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Spectrophotometric studies on the nature of iron complexes with pyridine- and quinoline-carboxylic acids
ANALYTICA
SPECTROPHOTOMETRIC COMPLEXES \VITH
CHIMICA
ACTA
549
STUDIES ON THE NATURE OF PYRIDINEAND QUINOLINE-CARBOXYLIC
IRON
ACIDS A I< MAJUML)AR Dcpurtntenf
AND
S
P
B?\G
of r,rorgan;c and A~ulytrcal Ckewtstry, Unrverszty, Calcutta (Indta) (Iiccc~vcd
Novcmbcr
qth,
Jadnvptrr
1959)
SKRAUPL observed that pyrldmc- and clumoline-carboxylic acids, with a carboxyl group in the a-position to the hetcrocyclic nitrogen atom produce intense yellow or red colours with ferrous iron; methods for the dctermmntlon of iron with quinaldinic2.3, plcolmica and bcnzo
Coloccr reactions
nnd nbsorfition
ntnximz~m
regions
The orange-yellow complex formed by ferrous ion with picolinic or quinolinic acid12 either in presence of potassium cyanide @,I 9.0) or in presence of a large excess of the reagent (pH 5.9) showed maximum absorption at 440 rnp. The pink-red complex of Anal.
Chim
Acla,
22
(x960)
549-553
A. I<. MAJUMDAI<,
550
S. I’. BAG
iron and quinaldinic acid in the absence of potassium cyanide at pH 5.9 gave the absorptron maximum at 480 rnn/lthough the optical density rcmamcd constant up to 500 m/A; the complex formed in the prcscnce of potassium cyanrdc hacl the maximum absorption at 515 m/A with no change in absorption values up to 520 rnbd.In Fig. I, curves In, Ib and Ic represent the optical density values in prescncc of potassium cyanide of the colourcd complexes formccl wrth 8 p.p.m. of iron; CUNCS IIa, IIb and IIc present the values obtained at pn 5.9 in abscncc of potassium cyanide with 12 p.p.m. of iron.
OOL
fao
171~
I.
Spectral
tr;rnsmlttanLy
I
*CO
f40
Wavelength
t4a
in rnp
SO0
520
SfO
J S60
-
cuzvcb
LOtlI~)IcX;
Conlposilion
WO
In, I In - pcol~~~ic acid con~plcx; Ib, I Lb - qwnolrnic IC, IIc - ~uilXLldll~lC nCld cornplcx
acid
of the cowlplrxcs
The composition of the complcxcs in solutron was determined by Jon0 and molar ratiolo methods. For Job’s rncthod, ccluimolnr solutions of iron and rcagcnt wcrc taken rn different quantities (total IO ml) in z5-ml flasks. The iron solution was mixed with I ml of hydroxylarnine I~ydrochlornIc, and the necessary amount of rcagcnt, I ml of potassium cyanide ancl water to make up the volume were adcled. Curves A, I3 and C (Fig. 2) reprcscnt the picolinrc, quinalclinic and quinolinic acid complex systems respectively. In the abscncc of potassium cyanide, a large C~C~SSof reagent was recluircd for maximum colour development. With cquimolar solutrons the reagent concentratron was small and the optical densrty of the colourcd compleses formed without cyanide was slightly higher at 420 rnp than at 440 m/c in the cast of picolinic and quinolinic acrds. The absorption maximum always occurred at 480 m/c with quinalclinrc acid. The compositions of the picolinic and quinolinic acid complexes were determined both at 420 m/t and at 440 ml4 and that of quinaldinic acid at 480 rnp by following the Auul.
Chtm.
Acta,
22
(1960)
549-553
SPECTROPHOTOMETRIC
STUDIES
OF
Fe
COMPLEXES
551
procedure given above except that 8 ml of the buffer pH 5.9 solution were added instead of I ml of the potassium cyanide solution. (Sodium acetate-acetic acid buffer was used in the picolinic and quinolinic acid systems while ammonium acetate-acetic acid buffer was more suitable for the quinaldinic acid complex; the former buffer
Lo0.9
-
0.a 0.1 08’ 0.9 OI’ 0.3
-
0.a
-
1
0.1 r
La
0
0.1
*
0.Z
1
*
0.3
OI+
[Fe]/[Fe]
I
*
05
46
*
0.7
I
0 8
*
09
I
U
+ [Reagmt]
Fig z Job’s mcthqd of continuous variation* .4 - I:c = picolinic acid = 2 5 * x0-3 &1 at 440 rnp; U - Fc = quinaldinic acid = 23. x0-3 Mat5x5 mp;C-Fe=qumolm~cac~d=zGG * 10-8 M at 440 rnp; D and I: - Fc = plcolinlc and qumohmc acids rcspcctwcly = 5 . IO-? M at 420 rnp; E - Fe = qumaldlmc acid = 5 * x0-3 M at 480 m,u; G and l-I - Fc = prcohmc and qwnolinlc acids rcspcctwely = 5 . 10-3 M at 440 rnp.
I23456
78 mole
9
IO
Fe Kg. 3. Molar rntm method I - z ml of z 5 * 1o-3 &l I% and 2 5 * lo-3 M picolinic acid at 440m~;II-2n~lof 5 - ro-3MITcand 5. x0-3 M quinaldlmc acrd nt 515 mp, III - I ml of 5,32' IO-~&~ l:cand I .064. x0-3 nf quinolinic acid at 440 rnp; IVand VI - z tnlof 5 *ro-~lW l+ and 5 * lo-3 lb1 plcolinic and quinolmic acids rcspcctwcly at 420 rnp; V - z ml of 5 - 10-a M J?c and 5 - IO-aA2 qumaldmic acid at 480 rnp; VII rrnclVIII - 2 ml of 5 * IO-JIM Fe and 5 * lo-3 fiI picolinic and quinolinic acids rcspcctivcly at 440 mj.4. Moles
of
reagent
per
ot
formed a precipitate in the latter system.) Curves D, E and F (Fig. 2) represent respectively the picolinic, quinaldinic and quinolinic acid systems formed without cyanide. From the cumes it can easily bc inferred that in presence of potassium cyanide, the metal forms a I : I complex with these acids, whereas without cyanide the ratio is always I : 2, For the molar ratio method, the optical density values of the solutions were obtained by adding varying amounts of the organic acids and a fixed amount of potassium cyanide to a constant amount of iron ; the values are shown in Fig. 3. The breaks in curves I, II and III indicate that for all the complexes the metal and the reagent were in a ratio of r : x. The data for the curves IV, V and VI (Fig. 3) were obtained by adding different amounts of the reagents (5 * I0 --3 M) to z ml of an iron solution of the same molarity and by adjusting the pH to 5.9, without adding cyanide. The curves IV and VI show the absorption at 420 rnp and curve V that at 480 mp. The breaks indicate a metal to reagent ratio of x : 2. Even when the measurements for the picolinic and quinolinic A*lal Ch~rtr Ada,
22
(xgfh)
549-553
A. I<.
552
MAJUMDAH,
S. I’. BAG
acid complexes were made at 440 m,u, after the addition of potassium nitrate to increase the ionic strength, the metal to reagent ratio of I : z remained unchanged. Curves G and H (Fig. 2) by Job’s method, and VII and VIII (Fig. 3) by the molar ratio method, support this statement. It is thus conclusively shown that m the absence of potassium cyanide, iron in solution is associated with pyridine and quinolme carboxylic acids in a ratio of I : z and that m presence of cyamde the ratio is I : I. The formulae of the complexes may be suggested as: __________---
__-__---Hru~est
- _-.-__-
Qulnolmlc ac-Prcol1n1cac1tl Quinaldrlnc ;tc~d ______ ____
wrlh
-----polasw4m
---potassrunrcyatrulc ___-----_-
__-_---
-------
cyuwlc
Wlf/lOUl
N;L~[I~~(C,~I~NO~)~(I~SO)Z] IC4[Fc(C,H3N04) (CN) r] Fc(CaH4NOz)z(1~120)2 IC1[1:c(CntI4N03)(CN)4] Fc(C~~IioNOz)z(1-Iz0)z I<3[Pc(C1alioNOn)(CN)4] ---.------.._-_. -. -.-_- _-.___-_-- ------------
Instabdity constants of the contplexes The instability constant I< of the complexes, formed m the presence or absence of ’ potassium cyanide, was calculated by the following equations”, CX=
Bnt -
BW
Es
and
I< =
a C(wd2)”
C(r a)
where 0, EP.w, Es, C and PZ hnvc their usual signiflcanccs. Table I.
_._ __-Col,,plr _-_-
----
___-___-_-----~
a-l%colunc acid Qulnrrldlnic acid Qulnohrnc nclcl
------
I~rslatd~ly
courta~;l,
_-_------
Wllil po:asrr11m
t wrth
I
yuwJt
2 5’ * 10-G 7 51 * 10-o 2 73 ’ 10-G
~--__-_____-__-_-_____._
The results are given
in
h-
wllilod
potclsslum
CyUMlC __ ---_
I 53. 10-e 2 02 * 10-a 1 72 - 10-Q
-... -..
MAJUMDAI~ AND SIGN 4 found a higher value (4.23 . x0-5) for ferrous picolinate possibly bccausc they used solutions of low lox. The instability constant found for ferrous-quinaldinntc agrees fairly well with the values of WENCEH et al.8 (z.6- x0-8). Increase of ionic strength by the addition of potassium nitrate had no effect on the final result. SUMMARY Thu cornpositlons of the fcrrons iron con~plcxcs with ar-picohmc, quinaldimc and qumohnic acids have been rcinvcstigatccl. In prcscncc of potnssium cynnidc, iron combmcs with thcsc reagents In a I , nt PEI 5.9, III abscncc of cyamdc, the metal to rcagcnt rat.10 is I : 2. The instablhty ratio of t constnnts of tlic complcxcs arc glvcn
Lcs nutcurs ont effect& unc dtudc spcctrophotonibtriquc fcrrcux tics ircldcs a-picoliquc, qumnldquc ct qulnolbquc
sur la composition
dcs complcxcs
Es wlrd cmc spcktropllotomctrlschc Untcrsnchung ubcr die Zusammcnsctzung Komplcxc von a-Picohn-, Clunnltlm- und Chinolins!rurc bcschrlcbcn.
dcr Elscn(II)-
ZUSAMMENFASSUNG
Arral. Cl~artt.A&z, 22 (1960) 549-553
SPLCTIZOI’IIOTOBIETRIC
STUDIES
OF
553
1’C. COMI’LESES
REFERENCES 1 Z 2 P J A
8‘ A t A 6 I<. 7 1’
u I-’ v I?
10 J 11
tl
12 i\ I3 c
I-l SKRAUP. Momdsti., 7 (1886) ZIO RAY AND M IC UOSE, II anul CJtern , 95 (1933) 400 K MAJUMDAR ANI) 13 Scs, J Indtan Chcrn Sot ,37 (1950) r4g Ii MAJUMDAR Ah']> I3 SLN , Aml Chlw Acta, 8 (19.53) 369. 378, 384; 9 (1953) 536 S1.N , .4wl 1; MAJUMDAR ANI> )j Clrrm Arlu. 0 (1953) _~rg SIIXNRA, K Yosmh \WA, T J
1; 12
~IAJUMDAH
ANO
I
AND
11 I) I, HASIMICK, l* E SUCHAHI>A,
bCP
G
J
S
P
Ii
13~0.
CJrrttr .*Icfu, II (1959) 32+_ CJrertr 50~ , 143 (1931) 440 123 (1923) 2882 17.?7 .4)1d
Ch.halo,J
Chrrrr
SOC
,#n(l()Z5)
,
Atral, Chrttr
THEIGMOLYSIS
44
OF
SULPHIDES
A&a,
PRECIPITATED
BY
22
(1960)
549-553
SODIUM
SULPHIDE II.
SULPHIDES
RUTHENIUM,
017 SELENIUM, LEAD,
UISMUTH, CADMIUM, AND INDIUM 1. I<
Ckomcal
TI~LLURIUM,
TAIMNl
Laboraforres, (Recc~ved
AND
S
Untverstly Scptcmbcr
GOLD,
PLATINUM,
SILVER,
PALLADIUM
N. TANDON
of ACIaJrabad zbth,
(Zndta)
1959)
The thermolysis of several sulphides precipitated by sodium sulphidc has already been studied’. The present investigation clcals with the tllermolysls of the remaining sulphides. Ir 2S 3 - 1oHa0 has been studied by Duv~r, eL~1.2. EXPERIMENTAL
The reagents and methods for the preparation of the prccipitatcs were as reported in earlier papers. The precipitates taken for thermolysis were in exactly the same condition as those used in the gravimctric determinations just before weighing. A standard Stanton thcrmobalance was used. The rate of heating was 5.3 j= 0.2~ per min. Palladium sulphide required a maximum temperature above 800’ ; to obtain automatically a linear rate of heating the high and low switches were preset at 3 and I respectively. The thermograms shown were obtained by plotting different points of the original graph on the X and Y axes. Awal. CJIWI
A&a,
22 (1960)
553-557
SPECTROPHOTOMETRIC COMPLEXES \VITH
CHIMICA
ACTA
549
STUDIES ON THE NATURE OF PYRIDINEAND QUINOLINE-CARBOXYLIC
IRON
ACIDS A I< MAJUML)AR Dcpurtntenf
AND
S
P
B?\G
of r,rorgan;c and A~ulytrcal Ckewtstry, Unrverszty, Calcutta (Indta) (Iiccc~vcd
Novcmbcr
qth,
Jadnvptrr
1959)
SKRAUPL observed that pyrldmc- and clumoline-carboxylic acids, with a carboxyl group in the a-position to the hetcrocyclic nitrogen atom produce intense yellow or red colours with ferrous iron; methods for the dctermmntlon of iron with quinaldinic2.3, plcolmica and bcnzo
Coloccr reactions
nnd nbsorfition
ntnximz~m
regions
The orange-yellow complex formed by ferrous ion with picolinic or quinolinic acid12 either in presence of potassium cyanide @,I 9.0) or in presence of a large excess of the reagent (pH 5.9) showed maximum absorption at 440 rnp. The pink-red complex of Anal.
Chim
Acla,
22
(x960)
549-553
A. I<. MAJUMDAI<,
550
S. I’. BAG
iron and quinaldinic acid in the absence of potassium cyanide at pH 5.9 gave the absorptron maximum at 480 rnn/lthough the optical density rcmamcd constant up to 500 m/A; the complex formed in the prcscnce of potassium cyanrdc hacl the maximum absorption at 515 m/A with no change in absorption values up to 520 rnbd.In Fig. I, curves In, Ib and Ic represent the optical density values in prescncc of potassium cyanide of the colourcd complexes formccl wrth 8 p.p.m. of iron; CUNCS IIa, IIb and IIc present the values obtained at pn 5.9 in abscncc of potassium cyanide with 12 p.p.m. of iron.
OOL
fao
171~
I.
Spectral
tr;rnsmlttanLy
I
*CO
f40
Wavelength
t4a
in rnp
SO0
520
SfO
J S60
-
cuzvcb
LOtlI~)IcX;
Conlposilion
WO
In, I In - pcol~~~ic acid con~plcx; Ib, I Lb - qwnolrnic IC, IIc - ~uilXLldll~lC nCld cornplcx
acid
of the cowlplrxcs
The composition of the complcxcs in solutron was determined by Jon0 and molar ratiolo methods. For Job’s rncthod, ccluimolnr solutions of iron and rcagcnt wcrc taken rn different quantities (total IO ml) in z5-ml flasks. The iron solution was mixed with I ml of hydroxylarnine I~ydrochlornIc, and the necessary amount of rcagcnt, I ml of potassium cyanide ancl water to make up the volume were adcled. Curves A, I3 and C (Fig. 2) reprcscnt the picolinrc, quinalclinic and quinolinic acid complex systems respectively. In the abscncc of potassium cyanide, a large C~C~SSof reagent was recluircd for maximum colour development. With cquimolar solutrons the reagent concentratron was small and the optical densrty of the colourcd compleses formed without cyanide was slightly higher at 420 rnp than at 440 m/c in the cast of picolinic and quinolinic acrds. The absorption maximum always occurred at 480 m/c with quinalclinrc acid. The compositions of the picolinic and quinolinic acid complexes were determined both at 420 m/t and at 440 ml4 and that of quinaldinic acid at 480 rnp by following the Auul.
Chtm.
Acta,
22
(1960)
549-553
SPECTROPHOTOMETRIC
STUDIES
OF
Fe
COMPLEXES
551
procedure given above except that 8 ml of the buffer pH 5.9 solution were added instead of I ml of the potassium cyanide solution. (Sodium acetate-acetic acid buffer was used in the picolinic and quinolinic acid systems while ammonium acetate-acetic acid buffer was more suitable for the quinaldinic acid complex; the former buffer
Lo0.9
-
0.a 0.1 08’ 0.9 OI’ 0.3
-
0.a
-
1
0.1 r
La
0
0.1
*
0.Z
1
*
0.3
OI+
[Fe]/[Fe]
I
*
05
46
*
0.7
I
0 8
*
09
I
U
+ [Reagmt]
Fig z Job’s mcthqd of continuous variation* .4 - I:c = picolinic acid = 2 5 * x0-3 &1 at 440 rnp; U - Fc = quinaldinic acid = 23. x0-3 Mat5x5 mp;C-Fe=qumolm~cac~d=zGG * 10-8 M at 440 rnp; D and I: - Fc = plcolinlc and qumohmc acids rcspcctwcly = 5 . IO-? M at 420 rnp; E - Fe = qumaldlmc acid = 5 * x0-3 M at 480 m,u; G and l-I - Fc = prcohmc and qwnolinlc acids rcspcctwely = 5 . 10-3 M at 440 rnp.
I23456
78 mole
9
IO
Fe Kg. 3. Molar rntm method I - z ml of z 5 * 1o-3 &l I% and 2 5 * lo-3 M picolinic acid at 440m~;II-2n~lof 5 - ro-3MITcand 5. x0-3 M quinaldlmc acrd nt 515 mp, III - I ml of 5,32' IO-~&~ l:cand I .064. x0-3 nf quinolinic acid at 440 rnp; IVand VI - z tnlof 5 *ro-~lW l+ and 5 * lo-3 lb1 plcolinic and quinolmic acids rcspcctwcly at 420 rnp; V - z ml of 5 - 10-a M J?c and 5 - IO-aA2 qumaldmic acid at 480 rnp; VII rrnclVIII - 2 ml of 5 * IO-JIM Fe and 5 * lo-3 fiI picolinic and quinolinic acids rcspcctivcly at 440 mj.4. Moles
of
reagent
per
ot
formed a precipitate in the latter system.) Curves D, E and F (Fig. 2) represent respectively the picolinic, quinaldinic and quinolinic acid systems formed without cyanide. From the cumes it can easily bc inferred that in presence of potassium cyanide, the metal forms a I : I complex with these acids, whereas without cyanide the ratio is always I : 2, For the molar ratio method, the optical density values of the solutions were obtained by adding varying amounts of the organic acids and a fixed amount of potassium cyanide to a constant amount of iron ; the values are shown in Fig. 3. The breaks in curves I, II and III indicate that for all the complexes the metal and the reagent were in a ratio of r : x. The data for the curves IV, V and VI (Fig. 3) were obtained by adding different amounts of the reagents (5 * I0 --3 M) to z ml of an iron solution of the same molarity and by adjusting the pH to 5.9, without adding cyanide. The curves IV and VI show the absorption at 420 rnp and curve V that at 480 mp. The breaks indicate a metal to reagent ratio of x : 2. Even when the measurements for the picolinic and quinolinic A*lal Ch~rtr Ada,
22
(xgfh)
549-553
A. I<.
552
MAJUMDAH,
S. I’. BAG
acid complexes were made at 440 m,u, after the addition of potassium nitrate to increase the ionic strength, the metal to reagent ratio of I : z remained unchanged. Curves G and H (Fig. 2) by Job’s method, and VII and VIII (Fig. 3) by the molar ratio method, support this statement. It is thus conclusively shown that m the absence of potassium cyanide, iron in solution is associated with pyridine and quinolme carboxylic acids in a ratio of I : z and that m presence of cyamde the ratio is I : I. The formulae of the complexes may be suggested as: __________---
__-__---Hru~est
- _-.-__-
Qulnolmlc ac-Prcol1n1cac1tl Quinaldrlnc ;tc~d ______ ____
wrlh
-----polasw4m
---potassrunrcyatrulc ___-----_-
__-_---
-------
cyuwlc
Wlf/lOUl
N;L~[I~~(C,~I~NO~)~(I~SO)Z] IC4[Fc(C,H3N04) (CN) r] Fc(CaH4NOz)z(1~120)2 IC1[1:c(CntI4N03)(CN)4] Fc(C~~IioNOz)z(1-Iz0)z I<3[Pc(C1alioNOn)(CN)4] ---.------.._-_. -. -.-_- _-.___-_-- ------------
Instabdity constants of the contplexes The instability constant I< of the complexes, formed m the presence or absence of ’ potassium cyanide, was calculated by the following equations”, CX=
Bnt -
BW
Es
and
I< =
a C(wd2)”
C(r a)
where 0, EP.w, Es, C and PZ hnvc their usual signiflcanccs. Table I.
_._ __-Col,,plr _-_-
----
___-___-_-----~
a-l%colunc acid Qulnrrldlnic acid Qulnohrnc nclcl
------
I~rslatd~ly
courta~;l,
_-_------
Wllil po:asrr11m
t wrth
I
yuwJt
2 5’ * 10-G 7 51 * 10-o 2 73 ’ 10-G
~--__-_____-__-_-_____._
The results are given
in
h-
wllilod
potclsslum
CyUMlC __ ---_
I 53. 10-e 2 02 * 10-a 1 72 - 10-Q
-... -..
MAJUMDAI~ AND SIGN 4 found a higher value (4.23 . x0-5) for ferrous picolinate possibly bccausc they used solutions of low lox. The instability constant found for ferrous-quinaldinntc agrees fairly well with the values of WENCEH et al.8 (z.6- x0-8). Increase of ionic strength by the addition of potassium nitrate had no effect on the final result. SUMMARY Thu cornpositlons of the fcrrons iron con~plcxcs with ar-picohmc, quinaldimc and qumohnic acids have been rcinvcstigatccl. In prcscncc of potnssium cynnidc, iron combmcs with thcsc reagents In a I , nt PEI 5.9, III abscncc of cyamdc, the metal to rcagcnt rat.10 is I : 2. The instablhty ratio of t constnnts of tlic complcxcs arc glvcn
Lcs nutcurs ont effect& unc dtudc spcctrophotonibtriquc fcrrcux tics ircldcs a-picoliquc, qumnldquc ct qulnolbquc
sur la composition
dcs complcxcs
Es wlrd cmc spcktropllotomctrlschc Untcrsnchung ubcr die Zusammcnsctzung Komplcxc von a-Picohn-, Clunnltlm- und Chinolins!rurc bcschrlcbcn.
dcr Elscn(II)-
ZUSAMMENFASSUNG
Arral. Cl~artt.A&z, 22 (1960) 549-553
SPLCTIZOI’IIOTOBIETRIC
STUDIES
OF
553
1’C. COMI’LESES
REFERENCES 1 Z 2 P J A
8‘ A t A 6 I<. 7 1’
u I-’ v I?
10 J 11
tl
12 i\ I3 c
I-l SKRAUP. Momdsti., 7 (1886) ZIO RAY AND M IC UOSE, II anul CJtern , 95 (1933) 400 K MAJUMDAR ANI) 13 Scs, J Indtan Chcrn Sot ,37 (1950) r4g Ii MAJUMDAR Ah']> I3 SLN , Aml Chlw Acta, 8 (19.53) 369. 378, 384; 9 (1953) 536 S1.N , .4wl 1; MAJUMDAR ANI> )j Clrrm Arlu. 0 (1953) _~rg SIIXNRA, K Yosmh \WA, T J
1; 12
~IAJUMDAH
ANO
I
AND
11 I) I, HASIMICK, l* E SUCHAHI>A,
bCP
G
J
S
P
Ii
13~0.
CJrrttr .*Icfu, II (1959) 32+_ CJrertr 50~ , 143 (1931) 440 123 (1923) 2882 17.?7 .4)1d
Ch.halo,J
Chrrrr
SOC
,#n(l()Z5)
,
Atral, Chrttr
THEIGMOLYSIS
44
OF
SULPHIDES
A&a,
PRECIPITATED
BY
22
(1960)
549-553
SODIUM
SULPHIDE II.
SULPHIDES
RUTHENIUM,
017 SELENIUM, LEAD,
UISMUTH, CADMIUM, AND INDIUM 1. I<
Ckomcal
TI~LLURIUM,
TAIMNl
Laboraforres, (Recc~ved
AND
S
Untverstly Scptcmbcr
GOLD,
PLATINUM,
SILVER,
PALLADIUM
N. TANDON
of ACIaJrabad zbth,
(Zndta)
1959)
The thermolysis of several sulphides precipitated by sodium sulphidc has already been studied’. The present investigation clcals with the tllermolysls of the remaining sulphides. Ir 2S 3 - 1oHa0 has been studied by Duv~r, eL~1.2. EXPERIMENTAL
The reagents and methods for the preparation of the prccipitatcs were as reported in earlier papers. The precipitates taken for thermolysis were in exactly the same condition as those used in the gravimctric determinations just before weighing. A standard Stanton thcrmobalance was used. The rate of heating was 5.3 j= 0.2~ per min. Palladium sulphide required a maximum temperature above 800’ ; to obtain automatically a linear rate of heating the high and low switches were preset at 3 and I respectively. The thermograms shown were obtained by plotting different points of the original graph on the X and Y axes. Awal. CJIWI
A&a,
22 (1960)
553-557