Investigation of droplet-distribution patterns in sprays by means of radioactive tracers
by Robert Itoh
A THESIS Submitted to the Graduate Faculty in partial fulfillment of the requirements for the degree
of Master of Science in Engineering Physics
Montana State University
© Copyright by Robert Itoh (1952)
Abstract:
A technique using radioactive tracers for determining the total volume of sprayed liquid droplets
deposited on glass slides is described. The process used to extract the tracer from RaSO4 flourescent
disks and dissolve it into water and oil is given. To compare with the volume found by using tracers, a
method of finding the. total volume by measurements of the droplets, themselves, was used. The
measurements by both methods using the oil solution compared well with each other. In general,
however, the results for the water droplets as measured by the tracer method were higher than those by
the droplet-measurement method. The major source of these differences wap apparently due to the
non-fa omogeneous nature of the particles emitted by the tracer. INVESTIGATION OF D RO PLET-DISTRIBUTION PATTERNS IN SPRAYS
' " ' ...... BY MEANS
OF 'H A D lo
W lV E TRACERS"
'
'
;
• • v . J ', 'v
-• .
by
ROBERT ITOH
A
THESIS
S u b m itted t o th e G raduate F a c u lty
'
. ■"
'
Lr.
• p a r t i a l f u l f i l l m e n t o f th e re q u ire m e n ts
f o r th e d e g re e o f
M aster o f S c ie n ce in E n g in e e rin g H iy sics
at
M ontana.S ta te C o lleg e
Bozemanj Montana
J u ly , 1952
H3 7 S1
J tu * .'
Z,
-2 -
TABLE OF CONTENTS
A b s tra c t . . . . . . . . . . . . .
3
...........................
I n t r o d u c t i o n .................................................... ....
4
P rocedure f o r D is so lv in g th e R a d io a c tiv e T ra c e r.
5
5
9
For W ater S o lu tio n .
For O il S o lu tio n . «
P r e p a ra tio n o f S lid e s and Measurements o f Spread F a c to r
For W ater d r o p le ts o
For O il D ro p le ts . .
o
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11
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15
17
S p ray in g th e R a d io a c tiv e S o lu tio n s on th e P rep ared S lid e s .
. . .
Methods o f D eterm ining Volumes o f S o lu tio n D ep o sited on S lid e s
By M easurements o f D ro p le ts . . . .
By th e Use o f T ra c e rs in D ro p le ts o
R e s u lts and Comparison o f Measurements
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D ro p le t S iz e s o o o o o o o o o o o o o o o o . © o © © © © © © ©
D iffe re n c e s Due t o th e T rac e r . . . . . . . . . . . . . . . . .
L i te r a tu r e C onsulted
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10333?
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ABSTRACT
A te c h n iq u e u s in g r a d io a c ti v e t r a c e r s f o r
d e te rm in in g th e t o t a l volume o f sp ray ed l i q u i d
d r o p le ts d e p o s ite d on g l a s s . s l i d e s i s d e s c rib e d .
The p ro c e ss u sed to e x t r a c t th e t r a c e r from RaSO^
f lo u r e s c e n t d is k s and d is s o lv e i t in to w a te r and
o i l i s g iv e n . To compare w ith th e volume fo u n d
by u s in g t r a c e r s , a method o f f in d in g th e . t o t a l
volume by m easurem ents o f th e d r o p le ts , them­
s e lv e s , was u s e d . The m easurem ents by b o th
methods u s in g th e o i l s o lu tio n compared w e ll
w ith each o th e r . In g e n e r a l, how ever, th e
r e s u l t s f o r th e w a te r . d r o p le ts as m easured by
th e t r a c e r method were, h ig h e r th a n th o se by th e
d ro p let-m easu rem en t m ethod. The m ajor so u rce o f
th e s e d if f e r e n c e s wap a p p a re n tly due t o th e n o n homogeneous n a tu r e oijf th e p a r t i c l e s e m itte d by th e
tra c e r,
6
, INTRODUCTION*
The e f f e c tiv e n e s s o f th e a p p lic a tio n o f i n s e c t i c i d e s , h e r b ic id e s , and
o th e r, l i q u i d s try means o f s p ra y in g depends upon th e number and th e s iz e s
o f th e . d r o p le ts d e p o s ite d upon a g iv en a r e a ,
There have been s e v e r a l
d i f f e r e n t methods d e v ise d f o r d e te rm in in g t h e .d r o p l e t s iz e s and th e amount
o f l i q u i d d e p o s ite d .
To d eterm in e th e s iz e o f d r o p le ts K0 Rc May (5)
d e v ise d a method by c o n s id e rin g them as le n s e s , w hereas W0 W„ Gibbs (2)
used th e ir r a te of f a l l .
L0 .D0 Goodhue and W0 N0 ,..Sullivan (3 ) u se d a dyed
s o lu tio n arid by em ploying a p h o to e le c tr ic p h o to m eter d eterm in ed th e amount
o f d e p o s it .
O ther w o rk ers determ in ed by ch em ical a n a ly s is th e r e l a t i v e ,
d e p o s itio n on w ire s o f d i f f e r e n t s i z e s , b u t t h e i r r e s u l t s d id n o t show
c l e a r l y th e range in s iz e s o f th e d r o p le ts (6 ) .
.This i n v e s t ig a ti o n
p ro p o ses t o determ in e th e amount o f l i q u i d d e p o s ite d by a method
in d e p en d e n t o f t h e .ones a lre a d y m en tio n ed .
t r a c e r s w ere u s e d .
In t h i s method r a d io a c tiv e
t5-
EREPARATION OF THE RADIOACTIVE SOLUTION
.
The r a d io a c ti v e t r a c e r u s e d i n t h i s i n v e s t ig a ti o n was e x tr a c te d from
f l o u r e s c e n t m arking d i s k s „
These d is k s w ere round p ie c e s o f card b o ard
w ith a h a rd f lo u r e s c e n t s a l t m ix tu re d e p o s ite d .on one s id e w hich was
s e a le d by a tr a n s p a r e n t o rg a n ic compound.
T h e ;s a l t m ix tu re.w a s composed
o f , ZnSj P h osphor,..RaSO^, and th e end .p ro d u c ts . o f th e ra d iu m . s e r i e s w hich
w ere presumed t o be su lp h a te s=
The amount o f Radium p e r d is k , ap p ro x i­
m a te ly 20 |JLg., was d e term in e d by com paring one o f th e d is k s w ith RaClz
stan d a rd s=
'
In o rd e r t o change. th e s a l t s i n t o s o lu b le compounds th e y w e r e - f i r s t
c ra ck e d o f f th e c a rd b o a rd .
The s a l t s w ere th e n p la ce d i n a i $6 ml= b eak er
which was about o n e -fo u rth f u l l o f c o n c e n tra te d , HCl=
.With th e b eak er
§ov§red th e _ § o lu tig n was e v a p o r a te d .to d ry n e s s , b u t was n o t allow ed to
b o i l ; so as .t o ‘e lim in a te - s p a tte rin g =
su lp h u r .fro m th e ZnS=
T h is p ro c e ss w.as u sed t o remove th e
C o n ce n tra te d HNO3 .was th e n ,added and th e s o lu tio n
was a g a in .e v a p o ra te d t o d ry n e ss i n o rd e r t o remove th e o rg a n ic m a tte r =
A lthough..the. .above s te p s w ere p o t a b s o lu te ly n e c e s sa ry th e y re d u c ed t o a
minimpm th e amount.,of m a t e r i a l t h a t had t o be f i l t e r e d a t th e .end . o f t h i s
procedure=,. ,The rem ain in g r e s id u e was h e a te d t o d ry n ess i n a s o lu tio n
NagGO^.. tra n s fo rm in g some o f th e s u lp h a te s i n t o c a rb o n a te s ,
wap agaip_,.M ded_ a n d .e v a p o ra te d to dryness=
Then HCl
This, l a s t p ro c e ss tra n sfo rm e d
th p „ c a $ b p n a tss _ e f t h e .p r e v i o u s .s t e p i n t o s o lu b le c h lo rid e s=
W ater was
th e n added t o th e rem ain in g s a l t , and th e m ix tu re was f i l t e r e d =
T he.m ajor
p o rtio n ..o f . th e s o lu te was NaCl along w ith , some, ZnCl2.= The r a d io a c tiv e
elem en ts w hich w ere p r e s e n t i n th e ,so lu te w e r e .in m inute q u a n titie s =
:
-
- -
,
'
1
.
• •
of
'
.
.•
•
1
1
'
A c tiv ity in C ounts/m in.
1000
\
100
\
-------CR--------------------------
&
V
100
200
300
400
500
Mg./cm . 2 o f Aluminum
F ig u re I .
A bsorption curve o f w ater sample
600
-7 -
TABLE I . The Radium S e rie s
Elem ent
Symbols
Energy o f R a d ia tio n
(Mev)
H a lf ULfe
Oi
Radium
Radon
88Ra226
86*"222
1600 y e a rs
4 .9 7
3 o825 days
5 .4 9
7-
0
—
0 .1 9
—
Polonium
Q4 Po2 1 8 (RaA)
3 «°5 m ino
5 .9 9
Lead
Q2 Pb2 1 4 (RaB)
26«8 min.
—
0.6 5
r
Bismuth
Q3Bi2 1 4 (RaC)
1 9 .7 min.
5 .5 0
3 .1 5
1 .8
Polonium
S4 Po2 1 4 (R a C )
1 .5 x 10”4 s e c .
7 .68
——
T hallium
Q1T i210 (R a c )
1.32 m in.
1 .8 0
—
Lead
Q2 Fb2 1 0 (RaD)
2 2 .2 y e a rs
0.025
0 .0 4 7
Bismuth
Q3Bi2 1 0 (RaE)
4 .9 7 days
— —
1 .1 7
— —' -
Polonium
Q4 Po2 1 0 (RaF)
139 days
5 .3 0
Lead
82Fb2°6
S ta b le
0
—
—
r
m.
————
e—DO-a—
N eutron Number
-8 -
RaC1
.R eaction
scheme
a Decay
& Decay
P ro to n number
f ig u r e 2 .
A N e u tro n -p ro to n p lo t o f radium and i t s decay p ro d u c ts .
=9=
A t e s t o f th e r e s id u e showed t h a t th e gamma r a d i a t i o n was
ap p ro x im a te ly e q u a l t o t h a t o f th e o r i g i n a l s a l t p la c e d i n th e b e a k e r.
A t e s t , o f th e f i l t r a t e showed l i t t l e in d ic a tio n o f gamma ra y s..
A
d ro p o f th e f i l t r a t e , was e v a p o ra te d bn a s l i d e and p la c e d n e x t t o an
end-window G eiger tu b e ,
i n a b s o rp tio n curve* f ig u r e I 5 shows a p lo t of
th e r e s u l t i n g a c t i v i t y i n co u n ts p e r m in u te a g a in s t a b s o rb e rs o f
aluminum g iv en i n m g./cm . 2 on a s e m i-lo g a rith m ic s c a le .
The curve shows
t h a t th e b e ta p a r t i c l e s would have been sto p p ed by a $00 m g./cm . 2
a b so rb e r which in d ic a te d th e p re sen c e o f p a r t i c l e s w ith en erg y o f about
1 .2 Mev C-Oo1 The f i l t r a t e ,showed grow th i n i t s a c t i v i t y , b u t due to
:<
i n i t i a l d i f f i c u l t i e s w ith th e c o u n te r th e grow th curve was n o t p lo tte d .
.
The f i l t r a t e re a c h e d i t s maximum a c t i v i t y a f t e r a p e rio d o f 3 t o 4 weeks'.
A fte r th e p ro d u c t had re a c h e d a maximum a c t i v i t y th e r e was no d e c re a se in
a c t i v i t y d u rin g th e p e r i o d ,o f o b s e rv a tio n s ta k e n over th e su b seq u en t two
m onths.
From th e s e d a ta and by means o f T able .I CO and f ig u r e 2 (4) i t was
concluded, t h a t t h e p r i n c i p a l elem ent o f th e f i l t r a t e was p ro b a b ly Pb
210
The la c k o f gamma r a d i a t i o n from th e f i l t r a t e in d ic a te d t h a t a l l elem
en ts
. .
- -
above Pb^® .in th e s e r i e s w ere a b s e n t.
•'
....
The 1 .2 Mey- b e ta p a r t i c l e s from
210
210
th e f i l t r a t e in d ic a te d th e p re sen c e o f B i1- . %S ince Bi.
h a s a v ery
s h o r t h a l f l i f e and th e r e was no m easu rab le d e c re a se o f a c t i v i t y over
th e p e rio d o f o b s e r v a tio n , i t was presumed t h a t P t / 19 was th^e n source",
o f th e a c t i v i t y p r e s e n t.
F or th e p r e p a r a tio n o f th e o i l s o lu tio n th e same p ro c e d p re was u sed
as f o r th e w a te r s o lu tio n up t o th e p o in t o f adding th e NagCO^.
“ ■ l O
"
H ere, i n s te a d , a b a s ic s o lu tio n o f ammonium a c e ta te was added t o change
some o f th e s u lp h a te s i n t o s o lu b le a c e t a t e s „
A fte r e v a p o ra tin g t o
d ry n e ss Ho, 3 d i e s e l o i l was added, and th e m ix tu re was th e n f i l t e r e d .
A lthough th e a c t i v i t y was h ig h enough t o be u s e f u l, i t was s t i l l to low
f o r an a b s o rp tio n curve t o be p l o t t e d .
F o r th e o i l s o lu tio n Pb^
was assumed t o be th e 'f so u rc e" o f a c t i v i t y b ecau se o f th e ch em ical
r e a c t i o n s which w ere b e lie v e d t o have ta k e n p la c e (%).
Both, o f th e above method's f a i l e d t o b r in g th e rad iu m , i t s e l f , in to
s o lu tio n .
The p re p a re d s o lu tio n s w ere c o lo re d w ith dyes in o rd e r t o le av e
v i s i b l e o u tlin e s , o f th e d r o p le ts a f t e r e v a p o ra tio n .
<°>11
=»
PREPiMTION OF SLIDES AND MEASUREMENTS OF SPREAD FACTOR
The s l i d e s u sed t o c o l l e c t th e l i q u i d d r o p le ts w ere o rd in a ry m icro­
scope c o v er g la s s e s w hich w e r e ,.on th e a v e ra g e , 2 2 .1 mm. sq u ares
The
c o m e r s o f th e s l i d e s w ere rounded t y f i l i n g i n o rd e r t h a t th e y c o u ld be
p la c e d i n th e r e c e p ta c le s u se d i n th e w indow less G eig er tu b e s (Q-Gas Flow
C o u n ter, M anufactured by th e N uclear In stru m e n t and Chem ical C o rp o ra tio n ).
A r e p e l l e n t , which i s u s e d I y la u n d r ie s f o r w a te r-p ro o fin g f a b r i c s ,
was o r i g i n a l l y t r i e d as a c o a tin g on th e s l i d e s u se d to c o l l e c t w a te r
d ro p le ts .
The purpose o f t h i s was t o keep th e s p re a d f a c t o r low .
The
Spread, f a c t o r i s d e fin e d as th e r a t i o o f th e d ia m e te r o f th e b a se o f a
d r o p le t r e s t i n g on a f l a t s u rfa c e t o th e d ia m e te r o f th e d r o p le t i n i t s
o r i g i n a l s p h e r ic a l sh a p e .
I t . was o b serv ed , how ever, t h a t as th e d r o p le t
e v a p o ra te d th e d ia m e te r o f th e base became s m a lle r w ith o u t le a v in g any
v i s i b l e ev id en ce o f i t s o r i g i n a l s i z e .
S in ce th e o r i g i n a l s i z e o f th e
b a se i s n e c e s s a ry f o r th e c a lc u la tio n Of t h e . c a lc u la tio n o f th e sp re ad
f a c t o r , th e r e p e l l e n t whs d is c a rd e d .
Y a s e lin e was found to be a much b e t t e r c o a tin g .
—~
'
.
1
The v a s e lin e was
sp re a d on th e c le a n s l i d e s , h e a te d to m e ltin g and allow ed to c o o l, g iv in g
a smooth s u r f a c e .
The^c o r r e c tio n f a c t o r ( in v e rs e o f s p re a d f a c t o r ) f o r w a te r d ro p le ts
r e s t i n g on a v a s e lin e b a se was c a lc u la te d by a method which was re v is e d
from t h a t g iv en in an a r t i c l e by K„ R. May (5)=
The d r o p le ts ob serv ed
u n d e r a m icroscope from th e s id e appeared t o be bounded by a s p h e r ic a l and
a p la n e s u rfa c e as i s shown i n f ig u r e 3 a .
To f i n d th e a c tu a l r a d iu s ( r ) o f th e o r i g i n a l d r o p le t b e fo re i t was
-1 2 -
c aught
th e s l i d e , we p ro ceed as fo llo w s .
l o t t i n g th e r a d iu s o f th e
observed sp h ere be R, th e u p p er h a l f o f th e sp h ere w i l l th e n have f o r i t s
volume
V1 = (2 /3 ) v r 3
To f i n d th e volume o f th e low er p o rtio n c o n sid e r f ig u r e 3b where R i s
th e r a d iu s o f th e d e p o s ite d sp h ere and A th e r a d iu s o f th e b a se .
f ig u r e 3 a .
d r o p le t
Side view o f
f ig u r e 3b. Diagram r e p r e s e n t­
in g low er h a l f o f d r o p l e t .
The volume o f t h i s p o r tio n i s th e n
- \|R^ - A'
(R2 - A2 ) ^Ir 2' - A2
3
V2 = TT (r 3/ 3 ) (2 + a2/ r2 )
\ i - A^/tP
The t o t a l volume o f th e d r o p le t on th e s lid e becomes
V = Vi + V2 = (2 /3 ) TT R3 + Tr (R3/ 3 ) (2 + a2/ r2 ) 'I I - A2ZR2
-1 3 -
Assuming t h a t th e o r i g i n a l d r o p le t, b e fo re i t s e t t l e s on th e s l i d e , h as a
r a d iu s ( r ) and a volume (v) th e n
V = V = (4 /3 ) TT
(4/ 3 ) TT r-3 = ( 2 /3 ) Tr R3
I + ( I + — - ) \ | l - A2Zr 2
2R2
Then
1/3
R /2^[ I + ( I + J L ) \ | l - A2ZR2]
D iv id in g b oth s id e s by A
1/3
I + (I + - 4 \ll - A2ZR2]
r/A
Now l e t
J
1/3
R
I +
2^A L
(I
+
4 )
^
A2Zr2
$(A/R)
or
r/A = $(A/R)
The l a s t e q u a tio n i s an e x p re s s io n t h a t r e l a t e s th e r a d iu s ( r ) o f th e
o r i g i n a l d r o p le t and th e c o rre sp o n d in g r a d iu s (A) o f th e base o f a d r o p le t
t o a fu n c tio n o f A/R„
F ig u re 4 r e p r e s e n ts a g ra p h ic a l s o lu tio n o f t h i s
e q u a tio n where r/A o r ^(R/A) i s a f u n c tio n o f A/R„
To f in d th e o r i g i n a l r a d iu s ( r ) o f a d r o p le t m easurem ents were f i r s t
made a t a , b , and c r e s p e c tiv e ly by means o f th e tr a v e lin g m icro sco p e« No
m easurem ents w ere ta k e n a t d because t h i s p o s itio n would have changed due
t o th e e v a p o ra tio n o f th e w a te r d u rin g th e tim e i n t e r v a l needed f o r th e
—
1
/> —
F ig u re 4„ Graph o f e q u a tio n f o r sp re ad f a c t o r c o r r e c tio n
o f w a te r d ro p s „
-1 5 h a i r l i n e t o t r a v e l from b t o c .
From th e m easurem ents o f a , b , and c th e
f a c t o r (A/R) was d eterm in ed = Eiy i n s e r t i n g th e v a lu e (A/R) i n t o th e l a s t
e q u a tio n th e c o r r e c tio n f a c t o r (r/A ) was founds. Since' th e s o lu tio n o f t h i s
e q u a tio n i s p l o t t e d in f ig u r e 4j> th e c o r r e c tio n f a c t 6r (r/A ) was ta k en from
th e c u rv e „
The o r i g i n a l r a d iu s ( r ) was th e n found by m u ltip ly in g th e
c o r r e c tio n f a c t o r (r/A ) by th e r a d iu s (A) o f th e b a s e .
For a c c u ra te
r e s u l t s th e c o r r e c tio n (r/A ) sho u ld have been d eterm in ed f o r each s iz e o f
d r o p le t w ith in th e ran g e t o be in v e s t i g a t e d .
In t h i s in v e s t i g a t i o n ,
how ever, o nly d r o p le ts o f 500p. o r l a r g e r ( tr u e d ia m e te r) w ere measured
becau se th e s m a lle r ones would e v a p o ra te b e fo re any v a l i d re a d in g s co u ld
be ta k e n .
These m easurem ents gave an average v a lu e o f u n ity f o r r/A .
The
m easurem ents w ere made a t te m p e ra tu re s ra n g in g from 40 t o 50 d eg rees
F a h re n h e it.
For h ig h e r te m p e ra tu re s th e p re c ed in g method does n o t h o ld
becau se th e d r o p le ts sprea<| o h t m ore.
F or a c o a tin g on s l i d e s u sed t o . c o l l e c t o i l d r o p le ts , G . . E. D r i- f ilm
was recommended, however t h i s was u n a v a ila b le .
A l i q u i d soap s o lu tio n o f
I p a r t soap t o 3 p a r t s w a te r was u sed in s te a d g iv in g f a i r r e s u l t s .
The
s l i d e s w ere d ip p ed i n t o th e s o lu tio n and allow ed t o d r y .
The sp re a d f a c t o r was c a lc u la te d by th e same method d e s c rib e d in th e
a r t i c l e by K. R. May ( 5) .
T his a r t i c l e , s t a t e s t h a t f o r a c c u ra te m easure­
m ents th e sp re a d f a c t o r s f o r th e s i z e s o f th e d r o p le ts t o be in v e s tig a te d
sh o u ld be c a lc u la te d f o r each s l i d e .
However f o r th e s e s l i d e s t h i s was
n o t p o s s ib le becau se t h e i r a re as .,were to o s m a ll.
In s te a d th e d r o p le ts
(d ia m e te rs o f 50- 500(1) w ere - m easured on s l i d e s o th e r th a n th e ones a c tu a lly
oJ-Sc=
u se d f o r s p ra y in g .
The average c o r r e c tio n f a c t o r (r/A ) f o r th e m easure­
m ents o f o i l d r o p le ts on th e soap c o a te d s l i d e s was 0 .4 5 .
W ith a soap
b a se th e o i l d r o p le ts had t o be m easured w ith in 2 o r 3 h o u rs a f t e r
sp ra y in g s in c e th e y s p re a d on s ta n d in g .
«*»
17
“
SPRAYING. THE RADIOACTIVE SOLUTION ON. THE PpPMED SLIDES
The. p r e p a r e d - s lid e s w ere ..se t on p ie c e s o f ..ty p e w ritin g p a p e r . .(H am erm i l l . Bpnd2. Wto;2G.).,.. a b o u t. 4 . in c h e s sq u are ...in. o rd e r t o g iv e .g o o d , o v e r a l l ....
p i c t u r e s o f th e d r o p le t .p a tte rn s ,.. .Though t h i s paper i s p o s s ib ly n o t th e
b e s t , i t i s .one o f th e more r e a d ily ...a v a ila b le ty p e s ,.........................
The sp ra y in g was f i r s t conducted in s id e a .s e a le d ch am b er.b u t t h i s .....
method, was abandoned b ecause th e chamber, r e t a i n e d th e .f o g ( d r p p le tp .whose
d ia m e te rs_ a re of. $0* . . * l e s s ) . l n . i t . . . _ T h e a ia m s te r s _ p f .th e s e d r o p ia ts ,
w hich w ere v e ry ..numerous 2 could, n o t b e m easured a c c u r a te ly .
The f i n a l s p ra y in g .,o p e ra tio n .was ...conducted o u td o o rs w ith an o rd in a ry
hand sp ray ..g u n , .A_ s lig h t..b r e e z e c a r r i e d m ost, o f th e fog., away,.. T his more
n e a r ] ? a p p r g x # a te d . a c tu a l f i e l d g o n d itio n s ^ . t h e ^ a p p l i c a t i o n s p f i n s e c t i c id e s and .h e r b ic id e s ,
.The sp ra y gun. i t s e l f ..was h e ld . a t. a d is ta n c e o f from
2 t o 4 f t , from th e s l i d e s which were p la c e d on th e p ap er s h e e ts ,
.
=oISc=
METHODS OF DETERMINING THE TOTAL VOLUME OF SOLUTION DEPOSITED ON SLIDES
. T w o d i f f e r e n t m ethods, were u sed t o .f in d .th e . to t a l ., sm gm t. .o f.U Q u id .......;
t h a t wag d ep o sited _ o n a s l i d e , ..One. method employed the.. a c t u a l measurements
o f th e s iz e s o f th e d r o p l e t s , and th e o th e r , th e r a d io a c tiv e p r o p e r tie s o f
th e s o lu t i o n ,...................
...........
....................
....
. ... I n ..t h e ^meagwement_method th e ..s p rg re d s l i d e s w e r e , f i r s t p la c e d on an
o rd in a ry m ic ro sc o p e . s l i d e w hich, was. s c ra tc h e d , w ith, lin e 's ,.form ing s m a l l .
s q u a r e s c_..When t h e . two. s l i d e s , were p la c e d , u n d e r^ a m icroscope, t h e ; sprayed..
§I i d e _appea re d ..as th o u g h . i t .w ere .d iv id e d _i n t e r s e c t i o n s . . .j^r. m easuring th e
d r o p le ts i n one.. s e c t i o n . b e f o r e .. going..t o th e. n e x t,,, th e p o s s i b i l i t y „o f.
. ..
co u n tin g , some, o f. th e d r o p le ts , tw ice was elim inated,..;..,The; d ia m e te rs ,o f. th e
.•.
•
'
.
"
•i
s t a i n s were m easured t o th e n e a r e s t IOu, and were th e n m u ltip l ie d by th e
c o r r e c tio n f a c t o r , .ITom t h e c o r r e c t e d d ia m e te rs th e .v o lu m e s o f ,% e
d r o p le ts w ere fo u n d , . The . . t o t a l o f th e s e was ta k e n , as t h e , volum e. w h ich ,
was d e p o s ite d on th e s l i d e .
T his method was u sed im m ediately a f t e r th e
s p ra y in g o f th e o i l s in c e th e o i l , d r o p le ts sp re a d on stan d in g o
On some
s l i d e s th e ,d ro p le ts ra n g in g from 50 t o IOOjji i n d ia m e ter w ere so numerous
t h a t th e y would have r e q u ir e d c o n s id e ra b le tim e t o m easure 0
Instead of
m easuring each o f th e s e d r o p l e t s , on th e e n t i r e s l i d e , a p p ro x im a tio n s.......
w ere made by m easuring th e d r o p le ts p e r u n i t a re a over a s m a ll p o rtio n o f
a s l i d e , and th e n m u ltip ly in g by th e t o t a l a r e a .
In th e r a d io a c tiv e method c a l i b r a t i o n s l i d e s were p re p a re d by
d e p o s itin g th e r a d io a c ti v e s o lu tio n s on th e s l i d e s by means o f m icro
•
p i p e t t e s which w ere c a l i b r a t e ^ f o r c o n te n t, one, f i v e , t e n , o r f i f t e e n
__„“ 19“
lam bdas,
.
"
A lambda i s one one th o u san d th o f a m i l l i t e r o r 10“ ^ l i t e r .
d r o p le ts w ere th e n e v a p o ra te d , le a v in g o n ly th e r e s id u e .
each amount, were p r e p a r e d ,.
....
The
S e v e ra l s l i d e s o f
,
There were two ty p e s o f th e s e c a l i b r a t i o n s l i d e s p re p a re d f o r m easuring
th e . t o t a l volume o f th e w a te r d r o p le ts j some t h a t had no b ase a t a l l , and .
o th e r s t h a t had a v a s e lin e c o a tin g .on them s im ila r to th e s l i d e s t h a t were
s p ra y e d ,
.................................
On th e n o n -c o a te d s l i d e s th e p i p e t t e s w ere touched t o th e s l i d e
s u rfa c e in . many d i f f e r e n t p la c e s le a v in g d r o p le ts whose d i s t r i b u t i o n .
p a tte r n s w ere s im ila r t o th e s l i d e s t h a t w ere sp ra y e d .
These d r o p le ts ,
how ever, w ere somewhat l a r g e r th a n th o s e t h a t were e n c o u n te re d u n d er
sp ra y in g c o n d itio n s .
A lthough th e s e c a l i b r a t i o n s l i d e s , w hich wehe u se d
f o r m easuring th e amount o f w a te r s o lu tio n d e p o s ite d , had d r o p l e t ............
d i s t r i b u t i o n s . s im ila r to th o s e t h a t were d e p o s ite d by s p ra y in g , th e y £ id
n o t h a v e , t h e ;v a s e lin e ^c o a tin g 6. .......................................................................................
Qri ,th e . v a s e lin e c o a te d c a l i b r a t i o n s l i d e s , how ever, o n ly , two ,o r th r e e
d r o p le ts w ere d e p o s ite d becau se th e p i p e t t e s co u ld n o t be p la c e d ip
c o n ta c t w ith th e v a s e lin e c o a tin g w ith o u t d is tu r b in g , i t , . . , Only th e f i f t e e n
lambda p i p e t t e was u se d w ith th e s e ..s lid e s b ecau se th e s o lu tio n had a
ten d en cy t o a d h e r e .to th e o u ts id e s u rfa c e o f th e p ip e tte s o f.,sm a lle r
v a lu e s a n d .co u ld n o t a l l be d is c h a rg e d , on, t q, th e s l i d e s „ ...The..d r o p le ts on
th e s e s lid e 's were.,much. l a r g e r . th a n ,th o s e w hich were .,sprayed and th o se ,
d e p o s ite d on th e u n c o a te d c a l i b r a t i o n .,s lid e s., ...A lthqugli^he c o a tin g , on
th e s e s l i d e s , which w ere a ls o u sed f o r m easu rin g th e amount o f w a ter
«»20'»
s o lu tio n d e p o s ite d was th e same as th e sp ra y ed s lid e s * th e d r o p le t
d i s t r i b u t i o n p a tte r n s w ere q u ite d i f f e r e n t ,
.. A fte r th e s e s l i d e s had been d r ie d t h e i r a c t i v i t y was m easured ty th e
end-windpw c o u n te r5 .th e .flo w ..c o u n te rs and. th e L a n d sy erk .„electro m eter.
For. m e a s u re m e n ts,u s in g .th e end-window c o u n t e r - t h e .s l i d e s w ere p la ce d
ap p ro x im a te ly . 0 , 5. cm .,from th e window .of th e c o u n te r. .
.....................
.
The a c t i v i t i e s o f th e s l i d e s w ith e q u a l amounts o f d e p o s its were
a v e ra g e d .
F ig u re 5 shows a p l o t o f w a te r s o lu tio n d e p o s ite d on th e non=
c o a te d s l i d e s v s . th e a c t i v i t y o f i t s r e s id u e i n c o u n ts/m in u te (c o rre c te d
f o r background) where th e a c tiv ity , was m easured t y th e end=window c o u n te r.
S im ila r cu rv es w ere p l o t t e d u s in g th e flo w c o u n te r and th e Landsverk
e le c tr o m e te r .
There w ere no graphs made f o r th e v a s e lin e c o a te d c a li b r a ­
t i o n s l i d e s because a l l o f th e s e w ere p re p a re d t y u s in g th e 15 lambda
p ip e tte .
F or w a te r sp ray ed s l i d e s which w ere compared w ith th e non=coated
c a l i b r a t i o n s l i d e s and whose a c t i v i t y was m easured by th e end-window
counter^ th e t o t a l volume o f th e d r o p le ts was found by m u ltip ly in g th e
a c t i v i t y o f th e r e s id u e s i n c o u n ts/m in u te (c o rre c te d f o r b ack g ro u n d )s try
th e slo p e, o f th e curve o f f ig u r e 5.
The same pro ced u re was u se d f o r
m easurem ents ta k e n try th e flow c o u n te r and th e Landsverk e le c tr o m e te r .
A d i r e c t com parison o f th e a c t i v i t i e s was u sed when th e volumes o f th e
w a te r sp ra y ed s l i d e s w ere d eterm in ed u s in g th e c o ate d c a l i b r a t i o n s l i d e s
,s in c e th e r e were no g rap h s p l o t t e d .
E r ro rs w ere in tro d u c e d f o r m easurem ents ta k e n by th e end-window
-2 1 -
/
T
/
Z-
/
Lambdas o f W ater
)
_/
/
/
/
/
Z
/
C
P------
/
/
//
/
/
,Z
100
C ounts/m lnute
F ig u re 5.
tu b e .
C a lib r a tio n curve f o r w ater s o lu tio n u s in g end window
=■22“=
and th e flo w c o u n te r s in c e th e a c t i v i t y o f th e s o lu tio n was Iow0
The
le n g th o f tim e r e q u ir e d t o f i n d th e a c t i v i t y had t o be lo n g in o rd e r t h a t
th e s ta n d a rd d e v ia tio n (4) c o u ld be re d u c ed t o a sm all f a c t o r .
In th e
m easurem ents o f some s l i d e s t h i s f a c t o r was as h ig h as O015.
The c a l i b r a t e d o i l s l i d e s were p re p a re d by d ip p in g in th e same soap
s o lu tio n u se d fo i8 th o s e on which th e o i l was s p ra y e d .
A fte r th e soap
s o lu tio n had d r ie d , th e c a l i b r a t e d amounts o f o i l were d e p o s ite d in th e
same way as w ere th e n o n -c o a te d c a l i b r a t i o n w a te r s l i d e s by to u c h in g th e
p i p e t t e s t o th e s l i d e s a t many p la c e s .
r e d h e a t lam p.
The o i l was e v a p o ra te d by an i n f r a ­
These c a l i b r a t i o n s l i d e s had th e same b ase and s im ila r
d r o p le t d i s t r i b u t i o n p a tte r n s as th e o i l sp ray ed s l i d e s .
S in ce th e
a c t i v i t y o f th e o i l s o lu tio n was v e ry low th e Landsverk e le c tro m e te r was
th e only in s tru m e n t u se d t o m easure a c t i v i t y .
For d e te rm in in g th e amount o f
o i l d e p o s ite d a curve s im ila r to f ig u r e 5 was u s e d .
The methods u sed t o m easure th e volume o f th e w a te r s o lu tio n a re
1
summarized as fo llo w s ;
I,
By m easuring and c o u n tin g d r o p l e t s ,
2 j -t Eiy u s in g end-window c o u n te r and n o n -c o a ted c a l i b r a t i o n s l i d e s ,
3,
Ey u s in g flow c o u n te r and n o n -c o a te d c a l i b r a t i o n s l i d e s ,
4,
Ey u s in g Landsverk e le c tro m e te r and n o n -c o a ted c a l i b r a t i o n s l i d e s , .
5 , - Ey u s in g end-window c o u n te r and v a s e lin e c o ate d c a l i b r a t i o n s l i d e s ,
6,
Ey u s in g flo w c o u n te r and v a s e lin e c o ate d c a l i b r a t i o n s l i d e s ,
7,
Ey u s in g L an d sv erk 1e le c tr o m e te r and v a s e lin e c o a te d c a l i b r a t i o n
s lid e s .
The methods u se d to m easure th e volume o f th e o i l s o lu tio n a re
«23“
summarized as .fo llo w s s
I0
Ety m easuring and c o u n tin g d r o p l e t s ,
2,
Eiy u s in g th e Landsverk e le c tro m e te r and soap c o a te d c a li b r a t io n
s l i d e s ,.
■=-
24
“
RESULTS MD COMPARISON OF MEASUREMENTS
The number o f d r o p le ts which w ere m easured on th e s l i d e s v a r ie d from
a p p ro x im a te ly 100 to 1000 depending on th e amount o f s o lu tio n d e p o site d on
th e s lid e .
The t r u e d ia m e te rs o f th e l a r g e s t w a te r d r o p le ts t h a t were
m easured w ere a p p ro x im a te ly 450 t o 550|i9 w hereas th e l a r g e s t o i l drops
h ad d ia m e te rs o f 300 t o 400|ac
The ra n g e o f th e tr u e d ia m e te rs o f th e
d r o p le ts t h a t were d e p o s ite d m ost f r e q u e n tly upon th e s l i d e s was 50 to
150(1 f o r w a te r d r o p le ts and 100 to 25Op, f o r th e o i l d r o p l e t s .
The
c o rresp o n d in g , d ia m e te rs o f th e s t a i n s on th e p a p er ran g ed from 200 to
35Ou f o r th e w a te r d r o p le ts and from 900 to 1200p f o r th e o i l d r o p l e t s ,
The sp re a d f a c t o r o f th e w a te r d r o p le ts on p ap er v a r ie d c o n s id e ra b ly .
F o r d r o p le ts o f 50 t o 100p i t ap p eared t o be a p p ro x im a te ly 1,5?. and th e
d r o p le ts o f 400p o r l a r g e r would s p l a t t e r upon s t r i k i n g th e p a p e r.
The
o i l d r o p le ts w ere im m ediately absorbed upon coming i n t o c o n ta c t w ith p a p er
a llo w in g no tim e t o ob serv e f o r v a r i a t i o n s o f th e sp re a d f a c t o r in
r e l a t i o n t o d r o p le t s i z e ,.
The Spread f a c t o r f o r th e o i l d r o p le ts on p a p er
was e s tim a te d t o be betw een 5 and 7 by com paring th e ra n g e s o f th e d r o p le t
s i z e s d eterm in ed from th e t r e a t e d . s l i d e s and t h e i r s t a i n s on p a p e r.
The r e s u l t s o f m easurem ents o f f o u r d i f f e r e n t w a te r sp ra y ed s l i d e s
and f o u r d i f f e r e n t o i l sp ray ed s l i d e s a re g iv en i n T ab les I I and I I I
re s p e c tiv e ly .
The d r o p le t p a tte r n s on th e p ap er upon w hich th e s e s lid e s
w ere p la c e d a re g iv e n i n f i g u r e s 6 a=6d f o r th e w a te r, and f ig u r e s 7a=7d
fo r ,th e o i l d ro p le ts ,
p e r a cre.
Under th e f i g u r e s th e dosages a re l i s t e d in g a llo n s
F or f i g u r e s 6 &=6d th e d o sag es w ere c a lc u la te d from th e 'm easure-
Table I I . T o ta l volume (g iv en in lam bdas) o f w a ter
d r o p le ts , l i s t e d by methods o f m easurem ents.
S lid e No.
D ro p le tmeasurement
method
T ra c e r method
C a lib ra te d amounts on v a s e lin e
C a lib ra te d amounts <Dn n o n -co ated
c o a te d s lid e s
s lid e s
End-window Flow
Landsverk
Landsverk
End-window Flow
c o u n te r e le c tro m e te r
c o u n te r e le c tro m e te r co u n ter
co u n ter
No.
No.
No.
No.
0.805
1.33
1 .5 7
3 .1 0
a 87
1.52
1.4 1
3 .0 6
I
2
3
4
1 .3 9
1 .9 0
1 .7 9
4 .9 4
1 .0 1
1.73
1.55
3 .6 9
1 .2 0
2 .1 0
2 .0 0
4 .4 0
2 .4 4
4 .3 0
3 .1 6
6 .6 0
3 .1 0
5.04
4.65
9.92
Table I I I . T o ta l volume (g iv en in lam bdas) o f o i l
d r o p le ts , l i s t e d by methods o f m easurem ents.
S lid e No.
D ro p le t measurement
method
T rac e r method w ith soap
c o ate d c a l i b r a t i o n s lid e s *
No.
No.
No.
No.
0.126
0.181
0 .261
0.343
0.150
0.157
0.206
0.375
5
6
7
8
*A11 re a d in g s ta k e n by th e Landsverk e le c tro m e te r.
—26—
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.*
■
i.
■.
.
...
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*-
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;-‘ v;
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x-v
i «
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fig u r e 6 a . Water d ro p let pat­
tern fo r s lid e No. I rep resen t­
in g 1 .9 g a llo n s per a cre.*
V
V /.V :-- •
fig u r e 6b. Water d ro p let pat­
tern fo r s lid e No. 2 rep resen t­
ing 3 .3 g a llo n s per a cre.*
X•
•».
I .
'r
* ' Te • «
"
-*■ :
. ..
# - **
••• . .
.
f ig u r e 6 c . W ater d r o p le t p a t­
t e r n f o r s l i d e No. 3 r e p r e s e n t­
in g 3 .1 g a llo n s p e r a c r e .*
'
" M g
1
' .
1 »
;
'
V .v .v ;
•-;.y
:• <
. ••
•
m m ■
.m - * - ' - - -
.
m
.
v •
...
r :
f ig u r e 6d . W ater d r o p le t p a t­
t e r n f o r s l i d e No. 4 r e p r e s e n t­
in g 6 .7 g a llo n s p e r a c re .*
*The p i c t u r e s show t h e t r u e s i z e s o f t h e d r o p l e t s t a i n s .
s p a c e s i n t h e c e n t e r s a r e w h e re t h e s l i d e s r e s t e d .
The c l e a r
-2 7 -
fig u r e 7a. O il d ro p let pattern
fo r s lid e No. 5 rep resen tin g
0 .3 3 g a llo n s per a c r e .*
f ig u r e Tb. O il d r o p le t p a tte r n
f o r s l i d e No. 6 re p re s e n tin g
0 .3 4 g a llo n s p e r a c r e . *
•• e •
• • :
.
»
.
• ■
v
f ig u r e 7 c . O il d r o p le t p a tte r n
f o r s l i d e No. 7 r e p r e s e n tin g
0 .4 5 g a llo n s p e r a c r e .*
>
f ig u r e 7d. O il d r o p le t p a tte r n
f o r s l i d e No. 8 re p r e s e n tin g
0.8 2 g a llo n s p e r a c re .*
*The p i c t u r e s show t h e t r u e s i z e s o f t h e d r o p l e t s t a i n s .
s p a c e s i n t h e c e n t e r s a r e w h e re t h e s l i d e s r e s t e d .
The c l e a r
-2 8 =
Table IV. The av erag e p e rc e n ta g e v a r i a t i o n o f m easurem ents
ta k e n by th e d i f f e r e n t t r a c e r methods as compared w ith th e
d ro p le t-m ea su rem e n t m ethod. In a l l c a se s th e m easurem ents
were on th e average h ig h e r by th e t r a c e r methods th a n by th e
d ro p le t-m ea su rem e n t m ethod.*_____ ______
______ _
Type of'
c a lib ra tio n
s l i d e u sed
In stru m e n t u s e d t o m easure a c tiv ity
■. Flow
Landsverk ■ ■
End-Window
e le c tro m e te r
c o u n te r
c o u n te r
N on-coated
4
.4 3
16
40
150
230 ■
V a s e lin e
c o ate d
* Bog. D e p o sits m easured b y .th e end-window c o u n te r u s in g th e
n o n -c o a te d c a l i b r a t i o n s l i d e s were oh th e average. 4 p e r c e n t
h ig h e r th a n th e m easurem ents ta k e n by th e d ro p let-m easu rem en t
m ethod.
"
29
“
merits made by th e end-window c o u n te r u s in g th e n o n -c o a ted c a l i b r a t i o n
s lid e s e
The dosages o f o i l l i s t e d u n d e r f ig u r e s 7a-7d w ere c a lc u la te d
from m easurem ents made by th e Landsverk e le c tr o m e te r .
• Table I ? g iv e s ah o v e r a ll com parison o f m easurem ents made by th e
t r a c e r methods as compared w ith th e r e s u l t s by th e method o f d r o p le t
measurement, f o r d a ta o f T able I I .
'
In g e n e r a l th e volumes o f th e w a ter
sp ra y e d s l i d e s d e term in e d by th e t r a c e r method a re h ig h e r th a n th e d r o p l e t m easurem ent m ethod.
From t h i s i t became obvious t h a t th e r e were more
p a r t i c l e s e m itte d p e r u n i t volume from th e sp ray ed s l i d e s th a n from e i t h e r
ty p e o f c a l i b r a t i o n s l i d e s .
The c o a te d c a l i b r a t i o n s l i d e s and th e sp ray ed s l i d e s w ere s im ila r
e x c e p t t h a t th e d r o p le ts on th e s e c a l i b r a t i o n s l i d e s w ere much l a r g e r .
T h is in d ic a te d t h a t th e d e p o s its l e f t by th e la r g e d ro p s w ere a b so rb in g
more p a r t i c l e s th a n th o s e l e f t by th e sm a ll o n es.
. To t e s t f o r s ie lf a b s o rp tio n two s l i d e s w ere p re p a re d each h aving th e
same amount o f w a te r s o lu tio n d e p o s ite d upon them .
had many d b o p le ts , and th e o th e r , o n ly one.
However, one s l i d e
The s l i d e w ith one drop had
a v e ry t h i n c o a tin g o f w a te r r e p e l l e n t (used f o r w a te r p ro o fin g f a b r i c s )
t o keep th e drop from s p re a d in g .
The a c t i v i t y as m easured by th e flo w
c o u n te r o f th e s l i d e w ith one d r o p le t was 55 p e r c e n t o f th e a c t i v i t y o f
th e s l i d e w ith many d r o p l e t s .
The a c t i v i t i e s o f th e s l i d e s w ere measured
a g a in u s in g th e end-window c o u n te r alo n g w ith a 3 .2 6 4 m g./cm .? aluminum
a b s o rb e r.
The window o f th e c o u n te r (e q u iv a le n t to 2 .7 m g./cm . 2 m ica) and
th e aluminum a b so rb e r w e r e .s u f f i c i e n t t o ab so rb th e a lp h a p a r t i c l e s o f
=3 0
=
b u t n o t th e b e ta p a r t i c l e s o f
( 4 ) d ' - Under th e s e c o n d itio n s th e .
a c t i v i t y o f th e s l i d e w ith oiie d ro p was 93 p e r c e n t o f th e a c t i v i t y o f th e
fs l i d e w ith many d ro p s ,
th e r e s u l t s o f th e s e t e s t s showed t h a t th e d e p o s its
.
o f th e l a r g e r d r o p le ts absorbed many more a lp h a p a r t i c l e s th a n th e s m a lle r
o n e s.
On th e o th e r-h a n d , th e b e ta p a r t i c l e s w ere n o t a f f e c t e d n e a r ly as
much by th e d if f e r e n c e s i n th e s iz e s o f th e d r o p le ts .
The m easurem ents o f th e w a te r sp ra y ed s l i d e s u s in g th e n o n -co ated
c a l i b r a t i o n s l i d e s w ere low er th a n th e m easurem ents u s in g th e co ated
c a lib ra tio n s lid e s .
T h e re fo re , th e number o f p a r t i c l e s from th e s e s l i d e s
(p e r u n i t volume o f d e p o s it) m ust have been l a r g e r th a n th e number from
th e c o ate d c a l i b r a t i o n s l i d e s .
These a d d itio n a l p a r t i c l e s w ere due to th e
g r e a t e r b a c k s c .a tte rin g o f th e b e ta p a r t i c l e s .
There w ere a ls o more a lp h a
p a r t i c l e s from th e s e c a l i b r a t i o n s l i d e s s in c e th e d r o p le ts on th e s e s l i d e s
w ere sm a lle r: th a n th o s e on th e c o ate d c a l i b r a t i o n s l i d e s .
The c o r r e c te d o v e r a l l m easurem ents f o r th e volumes o f th e o i l d r o p le ts
by th e t r a c e r method w ere a p p ro x im a te ly 4 p e r c e n t h ig h e r as compared
'i .
‘
w ith th e method o f d r o p le t m easurem ent. The m easurem ents by th e t r a c e r
method were n o t c o n s is te n tly h ig h , b u t v a r ie d above and below th e v a lu e s
ta k e n by th e d ro p le t-m ea su rem e n t m ethod.
Because o f t h i s , and s in c e th e
,
geom etry o f th e o i l c a l i b r a t i o n and sp ra y ed s l i d e s were s i m i l a r i t co u ld
n o t be determ ined, w hich o f th e two m ethods le d to th e g r e a t e r e r r o r .
S in ce th e e r r o r s o f t h i s in v e s t i g a t i o n were m ainly due to th e t r a c e r
we a re l e d t o b e l i e v e ;t h a t -by u s in g a t r a c e r w ith more n e a r ly homogeneous
e m issio n much b e t t e r m easurem ents w ould have r e s u l t e d .
” 31“
LITERATURE CONSULTED
1.
Curtmanj L„ J oj Q u a lita tiv e Chem ical A n aly sis (The M acm illan C o.,
New York, 1938)..
2.
G ibbs, W. W,;, Clouds and Smokes (P. B la k is to n 1s Sons and Co*,
.P h ila d e lp h ia , 1 9 2 4 ).
3*
Goodhue, L. D ., and S u lliv a n , W* N„, "Making, and T e s tin g Aers o ls " ,
Amer. A ssoc. Adv. S c i. P u b ., 20, 157 (1945)..
4.
Lapp, R. E ., and Andrews, H. L ., N u clear R a d ia tio n P h y sic s
(P re n tic e H a ll, New Y ork, 1948).
5.
May, K. R ., "The Cascade Im p acto r", J o u rn a l o f S c i e n t i f i c
In s tru m e n ts , 2 2 , 187 (1945).
6.
Yeomans, A. H ., " D ire c tio n s f o r D eterm ining P a r t i c l e S iz e o f
A erso ls apd F in e S p ra y s", U. S. D ept, o f Agr. E n t, and P la n t
Q u a r., ET-267 (1949).
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