O A N G . O R G A N , Ph.C., B E S S M . S T I L L , B . S c . , a n d F . C . J A C O B Y , Ph.D.
F l u o r e s c e n c e m e t h o d s a re w i d e l y e m p lo y e d t o e s t im a t e v i t a m i n s , a lk a lo id s a n d o t h e r ' p h y s i o l o g i c a l l y i m p o r t a n t s u b s ta n c e s , b u t a s t u d y o f t h e p r in c ip le s i n v o l v e d h a s h it h e r t o - b e e n l a c k in g . M o s t w o r k e r s m e a s u r e flu o re s c e n c e i n t e n s i t y b y p h o t o e le c t r ic m e t h o d s . T h e a p p a r a t u s u s e d h a s b e e n g iv e n v a r i o u s n a m e s
(e.g.,
f lu o r im e t e r , f lu o r o m e t e r , p h o t o - f lu o r o m e t e r ) . T h e t e r m a lw a y s u s e d in o u r c o m m u n i c a t i o n s is f lu o r im e t e r , w h i c h h a s n o w r e c e iv e d t h e a p p r o v a l o f t h e p a n e l a p p o in t e d b y t h e S . P . A . P u b l i c a t i o n s C o m m i t t e e.1 O u r in v e s t ig a t io n s h a v e b e e n m a d e w i t h t h e S p e k k e r i n s t r u m e n t,2 b u t t h e r e s u lt s a r e i n g e n e r a l a p p li c a b l e t o o t h e r t y p e s .U s e o f C a l i b r a t i o n C u r v e s t o D e t e c t Q u e n c h i n g— D i m i n u t i o n o r
quenching
o fflu o re s c e n c e , le a d in g t o lo w r e s u lt s , m a y b e d u e t o v a r i o u s c a u s e s ,
e.g., concentration quenching
,3 w h ic h in c r e a s e s w i t h in c r e a s in g c o n c n . a n d is d u e t o t o o h i g h a c o n c n . o f th e f lu o r e s c e n t m o le c u le s ,dilution quenching,
w h i c h in c r e a s e s w it h d e c r e a s in g c o n c n . a n d m a y b e d u e e it h e r t o in s t r u m e n t a l c a u s e s(e.g.,
r e f le c t io n i n cells) o r t o t h e s o lv e n t(e.g.,
flu o r e s c e n c e o f is o b u t a n o l i n a n e u r in e e s t im a tio n s ) . O t h e r c a u s e s o f q u e n c h in g a re u l t r a v i o l e t l i g h t , o x y g e n , s a lt s a n d v a r io u s im p u r it ie s , a ls o c h a n g e s i n
p'H..
Q u e n c h in g c a n b e d e t e c t e d b y
recovery experiments,
i n w h ic h a k n o w n a m o u n t o f t h e s p e c if ic s u b s t a n c e is a d d e d t o t h e m a t e r i a l b e in g t e s te d , a n d t h e % r e c o v e r y o f t h is a d d e d s u b s t a n c e is d e t e r m in e d a n d u s e d t o c o r r e c t t h e r e s u lt . S u c h r e c o v e r y e x p t s . a re e m p lo y e d w i t h s u c c e s s in t h e e s t im a t io n o f a n e u r in e i n f lo u r,4 b u t h a v e p r o v e d le ss s a t i s f a c t o r y w i t h o t h e r f o o d s t u f f s.5I n t h is c o m m u n i c a t i o n q u e n c h in g is d e m o n s t r a t e d b y c a l i b r a t i o n c u r v e s , t h e r e s u lt s b e i n g r e c o r d e d b y p l o t t i n g a g a in s t d if fe r e n t c o n e s , t h e o p t ic a l d e n s it y d iffe r e n c e p r o d u c e d b y d o u b l i n g t h e c o n c n . S in c e in t h e S p e k k e r f lu o r im e t e r t h e d i a p h r a g m c o n t r o llin g t h e a m o u n t o f l i g h t w h i c h r e a c h e s t h e flu o r e s c in g s o lu t io n is c a l i b r a t e d lo g a r i t h m i c a l l y , t h e o p t ic a l d e n s i t y d iffe r e n c e p r o d u c e d b y d o u b l i n g t h e c o n c n . s h o u ld b e lo g 2 o r 0 - 3 0 1 i f n o q u e n c h in g o c c u r s , a n d t h e q u e n c h in g w h i c h d o e s o c c u r c a n b e e x p r e s s e d a s . a p e r c e n t a g e b y m e a n s o f t h e f o r m u l a : 1 0 0 — (5 0X a n t i l o g . o f t h e o p t i c a l d e n s i t y d iffe r e n c e ) .
C a l i b r a t i o n o f F l u o r i m e t e r C e l l s— B e f o r e c o n s t r u c t in g c a l i b r a t i o n c u r v e s i t is n e c e s s a r y t o c a lib r a t e t h e f lu o r im e t e r c e lls . I n t h e S p e k k e r f lu o r im e t e r 3 t y p e s o f c e lls
Through the North of England Section.
1
2
W O K E S , O R G A N , S T IL L A N D J A C O B Y : T H E C A L IB R A T IO N O F F L U O R IM E T E R Sh a v e b e e n e m p l o y e d : (1) w i t h lo o s e lid s , (2) a n d (3) w i t h s e a le d lid s , c o n t a i n i n g r e s p e c t iv e ly s t o p p e r e d s p o u t s o r s t o p p e r e d o r ific e s f o r f illin g . T y p e (1) is t h e c o m m o n e s t . T y p e s (2) a n d (3), w h i c h w e re in t r o d u c e d a t t h e r e q u e s t o f o n e o f u s,6 p o ss es s t h e a d v a n t a g e s t h a t t h e y c a n r e a d i l y b e f ille d w i t h o u t s p illin g , t h a t t h e s o ln s . t h e y c o n t a i n c a n b e s t a b ilis e d a g a in s t o x y g e n q u e n c h in g b y b u b b l i n g n i t r o g e n t h r o u g h t h e c e ll, a n d t h a t t h e l id s c a n n o t b e i n t e r c h a n g e d . S in c e a c o n s id e r a b le a m o u n t o f t h e d i l u t i o n q u e n c h in g is d u e t o r e f le c t io n o f u l t r a - v i o l e t l i g h t f r o m t h e l id s o f c e lls (see F i g . 1), in t e r c h a n g in g o f th e s e l i d s m a y l e a d t o
5 10 15 20 25 30 35
e r r o r s . D a t a o b t a i n e d w h e n c a l i b r a t i n g c e lls o f t h e s e 3 t y p e s w i t h q u i n i n e a n d w i t h th io c h r o m 'e in n o r m a l c o n c e n t r a t io n s s h o w t h a t v a r i a t i o n s a s h i g h a s 9% m a y o c c u r b e t w e e n d if f e r e n t c e lls (see T a b l e I). A l l n e w c e lls s h o u ld t h e r e fo r e b e c a l i b r a t e d w i t h t h e k i n d s o f s o ln s . b e in g s t u d ie d . I t w o u l d s e e m b e s t t h a t s u c h c a l i b r a t i o n s s h o u ld f o r m p a r t o f t h e t e s t i n g o f a ll f lu o r im e t e r s b e fo r e t h e y a r e s e n t o u t b y t h e m a n u f a c t u r e r s .
C a l i b r a t i o n C u r v e s w i t h D i f f e r e n t S u b s t a n c e s— H a v i n g c a l i b r a t e d a s e rie s o f 9 f lu o r im e t e r c e lls , w e u s e d t h e m o s t a c c u r a t e o f th e s e ( B , C a n d G ) f o r c o n s t r u c t i n g c a l i b r a t i o n c u r v e s w i t h s o ln s . o f d if fe r e n t q u i n i n e s a lt s i n iV/ 1 0 s u l p h u r i c a c id . O u r r e s u lt s w i t h q u i n i n e s u lp h a t e , p l o t t e d a s d e n s i t y d if fe r e n c e a g a in s t c o n c n ., a re g iv e n i n F i g . 2.
i/z
D i l u t i o n o f Q u i n i n e S t a n d a r d
Fig. 1. Dilution quenching caused by
reflection from lids of fluorimeter cells. C o n c e n t r a t i o n In u g . p e r m l.
Broken curve obtained with ordinary Fig. 2. Calibration of fluorimeter with different glass hds; continuous curve obtained fluorescent substances. Decrease in density with black glass hds. difference as concn. increases due to concn.
quenching and as concn. decreases due to dilution quenching. In absence of quenching density difference should remain constant at 0.301 (log. 2).
Ta b l e I— Ca l i b r a t i o n o f Fl u o r i m e t e r Ce l l s
Mean Coeff. of
value Average variation
Cell as % error of mean
of B % value
Loose lid
A 102-4 2-4 1-3
D 108-6 8-6 1-1
F 108-7 8-7 1-4
Spouts
B 100-0 — —
C 100-1 0-1 1-0
G 100-0 0-0 1-1
Orifices H I J
106-8 109-1 104-8
D i l u t i o n o f Q u i n i n e S t a n d a r d
Fig. 3. Quenching caused by fluorescent impurities in different samples of isobutanol.
U S E D F O E E S T IM A T IN G V IT A M IN S , A L K A L O ID S , A N D O T H E R S U B S T A N C E S 3
T h i s a ls o in c lu d e s c a l i b r a t i o n d a t a w e o b t a in e d w i t h e o s in , w h ic h h a s b e e n r e c o m m e n d e d a s a s t a n d a r d in r i b o f l a v i n e s t im a t io n s, 7 w i t h flu o r e s c e in (u sed b y C o h e n8 t o c a lib r a t e h is f lu o r im e t e r ) a n d w i t h t h io c h r o m e o b t a i n e d f r o m a n e u r in e .* T h e c u r v e s a ll s h o w m a r k e d c o n c e n t r a t io n a n d d i l u t i o n q u e n c h in g , w h i c h m i g h t e x c e e d 1 0% i n t h e c o m p a r is o n o f 2 s o ln s ., o n e o f w h i c h p o s s e s s e d a flu o re s c e n c e i n t e n s i t y 2 o f 3 t im e s t h a t o f t h e o t h e r , a d if fe r e n c e o f t e n e n c o u n t e r e d in p r a c t ic e . T h e q u e n c h in g c a n b e d im in is h e d b y c h o o s in g c o n c e n t r a t i o n s n e a r t h e t o p o f t h e c u r v e s , a s i n f a c t o c c u r s i n t h e m e t h o d o f N i c h o l l s
et al.iJ
f o r e s t im a t in g a n e u r in e i n flo u r , b u t t h e r e m a y s t i l l b e a c o n s id e r a b le a m o u n t o f s u c h q u e n c h in g w h e n t h e flu o re s c e n c e o f t h e b l a n k s is b e in g m e a s u r e d . T h e o c c u r r e n c e o f t h is q u e n c h i n g w i t h q u i n i n e o r w i t h t h io c h r o m e h a s b e e n o b s e r v e d b y v a r io u s w o r k e r s, 10•11>12’13 u s in g v i s u a l o r p h o t o e le c t r ic m e t h o d s . S in c e th e s e r e s u lt s h a d a b e a r in g o n t h e f lu o r im e t r ic e s t i m a t i o n o f v i t a m i n B j w e s t u d ie d t h e q u e n c h in g in g r e a t e r d e t a il.
Q u e n c h i n g b y I s o b u t a n o l F l u o r e s c e n c e— I s o b u t a n o l, a s o b t a in e d f r o m t h e m a n u f a c t u r e r , a lw a y s e x h i b i t s s o m e flu o re s c e n c e i n u l t r a - v i o l e t li g h t . T h i s flu o re s c e n c e
•can b e c o n s id e r a b ly d i m in is h e d b y f r a c t i o n a l d i s t i l l a t i o n i n a ll- g la s s a p p a r a t u s , b u t w e h a v e n o t y e t s u c c e e d e d i n o b t a i n i n g a s a m p le e n t i r e l y fre e f r o m flu o re s c e n c e . M o r e o v e r , th e m o r e o f t e n ¿ s o b u t a n o l is u s e d a n d r e c o v e r e d , t h e m o r e d if f ic u lt i t is t o r e m o v e t h e flu o r e s c e n c e . T h e s e f in d in g s h a v e b e e n c o n f ir m e d o n a s e rie s o f s a m p le s o b t a in e d f r o m o t h e r la b o r a t o r ie s , i n c l u d i n g a l l t h a t h a d c o lla b o r a t e d in t h e p a p e r b y N i c h o l l s
et al.
T h ef lu o r e s c e n c e i n t e n s i t y o f e a c h s a m p le w a s e s t im a t e d a g a in s t a s e rie s o f v e r y d il. q u in in e s o ln s ., t h e w e a k e s t o f w h ic h w a s Q/ 1 2 8 c o n t a i n i n g O-OOSpg o f q u i n i n e s u lp h a t e p e r m l. I n o r d e r t o m e a s u r e t h e v e r y lo w flu o re s c e n c e in t e n s it ie s w e h a d t o u s e 3 o r 4 n e u t r a l g la sse s b e f o r e t h e l e f t - h a n d p h o t o c e ll a n d t o in c r e a s e t h e s e n s i t i v i t y o f o u r g a lv a n o m e t e r b y p l a c i n g i t a t a d is t a n c e o f 3 1 m f r o m t h e s c a le . T h e r e s u lt s s u m m a r is e d i n T a b l e I I
T a b l e I I — M e a s u r e m e n t o f F l u o r e s c e n c e in D i f f e r e n t S a m p l e s o f I s o b u t a n o l Mean optical density against the Dilution of
following quinine standards Q to which
Sample A I is approx,
Q/16 Q/32 Q/64 Q/128 equivalent
A as received (Q. at zero) .. 0-016 0-202 0-401 0-565 Q/15
I Q Q Q
distilled by sender 0-087 0-144 0-299 Q/22
„ \„ F .. 0-072 0-151 0-318 — Q/20
F .. 0-043 0-140 0-309 0-469 Q/21
I Q Q
B i, ,, 0-254 — 0-113 — Q/40
F .. 0-266 — 0-118 — Q/40
F . . 0-202 — 0-110 — Q/40
I I Q Q
C ,, ,, ,, 0-341 0-080 0-043 Q/55
F .. 0-414 0-119 0-044 — Q/58
F 0-290 0-056 0-107 0-215 Q/60
I I Q
ID ft ft it — 0-114 — 0-063 Q/85
F .. — 0-199 — 0-088 Q/87
F .. 0-362 0-154 — 0-055 Q/95
I I I I
E „ „ F .. 0-412 0-210 0-113 — Q/250
I I i I
F „ F .. 0-525 0-310 0-145 0-039 Q/250
G F .. 0-578 0-4-12 0-210 0-061 Q/300
H ... F .. 0-575 0-353 0-163 0-073 Q/320
N o tes— Samples marked F examined with blue filter in front of right-hand photo-cell.
Q, obtained with quinine standard at zero.
I, obtained with ¿sobutanol standard at zero.
s h o w e d w i d e v a r i a t i o n s i n t h e flu o re s c e n c e o f ¿ s o b u t a n o l b e in g u s e d b y d if fe r e n t w o r k e r s , w h i c h m i g h t l e a d t o c o n s id e r a b le q u e n c h in g w i t h b l a n k s . A ll o w a n c e f o r s u c h q u e n c h in g c a n b e m a d e b y m e a n s o f c a l i b r a t i o n c u r v e s o b t a in e d w i t h t h e g iv e n b a t c h o f ¿ s o b u t a n o l,
* These curves summarise a very considerable number of experimental data. For example, each point in the quinine and thiochrome curves is based on the mean result of 4 separate assays, in each of which sufficient readings were taken to ensure that the differences between the results are statistically significant. The detailed data have been omitted in order to save space.
4 W O K E S , O R G A N , S T IL L A N D J A C O B Y : T H E C A L IB R A T IO N O F F L U O R IM E T E R S
b u t f o r c r i t i c a l w o r k i t w o u l d s e e m p r e f e r a b le n o t t o u s e f r e q u e n t l y r e c o v e r e d is o b u t a n o l . I t is o f g r e a t i m p o r t a n c e t o s to r e a ll t h e s o lv e n t s i n g la s s s t o p p e r e d b o t t le s . " A n a l a R ’ ' m e t h a n o l a n d e t h a n o l, w h e n s u p p l ie d i n c o r k e d b o t t le s , h a v e b e e n f o u n d t o e x h i b i t m a r k e d f lu o r e s c e n c e , a n d s h o u ld t h e r e f o r e b e r e d is t ille d i n a ll- g la s s a p p a r a t u s .
Q u e n c h i n g b y U l t r a - v i o l e t L i g h t— T h i o c h r o m e flu o re s c e n c e is g r a d u a l l y q u e n c h e d b y i r r a d i a t i o n14 (see F i g . 4). T h i s d i f f i c u l t y is o v e r c o m e b y m a t c h i n g t h e t h i o c h r o m e
Fig. 6. Reduction of quenching by dilution and by washing with isobutanol. Broken curve- obtained when estimations made at different dilutions by ordinary methods; continuous curve obtained when quenching substances have been partially removed by washing aqueous extract with isobutanol. • If no- quenching occurs density difference should
pH o f T h i o c h r o m e S o l u t i o n 0.101.
Fig. 5. Effect of p H on fluorescence intensity of thiochrome solns. in water (continuous line) and in zsobutanol containing traces of water (broken line).
flu o r e s c e n c e a g a in s t t h e m o r e in t e n s e flu o re s c e n c e o f q u in in e . T h e z e r o is o b t a i n e d o n t h e f lu o r im e t e r w i t h n o t m o r e t h a n 2 0 o r 3 0 se c. i r r a d i a t i o n , r e a d in g s a re t a k e n w i t h t h e q u i n i n e s o ln s . a t le is u r e , a n d a q u i c k c h e c k is m a d e o n t h e z e r o . T h u s t h e t h io c h r o m e i s e x p o s e d t o n o t m o r e t h a n 4 0 o r 6 0 sec. t o t a l i r r a d i a t i o n , w h i c h c a u s e s n o s ig n if ic a n t q u e n c h in g . T h i o c h r o m e s o ln s . s h o u ld b e s t o r e d i n g la s s - s t o p p e r e d a m b e r b o t t le s a n d s t a b i l i s e d w i t h n i t r o g e n a s d e s c r ib e d b e lo w . T h e f lu o r e s c e n c e o f q u i n i n e s o ln s . m a y b e g r a d u a l l y a f f e c t e d b y i r r a d i a t i o n , b u t u n d e r u s u a l c o n d i t i o n s t h e d e g re e o f q u e n c h in g is n o t s e r io u s .
O x y g e n Q u e n c h i n g— T h i o c h r o m e s o ln s . i n i s o b u t a n o l a r e g r a d u a l l y d e c o m p o s e d b y e x p o s u r e t o a ir . T h i s is d u e t o a t m o s p h e r ic o x y g e n a n d c a n b e p r e v e n t e d b y t h e ir s t o r a g e - i n n i t r o g e n - f ille d c o n t a in e r s , u n d e r w h ic h c o n d it io n s n o d i m i n u t i o n i n flu o re s c e n c e w a s o b s e r v e d a f t e r 3 w e e k s . O u r r e s u lt s o n t h e s t a b i l i s i n g e ffe c t o f n i t r o g e n w e r e c o n f ir m e d b y D r s . S . K . K o n a n d S . Y . T h o m p s o n .
E f f e c t o f
pH
o n T h i o c h r o m e F l u o r e s c e n c e— F i g . 5 s u m m a r is e s d a t a o b t a in e d o n t h is e ffe c t, u s in g t h io c h r o m e p r e p a r e d f r o m a n e u r in e b y t h e u s u a l m e t h o d,4 b u t v a r y i n g t h e p r o p o r t i o n o f s o d i u m h y d r o x i d e t o a lt e r t h epH,
a s d e t e r m in e d w i t h g la s s e le c t r o d e a n d a g a r b r id g e . T h e r e s u lt s s h o w t h a t , t o a v o i d s ig n if ic a n t q u e n c h in g , t h epH
s h o u ld b e b e tw e e n 9 - 5 a n d 1 0-5. T h i s w i l l n o r m a l l y r e q u ir e 0 - 0 5 t o 0-3% o f s o d i u m h y d r o x i d e i n t h e i s o b u t a n o l, a c o n c n . u s u a l l y o b t a i n e d i n t h e a b o v e m e t h o d s , b u t s u b j e c t t o a lt e r a t io n b y p r e s e n c e o f b u f f e r in g s u b s t a n c e s o r o f s u b s t a n c e s a f f e c t i n g t h e d i s t r i b u t i o n c o e ff ic ie n t o f s o d i u m h y d r o x i d e b e t w e e n w a t e r a n d is o b u t a n o l.85.
T i m e In m i n u t e s
Fig. 4. Quenching by ultra-violet light. Shaded sections of time scale indicate periods during which the thiochrome soln. in fluorimeter cell was exposed to radiation from the fluorimeter lamp with diaphragm at full aperture. 75 mins.
elapsed between third and fourth exposuies.
U S E D FO R E S T IM A T IN G V IT A M IN S , A L K A L O ID S , A N D O T H E R S U B S T A N C E S 5 Q u e n c h i n g b y Impurities— T h i s c a n b e d im in is h e d b y w a s h in g th e a q u e o u s e x t r a c t w i t h f s o b u t a n o l o r b y d i l u t i o n . F i g . 6 s h o w s t h e e ffe c t o f b o t h th e s e m e t h o d s w h e n a p p lie d t o m a l t e x t r a c t , w h ic h is s u b je c t t o m a r k e d i m p u r i t y q u e n c h in g . C o r r e c t io n f o r i m p u r i t y q u e n c h i n g m a y b e m a d e b y m e a n s o f r e c o v e r y e x p t s .; w h i l s t th e s e h a v e p r o v e d q u it e s a t i s f a c t o r y w i t h m a t e r ia ls s u c h a s f lo u r,4 t h e y n e e d m o d if ic a t io n w h e n a p p lie d t o c e r t a in o t h e r m a t e r ia ls .
S u m m a r y— F lu o r e s c e n c e m e a s u r e m e n t s i n g e n e r a l a r e c o m p l i c a t e d b y v a r io u s f a c t o r s w h i c h d i m i n i s h (q u e n ch ) t h e flu o re s c e n c e , c a u s in g t o o lo w r e s u lts .
Concentration quenching,
d u e t o a h i g h c o n c n . o f flu o r e s c e n t m o le c u le s , m a y b e a v o id e d b y d i l u t i o n , b u t t h is , i f
■carried t o o f a r , w i l l le a d t o
dilution quenching,
d u e e it h e r t o in s t r u m e n t a l o r s o lv e n t c a u s e s . T h i s c a n b e r e d u c e d b y r e - d e s ig n in g t h e i n s t r u m e n t[e.g.,
so a s t o m in im is e r e f le c t io n o f u l t r a - v i o l e t l i g h t f r o m t h e s id e s o r l i d o f t h e cell) o r b y c a r e f u l p u r if ic a t io n o f s o lv e n t s{e.g.,
f s o b u t a n o l, m e t h a n o l, e th a n o l) , b u t i n p r a c t ic e s o m e d i l u t i o n q u e n c h in g is u n a v o i d a b l e . F l u o r i m e t e r c e lls g iv e v a r y i n g r e s u lt s a n d s h o u ld b e c a lib r a t e d w it h ' th e s o ln . b e in g t e s te d . Q u e n c h i n g o f s o m e s u b s ta n c e s ,e.g.,
t h io c h r o m e o r r ib o f la v in , b y u l t r a v i o l e t l i g h t m u s t b e p r e v e n t e d b y a c a r e f u l t e c h n iq u e f o r t a k i n g r e a d in g s a n d b y u s in g m o r e s t a b le s t a n d a r d s , s u c h a s q u i n i n e o r e o s in . O x y g e n q u e n c h in g c a n b e a v o id e d b y s t a b ilis in g t h e s o ln s . w i t h n i t r o g e n . T h e e ffe c t o ffill
o n t h io c h r o m e flu o re s c e n c e h a s b e e n s t u d i e d . Q u e n c h i n g d u e t o t h efill
d e v i a t i n g f r o m t h e o p t i m a l r a n g e o f 9 - 5 t o 1 0 - 5 s h o u ld b e a v o id e d b y e n s u r in g t h a t t h e f s o b u t a n o l e x t r a c t c o n t a in s a s u it a b le c o n c n . o f s o d iu m h y d r o x i d e ( b e tw e e n 0 - 0 5 a n d 0-3% a c c o r d in g t o e x p e r im e n t a l c o n d it io n s , i n c l u d i n g p r e s e n c e o f b u f f e r in g s u b s ta n c e s ) . Q u e n c h i n g b y i m p u r i t i e s c a n b e d i m i n i s h e d b y w a s h in g w i t h f s o b u t a n o l a n d b y d i l u t i o n . C o r r e c t io n f o r s u c h q u e n c h i n g b y r e c o v e r y e x p t s . m a y i n v o l v e■ difficulties w i t h c e r t a in m a t e r ia ls .
W e w is h t o t h a n k a ll t h e a u t h o r s ' o f t h e A n a l y s t p a p e r, 9 a ls o D r s . E . R . D a w s o n , A '. G r e e n , L . J . H a r r i s , G . V . J a m e s , S . K . K o n , R . A . M o r t o n a n d Y . L . W a n g f o r a d v ic e a n d c o - o p e r a t io n . W e a r e in d e b t e d to D r . T . A . H e n r y f o r s p e c im e n s o f q u i n i n e s a lt s a n d t o M e s s rs . M e r c k & C o . o f R a h w a h , N . Y . , f o r a s p e c im e n o f t h io c h r o m e .
Re f e r e n c e s 1. An a l y s t, 1942. 67, 1C4.
2. Lothian, G. P., J . S ci. In str., 1941, 18, 200.
3. Bowen, E. J., " T h e C h e m ica l A sp e cts o f L ig h t , ’ ’ Oxford, 1942, 110.
4. Report by Vitamin B, Sub-Committee of the Accessory Food Factors Committee of the Medical Research Council and the Lister Institute, B io chem . J . , 1943, 37, 433.
5. Wokes, F., and Organ, J. G., P r o c . B io ch e m . Soc., 1943, 37, iii.
6. Wokes, F., An a l y s t, 1942, 67, 135.
7. Booth, R. G., J . Soc. Chem . I n d . (Trans.), 1940, 59, 181.
8. Cohen, F. H., Rec. trav. chim . P a y s -B a s , 1935, 54, 133.
9. Nicholls, J. R., Booth, R . G., Kent Jones, D. W., Amos, A. J., and Ward, H. H., An a l y s t, 1942, 67, 15.
10. Kuhn, R., and Vetter, Hi, B e r., 1935, 68, 2375.
11. Wokes, F., Organ, J. G., and Jacoby, F. C., B io chem . J . , 1942, 36, vii.
12. Dawson, E. R „ private communication.
13. Ward, H. H., private communication.
14. Wokes. F., and Still, B. M., Chcm . a n d In d ., 1941, 60, 722.
Ov a l t i n e Re s e a r c h La b o r a t o r i e s
Ki n g’s La n g l e y, He r t s. A p r i l , 1 9 4 3
D e t e r m i n a t io n of th e V o l u m e of G a s C o n t a in e d in the P a r t ic le s of D r i e d M i l k P o w d e r
B y M . M . M U E R S , Ph.D . , F . I . C . , a n d E . B . A N D E R S O N , M . S c . , F . I . C .
I. I n t r o d u c t i o n— I t is n o w w e ll k n o w n t h a t t h e p a r t ic le s o f s p r a y - d r ie d m i l k p o w d e r c o n s is t p a r t l y o f h o llo w s p h e r e s o f v a r y i n g s iz e a n d d e n s it y . I n c o n n e c t io n w i t h a n i n v e s t i g a t i o n i n t o t h e p a c k i n g o f s u c h p o w d e r s i t b e c a m e n e c e s s a r y t o a s c e r t a in t h e v o lu m e a n d c o m p o s it io n o f t h e g a s c o n t a in e d i n t h e p a r t ic le s . T h e o n l y m e t h o d p r e v i o u s l y d e s c r ib e d w a s t h a t e m p lo y e d b y L e n d r i c h,1 l a t e r s l i g h t l y m o d if ie d b y H e r m a n n,2 i n w h ic h t h e c h a n g e i n v o l u m e ( c o n tr a c tio n ) o f a s u s p e n s io n o f m i l k p o w d e r i n b e n z e n e o r a lc o h o l w a s d e t e r m in e d a f t e r it s s o lu t io n b y a d d i t i o n o f a q u e o u s a m m o n ia . A s v o l u m e d iffe r e n c e s o f 0-5-2 - 0 m l o n l y w e re b e in g m e a s u r e d , t h e d e s c r ip t io n o f t h e a p p a r a t u s u s e d , a 1 0 0 m l
0 , M U E R S A N D A N D E R S O N : D E T E R M I N A T I O N O F T H E V O L U M E O F GAS
m e a s u r in g c y lin d e r , d i d n o t s u g g e s t t h a t t h e a c c u r a c y w a s s u c h a s w e d e s ire d . M o r e o v e r , L e n d r i c h s a y s — " t h e n ^ lk p a r t ic le s a re d is s o lv e d t o s u c h a n e x t e n t t h a t t h e e n c lo s e d a i r is lib e r a t e d . ” I n a b s e n c e o f e x p e r im e n t a l p r o o f , t h is s t a t e m e n t is o p e n t o q u e s t io n . T h e fig u r e s f o u n d b y L e n d r i c h v a r i e d f r o m 0 -1 to 1 -4 m l/ g a n d b y H e r m a n n f r o m 0 - 2 t o 0 - 3 m l/ g .
I I . E X P E R I M E N T A L— A n o b v i o u s m e t h o d f o r t h e p u r p o s e i n v ie w is, u s in g s u it a b le a p p a r a t u s , to d is s o lv e th e p a r t ic le s c o m p l e t e l y a n d c o lle c t t h e g a s lib e r a t e d . T h i s i s e s s e n t ia l w h e n an a n a ly s is o f t h e g a s is a ls o r e q u ir e d . T h i s le d t o a s t u d y o f e b u l l i t i o n t e c h n i q u e , a s a r e s u lt o f w h ic h th e firs t m e t h o d d e s c r ib e d b e lo w w a s e v o lv e d .
(i)
Ebullition Method
— F i t a 5 0 0-rn l c o n ic a l f la s k A w i t h a 5 0- m l d r o p p i n g f u n n e l B h a v i n g a 5- m m b o r e t a p a n d w i t h a d e l i v e r y t u b e C w h ic h d ip s i n t o a s m a l l t r o u g h f ille d w i t h w a t e r a n d p r o v i d e d w i t h a g a s c o lle c t in g t u b e D . C a r r y o u t a b l a n k w i t h e a c h t e s t a s fo llo w s .F i l l t h e fla s k c o m p l e t e l y w i t h w a t e r , a d d a fe w g la s s b e a d s t o p r e v e n t b u m p i n g , a n d rin s e t h e f u n n e l i n t o t h e f la s k w i t h a fe w m l o f » - p r o p y l a lc o h o l. B o i l t h e w a t e r v i g o r o u s l y u n t i l 1 5 0 - 2 0 0 m l h a v e b e e n e x p e lle d o r e v a p o r a t e d ; a t e s t t u b e in v e r t e d o v e r t h e o u t le t o f C p r e v e n t s s p la s h in g . P l a c e 3 0 m l o f « - p r o p y l a lc o h o l i n t h e f u n n e l a n d t h e g a s c o lle c t in g t u b e f u l l o f w a t e r o v e r t h e e n d o f C . R u n t h e a lc o h o l c o n t i n u o u s l y i n t o t h e fla s k d u r i n g 1 m in . „ a p p l y i n g g e n t le p r e s s u r e b y m o u t h t o B b y m e a n s o f t h e a t t a c h m e n t ( F ig . 1), t o p r e v e n t t h e s t e a m e s c a p in g i n t o B . C o n t in u e b o ilin g f o r a t o t a l t i m e o f 2 m i n . f r o m t h e t im e D is p la c e d o v e r t h e o u t l e t . T r a n s f e r t h e g a s in D t o a g a s b u r e t t e a n d , a f t e r a g i t a t i n g w i t h w a t e r t o r e m o v e a l c o h o l v a p o u r , m e a s u r e a n d a n a ly s e i n a n y a p p r o p r i a t e w a y .
M a k e t h e a c t u a l d e t e r m i n a t i o n in e x a c t l y th e s a m e w a y , u s in g a w e ll- s t ir r e d s u s p e n s io n o f 2 0 g . o f p o w d e r i n 2 5 m l o f « - p r o p y l a lc o h o l, t a k i n g c a r e t o b r e a k d o w n lu m p s a n d e l i m i n a t e e n t a n g le d a i r b u b b le s . I n t r o d u c e t h e s u s p e n s io n t h r o u g h t h e f u n n e l B in t o A , a s s o o n a f t e r p r e p a r a t i o n a s p o s s ib le , i n s u c c e s s iv e s m a l l a m o u n t s w i t h m i n i m u m i n t e r v a l s , o t h e r w is e t h e s t e m o f B m a y b e c o m e b lo c k e d . F i n a l l y r in s e B w i t h 5 m l o f t h e a lc o h o l.
T h e p o w d e r d is s o lv e s . C o l l e c t t h e e v o l v e d g a s a n d m e a s u r e a n d a n a ly s e a s b e fo r e , c o r r e c t i n g f o r t h e b la n k .
D u p l i c a t e s a g r e e w i t h i n 5-1 0% a n d t h e l i m i t o f a c c u r a c y is 0 - 0 3 m l/ g . « - P r o p y l a l c o h o l w a s c h o s e n b e c a u s e i t c o m b in e s t h e r e q u ir e d p r o p e r t ie s o f m i n i m a l s o lv e n t a c t i o n o n t h i s t y p e o f p o w d e r , lo w d e n s it y , m i s d b i U t y w i t h w a t e r a n d b . p . j u s t b e lo w t h a t o f w a te r .
T h e o b j e c t io n s to t h e m e t h o d a r e («) t h e r e l a t i v e l y la r g e b l a n k , (6) t h e d i f f i c u l t y o f o b t a i n i n g b u b b le - fr e e s u s p e n s io n s w i t h lo w - d e n s it y p o w d e r s , (c) t h e m a n i p u l a t i o n o f i n t r o d u c in g t h e s u s p e n s io n is n o t e a s y , (a’) i f t h e p o w d e r h a s b e e n p a c k e d i n C O ., t h i s i s p a r t i a l l y lo s t b y s o l u t i o n i n t h e w a t e r o f t h e c o l l e c t i n g a p p a r a t u s , a n d (e) g a s , e s p e c ia lly C O , , d is s o lv e d i n th e f a t p h a s e o f w h o le m i l k p o w d e r s is l ib e r a t e d t o g e t h e r w i t h t h e e n c lo s e d g a s . F o r th e s e r e a s o n s a t t e n t i o n w a s d ir e c t e d t o a d e n s i t y m e t h o d .
(ii)
Density Method*
— F o r h o llo w p a r t ic le s o f d e n s i t yJ
w i t h s o lid s h e lls o f d e n s i t y D t h e v o l u m e o f t h e h o llo w s p a c e is n i l g .F o r d e t e r m i n i n g «’ t h e m a i n p r o b l e m is t h e s e le c t io n o f t h e l i q u i d t o b e u s e d . I t s h o u l d h a v e
(a)
a d e n s i t y le s s t h a n t h a t o f t h e p o w d e r , (6) m i n i m u m s o l v e n t o r o t h e r a c t i o n , (e) l o w v i s c o s i t y m i d g o o d w e t t i n g p o w e r . A f t e r s e v e r a l t r i a l s « - p r o p y l a l c o h o l w a s* This paper had been prepared tor publication before receipt of the J e u r t m i o f D a i r y R t s t j r c h , 1S43, td, ilS, it', which Lea . ' derive another formula for calculating the gas content oi spray-dried powders.
C O N T A IN E D I N T H E P A R T IC L E S OF D R IE D M IL K P O W D E R 7 f o u n d m o s t n e a r l y to f u l f i l t h e s e c o n d it io n s , as, a p a r t f r o m t h e o t h e r p r o p e r t ie s , i t h a s l it t le a c t io n o n s p r a y m i l k p o w d e r i n le ss t h a n 3 0 m in . c o n t a c t ; b e y o n d t h i s t i m e a l i t t l e f a t is e x t r a c t e d a n d s o m e g a s lib e r a t e d .
F o r t h e a c t u a l d e t e r m in a t io n , u s e a 2 5- m l s p .g r . b o t t l e a t 2 5° C . ; a d j u s t t o t h is t e m p , a s r a p i d l y a s p o s s ib le , b u t g r e a t a c c u r a c y is n o t n e c e s s a r y . D u p l i c a t e s a g re e w i t h i n 5% .
D e t e r m i n a t i o n o f D f o r f u l l c r e a m (2 6% fa t) g a s -fre e m i l k s o lid s g a v e a r a n g e o f 1-2 6-1-2 8, m e a n 1-2 7; s k im m i l k s o lid s g a v e 1-4 6, w h i c h is i n g o o d a g r e e m e n t w i t h S t a m b e r g a n d B a i l e y ’s3 fig u r e o f 1-4 5 9. T a k i n g t h e D /2 5° C . o f b u t t e r f a t as 0-9 2 0, a n d th e fig u r e o f 1 - 4 5 9 f o r s k im m i l k s o lid s , t h e c a lc u la t e d v a lu e f o r f u l l c r e a m m i l k s o lid s is 1-2 6 6.
D i f f i c u l t i e s w e re a g a in e x p e r ie n c e d w i t h c e r t a in l o w - d e n s it y p o w d e r s h a v i n g p a r t ic le s w i t h s o m u c h e n c lo s e d g a s t h a t t h e y .w e re l i g h t e r t h a n t h e a lc o h o l.
I I I . R e s u l t s— T a b l e I g iv e s t y p i c a l r e s u lt s f o r t h r e e t y p e s o f f u l l c r e a m p o w d e r i n t h e r a n g e w i t h i n w h ic h a ll o t h e r s a m p le s f a ll. S a m p le s 1 - 5 a r c n o r m a l p o w d e r s p r o d u c e d b y t h e M i l k a l p ro c e s s , 6 - 1 0 l o w - d e n s it y p o w d e r s , a n d 1 1 - 1 4 v e r y h i g h d e n s it y o n e s . C o m p a r is o n o f r e s u lt s o b t a in e d b y t h e t w o m e t h o d s s h o w s f a i r a g r e e m e n t , e x c e p t f o r s o m e lo w - d e n s i t y s a m p le s , w h ic h c o n t a i n e d d is s o lv e d C0 2 a n d g a v e h i g h v a lu e s b y t h e e b u l l i t i o n m e t h o d .
T a b l e I
Gas, ml/g N.l'.P.
A_______
Expt.
No.
f
Density method A__
Ebullition method
1 010 0-15
2 0-07 0-10
3 0-11 0-09
4 0-07 0-10
5 0-09 0-05
6 0-35 0-29
7 0-31 0-65
8 0-23 0-3S
9 0-19 0-56
10 0-23 0-68
11 0-04 <0-05
12 0-03 <0-05
13 0-02 0-06
14 0-03 <0-05
T h e s e fig u r e s a re , o f c o u r s e , a v e r a g e v a lu e s f o r t h e e n c lo s e d g a s in a s a m p le . R e fe r e n c e h a s a lr e a d y b e e n m a d e t o d if fic u lt ie s e x p e r ie n c e d w i t h c e r t a i n p o w d e r s c o n t a i n i n g l i g h t p a r t ic le s , a n d o n e s u c h w a s s e p a r a t e d i n t o a l i g h t a n d h e a v y f r a c t io n u s in g « - p r o p y l a lc o h o l as t h e v e h ic le a n d c e n t r if u g a l a c t i o n f o r t h e s e p a r a t io n . T h e r e s u lt s w h ic h a re o f in t e r e s t a p p e a r i n T a b l e I I .
T a b l e I I
Gas, ml/g N.T.P.
, *---
Density method Ebullition method
Original powder .. .. 0-39 — • *
Light fraction .. .. 0-88 ' 0-88
Dense fraction . . . . 0-14 0-14
S u m m a r y— T h e n e c e s s it y h a v i n g a r is e n f o r d e t e r m i n i n g t h e g a s c o n t e n t o f s p r a y - d r ie d m i l k p o w d e r p a r t ic le s , a s e a r c h o f t h e lit e r a t u r e f a d e d t o r e v e a l a m e t h o d o f s u ff ic ie n t a c c u r a c y f o r t h e p u r p o s e i n v ie w . T w o m e t h o d s h a v e b e e n w o r k e d o u t , o n e d e p e n d in g o n t h e lib e r a t i o n o f t h e g a s o n c o m p le t e s o lu t io n o f t h e p a r t ic le s , t h e o t h e r o n a d e t e r m in a t io n o f t h e i r d e n s i t y . F r o m a m a n i p u l a t i v e p o i n t o f v i e w t h e l a t t e r is f a r s u p e r io r , b u t i f a n a n a ly s is o f t h e g a s is r e q u i r e d a ls o , t h e f o r m e r is r e c o m m e n d e d .
T h e g a s c o n t e n t o f t h e p o w d e r s e x a m in e d r a n g e d f r o m 0 - 0 2 t o 0 - 3 5 m l p e r g . T h e r e s u lt s o b t a in e d s u g g e s t t h a t f o r n o r m a l p o w d e r s t h e fig u r e s q u o t e d b y p r e v io u s w o r k e r s a r e h ig h .
O u r t h a n k s a r e d u e t o t h e D i r e c t o r s o f U n i t e d D a i r i e s , L t d . , f o r p e r m is s io n t o p u b lis h . Re f e r e n c e s
1. Lendrich, K., M ilc h w . F o rsch ., 1923-4, 1, 231-293.
2. Hermann, A., id ., 1928, 6. 147-186.
3. Stamberg, O. E., and Bailey, C. H., F o o d Res., 1940, 5, 175-280.
Un i t e d Da i r i e s Lt d., Ce n t r a l La b o r a t o r y
Wo o d La n e, Lo n d o n, W.12 October, 1943
