I . S p e c tro g ra p h ic D ete rm in a tio n of Calcium,
Magnesium, p o ta ssiu m , Manganese, Iro n and
Phosphorus in Small Samples
I I . S p e c tro g ra p h ic D ete rm in a tio n o f Zinc,
Cadmium, Copper and Ir o n in C on cen trated
N ic k e l S u l f a t e S o lu tio n s

By
MABEL FLOREY WILSON

A THESIS

P re s e n te d t o t h e Graduate School of Michigan
S t a t e C ollege of A g r ic u ltu r e and .Applied
S cience in P a r t i a l F u l f i ll m e n t of Requirements
f o r th e Degree of Doctor of P hilo sop hy

C hem istry Department
E ast L ansing, Michigan
1 9 3 7

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I

S p e c tro g ra p h ic D ete rm in a tio n of Calcium,
Magnesium, P otassium , Manganese, Iro n and
Phosphorus i n Small Samples

I n tr o d u c ti o n
The s p e c tro g ra p h i s p a r t i c u l a r l y a d a p te d to two
t y p e s of a n a l y s i s :

f i r s t , th e d e te r m in a tio n of t r a c e s

o f m e t a l l i c s u b s ta n c e s or i m p u r i t i e s , such a s manganese
i n s t e e l ; second, th e a n a l y s i s of samples when only
v e ry sm all amounts a r e a v a i l a b l e , such a s b i o l o g i c a l
ash.

This a r t i c l e w i l l be c o n fin e d t o th e second ty p e ,

t h a t i s , t o th e d e te r m in a tio n of calcium , magnesium,
manganese, p o tassiu m , phosphorus and i r o n in samples
where th e amount i s to o sm all t o be an a ly z e d by
o r d i n a r y wet methods.

The method employed i s s i m i l a r to t h a t f i r s t u sed
by N itc h ie and Standen ( N itc h ie and Standen, In d . and
Eng. Chem. Anal. E d., ]L, 1 -7 (1 9 3 9 )), of ex p o sin g th e
s p e c t r a of th e samples between th o se of a s e r i e s of
s ta n d a r d s o l u t i o n s c o n ta in in g v a ry in g known amounts of
th e su b sta n c e b e in g determ in ed .

M clc-We io i v« a

From th e d e n s i t i es of

th e l i n e s working curves were fo rm u la te d a c c o rd in g t o

2

.

t h e method of Twym&n and H itchen (Twyman and H itchen,
P ro o . of Royal Soc. of London, S e r ie s A, 1 3 3 , 7 2 .)
From th e s e s ta n d a r d cu rv es, unknowns were d i r e c t l y
d e te rm in e d .

E xperim ental
A pparatus.

A Bausch and Lomb medium q u a r tz

s p e c tr o g r a p h g iv in g a d i s p e r s i o n of about n in e inch es
f o r wave l e n g t h s of 2000 to 8000 A° was employed in th e
e x p e rim e n ta l p ro c e d u re .

The e l e c t r o d e s were h e ld toy

a n a d j u s t a b l e Bausch and Lomb e l e c tr o d e s ta n d .

A

r e v o l v i n g s e c t o r c u t down the p e rc e n ta g e of l i g h t from
t h e a r c re a c h in g th e s l i t .

E x c i t a t i o n of th e samples

was o b ta in e d by a r c i n g g ra p h ite e l e c t r o d e s w ith d i r e c t
c u r r e n t f u r n is h e d by a 15 am pere-300 v o lt motora c k ( ? Y ) i Y '- c j S

g e n e r a to r .

Line de n s i t -i es were determ ined by means o f

a Bausch and Lomb d e n s i t y com parator.

p r e p a r a t i o n of E le c tr o d e s .

Acheson g r a p h ite ro d s

5/16 in c h e s in d ia m e te r were c u t in co n v en ien t l e n g t h s
f o r a rc in g ,

(toe end of each was d r i l l e d ap p ro x im ately

se v e n m i ll i m e t e r s deep; o n e - te n th m i l l i l i t e r of th e
s o l u t i o n was p la c e d i n each c r a t e r ; th e e l e c t r o d e s were
d r i e d a t 110°, and were used a s low er e l e c t r o d e s or
an o d e s.

The c a th o d e s c o n s i s t e d of s i m i l a r le n g t h s

b ro k e n from th e same ro d .

s p e c ia l g r a p h it e ro d s very

f r e e of m e t a l l i c i m p u r i t i e s were u sed i n t h e calcium
de t e r mi n a t i on e .

S e le c tio n of Base.

The f i r s t problem t o be con­

s i d e r e d i n th e p r e p a r a t i o n of s ta n d a rd s was th e m a te r i a l
f o r use a s a b a s e .

This su b stan ce se rv e s two p u rp o se s:

f i r s t , a s a Hf i l l e r H, g iv in g a g r e a te r amount of sub­
s ta n c e in th e e le c tr o d e ; second, a s a means of h o ld in g
back th e carbon u n t i l v o l a t i l i z a t i o n of th e sample i s
c o m p le te .

Much more even ex p o su res and l i g h t e r back­

groun ds were o b ta in e d by employing a b ase.

Since i t i s w e ll known t h a t c h l o r i d e s give much
s h a r p e r l i n e s th a n o th e r n e g a tiv e r a d i c a l s , a l l d e t e r ­
m in a tio n s were c a r r i e d out in h y d ro c h lo ric a c id s o l u t i o n .
Samples of a type a n a ly z ed by t h i s method were found t o
be r e a d i l y s o lu b le in h y d ro c h lo ric a c id .

T h e re fo re , only

c h l o r i d e s were c o n s id e re d f o r a base m a t e r i a l .

Zinc

c h l o r i d e was found t o v ap o riz e too r e a d i l y ; le a d
c h l o r i d e was to o in s o lu b le ; sodium c h lo r id e in l a r g e
amounts caused th e a r c t o f l a r e g iv in g very uneven
ex p o su re s; very s a t i s f a c t o r y a r c i n g c o n d itio n s and even
e x p o s u re s r e s u l t e d from th e u se of ammonium c h lo r id e
b u t th e s p e c t r a l l i n e s of th e su b sta n c e s d e s i r e d f o r
u s e in a n a l y s i s were n o t sharp and c l e a r .

A number of m ix tu re s of sodium and ammonium
c h l o r i d e were t r i e d and one c o n s i s t i n g of 10$ sodium
c h l o r i d e and 9C)$ ammonium c h l o r i d e was found t o give
s a t i s f a c t o r y r e s u l t s f o r a r c i n g and f o r s h a rp n e s s of
lin e s.

Both s u b s ta n c e s a r e e a s i l y o b ta in a b le in very

p u re c o n d itio n and d is s o lv e r e a d i l y .

The base s o l u t i o n

f i n a l l y s e l e c t e d c o n s i s t s of f i v e grams of sodium
c h l o r i d e and f o r t y - f i v e grams of ammonium c h l o r i d e i n
4 .5 $ h y d ro c h lo ric a c i d s o l u t i o n .

Calcium S ta n d a rd s.

No two elem ents u nd er i d e n t i c a l

a r c i n g c o n d itio n s gave th e same v a r i a t i o n in l i n e dens4»t^t e s f o r an equal change in c o n c e n tr a tio n .

Thus i t was

n e c e s s a r y t o t r y v a rio u s c o n c e n tr a tio n s u n t i l a s e r i e s
o f d i l u t i o n s was o b ta in e d which gave a g r a d a tio n of
b l a c

^ Yt \

l i n e d e n s itie s s u ita b le fo r a n a ly sis.

Enough pure caloium n i t r a t e was d is s o lv e d in th e
b ase s o l u t i o n t o y i e l d 2 grams of calcium p e r l i t e r .
From t h i s , u s i n g th e base s o l u t i o n f o r d i l u t i n g , a s e r i e s
o f s ta n d a r d s was p re p a re d c o n ta in in g 1 .0 , 0 .5 , 0 .3 , 0 .2 ,
0 .1 , 0 .075 , 0 .0 5 , 0.03, 0 .0 2 , 0 .0 1 , 0.005 and 0.0025
grams of calcium p e r l i t e r .

Magnesium S ta n d a rd s.

Magnesium s o l u t i o n s were

p r e p a r e d i n e x a c t l y th e same manner u s in g magnesium

c h l o r i d e , g iv in g a f i n a l s e r i e s c o n ta in in g 5 .0 , 2 .5 ,
1 . 0 , 0 .5 , 0 .3 , 0 .2 5 , 0 .2 , 0 .1 , 0.05 , 0.025 , 0.01 and
0 .0 0 5 grams of magnesium p er l i t e r .

Manganese S ta n d a rd s.

Manganese c h l o r i d e was

d i s s o l v e d i n th e base s o l u t i o n to y i e l d 2 grams of
manganese p e r l i t e r .

Lower c o n c e n tr a tio n s of 1 .0 ,

0 . 5 , 0 .2 5 , 0 .1 , 0 .0 5 , 0 .02 5, 0.01 and 0.005 grams p e r
l i t e r were p re p a re d by combining th e manganese s o l u t io n
w ith p ro p e r amounts of base.

Potassium S ta n d a rd s.

The behavior of p otassiu m

i s d i f f e r e n t th a n t h a t of magnesium, manganese and
c a lc iu m .

Large amounts of p o tassiu m show a marked
bl<xG.Ue~r> t-yi a •
g r a d a t io n of l i n e den s i t i e s . Thus h ig h e r p e rc e n ta g e s
may be s u c c e s s f u l l y an aly zed d i r e c t l y from th e sample

w ith o u t employing a “ f i l l e r "

or d i l u t i o n o f sam ples.

Four groups of p o tassiu m s ta n d a r d s were p re p a re d in t h i s
in v e s tig a tio n .

The f i r s t group combined potassium and phosphorus
i n a calciu m and magnesium b a s e .
A and B were p re p a re d .

Two s e p a r a te s o l u t i o n s ,

S o lu tio n A c o n ta in e d enough

p o ta s s iu m c h l o r i d e and p o tassiu m a c id p hosphate in
4 .5 $ h y d ro c h lo ric a c id s o l u t i o n t o y i e l d 4 grams of
phosphorus and 96 grams of p o tassiu m p e r l i t e r ,

so lu tio n

6

.

B c o n ta in e d 50 grams each of calcium and magnesium in
4 .5 $ a c i d .

By com bining th e two s o l u t i o n s in th e p ro p e r

p r o p o r t i o n s a s e r i e s c o n ta in in g 48 , 40, 38, 24, 16, 12,
8, 4 .8 , 2 .4 , 1 .2 , 0 .2 4 and 0.12 grams of p o tassiu m p e r
l i t e r were made up.

The phosphorus c o n te n t was in a

r a t i o of 2 t o 48 t o th e p o tassiu m c o n te n t.

The second group was a d u p l i c a t e of th e f i r s t group
e x c e p t f o r th e a d d i t i o n of i r o n in a c o n c e n tr a tio n equal
t o t h a t of phosphorus.

Since iro n was added in th e form

o f f e r r o u s ammonium s u l f a t e which has a tendency t o
p r e c i p i t a t e calciu m , s p e c ia l a t t e n t i o n was given t o th e
o r d e r of a d d i t i o n .

The f e r r o u s ammonium s u l f a t e , po­

ta s s iu m a c id phosphate and p o tassiu m c h l o r id e were a l l
d i s s o l v e d s e p a r a t e l y , th e f i r s t two combined and slo w ly
added t o th e t h i r d .

This combined m ix tu re , 9$ a c id ,

was d i l u t e d w ith a calcium-magnesium base c o n ta in in g
no a c i d .

For the t h i r d group enough potassium c h l o r id e t o
y i e l d 30 grams of p o tassiu m p e r l i t e r was d is s o lv e d in
t h e sodium-ammonium c h lo r id e b ase.

D ilu tio n s w ith th e

base were made g iv in g a s e r i e s c o n ta in in g 30, 25, 20,
1 7 .5 , 15, 1 2 .5 , 10 and 5 grams of p o tassiu m per l i t e r .

A f o u r t h group was p re p a re d f o r th o s e samples i n

w hich th e p o ta ssiu m c o n te n t was low and a g r e a t e r amount
o f th e su b stan ce was n e c e s s a r y ,

p o tassiu m c h lo r id e was

d i s s o l v e d i n 9$ a c i d t o give 25 grams of p o tassiu m p e r
lite r.

D ilu tio n s were made t o y i e l d 20, 15, 1 2 .5 , 10,

7 .5 , and 5 grams o f p o tassiu m p e r l i t e r .

Phosphorus and Iro n S ta n d a rd s.

In a d d i t i o n t o th e

pho sph orus and i r o n s ta n d a rd s combined w ith potassium
a n o t h e r s e r i e s was p re p a re d in th e sodium-ammonium
c h lo rid e base.

The ir o n c o n c e n tr a tio n was 1, 0 .5 , 0 .2 5 ,

0 . 1 , 0 .0 5 , 0 .025 , O.Ql, 0.005 and 0.0025 grams p e r l i t e r .
The phosphorus c o n te n t was double t h a t of ir o n .

P r e p a r a t i o n of sam ples.

When ash samples were t o

be an a ly z ed , 0 .0 5 gram samples were weighed out and
t r e a t e d w ith 1 m i l l i l i t e r of c o n c e n tra te d h y d ro c h lo ric
a c id .

This was allow ed t o s ta n d f o r an hour; a base of

sodium-ammonium c h lo r id e s o l u t i o n was th e n added t o a
t o t a l of 10 m i l l i l i t e r s so t h a t th e r e s u l t i n g concen­
t r a t i o n was 5 grams of a sh in 4 .5 $ a c id , c o n t a in in g 5
grams sodium c h lo r i d e and 45 grams of ammonium c h l o r i d e
per l i t e r .

Samples f o r p otassium a n a l y s i s were s i m i l a r l y
p r e p a r e d , but c o n ta in e d 20 grams of a sh p e r l i t e r .

A s y n t h e t i c a s h was p re p a re d f o r a n a l y s i s by
d i s s o l v i n g th e s a l t s i n a 4 .5 $ a c id s o l u t i o n so t h a t th e
r e s u l t i n g c o n c e n t r a t i o n s were:

0.7 grams of calcium ,

0 . 4 grams of magnesium, 0.01 grams of manganese, 0.15
grams of phosphorus, 0.05 grams of ir o n and 14 grams of
p o ta ss iu m p e r l i t e r .

C o n d itio n s of Exposure.

Eastman 1133“ commercial

p l a t e s were u sed f o r a l l a n a ly s e s except th o se in which
i r o n i n t e r f e r e d w ith p o tassiu m .

W ratten - Wainwright

p r o c e s s Panchrom atic p l a t e s gave s a t i s f a c t o r y r e s u l t s
in t h i s case.

The “ 33“ p l a t e s were chosen because t h e i r

c h a r a c t e r i s t i c s were s u i t a b l e f o r th e p a r t i c u l a r condi­
t i o n s r e q u ir e d f o r such a n a ly s e s .

Both ty p e s of p l a t e s

were developed in Eastman d e v e lo p e r form ula D -ll f o r
f i v e m inutes a t 18^.

The method of “co n tin u o u s exposure11 e x t e n s i v e l y
employed by t h i s l a b o r a t o r y f o r some time was used t o
d e te rm in e th e b e h a v io r of th e s i x su b s ta n c e s upon
v o la tiliz a tio n .

The p l a t e was p la c e d in r e a d in e s s f o r

e x p o s u re , th e s l i t opened and th e e l e c t r o d e s a d ju s te d .
Each f i f t e e n seconds from th e i n s t a n t of a r c i n g , th e
p l a t e was moved r a p i d l y , a llo w in g th e a r c t o burn
c o n t i n u o u s ly f o r fo u r or f i v e m inutes.

In t h i s manner

t h e com parative amounts of each su b stan ce v o l a t i l i z e d

9.

in any f i f t e e n second i n t e r v a l co u ld be d eterm in ed a s
w e ll a s th e tim e r e q u ir e d f o r th e v o l a t i l i z a t i o n of each
t o p ro c e e d t o a p o i n t where no e f f e c t was shown on the
p h o to g ra p h io p l a t e under th e c o n d itio n s of exposure
employed.

From th e d a ta o b ta in e d on such a p l a t e th e time f o r
ex p o su re of each su b stan ce was found.

The amount of

l i g h t used was a l s o found e x p e rim e n ta lly .

Enough l i g h t

was u se d so t h a t th e h e a v ie s t l i n e s t o be used f o r
a n a l y s i s were w ell under maximum b la c k e n in g . In t h i s
bWdkcTO \V\-3
way a g ra d a tio n o f l i n e d o n s i t i e s was o b ta in e d f o r th e
lo w e r c o n c e n t r a t i o n s .

The amount of l i g h t re a c h in g th e

s l i t was r e g u la te d by th e a d j u s t a b l e r e v o lv in g s e c t o r .
The fo llo w in g t a b l e shows th e c o n d itio n s of exposure used
f o r each su b stan ce when a c u r r e n t of t e n amperes was
c a r e f u l l y m a in ta in e d .

10.

TABLE I
Seconds
Time

£ L ight

S e c to r

Potassium
i n 9f0 a c id
in NHH-Na base
i n Ca-Mg base

40
40
SO

5
5
6 .2 5

1 /1 0
1 /1 0
1 /8

I r o n and Phosphorus
i n NH^-Na base
i n Ce^Mg base

60
90

5
6 .2 5

HH

I r o n (a lo n e )

60

2

1/2 5

Magnesium

40

3.125

1/16

Manganese

40

2

1/2 5

Calcium

40

1.625

1/3 2

o

Substance

S l ig h t v a r i a t i o n s were made when only th e h ig h e r or
lo w er c o n c e n tr a tio n s of a s e r i e s were u sed.
L'.vve
E v a lu a tio n of pla ^ e - Be n s i t i g B .

The d e n s i t i e s of

t h e p ro p e r l i n e s from the v a rio u s a n a ly s e s were re a d on
t h e d e n s i t y com parator.

Only p l a t e s f r e e o f fo g g in g were

u se d ; any which were s l i g h t l y fogged or n o t e n t i r e l y
c l e a r were d is c a r d e d .

A re a d in g f o r b la c k n e ss when no

l i g h t e n te r e d th e s l i t was ta k e n f i r s t .

Each l i n e was

r e a d in d e p e n d e n tly u n t i l an a c c u r a te check was o b tain ed .
The p l a t e was th e n moved to a c l e a r background in th e
same re g io n .
ground" .

This re a d in g was re c o rd e d a s th e «back­

The d i f f e r e n c e s between th e d e n s i t y of th e

l i n e and a b s o lu te b la c k n e s s and a l s o between th e back­
ground and a b s o l u t e b la c k n e s s were c a l c u l a t e d .

The r a t i o s

of th e s e d i f f e r e n c e s wesfeplotted a g a in s t th e lo g a rith m s
of c o n c e n t r a ti o n s t o o b ta in th e working curv e or
“ s ta n d a r d c u rv e ” , th e method of Tyman and H itchen
(trie b>Iqc
p r e v i o u s l y c i t e d . The d e n o ity r a t i o s f o r th e unknowns
were l o c a t e d on th e s ta n d a rd curve and th e c o rre sp o n d in g
c o n c e n t r a t i o n s re a d d i r e c t l y from th e c u rv e .

No

a tte m p t was made t o c a l i b r a t e th e p l a t e s a s th e
s ta n d a r d curve and unknowns t o be determ in ed were a l l
p l a c e d on one p l a t e .

D u p licate p l a t e s were made t o

check r e s u l t s .

R esu lts
"C ontinuous E x posu re.11

The b eh av io r of each of

t h e s i x su b s ta n c e s upon v o l a t i l i z a t i o n was i n d i v i d u a l .

P otassiu m , a lth o u g h p r e s e n t in th e l a r g e s t amount,
v o l a t i l i z e d most r a p i d l y and d isa p p e a re d in f o r t y - f i v e
seco n d s.

phosphorus a l s o v o l a t i l i z e d t o an e x te n t t h a t no
e f f e c t co u ld be observed on a p h o to g rap h ic p l a t e .

It

was unique in b e h a v io r, v o l a t i l i z a t i o n b e g in n in g slow ly,
g r a d u a l l y i n c r e a s i n g t o a peak and th en slo w ly d e c re a s ­
in g .

About two m inutes were r e q u ir e d , a lth o u g h th e

b u lk of i t v a p o riz e d in s i x t y seconds, th e time of
ex p o su re u sed f o r a n a l y s i s .

Manganese v o l a t i l i z e d very r a p i d l y a t f i r s t , most
o f i t d is a p p e a r in g in f o r t y - f i v e seconds.

A f a in t trace

re m a in e d f o r f o r t y - f i v e t o s i x t y seconds lo n g e r.

Magnesium d i d not v o l a t i l i z e co m p letely .

As in

t h e ca se of manganese, f o r t y - f i v e seconds were s u f f i c i e n t
f o r th e g r e a t e r p o r t i o n to b urn out.

A fte r t h a t time th e

amount v o l a t i l i z e d in each i n t e r v a l g r a d u a lly d e c re a se d
and f i n a l l y re a c h e d a c o n s ta n t.

Calcium acted somewhat s i m i l a r t o magnesium, except
t h a t i t behaved very e r r a t i c a l l y when only a t r a c e re m a in i.

I r o n was found to be th e most p e r s i s t e n t of any of
th e s i x s u b sta n c e s ■under i n v e s t i g a t i o n .

However, very

c o n s i s t e n t r e s u l t s were o b ta in e d when s i x t y second
e x p o s u re s were u se d .

F ig u re 1 shows g r a p h ic a l ly how th e s u b s ta n c e s com­
p a r e in speed of v o l a t i l i z a t i o n and in th e amounts of
e a c h v o l a t i l i z e d i n any time i n t e r v a l .

Q t k e-vi \ w c* s

Line den% i4ies

a r e p l o t t e d a s o r d in a t e s a g a in s t time i n t e r v a l s a s
a b sc issa e .

P otassium has th e s t e e p e s t slo p e ; magnesium,

33

31
30
29
28

2?

20
IS

18

1

2

3

4

5 6
7
T im e I n t e r v a l e

8

9

10

11

12

FIGURE 1 .
BEHAVIOR UPON VOLATILIZATION
1 . P h o s p h o r u s - 2 5 3 6 . 38 A
2 . M a g n e siu m - 2 7 7 6 .7 1 A
3 . iT on - 3 0 2 0 .6 5 A
4 . M a n g a n e s e - 2 5 7 6 .1 2 A
5 . C a lc i u m - 3 1 5 8 .8 7 A
6 . P o t a s s i u m - 3 4 4 7 .3 8 A

13

manganese and i r o n behave somewhat a l i k e ; calcium
shows a slow er r a t e of v o l a t i l i z a t i o n ; and th e e r r a t i c
b e h a v io r of phosphorus i s very e v id e n t.

S u i ta b le L ines f o r A n a ly s is .

Very few Mr a i e s

u l ti m e s ” a r e s u i t a b l e f o r use i n q u a n t i t a t i v e a n a l y s i s
u s i n g th e method of a rc e x c i t a t i o n a s th e y show maximum
b la c k e n in g in c o m p a ra tiv e ly low c o n c e n tr a tio n s .

A lin e

u s e d e f f e c t i v e l y must show two c h a r a c t e r i s t i c s :

first,

i t must be p e r s i s t e n t even i n very low c o n c e n tr a tio n s ;
a n d second, i t must show a d e f i n i t e change in l i n e
d ens-gty f o r a sm all change in c o n c e n tr a tio n .

L in es

w hich f u l f i l l th e s e re q u ire m e n ts give very s a t i s f a c t o r y
s t a n d a r d curves over a s h o rt range of c o n c e n t r a t i o n s .
Many l i n e s of each substance were i n v e s t i g a t e d and
th o s e s e l e c t e d

were found to be most s a t i s f a c t o r y

u n d e r th e c o n d itio n s of e x c i t a t i o n and exposure
employed.

They a r e a s fo llo w s :
P otassium 3446.37 and
Magnesium 2776.71 and
Calcium
3158.87 and
Iro n
2598.08 and
Phosphorus 2536.38 Ab
Manganese 2576.12 and

3447.38
2779.85
3179.33
2599.40

A°
Jf
A°
A°

2605.69 A^

In s p e c ia l c a s e s o th e r l i n e s had to be employed.
I n th e case of h ig h i r o n c o n te n t, th e calcium l i n e a t
3 179.33 A° was n o t s a t i s f a c t o r y .

For th e same re a s o n ,

14

t h e p o ta ssiu m l i n e s m entioned above were u n s a t i s f a c t o r y .
I n t h a t case th e p o tassiu m l i n e a t 5782.6 A was
employed.

This n e c e s s i t a t e d th e use of W ratten-

W ainwright P ro c e ss Panchrom atic p l a t e s .

For hig h con­

c e n t r a t i o n s of i r o n th e d o u b le t m entioned d id n ot show
s a t i s f a c t o r y g r a d a tio n and th e u n re so lv e d d o u b let a t
3021.08 and 3020.65 A was used.

Table I I shows a t y p i c a l s e t of d a ta from which th e
s t a n d a r d curve f o r po tassium and th e c o n c e n tr a tio n s of
t h e unknowns a r e o b ta in e d .

TABLE I I
g /l
of K
25
20
15
( l ) unknown
1 2 .5
1 0 .0
7 .5
5 .0
( 2 ) unknown

3446.37 X
2 9 .0
26.7
24.6
2 2 .4
2 3 .3
2 2 .3
2 2 .2
2 3 .4
23.6

Complete b la c k n e s s : 36.2

Background

R atio

15 .8
1 6 .4
1 6 .4
1 6 .5
16.7
16.7
1 7 .3
1 7 .9
1 6 .3

.35
.48
.59
.70
.66
.71
.7 4
.70
.63

15

A sample c a l c u l a t i o n of r a t i o s i s shown below.
36.2

-

2 9 .0

=

7 .2

36.2

-

1 5 .8

= 2 0 .4

—

2 0 .4

F ig u re 2 shows the s ta n d a rd curve f o r p otassiu m
p l o t t e d from th e d a t a given in Table I I , and th e
d e t e r m i n a t i o n of th e c o n c e n tr a tio n s of two unknowns.

F ig u re 3 g iv e s t y p i c a l s ta n d a rd cu rv es f o r
p h o sp h o ru s, i r o n , manganese, magnesium and calcium ,
a l l p l o t t e d from ex p e rim e n ta l d a ta .

Table I I I shows th e r e s u l t s o b ta in e d by th e
a p p l i c a t i o n of t h e s e methods t o th e a n a l y s i s of a
s y n t h e t i c a sh of d e f i n i t e com position in grams p e r l i t e r .

45

.5 0
to

U/n/e

°

.5 5

.7 5

7 .5

10:

10.5

1 2 .5 ? 15

14

Lo^ari-Mm* c* couocatratUon,
STANDARD

C

U

x f Uh

t

1 ^ * 1 L*

20

18

10
3
SO

.3 0

S .4 0
.5 0

c

60

*
J

.7 0

£0
I

.8 0

.01

08 .0 8 5

.0 5

.a .9ft

.ft

Logarithms of Concentration

riGURE

3.
STANDARD CURVES.
1 . P h o s p h o r u s - 2 5 3 6 .3 8 A
3. M anganese - 2 6 0 5 .6 9 A

2.
4.

I r o n - 2 5 9 9 .4 A
M agnesium - 2 7 7 9 .8 5 A

16

TABLE I I I .

S ubstance

S p e c tro g ra p h ic

Chemical

$ E rro r

Magnesium

0.370
0 .4 0 0
0.390

0.400
0.400
0.400

7 .5
0
2 .5

Manganese

0.0112
0.0103
0.0099

0.Q100
0.0100
0.0100

1 2 .0
3 .0
6 .0

phosphorus

0.148
0.148
0 .1 5 3

0.150
0.150
0.150

1 .3
1 .3
2 .0

P otassium

1 5 .0 0
1 4 .2 5
1 3 .0 0
1 4 .0 0

14.00
1 4 .0 0
1 4 .0 0
1 4.00

6 .7
1 .7
6 .7
0

Iro n

0.048
0.0 52

0.05
0.05

4 .0
6 .0

Calcium

0.68
0 .6 8

0.7
0.7

3 .0
3 .0

F ig u re 4 i s ta k e n from an a n a l y s i s f o r phosphorus
an d i r o n .

The phosphorus l i n e 2536.38 A and th e ir o n

d o u b le t 2598.08 and 2599.40

a

a re shown d o t te d .

The

g r a d a t io n s of b o th a r e a p p a re n t t o th e eye.

F ig u re 5 shows two a n a ly s e s of a sample, one f o r
magnesium and one f o r manganese.

The magnesium group

o f f i v e l i n e s in th e re g io n of 2780 A i s marked and
a l s o t h r e e manganese l i n e s in th e re g io n of 2600

a

.

FIGURE 4

17

D is c u s sio n
V a r ia tio n of Line D engitrtee Due t o Other S ubstances.
I n an a r t i c l e d e a l i n g w ith th e a n a l y s i s of s o l u t i o n s by
means of th e sp e c tro g ra p h by Duffendach, Wylie and Owens
(D u ffen d ach , Wylie and Owens, Ind. and Eng. Chem., Anal.
E d ., 7_, 410-413, (1 9 3 5 )) i t was found t h a t magnesium,
c a lc iu m , sodium and p o tassiu m a f f e c t e d th e r e l a t i v e
i n t e n s i t y of th e s p e c t r a l l i n e s of each of th e o th e r
e le m e n ts w ith r e g a rd t o th e s p e c t r a l i n t e n s i t y of an
i n t e r n a l s ta n d a r d .

They a l s o found t h a t th e a d d i t i o n

o f Zfo sodium had th e e f f e c t of e li m in a t in g f u r t h e r
v a r i a t i o n s due t o th e o th e r elem en ts.

The e f f e c t o f calcium , p o tassiu m and sodium on th e
k^n i
l i n e d e n s i t i e s o f magnesium was measured and found t o
be w e ll w ith in th e range of experim en tal e r r o r f o r the
c o n d i t i o n s of exposure employed.

The a d d i t i o n of

sodium c h lo r id e i n th e base m a t e r ia l would a l s o e lim in a te
s l i g h t v a r i a t i o n s due t o sm all amounts of o th e r
s u b s ta n c e s .

No a tte m p t was made t o remove any su b sta n c e from
t h e a s h b e fo re a n a ly z in g f o r th e s i x su b sta n c e s
d e te rm in e d .

As shown by th e graph r e s u l t i n g from a

c o n tin u o u s ex p o su re , a l l su b sta n c e s were v aporized
co n c u rre n tly .

18

P hosphorus.

The p o s s i b l e e x c e p tio n t o th e g e n e ra l

r a t e of v o l a t i l i z a t i o n i s phosphorus.

However, an

i n c r e a s e in th e tim e of exposure compensated f o r the
d i f f e r e n c e in r a t e .

The f a c t t h a t 0.148 of th e 0.150

grams of phosphorus i n th e s y n t h e t i c ash were re g a in e d
by t h i s method p o i n t s t o i t s f e a s i b i l i t y .
was o n ly 1 .3 $ .

The e r r o r

However, th e range w ith in which phos­

p h o ru s can be d eterm in ed i s l i m i t e d .

No a tte m p t to

show i t in l e s s th a n 0.01 gram p e r l i t e r was s u c c e s s f u l.
I n c a s e s where th e phosphorus c o n te n t was low, th e
sample was no t d i l u t e d as much.

Even i n i n s t a n c e s

where phosphorus was no t a t f i r s t shown t o be p r e s e n t ,
a c o n c e n t r a t i o n o f th e a s h s o l u t i o n y ie ld e d a p o s i t i v e
ph o sp h o ru s d e te r m in a tio n .

The s o l u t io n s f o r phosphorus

y i e l d e d a very s a t i s f a c t o r y s ta n d a r d curve between th e
l i m i t s of 0.01 and 10 grams p e r l i t e r , making d e t e r ­
m in a tio n s of unknowns w ith a h ig h degree of accu racy .
There were no l i n e s of any s u b s ta n c e s used o r im puri­
t i e s o c c u rrin g in th e re g io n of th e phosphorus l i n e ,
namely 2536.38 A and no background to i n t e r f e r e .

The

l i n e was e a s i l y r e a d on th e d e n s i t y com parator and gave
a smooth curve when p l o t t e d .

Iro n .

I r o n had the advantage of h av in g a number

o f l i n e s which showed a d e f i n i t e g ra d a tio n of l i n e
s a t i s f a c t o r y s ta n d a rd c u rv e s.

The

19

u n re s o lv e d d o u b le t a t 3020.65 and 3021.08 A gave a
u s a b l e curve f o r c o n c e n tr a tio n s of iro n from 0.05 up
t o 20 grams p e r l i t e r .

This d o u b le t would be more

e f f e c t i v e on an in stru m e n t w ith h ig h e r r e s o l v i n g power.
The p a i r a t 2598.38 and 2599.40 A a re th e most s a t i s ­
f a c t o r y over a lo n g range.

From a range of 2 gram p e r

l i t e r down t o a s low a s 0.0005 grams p e r l i t e r , a
s t a n d a r d curve can be made.

However, i t h a s l e s s change

i n deft c i t y - f o r a sm all change in c o n c e n tr a tio n th a n does
t h e d o u b le t a t about 3020 A .

When only i r o n i s b ein g

d e te rm in e d , th e l a t t e r i s t o be p r e f e r r e d except in
e x tre m e ly low c o n c e n t r a t i o n s .

I n c o n ju n c tio n w ith phos­

p h o r u s , th e p a i r a t 2598.38 and 2599.4 A were most
e x t e n s i v e l y u sed .

They occur in a re g io n c l e a r of

background, f r e e of i n t e r f e r i n g l i n e s and a re brought
o u t s a t i s f a c t o r i l y “u nder th e same c o n d itio n s u sed f o r
p h o sp h o ru s.

I t i s w e ll, however, in a s e r i e s of

a n a l y s e s t o use th e same l i n e th ro u g h o u t.

An ac c u ra c y

o f 6f0 was found in th e ca se of iro n in a c o n c e n tr a tio n
o f 0 .0 5 grams p e r l i t e r .

Manganese.

o
Two l i n e s , m ainly 2576.13 and 2605.69 A

giv e s ta n d a r d c u rv e s f o r manganese over a range of
0.00 1 t o 5 .0 grams p e r l i t e r by v ary in g th e amount of
lig h t.

In th e ca se of an an aly zed s y n th e t i c ash c o n ta in ­

i n g 0.01 grams p e r l i t e r , th e e r r o r was e s tim a te d a t

20

5 t o 10^.

As th e manganese was found t o c o n ta in a

s m a ll amount of i r o n , th e e r r o r was n o t extrem e.

The

c u rv e f o r manganese was very smooth, g iv in g both th e
s h o u ld e r and to e of th e curve a s w ell a s th e s t r a i g h t
p o rtio n .

D e te rm in a tio n s of h ig h e r c o n c e n tr a tio n s are

more e a s i l y made, bein g on a s t r a i g h t p a r t of th e curve.

Magnesium.

Magnesium was th e e a s i e s t t o an aly ze

o f any of th e s i x s u b s ta n c e s .

The curves o b ta in e d from

t h e l i n e s a t 2776.71 and 277S.85 A more n e a r ly
re se m b le d E u rte r and D r i f f i e l d cu rv es th a n any of th e
o t h e r s h an d led .

Over th e c o m p a ra tiv e ly s h o rt range of

0 .0 1 t o 1 . 0 gram p e r l i t e r a complete curve was o b ta in e d
by p ro p e r e x p o su re .

R e s u lts on magnesium showed a l s o ,

t h e s m a lle s t p e rc e n ta g e of e r r o r ,
a n a l y s e s , th e a v e ra g e e r r o r was 3$.

i n a group of f i v e
Magnesium may be

d e te rm in e d very s a t i s f a c t o r i l y in a range of 5 .0 down
t o 0.001 grams p e r l i t e r .

A lso, i t i s p ro b a b ly th e

most a c c u r a te of th e s i x a n a ly s e s .

P o tassiu m .

The most d i f f i c u l t t o o b ta in s u c c e ss ­

f u l l y by th e method employed was p o tassiu m .

Many

d i f f e r e n t e r r o r s e n t e r i n t o such a d e te rm in a tio n .
t h e f i r s t p l a c e , th e range i s very l i m i t e d .

In

G radation

o f l i n e den o itipes may be o b ta in e d only between 1 . 0 and
50 grams p e r l i t e r , and on ly w ith g r e a t d i f f i c u l t y u nder

21

5 grams p e r l i t e r .

The sample must he heavy in

p o ta s s iu m t o he an a ly z e d a t a l l ; t h i s i s s c a r c e l y
f e a s i b l e in most c a s e s , a s th e advantage of th e g e n e ra l
method i s t o u t i l i z e very sm all sam ples.

I r o n in any c o n c e n tr a tio n g r e a t e r th a n 0.1 grams
p e r l i t e r i n t e r f e r e s w ith th e u n re so lv e d d o u b le t a t
3446.37 and 3447.38 A making th e employment of th e se
l i n e s f o r a n a l y s i s im p o ssib le .

An attem p t t o c u t down

on th e exposure and use th e p a i r a t 4044.16 and 4047.22 A
was o n ly p a r t i a l l y s u c c e s s f u l.

Potassium l i n e s a r e

accom panied by a co n tin u o u s background in th e same
r e g io n g r e a t l y i n c r e a s i n g th e background re a d in g ,
r e s u l t i n g i n very sm all r a t i o s much l e s s s e n s i t i v e th a n
f o r o th e r s u b s ta n c e s .

Another l i n e o b ta in a b le on

s p e c i a l r e d - s e n s i t i v e p l a t e s , 5782.6 A , can be used
betw een l i m i t s f o r ap p ro x im atio n s but has to o much
c o n tin u o u s background t o be used f o r fo rm u la tin g a
s t a n d a r d cu rv e.

The s ta n d a r d curve o b ta in e d f o r p o tassiu m u s in g
3447.38 A in a range of c o n c e n tr a tio n s from 5 t o 30
grams p e r l i t e r i s very e a s i l y o b ta in e d and s a t i s f a c t o r y
f o r c o n c e n t r a t i o n s w ith in t h a t range when ir o n i s
a b s e n t or p r e s e n t in an amount l e s s than 0.05 gram p e r
lite r.

A s p e c tr o g ra p h g iv in g a g r e a t e r r e s o l u t i o n of

22

th e d o u b le t, th u s f r e e i n g i t from i n t e r f e r e n c e by ir o n ,
would y i e l d v ery s a t i s f a c t o r y r e s u l t s .

R e s u lts o b ta in e d on f o u r samples of p o tassiu m
c o n t a i n i n g l e s s th a n 0,05 grams of iro n p e r l i t e r , and
known t o c o n ta in 14 grams of potassium , gave th e
r e s u l t s of 1 5 .0 , 1 4 .2 5 , 1 3 .0 and 1 4 .0 grams p e r l i t e r ,
a n av e rag e of ab out 5$ e r r o r .

Calcium.

Calcium i s p r e s e n t in an a p p r e c ia b le

amount i n most g r a p h ite ro d s o r d i n a r i l y used f o r
a n a ly sis.

I t was n e c e s s a ry f o r c o n s i s t e n t and r e l i a b l e

r e s u l t s t o use v ery pure c a rb o n s.

Calcium g iv es a

s t a n d a r d curve w ith a slope n e a r l y h o r i z o n t a l .

Although

a s e r i e s of s ta n d a r d s o l u t i o n s give a smooth curve,
b>l<3.c
t h e r e i s v ery l i t t l e change in d o n o ity f o r a l a r g e
change in c o n c e n t r a t i o n , due t o th e extreme p e r s i s t e n c e
o f ca lc iu m even i n very m inute amounts.

Thus th e

d e te r m in a tio n of unknowns i s much l e s s a c c u ra te f o r
c a lc iu m th a n , f o r example, magnesium.

Only two l i n e s

o f c a lc iu m were found t o y i e l d s a t i s f a c t o r y sta n d a rd
c u r v e s ; 3158.87 and 3179.33 A .

Between th e co n c e n tra ­

t i o n s of O.QQl and 5 grams p e r l i t e r , smooth s ta n d a rd
c u r v e s were o b ta in e d and s u c c e s s fu l d e te rm in a tio n s made.
However, th e p e r c e n t e r r o r was h ig h e r f o r calcium th an
f o r magnesium, manganese, i r o n or phosphorus, p a r t i c u -

23

l a r l y when th e c o n c e n tr a tio n of th e unknown was very low.

A ctual a p p l i c a t i o n s of th e methods j u s t d is c u s s e d
were made i n th e a n a ly s e s o f p l a n t ash t i s s u e s f o r th e
B otany departm ent under th e d i r e c t i o n of Dr. R. p .
H ib b ard .

The r e s u l t s w i l l a p p e ar in a forthcom ing

p u b l i c a t i o n o f t h a t departm ent.

Summary
Calcium, magnesium, manganese, po tassiu m ,
ph o sp h o ru s and ir o n may be determ ined i n a s o l u t io n
o f t h e i r s a l t s by means of th e sp e c tro g ra p h by th e
methods j u s t d esc rib ed *

Under th e c o n d itio n s of

e x p o su re and a r c i n g used, a d e f i n i t e range of concen­
t r a t i o n s f o r each element was found s a t i s f a c t o r y ;
th e y are :
(1 ) For calciu m , Q.OQl t o 5 grains p e r l i t e r .
(2 ) For p o tassiu m , 1 t o 50 grams p e r l i t e r .
(3 ) For i r o n , 0.0005 to 2 grams p e r l i t e r .
(4 ) For magnesium, 0.001 to 5 grams p e r l i t e r .
(5 ) For manganese, O.OQI t o 5 grams p e r l i t e r .
( 6 ) For phosphorus, 0.01 t o 10 grams p e r l i t e r .

24

L in es s a t i s f a c t o r y f o r th e a n a l y s i s of th e rang es
j u s t m entioned u n d er th e c o n d itio n s of exposure
em ployed a r e a s fo llo w s :
Calcium

3158.87 and

3179.33 A

P o tassiu m

3446.37 and

3447.38 A

Iron

2598.08 and 2599.40 A

Magnesium

2776.71 and 2779.85 A

Manganese

2576.12 and

Phosphorus

2536.38 A

2605.69 A

25

II
S p e e tro g ra p h ic D ete rm in atio n of Z inc, Cadmium,
Copper and I r o n in C o n cen trated B ickel S u lf a te
S o lu tio n s .

I n tr o d u c ti o n
I t has been found t h a t sm all amounts of z in c ,
cadmium, copper and ir o n m a t e r i a l l y e f f e c t th e
p h y s i c a l p r o p e r t i e s of n i c k e l when e l e c t r o l y t i c a l l y
d e p o s i te d from s u l f a t e s o l u t i o n .

O rdinary chemical

methods of a n a l y s i s f o r th e s e m e tals when p r e s e n t in
amounts o f a few m illig ra m s p e r l i t e r of s o l u t i o n a r e
d i f f i c u l t , te d i o u s and n o t very a c c u r a t e .

The

s p e c tr o g r a p h ic method i s very r a p i d and a c c u ra te even
f o r t h e s e e x c e e d in g ly sm all amounts.

In th e p ro c ed u re fo llo w ed in t h i s i n v e s t i g a t i o n
th e s o l u t i o n s a r e p la c e d in hollow g r a p h ite e l e c t r o d e s ,
a r c e d and th e s p e c t r a photographed.

t> la c N

The den p i t y of

th e l i n e s of th e m etal t o be determ ined i s compared
w ith th e d e n s i t y of th e c o rre sp o n d in g l i n e s made by
t h e s ta n d a r d s o l u t i o n s and th e r e s u l t s r a p i d l y
in te rp re te d .

26

p r e p a r a t i o n of M a te r ia ls
A ll s u b s ta n c e s u sed in th e d e te r m in a tio n s were
f i r s t a n a ly z e d s p e c t r o g r a p h i c a l l y f o r t r a c e s of th e
m e ta ls t o be d eterm in ed and were found t o be s u f f i ­
c i e n t l y f r e e of c o n ta m in a tio n .

S u f f i c i e n t z in c s u l f a t e t o make a s o l u t i o n
c o n t a i n i n g one gram of zinc p e r l i t e r was d is s o lv e d
i n d i s t i l l e d w a te r.

To 70 m i l l i l i t e r s of t h i s

s o l u t i o n were added 30 grams of n ic k e lo u s s u l f a t e
an d th e r e s u l t i n g s o l u t io n made up t o 100 m i l l i ­
l i t e r s v o lu m e tr ic a lly .

S im i la r l y , o th e r s o l u t io n s

w ere p re p a re d so t h a t th e f i n a l range of c o n c e n tra ­
t i o n s was 700, 350, 300, 250, 200, 150, 100 and 50
m illig ra m s of zin c p e r l i t e r of s o l u t i o n c o n ta in in g
a l s o 6 2 .7 grams of n i c k e l .

A s to c k s o l u t i o n of n i c k e l s u l f a t e g iv in g a
c o n c e n t r a t i o n of 6 2 .7 grams of n ic k e l p e r l i t e r was
p r e p a r e d w ith d i s t i l l e d w a te r.

Another s o l u t io n

c o n t a i n i n g enough cadmium s u l f a t e t o y i e l d 1400
m illig ra m s p e r l i t e r of cadmium was a l s o p re p a re d .
From t h e s e two s to c k s o l u t i o n s a s e r i e s o f d i l u t i o n s
was made y i e l d i n g a f i n a l range of 1400, 700, 350,
200 and 50 m illig ra m s p e r l i t e r of cadmium in a
s o l u t i o n of n i c k e l s u l f a t e c o n t a i n i n g 62.7 grams of

27

n ic k e l per l i t e r .

Enough copper s u l f a t e t o y i e l d 200 m illig ra m s
o f copper p e r l i t e r was d is s o lv e d in 100 m i l l i l i t e r s
of th e sto c k s o l u t i o n of n i c k e l s u l f a t e .

To 10

m i l l i l i t e r s of t h i s s o l u t i o n were added 90 m i l l i ­
l i t e r s of th e n i c k e l s o l u t i o n y ie ld in g one c o n ta in in g
20 m illig ra m s p e r l i t e r of co p p er.

S im ila r ly , one was

p r e p a r e d c o n t a i n i n g 2 m illig ra m s of copper p e r l i t e r .

I n e x a c t l y th e same manner, u s in g f e r r o u s
ammonium s u l f a t e , t h r e e s o l u t i o n s c o n ta in in g 200, 20
and 2 m illig ra m s of ir o n p e r l i t e r were p re p a re d .

R e - g r a p h itiz e d Ache son g r a p h ite rod s were cu t
i n t o co n v e n ie n t l e n g t h s f o r a r c i n g .

One h a l f were

d r i l l e d a t one end t o make c r a t e r s f o r th e s o lu tio n ;
th e o th e r h a l f were f i l e d wedge shaped.

One t e n t h m i l l i l i t e r p o r t i o n s of th e s o l u t io n s
were p i p e t t e d i n t o th e p re - i g n i t e d c r a t e r s while th e
c a rb o n s were s t i l l warm.
i n an e l e c t r i c oven a t 100

A fte r b e in g th o ro u g h ly d r i e d
th e y were re a d y f o r a rc in g .

28

P ro ced u re
Eastman

p l a t e s were used on a medium q u a rtz

s p e c tr o g ra p h g iv in g a n in e in c h d i s p e r s i o n co v e rin g
wave l e n g t h s from a p p ro x im a te ly 2100 t o 5000 angstrom
u n its.

The e l e c t r o d e s c o n ta in in g th e s o l u t i o n s were made
t h e anodes and were a rc e d u s in g 300 v o l t s D.C.

The l e n g t h of th e exposure depended upon th e
m etal t o be d eterm in ed .

In th e case of z in c , one

m in u te ex posures were made a t nine amperes.

The

l i g h t from th e a r c was c u t down t o 1 p e rc e n t by a
r o t a t i n g s e c to r a f t e r p a s s in g thro ugh a l e n s .
M e t a l l i c zin c was f l a s h e d on t o give th e R.U. l i n e s
f o r q u ic k i d e n t i f i c a t i o n .

One minute exposures of

each zin c sample were made, b e g in n in g w ith the
g r e a t e r c o n c e n t r a ti o n and en d in g w ith n i c k e l s o l u t io n
f r e e of z in c .

The method of d ete rm in in g th e amount of zinc in
com m ercial b a th s c o n s i s t s of exposing t h r e e known
c o n c e n t r a t i o n s of zinc in n i c k e l ; one of a concen­
t r a t i o n j u s t e q u a l t o th e Ms a f e t y H p o i n t , one g r e a t e r
a n d one l e s s .

The spectrum of th e sample t o be

a n a ly z e d i s p la c e d between t h e s e s p e c t r a l s ta n d a rd s

29

u s i n g a s n e a r l y a s p o s s i b l e th e same c o n d itio n s of
e x p o s u re .

\d \a c

k e-TO \

5

By a com parison of l i n e ebcf t o i t i o s- th e

unknown can be v ery r a p i d l y determ ined a s f a l l i n g
betw een d e f i n i t e l i m i t s .

I n th e case o f cadmium th e same p ro ced u re may be
employed ex cep t t h a t th e le n g t h of exposure may be
s h o r te n e d t o f o r t y - f i v e seconds a s cadmium v o l a t i l i z e s
more r a p i d l y .

S o lu tio n s c o n ta in in g 1400, 700, 350,

200 and 50 m illig ra m s of cadmium p e r l i t e r were used.

N e ith e r i r o n nor copper w i l l vap orize t o th e
p o i n t of n o t a f f e c t i n g a ph otograp hio p l a t e and th u s
t h e method f o r t h e i r d e te rm in a tio n depends e n t i r e l y
upon un ifo rm ex p o su re .
f o r cop per.

T h ir ty seconds a r e s u f f i c i e n t

I r o n r e q u i r e s a s l i g h t l y lo n g e r tim e.

Very sm a ll amounts of bo th a r e r e a d i l y d i s c e r n i b l e in
n ic k e l so lu tio n s.

Although th e g r a d a tio n s of v ary in g amounts of
t h e s e m e ta ls a r e a p p a re n t t o th e eye, p r e c i s i o n measures
W a c k e 'Y u - r v ^
were made of th e d e n s it-le s of th e l i n e s w ith th e
d e n s i t y com parato r.

Readings on b o th l i n e s and backgrounds were
r e p e a t e d ■until s a t i s f a c t o r y checks were o b ta in e d .

A

30

r e a d in g of th e galvanom eter when no l i g h t re ach ed th e
c e l l was a l s o ta k e n and term ed th e 11zero11 re a d in g .

The

d i f f e r e n c e of both th e l i n e and background re a d in g s
from ze ro were c a lc u l a t e d .

The r a t i o s of th e s e

d i f f e r e n c e s were p l o t t e d as o r d i n a te s a g a i n s t th e
l o g a r i t h m s of th e c o n c e n tr a tio n s a s a b s c is s a e .

The

r e s u l t i n g curve resem bles an H urter and D r i f f i e l d curve
o l o s e l y , and i s term ed th e s ta n d a rd cu rv e.

T a b u la tio n of Data
T y p ical s e t s of re a d in g s and c a l c u l a t e d r a t i o s
f o r th e s ta n d a rd cu rv es of zin c and cadmium a r e shown
i n th e fo llo w in g t a b l e s .

TABLE I
ZINC IN NICKEL SULFATE SOLUTION
mg
Zn/1

Zinc l i g e
3303.6 A

Zinc l i n e
3345.0 A

Back
Ground

700
350
300
350
300
150
100
50

3 6 .4
35.6
35.7
3 5 .0
3 4 .4
33.5
31.6
31.7

38 .5
37.6
37.8
37.1
36.8
35.8
34.3
2 3 .9_

30.7
3 0 .3
30.8
30.7
30.5
3 0 .0
1 9 .9
31 .0

Complete b la c k n e ss:

35.5

_____

5 at i o s
3303.6 A 3325.0 A
.61
.65
.67
.73
.74
.77
.89
.95

.47
.53
.53
.57
.58
.63
.72
.80

31

TABLE I I
CADMIUM IN NICKEL SULFATE SOLUTION

mg
Cd/1

Line
3261.05
k

Back
Ground

1400
700
350
300
50

30,9
3 0 .4
3 0.0
2 3 .8
26.6

1 9 .4
1 9 .5
1 9 .3
1 8 .3
1 8 .8

R a tio

Line
4799.91
k

Back
Ground

R a tio

.29
. 32
.34
.39
.53

30.5
2 9 .4
2 6 .4
2 4 .0
22.7

21.5
2 1 .5
21.6
2 0 .4
2 0 .4

.36
. 37
.65
.76
.85

Complete b la c k n e s s : 35.5
The d e n s i t y com parator g iv e s very s e n s i t i v e and
a c c u r a te measurements n o t a p p a re n t t o th e eye.

For a l l

a c c u r a t e q u a n t i t a t i v e work i t sho uld he u sed , h u t f o r
c o n t r o l work, t h a t i s t o say , between d e f i n i t e l i m i t s ,
b>lac

t h e l i n e den s i t i e s- do not need t o he measured.

Care

must he tak en n o t t o re ach th e p o in t of complete
b la c k e n in g of th e l i n e s or th e d i f f e r e n c e s in imnnitqi
due t o change i n c o n c e n tr a tio n a re not a p p a re n t.

F ig u re 1 shows fo u r t y p i c a l cu rves o b ta in e d by
(vne \o\cxc.

e~n \ m

p l o t t i n g r a t i o s o f dens-i t i ee a g a in s t th e lo g a rith m s of
c o n c e n t r a t i o n ; ( l ) and (2 ) a r e f o r zin c and (3 ) and (4 )
a r e f o r cadmium.

The two cu rv es f o r zin c a re very

n e a r l y p a r a l l e l , th e l i n e of th e g r e a t e r i n t e n s i t y
l y i n g above th e l i g h t e r l i n e .

30
35

45
.5 0
55
60
.6 5

V *70
. 75
. 80

85
90

L o g a rith m s o f C o n c e n tr a tio n
FIGURE 1 .
STANDARD CURVES.
1 . Z in c - 3 3 0 2 .6 A
2 . Z i n c - 3 3 2 5 .0 A
3 . Cadmium - 3 2 6 1 .0 5 A 4 . Cadmium - 4 7 9 9 .9 1 A

32

The two cadmium l i n e s shown a re from d i f f e r e n t
r e g i o n s of th e spectrum .

The one ahove (326 1.05 A )

i s v ery n e a r l y maximum b la c k e n in g and g iv e s only th e
u p p e r p a r t of th e s ta n d a rd c u rv e.

The low er l i n e

(4 79 9 .9 1 A ) g iv e s a t y p i c a l curve f o r c o r r e c t exp o su re.

F ig u re 2 i s a p r i n t of th e p l a t e from which
r e a d i n g s on th e d e n s i t y com parator were made and
r e c o r d e d in Table I .

The two used in p r e p a r in g th e

s t a n d a r d cu rv es a r e shown d o tte d on th e p l a t e .

A

p e c u l i a r phenomenon was observed on t h i s p l a t e .

A lin e

j u s t t o th e r i g h t of 3302.60 A appeared t o in c re a s e
i n i n t e n s i t y a s th e zinc l i n e d ec rease d .

However, upon

m easu rin g i t on th e d e n s ity com parator, i t was found
t o be c o n s ta n t and m erely an o p t i c a l i l l u s i o n .

The

l i n e was i d e n t i f i e d as an i r o n l i n e , 3305.978 A , ir o n
o c c u r r in g a s an im p u rity in th e zin c.

F ig u re 3 shows the p l a t e from which l i n e s of
cadmium were s e l e c t e d t o make th e s ta n d a rd cu rv es
shown in f i g u r e 1 .

The two l i n e s of cadmium marked

a r e 3261.05 and 4799.91 A .

F ig u re 4 shows how iro n may be d e te c te d in n i c k e l
i n v ery sm all amounts.

The d o u b le t 2598.377 and

2 5 9 9 .4 A was found t o be most s a t i s f a c t o r y f o r very

FIGURE 2

FIGURE 3

FIGURE 4

33

sm all amounts of i r o n .

The upper spectrum r e p r e s e n t s

300 m illig ra m s p e r l i t e r , th e second 30 m illig ra m s p e r
l i t e r and th e t h i r d 3 m illig ra m s p e r l i t e r .

The l a s t

one i s pure n i c k e l .

Copper a n a ly s e s were made in th e same manner a s
th o s e f o r ir o n .

Although th e methods were worked out u s in g a
medium q u a r tz sp e c tro g ra p h , i t has been ad ap ted in t h i s
l a b o r a t o r y t o th e use of an in stru m en t of l e s s d i s p e r ­
sio n .

The r e s u l t s w i l l be s e t f o r t h i n a forthcom ing

p u b lic a tio n .

Summary
Very sm all amounts of z i n c , cadmium, iro n and
co p p e r in n i c k e l s u l f a t e s o l u t io n s were r e a d i l y
d e te rm in e d by s p e c tr o g ra p h ic methods u s in g s o lu tio n s
i n g r a p h it e e l e c t r o d e s .

L in e s of each substance were s e l e c te d which showed
li vie b Uc

y>'

3

d e f i n i t e g r a d a t io n s of dassafcfcy f o r small changes in
c o n c e n t r a t i o n , and which were p e r s i s t e n t in very low
co n c e n tra tio n s.

Such l i n e s a r e : z in c , 3302.60 and

3345.60 A ; cadmium, 3261.05, 4799.91 and 3763.9 A ;
i r o n , 2598.36 and 2599.39 A J and copper, 3273.96 A .