- Email: [email protected]
A precise direct heterometric determination of traces of copper with diethyldithiocarbamate in excesses of metals
ANALYTfCA
CJ[IMICA
ACT.4
VOL. 14 (rg+)
A PRECISE Df RECT HETEROMETRIC DETERMINATION OF TRACES OF COPPER WITH DI~rHYL~I~rH~OCAR~AM~r~ IN EXCESSES OF METALS
“I&c dctcrminrrtion ctf trnccs of copper with ciicthyldithiocnrl,amate (= CBM) has lxxn studied extensively in recent years ancl thcrc are numerous publicrttions on this subject’. Thcsc studies were mostly conccrncd with the determination of copper in water, milk, 0th~ foocl stuffs ctnd biological xnc~terials. Sl3ecial attention was given to the detcrminrrtion of coppcc in excess of ferric iron. It was the purpose of the investigation to find the ncccsukry conditions for ik precise hctctometric determination of copper with CUM. In previous investigations the reaction between mercury and CUM was studied by the authors 2a As the material presented in this prclxzr shows, the hetcromctric determination could be carried out very successfully in the suitable milicrt with the prcsencc of coml~lexing agents. The reaction concerned is ~~l~l~rosinl~ltcly of the same sensitivity as the reaction bctwccn cobalt and a-nitroso Jj-nq3hthol; (I. I’-0.3 mg col313crin 20 ml sohttion can be determincd.CVorkingconditions iu-c presented which cnablc the hetcromctric determination of copper to bc carried out in 7-m minutes, l’hc 13rccision achieved was so great that in almost all casts theorcticnl vah~cs for copper were obtained without dependence on the amount of copper present. Generally, the copper made up only o.r-o.zo(, of the total metal content. The determination of o.oG”/* of copper in iron prcscnted no difficulties whntsocver. Compared with tfrc hctcromctric titration of cobalt with a-nitroso ~-nal3hthol3 the reactions bctwccn copper :md C13M rcrluircd only WC U&YE of the time for a coml3lctc titration.
VOL.
14 (zg56)
HETEROMETRIC
DETERMIXA’IXOX
OF COPPER
559
is independent of the tcmpcraturc in the limits of ordinary room tcmpcmtures. Only the nbsolutc vultces of the optlcal clcnslty arc influcncccl by the tempcrnturc; tllcsc are more constant and more easily controllcd when cxpcrimonts, carried out at cliffercnt times and nt a constant tcmp~rature, arc compared.
Rendirrgs. Rcaclings of the gnlvnnomctcr wcrc constant in a few sccontls in the prcscncc of the supplcmcntary neutr;ll electrolyte (PU’I-1,NO.J. Thts was just as fast as 1n :I regular honio~encous titration. Z?e~vodfccibil2~y. On repeating titrations at cliffcrcnt times it was ft~ncl that the n’tRxlmum optical density Vail163 obtnincd clrtf nt>tchange by mOrt: thnn o!le unit in the second tlccimal place,
In the following tables and figures a selection of results obtained in the heterometric study of the reaction between copper and carbamatc (--- CSM), arc presented. The numeration is the same in the tables and in the figures. The copper can be prccipitatcd from acidic, neutral or alkaline solutions and the ptr of the solution in a is probably not of primary importance. The presence of neutral electrolytes sufficient concentration is of greater importance for the hctcrometric titration. This factor dctcrmines whether prccil,itation occnrs at all, and whether the precipitate can be used, for a quick an precise determination of copper. -4 further problem is the kind of complcxing agents and their concentration which could be used without interfering with the heteromctric precipitation of copper. Table I and Fig. r present some results obtained in the absc?tce of foreign metals on changing the composition and the concentration of the electrolytes in the solution. As was ascertained the nnz~~o~~iacrrlc&ale solution was t/20 ~tost favor&r: for the lzctc~bmet& titrations. In the presence of ~OWIO~~.~W nitrr& the titration proceeded very quickly, and the fi& maximum optical density point was determined easily and maximwtt line was obtained with precision. 1% ihe prcse~ce of citrate LZ horizontut immediately after the first maximum point. In the absence of citrate the densities generally dropped after the first maximum. From previous studic@ on the composition and the structure of citrate complexes we know that thcsc are mostly stable in the alkaline solution. No other complcxing agents could compete with citrate in these hetcrometric titrations. A large number of esperimcnts were carried out by us with ethyLevtcJia),ti?Edtctrcincetute ( = EDTA) in an alkaline medium both in the presence and in the abscncc of excesses of foreign metals. Although the end-point of the titration could be fixed in many cases, the results were not sufficiently sure, smooth curves were not obtained and the titration generally lasted a longer time. References p. 567.
3.00
O.jI*"
0.X
0,2g*"**
* after the maximum a horizontal density line; ** after the maximum density decreases; **+ no smaoth ti~tio~ curve; **** fluctuation.
3.m
0.0
3** k5
0.0
20
3.oo
0.jj**
0.1
46-1
o-77
0.X
2.20
O,jO**
0.1
10
15 15
2.2j
1.50
1.00
0.1
IO
t-5
x2-3
0.34**
0.1
20
2.2" 3
2.30 3.00 3.00
0.45""
0.1
20
2.25
0.9 -2.L
.s
0.0
8
0.0
2.2
8 ii
3.00 3%00
0.O
T
s
4.50
0.0
P
01
10
3.00
0.1
10
3.00
0.0 0.0
F rs
O$j"*
0.1
IO
2.23
3-5
F
O.$
0.1
3.00
0.0
s
2.27
O.jI*'
0.X
f0 SO
2.2j
2.30 3.00
0.p
0.1
13
2.?j
0-e
0.1
IO
3.00
3%” 3.00
0.jiP*'
1.6
20
0.62””
0.1
22
3oo 3.00
o-9 2.2 0.0 0.0 o.0
t-so 3-m 3.oo a.33 3.00
CBM = Sodium diethyldithiocarbamate; EDT& = EthyIenediamiaetc~acetate;
45
OjI*
0.1
X0
o.js*
0.1
IO
0.W
0.1
qo* 0.3j*
0.0
w
VOL. 14 (1956)
HETEROMETRIC
DETERMINATION
:
. ~:.,:::I:::::::::: z
“”
2 :
:I2
:
:
:
:
2:::: *L
,:::::::2:::::::
33+t-63-r3333-r3-$-7-r336
++++ff-i-+-f-+-!-4+++f-f-+ b-2
COPPER
OF
~::::::::‘:::I’::‘~:::::::
2::::: -f-f-r’666
-f- -I- f
+ -I- f
:
Ttrvlmtc in alkaline solution cotild in no way compctc with tltc citrate: in the former C:LSC a Jx-cciJ)itato usually a.lqw.~rcd in the Jwescnccof foreign mctuls &T/WY the cw%amatc was ML clccl. l’itrationswitll CarlXllni~tC could only lx carriccl out wlwn the concentration of the foreign metal was low. In spite of $ltis there at-c’ many special cases in wllich t~~rtratcco~tldl~cuscctmorc~successfully than citrate (e.g. St,). ‘J-1lC uSi! Of jh~V~Jf3hO.~jb,lldl: cvichitty gave Ixt tcr I10 results, Furthcrmuro, t1w salubility of sodium pyroJdiosJtl~ntc is many times lower than that of trisoclittmcitratc or tartrutc.
l’ablc f I ancl Figs, 2 nnd -3 present results ohtainctl in the prcscncc of cscc’sscs of foreign metals in dkdinc citrate: solutions. Titblc J I I and JTig. .I likewise show these rctstllts in tllc prcscncc of tartrate. Tl‘hr:rcstdts prcscntccl in this work arc of interest for many reasons. Firstly, tile amount of the foreign metals which may be present in solution, without any influence on the titration of copper, isvcry high, l’his concerns mctds which could not 1~2 satisfactorily clctectecl by clircct methods or for the dctcction of which no direct mcthoclscsist. Secondly, the copper could bc clutcrminccl in almost all casts WM cz)c MYQY
Wlilxl
is
cqmd
to
ZCY0.
In spite of this, the hetcrometric titrations of copper with cnrbnmate rcquirccl no more I~eferetrces p. 567.
14 (1956)
VOL.
HETEHO~IETRIC
DETER~fISATIOS
OF
COPPER
563
S-
5-
C-
3-
2-
a?! ; ml Sod/urn
i:ig.
I.
4 O~ethyldrthiocarbamate
5
~~‘itrxLtllJnScJf CrJppcr 111the
prcscncc
of coniplcsing
ngcnts.
0 7.5-
f14-
13.3.
0,2-
C>.I
IQ. 2. Titrations of copper in citrirte solution in the prcscncc of cwxsbcs of forclgn nlctnls.
L 0
2 ml Sodium
i
3
Oiethyld~thiocarbamate
4
564
M. BOBTELSKY,
Fig. 3. Titriltionh of copper in citrate solution in the prcscncc of CXCCSH~ of polyvnlcnt cations.
R. RAFAILOFF
VOL.
14 (1956)
ml Sodiu rm Dlr~yldlthiocorbama~e
Fig. 4. Titrations of copper in tartrato solution in the presence of excesses of foreign metals.
VOL.
14 (x956)
l&ETEWOMETRIG
DETERMINATION
OF
COPPER
565
than 7 to ro minutes. The following calculation demonstrates the sensitivity and the precision of the direct heterometric determination of traces of copper with CBM in the presence of 2~ 99.8% other metals. In analysing 0.2 mg copper in 30 ml solution, r part of copper in 1’00,000 parts of solution is determined. Since the titrant is added in increments of o.t ml and the copper is determined with a zero error (using 3 ml CBM for a full titration) an amount of copper which is 30 times less than that contained in the analysed solution can be safely determined. This means that I part of copper in 3,ooo,ooo parts of solution can be determined with an error equal to zero. Ti&ations
in the $vesencc
of ?tetctval sq’q5lcments
and contfilexing
age&s
In the presence of sodium acetate (expt. 2) the titration was unsafe because the readings fluctuated. A satisfactory end-point could not be obtained, When the titration was carried out in the presence of an excess of amntonia but in the absence of ammonium nitrate (expt. I) the titration lasted about five times cls long as in the presence of the latter. Apart from this, the maximum density values and the precision were the same in both cases. It is likely that the favorable action of amnntonizcnt nitrate W;LScaused by its presence as a concentrated neutral electrolyte. A sufficient amount of ammonium nitrate was therefore added to all solutions to be analysed, In the very dihtte solutions of copper, excesses of ammonium nitrate seemed to decrease the maximum density value somewhat (expts. 5 and 7). Even in the presence of sodium citrate no horizontal maximum density line was obtained and the density values dropped after the maximum point. In general the addition of excesses of tvisodium cilvute to the analysed copper solutions was favorable for the titration. Smooth titration curves were obtained in al1 cases. The precise location of the first maximum density point was very simple because a horizontnZ dcmity line was obtained immediately after the first maximum point (expts. g-13). If, however, too great an excess of titrant was added the density values began to decrease again. tripolyphosphate and ethyleneTo a certain extent, tartrate, pyrophosphate, diaminetetraacctate ( = EDTA) could be used as complexing agents (expts. rg and ~2%). In the presence of EDTA in ammoniacal solution the end-point of the titration was located but the curves were not smooth and the titration time was longer than usual (expts. rg and rga). Summarizing, it may be said that the titvalion of cojq!w~ @oweded qtcickly and safely zvlze~~an ammoniacal so&ion was gcsed, containing excesses b&t of ~?~tnton~zt~?z&rate and of sodiwrt citrate. Titrations
i?t the $wesemc
In ilrc presence
of excesses
of foreign
metals
of Ca, Sr, Bu and Itlg. No complexing agents whatever were necessary (expts. 20-23). The influcncc on the maximum density value of the blank was not appreciable. Probably the salts could.l~avo been present in much higher concentrations. In all cases the pcrcentagc of copper was 0.x5-0.3o4,. At the higher concentration of magnesium the maximum value decreased (cxpt. 24) ‘and in this case the USC of a somewhat highcr amount of copper would havo been prcfcrablc. ipt fire @resemc of i?n+a and Cd+a. The dctcrmination was carried out most successfully with trisodium citrate in a molt per mole amount at least equal to the foreign metal (expts. 25 and 30). Probably the concentration of the foreign metals could have been higher than that used. The copper made up 0.1-0.2~/~ of the total metal content. Tartrate lvas also usod as a comploxing R@evenccs p. 567.
hf. BOBTELSKY,
566
cipit& f tt
wlwn
l’SCt?bSi’S
of
t11& .Y!l+:‘.
hdtw~l ‘I’he
WII~;LIIW~
nmo~~nt
of
silver
Sb+:I
I<. RAFAftCWF
(cxpt.
which
VOL.
33). cotIk1 1;~ fn t.hc :irllrlrtrniilcnl
14
citrntc
(rgg6)
holtttion
VOL.
14 (rg56)
IiETERObLETRIC
DETERMINA’TION
OF
COPPER
567
CJ[IMICA
ACT.4
VOL. 14 (rg+)
A PRECISE Df RECT HETEROMETRIC DETERMINATION OF TRACES OF COPPER WITH DI~rHYL~I~rH~OCAR~AM~r~ IN EXCESSES OF METALS
“I&c dctcrminrrtion ctf trnccs of copper with ciicthyldithiocnrl,amate (= CBM) has lxxn studied extensively in recent years ancl thcrc are numerous publicrttions on this subject’. Thcsc studies were mostly conccrncd with the determination of copper in water, milk, 0th~ foocl stuffs ctnd biological xnc~terials. Sl3ecial attention was given to the detcrminrrtion of coppcc in excess of ferric iron. It was the purpose of the investigation to find the ncccsukry conditions for ik precise hctctometric determination of copper with CUM. In previous investigations the reaction between mercury and CUM was studied by the authors 2a As the material presented in this prclxzr shows, the hetcromctric determination could be carried out very successfully in the suitable milicrt with the prcsencc of coml~lexing agents. The reaction concerned is ~~l~l~rosinl~ltcly of the same sensitivity as the reaction bctwccn cobalt and a-nitroso Jj-nq3hthol; (I. I’-0.3 mg col313crin 20 ml sohttion can be determincd.CVorkingconditions iu-c presented which cnablc the hetcromctric determination of copper to bc carried out in 7-m minutes, l’hc 13rccision achieved was so great that in almost all casts theorcticnl vah~cs for copper were obtained without dependence on the amount of copper present. Generally, the copper made up only o.r-o.zo(, of the total metal content. The determination of o.oG”/* of copper in iron prcscnted no difficulties whntsocver. Compared with tfrc hctcromctric titration of cobalt with a-nitroso ~-nal3hthol3 the reactions bctwccn copper :md C13M rcrluircd only WC U&YE of the time for a coml3lctc titration.
VOL.
14 (zg56)
HETEROMETRIC
DETERMIXA’IXOX
OF COPPER
559
is independent of the tcmpcraturc in the limits of ordinary room tcmpcmtures. Only the nbsolutc vultces of the optlcal clcnslty arc influcncccl by the tempcrnturc; tllcsc are more constant and more easily controllcd when cxpcrimonts, carried out at cliffercnt times and nt a constant tcmp~rature, arc compared.
Rendirrgs. Rcaclings of the gnlvnnomctcr wcrc constant in a few sccontls in the prcscncc of the supplcmcntary neutr;ll electrolyte (PU’I-1,NO.J. Thts was just as fast as 1n :I regular honio~encous titration. Z?e~vodfccibil2~y. On repeating titrations at cliffcrcnt times it was ft~ncl that the n’tRxlmum optical density Vail163 obtnincd clrtf nt>tchange by mOrt: thnn o!le unit in the second tlccimal place,
In the following tables and figures a selection of results obtained in the heterometric study of the reaction between copper and carbamatc (--- CSM), arc presented. The numeration is the same in the tables and in the figures. The copper can be prccipitatcd from acidic, neutral or alkaline solutions and the ptr of the solution in a is probably not of primary importance. The presence of neutral electrolytes sufficient concentration is of greater importance for the hctcrometric titration. This factor dctcrmines whether prccil,itation occnrs at all, and whether the precipitate can be used, for a quick an precise determination of copper. -4 further problem is the kind of complcxing agents and their concentration which could be used without interfering with the heteromctric precipitation of copper. Table I and Fig. r present some results obtained in the absc?tce of foreign metals on changing the composition and the concentration of the electrolytes in the solution. As was ascertained the nnz~~o~~iacrrlc&ale solution was t/20 ~tost favor&r: for the lzctc~bmet& titrations. In the presence of ~OWIO~~.~W nitrr& the titration proceeded very quickly, and the fi& maximum optical density point was determined easily and maximwtt line was obtained with precision. 1% ihe prcse~ce of citrate LZ horizontut immediately after the first maximum point. In the absence of citrate the densities generally dropped after the first maximum. From previous studic@ on the composition and the structure of citrate complexes we know that thcsc are mostly stable in the alkaline solution. No other complcxing agents could compete with citrate in these hetcrometric titrations. A large number of esperimcnts were carried out by us with ethyLevtcJia),ti?Edtctrcincetute ( = EDTA) in an alkaline medium both in the presence and in the abscncc of excesses of foreign metals. Although the end-point of the titration could be fixed in many cases, the results were not sufficiently sure, smooth curves were not obtained and the titration generally lasted a longer time. References p. 567.
3.00
O.jI*"
0.X
0,2g*"**
* after the maximum a horizontal density line; ** after the maximum density decreases; **+ no smaoth ti~tio~ curve; **** fluctuation.
3.m
0.0
3** k5
0.0
20
3.oo
0.jj**
0.1
46-1
o-77
0.X
2.20
O,jO**
0.1
10
15 15
2.2j
1.50
1.00
0.1
IO
t-5
x2-3
0.34**
0.1
20
2.2" 3
2.30 3.00 3.00
0.45""
0.1
20
2.25
0.9 -2.L
.s
0.0
8
0.0
2.2
8 ii
3.00 3%00
0.O
T
s
4.50
0.0
P
01
10
3.00
0.1
10
3.00
0.0 0.0
F rs
O$j"*
0.1
IO
2.23
3-5
F
O.$
0.1
3.00
0.0
s
2.27
O.jI*'
0.X
f0 SO
2.2j
2.30 3.00
0.p
0.1
13
2.?j
0-e
0.1
IO
3.00
3%” 3.00
0.jiP*'
1.6
20
0.62””
0.1
22
3oo 3.00
o-9 2.2 0.0 0.0 o.0
t-so 3-m 3.oo a.33 3.00
CBM = Sodium diethyldithiocarbamate; EDT& = EthyIenediamiaetc~acetate;
45
OjI*
0.1
X0
o.js*
0.1
IO
0.W
0.1
qo* 0.3j*
0.0
w
VOL. 14 (1956)
HETEROMETRIC
DETERMINATION
:
. ~:.,:::I:::::::::: z
“”
2 :
:I2
:
:
:
:
2:::: *L
,:::::::2:::::::
33+t-63-r3333-r3-$-7-r336
++++ff-i-+-f-+-!-4+++f-f-+ b-2
COPPER
OF
~::::::::‘:::I’::‘~:::::::
2::::: -f-f-r’666
-f- -I- f
+ -I- f
:
Ttrvlmtc in alkaline solution cotild in no way compctc with tltc citrate: in the former C:LSC a Jx-cciJ)itato usually a.lqw.~rcd in the Jwescnccof foreign mctuls &T/WY the cw%amatc was ML clccl. l’itrationswitll CarlXllni~tC could only lx carriccl out wlwn the concentration of the foreign metal was low. In spite of $ltis there at-c’ many special cases in wllich t~~rtratcco~tldl~cuscctmorc~successfully than citrate (e.g. St,). ‘J-1lC uSi! Of jh~V~Jf3hO.~jb,lldl: cvichitty gave Ixt tcr I10 results, Furthcrmuro, t1w salubility of sodium pyroJdiosJtl~ntc is many times lower than that of trisoclittmcitratc or tartrutc.
l’ablc f I ancl Figs, 2 nnd -3 present results ohtainctl in the prcscncc of cscc’sscs of foreign metals in dkdinc citrate: solutions. Titblc J I I and JTig. .I likewise show these rctstllts in tllc prcscncc of tartrate. Tl‘hr:rcstdts prcscntccl in this work arc of interest for many reasons. Firstly, tile amount of the foreign metals which may be present in solution, without any influence on the titration of copper, isvcry high, l’his concerns mctds which could not 1~2 satisfactorily clctectecl by clircct methods or for the dctcction of which no direct mcthoclscsist. Secondly, the copper could bc clutcrminccl in almost all casts WM cz)c MYQY
Wlilxl
is
cqmd
to
ZCY0.
In spite of this, the hetcrometric titrations of copper with cnrbnmate rcquirccl no more I~eferetrces p. 567.
14 (1956)
VOL.
HETEHO~IETRIC
DETER~fISATIOS
OF
COPPER
563
S-
5-
C-
3-
2-
a?! ; ml Sod/urn
i:ig.
I.
4 O~ethyldrthiocarbamate
5
~~‘itrxLtllJnScJf CrJppcr 111the
prcscncc
of coniplcsing
ngcnts.
0 7.5-
f14-
13.3.
0,2-
C>.I
IQ. 2. Titrations of copper in citrirte solution in the prcscncc of cwxsbcs of forclgn nlctnls.
L 0
2 ml Sodium
i
3
Oiethyld~thiocarbamate
4
564
M. BOBTELSKY,
Fig. 3. Titriltionh of copper in citrate solution in the prcscncc of CXCCSH~ of polyvnlcnt cations.
R. RAFAILOFF
VOL.
14 (1956)
ml Sodiu rm Dlr~yldlthiocorbama~e
Fig. 4. Titrations of copper in tartrato solution in the presence of excesses of foreign metals.
VOL.
14 (x956)
l&ETEWOMETRIG
DETERMINATION
OF
COPPER
565
than 7 to ro minutes. The following calculation demonstrates the sensitivity and the precision of the direct heterometric determination of traces of copper with CBM in the presence of 2~ 99.8% other metals. In analysing 0.2 mg copper in 30 ml solution, r part of copper in 1’00,000 parts of solution is determined. Since the titrant is added in increments of o.t ml and the copper is determined with a zero error (using 3 ml CBM for a full titration) an amount of copper which is 30 times less than that contained in the analysed solution can be safely determined. This means that I part of copper in 3,ooo,ooo parts of solution can be determined with an error equal to zero. Ti&ations
in the $vesencc
of ?tetctval sq’q5lcments
and contfilexing
age&s
In the presence of sodium acetate (expt. 2) the titration was unsafe because the readings fluctuated. A satisfactory end-point could not be obtained, When the titration was carried out in the presence of an excess of amntonia but in the absence of ammonium nitrate (expt. I) the titration lasted about five times cls long as in the presence of the latter. Apart from this, the maximum density values and the precision were the same in both cases. It is likely that the favorable action of amnntonizcnt nitrate W;LScaused by its presence as a concentrated neutral electrolyte. A sufficient amount of ammonium nitrate was therefore added to all solutions to be analysed, In the very dihtte solutions of copper, excesses of ammonium nitrate seemed to decrease the maximum density value somewhat (expts. 5 and 7). Even in the presence of sodium citrate no horizontal maximum density line was obtained and the density values dropped after the maximum point. In general the addition of excesses of tvisodium cilvute to the analysed copper solutions was favorable for the titration. Smooth titration curves were obtained in al1 cases. The precise location of the first maximum density point was very simple because a horizontnZ dcmity line was obtained immediately after the first maximum point (expts. g-13). If, however, too great an excess of titrant was added the density values began to decrease again. tripolyphosphate and ethyleneTo a certain extent, tartrate, pyrophosphate, diaminetetraacctate ( = EDTA) could be used as complexing agents (expts. rg and ~2%). In the presence of EDTA in ammoniacal solution the end-point of the titration was located but the curves were not smooth and the titration time was longer than usual (expts. rg and rga). Summarizing, it may be said that the titvalion of cojq!w~ @oweded qtcickly and safely zvlze~~an ammoniacal so&ion was gcsed, containing excesses b&t of ~?~tnton~zt~?z&rate and of sodiwrt citrate. Titrations
i?t the $wesemc
In ilrc presence
of excesses
of foreign
metals
of Ca, Sr, Bu and Itlg. No complexing agents whatever were necessary (expts. 20-23). The influcncc on the maximum density value of the blank was not appreciable. Probably the salts could.l~avo been present in much higher concentrations. In all cases the pcrcentagc of copper was 0.x5-0.3o4,. At the higher concentration of magnesium the maximum value decreased (cxpt. 24) ‘and in this case the USC of a somewhat highcr amount of copper would havo been prcfcrablc. ipt fire @resemc of i?n+a and Cd+a. The dctcrmination was carried out most successfully with trisodium citrate in a molt per mole amount at least equal to the foreign metal (expts. 25 and 30). Probably the concentration of the foreign metals could have been higher than that used. The copper made up 0.1-0.2~/~ of the total metal content. Tartrate lvas also usod as a comploxing R@evenccs p. 567.
hf. BOBTELSKY,
566
cipit& f tt
wlwn
l’SCt?bSi’S
of
t11& .Y!l+:‘.
hdtw~l ‘I’he
WII~;LIIW~
nmo~~nt
of
silver
Sb+:I
I<. RAFAftCWF
(cxpt.
which
VOL.
33). cotIk1 1;~ fn t.hc :irllrlrtrniilcnl
14
citrntc
(rgg6)
holtttion
VOL.
14 (rg56)
IiETERObLETRIC
DETERMINA’TION
OF
COPPER
567