need be determined for each sample of substance investigated, and much of the time and expense required for extended measurements can often be saved. TABLEV. JOULE-THOMSOS EFFECTSFOR CARBOX DIOXIDEAT OSE .%TYOSPHERE PRESSURE ESTIMATED FROM FIGURE 8 A S D COMPARED WITH OBSERYED VALUES (Data from International Critical Tables. 1 1 ) P
x
10 F O R CO?
@
x
10 F O R GO?
~E\IP
Obsvd
Calcd
TEMP.
Obsvd
135 145
10.4 9.1
10.3 9 1
155 175
8.2 6.7
Calcd 8.2 6.7
TABLEVI. COMPARISOS OF ESTIMATED ASD ORSERYED ABSORPTIOS COEFFICIESTS OF ETHASOL FOR SITROCF OXIDE USISG METHASOL FOR REFERESCE SOLVEST fFigure 9 )
BUSSEN.\DSORPTIOS
nrxSEs . ~ R S O R P T I O X
TEMP. 0 I‘. 20
COEFYICIEPT Calcd.
_.,-
,-2.7Ci . . i n-
TmiP.
Ohsvd.
23 24
2.66 2.61
c.
2.79 2.75 2.70
2.70
I
C O E F F l CIENT
Obsi-d. 1
21
Calcd.
;:;!
COMPARISOS OF OBSERVED ISDUCTIOS PERIODS OF GASOLISES WITH T-ALC-ES COMPUTED FROM FIGURE 11
TAHLE VII.
_.___ JI\lPLE 3
i-
p,
c. 90 100 110
199
I N D U S T R I A L A N D E N G I X E E R I N G C H E M I S T l< Y
Februar), 1933
ISDCCTION PERIOD---
Obsvd.
Calcd.
Houri 16.5 6.9
ifourr 16.6 6.: 2.,
9.5
3hYPl.E 6
Obsrd. NOILTS
11.3 4.25 1.3
Calcd. Hours 11.5 4 .3 1.4
?ICKSOKLEDGMEST The authors wish t,o express their appreciation to E. R. Weaver, chief of the gas section of the Bureau of Standards, for suggesting the use of the “transfer” plot and for helpful adrice in preparing the manuscript.
LITERATURE CITED Badger, W. L., a n d McCabe, W. L . , “ E l e m e n t s of Chemical Engineering,” 1st e d . , pp. 1T6-8, McGraw-Hill, 1931. Baker, E. M., a n d W a i t e , V. H., Chem. &. M e t . Enp., 25, 1 1 3 i
(1921).
Cox, E.R., IXD.ESG. CHEM.,15, 593 (1923). Dodge, B. F., Ibid.. 14, 569 (1922). D u h r i n g , “Neue Grundgesetze zur rationelle PhyJik und Chemie,” Leipzig, 1878. Eiseman, J. H . , Weayer, E. R., a n d S m i t h , F. A , , Bur. Standards J . Research, 8, 703-4 (1932). Gordon, h.R., a n d Barnes, C . , J . Phys. Chem., 36, 1119 (1032). Harris, R.L., ISD.ESG. C H E Y . , 24, 455 (1932). International Critical Tahlej, Yol, 111. p. 264, AicGraw-Hill, 1926. I b i d . , Vo1. V, pp. 83-G. Ibid., Vol. pp. 144-5, Johnston, J., Z. p h u s i k . C h i n . , 62, 336 (1908). Kitchin, D. IT.,ISD.ESG. CHEU.,24, 551 (1932). Leslie, E. H., and Carr, A. R., Ibid.,17, 810 (1925). LeTvis, G . S . , ant1 Randall, SI.,J . .Am. Chorc. Soc., 43, I 1 4 1 (19211 . Lewis, W.K., a n d TYeber, H . C., J. ISD. ESG. C m i f . , 14, 4 i O (1922). N a x v e l l , J. B., Ibitf., 24, 503 (19:3‘71. Slonrad, C . C..Ibid., 21, 139 (1929). Onsager, L., Physii;. Z . , 28, 277 (1927); T r a m . J’aruduy S u c . , 23, 341 (1927). Porter, -1.11-.,Phil. M a g . , 23, 45s (1912); see also referelice ( 2 4 ) . Ranisay, J. W., ISD. ESG. C H E X ,24. 541 (1932). Ramsay, IT., a n d T o n n g , 3., Phil. Mag., [5] 20, 515 (1’583); 21, 33 (1Sb5); 22, 3T (1SXG); 33, 153 (189%). Schultz, J. IT., IND. ESG. CHZII.,21, 557 (1929). Walker, TT. H . . Lewis, IT-. K . , and Mc..ldams, W. H . , “Principles of Cheniical Engineering,” 1 s t ed., p. SO, .\id2rn\VHill, 1923. Ibid., p. 429. White, -1.M.,ISD. ESG. CHEX.,22, 230 (1930).
v,
RECEIVED August 25, 1932. Published by permission o f the Director. S a :ional Bureau of Standards.
Effect of Oxygen. and Water on Polymerization of Chloroprene h.4
T
WILLI-US AND H. W.W-QLKER, E. I. du Pont de Yeinours & Company, Wilmington, Del.
H E polymerization of chloroprene with respect to the types of polymer and to the rate of polynierization is influenced by the presence of most foreign materials. This condition makes control of the polymerization difficult, and it has been necessary to study the effect of certain -elected substances including oxygen and water which are always present. Many foreign materials in concentrations of one part in ten thousand n-ill inhibit polymerization almost conipletc~lyor modify the type of polymer produced. Many of tlie effectc: are unexpected and unexplained, w c h as the inliiliting action of abietic and oleic acids and the abfence of effect n itli liydrogeilated abietic and stearic acids. Copper d t - are strong inhibitors of polymerization, iron salts direct the polynwrization toward the balata-type polymer, TT hile nickel zaltc liaye little effect. ( kycen and watw wliich are commonly present were knonx t o infliience polymerization. I n a previous coiiimuiiication ( 1 ) tlw qtrong catalytic effect of oxygen was shown. IT-hile oxygen lias an influence, it seems to promote the formation of 1mlat:i polynier rather than a-polychloroprene :md is not nece-ary for either tlie polymerization to a-polymer or the conversion of a- to p-polycliloroprene. I t has also been found tliat, altliougli water is an accelerator, the rapid poly-
merization of chloroprene einulsions is not due priniarily to the water or chloroprene-water interface but to the conceiitration of certain dispersing agents in the interface.
ISFLUESCE OF OXYGES o s POLYMERIZATIOS Chloroprene freshly distilled in tlie presence of air and coiitaining traces of moisture mas placed in closed glass containers with a volume of air varying from 0 to 400 per cent of the volume of chloroprene and expo-ed to the light from a niercury arc in glass for 30 hours. At the end of this time the extent of polymerization was determined. The catalytic action of oxygen is clearly shown as follon z ’ R*TIOAIR TO CHLOROPRE~E 0.0 0.33 0,50
n 4110 .kIR
7 13
POLIVER CHLOROPRE\E
sc
20 2; 30
P O L 1 \IF R c, IO
1.00 4.00
40 48
An examination of the resulting polymer sIio~~--ed that tlie content of oxides as indicated by the color and the concentration of free hydrochloric acid increased with the amount of air. The large amount of air a!oo produced a more balata-
Vol. 25, No. 2
INDUSTRIAL AND ENGINEERING CHEMISTRY
200
like polymer which vulcanized with difficulty and which, after vulcanization, was i n f e r i o r in tensile strength.
POLYMERIZATION IN ABSEXE OF OXYQEN T h e f o l l o w i n g experiment was devised to determine the n e c e s s i t y for the presence of oxygen during polymerization: The apparatus shown in Figure
1 was c o n s t r u c t e d of glass and
Oxygen increases the rate of polymerization of chloroprene and tenth to promote the formalion of balata-like and unuulcanizable polymer rather than a-polychloroprene, but it is not necessary for either the polymerization to a-polymer or for the conversion of a- to p-polychloroprene during vulcanization. Traces of suspended water in chloroprene accelerate the polymerization mildly. The polymerization in emulsions of the chloroprene-in-water or water-in-chloroprene type with oriented polar dispersing agents, such as sodium oleate, proceeds rapidly to p-polymer. The nature of the polar interface appears to be the prime factor in causing the rapid polymerization of these emulsions. I n addition, it appears that the chloroprene must be confined between two polar interfaces, the distance between which is of the order of l p or less.
sealed together. Column F was loosely p a c k e d w i t h Carborundum to prevent spray from being c a r r i e d over during distillation. A s t r e a m of n i t r o g e n deoxygenated by passage through fine filtros distributors in two separate bottles of so d i u m h y d r o x i d e sodium hyposulfite solution was led in through a stopcock a t G which was t h e n closed. The a p p a r a t u s was then evacuated t h r o u g h t h e opening, N , to a pressure of 2 mm. of mercury while the entire apparatus was heated by means of a free flame to a temperature of about 200' C. Washed nitrogen was then admitted to break the vacuum while the apparatus was kept heated; the vacuum was again ap lied. After several such operations, the apparatus was allowecfto cool to room tem era ture under vacuum. This vacuum was maintained througfoue the remainder of the operations. Flask A was further cooled with solid carbon dioxide in alcohol, and 800 cc. of chloroprene freshl distilled under nitrogen were admitted through the opening, which was then sealed. Flask E was cooled and flask A permitted to warm until about 100 cc. of chloroprene were collected in E. Flask B was then cooled, and 500 cc. of chloroprene were collected, after which flask A , containing the remainder of the chloroprene, was sealed off a t H. Flask B was now rmitted to warm and about 150 cc. were permitted to distiTinto E, after which chamber D was cooled and about 60 cc. of chloroprene were collected. Chambers C and D were then removed by sealing off a t K and M . As a result of these operations the chlororene collected in D was the middle fraction distilled twice a t pow ressure in the absence of free oxygen. FEsk B and chambers C and D were then exposed to the light of a mercury arc in glass, and the polymerization followed by watching the change in viscosity. Chambers C and D were placed in such position that the chloro rene was contained in D in the portion between 0 and M . Ciamber C is included for use in an experiment which will be subsequently described.
After cooling, the polymer was removed from the tubes and examined, No difference could be detected between the two. Each had become elastic, would swell but not dissolve in benzene, and could not be w o r k e d i n t o a smooth sheet on the rubber mill. It would appear that, under the conditions of t h i s experiment , oxygen has had no part in vulcanization.
INFLUESCE OF WATERo s POLYMERIZATIOS
After drying o v e r calciiim chloride, chloroprene still contains a n appreciable amount of water which will collect in the first fraction of the distillate t o produce a distinct turbidity. I t was shown by H. W. Starkw e a t h e r that the more rapid polymerization of t h e t u r b i d fraction was due to the Presence of water. It has been further observed that the-greatest influence is derived from the suspended, rather than dissolved, water. The turbid fraction, after clarifying by filtration, polymerizes a t the same rate as more rigidly dried material, but more slowly than a turbid sample. This comparison is shown as follows:
A
4
During the polymerization which was carried out at 2527" C., the chloroprene remained entirely colorless, and no difference in the rate of polymerization of any of the fractions was noticed. The rate of polymerization was, however, 20 to 30 per cent slower than a portion of the original chloroprene which had been distilled at normal pressure in contact with air. The same results were obtained in three separate experiments, all of which agreed closely with respect t o the rate of polymerization. After the polymerization in chamber D had proceeded to give the chloro rene a viscosity slightly greater than that of glycerol, chamber was inverted in an alcohol bath cooled with solid carbon dioxide. By this means the unpolymerized chloroprene remaining in the viscous mass was distilled out and collected in chamber C while the a-polymer concentrated as a layer in the bottom of chamber D. When the distillation was complete, the two chambers were separated by sealing off a t L. Flask B was opened, with no precautions being taken to protect the contents from air. The contents was used to prepare a strip of a-polymer in a test tube similar to the strip of polymer in chamber D. After the polymer had been exposed to the air for some time, the test tube was loosely closed with cotton. The two strips were now vulcanized by placing the test tube and chamber D side by side in an air oven at 140' C. for 30 minutes.
8
MATERIAL Turbid chloroprene Chloroprene after removal of turbidity by filtration Chloroprene filtered and dried over CaClz
POLYMER AFTER POLYMERIZATIOX 75 HOURS IN DARK Sample 1 Sample 2
%
%
30.2
28.6
16.3
15.6 18.0
15.0
POLYMERIZATION OF EMULSIONS The preparation of emulsions of chloroprene in dilute sodium oleate solution has already been described. Other protective agents which have been used for the preparation of chloroprene-in-water emulsions by the same method are Turkey-red oil, casein dispersed with either dilute caustic or 30 per cent acetic acid, triethanolamine oleate, sodium stearate, and Irish moss. All of these substances produce stable emulsions of similar particle size of the order of 0.1 to 1p as determined with a microscope. The polymerization of these emulsions can be easily followed by pouring a portion into alcohol. The polymerized portions are precipitated and can be isolated by filtration. It was found in each case that the chloroprene was completely converted into p-polymer in the course of a few hours, with the exception of the emulsion prepared with Irish moss. I n this case the polymerization was not accelerated and the material separated was the plastic a-polymer. INFLUENCING FACTORS. The principal factors which suggest themselves as affecting polymerization of emulsions are particle size, extent of surface, the polar nature of the surface due t o concentration and orientation of the polar protective agent at the interface, and the possible inhibiting or accelerating action of the dispersing agent. While the interfacial tension of the above emulsions has not been measured, NOTE: The surface tension at 30" c. is a8 follows: Dgnes/cm. 1 % Sodium oleate 28.8 1% Irish moss 1% NaOH casein 40.2 Chloroprene 1% Turkey-red oil 40 1
Dgnes/cm. 55.2 27.0
February, 1933
IXDUSTRIAL AND ENGINEERING CHEMISTRY
the effect of pressure on polymerization is known and the pressure inside the chloroprene particle cannot be great enough to be significant. Since each of the above dispersing agents is without appreciable effect on the polymerization of unemulsified chloroprene, the differences are probably due to the nature of the interface. INFLUEWE OF TYPEOF INTERFACE. Some effects of the nature of the interface can be determined by means of the emulsions stabilized with Irish moss. I n this case it is possible to add to an already stable emulsion small amounts of material which could change the nature of the interface or amounts of other dispersing agents insufficient to produce emulsions alone. When sodium oleate alone is used as a stabilizing agent, 100 grams of 0.25 per cent solution are sufficient to prepare a stable emulsion containing 40 grams of chloroprene. This is only slightly more than the calculated amount necessary to form an oriented monomolecular film at the chloroprene-water interface (3). Such an emulsion polymerizes a t 11 rate equal to an emulsion prepared with a 1 per cent solution of sodium oleate. The addition of an equal amount of sodium oleate to an Irish moss emulsion produces similar results. Sodium oleate added to produce concentrations of 0.05, 0.10, and 0.12 per cent had no influence on the rate of polymerization. With 0.15 per cent, a slight acceleration is observed, whereas concentrations of 0.25 per cent, and above, produce polymerization equal to the rate of the 1 per cent sodium oleate emulsions. These experiments indicate that the nature, rather than the extent of the interface, is of prime importance. WATER-IX-CHLOROPRESE Emmross. It is possible to prepare stable emulsions in which water is the dispersed and chloroprene the continuous phase. This type of emulsion exhibits distinctly different changes during polymerization from the chloroprene-in-water type. If the polymerization produces p-polymer, the entire mass first gels and finally bets to a solid mass through which the water is dispersed, I n this case no analytical method is available to determine the extent of polymerization, which must be judged only by the rigidity of the mass and by the cessation of the evolution of liest. If the polymerization is not catalyzed, a-polymer results and the mass gradually becomes viscous in a manner similar to pure chloroprene. The slow addition of water with vigorous agitation to chloroprene containing 1 per cent of magnesium oleate, barium oleate, or zinc stearate produces stable emulsions in which the water particles vary in size between 0.5 and 2p. These emulsions polymerize a t only a ilightly accelerated rate with the production of a-polymer, which again indicates that the extension of the chloroprenewater interface alone is a minor factor in increasing the rate of polymerization. The result of the polymerization of emulsion prepared with a 1 per cent solution of zinc stearate In chloroprene is as follows: CHLOROFRENE Grams 100 100 100
WATER Grams 80
10 0
POLYJIIERIZATION AFTER 24 H o c ~ a AT 30° C. % 28.7 29.4 19.4
The preparation of a water-in-chloroprene emulsion containing sodium oleate was accomplished as follows: Three per cent of plasticized pale crepe rubber was dispersed in chloroprene by continued shaking. Pale crepe rubber acts as R mild accelerator for the production of a-polymer in massive chloroprene, but the action is not sufficient to interfere with observations of the more rapid polymerization in emulsions. T a t e r containing 1 per cent sodium oleate was added dropwise to the chloroprene with vigorous agitation. By this means stable emulsions were prepared in which the diameter of the water particles was of the order of 1,u.
201
NOTE: Emulsions were also prepared by incorporating the sodium oleate in the rubber b y means of a rubber mill before dissolving the rubber in the chloroprene. Water was then dispersed through this medium. The polymerization of such emulsions was not accelerated, probably owing to the low solubility of sodium oleate in chloroprene and the consequent difficult transfer to the water.
The preparation of water-in-chloroprene emulsions permits the accomplishment of conditions which might exist in chloroprene-in-water emulsions if the size of the particles could be increased. Unfortunately, it has not yet been possible to prepare stable chloroprene-in-water emulsions in which the size of the chloroprene particles is materially increased. Dispersed chloroprene is entirely surrounded by a polar interface, and all the material within the particle comes within the influence of this surface. The distance through the chloroprene between polar surfaces can be controlled in the waterin-chloroprene emulsions by varying the water content. By increasing the dispersed water content, the interstices between the dispersed spheres decrease until the spheres touch, the
m I
1
FIGURE
I
l
l
n
1
/A1
1. APPARATUS FOR
POLYXERIZATION I N
ABSEXCEOF OXYGEN
exact volume depending upon the uniformity of the size of the dispersed particles. An increase in the amount of water beyond this amount results in flattening of the points of contact with the production of thin films of chloroprene between. The action of emulsions prepared in this manner appears to depend entirely upon the amount of water dispersed through the chloroprene. Small amounts of water have very little effect, the polymerization being slow and producing a-polymer. This condition exists with emulsions containing as much as 28.5 per cent of dispersed water. When the amount of water is increased to 37.5 per cent or more, the polymerization is rapid and p-polymer results. WATERCONTENT ON POLYTABLEI. EFFECTOF INCREASING MERIZATION OF WATER-IN-CHLOROPRENE EMULSIONS APPROX.DISTAYCEYIELD OF TYATER B E T W E E N P A R T I C L E S P O L Y M E R
%
Micron
%
44 5
0.22 0.32
95
37.4 33.3 28.6 23.1 16.7
0.42 0.52 0.66 0.84
38 18 11 10 9
TYPEOF POLYXER Elastic Semi-elastic Plastic Plastic PlRStiC Plastic
TIME O F POLYMERIZATION
Hours 3 18 18 18
1s
18
The result of increasing the amount of water is shown in Table I. The distance shown between particles is only approximate, because of the fact that the dispersed particles are not entirely uniform in size and do not maintain a fiwd position. The rapid polymerization of emulsions containing large amounts of dispersed water indicates that not only is it necessary to produce the correct type of polar interface, but also that the chloroprene be confined by means of this interface before polymerization is materially accelerated. The distance to which the two surfaces must approach is not entirely defined, but is less than lp. This close approach produces reduced mobility of the chloroprene which is revealed by
INDUSTRIAL AND ESGINEERING CHEMISTRY
202
the increased viscosity of the emulsions. This reduced mobility combined with the orienting effect of the polar interface appears to be responsible for the rapid polymerization. It is probable that emulsions containing chloroprene particles of the order of 2 p in diameter will polymerize slowly enough so that a-polymer can be isolated. It would be desirable to study chloroprene dispersed through a continuous phase which would eliminate water from consideration. h~~other mater,al suitable for preparing such has been found, the exception Of glycol which, because of the hydroxyl groups, is quite analo-
Vol. 23, Yo. 2
gous to water. Chloroprene dispersions made in ethylene glycol behave in a manner similar to water emulsions. LITERATURE CITED (1) Carothers, Tyilliams, Collins, a n d K i r b y , J. Am. Chem.
,Sot
,
53, 4203 (1931). (2) Ibid., 53, 4221 (1931). (3) ~ ~ i f fE, i ~L,, , Ibid., 45, 1651 (1923). RECEIVEDAugust 29, 1932. Presented before the Division 01 Rubber Chemistry a t the 84th Meeting of the American Chemical Society, Den.,er, Colo., August 22 t o 26, 1932. Thie paper is Contribution 27 from Jackson Laboratory, E. I. du Pont de gemours & Company.
Electrolysis of Silver-Bearing Thiosulfate Solutions K. HICKMIAX, W, WEYERTS,AIVD 0. E. GOEHLER,E a s t m a n Kodak Company, Rochester, N. Y.
A
T LEAST 100 tons of s i l v e r halides are dissolved annually in America alone in photographic thiosulfate baths. The s i l v e r has been recovered in a number of ways ( 7 ) ,perhaps the favorite being the precipitation as sulfide ( I S ) , followed by smelting. The separation of silver sulfide is an unpleasant operation lvhich may well be replaced by electrolysis (l6),l if the latter can be done conveniently in thiosulfate solution. The procedure might be extended to the treatment of silver ores to the exclusion of the more dangerous and expensive cyanide. It is the purpose of this paper to describe recent developments in the electrolysis of silver-bearing hypo (thiosulfate) solutions on an industrial scale. CHEMICBL CONSIDERATIONS
simple thiosulfate solution may contain or present to a suitable chemical host all or any of the above, together with liydrosulfurous and sulfoxylic acid.. If we consider these in p a r t i a l i o n i c dissociation, adding the water molecule, hydrogen and h y d r o x y l ions, and diswlved oxygen and hydrogen a t T arying oxidation-reduction potentials, we comprehend in some measure the number of events which may occur to the d v e r ion in free solution or 111 the neighborhood of the electrodes. T h e p r a c t i c a l evidence of this complex situation i- the immediate formation of colloidal s i l v e r sulfide when a silverbearing thiosulfate solution i. e l e c t r ol y z e d under ordinary l a b o r a t o r y c o n d i t i o n s . -45 soon as the current is applied, brown s t r e a m s of c o l l o i d a l silver sulfide fall a w a y f r o m the cathode, yielding a dirty unfilterable liquid. Crabtree and Ross (S), in their comprehensive review of fixinn-bath recovery methods, dismiss the electrolysis of hypo as impracticable for this reason. When the simple stationary electrode is replaced by a rotating cathode, and electrolysis is performed under varying pH conditions, a wide region is found where satisfactory separation of silver occurs. I n general, the proper solutions contain acid, which thiosulfate will not tolerate except in the pre.sence of sulfite, and, accordingly, all the solutions described in this paper contain sulfite. The equilibrium
-Much of the siltier accumulating in motion picture fixing baths, which used to be reclaimed as silver sulfide, is now recovered as metallic silver by electrolysis, and Ihe bath which used to be thrown io waste is replenished and recirculated. The electrolytic regenerat ion incokes the use of large cells containing 100 square ,feet of cathode surface through which a current of 300 amperes is passed at 1 to 1.5 colts. At the anode, thiosulfate is oxidized io tetrathionate and trithionate sulfate; at the cathode, silver is deposited with small quantities of silver sulfide and gelatin; some of the tetrathionate is reduced to thiosulfate. The adjustment of the bath to secure good plating must be made within certain critical limits: cigorous agitation, together with the presence of acid, sulfite, and certain promoting agents is essential. The electrical plating eficiency caries between 65 and 80 per cent in large installations, and the yield per million feet of Jilm is about 1200 ounces ( 1 kg. per 10,000 meters). The consumption of fixing baths is reduced to 35 per cent of the quantity previously used.
When thiosulfates are electrolyzed in aqueous solution with moderate current densities applied through inert electrodes, no gases are evolved, both the oxygen and hydrogen being absorbed by the solution. I n general, tetrathionates (IO) are generated a t the anode, and sulfides (21) or derivatives of sulfoxylic acid a t the cathode. The substances mix by natural convection to reform thiosulfate. The quantity of salt lost by irreversible decomposition to sulfur or sulfate (6) is small. The great number of substances existing in a solution Tvhich purports to contain thiosulfate, and the variety and ease of their mutual transformations is remarkable. A study of the literature (20) concerning the thionic acids ( 2 ) indicates that a solution of sulfide or colloidal sulfur exposed to the air may soon contain hydrogen sulfide, sulfur dioxide, thiosulfate, the four thionic acids, and sulfate. Conversely, a 1 Many so-called electrolytic processes have been used in which metal strips or bimetallic packs are immersed in the exhausted fixing bath. The silver is removed but another metal takes its place.
HA03 eH2SOa
+S
apparently (3) involves the intermediate formation of trithionate and hydrogen sulfide, thus: 2HiS Oa
F-'
H2S
and the reformation of thiosulfate:
+ HA08
