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The absorptiometric determination of molybdenum as molybdenum(v) thiocyanate in steel
ANALYTICA
THE
ABSOIWTIOMETRIC
MOLYBDENUM(V)
N. LOUNAhIAh /fklicimluget Uofors, (I
21
CHIblICA ACTA
Scptcmbcr
Dl3TEIIMINATION
THIOCYANATE
Uofors
OF MOLYBDENUM
AS
IN STEEL’
(Swcdm)
4th. rgG4)
Few methods for the determination of an clement have been subjected to so many studies as the photometric thiocyanate method for molybdenum. Scvcral of these stucliesl-“~shavc been quite extcnsivc and systematic; an excellent summary can be found in the text book of S~sua~r_ 0,'Tilemany studies indicate that the conditions of the method are inherently critical, and also that other methods of determination arc not very satisfactory. In a recent study of HIBBITS AXJD WILLIAMSH, the nature of the method was itnlicatcd by the statcmen t that “the dcvclopccl m&hod is accurate to if applicable to contents of, say, I-Z% in steel, is within &- 4%“. This accuracy, definitely unsatisfactory. a modified proccdurc has been in USCfor In our steel analytical laboratory, several years, which is very similar to that described by B.I.S.R.A,lO. Tlrc metllocl in this form, howcvcr, is scnsitivc to interferences from copper, as well as from colored ions. It gives reasonably good short-term precision (relative standard deviation I-zO/~ within one series of samples), but the long-term precision is not ncnrly so good, and a change of analysts results in much too large deviations: ~-5% at a level of 0.5-I%. The color of molybdenum thiocyanatc in the aqueous phase is, however, very stable. A method with better stability and accuracy was highly dcsirablc in order to be able to check high-speed mcthocls (optical and X-ray spectrometry). A comparison of the published thiocyanatc m&hods for molybdenum, together with some prcliminary experiments, was tlrcrefore made to determine whether this method would be worth investigating in detail, in order to dcvclop a method which would meet the following requirements : 0.01 to 10% MO in steel range : precision : content o.x0/o 1% 10°/ rel, st, dcv. ($8= 10) 3 I 0.5 interferences: no interferences > z 6 for Mo = o.~o~/~ from the following elements up to the content indicated (only probable interfercncc elements are listed) v CV Ti Nb Co Cu Cr Ni Mn ‘Fe ropcrcent 20 5 5 20 I 20 20 zooomg 5 of the ~ddisIm2 dh0as and resdts Apart from the fact that a thiocyanatc
Cont$uvison
o/some
preliminary
of molybdenum(V)
cxfierimcnts
is involved
in the
N. LOUNAMAA
22
reaction, different opinions have been expressed concerning almost all other relevant details. The situation is summarized in Table I. A study of the method should obviously include the effect of all these parameters, and also possible interactions. However, some practical limitations, together with some preliminary experiments. made the picture less confusing as indicated below.
color
TIIE XIWISC’T OIr
I>IPPElC1SNT PhllhMISTlt,RS ON ‘flYIS ~~o-TltIOCYANATl~ COLOR I’UULISI~IIZD METIIODS -. . . .. . - ---. -.- . ..._ . . . _-__. ..____-..__--.---._-. .- ._.-. - . ..- .___.. . ..-. .. . . . .... .I~c_fcrcrr CFS J’Ul’lWIPf~Y _--______._____ ... .. .. -.-- -..-. ____.--._...-..-._. - _....__ .Mlg/rt effect .stvo,,g cffc1:t No c_fpcl __ _...__.__.
..___.-
. .._ ____,__
__
.._. _.__
I-ICI
8
EIC104, I-IrSO.1 NH&CN
K) , 11
--,
SIlClP
Lit Cl1 Ti
10
.-... --
_..
.
TO
_ . .._.___.
I, 2 8
3 1, 11 1, 2. 11, 3 4, 2.3 (2), 11 1, ‘),8. 10 2 -__-_.--
--___-____---
--__
_._ _.....,.._.- __ ----
ACCORDING
4, 8
8 3, 4 I-_-._
__......_ _.._..._.._
I’he cJfect of iron and cop@w. In the presence of iron and copper, molybdenum(V1) is not easily recluced to the trivalent state by tin(H) chloride. In their absence, the color of molybdenum(V) thiocyanate disappeared rapidly, when an excess of tin(I1) was added, but could be redeveloped if some iron or copper was added. It is thus sufficient to know the concentration ranges of iron (copper) and tin(I1) chloride within which the reduction to only molybdenum(V) is valid. Some preliminary experiments indicated that these limits were not too narrow. Tlte effects of thiocyanatc altd hydroclrlovic acid. A very large excess of thiocyanate tended to bleach the color, but the amount of thiocyanate was not very critical. Preliminary experiments gave evidence of a very strong effect of hydrochloric acid. Organic extracts containing IOO ~8 MO and with an absorbance of 0.300 were discolored when shaken with an equal volume of IO N hydrochloric acid. The recommended USC of nitric acid” and perchloric acid12 as stabilizers for the molybdenum(V) thiocyanate color is advantageous because thcsc acids do not promote the reduction of Ma(V) to MO (III). Use of ovgaGc extmctant. Through the use of organic cxtractant, the interfcrcnccs of copper ancl colored ions such as Cr(II1) and Ni(II), could be eliminated ancl probably the concentration of interfering anions controlled more effectively than
in the aqueous Based
Preliminary
phase. on
these
considerations,
an initial
method
was
outlined
as described
nlelhod
Into 8 23o-ml separatory funnel, place IOO pg MO and add 2 ml of concentrated phosphoric acid, 25 ml of I : I sulfuric acid, 20 mg of iron and 0.6 g of potassium thioa4nnl. Ctriw. .4cttr, 33 (1965) 2x-35
A’BSORPTIOMETRIC DETER~lINATION OF Mo IN STEELS
23
cyanate. After shaking, add IO ml of water containing I g of SnCla * 2HrO and I ml of hydrochloric acid and shake again. Adjust the volume to IOO ml, add 50.0 ml of amyl acetate and shake for 30 sec. Discard the aqueous phase and wash the organic phase with 50 ml of wash solution containing 2 g of potassium thiocyanate, 0.5 g of tin(I1) chloride dihydrate and xx ml of concentrated hycl_rochloric acid. Discard the aqueous phase and filter the extract through a dry filter paper into the cell. Measure the absorbance at 470 nyr.
Effect of variables Effect of
ivon. According to PERHXN~ “for 4 rug MO, at least 0.5-x mg Fe is and up to 10-30 mg causes no further change”. CUNNINGHAM AND necessary, HAMNER~~ had up to 200 mg Fe present, whereas HIBBXTS AND WILLIAMS~ found no interference from 500 mg and IO mg was always added. In the procedure of CROUT~IAMEL AND JOHNSON" more than 2 mg Fe interfered. When the preliminary method wls usccl, it was found that the stability and reproducibility (absorbance 0.378-0.380) were good in the presence of 2-200 mg of iron. As much as 500 mg did not interfere if the initi,al addition of tin(II) chloride was 3 g and the wash solution c6ntaincd I g of tin(I1) chloride. The extra quantities of tin(H) did not affect the absorbance readings even when only 20 mg of iron was present. Effect of /tydvoc/doric acid. According to PERRIN~, the amount of hydrochloric acid is critical and “must be controlled to at least -& I ml of 4 ml adclcd if the error is not to exceed 3%“- HURD~ also stated that the amount of hydrochloric acid is critical. l3.I.S.R.A.10 and HAYWOOD AND Woou 12 did not add hydrochloric acid and HII~BITS AND WILLIAMS*, who used about x.5 N solution, stated, that its amount had “no significant effect on the results”. Table 11 contains the results obtained with various amounts of hydrochloric acid according to the preliminary method, but with omission of sulfuric acid. Interesting conclusions could bc drawn from these results as regards the reduction of iron and molybdenum, but for use as a method for the determination of molybdenum, the system was far too critical. Hydrochloric acid was not used in any further studies.
_____ HCl
.__.__.. (d=
rrcldcd(9~ I)
G 8
x.29)
___
..__
-_.--__
._ __...._._.
_.. ...-__
Nor*~lnZify of HCL dS cr/lcr dilufiort _-__..-_-_--..___._I_.---Addrd
Undil. 0.7 CJndil. X.0 Untfil. r-5 Untlil Dj1.r -t I ::;
.- ,._.-
_... .. . -__
R6sor6nncc A f&r 0 min
..-...
__.._
.___...----.-
.4/h? r I 11
0.235
(0.379) 0.232 0.3%
.__
(0.373) o 0.232 0.376
0.379 0.182 0.182 0_17.5 0.378 0.376 0.379 O.@I 12.5 0.384 y;fl -I- 4 I.5 0.379 0.370 0.375 3.0 0.373 25 IJntlil: 0.322 0.325 0.323 37.5 2:: Undil. Almost colorless 50 ____-__ -._____-_-_. --_-.--8 Thcsc nbsorbanccs inclutlc the color of unrcduccd iron thiocyanatc. 12.5
X2.5 12.5
. .. ____--_
After 20 It
-_.. . ____._I_.
(0.379)
-_
f2c,,tar/rs
470 rrrp -_.____
And.
_~.._ ____ .__-._._.. .__ Iron not rcduccd Extraction after x5 min Extraction immcdiatcly Extraction after x min Extrilction after 1 min Extraction immctliatcly Extraction immctliatcly I~xtrnction inimctlintcly Extraction inimccliatcly
.__..___-..
Claim, Acfa,
33 (r965)
21-35
N. LOUNAMAA
24
of ficvchloric
acid is a WOODED state, that “pcrchloric stabilizing medium for the ferric thiocyanate and so also for molybdenum thiocyanate”. However, perchloric acid is not used in any method to which rcfercnce is made, other than the B.I.S.R.A. method’“. Table III gives the results obtainecl with varying amounts of pcrchloric acid according to the preliminary method. Compared with corresponding determinations in sulfuric acid media, the results with the higher concentrations of perchloric acid tended to 1~ low. Moreover, tllc rcl~roclucil~ility was not good enough. Separate expcrimerk showccl that with larger amounts of tin(U) chloride, correct results could bc obtained even with the higher l:oncentrrttions of perchloric acid; but, obviously, perchloric acid can not gcncrally be recommenclcd, because of its oxidizing power. Effect
_.__._-._..___.___ .
mid.
. Nwrmlify
JfCl0.I 11dtlcd
~il\Ywoor,
._
__
uf
Norrmrlify cr/lcv diltttimr
tlevclopl~lcrrL
(?lll)
G (J
’3 ‘3’ 20
26” 39 3’J’ (is
-
._
.-.
I .O
3.0 3.9 5.8
I.5 1.5 3.0
O.#O
0.:18X
0.385 o..jsH
O.#Z
!i.H
ij.0
7. l 7.1
4.5
O.;j(iC)
*I*5
0.378
0.0
0.3
7.5
I\llncJSt
..---.- I_____.
cl;c,;-lx)
..
-.
Ilesfrlti~r~ norndity Of f-Ia.SU4~
(Id)
H 12 25 38 44 50
._...
_._._..._
..
._,,.
,_ __.,
_. . ..^._.
.
_.... ___. ._____
0.307 0.373 0.378 0.378
0.358
0.355 0.377 0.375
0,353 0.370 0.370 ‘J-345
cJ.338
15
_ ._.._ After a0 t1
. _..._._ .-.. _-
~J.SJ.5
O.S!YJ
._.__._.
“A377 0.378
_
110 C&Jr
,._......
_
.._...
.._
_.__..___.._^.
...
I)ctcrmitlkitiorl carrictl aut krtcr to test rcprotlucibility.
I-l&Y~.,
10
.- ._-...
3.2
;:7; _ .,... _.. .-.
A bsori~cimw 470 rJrp . .__.._._. -. ____-. ._ .il/lt!r Ajtcr 0 mitt a-g Ir
0.377 0.378
.5a _.._.._.
,.
to V)olllm! Lf Ilra COIOV _._._... ._. .____. ___..... ..._. . .._._... . 2.2 0.7
____x___-.-
a
AND
t*.+ .%f-)
3.5 .I.0 (3.0
b::: -.1------.._._
0 ‘The solution
___. .._ .._ .__, - ___.__..._._ . _._. . __ ._.__..^__ /I.-...-.fmxba,lcl! UC 470 8qJ --._-______ _. ._ __... -_ _ . .._- ..-.-. .. .._. - ..__..._ ___.... -. ..__ .._._._.. _-__.--_-._._I. ‘I’irrrc Octwcoi deVdtJ/WlCJat mid cslrrtctiou __ -._....-. _. .._.- .__._.._.__... __ ., . ..-.-__..__ . .._ _. . _-...._... _- ...... ..-._. - ~‘---r----0 JJlaJb _- -__-.._- .. .., _ .._ ro #)ll#l m1ti 30 #/IL)& -.._- - . . - Go ____...__.-_- __... ._. _.__-_. ._.__..__ -_ .___.__._ ;I’imc trftrv .w+ctrtition of or~u~~ic: /d~asc ._.._ __.._ -. _.. ... . .._..-..... . . .--. ._. ._- . . .. . .. __..-. ..0 ruiu ao I,‘ 0 rniu I Ir 0 rrii,, x Ii r lb 20 11 0 ruirr 1 II a0 /I _ . . -.. __.... __ _._...__..._..._. _.._._- . _ ._..._,...__.._.. . ._ __. _ _ _ ._.. .._. (0.370) (0.379) (0,378) 0.338 0.337 0,335 0.302 0.300 O.Z# (0.380) (o.3Ho) 0.371 0.371 0.368 0.370 0.380 0.381 0.380 0.379 0.37tJ 0.379 0.379 0.37CJ 0.378 0.38C 0.38x 0.382 0.383 0.382 0.379 0.378 0.379 0.370 0.379 0.379 0.379 0.37’
_._
o.:j80
0.380
0.378 0.352
0.381
0. JO0 -._._ .___
0.378 0.3Go
o.gHo 0.380 0.379 0.$30 0.35~ 0.357 --._-.
0.380 0,358
0.378 0.379
0.378 0,379
0.381
_..-...-V-w--
W~?Hitl\Vnys tlilutccl to constant volunw bcforc otlcling tlw rcagcnts: Values in bracltcts intliciltc tlrnt ttlc iron(II1) thiocyanntc color is incluclcd
0.378 0.378
0*37< 0*37(
.-- .-_._ -___
Fe, ICSCN atw
ARSORPTIOMETRIC
DETERMINATION
OF
MO TN STEELS
25
Effect of srdfzrric acid. Little mention is made of sulfuric acid in published studies. HIBBITS AND WILLIAM@ stated that its concentration is critical. The influence of sulfuric acid was investigated in somewhat greater detail than the other acids; the variation of the time between the development of the color and the extraction was also studied. The results arc given in Table IV. Obviously the reduction was too slow at acidities below 3 N. Above 7 N, low results were obtained, possibly because of a sulfate complex of molybdenum. However, the range between 3.5 and 7 N sulfuric acid was considered big enough for the determination and the stability and reproducibility were good. Effect of t/tiocyamzte. Almost all authors point out thnt the amouut is not critical but that excessive amounts bleach the color. In the aqueous phase 0.5-3% thiocyanate (0.075-0.45 N) is generally used. Obviously the amount of thiocyanate in tlrc organic phase depends not only on its concentration in the sample solution but also on the thiocyanate concentration of the wash solution, and thus both concentrations were varied. The results (Table V) indicated that concentrations below 0.05 N in the aqucous phase tended to give low results which, however, could be somewhat improved hy high concentrations of thiocyanatc in the wash solution. Concentrations in cxwss of 0.20 N in the aqueous phase definitely gave low results, which could only be very slightly improved by having little or no thiocyanate in the wash solution. The thiocyanatc concentration in tile wash solution was less critical, though more than 0.5 N
TA131,IS v .--.---
..___. _ __ _ _.. ---__--._.
-.._._.....
.
_ ..__,_.._.-
--------_
..- --.-.---_...--
,.
_._- ____
_.._--_ . ..
pilust?(iv)
~Vortwlily o/ wr1slr soltitiorr (A?)
A bsorbnmz after Norwinlily A’ortmtlily .,Ibsorba UCPaj’lcr _---_.-____-___.__ _-. _.__._....._. __.__-.._ of uqrreorrs of wnsh 0 mitr I I1 20 Ir a0 Id jhise (8) sollrliou (IV) 0 rtii*r I Ib
0.0
1 .OO
0.310
Novnudily of Nqlrcolts
_______.___.__._.__.__...._ I
.
0.0 1 0.01 0.01
0.075
0.05 0.05 0.05 0.05
I.00 0.50 0.25 0.075
0.05
.-I)
0.50 0.25
0.065 o.oGg 0.065 0.065 0.08
0.50 0.25
0.075 I .oo 0.50
0.08
0.08 0.08 0.08 0.08 J
.
0.25 0.10
0.05 =
No thiocyanatc
..
._.-.----_-..
0.316 0.332 0.285
_....----_-_---_I--
o.3r.t
0.320 0.332
o**3 0.13 0.13 O,T3 0.21 0.21 O.? 1 0.21
0.285
0.37.5 0.382 0.jH(i 0.385 0.355
0.369 0.375
0.371 0.381
0.382
0,382
0.383 0.384 “a383 0.34 *
0.381 o.3w 0.38‘1 0.375
0.375 0.383 0.390 o-387 0.38G 0.385 aklcd
0.370 0.367
-....-
0.313 0.320 0.330
0.379 0.3G7 0.381 0.384 0,384 0.379
.--
-.....-
.._---.----
0.378 0.384 0.385 0.384
0.380 0.382 0.387 0.388 0.391 0.387 0.392 0.387
I.00
0.372 0.381 o-384 0.384 0.385
0.372 0,375 o-37!, 0.383 o-385
0.378 0.372 o..z73
o.!YJ
0.353 0.349 0.315 o-372
0.359 o-356 0.3zfi 0.375
o-357 0.355 0.335 0.375
1.00 0.50 0.25 0.075
0.319 0.236
0.31s 0.255 0,245 0,235
0.5’1 0.25
0.075
0.21
-
0.30 0.30 0.30 0.30
0.2.5 0.075 -
0.370 0.374 0.50 0.383 0.380 0.50 0.380 0,384 0.50 0.307 0.382 0.50 0.384 0.383 0.380 0.380 .. ..._ to the wash solution.
-.
0.5” 0.25 0.075 -
rivial. Chirll.
0.220 0.205
Acta, 33 (1965)
0.3N2
0.38.1
21-35
26
N.
LOUNAMAA
results. Thus the permittccl limits of the thiocyanate concentrations in the solution to 1~ extracted and in the wash solution were 0.05-0.x5 N and 0.10-0.35 N respectively. ‘Thcsc figures are, of course, dependent on the amounts of iron, molybclcnum and other ions forming thiocyanatcs, but no effect hvas found for amounts of 0.5-500 mg Fe and 0.5-300 /~g MO. Effect of tin(II) c/zforidc. According to the generally accepted explanation of the reaction mechanisms involve& the color intensity should depend on the amount
gave
low
‘tfilf ILl~lWCT _.__._--___._.
-.-
Norrmdity __________
Ill
OP Till:
CONClfNTRATION
-
-
. .. . . . -..-....
of SIICIZ ( N) .__._-_.-_
Cl~llC~JftS
I t1 wt1slr
OF TfN(11)
--.
.-
Norr~rcclity
. ._ salrr.
CflLORIDlZ
. . . . ---.-----.-.-----
_-...
_______.___-__
-._.___-__-_-__.____
I,r
rtl
c~q”“““.~
W~I
.W~L
., .--.
A l~swbtoux 10
bnirr
---..
470 nrp tr$tcr
--
1 lr
ao k
0.308
0.218
0.393 o.391 o.38G
0.392 0.388
ph5C
fillclsl! 0.10
0.00
0.10
0.
0.10
0.10
0.20 o.,p 0.60 0.80
0.10
0.00
0.10
2.00
0.10
0.10
0.10
2.02
0.10 0.10
IO
o.oa5
‘2.00
0.025
2.02
0.025
2.v5
0.025 0.025
2.10 2.15 2.20
0.025
v.335 0.390 0.385 0.382 0.34G 0.336
O.fO
0.20
0.10
0.10
0.40
0.10
2.05 2. IO
0.x0
0.60
0.10
2.t5
0.x0
0.80
0.10
2.20
0.00
0.0375
2.00
0.10
0.0375 o.o175 0.0375 0*0375
2.02
0.1s
0.15 0.15 v.rg 0.15
0.20 OS10 0.60
0.20
0.00
0.20
0.10
0.20
0.20 0.40 o.Go o.Ho
0.20
v.20 0.20
0.25 0.25 0.25 0.25 0.25
0.00 0.10
0.20 o.,\o o.Go
0.30
Ada,
33
0.387 0.388
0,395 0.395 a.395 0.385 0.382
0.400
2.15 2.VO
0.388
2.02
v-392 o-39G o-377 0.355
0.394 0.395 0.390 0.384 0.383
0.389 0.396 0.400
2.00
0.390 0.390 0.389 o-377 0.347 0.338
0.394 0.394 o-391 0.387 0.3G5 0.365
0.384 0.384 0.383 0.38r
IO
0.10
2x-35
o.39G 0.397 0.393 o-397 0.389 0.375
0.394 0.392 0.394 0.385 o.3Go
0.10 0. to 0.10 0. IO
(x965)
0.391 0.389 0.385 0.382 0.381
2.00
2.02 2.05 2.10
2.02 2.05 2.
IO
2.05 2.10
2.15
2.02
2.05 2.10
2.15 2.20
Chim.
o.rto t o.rto1 0.399 0.394 0.392
o,oG75 o,oG75 0,0075 0.0675 o,oG75
0.
0.20
o.39G 0.39G 0.39G 0.388 0.382
0.384 0.3cJ8
0.193 o-393 0.389
0*34G
0.00
0.40 0.00 0.80
0.3G3
0.3’34 0.383 0.380
0.393 0.388
2.15
0.40
0.10
0.346
2.20
0.40 o.Go
0.40 0.40 0.40 0.40 O-40
0.370 0.395 0.390 0.383 0.348 0.343
0.39G 0.397 0.395 0.389 0.300
0.075 0,075 0.075 0.075 a.075
0.20
2.15
0.383 0.377 0.377
2.00
0.10
0.00
2.05 2.10
0.378 o-358
0.05 0.05 0.05 0.05 0.05 a05
v-30 0.30 0.30 0.30
And.
-.----.----._-..-.-..-.-..-.--
oj I-iC1 (N)
0.399 0.40 I 0.393 0.384
0.383 0,388 0.384 0.380
0.387 0.385
0.378 0.379
ABSORPTIOMIYWIC
DETERMINATION
OF
MO IN
STEELS
27
of the reductant ; if insufficient tin(H) is added Mo(V1) is not completely reduced to MO(V), and if too much is added, the reduction continues to form Mo(III), in which case the MO(V)-thiocyanate color fades. Most authorsr-3 point out that the excess of tin(II) is not very critical, but that the amount of acid added with tin(II) chloride is important. The effects of varying both the tin(H) and the hydrochloric acid concentrations are shown in Table VI (the procedure on p. 22-23 was used). Although the results obtained confirmed earlier results 1-a they still indicated that if the best precision is to be attained, the concentration of tin(H) chloride is quite critical.
Interactio?ts between molybdenum, szdftcrric acid, tin(I1) chloride, tltiocyanate and iron. It was considered advisable to study possible interactions between reagents only within certain limits of the reagents used. The levels were chosen arbitrarily to correspond to twice as great variations as could be expected in practical determinations. The results of thcsc tests, which were carried out according to the procedure given on p. 22-23 in other respects (but with only 25 ml of amyl acetate) are given in Table VII. Although significant interactions can bc traced from these results, the probability of obtaining errors larger than I%, due to interactions in practical determinations, is very slight, considering that such great variations of rcagcnt concentrations would be excluded and that the standing time would be much more constant.
INTISHACTIONS . -... --hxd~
____ .._
13E7’Wli&N . . -_-.
RISAGENTS
. ._-_..
-.__----_--
DIPPISRHNT
lhxovery, --.-
__..--___
KC NS
.Sd&
LRVELS ----
--e-B-_
oJ
-_.._ ._._ -_- _.-___ IWO Ji&‘O.~ Fe
AT
rafter
4 11
0.157 0.158 0.780 0.780
0.158 0.157 0.780 0.781
99.3 98.8 90.2 99.4 X01.0 97.0 99.5 x01.3
rot.3 98.6 99-j 98.7 x00.0 101.0 95.5 99.0 too.6
98.2 99.8 98.8 99.0 99.4 102.3 95.5 x00.0
100.2
100.2
o-779 0.78x IVO.0
98.8
99.4
:_; 1-i l
The
100.2
lOI.fj
97.5 100.5
X01.5
100.0
I, I-i 1-i
1oo.G
100.g
100.8 99.4 99.5
100.6
99.3
\
Val1w.r calculntcrl as pcrccntage of the * irbovc absorbance values
10x.8 98.2
99.4 100.0
VOlllCS lltJC!ClilY rcfcrcncc for cnlculntion of rccovcq
I
100.0
100.2
I,
._ _--
--
Itcurarhs
--_
0.158
nl
-_---a-
I Jr
0 niitr O.I$l
M I.
- ---
tr6sorb. ~wcustrrcd.. ’
97.0 100.0 102.1 roo.0
99.8
,
-
concentrations of rcagcntu wc?rcDYfollowe :
L = Low lcvcl M = Medium lcvcl IS = High lcvol
MO 20 Pg so Pg =oo l(g
I-iaso4 4N 5N 7N
.
Fc 5 mg 20 mg 200 mg
Asal.
KSCN
0.07 N 0.10 N 0.15 N
Chim. Ada,
SnCh 0.10
0.20 0.30
N N N
33 (xgG5) 21-35
N.
28
l.OUNAhlAA
The following procedure was accepted for the determination of molybdenum the modification required contents of o.or-xoo/o in all steels. For convenience, tungsten-containing steels is incluclcd.
in for
*I’igz(II) chloride. Stock sol&ion IO N. Dissolve zz5 g of SnClz zHt0 in 50 ml of concentrated hydrocllloric acid and dilute to zoo ml with water. Add r-5 g of tin. Preparc R 2 N solution claily by dilution with boiled water. Was/l solr&on. Stock solution 0.5 N Sncl~. Dissolve 56 g of SnClc - zHz0 in 1000 ml of concentrated hydrocliloric acid. Prepare the was11 mixture immediately bcforc use from 10 ml of 0.5 N SnC12, 5 ml of I N ICSCN and 35 ml of water. A~tyl crcetate. Iie;Lgent grade is not necessary, but a quality which is colorless as well DS free from oxidants, is essential. Sc~arntory fmnels. 250 ml, marked at 80 ml and prcfcrably with teflon stopW&S (to avoid grease). ‘I’lfem~ostat device, whiclt allows handling of the solutions involved at a convcnicnt tainpcraturc (zo--25”) controlled to & 0.5”. l
Proctdiirc
Dcpcncling on tllc expectccl corltcnt of MC), weigh out IOOCJ--100 m& (d K 0.x0/,) (WC Table VIII), and dissolve in I0 ml of sulfuric acid (d = x.84), 5 ml of phosplloric acid (cl = r.G8) and 50 ml of water. Oxidize iron wit!1 II. few drops of nitric acid x.42). Dissolve higIl-alloy steels in hydrocllloric and nitric acids and evaporate (d = to rcmovc tlicsc acids with the same iLlll0Unts of sulfuric and pliosphoric acid as mcntionecl :ibovc. Expel silicic acid with a few drops of liydrofluoric acicl.
OI’TIaltIM
S1ZH
Il.10 ‘g
SAhlI’LRS.
012
_ __________
_. .
__
e.r/x!ctcd
ALIQUOTS
.._. - _.._ Strt~~plc
IC’TC.
.-___.._ _ . rocighl
(WY) - _...
.
_-__._._
._..
1000 500
‘200 100
0.p4.0 r.O-g.fJ
IO0
g.CPfC3.O _._.
_ ._ . .._..._-
if W
1’ Only
.-.-...
ACCOI1l~lNG TO TiIlS -_.... _.-_.- . .. . Citric: (IT)
. .. -.. _._.. ,... . .--
.I_._.
0.01-0, IO O.lO-0.50
-
AMOUNT ._ .-_--
tcciu?
n
IJillllCd
21 lir/uot (wrl)
(wl)
5
1,01>
5 5
500
500 .__ ____
.___._
1 :t: tctihl (w)
20, 10
-
20, 20.
10 10
-
20,
10
20
15, 10
1000 ____-__..
15X1’13CT15D
to
-__. .--.. --.--.-.----. __-..-._._.___--__ 10 IO0
IO
._.. . . .._____ .-_-_-...
01; ido
‘Lo 20
- .___
pwwnt.
Dilute
tllc soJution to volume (Table VIII) with water, at a tcmpcrature of In the presence of tungsten, add citric acid bcforc dilution. Transfer a suitable aliquot (‘Table VIII) to ;L 25o-ml separatory funnel, add 25 ml of I : I sulfuric acid ancl adjust the volume to 80 ml. Mis well, add IO ml of I N potassium thiocyanate, shake, add IO ml of 2 N tin(I1) cllloridc and mix again. (This solution is 25”
Am-d.
-4:
0~5”.
Claim.
Actn,
33
(rgG5)
21-35
AHSORP‘TIOBIETRIC
l)ETERMISATION
OF
MO
IN
STEELS
23
5 N 112SO4,0.10 N KSCN and 0.20 N SnCl2.) Add 25.0 ml of amyl acetate at 25O and shake for 30 sec. Remove the aq~~us phase, and wash the organic phase with 50 ml of solution containing IO ml of HCl, IO ml of 0.5 N SnCI2 and 5 ml of I iV KSCN. Filter the organic phase through an iron-free filter paper into a dry volumetric flask, at a temperature of 25”. iMeasure the absorbance of the solution with a Ueckman DU spectrophotometer at 470 mp in a x-cm ccl1 against arnyl acetate as reference.
It is necessary to avoid contamination of iron(II1) greater than that which can be eliminated by the tin(lI) chloride in the organic phase. Avoiding excessive oxidation from strong oxidants is also essential. The freshness of the tin(II) solutions is important. RESULTS
ASD
DISCUSSIO.\J
of various ciemwts olt the color rievclojmcnt The effect of ions present in solutions obtained from steel samples was invcstigatecl by adding varying amounts of the ions to the scparatory funnel, togetlwr with 50 pg of molybdenum after whicI1 n~olylxleuun~ was determined as clcscrilxx~ above
‘I’lte effect
(50
jrg
__ _.___ _.
MO ._
prcscnt;
20
__^_ __ _.____,___..
mg
Fc
m.ltlcrl)
__
._..-
_..__ --
__.. -_
__._ __.._-
J
1V
kcc.
(*,I69 _. .
fw ( w -.. . .__-.-_.__._._-
co
(‘xl) ..- -----
-._--
.._.,.-._
(wd ( ‘%I ____._____-____-______-_.._-
__.-____._.-...__ Idly.
SD
(w)
(W
f wrl .- __ _.. . .--.----
100.3
93.5
0
100.0
100.0
1 C)
100.0 100.5
0
5
2.5
v&s
10
loo.H
20
100.0
5
20
100.0
1 1.5 5
99.8 100.0 9g.y - 90.5
.I”
09.5
2:
___
__
_____..
100.3
IO0 HO
09.0
__________ _.._._.._
,., -.
__. ...__. _____...-._ J?CC.
.
100.0
7.5
x00.0
10
100.3 _.. -..._..- ._. -.
‘5
IO0.j
102.0 IOf. .,
_ .__ _..- _.- - .--
-10 _.
_._--._.__ ----.
._..
7-i
0
Cl6
0
__
..,..__.__
Jtcc.
I’
- _____--_-
0
I 2 3.5 10 5
_.-....__. -.________ .___.__..__.. .....___...._.-.. . .._ .___. ____._....-__-Xi J&VT. itcc.
&)
99-s 100.3
20
f 00.0
20
100.5
40
40
100.3
100
60
X00.0
3
100.5
_-.
100.3 IOO.3 -
-
--
.--
--
2
99.8
___. .._..._.._
-
- .__. ._ ___... _.__
-.-_.
5
15 30 -
100.3
80
100 .__._
IOI.0 _-
. ._..-.__..-.---___- ._....--
_
100.5 100.5 xor.0 103.8 102.0
..__.-.--..-...-_--
iv,8 (W)
.---_---.-we-
I
100.0
_.._._-.-_-__-.I---
owY9 (twl (‘xl) __,._ (%ol ____.._ __._ ____.___^_ _...- -...._.._.-.-......_._-.-_-.. - ._._ ___-._...-_--__ - --.-_ (%J -_..---. 0
J
ht.
(%I 100.5 10’0.5
100.3 -
a-_-...-----.--
(Table IX). In the cast of a color interference, the observed interference is better cxprcssed as the absolute percentage error caused by 1% of the interfering elcrnent in the original sample. As can bc seen from Table X, the interferences from the io:ns tested can be considered negligible in the analysis of steel. AWL
C/rim.
Acta,
33 (IgGg)
21-35
30
N. LOUNAMAA
In the analysis of some steels containing tungsten, surprisingly low results were obtained. This error was evident only when solutions of samples were diluted to large volumes, and thus some kind of cohydrolysis of molybdenum and tungsten was suggested, The low results could be remedied by adding citric acid which had no effect on molybdenum alone. With extremely high concentrations of tungsten + vanadium, a slight positive intcrfercnce was also indicated; the error corresponding to 1% V (with excess W) was only o.oor%, Mo. Precision From previous measurements with the Beckman DU spectrophotomcter (xc)58 model) used, it was known that if a solution with a stable color (CoSO4) was measurccl repcatcclly at the wavelength in question (525 mp) and at the absorbance lcvcl of 0.40.5 units, a relative standard deviation of the order of o.~o-o.~~~/~ could bc expected. The reproducibility of the color development includes variations in the color and volume measurements, and in the chemical reactions involvccl, but not variations in the dissolution of the sample or in the homogeneity of the sample, as only aliyuots of one solution taken with one pipet are compared. ‘I’hcsc tests were carried out as described on p. 28 and the results are given in Table XI (I).
____. - ___._.__..___.-
-_-_.
‘I’i
--.. .-. _. -.-. __.--.-_ _.-.-__ -_
o.ooor~~
-. .- - . ..._.._. - __..______..._.......__._.__..__.._-.--___ -.- ..,.._..._.. b
co
-__-_
1’ Would probabtc.
.._____._.... ._ _....
corrcspoml
. . .. ..__._, ---
to o.oz’~~
ND
0.0002a _ . ..-.-.
C’.lf
_--. - .--. .--_
uwd
..-.. -..
_.__......__ -__.-..-..__
Ni
l317t
_ . _ .-._ .-_I_____ ._._ . -.- .._ - . ..--.__.-
O.000 I _..-_- __.... .
IWOin tllo NL Illutul
_ ___.....,._-.._-.
cv
c.0.0u000 _ __.. .___.._,...__-_
(Spccpurc
< 0.0000 (0.0000 --._ _ _-... ._._ . ___.. .._ . _ .
hliltt,l\cy
Niubiunl)
wllic11 is not
‘fhc short-term reproducibility of the cntirc procedure was cletcrminecl by analyses of tlirec samples, with cliffcrcnt amounts of tlic sample in one series of mcasurcments ; the results arc given in ‘I’ablc SI (Ii). The long-term reproducibility of the cntirc proccdurc is of decisive importance to the practical analyst. This reproducibility includes variations due to cliffercnt volumetric vcsscls and newly prcpnred rcagcnts, in addition to the variations listed above but not a change of analysts. The results ot analyses over a x-month period are shown in Table XI I.
IXpCiltCtl
As on (n) the the curve ical curve Araak Chim
in all proccdurcs of this type, obtaining the correct level of results depends value of the blank, (t) the purity of the molybdenum usccl for establishing (factor), and (c) differences in the conditions for preparation of the analytand for analysis of unknown samples, i.e. interferences. Since the effects of Acla,
33 (1965)
21-35
AUSOIll”IXOMETRIC T.413LIi:
STANDARD
_.--.-..-
____--
I~I~VIATION
,.... _. - - -
OF
.-_ .---._.-.
i*r
determind
MO
OF BfO
Ih’ STEELS
31
SK
I
DETERMI~A’I’IOS
---
‘I-IlIZ
I~BTISRAlINATION
..-..-.-....
Gl’
310
()I
_ - __.___
--_.-.-.-------
=
IO)
-_ ___-_____
- ___. -
_______
Smlplen -. IK_$.
______.
_.__ _____ .,_..__.___.-._ -.._-.._. __.-
aliquots of the sam7c solution (I) S.D. for diffcrcnt weights S.D.
for
0.32 O..(cJO--0.
500
IO/too o.~~Cq-o.jOr)
(ml)
___________. . .._...
. _ .. ._. .._- _-.-
.
o.og
of the smnc ~ilrrqh (11) Snll~ylc ;rnloutlt tibkcttl (6)
Aliquot taken Alx~rbnncc
--
i3C6H
...__....
... -
..
f&H
V. J I
-
--
0.36
0.30
O.IC)l-O.‘Ol
0.202-0.?0c)
0*44
o-43 0.487-0.529
I o/500 0. $37~-0,‘+0.1
IO/500 0.413--0.437
0. tgr-0.19s
10/1000 0.(>4J-o.C,67
25/roe
o.3.%-0.4
13 - --.--- ..-..-.._- .___._
.- .._-...- -.-_- ._-. .-.._
0.1~) MO, 0.j C, 0.3 Si, 0.6 bin, 0.02 I’, 0.02 1.3 Xi, 0.0.) V -I- \V, 0.06 Cu. 1.~10 Alo, 0.4 C, 1.1 Si, 0.5 Mn, 0.02 I’, 0.008 0.2 Xi. 1.1 \‘, 0.07 Cu, 0.02 Co. 1.22 110, 0.8 C, o..~ Si, 0.2 Ma, 0.02 I>, 0.005 0.18 Xi, 1.4 V, 0.06 Cu. 16.8 \\‘, 2.3 co. 8.85 MO, 0.8 C. 0.2 Si, 0.2 3ln,o.o2 I’, 0.007 0.2 Ni, ‘1.\‘, 1.7 \\?, o.og Cu, X.5 Co. Carbon !dCd.
___.._-
____._ - ..,_.
_, .
-_.
-..
-
-
-.
_..
.._._.. “...
l3C51.a no. 0.1gt XIwn (%) 0.0008.( ‘;{, Absolute standcrrtl tlcviation “._I‘t Rclutivc stanthrtl dcviution (“/o) 8 Ko. of dctcrminations ___.__ _____ __ _.,,,._ ,_.____ __ ,. _..__. __._..._ ..__ . .._......__.- -.-.
Satnplc
n Sarnplc
composition:
SW Tnblc
Sl.
-
0.22
. .._____. ._-_.-.
-...
_. ..-
_ ‘JJi2.4
hr&~l&.d .- ..-. ..-.. -_----.----.-_--.-_-...
. ...__.
.
.,._ _-.-..-...
13CGH I .yjH o.ooy)‘y”
. ._..
J I<813 2.674 O.OlO”/” 0.37 cl
0.28
18
-
S, 1.5 Cr, S, 5..1 Cr, S, 4.5 Cr, S, 3.7‘Cr,
.- ..-.... . -_-_
-
-.-
Pure MO solution 50 P6 0.X2 116 0.2.)
54
..._._. ._ .._ . .. _-.-.-...._.-...._._ --.. .-..-.I..-.-.--------_
J I<813 is a r8CrrorVi-s&cl.
all the known variable interferences were discussed on p. 23-27 and 29, only (a) and (0) arc discussed here. Molybdenum does not generally occur as an impurity in rcagcnts; no special difficulty was experienced from this source, except that iron from some? sources was found to contain a few thousandths of a pcrccnt of molybdenum and iron of the highest purity must tlicrefore be usccl. The solution to be measured must not be colored by other substances absorbing at the wavelength used for Mo-thiocyanatc; colorless amy acetate must be used, although it is used as a reference. As pointed out on p, 29, iron contamination after the extraction must bc avoided. When due consideration was given to thcsc factors, the blank values were always less than 0.002 absorbance units. With samples of high-purity molybdenum metal of different origin*, absorbance values conforming to each other and lying on a straight line between the absorbance values of 0.000 and 1.00 all within the precision claimed bcforc were obtained; thus the calibration factor between the absorbance and the amount of molybdenum * Johnson
Matthcy
Spccpurc Molybdenum
and Light Co,
MO 3N. Aural. Cirirn. Ada,
33 (x965) 21-35
2-g
o.gr
0.229
I.46
1.0’
O.SI
2.40
2.66
0.12 C, 0.3 Si, 0.4 Nn, 2.4 Cr, 0.24 Xi, 0.11 Cu
0.4 C, 0.3 Si, 1.9 Mn, 0.06 Cr. 0.03 Xi, o.oG Cu
\',O.jj CU
0.4 Si, I.5 JIn, 0.j Cr. I.2 Xi, Ohj
0.3 Si, 0.3 JIn, 0.4 Cr. 2.1 Xi, 0.23 Y, 0.20CU
O.gSi,O.~.\ln,
0.04 C, oh Si, 1.2 Nn, 17.5 Cr. 11.2 Si. 0.03 V, 0.03 Ti, 0.1, Cu
0.05 C, 0.4 Si, 1.8 MII, I&O Cr, 9.5 Xi, 0.36 Cu, o.o.+ \; 0.1s Co
KBS3Ga
XBSIoob
BCSzjI/I
J KSX
JIiSB
SBSrore
!.3Cr,O.jjSi,O.jjY,O.IjCU
_-
O..+-l
0.q
0.0 j6
0.t9C.O.2 Si. 0-jJIll,O.Oj Cr. 0.32Si.O.IjCU
NBSrgf
BCSzjS/I
1.11
0.001
0.08C, 0.02 Si, 0.51 Mn, 0.02 CU
KBSSi
o-43
2.74
I.jj
0.243
0.930
o.otio
O.OOj
0.2j6
0.24
Xi,O.OjCU
0.3j C, 0.1 Si, 1.1 j 0, 3.3
J 1<71\
0.045
0.03s
0.2 C, 0.3 Si, 0.5 Yn, 0.03 Cr, 0.07 Xi, 0.16 Cu
Cottiposifion of the sutttple(X)
Jli2B
PlO_
Sl4ttlple
DETER3llSATIOSS OF 110 IS STASDARD SAMPLES
jS
_I_-..----.-
O.)ZG
2.6s
o.sj
I.Oj
I.jI
0.2jj
0.920
0.0
O.OOj
0.2j
0.042
j
043o
2.67
0.83 j
1.11
I.jti
0.2 39
.
0.91
0.0jS
o.ooq
0.2jj
0.040
0.040
-
qr6 2.417
?._I’1 ?..#I0
-._.-
043u O.&w
0.431 o..pS
2.66s 2.666
o-s39 D-S39
o.s32 0.s30
2.668 a.672
1.10s I.112
I.jGj I.562
I.556 I.562 1.111 I.104
0.239 0.240
0.237, 0.23s
0.91s 0.919
0.91; 0.913
O.Oj9 O.OjS
O.OjS
0.0027 0.00X3
O.Zjj 0.2j;
0.0399 0.0399
O.OjS
0.0026 0.0026
O.ljJ
0.2jj
0.040
P
?
s g
or
?
33
Aaul,
Clritn,
Actcc, 33 (lgC5)
21-35
S.
34
LOUSAhlAA
Of less than 0.20/o. ‘I’llis statement is based on 40 measurements with cliffcrcnt amounts of molybclcnum. In the method clescribcd and with the particular instrument used, the equation was ,ug Mo (/25 ml amyl acetate) = 1.285 x absorbance (I cm, 470 m/l, 25”). In orclcr to obtain an i&a of the practic2.1 utility of the mcthocl clcvclol~acl, scvcral standard samples were andyzcd (Tddc XI II). The detcrrnin~tions describccl show that even in the ivlo-tlriocyanatc system, iL precision clc~sc to tile limit set by the precision of all volumetric work, and also absorptiometric measurements. Can bc obtained. This is considered to clepcnd mostly on the climinution of certain sources of error, whicll inqGr millly mctl~ocls involving bilsidacicl and, to ELsmaller ly the silmc chcrnical system. The exclusion of hydrochloric is c3scntinl. One: of tllc special extent, of l)crcldoric :uzitl from tlic aqueous plizz, attvanta~cs is that tungsten is not rcducccl in tlie absence of liyclrocliloric acid, and does not intcrfcrc. Tlic inclusion of l~yclrrdiloric ncicl in the wasli solution might bc then cr~risiclcrcd controvcrsi:d. In fact, liyclrocliloric acitl cannot promote any tungstcn intcrfcrcncc, and chloriclc ions must be prcscnt as a carrier to cnsurc the presence any atmospheric oxidation and of tin(II) in tlic organic phnsc, which climinatcs The most critical point of the mcthocl is consiclcrcrd also prevents iron contamination. to be the interaction of chloriclc ion and tin(I1) in the molybdcnurn reduction. The extraction of molybdenum into the orpanic phase was dways c~l~scrvecl to bc rapid :rncl complete, A spectrographic cheek of the nqucous pliasc after tlic extraction rcvcalecl no molybrlcnum (113s than c~.oo2~/;), with I’%, in sample). From the point of view of intcrfcrcnccs, the mcthotl is considered to bc very satisfactory. Tlic obscrvccl intcrfcrcnccs (Nb, V) arc of no sijinificancc in pXctiCCL1 steel annlysis. Consiclcring that the number of colorecl tldocyanatcs is large, tlic selcctivity of the method is good. Mowcvcr, platinum mctrzls :mcl rhenium were not invcstigatecl. T11e ovcrnll stGlity and accurncy of the mctllod appe;Lr to be satisfactory as ITgiLtdS tlic critical nnturc of the reaction mcclianism involvccl. It must be stressed thd the rengcnts must be fresh and always aclclccl in exactly the same amounts, if the best long-term precision is to bc ohtninccl. For contents hi&er than, say, 2% Mo in steels, a method of better accuracy would be desirable if the values wcrc to be used for nndyzin~ samples of standards. WilS
collSiCierC!d
tCJ have
an
WrOr
The author thanks the Directors of Alcticbolnjict 13ofors for permission to this work. The nuthor ;lIRo wishes to express his specid thanks to Mr. TARS EKMAN, who has cnrriccl out most of the cxperinlcntrd work with outstimding pcrscvcrancc Rncl skill.
publish
SUnmARY
The absorptiomctric thiocyanatc method for molybclenum has been thoroughly stucliccl with rcg~rcl to the role of the following rcagcnts: I-ICI, Md304, HClOs, KSCN, SnClz nncl Fe. A mcthocl is clcscribcd, which nllows the clctcrminntion of O.OI--foOA, Mo in steel with a rclativc standard clcviation of less than 0.5%. The only interfcrcnccs (sligllt) arc Nb and the combination V and W. The mcthd gives better than gQ30/, recoveries. Results for the dctcrmitiation of molybdenum in standard samples arc presented.
ABSORPl’IO~lETRIC
DETERMINATION
OF
MO IN
STEELS
35
RBsunlB
L’autcur a effect& une etude sur le dosage absorptiometrique du molybdene, HC104, KSCN, SnCl2 et Fe a 6th au thiocyanate. L’influence de : HCl, H&04, examinee. Le procCd8 deerit permet le dosage du molybdene dans l’acier (0.01 h 10% MO), avec unc deviation standard relative inferieure Q 0.5%. Seuls Nb, V + W rrcncnt. Des resultats sont donnk ZUSAMMENFASSUNG
Die absorptiometrisclre Thiocyanatmcthodc zur Destimmung des Molybdgns wurdc nusflihrlich untersucht, untcr Bcriicksichtigung folgcndcr Kcagenzicn : HCl, H&04, HC104, KSCN, SnCla und Fe. Es wird einc Mcthodc beschrieben, die die 13estimmung von 0.01 bis x00/~MO in Stahl mit ciner relativen Standardabweichung von wenigcr als 0.5% erlaubt. In gcringem Masse stijrt nur Nb und die Kombinntion von V und W. Die Mcthodc crgibt Ausbcuten von mehr als og.S”/o. 1UZPERENCES I,. C. HURU AND I-i. 0. ALLEN, fnd. 1hg. C/rmr., Atral. Ed., 7 (1953) 396 IX D. PISRRIN, h’ew %enland f. .%i. T&r., z7A (r~).#) 396 A. ‘I?. DICK AND J_ !3. ~XNGLllY. f?zlSitdiC4U J. I;-‘xpll. HiO!. kflcd. .%i., 25 (19.17) X93. C. IL CROUTIIAMIZI. AND C. 1:. JOIINSO~J. AmI. Clrcm., ZG (1954) 1284. I,. J_ \VItANGIZLI., 13. C. hlWA&l, 1). 1:. ~
F.
R.
Clrmr..
HIDBITS, W. NEI~I~, %. Aaaf.
I)AVIS,
182
hl.
I<. NISNKE
(x961)
AND
S.
IiAI.LMAN,
‘I’crhrlu,
.I (1960)
IO.+.
IO.
J. 0. HIBBITS AND 1~. ‘I’. \VII~LIAMS, .4t~nl. Clrittl. Acfu, 26 (xgGz) 3G3. 15. B. SANDI~LL, Coloriwclric Dclcrruirtcctio,r o/ Trnccs of hlctafs, 3rd Eel., Intcrscicncc, York, 195g. B.T.S.R.A., J. Irotr SIcct Iusl. (Lorrdotr), 178 (195.)) 35G. J. 130~ca~, Arc/~. I~ise)~Irrtctfenw., 26 (1055) 333. 12. W. MlrY~vocm AND A. A. IC. WOOD, ~9elallrlr~icul .,lrrolysis, zntl Etl., I.ontIon, x957. T. R. CUNNINGIIAM AND 1-I. 1,. HAMNKSX, 1.d. Etrg. Clrorr., AtId. Ed., 3 (1931) IO& A ml.
Claim.
New
.*Ictu. 33 (xgG5) 21-35
THE
ABSOIWTIOMETRIC
MOLYBDENUM(V)
N. LOUNAhIAh /fklicimluget Uofors, (I
21
CHIblICA ACTA
Scptcmbcr
Dl3TEIIMINATION
THIOCYANATE
Uofors
OF MOLYBDENUM
AS
IN STEEL’
(Swcdm)
4th. rgG4)
Few methods for the determination of an clement have been subjected to so many studies as the photometric thiocyanate method for molybdenum. Scvcral of these stucliesl-“~shavc been quite extcnsivc and systematic; an excellent summary can be found in the text book of S~sua~r_ 0,'Tilemany studies indicate that the conditions of the method are inherently critical, and also that other methods of determination arc not very satisfactory. In a recent study of HIBBITS AXJD WILLIAMSH, the nature of the method was itnlicatcd by the statcmen t that “the dcvclopccl m&hod is accurate to if applicable to contents of, say, I-Z% in steel, is within &- 4%“. This accuracy, definitely unsatisfactory. a modified proccdurc has been in USCfor In our steel analytical laboratory, several years, which is very similar to that described by B.I.S.R.A,lO. Tlrc metllocl in this form, howcvcr, is scnsitivc to interferences from copper, as well as from colored ions. It gives reasonably good short-term precision (relative standard deviation I-zO/~ within one series of samples), but the long-term precision is not ncnrly so good, and a change of analysts results in much too large deviations: ~-5% at a level of 0.5-I%. The color of molybdenum thiocyanatc in the aqueous phase is, however, very stable. A method with better stability and accuracy was highly dcsirablc in order to be able to check high-speed mcthocls (optical and X-ray spectrometry). A comparison of the published thiocyanatc m&hods for molybdenum, together with some prcliminary experiments, was tlrcrefore made to determine whether this method would be worth investigating in detail, in order to dcvclop a method which would meet the following requirements : 0.01 to 10% MO in steel range : precision : content o.x0/o 1% 10°/ rel, st, dcv. ($8= 10) 3 I 0.5 interferences: no interferences > z 6 for Mo = o.~o~/~ from the following elements up to the content indicated (only probable interfercncc elements are listed) v CV Ti Nb Co Cu Cr Ni Mn ‘Fe ropcrcent 20 5 5 20 I 20 20 zooomg 5 of the ~ddisIm2 dh0as and resdts Apart from the fact that a thiocyanatc
Cont$uvison
o/some
preliminary
of molybdenum(V)
cxfierimcnts
is involved
in the
N. LOUNAMAA
22
reaction, different opinions have been expressed concerning almost all other relevant details. The situation is summarized in Table I. A study of the method should obviously include the effect of all these parameters, and also possible interactions. However, some practical limitations, together with some preliminary experiments. made the picture less confusing as indicated below.
color
TIIE XIWISC’T OIr
I>IPPElC1SNT PhllhMISTlt,RS ON ‘flYIS ~~o-TltIOCYANATl~ COLOR I’UULISI~IIZD METIIODS -. . . .. . - ---. -.- . ..._ . . . _-__. ..____-..__--.---._-. .- ._.-. - . ..- .___.. . ..-. .. . . . .... .I~c_fcrcrr CFS J’Ul’lWIPf~Y _--______._____ ... .. .. -.-- -..-. ____.--._...-..-._. - _....__ .Mlg/rt effect .stvo,,g cffc1:t No c_fpcl __ _...__.__.
..___.-
. .._ ____,__
__
.._. _.__
I-ICI
8
EIC104, I-IrSO.1 NH&CN
K) , 11
--,
SIlClP
Lit Cl1 Ti
10
.-... --
_..
.
TO
_ . .._.___.
I, 2 8
3 1, 11 1, 2. 11, 3 4, 2.3 (2), 11 1, ‘),8. 10 2 -__-_.--
--___-____---
--__
_._ _.....,.._.- __ ----
ACCORDING
4, 8
8 3, 4 I-_-._
__......_ _.._..._.._
I’he cJfect of iron and cop@w. In the presence of iron and copper, molybdenum(V1) is not easily recluced to the trivalent state by tin(H) chloride. In their absence, the color of molybdenum(V) thiocyanate disappeared rapidly, when an excess of tin(I1) was added, but could be redeveloped if some iron or copper was added. It is thus sufficient to know the concentration ranges of iron (copper) and tin(I1) chloride within which the reduction to only molybdenum(V) is valid. Some preliminary experiments indicated that these limits were not too narrow. Tlte effects of thiocyanatc altd hydroclrlovic acid. A very large excess of thiocyanate tended to bleach the color, but the amount of thiocyanate was not very critical. Preliminary experiments gave evidence of a very strong effect of hydrochloric acid. Organic extracts containing IOO ~8 MO and with an absorbance of 0.300 were discolored when shaken with an equal volume of IO N hydrochloric acid. The recommended USC of nitric acid” and perchloric acid12 as stabilizers for the molybdenum(V) thiocyanate color is advantageous because thcsc acids do not promote the reduction of Ma(V) to MO (III). Use of ovgaGc extmctant. Through the use of organic cxtractant, the interfcrcnccs of copper ancl colored ions such as Cr(II1) and Ni(II), could be eliminated ancl probably the concentration of interfering anions controlled more effectively than
in the aqueous Based
Preliminary
phase. on
these
considerations,
an initial
method
was
outlined
as described
nlelhod
Into 8 23o-ml separatory funnel, place IOO pg MO and add 2 ml of concentrated phosphoric acid, 25 ml of I : I sulfuric acid, 20 mg of iron and 0.6 g of potassium thioa4nnl. Ctriw. .4cttr, 33 (1965) 2x-35
A’BSORPTIOMETRIC DETER~lINATION OF Mo IN STEELS
23
cyanate. After shaking, add IO ml of water containing I g of SnCla * 2HrO and I ml of hydrochloric acid and shake again. Adjust the volume to IOO ml, add 50.0 ml of amyl acetate and shake for 30 sec. Discard the aqueous phase and wash the organic phase with 50 ml of wash solution containing 2 g of potassium thiocyanate, 0.5 g of tin(I1) chloride dihydrate and xx ml of concentrated hycl_rochloric acid. Discard the aqueous phase and filter the extract through a dry filter paper into the cell. Measure the absorbance at 470 nyr.
Effect of variables Effect of
ivon. According to PERHXN~ “for 4 rug MO, at least 0.5-x mg Fe is and up to 10-30 mg causes no further change”. CUNNINGHAM AND necessary, HAMNER~~ had up to 200 mg Fe present, whereas HIBBXTS AND WILLIAMS~ found no interference from 500 mg and IO mg was always added. In the procedure of CROUT~IAMEL AND JOHNSON" more than 2 mg Fe interfered. When the preliminary method wls usccl, it was found that the stability and reproducibility (absorbance 0.378-0.380) were good in the presence of 2-200 mg of iron. As much as 500 mg did not interfere if the initi,al addition of tin(II) chloride was 3 g and the wash solution c6ntaincd I g of tin(I1) chloride. The extra quantities of tin(H) did not affect the absorbance readings even when only 20 mg of iron was present. Effect of /tydvoc/doric acid. According to PERRIN~, the amount of hydrochloric acid is critical and “must be controlled to at least -& I ml of 4 ml adclcd if the error is not to exceed 3%“- HURD~ also stated that the amount of hydrochloric acid is critical. l3.I.S.R.A.10 and HAYWOOD AND Woou 12 did not add hydrochloric acid and HII~BITS AND WILLIAMS*, who used about x.5 N solution, stated, that its amount had “no significant effect on the results”. Table 11 contains the results obtained with various amounts of hydrochloric acid according to the preliminary method, but with omission of sulfuric acid. Interesting conclusions could bc drawn from these results as regards the reduction of iron and molybdenum, but for use as a method for the determination of molybdenum, the system was far too critical. Hydrochloric acid was not used in any further studies.
_____ HCl
.__.__.. (d=
rrcldcd(9~ I)
G 8
x.29)
___
..__
-_.--__
._ __...._._.
_.. ...-__
Nor*~lnZify of HCL dS cr/lcr dilufiort _-__..-_-_--..___._I_.---Addrd
Undil. 0.7 CJndil. X.0 Untfil. r-5 Untlil Dj1.r -t I ::;
.- ,._.-
_... .. . -__
R6sor6nncc A f&r 0 min
..-...
__.._
.___...----.-
.4/h? r I 11
0.235
(0.379) 0.232 0.3%
.__
(0.373) o 0.232 0.376
0.379 0.182 0.182 0_17.5 0.378 0.376 0.379 O.@I 12.5 0.384 y;fl -I- 4 I.5 0.379 0.370 0.375 3.0 0.373 25 IJntlil: 0.322 0.325 0.323 37.5 2:: Undil. Almost colorless 50 ____-__ -._____-_-_. --_-.--8 Thcsc nbsorbanccs inclutlc the color of unrcduccd iron thiocyanatc. 12.5
X2.5 12.5
. .. ____--_
After 20 It
-_.. . ____._I_.
(0.379)
-_
f2c,,tar/rs
470 rrrp -_.____
And.
_~.._ ____ .__-._._.. .__ Iron not rcduccd Extraction after x5 min Extraction immcdiatcly Extraction after x min Extrilction after 1 min Extraction immctliatcly Extraction immctliatcly I~xtrnction inimctlintcly Extraction inimccliatcly
.__..___-..
Claim, Acfa,
33 (r965)
21-35
N. LOUNAMAA
24
of ficvchloric
acid is a WOODED state, that “pcrchloric stabilizing medium for the ferric thiocyanate and so also for molybdenum thiocyanate”. However, perchloric acid is not used in any method to which rcfercnce is made, other than the B.I.S.R.A. method’“. Table III gives the results obtainecl with varying amounts of pcrchloric acid according to the preliminary method. Compared with corresponding determinations in sulfuric acid media, the results with the higher concentrations of perchloric acid tended to 1~ low. Moreover, tllc rcl~roclucil~ility was not good enough. Separate expcrimerk showccl that with larger amounts of tin(U) chloride, correct results could bc obtained even with the higher l:oncentrrttions of perchloric acid; but, obviously, perchloric acid can not gcncrally be recommenclcd, because of its oxidizing power. Effect
_.__._-._..___.___ .
mid.
. Nwrmlify
JfCl0.I 11dtlcd
~il\Ywoor,
._
__
uf
Norrmrlify cr/lcv diltttimr
tlevclopl~lcrrL
(?lll)
G (J
’3 ‘3’ 20
26” 39 3’J’ (is
-
._
.-.
I .O
3.0 3.9 5.8
I.5 1.5 3.0
O.#O
0.:18X
0.385 o..jsH
O.#Z
!i.H
ij.0
7. l 7.1
4.5
O.;j(iC)
*I*5
0.378
0.0
0.3
7.5
I\llncJSt
..---.- I_____.
cl;c,;-lx)
..
-.
Ilesfrlti~r~ norndity Of f-Ia.SU4~
(Id)
H 12 25 38 44 50
._...
_._._..._
..
._,,.
,_ __.,
_. . ..^._.
.
_.... ___. ._____
0.307 0.373 0.378 0.378
0.358
0.355 0.377 0.375
0,353 0.370 0.370 ‘J-345
cJ.338
15
_ ._.._ After a0 t1
. _..._._ .-.. _-
~J.SJ.5
O.S!YJ
._.__._.
“A377 0.378
_
110 C&Jr
,._......
_
.._...
.._
_.__..___.._^.
...
I)ctcrmitlkitiorl carrictl aut krtcr to test rcprotlucibility.
I-l&Y~.,
10
.- ._-...
3.2
;:7; _ .,... _.. .-.
A bsori~cimw 470 rJrp . .__.._._. -. ____-. ._ .il/lt!r Ajtcr 0 mitt a-g Ir
0.377 0.378
.5a _.._.._.
,.
to V)olllm! Lf Ilra COIOV _._._... ._. .____. ___..... ..._. . .._._... . 2.2 0.7
____x___-.-
a
AND
t*.+ .%f-)
3.5 .I.0 (3.0
b::: -.1------.._._
0 ‘The solution
___. .._ .._ .__, - ___.__..._._ . _._. . __ ._.__..^__ /I.-...-.fmxba,lcl! UC 470 8qJ --._-______ _. ._ __... -_ _ . .._- ..-.-. .. .._. - ..__..._ ___.... -. ..__ .._._._.. _-__.--_-._._I. ‘I’irrrc Octwcoi deVdtJ/WlCJat mid cslrrtctiou __ -._....-. _. .._.- .__._.._.__... __ ., . ..-.-__..__ . .._ _. . _-...._... _- ...... ..-._. - ~‘---r----0 JJlaJb _- -__-.._- .. .., _ .._ ro #)ll#l m1ti 30 #/IL)& -.._- - . . - Go ____...__.-_- __... ._. _.__-_. ._.__..__ -_ .___.__._ ;I’imc trftrv .w+ctrtition of or~u~~ic: /d~asc ._.._ __.._ -. _.. ... . .._..-..... . . .--. ._. ._- . . .. . .. __..-. ..0 ruiu ao I,‘ 0 rniu I Ir 0 rrii,, x Ii r lb 20 11 0 ruirr 1 II a0 /I _ . . -.. __.... __ _._...__..._..._. _.._._- . _ ._..._,...__.._.. . ._ __. _ _ _ ._.. .._. (0.370) (0.379) (0,378) 0.338 0.337 0,335 0.302 0.300 O.Z# (0.380) (o.3Ho) 0.371 0.371 0.368 0.370 0.380 0.381 0.380 0.379 0.37tJ 0.379 0.379 0.37CJ 0.378 0.38C 0.38x 0.382 0.383 0.382 0.379 0.378 0.379 0.370 0.379 0.379 0.379 0.37’
_._
o.:j80
0.380
0.378 0.352
0.381
0. JO0 -._._ .___
0.378 0.3Go
o.gHo 0.380 0.379 0.$30 0.35~ 0.357 --._-.
0.380 0,358
0.378 0.379
0.378 0,379
0.381
_..-...-V-w--
W~?Hitl\Vnys tlilutccl to constant volunw bcforc otlcling tlw rcagcnts: Values in bracltcts intliciltc tlrnt ttlc iron(II1) thiocyanntc color is incluclcd
0.378 0.378
0*37< 0*37(
.-- .-_._ -___
Fe, ICSCN atw
ARSORPTIOMETRIC
DETERMINATION
OF
MO TN STEELS
25
Effect of srdfzrric acid. Little mention is made of sulfuric acid in published studies. HIBBITS AND WILLIAM@ stated that its concentration is critical. The influence of sulfuric acid was investigated in somewhat greater detail than the other acids; the variation of the time between the development of the color and the extraction was also studied. The results arc given in Table IV. Obviously the reduction was too slow at acidities below 3 N. Above 7 N, low results were obtained, possibly because of a sulfate complex of molybdenum. However, the range between 3.5 and 7 N sulfuric acid was considered big enough for the determination and the stability and reproducibility were good. Effect of t/tiocyamzte. Almost all authors point out thnt the amouut is not critical but that excessive amounts bleach the color. In the aqueous phase 0.5-3% thiocyanate (0.075-0.45 N) is generally used. Obviously the amount of thiocyanate in tlrc organic phase depends not only on its concentration in the sample solution but also on the thiocyanate concentration of the wash solution, and thus both concentrations were varied. The results (Table V) indicated that concentrations below 0.05 N in the aqucous phase tended to give low results which, however, could be somewhat improved hy high concentrations of thiocyanatc in the wash solution. Concentrations in cxwss of 0.20 N in the aqueous phase definitely gave low results, which could only be very slightly improved by having little or no thiocyanate in the wash solution. The thiocyanatc concentration in tile wash solution was less critical, though more than 0.5 N
TA131,IS v .--.---
..___. _ __ _ _.. ---__--._.
-.._._.....
.
_ ..__,_.._.-
--------_
..- --.-.---_...--
,.
_._- ____
_.._--_ . ..
pilust?(iv)
~Vortwlily o/ wr1slr soltitiorr (A?)
A bsorbnmz after Norwinlily A’ortmtlily .,Ibsorba UCPaj’lcr _---_.-____-___.__ _-. _.__._....._. __.__-.._ of uqrreorrs of wnsh 0 mitr I I1 20 Ir a0 Id jhise (8) sollrliou (IV) 0 rtii*r I Ib
0.0
1 .OO
0.310
Novnudily of Nqlrcolts
_______.___.__._.__.__...._ I
.
0.0 1 0.01 0.01
0.075
0.05 0.05 0.05 0.05
I.00 0.50 0.25 0.075
0.05
.-I)
0.50 0.25
0.065 o.oGg 0.065 0.065 0.08
0.50 0.25
0.075 I .oo 0.50
0.08
0.08 0.08 0.08 0.08 J
.
0.25 0.10
0.05 =
No thiocyanatc
..
._.-.----_-..
0.316 0.332 0.285
_....----_-_---_I--
o.3r.t
0.320 0.332
o**3 0.13 0.13 O,T3 0.21 0.21 O.? 1 0.21
0.285
0.37.5 0.382 0.jH(i 0.385 0.355
0.369 0.375
0.371 0.381
0.382
0,382
0.383 0.384 “a383 0.34 *
0.381 o.3w 0.38‘1 0.375
0.375 0.383 0.390 o-387 0.38G 0.385 aklcd
0.370 0.367
-....-
0.313 0.320 0.330
0.379 0.3G7 0.381 0.384 0,384 0.379
.--
-.....-
.._---.----
0.378 0.384 0.385 0.384
0.380 0.382 0.387 0.388 0.391 0.387 0.392 0.387
I.00
0.372 0.381 o-384 0.384 0.385
0.372 0,375 o-37!, 0.383 o-385
0.378 0.372 o..z73
o.!YJ
0.353 0.349 0.315 o-372
0.359 o-356 0.3zfi 0.375
o-357 0.355 0.335 0.375
1.00 0.50 0.25 0.075
0.319 0.236
0.31s 0.255 0,245 0,235
0.5’1 0.25
0.075
0.21
-
0.30 0.30 0.30 0.30
0.2.5 0.075 -
0.370 0.374 0.50 0.383 0.380 0.50 0.380 0,384 0.50 0.307 0.382 0.50 0.384 0.383 0.380 0.380 .. ..._ to the wash solution.
-.
0.5” 0.25 0.075 -
rivial. Chirll.
0.220 0.205
Acta, 33 (1965)
0.3N2
0.38.1
21-35
26
N.
LOUNAMAA
results. Thus the permittccl limits of the thiocyanate concentrations in the solution to 1~ extracted and in the wash solution were 0.05-0.x5 N and 0.10-0.35 N respectively. ‘Thcsc figures are, of course, dependent on the amounts of iron, molybclcnum and other ions forming thiocyanatcs, but no effect hvas found for amounts of 0.5-500 mg Fe and 0.5-300 /~g MO. Effect of tin(II) c/zforidc. According to the generally accepted explanation of the reaction mechanisms involve& the color intensity should depend on the amount
gave
low
‘tfilf ILl~lWCT _.__._--___._.
-.-
Norrmdity __________
Ill
OP Till:
CONClfNTRATION
-
-
. .. . . . -..-....
of SIICIZ ( N) .__._-_.-_
Cl~llC~JftS
I t1 wt1slr
OF TfN(11)
--.
.-
Norr~rcclity
. ._ salrr.
CflLORIDlZ
. . . . ---.-----.-.-----
_-...
_______.___-__
-._.___-__-_-__.____
I,r
rtl
c~q”“““.~
W~I
.W~L
., .--.
A l~swbtoux 10
bnirr
---..
470 nrp tr$tcr
--
1 lr
ao k
0.308
0.218
0.393 o.391 o.38G
0.392 0.388
ph5C
fillclsl! 0.10
0.00
0.10
0.
0.10
0.10
0.20 o.,p 0.60 0.80
0.10
0.00
0.10
2.00
0.10
0.10
0.10
2.02
0.10 0.10
IO
o.oa5
‘2.00
0.025
2.02
0.025
2.v5
0.025 0.025
2.10 2.15 2.20
0.025
v.335 0.390 0.385 0.382 0.34G 0.336
O.fO
0.20
0.10
0.10
0.40
0.10
2.05 2. IO
0.x0
0.60
0.10
2.t5
0.x0
0.80
0.10
2.20
0.00
0.0375
2.00
0.10
0.0375 o.o175 0.0375 0*0375
2.02
0.1s
0.15 0.15 v.rg 0.15
0.20 OS10 0.60
0.20
0.00
0.20
0.10
0.20
0.20 0.40 o.Go o.Ho
0.20
v.20 0.20
0.25 0.25 0.25 0.25 0.25
0.00 0.10
0.20 o.,\o o.Go
0.30
Ada,
33
0.387 0.388
0,395 0.395 a.395 0.385 0.382
0.400
2.15 2.VO
0.388
2.02
v-392 o-39G o-377 0.355
0.394 0.395 0.390 0.384 0.383
0.389 0.396 0.400
2.00
0.390 0.390 0.389 o-377 0.347 0.338
0.394 0.394 o-391 0.387 0.3G5 0.365
0.384 0.384 0.383 0.38r
IO
0.10
2x-35
o.39G 0.397 0.393 o-397 0.389 0.375
0.394 0.392 0.394 0.385 o.3Go
0.10 0. to 0.10 0. IO
(x965)
0.391 0.389 0.385 0.382 0.381
2.00
2.02 2.05 2.10
2.02 2.05 2.
IO
2.05 2.10
2.15
2.02
2.05 2.10
2.15 2.20
Chim.
o.rto t o.rto1 0.399 0.394 0.392
o,oG75 o,oG75 0,0075 0.0675 o,oG75
0.
0.20
o.39G 0.39G 0.39G 0.388 0.382
0.384 0.3cJ8
0.193 o-393 0.389
0*34G
0.00
0.40 0.00 0.80
0.3G3
0.3’34 0.383 0.380
0.393 0.388
2.15
0.40
0.10
0.346
2.20
0.40 o.Go
0.40 0.40 0.40 0.40 O-40
0.370 0.395 0.390 0.383 0.348 0.343
0.39G 0.397 0.395 0.389 0.300
0.075 0,075 0.075 0.075 a.075
0.20
2.15
0.383 0.377 0.377
2.00
0.10
0.00
2.05 2.10
0.378 o-358
0.05 0.05 0.05 0.05 0.05 a05
v-30 0.30 0.30 0.30
And.
-.----.----._-..-.-..-.-..-.--
oj I-iC1 (N)
0.399 0.40 I 0.393 0.384
0.383 0,388 0.384 0.380
0.387 0.385
0.378 0.379
ABSORPTIOMIYWIC
DETERMINATION
OF
MO IN
STEELS
27
of the reductant ; if insufficient tin(H) is added Mo(V1) is not completely reduced to MO(V), and if too much is added, the reduction continues to form Mo(III), in which case the MO(V)-thiocyanate color fades. Most authorsr-3 point out that the excess of tin(II) is not very critical, but that the amount of acid added with tin(II) chloride is important. The effects of varying both the tin(H) and the hydrochloric acid concentrations are shown in Table VI (the procedure on p. 22-23 was used). Although the results obtained confirmed earlier results 1-a they still indicated that if the best precision is to be attained, the concentration of tin(H) chloride is quite critical.
Interactio?ts between molybdenum, szdftcrric acid, tin(I1) chloride, tltiocyanate and iron. It was considered advisable to study possible interactions between reagents only within certain limits of the reagents used. The levels were chosen arbitrarily to correspond to twice as great variations as could be expected in practical determinations. The results of thcsc tests, which were carried out according to the procedure given on p. 22-23 in other respects (but with only 25 ml of amyl acetate) are given in Table VII. Although significant interactions can bc traced from these results, the probability of obtaining errors larger than I%, due to interactions in practical determinations, is very slight, considering that such great variations of rcagcnt concentrations would be excluded and that the standing time would be much more constant.
INTISHACTIONS . -... --hxd~
____ .._
13E7’Wli&N . . -_-.
RISAGENTS
. ._-_..
-.__----_--
DIPPISRHNT
lhxovery, --.-
__..--___
KC NS
.Sd&
LRVELS ----
--e-B-_
oJ
-_.._ ._._ -_- _.-___ IWO Ji&‘O.~ Fe
AT
rafter
4 11
0.157 0.158 0.780 0.780
0.158 0.157 0.780 0.781
99.3 98.8 90.2 99.4 X01.0 97.0 99.5 x01.3
rot.3 98.6 99-j 98.7 x00.0 101.0 95.5 99.0 too.6
98.2 99.8 98.8 99.0 99.4 102.3 95.5 x00.0
100.2
100.2
o-779 0.78x IVO.0
98.8
99.4
:_; 1-i l
The
100.2
lOI.fj
97.5 100.5
X01.5
100.0
I, I-i 1-i
1oo.G
100.g
100.8 99.4 99.5
100.6
99.3
\
Val1w.r calculntcrl as pcrccntage of the * irbovc absorbance values
10x.8 98.2
99.4 100.0
VOlllCS lltJC!ClilY rcfcrcncc for cnlculntion of rccovcq
I
100.0
100.2
I,
._ _--
--
Itcurarhs
--_
0.158
nl
-_---a-
I Jr
0 niitr O.I$l
M I.
- ---
tr6sorb. ~wcustrrcd.. ’
97.0 100.0 102.1 roo.0
99.8
,
-
concentrations of rcagcntu wc?rcDYfollowe :
L = Low lcvcl M = Medium lcvcl IS = High lcvol
MO 20 Pg so Pg =oo l(g
I-iaso4 4N 5N 7N
.
Fc 5 mg 20 mg 200 mg
Asal.
KSCN
0.07 N 0.10 N 0.15 N
Chim. Ada,
SnCh 0.10
0.20 0.30
N N N
33 (xgG5) 21-35
N.
28
l.OUNAhlAA
The following procedure was accepted for the determination of molybdenum the modification required contents of o.or-xoo/o in all steels. For convenience, tungsten-containing steels is incluclcd.
in for
*I’igz(II) chloride. Stock sol&ion IO N. Dissolve zz5 g of SnClz zHt0 in 50 ml of concentrated hydrocllloric acid and dilute to zoo ml with water. Add r-5 g of tin. Preparc R 2 N solution claily by dilution with boiled water. Was/l solr&on. Stock solution 0.5 N Sncl~. Dissolve 56 g of SnClc - zHz0 in 1000 ml of concentrated hydrocliloric acid. Prepare the was11 mixture immediately bcforc use from 10 ml of 0.5 N SnC12, 5 ml of I N ICSCN and 35 ml of water. A~tyl crcetate. Iie;Lgent grade is not necessary, but a quality which is colorless as well DS free from oxidants, is essential. Sc~arntory fmnels. 250 ml, marked at 80 ml and prcfcrably with teflon stopW&S (to avoid grease). ‘I’lfem~ostat device, whiclt allows handling of the solutions involved at a convcnicnt tainpcraturc (zo--25”) controlled to & 0.5”. l
Proctdiirc
Dcpcncling on tllc expectccl corltcnt of MC), weigh out IOOCJ--100 m& (d K 0.x0/,) (WC Table VIII), and dissolve in I0 ml of sulfuric acid (d = x.84), 5 ml of phosplloric acid (cl = r.G8) and 50 ml of water. Oxidize iron wit!1 II. few drops of nitric acid x.42). Dissolve higIl-alloy steels in hydrocllloric and nitric acids and evaporate (d = to rcmovc tlicsc acids with the same iLlll0Unts of sulfuric and pliosphoric acid as mcntionecl :ibovc. Expel silicic acid with a few drops of liydrofluoric acicl.
OI’TIaltIM
S1ZH
Il.10 ‘g
SAhlI’LRS.
012
_ __________
_. .
__
e.r/x!ctcd
ALIQUOTS
.._. - _.._ Strt~~plc
IC’TC.
.-___.._ _ . rocighl
(WY) - _...
.
_-__._._
._..
1000 500
‘200 100
0.p4.0 r.O-g.fJ
IO0
g.CPfC3.O _._.
_ ._ . .._..._-
if W
1’ Only
.-.-...
ACCOI1l~lNG TO TiIlS -_.... _.-_.- . .. . Citric: (IT)
. .. -.. _._.. ,... . .--
.I_._.
0.01-0, IO O.lO-0.50
-
AMOUNT ._ .-_--
tcciu?
n
IJillllCd
21 lir/uot (wrl)
(wl)
5
1,01>
5 5
500
500 .__ ____
.___._
1 :t: tctihl (w)
20, 10
-
20, 20.
10 10
-
20,
10
20
15, 10
1000 ____-__..
15X1’13CT15D
to
-__. .--.. --.--.-.----. __-..-._._.___--__ 10 IO0
IO
._.. . . .._____ .-_-_-...
01; ido
‘Lo 20
- .___
pwwnt.
Dilute
tllc soJution to volume (Table VIII) with water, at a tcmpcrature of In the presence of tungsten, add citric acid bcforc dilution. Transfer a suitable aliquot (‘Table VIII) to ;L 25o-ml separatory funnel, add 25 ml of I : I sulfuric acid ancl adjust the volume to 80 ml. Mis well, add IO ml of I N potassium thiocyanate, shake, add IO ml of 2 N tin(I1) cllloridc and mix again. (This solution is 25”
Am-d.
-4:
0~5”.
Claim.
Actn,
33
(rgG5)
21-35
AHSORP‘TIOBIETRIC
l)ETERMISATION
OF
MO
IN
STEELS
23
5 N 112SO4,0.10 N KSCN and 0.20 N SnCl2.) Add 25.0 ml of amyl acetate at 25O and shake for 30 sec. Remove the aq~~us phase, and wash the organic phase with 50 ml of solution containing IO ml of HCl, IO ml of 0.5 N SnCI2 and 5 ml of I iV KSCN. Filter the organic phase through an iron-free filter paper into a dry volumetric flask, at a temperature of 25”. iMeasure the absorbance of the solution with a Ueckman DU spectrophotometer at 470 mp in a x-cm ccl1 against arnyl acetate as reference.
It is necessary to avoid contamination of iron(II1) greater than that which can be eliminated by the tin(lI) chloride in the organic phase. Avoiding excessive oxidation from strong oxidants is also essential. The freshness of the tin(II) solutions is important. RESULTS
ASD
DISCUSSIO.\J
of various ciemwts olt the color rievclojmcnt The effect of ions present in solutions obtained from steel samples was invcstigatecl by adding varying amounts of the ions to the scparatory funnel, togetlwr with 50 pg of molybdenum after whicI1 n~olylxleuun~ was determined as clcscrilxx~ above
‘I’lte effect
(50
jrg
__ _.___ _.
MO ._
prcscnt;
20
__^_ __ _.____,___..
mg
Fc
m.ltlcrl)
__
._..-
_..__ --
__.. -_
__._ __.._-
J
1V
kcc.
(*,I69 _. .
fw ( w -.. . .__-.-_.__._._-
co
(‘xl) ..- -----
-._--
.._.,.-._
(wd ( ‘%I ____._____-____-______-_.._-
__.-____._.-...__ Idly.
SD
(w)
(W
f wrl .- __ _.. . .--.----
100.3
93.5
0
100.0
100.0
1 C)
100.0 100.5
0
5
2.5
v&s
10
loo.H
20
100.0
5
20
100.0
1 1.5 5
99.8 100.0 9g.y - 90.5
.I”
09.5
2:
___
__
_____..
100.3
IO0 HO
09.0
__________ _.._._.._
,., -.
__. ...__. _____...-._ J?CC.
.
100.0
7.5
x00.0
10
100.3 _.. -..._..- ._. -.
‘5
IO0.j
102.0 IOf. .,
_ .__ _..- _.- - .--
-10 _.
_._--._.__ ----.
._..
7-i
0
Cl6
0
__
..,..__.__
Jtcc.
I’
- _____--_-
0
I 2 3.5 10 5
_.-....__. -.________ .___.__..__.. .....___...._.-.. . .._ .___. ____._....-__-Xi J&VT. itcc.
&)
99-s 100.3
20
f 00.0
20
100.5
40
40
100.3
100
60
X00.0
3
100.5
_-.
100.3 IOO.3 -
-
--
.--
--
2
99.8
___. .._..._.._
-
- .__. ._ ___... _.__
-.-_.
5
15 30 -
100.3
80
100 .__._
IOI.0 _-
. ._..-.__..-.---___- ._....--
_
100.5 100.5 xor.0 103.8 102.0
..__.-.--..-...-_--
iv,8 (W)
.---_---.-we-
I
100.0
_.._._-.-_-__-.I---
owY9 (twl (‘xl) __,._ (%ol ____.._ __._ ____.___^_ _...- -...._.._.-.-......_._-.-_-.. - ._._ ___-._...-_--__ - --.-_ (%J -_..---. 0
J
ht.
(%I 100.5 10’0.5
100.3 -
a-_-...-----.--
(Table IX). In the cast of a color interference, the observed interference is better cxprcssed as the absolute percentage error caused by 1% of the interfering elcrnent in the original sample. As can bc seen from Table X, the interferences from the io:ns tested can be considered negligible in the analysis of steel. AWL
C/rim.
Acta,
33 (IgGg)
21-35
30
N. LOUNAMAA
In the analysis of some steels containing tungsten, surprisingly low results were obtained. This error was evident only when solutions of samples were diluted to large volumes, and thus some kind of cohydrolysis of molybdenum and tungsten was suggested, The low results could be remedied by adding citric acid which had no effect on molybdenum alone. With extremely high concentrations of tungsten + vanadium, a slight positive intcrfercnce was also indicated; the error corresponding to 1% V (with excess W) was only o.oor%, Mo. Precision From previous measurements with the Beckman DU spectrophotomcter (xc)58 model) used, it was known that if a solution with a stable color (CoSO4) was measurccl repcatcclly at the wavelength in question (525 mp) and at the absorbance lcvcl of 0.40.5 units, a relative standard deviation of the order of o.~o-o.~~~/~ could bc expected. The reproducibility of the color development includes variations in the color and volume measurements, and in the chemical reactions involvccl, but not variations in the dissolution of the sample or in the homogeneity of the sample, as only aliyuots of one solution taken with one pipet are compared. ‘I’hcsc tests were carried out as described on p. 28 and the results are given in Table XI (I).
____. - ___._.__..___.-
-_-_.
‘I’i
--.. .-. _. -.-. __.--.-_ _.-.-__ -_
o.ooor~~
-. .- - . ..._.._. - __..______..._.......__._.__..__.._-.--___ -.- ..,.._..._.. b
co
-__-_
1’ Would probabtc.
.._____._.... ._ _....
corrcspoml
. . .. ..__._, ---
to o.oz’~~
ND
0.0002a _ . ..-.-.
C’.lf
_--. - .--. .--_
uwd
..-.. -..
_.__......__ -__.-..-..__
Ni
l317t
_ . _ .-._ .-_I_____ ._._ . -.- .._ - . ..--.__.-
O.000 I _..-_- __.... .
IWOin tllo NL Illutul
_ ___.....,._-.._-.
cv
c.0.0u000 _ __.. .___.._,...__-_
(Spccpurc
< 0.0000 (0.0000 --._ _ _-... ._._ . ___.. .._ . _ .
hliltt,l\cy
Niubiunl)
wllic11 is not
‘fhc short-term reproducibility of the cntirc procedure was cletcrminecl by analyses of tlirec samples, with cliffcrcnt amounts of tlic sample in one series of mcasurcments ; the results arc given in ‘I’ablc SI (Ii). The long-term reproducibility of the cntirc proccdurc is of decisive importance to the practical analyst. This reproducibility includes variations due to cliffercnt volumetric vcsscls and newly prcpnred rcagcnts, in addition to the variations listed above but not a change of analysts. The results ot analyses over a x-month period are shown in Table XI I.
IXpCiltCtl
As on (n) the the curve ical curve Araak Chim
in all proccdurcs of this type, obtaining the correct level of results depends value of the blank, (t) the purity of the molybdenum usccl for establishing (factor), and (c) differences in the conditions for preparation of the analytand for analysis of unknown samples, i.e. interferences. Since the effects of Acla,
33 (1965)
21-35
AUSOIll”IXOMETRIC T.413LIi:
STANDARD
_.--.-..-
____--
I~I~VIATION
,.... _. - - -
OF
.-_ .---._.-.
i*r
determind
MO
OF BfO
Ih’ STEELS
31
SK
I
DETERMI~A’I’IOS
---
‘I-IlIZ
I~BTISRAlINATION
..-..-.-....
Gl’
310
()I
_ - __.___
--_.-.-.-------
=
IO)
-_ ___-_____
- ___. -
_______
Smlplen -. IK_$.
______.
_.__ _____ .,_..__.___.-._ -.._-.._. __.-
aliquots of the sam7c solution (I) S.D. for diffcrcnt weights S.D.
for
0.32 O..(cJO--0.
500
IO/too o.~~Cq-o.jOr)
(ml)
___________. . .._...
. _ .. ._. .._- _-.-
.
o.og
of the smnc ~ilrrqh (11) Snll~ylc ;rnloutlt tibkcttl (6)
Aliquot taken Alx~rbnncc
--
i3C6H
...__....
... -
..
f&H
V. J I
-
--
0.36
0.30
O.IC)l-O.‘Ol
0.202-0.?0c)
0*44
o-43 0.487-0.529
I o/500 0. $37~-0,‘+0.1
IO/500 0.413--0.437
0. tgr-0.19s
10/1000 0.(>4J-o.C,67
25/roe
o.3.%-0.4
13 - --.--- ..-..-.._- .___._
.- .._-...- -.-_- ._-. .-.._
0.1~) MO, 0.j C, 0.3 Si, 0.6 bin, 0.02 I’, 0.02 1.3 Xi, 0.0.) V -I- \V, 0.06 Cu. 1.~10 Alo, 0.4 C, 1.1 Si, 0.5 Mn, 0.02 I’, 0.008 0.2 Xi. 1.1 \‘, 0.07 Cu, 0.02 Co. 1.22 110, 0.8 C, o..~ Si, 0.2 Ma, 0.02 I>, 0.005 0.18 Xi, 1.4 V, 0.06 Cu. 16.8 \\‘, 2.3 co. 8.85 MO, 0.8 C. 0.2 Si, 0.2 3ln,o.o2 I’, 0.007 0.2 Ni, ‘1.\‘, 1.7 \\?, o.og Cu, X.5 Co. Carbon !dCd.
___.._-
____._ - ..,_.
_, .
-_.
-..
-
-
-.
_..
.._._.. “...
l3C51.a no. 0.1gt XIwn (%) 0.0008.( ‘;{, Absolute standcrrtl tlcviation “._I‘t Rclutivc stanthrtl dcviution (“/o) 8 Ko. of dctcrminations ___.__ _____ __ _.,,,._ ,_.____ __ ,. _..__. __._..._ ..__ . .._......__.- -.-.
Satnplc
n Sarnplc
composition:
SW Tnblc
Sl.
-
0.22
. .._____. ._-_.-.
-...
_. ..-
_ ‘JJi2.4
hr&~l&.d .- ..-. ..-.. -_----.----.-_--.-_-...
. ...__.
.
.,._ _-.-..-...
13CGH I .yjH o.ooy)‘y”
. ._..
J I<813 2.674 O.OlO”/” 0.37 cl
0.28
18
-
S, 1.5 Cr, S, 5..1 Cr, S, 4.5 Cr, S, 3.7‘Cr,
.- ..-.... . -_-_
-
-.-
Pure MO solution 50 P6 0.X2 116 0.2.)
54
..._._. ._ .._ . .. _-.-.-...._.-...._._ --.. .-..-.I..-.-.--------_
J I<813 is a r8CrrorVi-s&cl.
all the known variable interferences were discussed on p. 23-27 and 29, only (a) and (0) arc discussed here. Molybdenum does not generally occur as an impurity in rcagcnts; no special difficulty was experienced from this source, except that iron from some? sources was found to contain a few thousandths of a pcrccnt of molybdenum and iron of the highest purity must tlicrefore be usccl. The solution to be measured must not be colored by other substances absorbing at the wavelength used for Mo-thiocyanatc; colorless amy acetate must be used, although it is used as a reference. As pointed out on p, 29, iron contamination after the extraction must bc avoided. When due consideration was given to thcsc factors, the blank values were always less than 0.002 absorbance units. With samples of high-purity molybdenum metal of different origin*, absorbance values conforming to each other and lying on a straight line between the absorbance values of 0.000 and 1.00 all within the precision claimed bcforc were obtained; thus the calibration factor between the absorbance and the amount of molybdenum * Johnson
Matthcy
Spccpurc Molybdenum
and Light Co,
MO 3N. Aural. Cirirn. Ada,
33 (x965) 21-35
2-g
o.gr
0.229
I.46
1.0’
O.SI
2.40
2.66
0.12 C, 0.3 Si, 0.4 Nn, 2.4 Cr, 0.24 Xi, 0.11 Cu
0.4 C, 0.3 Si, 1.9 Mn, 0.06 Cr. 0.03 Xi, o.oG Cu
\',O.jj CU
0.4 Si, I.5 JIn, 0.j Cr. I.2 Xi, Ohj
0.3 Si, 0.3 JIn, 0.4 Cr. 2.1 Xi, 0.23 Y, 0.20CU
O.gSi,O.~.\ln,
0.04 C, oh Si, 1.2 Nn, 17.5 Cr. 11.2 Si. 0.03 V, 0.03 Ti, 0.1, Cu
0.05 C, 0.4 Si, 1.8 MII, I&O Cr, 9.5 Xi, 0.36 Cu, o.o.+ \; 0.1s Co
KBS3Ga
XBSIoob
BCSzjI/I
J KSX
JIiSB
SBSrore
!.3Cr,O.jjSi,O.jjY,O.IjCU
_-
O..+-l
0.q
0.0 j6
0.t9C.O.2 Si. 0-jJIll,O.Oj Cr. 0.32Si.O.IjCU
NBSrgf
BCSzjS/I
1.11
0.001
0.08C, 0.02 Si, 0.51 Mn, 0.02 CU
KBSSi
o-43
2.74
I.jj
0.243
0.930
o.otio
O.OOj
0.2j6
0.24
Xi,O.OjCU
0.3j C, 0.1 Si, 1.1 j 0, 3.3
J 1<71\
0.045
0.03s
0.2 C, 0.3 Si, 0.5 Yn, 0.03 Cr, 0.07 Xi, 0.16 Cu
Cottiposifion of the sutttple(X)
Jli2B
PlO_
Sl4ttlple
DETER3llSATIOSS OF 110 IS STASDARD SAMPLES
jS
_I_-..----.-
O.)ZG
2.6s
o.sj
I.Oj
I.jI
0.2jj
0.920
0.0
O.OOj
0.2j
0.042
j
043o
2.67
0.83 j
1.11
I.jti
0.2 39
.
0.91
0.0jS
o.ooq
0.2jj
0.040
0.040
-
qr6 2.417
?._I’1 ?..#I0
-._.-
043u O.&w
0.431 o..pS
2.66s 2.666
o-s39 D-S39
o.s32 0.s30
2.668 a.672
1.10s I.112
I.jGj I.562
I.556 I.562 1.111 I.104
0.239 0.240
0.237, 0.23s
0.91s 0.919
0.91; 0.913
O.Oj9 O.OjS
O.OjS
0.0027 0.00X3
O.Zjj 0.2j;
0.0399 0.0399
O.OjS
0.0026 0.0026
O.ljJ
0.2jj
0.040
P
?
s g
or
?
33
Aaul,
Clritn,
Actcc, 33 (lgC5)
21-35
S.
34
LOUSAhlAA
Of less than 0.20/o. ‘I’llis statement is based on 40 measurements with cliffcrcnt amounts of molybclcnum. In the method clescribcd and with the particular instrument used, the equation was ,ug Mo (/25 ml amyl acetate) = 1.285 x absorbance (I cm, 470 m/l, 25”). In orclcr to obtain an i&a of the practic2.1 utility of the mcthocl clcvclol~acl, scvcral standard samples were andyzcd (Tddc XI II). The detcrrnin~tions describccl show that even in the ivlo-tlriocyanatc system, iL precision clc~sc to tile limit set by the precision of all volumetric work, and also absorptiometric measurements. Can bc obtained. This is considered to clepcnd mostly on the climinution of certain sources of error, whicll inqGr millly mctl~ocls involving bilsidacicl and, to ELsmaller ly the silmc chcrnical system. The exclusion of hydrochloric is c3scntinl. One: of tllc special extent, of l)crcldoric :uzitl from tlic aqueous plizz, attvanta~cs is that tungsten is not rcducccl in tlie absence of liyclrocliloric acid, and does not intcrfcrc. Tlic inclusion of l~yclrrdiloric ncicl in the wasli solution might bc then cr~risiclcrcd controvcrsi:d. In fact, liyclrocliloric acitl cannot promote any tungstcn intcrfcrcncc, and chloriclc ions must be prcscnt as a carrier to cnsurc the presence any atmospheric oxidation and of tin(II) in tlic organic phnsc, which climinatcs The most critical point of the mcthocl is consiclcrcrd also prevents iron contamination. to be the interaction of chloriclc ion and tin(I1) in the molybdcnurn reduction. The extraction of molybdenum into the orpanic phase was dways c~l~scrvecl to bc rapid :rncl complete, A spectrographic cheek of the nqucous pliasc after tlic extraction rcvcalecl no molybrlcnum (113s than c~.oo2~/;), with I’%, in sample). From the point of view of intcrfcrcnccs, the mcthotl is considered to bc very satisfactory. Tlic obscrvccl intcrfcrcnccs (Nb, V) arc of no sijinificancc in pXctiCCL1 steel annlysis. Consiclcring that the number of colorecl tldocyanatcs is large, tlic selcctivity of the method is good. Mowcvcr, platinum mctrzls :mcl rhenium were not invcstigatecl. T11e ovcrnll stGlity and accurncy of the mctllod appe;Lr to be satisfactory as ITgiLtdS tlic critical nnturc of the reaction mcclianism involvccl. It must be stressed thd the rengcnts must be fresh and always aclclccl in exactly the same amounts, if the best long-term precision is to bc ohtninccl. For contents hi&er than, say, 2% Mo in steels, a method of better accuracy would be desirable if the values wcrc to be used for nndyzin~ samples of standards. WilS
collSiCierC!d
tCJ have
an
WrOr
The author thanks the Directors of Alcticbolnjict 13ofors for permission to this work. The nuthor ;lIRo wishes to express his specid thanks to Mr. TARS EKMAN, who has cnrriccl out most of the cxperinlcntrd work with outstimding pcrscvcrancc Rncl skill.
publish
SUnmARY
The absorptiomctric thiocyanatc method for molybclenum has been thoroughly stucliccl with rcg~rcl to the role of the following rcagcnts: I-ICI, Md304, HClOs, KSCN, SnClz nncl Fe. A mcthocl is clcscribcd, which nllows the clctcrminntion of O.OI--foOA, Mo in steel with a rclativc standard clcviation of less than 0.5%. The only interfcrcnccs (sligllt) arc Nb and the combination V and W. The mcthd gives better than gQ30/, recoveries. Results for the dctcrmitiation of molybdenum in standard samples arc presented.
ABSORPl’IO~lETRIC
DETERMINATION
OF
MO IN
STEELS
35
RBsunlB
L’autcur a effect& une etude sur le dosage absorptiometrique du molybdene, HC104, KSCN, SnCl2 et Fe a 6th au thiocyanate. L’influence de : HCl, H&04, examinee. Le procCd8 deerit permet le dosage du molybdene dans l’acier (0.01 h 10% MO), avec unc deviation standard relative inferieure Q 0.5%. Seuls Nb, V + W rrcncnt. Des resultats sont donnk ZUSAMMENFASSUNG
Die absorptiometrisclre Thiocyanatmcthodc zur Destimmung des Molybdgns wurdc nusflihrlich untersucht, untcr Bcriicksichtigung folgcndcr Kcagenzicn : HCl, H&04, HC104, KSCN, SnCla und Fe. Es wird einc Mcthodc beschrieben, die die 13estimmung von 0.01 bis x00/~MO in Stahl mit ciner relativen Standardabweichung von wenigcr als 0.5% erlaubt. In gcringem Masse stijrt nur Nb und die Kombinntion von V und W. Die Mcthodc crgibt Ausbcuten von mehr als og.S”/o. 1UZPERENCES I,. C. HURU AND I-i. 0. ALLEN, fnd. 1hg. C/rmr., Atral. Ed., 7 (1953) 396 IX D. PISRRIN, h’ew %enland f. .%i. T&r., z7A (r~).#) 396 A. ‘I?. DICK AND J_ !3. ~XNGLllY. f?zlSitdiC4U J. I;-‘xpll. HiO!. kflcd. .%i., 25 (19.17) X93. C. IL CROUTIIAMIZI. AND C. 1:. JOIINSO~J. AmI. Clrcm., ZG (1954) 1284. I,. J_ \VItANGIZLI., 13. C. hlWA&l, 1). 1:. ~
F.
R.
Clrmr..
HIDBITS, W. NEI~I~, %. Aaaf.
I)AVIS,
182
hl.
I<. NISNKE
(x961)
AND
S.
IiAI.LMAN,
‘I’crhrlu,
.I (1960)
IO.+.
IO.
J. 0. HIBBITS AND 1~. ‘I’. \VII~LIAMS, .4t~nl. Clrittl. Acfu, 26 (xgGz) 3G3. 15. B. SANDI~LL, Coloriwclric Dclcrruirtcctio,r o/ Trnccs of hlctafs, 3rd Eel., Intcrscicncc, York, 195g. B.T.S.R.A., J. Irotr SIcct Iusl. (Lorrdotr), 178 (195.)) 35G. J. 130~ca~, Arc/~. I~ise)~Irrtctfenw., 26 (1055) 333. 12. W. MlrY~vocm AND A. A. IC. WOOD, ~9elallrlr~icul .,lrrolysis, zntl Etl., I.ontIon, x957. T. R. CUNNINGIIAM AND 1-I. 1,. HAMNKSX, 1.d. Etrg. Clrorr., AtId. Ed., 3 (1931) IO& A ml.
Claim.
New
.*Ictu. 33 (xgG5) 21-35