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The use of silver vanadates as absorbents for sulphur dioxide
VOL.
3
ANALYTICA
(1949)
THE
USE
OF
SILVER
CHIMICA ACTA
VANADATES
SULPHUR
AS
137
ABSORBENTS
FOR
DIOXIDE
G. INGIZA&I Courlauids Ltd., Mcttrlenhead. Berirs. (IZq$artd)
INTRODUCTION Silver orthovanadate has been recommended by the present author1 as an absorbent for sulphur dioxide and halogens in the micro determination of carbon and hydrogen in organic componnds. The reagent is mounted on granules of pumice and is contained in a long porcelain boat which is heated to a temperature of 650” C. More recently, the absorptive properties of silver orthovanadate for sulphur dioxide at room temperatures have been investigated by BELCH~R~. The purpose of his investigation was to find solid reagents capable of absorbing sulphur dioxide but not carbon dioside, which could be used as external absorbents in the determination of carbon in steels. In the course of this latter investigation, the silver orthovanadate was found to behave irregularly as regards its reaction with sulphur dioxide: the first preparation to be used proved to be an effective reagent for sulphur dioxide in the cold, giving a pronounced colour change as it was exhausted, but later preparations were unreactive. BIILCHER suggested that an explanation of this irregular behaviour might lie in the fact that a number of different silver salts of the hypothetical vanadic acids is obtained under similar conditions. Only very exact conditions can guarantee the production of one particular type. Although information in the literature concerning the vanadates of silver is meagre, such as exists supports the foregoing explanation. However, in some cases the conditions given for the production of a particular silver vanadate are conflicting. Many types of silver vanadates are reported and the possibility of polymerization cannot be ruled out. Some of the products obtained in the present investigation differed markedly in colour although they had the same empirical composition. The most important work dealing with the vanadates of silver is that of BRITTON AND ROBINSON~. They carried out a physico-chemical study of the silver vanadates to establish how many true compounds actually exist. They concluded that only the ortho-, pyro- and metavanadates or, to use the nomenclatures they prefer, Referexces
p.
143.
G.INGRAM
138
VOL.
3 (1949)
the 3 : I, (Ag,O : V,O,), the 2 : I and I : I compounds can be formed. However, one particular vanadate could readily be converted to another by varying the proportions of the reactants used and, in general, mixtures were thus obtained. Boiling or aging also effected the composition of the precipitates. Although, as stated earlier, this evidence appears to explain the capricious behaviour of the silver vanadates prepared by BELCHER, some further work has since been carried out by the present author, with the object of establishing the correct conditions for the preparation of an “active” sample of silver vanadate. The products obtained under different conditions have been analysed to find the ratio of silver to vanadium and the reactivity towards sulphur dioxide at room temperatures has been examined.
EXPERIMENTAL 1.
PREPARATION
OF
SILVER
VANADATES
FROM
THE
CORRESPONDING
SODIUM
SALTS
The inethods used for the first series of preparations were essentially those described by BRITTON AND ROBINSON~ starting with the corresponding pure sodium salts. The ortho-, pyro- and metavanadates thus obtained yielded analytical figures which were in good agreement with the theoretical figures (Table Ia) but none of these dried compounds would absorb sulphur dioxide in the cold. The method of MOSER AND BRANUL~ was also used for the preparation of silver orthovanadatc, but the analytical figures (Table Ib) for silver and vanadium approached those demanded by the pyrovanadate; a fact also noted by BRITON AND ROBINSONS. It may therefore be concluded that erroneous figures would be obtained if vanadium is determined by this methodG. Although none of the three compounds obtained by the method of BRITTON AND ROBINSON would absorb sulphur dioxide when dry, it was found that the moist salts absorbed the gas quantitatively with a marked change in colour. Similarly, the dried products when mixed intimately with an equal weight of sodium sulphate decahydrate were also effective. TABLE Silver
&Ictrl Pyre Ortho
’
Vnn;Lcl:ltc
l?ound . . . . T
References p. 143.
&%
1 v%
I
1
&%
a
. . . . . .
. . . . . .
51.9 51.7 66.3 66.6 73.7 73.8
1 v%
24.5 24.6 15.9 IS.7 11.5 11.6
G6.8
v%
4~ %
b
C
15.6 74-z
II.2
VOL. 3 (1949)
SILVER II.
VANADATES
PREPARATION
OF
AS
ABSORBENTS
MIXED
FOR
VANADATES
OF
SOa
139
SILVER
Mixed silver vanadates were prepared by dissolving vanadium pentoxide in a solution of sodium hydroxide and adding varying quantities of acetic acid prior to precipitation with silver nitrate. None of those preparations would absorb sulphur dioxide in the cold after intensive drying. The moist preparations were not examined. It was noted however that drying had an effect on the colour of the products, which was more pronounced than in the case of the preparations described earlier. III.
PREPARATION
OF
VANADATES
OF
WITH
SILVER
SODIUM
BY
FUSION
OF
VANADIUM
PENTOXIDE
HYDROXIDE
Silver orthovanadate was prepared from the corresponding pure sodium salt obtained from the fusion of vanadium pentoxide and caustic soda. In this case also, the dry product would not absorb sulphur dioxide. One particular silver salt which was obtained by the above method, but without first separating the sodium salt from the water solution of the fused mass, changed colour after drying at 120~ C from an orange yellow to a green colour. The analytical results (Table Ic) showed that it was similar in composition to the orthovanadate. It was found, however, that this product when completely dry absorbed sulphur dioxide until exhausted, with a marked change of colour. Although all the vanadium pentoxide had reacted during the fusion period, it was suspected that some free alkali was still present in solution when the fused mass was taken up with water resulting in the formation of some silver oxide. From the analytical figures it was obvious that only one of the following mixtures could have been obtained, each having a silver and vanadium content corresponding to silver orthovanadate : I.
Ag,O . AgVO,
2.
Ag,O - Ag,V,O,
-+ Ag,VO, + zAg,VO,
To establish the composition of the active,Yx$xture and to ascertain which silver vanadate was present, molecular quantities & each of the ortho, pyro and metavanadates were mised with molecular quantities of silver oxide and the reactivity of each mixture towards sulphur dioxide examined. The mixture containing silver metavanadate was the only one which absorbed sulphur dioxide Such a mixture corresponding to AgVO, - Ag,O has a similar silver and vanadium content to the product described. Also, the properties of each are alike in that both absorb sulphur dioxide in the cold and when completely dry. IV.
PREPARATION
OF
AN
“ACTIVE”
REAGENT
To establish the correct conditions for the preparation of the absorbent, the Refevenccs
p.
x43.
G. INGRAM
140
VOL.
3 (1949)
following tests were carried out based on the fact that when silver oxide is extracted with water it partially dissolves forming an alkaline solution. The various mixtures were also examined for their reactivity towards sulphur dioxide and carbon dioxide. For the latter, a U-tube filled with the test material was placed between the water and carbon dioxide absorption tubes of a micro combustion apparatus. Organic compounds of known carbon content were combustcd. In cases where low results were obtained it was assumed that carbon dioxide had been absorbed by the vansdate filling. For the sulphur dioxide reactivity tests, the gas was generated from a sodium bisulphitc solution, dried by means of anhydrone, and swept through the U-tube by means of a stream of oxygen at a rate of IO ml per minute. The presence of sulphur dioxide issuing from the absorption tube was indicated by means of a bubbler containing I ml of acidified 0.001 N potassiurn permanganate solution. During this esperimental work it was found impossible to prepare an “active” absorbent, unless precipitation of the silver metavanadate was carried out at room temperature. Analysis of products obtained by precipitation at temperatures of IOOO, 50" and 15" C showed that in each case the metavanadate was obtained. Presumably at these higher temperatures the silver salts underwent some change producing mixtures similar in composition to the metavanadatc. I. Silver Oxide
alone,
heated
at 150~ C
Silver oxide, heated at 150~ C for 24 h, either dry or first made into a paste with water, gave a positive alkaline test with phenolphthalein when shaken up with water. Carbon dioxide was absorbed, but sulphur dioxide did not react. When the silver oxide was heated for periods of upwards to 14 days the same reactions were still observed. z. Silver oxide
and motavanadatc
hated
at 150~ C
The preparation (2.31 g Ag20 and 2.07 g AgVO,) was intimately mixed by grinding and left in the oven at ISO’=’ C for 24 hours. Large quantities of sulphur dioxide were absorbed by this reagent and only a slight alkaline reaction was obtained when it was extracted with water. All carbon figures (Table II) were TABLE Substance
Wt
Phcnncctiu ............ Phcnncctln ............ Phcnacctin ............ Phcmcctin ............ Picric hcicl ............ Bcnzoic Acid
mg
-‘___
Found C O/o
IO.430
GG.
10.1~0
GG.g
X0.660 3.814 4.127 ro.o,go 4.150 I oA30
...........
Rcfc~e~rccs 9. x43.
II
I
67.06 67.07 31 *4 31.72
68.75 G8.85
licquircd
C yO
67.o.t 67.04 67.04 67.04 31.44 3 I-44 68.8 68.8
SILVER VANADATES AS ABSORBENTS FOR SO,
VOL.*3 (1949)
141
reasonably satisfactory except the first which was low, presumably because of the slight traces of alkaline material present in the mixture. Exhaustion of the filling was accompanied by a change in colour from green to brown. It was noticed that fine particle size powder was more efficient than granular size of 10-14 mesh and gave a sharper colour change at the point of exhaustion. With pure sulphur dioxide gas alone, absorption was very rapid with the production of much heat. 3. SiZver oxirte and motavanadate,
heated at r50” C after moistening
2.31 g silver oxide and 2.07 g of the metavanadate were ground into a paste with water and dried at 150“ C for 24 hours. Sulphur dioxide was absorbed and no alkaline reaction could be observed. Carbon dioxide was not absorbed. At this stage of the experiments it was observed that when silver oxide in excess of the theoretical amount was included in the mixture the water extract gave an alkaline reaction, whether the mixture was heated moist or dry. Low carbon figures were also obtained showing that some carbon dioxide was also absorbed. 4. Silver oxide und metavanadate
whated
Finally a mixture was tested which was mixed dry and without heating. Sulphur dioxide was absorbed but low carbon figures were obtained. An alkaline reaction was obtained when the mixture was extracted with water and tested with phenolphthalein indicator. 5. C0n&si07ts The evidence obtained from the above experiments indicate that although a preparation capable of absorbing sulphur dioxide is produced by grinding together molecular amounts of silver oxide and silver metavanadatc, heating_$t 150~ C for several hours is necessary when a product is required which will not absorb carbon dioxide. DISCUSSION The evidence obtained during the investigation suggests that combination occurs when silver oxide and silver metavanadate in the proportions of r : I are takes place is heated together for any length of time. That such a combination substantiated by the fact that although the final product has the same empirical the materials have entirely dissimilar composition as silver orthovanadate, properties. Thus, silver orthovanadatc prepared by the usual precipitation methods will only react with sulphur dioxide at room temperatures in the presence of water, whereas the heat treated mixture reacts quite readily when dry. Further, if the References
p.
r43.
G. INGRAM
142
VOL. 3
(1949)
unheated mixture, is extracted with water partial solution of the silver oxide occurs, which may readily be detected by means of its alkaline reaction or by the addition of a chloride solution. The heat treated mixture gives neither of these tests if the two components are in equal molecular proportions. Silver orthovanadate is also markedly different in colour from the mixture, which assumes a dark green colour after heating for several hours. Finally, the unheated mixture will absorb carbon dioxide due to the presence of free silver oxide whereas the heated one does not. Therefore as it is known that polymers of vanadic acids exist, it seems possible that polymers of the silver salts may also exist which seems to be the only explanation of this phenomenon. The product just described is very suitable as an cxtemal absorbent for sulphur dioxide at room temperatures. Such an absorbent has great application especially in the determination of carbon in sulphur containing steels. Whilst presumably the product could be obtained by precipitation methods directly, this investigation confirms the uncertainties involved in preparing such a product. The silver oxide-metavanadate method ensures much more effectively the production of an “active” reagent. Two other vanadium compounds were examined as possible absorbents of sulphur dioxide during the course of this investigation, namely, vanadium pentoxide and vanadyl di-sulphate, but both proved ineffective Manganese dioxide and silver permanganate were also recommended by B@LCHER~ who found that the former is extremely efficient for removing sulphur dioxide. He preferred it to the silver permanganate owing to its cheapness and ease of preparation. The commercial product is stated to be readily convertible to an “active” state. However, as the (Ag20.AgV0,) product gives an indication of its exhaustion by a sharp colour change, preference for its use may arise. The colour change indicating the exhaustion of silver permanganate is also extremely good, but owing to the tedious and inconvenient method required for its preparation, the other absorbents are to be preferred. The vanadium compound might find special application in the determination of carbon in compounds containing halogens besides sulphur and would have advantages in this particular case. SUMMARY A new solid absorbent for sulphur dioxide is dcscribcd which is cffcctivc at room tcmpcraturcs, and which dots not absorb carbon dioxide. Exhaustion of the filling is indicated by a chnngc in colour from green Co brown. The rcngcnt is prcpnrcd by hcnting molcculnr quantities of silver oxide and silver mctavanndatc togcthcr at 150~ C. Evidcncc is given that on such trcntmcnt the two silver salts combine, forming a product having the snmc cmpirica1 composition as silver orthovanadatc but diffcrcnt as rcgnrds its propcrtlcs from the orthovanadatc produced by the usual prccipitntion m&hod. Rcferemes
p. 143.
VOL. 3 (1949)
SILVER
VANADATES
AS ABSORBENTS
FOR SO,
=43
On propose un nouvel absorbant dc l’anhydridc sulfurcux, h tcmp&raturc ordinairc, ne rctcnant pas l’anhydride carbonique. La saturation est indiquec par un changcment de coulcur, du vert au brun. Le rQctii est prepare par chauffagc L 150” C dc l’oxydc d’argcnt ct du mbtavanadatc d’argent, en quamites environ BquimolCculaires. Amsi lcs dcux compos6.s SC combinent, en dormant UP produit ayant la composition dc l’orthovanadatc d’argcnt, mais pr&.scntnnt dcs proprrQt&s differcntes du scl obtcnu par prkipitation. ZUSAMMENFASSWNG Rin PCUCS,fcstcs, Adsorbcns fiir Schwcfeldioxyd wird bcschricbcn, dos bci Zimmcrtcmperaturen wirksam ist und kern Kohlcndioxyd nbsorbicrt. Erschbpfung clcr Ftillung wird durch eincn Farbwcchsel von griin nach braun angczcigt. Das Reaacns wird bercitct. mdcm man molckulnrc Mcnncn Silbcroxvd und Silbcrmctavanadat zusammen auf 150~ crhitzt. Rs wirtl bcwicsen, dass bci dicscr Bchandlung die bciden Silbersalze sich vcrbinden. wobei tin Produkt cntstcht, dns dicsclbe cmpirischc Zusammcnsctzung wit Silbcrorthovanadat hat, sich abcr in scincn Eigenschaften von dcm nach dcr gcwijhnlichcn Prhzipitationsmcthodc bcrcitctcn Produkt untcrschcidct. REFERENCES 1 s s 4 6
G. INGKAM, J. Sot. Chcnr. Ind., 62 (1943) 175. R. BELCHER, Ibid., 64 (1945) III. H. ‘I’. S. BRITTON AND R. A. ROBINSON, J. Chon. Sot., (1930) 2328 (x933) 516. MOSI~R AND BRANDL, Mo?talsh., 51 (rozg) I 69. A. I. VOGEL, Quantifalive Inorganic Analysis, (1945) 556.
Received
July yth, rgq8
3
ANALYTICA
(1949)
THE
USE
OF
SILVER
CHIMICA ACTA
VANADATES
SULPHUR
AS
137
ABSORBENTS
FOR
DIOXIDE
G. INGIZA&I Courlauids Ltd., Mcttrlenhead. Berirs. (IZq$artd)
INTRODUCTION Silver orthovanadate has been recommended by the present author1 as an absorbent for sulphur dioxide and halogens in the micro determination of carbon and hydrogen in organic componnds. The reagent is mounted on granules of pumice and is contained in a long porcelain boat which is heated to a temperature of 650” C. More recently, the absorptive properties of silver orthovanadate for sulphur dioxide at room temperatures have been investigated by BELCH~R~. The purpose of his investigation was to find solid reagents capable of absorbing sulphur dioxide but not carbon dioside, which could be used as external absorbents in the determination of carbon in steels. In the course of this latter investigation, the silver orthovanadate was found to behave irregularly as regards its reaction with sulphur dioxide: the first preparation to be used proved to be an effective reagent for sulphur dioxide in the cold, giving a pronounced colour change as it was exhausted, but later preparations were unreactive. BIILCHER suggested that an explanation of this irregular behaviour might lie in the fact that a number of different silver salts of the hypothetical vanadic acids is obtained under similar conditions. Only very exact conditions can guarantee the production of one particular type. Although information in the literature concerning the vanadates of silver is meagre, such as exists supports the foregoing explanation. However, in some cases the conditions given for the production of a particular silver vanadate are conflicting. Many types of silver vanadates are reported and the possibility of polymerization cannot be ruled out. Some of the products obtained in the present investigation differed markedly in colour although they had the same empirical composition. The most important work dealing with the vanadates of silver is that of BRITTON AND ROBINSON~. They carried out a physico-chemical study of the silver vanadates to establish how many true compounds actually exist. They concluded that only the ortho-, pyro- and metavanadates or, to use the nomenclatures they prefer, Referexces
p.
143.
G.INGRAM
138
VOL.
3 (1949)
the 3 : I, (Ag,O : V,O,), the 2 : I and I : I compounds can be formed. However, one particular vanadate could readily be converted to another by varying the proportions of the reactants used and, in general, mixtures were thus obtained. Boiling or aging also effected the composition of the precipitates. Although, as stated earlier, this evidence appears to explain the capricious behaviour of the silver vanadates prepared by BELCHER, some further work has since been carried out by the present author, with the object of establishing the correct conditions for the preparation of an “active” sample of silver vanadate. The products obtained under different conditions have been analysed to find the ratio of silver to vanadium and the reactivity towards sulphur dioxide at room temperatures has been examined.
EXPERIMENTAL 1.
PREPARATION
OF
SILVER
VANADATES
FROM
THE
CORRESPONDING
SODIUM
SALTS
The inethods used for the first series of preparations were essentially those described by BRITTON AND ROBINSON~ starting with the corresponding pure sodium salts. The ortho-, pyro- and metavanadates thus obtained yielded analytical figures which were in good agreement with the theoretical figures (Table Ia) but none of these dried compounds would absorb sulphur dioxide in the cold. The method of MOSER AND BRANUL~ was also used for the preparation of silver orthovanadatc, but the analytical figures (Table Ib) for silver and vanadium approached those demanded by the pyrovanadate; a fact also noted by BRITON AND ROBINSONS. It may therefore be concluded that erroneous figures would be obtained if vanadium is determined by this methodG. Although none of the three compounds obtained by the method of BRITTON AND ROBINSON would absorb sulphur dioxide when dry, it was found that the moist salts absorbed the gas quantitatively with a marked change in colour. Similarly, the dried products when mixed intimately with an equal weight of sodium sulphate decahydrate were also effective. TABLE Silver
&Ictrl Pyre Ortho
’
Vnn;Lcl:ltc
l?ound . . . . T
References p. 143.
&%
1 v%
I
1
&%
a
. . . . . .
. . . . . .
51.9 51.7 66.3 66.6 73.7 73.8
1 v%
24.5 24.6 15.9 IS.7 11.5 11.6
G6.8
v%
4~ %
b
C
15.6 74-z
II.2
VOL. 3 (1949)
SILVER II.
VANADATES
PREPARATION
OF
AS
ABSORBENTS
MIXED
FOR
VANADATES
OF
SOa
139
SILVER
Mixed silver vanadates were prepared by dissolving vanadium pentoxide in a solution of sodium hydroxide and adding varying quantities of acetic acid prior to precipitation with silver nitrate. None of those preparations would absorb sulphur dioxide in the cold after intensive drying. The moist preparations were not examined. It was noted however that drying had an effect on the colour of the products, which was more pronounced than in the case of the preparations described earlier. III.
PREPARATION
OF
VANADATES
OF
WITH
SILVER
SODIUM
BY
FUSION
OF
VANADIUM
PENTOXIDE
HYDROXIDE
Silver orthovanadate was prepared from the corresponding pure sodium salt obtained from the fusion of vanadium pentoxide and caustic soda. In this case also, the dry product would not absorb sulphur dioxide. One particular silver salt which was obtained by the above method, but without first separating the sodium salt from the water solution of the fused mass, changed colour after drying at 120~ C from an orange yellow to a green colour. The analytical results (Table Ic) showed that it was similar in composition to the orthovanadate. It was found, however, that this product when completely dry absorbed sulphur dioxide until exhausted, with a marked change of colour. Although all the vanadium pentoxide had reacted during the fusion period, it was suspected that some free alkali was still present in solution when the fused mass was taken up with water resulting in the formation of some silver oxide. From the analytical figures it was obvious that only one of the following mixtures could have been obtained, each having a silver and vanadium content corresponding to silver orthovanadate : I.
Ag,O . AgVO,
2.
Ag,O - Ag,V,O,
-+ Ag,VO, + zAg,VO,
To establish the composition of the active,Yx$xture and to ascertain which silver vanadate was present, molecular quantities & each of the ortho, pyro and metavanadates were mised with molecular quantities of silver oxide and the reactivity of each mixture towards sulphur dioxide examined. The mixture containing silver metavanadate was the only one which absorbed sulphur dioxide Such a mixture corresponding to AgVO, - Ag,O has a similar silver and vanadium content to the product described. Also, the properties of each are alike in that both absorb sulphur dioxide in the cold and when completely dry. IV.
PREPARATION
OF
AN
“ACTIVE”
REAGENT
To establish the correct conditions for the preparation of the absorbent, the Refevenccs
p.
x43.
G. INGRAM
140
VOL.
3 (1949)
following tests were carried out based on the fact that when silver oxide is extracted with water it partially dissolves forming an alkaline solution. The various mixtures were also examined for their reactivity towards sulphur dioxide and carbon dioxide. For the latter, a U-tube filled with the test material was placed between the water and carbon dioxide absorption tubes of a micro combustion apparatus. Organic compounds of known carbon content were combustcd. In cases where low results were obtained it was assumed that carbon dioxide had been absorbed by the vansdate filling. For the sulphur dioxide reactivity tests, the gas was generated from a sodium bisulphitc solution, dried by means of anhydrone, and swept through the U-tube by means of a stream of oxygen at a rate of IO ml per minute. The presence of sulphur dioxide issuing from the absorption tube was indicated by means of a bubbler containing I ml of acidified 0.001 N potassiurn permanganate solution. During this esperimental work it was found impossible to prepare an “active” absorbent, unless precipitation of the silver metavanadate was carried out at room temperature. Analysis of products obtained by precipitation at temperatures of IOOO, 50" and 15" C showed that in each case the metavanadate was obtained. Presumably at these higher temperatures the silver salts underwent some change producing mixtures similar in composition to the metavanadatc. I. Silver Oxide
alone,
heated
at 150~ C
Silver oxide, heated at 150~ C for 24 h, either dry or first made into a paste with water, gave a positive alkaline test with phenolphthalein when shaken up with water. Carbon dioxide was absorbed, but sulphur dioxide did not react. When the silver oxide was heated for periods of upwards to 14 days the same reactions were still observed. z. Silver oxide
and motavanadatc
hated
at 150~ C
The preparation (2.31 g Ag20 and 2.07 g AgVO,) was intimately mixed by grinding and left in the oven at ISO’=’ C for 24 hours. Large quantities of sulphur dioxide were absorbed by this reagent and only a slight alkaline reaction was obtained when it was extracted with water. All carbon figures (Table II) were TABLE Substance
Wt
Phcnncctiu ............ Phcnncctln ............ Phcnacctin ............ Phcmcctin ............ Picric hcicl ............ Bcnzoic Acid
mg
-‘___
Found C O/o
IO.430
GG.
10.1~0
GG.g
X0.660 3.814 4.127 ro.o,go 4.150 I oA30
...........
Rcfc~e~rccs 9. x43.
II
I
67.06 67.07 31 *4 31.72
68.75 G8.85
licquircd
C yO
67.o.t 67.04 67.04 67.04 31.44 3 I-44 68.8 68.8
SILVER VANADATES AS ABSORBENTS FOR SO,
VOL.*3 (1949)
141
reasonably satisfactory except the first which was low, presumably because of the slight traces of alkaline material present in the mixture. Exhaustion of the filling was accompanied by a change in colour from green to brown. It was noticed that fine particle size powder was more efficient than granular size of 10-14 mesh and gave a sharper colour change at the point of exhaustion. With pure sulphur dioxide gas alone, absorption was very rapid with the production of much heat. 3. SiZver oxirte and motavanadate,
heated at r50” C after moistening
2.31 g silver oxide and 2.07 g of the metavanadate were ground into a paste with water and dried at 150“ C for 24 hours. Sulphur dioxide was absorbed and no alkaline reaction could be observed. Carbon dioxide was not absorbed. At this stage of the experiments it was observed that when silver oxide in excess of the theoretical amount was included in the mixture the water extract gave an alkaline reaction, whether the mixture was heated moist or dry. Low carbon figures were also obtained showing that some carbon dioxide was also absorbed. 4. Silver oxide und metavanadate
whated
Finally a mixture was tested which was mixed dry and without heating. Sulphur dioxide was absorbed but low carbon figures were obtained. An alkaline reaction was obtained when the mixture was extracted with water and tested with phenolphthalein indicator. 5. C0n&si07ts The evidence obtained from the above experiments indicate that although a preparation capable of absorbing sulphur dioxide is produced by grinding together molecular amounts of silver oxide and silver metavanadatc, heating_$t 150~ C for several hours is necessary when a product is required which will not absorb carbon dioxide. DISCUSSION The evidence obtained during the investigation suggests that combination occurs when silver oxide and silver metavanadate in the proportions of r : I are takes place is heated together for any length of time. That such a combination substantiated by the fact that although the final product has the same empirical the materials have entirely dissimilar composition as silver orthovanadate, properties. Thus, silver orthovanadatc prepared by the usual precipitation methods will only react with sulphur dioxide at room temperatures in the presence of water, whereas the heat treated mixture reacts quite readily when dry. Further, if the References
p.
r43.
G. INGRAM
142
VOL. 3
(1949)
unheated mixture, is extracted with water partial solution of the silver oxide occurs, which may readily be detected by means of its alkaline reaction or by the addition of a chloride solution. The heat treated mixture gives neither of these tests if the two components are in equal molecular proportions. Silver orthovanadate is also markedly different in colour from the mixture, which assumes a dark green colour after heating for several hours. Finally, the unheated mixture will absorb carbon dioxide due to the presence of free silver oxide whereas the heated one does not. Therefore as it is known that polymers of vanadic acids exist, it seems possible that polymers of the silver salts may also exist which seems to be the only explanation of this phenomenon. The product just described is very suitable as an cxtemal absorbent for sulphur dioxide at room temperatures. Such an absorbent has great application especially in the determination of carbon in sulphur containing steels. Whilst presumably the product could be obtained by precipitation methods directly, this investigation confirms the uncertainties involved in preparing such a product. The silver oxide-metavanadate method ensures much more effectively the production of an “active” reagent. Two other vanadium compounds were examined as possible absorbents of sulphur dioxide during the course of this investigation, namely, vanadium pentoxide and vanadyl di-sulphate, but both proved ineffective Manganese dioxide and silver permanganate were also recommended by B@LCHER~ who found that the former is extremely efficient for removing sulphur dioxide. He preferred it to the silver permanganate owing to its cheapness and ease of preparation. The commercial product is stated to be readily convertible to an “active” state. However, as the (Ag20.AgV0,) product gives an indication of its exhaustion by a sharp colour change, preference for its use may arise. The colour change indicating the exhaustion of silver permanganate is also extremely good, but owing to the tedious and inconvenient method required for its preparation, the other absorbents are to be preferred. The vanadium compound might find special application in the determination of carbon in compounds containing halogens besides sulphur and would have advantages in this particular case. SUMMARY A new solid absorbent for sulphur dioxide is dcscribcd which is cffcctivc at room tcmpcraturcs, and which dots not absorb carbon dioxide. Exhaustion of the filling is indicated by a chnngc in colour from green Co brown. The rcngcnt is prcpnrcd by hcnting molcculnr quantities of silver oxide and silver mctavanndatc togcthcr at 150~ C. Evidcncc is given that on such trcntmcnt the two silver salts combine, forming a product having the snmc cmpirica1 composition as silver orthovanadatc but diffcrcnt as rcgnrds its propcrtlcs from the orthovanadatc produced by the usual prccipitntion m&hod. Rcferemes
p. 143.
VOL. 3 (1949)
SILVER
VANADATES
AS ABSORBENTS
FOR SO,
=43
On propose un nouvel absorbant dc l’anhydridc sulfurcux, h tcmp&raturc ordinairc, ne rctcnant pas l’anhydride carbonique. La saturation est indiquec par un changcment de coulcur, du vert au brun. Le rQctii est prepare par chauffagc L 150” C dc l’oxydc d’argcnt ct du mbtavanadatc d’argent, en quamites environ BquimolCculaires. Amsi lcs dcux compos6.s SC combinent, en dormant UP produit ayant la composition dc l’orthovanadatc d’argcnt, mais pr&.scntnnt dcs proprrQt&s differcntes du scl obtcnu par prkipitation. ZUSAMMENFASSWNG Rin PCUCS,fcstcs, Adsorbcns fiir Schwcfeldioxyd wird bcschricbcn, dos bci Zimmcrtcmperaturen wirksam ist und kern Kohlcndioxyd nbsorbicrt. Erschbpfung clcr Ftillung wird durch eincn Farbwcchsel von griin nach braun angczcigt. Das Reaacns wird bercitct. mdcm man molckulnrc Mcnncn Silbcroxvd und Silbcrmctavanadat zusammen auf 150~ crhitzt. Rs wirtl bcwicsen, dass bci dicscr Bchandlung die bciden Silbersalze sich vcrbinden. wobei tin Produkt cntstcht, dns dicsclbe cmpirischc Zusammcnsctzung wit Silbcrorthovanadat hat, sich abcr in scincn Eigenschaften von dcm nach dcr gcwijhnlichcn Prhzipitationsmcthodc bcrcitctcn Produkt untcrschcidct. REFERENCES 1 s s 4 6
G. INGKAM, J. Sot. Chcnr. Ind., 62 (1943) 175. R. BELCHER, Ibid., 64 (1945) III. H. ‘I’. S. BRITTON AND R. A. ROBINSON, J. Chon. Sot., (1930) 2328 (x933) 516. MOSI~R AND BRANDL, Mo?talsh., 51 (rozg) I 69. A. I. VOGEL, Quantifalive Inorganic Analysis, (1945) 556.
Received
July yth, rgq8