April, 1929
INDUSTRIAL AND ENGINEERING CHEMISTRY
checked very well with the figures obtained by von KovitcsZorkhczy, l1 who found that 1 gram-molecule of pyrogallol would absorb approximately 40 grams of oxygen, which is equivalent to saying that at 86" F. (30"C.)and 740 mm. pressure, which are the conditions under which the writers' determinations were made, 1 gram of alkaline pyrogallol would absorb 253 cc. of oxygen. 11
Von KovLcs-Zork6czy. Biochem. 2.. 162, 161 (1925).
359
Conclusion
The foregoing experiments justify the belief that commercial tannins, in alkaline solution, have the property of absorbing large amounts of oxygen, and show the relative absorptive power of extracts from various sources. The principal industrial application of this property is in the prevention of corrosion in steam boilers where the presence of oxygen is the chief corrosion accelerator.
The Toxic Property of Sulfur' Chemistry in Relation to Toxic Factors Robert C. Williams and H. C. Young OHIOAGRICULTURAL EXPERIMENT STATION,WOOSTER,OHIO
Ordinary pure commercial sulfur for fungicidal The object of the present HE toxicity of sulfur to purposes has associated with it sulfurous acid, sulfuric i n v e s t i g a t i o n has been t o fungi has been attribacid, and pentathionic acid (tetrathionic acid). study the toxicity of sulfur in uted to various facA study has been made of the chemical and fungiits ordinary commercial forms tors-name1 y, sulfur itself, 11,* cidal properties of the acids of sulfur that are either and of the products accomsulfur dioxide or s u l f u r o u s associated with sulfur or are quite commonly known, panying or thought to be asacid,l2 sulfuric acid,' hydroand it has been found that the most toxic to spores of sociated with it. The invesgen s u l f i d e , * t h i o s u l f u r i c tigation includes both chemiacid,lo a n d p e n t a t < h i o n i c S. cinerea are the polythionic acids. Sulfur freed from this type of acid is not toxic. cal and fungicidal relationacid.16J6 ships. Filtrates from sulfur which has been quite thoroughly Of these, hydrogen sulfide wet owe a large part of their acidity to sulfuric acid. is definitely out of the controChemical Relationships of A solution of sulfuric acid, however, which has a total versy. Its identification unAcids of Sulfur acidity equivalent to that of a sulfur filtrate is not der conditions ordinarily asIn studying the chemical sociated with sulfur has not toxic. and fungicidal relationships of been established. FurtherArtificially oxidized sulfurs are very effective in the s u l f u r , t h e investigation of control of V. inaequalis provided the oxidizing agent more, solutions of it, even colloidal sulfur was not conthough equivalent in concenis not so effective as to destroy the polythionic acids. tinued, but ordinary stable trations to those acids which Field tests confirm laboratory tests. commercial forms of rhombic are toxic, may actually stimuA theory for the failure of sulfur applications conlate the germination of spores s u l f u r were used. Resubtaining alkaline constituents to control as well as those of X.cinerea. limed flowers of sulfur and which are acid is offered. Sulfur dioxide, or sulfurous high grades of ground roll acid, has no marked toxicity as such. Any toxicity that its sulfur were especially investigated. I n a preliminary note Young and WilliamslG gave evidence solution possesses is due to its hydrogen-ion concentration. Moreover, the quantity of sulfur dioxide associated with ordi- that pentathionic acid is associated with sulfur. This work nary sulfur is too small to be considered as a toxic factor. has been extended and the results are presented here. Sulfuric acid owes its toxicity to its hydrogen-ion concenWhen resublimed flowers of sulfur or ground roll sulfur was tration. Sulfur itself possesses no toxic effect when freed triturated with water to effect wetting and then filtered, the from accompanying products. YoungI5 and Young and Wil- filtrate was clear and possessed a definite titratable acidity. liamsI6working with various sulfur preparations, showed defi- Qualitative tests showed only the following acids in solution: nitely that pentathionic acid is toxic and pointed out that it sulfurous, sulfuric, and pentathionic (tetrathionic). It was accounted for the toxicity of all forms of sulfur. Their work noteworthy that sulfide ion and trithionate ion were absent. dealt with the study of Oden sulfur sols, acids of sulfur, and The reagents used for the qualitative tests were: finely divided ordinary sulfur. Pentathionic acid is present (sos)--: Iodine titration in considerable quantity in sulfur sols of that type and also (S20s) --: Iodine titration, with (SOa) -- bound by formalresults from oxidation in the presence of air and moisture in dehyde (SaOe) --: Mercurous nitrate the case of particulate sulfur. Tisdale14also considered penS--:Lead acetate, copper sulfate tathionic acid a toxic factor of sulfur. (SjO6) --: Ammoniacal silver nitrate, potassium hydroxide Recent work by Roach and Glynnelo was interpreted by ( 5 0 4 ) --: Barium chloride them as pointing to thiosulfuric acid as a toxic factor. HowTable I-Analysis of Filtrates f r o m Sulfurs ever, since thiosulfuric acid is a very unstable acid and since (Concentrations are given with reference to normal H ion) the conditions of their experiments were such as to insure the POLY- PERCENT presence of polythionic acids, the toxicity which they measTHIONIC POLYSULFUR TESTED ~~~~& H2SO4 A C I D ~ ~ THIONIC ured was undoubtedly that of the polythionic acids. Further(Bv diff.) ACIDS more, the tables given by them show a notable toxicity of Resublimed flowers 0,00253 0.00224 0.00029 11.5 pentathionic acid itself when compared with other acids Resublimed flowers 0.00190 0,00164 0.00026 13.7 tested. Ground roll 0.00129 0.00121 o.o0Oos 0.2
T
1
Received November 28, 1928. text refer to bibliography at end of article.
* Numbers in
Ground roll a
0.00335
Tetra- and pentathionic acids.
0.00312
0.00023
8.7
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INDUSTRIAL AND ENGIATEERING CHEMISTRY
I n the case of tetrathionic acid no specific test is known. Mercurous nitrate gives yellow precipitates with tetrathionio acid and pentathionic acid, while ammoniacal silver nitrate gives a brownish black precipitate with pentathionic acid. The ammoniacal silver nitrate test for pentathionic acid is specific considering the polythionic acids. Dithionic acid gives no precipitate with this reagent. Thiosulfate ion yields no precipitate with it. Higher oxidized forms of sulfur in combinations such as (Sod)-- and (SzOs)-- give white precipitates with it. Sulfide ion is the only one that might lead to confusing results, since it, too, gives brownish black silver sulfide. The sulfur acid with which potassium hydroxide reacts is pentathionic acid. During the titration of sulfur filtrates with this reagent a turbidity was produced which flocculated later. This turbidity was due to sulfur. The filtrate from sulfur gave no indication of S--with lead acetate. No change of color or precipitation was noticed when the filtrate was treated with ammoniacal copper sulfate. Hence, the effect of any possible excess of ammonium hydroxide is not such as to produce sulfide ion during the test. With known solutions containing pentathionic acid ammoniacal copper sulfate remained unchanged. Tests show that no S--is present and that the conditions of the experiment do not lead to subsequent formation of S--,which would make the test worthless as an indication of (Ss06)--. When the tests were applied to sulfur itself in a water suspension, the color changes took place on the sulfur in a manner analogous to that in solution. It is noteworthy that here again ammoniacal copper sulfate underwent no change. In fact, sulfur treated with ammonium hydroxide a t room temperature yielded no sulfide ion after standing for 1 month. Lead acetate likewise indicated no S--after being in contact with sulfur for 2 months, Nitric acid destroyed known solutions of pentathionic acid. Sulfur treated with nitric acid no longer gave a positive test for pentathionic acid. The possibility of having adsorbed S- -,which reacts only with ammoniacal silver nitrate, was not supported by facts. Sulfur was treated with 0.003 N hydrogen sulfide in an atThe sulfur was then washed slightly tempt to adsorb S to remove mechanically held hydrogen sulfide solution. A test for S-- on sulfur treated in this manner was positive with lead acetate and ammoniacal copper sulfate. Any possibility that the black precipitate is metallic silver may be discarded. Analysis of the precipitate formed showed it to be silver sulfide, which is the end product when pentathionic acid reacts with the reagent. That the precipitate is not silver oxide was also shown by the analysis, Silver oxide might possibly be expected as a result of decomposition of the silver complex ion by the acids tested. Silver oxide is soluble in an excess of ammonium hydroxide, whereas this precipitate is not dissolved. The suggested possibility that metals lower than silver in the e. m. f. series, which also form complexes with ammonium hydroxide, might analogously yield a black precipitate due to the ease of reduction to the metal or to subsequent combination with sulfur is not supported by evidence afforded by the use of the ammonium-platinic chloride complex. Although in this case the platinum is in the negative group, its ease of reduction is marked. However, no color change was noted on sulfur with this reagent. With pentathionic acid it gave a grayish orange precipitate. The presence of tetrathionic acid is quite probable, since it is so closely linked with pentathionic acid. I n fact, Spring13 considers pentathionic acid as a solution of sulfur in tetrathionic acid rather than as a definite chemical compound. Solutions of this type may be easily analyzed by a method
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given by Kurtenacker and G ~ l d b a c h . Most ~ of the constituents may be estimated iodometrically. This scheme of analysis was employed quite successfully with polythionate solutions made by the ultra-filtration of sulfur sols, but in the case of the dilute filtrates from ordinary sulfur the resolution of constituent acids involved uncertainties so great in blank determinations on reagents that no emphasis could be placed on the figures. Sulfurous acid, or SOa--, was easily determined by iodine titration and was found to be measurable but very low in quantity. Sulfuric acid accounted for a large part of the acidity. Since the component polythionic acids, pentathionic and tetrathionic, could not be determined accurately, no serious error would be incurred in ascribing the difference between the total acidity and the acidity due to sulfuric acid to the polythionic acids. The greatest total acidity of any filtrate tested was 0.0103 N with respect to hydrogen ion. This total acidity depends on the degree of wetting during the solution of the acids associated with sulfur, the history of the sulfur, temperature, and amount of water used in washing or wetting the sulfur, and other factors. I n the case where an acidity of 0.0103 N was obtained, the sample of ground roll sulfur was triturated in a mortar with just sufficient water to make a stiff mud. The filtrate was obtained by using suction. Fungicidal Properties of Sulfur Acids
PREPARATION OF Acms-Attempts were made to prepare the various acids of sulfur, the ones associated with sulfur, and others, in order to study their fungicidal properties. Dithionic acid was made by the common method of passing sulfur dioxide into a suspension of manganese dioxide, filtering, and precipitating the MnTT and (SO4)-- in solution by using barium hydroxide. The barium dithionate remaining in solution was then treated with sulfuric acid to precipitate barium sulfate and release dithionic acid. Trithionic acid was not obtained in pure solution. By passing sulfur dioxide into a solution of potassium thiosulfate, which gives potassium trithionate, and acidifying with sulfuric acid, a solution of trithionic acid in equilibrium with the nontoxic sulfuric acid and salts was obtained whose toxicity was due primarily to trithionic acid. This preparation became slightly turbid on standing, however. Some colloidal sulfur was formed, which indicated polythionic acids. The use of hydrofluosilicic acid to obtain the free trithionic acid is precluded because hydrofluosilicic acid is itself toxic. Mixtures of pentathionic and tetrathionic acids were made by bubbling sulfur dioxide and hydrogen sulfide simultaneously into water, the sulfur dioxide being in excess. The colloidal sulfur was removed by ultra-filtration and the sulfur dioxide by aeration. Analysis of this solution by the previously mentioned method showed only these two acids to be present, exclusive of a small amount of sulfuric acid. TOXICITY TESTS-In all toxicity tests spores of Xclerotinia cinerea were used, A drop of the solution to be tested was impregnated with spores, which were then germinated in modified Van Tieghem cells a t room temperature (about 24" C.) for 16 hours. Counts of individual spores were made; a spore with no germ tube or with a dead germ tube was considered not germinated. Tests were made in both buffered and unaltered solutions. The buffered tests were made to bring out definitely the effect of the anion a t the same pH and the unaltered tests to show the effect of absolute quantities of toxic factors. (Table 11) The results given in Table I1 show that the polythionic acids are definitely more toxic than the other acids tested. Dithionic acid showed slightly greater toxicity than sulfuric acid.
Ih'Di7STRIA.L AiYD ENGINEERING CHEMISTRY
April, 1929
The toxic effects of pentathionic acid and tetrathionic acid are grouped together because it is quite probable that they mag be associated with each other on sulfur. Furthermore, it is impossible to obtain one without the other being present in quantity sufficient to vitiate toxicity values assigned to either. Table 11-Toxicity NORMALITY
of Acids of Sulfur
HzSOI
I
(H-ION COXCh )
"c
Series 1, unaltered: 0.1 0.01 0.001 0.0005 0.0001 Check
lfi 2 6 3 6 4 0 5 0 5 6
0 0 Trace 112 8fi1 92,
a I n Series 2 t h e solutions were brought t o p H 5 4 with S a O H and buffered there with K?HE'Ol-citric acid.
A direct comparison of sulfur filtrates of a given normality, with respect to hydrogen-ion concentration, with sulfuric acid of the same normality showed a distinct difference in toxicity, the sulfur filtrates being more toxic. (Table 111)
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This hydrolysis no doubt occurs a t ordinary temperatures, which accounts in part for the formation of polythionic acids. Solutions of polythionic acids of a 0.0005 N concentration are quite toxic to spores of S. cinerea and V . inaequnlis. In view of this fact, it is plainly seen how sulfur may exert its toxic effect. Practical experiments in the field lend confirmatory evidence to the laboratory tests. Certain oxidized sulfurs which employ potassium permanganate of nitric acid in small quantities apparently increase the toxicity of sulfur noticeab1p.j However, it was observed in the control of V . inaequalis that sulfurs treated with even 0.25 per cent of nitric acid tended to lose their effectiveness. These observations, although made in a limited number of cases during the course of one season, indicated that, as in laboratory tests, polythionic acids are destroyed by nitric acid, but not by potassium permanganate. Whether or not the potassium permanganate measurably increases the polythionic acid content has not been determined. Nevertheless, the permanganate sulfur was more effective in the field than any other form of sulfur dust. The potassium permanganate may possibly exert an oxidizing action such as that observed by Raschiggwhere C U - ~ oxidizes (S203)-- to (SAO~)--. Reactions which might be written as merely representative of how pentathionic acid is formed are:
s + o.+so.
Sulfur dioxide, as was stated previously, is present only in very small quantities associated with sulfur. This is ACID PERCENT SOLUTIO^ NORMALITY pH GERMINATION plainly shown by the titration of 50 cc. of a 0.003 N sulfur filtrate. One-tenth cubic centimeter (corrected) of 0.04 ili io0.01 2.1 16. 1 Filtrate from ground sulfur dine was necessary to titrate the Sos- -. This corresponds to 0.01 2.1 13.9 Sulfuric acid a molarity of 0.00008. KO more iodine was decolorized even Filtrate from ground sulfur 0.01 5.4 17.2 Sulfuric acid 0.01 5.4 96.2 when added to the sulfur suspension which contained 50 cc. Filtrate from ground sulfur 0,003 2.9 62.1 of water. Filtrate from flowers 0 003 2.7 54.4 Sulfur dioxide must be a transition product in the oxidation 0.003 2.6 87 4 Sulfuric acid of sulfur. Most of it goes to form sulfuric acid, while the Filtrate from sulfurs contained polythionic a n d sulfuric acids, the remainder is used in the formation of polythionic acids. latter in excessive amounts b When t h e reaction was too low t o permit good germination the soluBassett and Durrantl are of the opinion that trithionic acid tions were brought u p t o p H 5 4 with N a O H is the first one of that group to be formed in such a transformaAnother confirmatory evidence is that furnished by toxicity tion. No evidence of trithionic acid was obtained in the tests which involve the treatment of sulfur to remove the acids filtrates from sulfur, however. associated with it. Ammonium hydroxide and nitric acid Table IV-Increased Toxicity with Increased Aeration of Acid-Free Sulfur both possess the property of destroying polythionic acids. -, and AERATION s',",,",", GERMIXATIOX Ammonium hydroxide treatment forms (SZOJ-, (SO?) REMARK5 sulfur, while nitric acid causes the formation of SO4--- and sulfur. When sulfur was treated with these reagents and Hours Per cent then washed thoroughly with boiled water, germination proS E R I E S 1 . S U L P U R TREATED W I T H AMMONIA h-me 6.8 80.1 Tubes of normal length ceeded fairly well till the suspension became toxic owing to 1 6.05 82.0 Normal germination reaction with water and oxygen from the air. The untreated 3 5.8 47.2 Average length tubes, many dead and withered sulfur inhibited germination almost completely. Adjust8 5.2 12.1 Dead spores and tubes black 24 5.0 10.7 Same ments were made to a suitable pH for germination. S E R I E S 2, S U L F U R TREATED W l T H NITRIC ACID To show the effect of air and moisture on the formation of Sone 6.2 95.6 ?iormal germination toxic factors, filtrates were taken from sulfur that had been 1 5.8 97.2 Stimulated growth 4 5.8 27.2 M a n y tubes, long, branched made acid-free, at varying intervals of time after treatment. dark, a n d withered, dead S 4.5 Trace Few germ tubes The toxicity increased as the time of exposure of the treated 24 4.2 Trace Few germ tubes sulfur increased. (Table IV) The foregoing tests also show that ordinary sulfur itself Toxicity of Lime-Sulfur Sprays and Sulfur-Lime Dusts is not toxic but must have the polythionic acids associated with it. That this effect is due to the formation of polythionic When calcium hydroxide neutralizes pentathionic acid, acids by air oxidation of sulfur is shown by the fact that when calcium pentathionate is among the products formed. When sulfur was freed from pentathionic acid, washed, and treated this salt is acidified, pentathionic acid is again present in the with ammoniacal silver nitrate, the characteristic color ap- solution. Although calcium pentathionate itself is not toxic, peared more rapidly where aeration was used. any local condition of acidity would permit the toxic effects It is well known that sulfur hydrolyzes at high tempera- of pentathionic acid. Similar reasoning may be followed in tures2 to form products that give rise to polythionic acids. the case of lime-sulfur sprays. Considering the alkalinity of Table 111-Toxicity 11
4
of Sulfur Filtrate" a n d Sulfuric Acid
362
I N D U S T R I A L A N D ENGINEERING CHEMISTRY
lime sulfur and the partially soluble products (CaSO3,CaS203, CaSOd) when it is decomposed on foliage, it is entirely within reason to expect weathering to allow the production of polythionic acids on the precipitated sulfur. It was observed that sunlight and other natural conditions accelerate the formation of the acids of sulfur. This was quite strikingly shown when two sulfur-lime dust suspensions in water were exposed for 2 days, one closed in a flask in the laboratory and the other to open natural conditions. The suspension exposed to natural conditions lost its alkalinity so that phenolphthalein was colorless when added to the suspension, while the other remained sufficiently alkaline to give a basic reaction. It is well to consider a possible reason why the pentathionate ion from calcium pentathionate is not toxic in neutral or alkaline solution. It is not unreasonable to suppose that spore tissues are amphoteric in nature. A behavior analogous to that of amphoteric protein does not necessarily depend , ~ example, found that he on a protein-like tissue. K r ~ y tfor could duplicate Loeb’s6 work on protein by using agar, a carbohydrate. I n any case, it is conceivable that there is a
Vol. 21, No. 4
sharp line of demarcation at a certain pH, when the effect of anions becomes very marked, as in the case of Loeb’s well-known work, and this line is apparently on the acid side of neutrality. Bibliography 1-Bassett and Durrant, J . Chem. Soc., 1927, 1401. 2-Freundlich, “Colloid and Capillary Chemistry,” p. 616, E. P. Dutton & co. 3-Kruyt, “Colloids,” p. 201, John Wiley and Sons, 1927. 4-Kurtenacker and Goldbach, 2. anorg. allgem. Chem., 166, 177 (1917). 5-Lee and Martin, Science, 66, 178 (1927). 6-Loeb, “Proteins and the Theory of Colloidal Behavior,” McGrawHill Book Co., 1922. 7-Marcille, Compt. rend., 152, 780 (1911). 8-Pollacci, A f t i congrcsso intern. ckim. appl. Roma, 1, 482 (1907). 9-Raschig, “Schwefel und Stickstoff Studien,” p. 273, Leipzig University, Berlin, 1924. 10-Roach and Glynne, Ann. A p p l . Biol., 15, 168 (1928). 11-Smith, Calif. Agr. Expt. Sta., Bul2. 172, 1 (1906). 12-Sostegni and Mori, Staz. spcr. agrar. iial., 19, 257 (1890). 13-Spring, Ann., 213, 329 (1882). 14--Tisdale, Ann. Missouri Bolan. Gardens, 12, 381 (1925). 15-Young, Ibid., 9, 403 (1922). 16-Young and Williams, Sciencc, 67, 19 (1928).
Chart for the Estimation of Equivalent Cures’ C. L. Brittain GUTTAPERCHA & RUBBER, LIMITED,TORONTO, CANADA
I
N ALL heavy rubber articles the temperature conditions which obtain during curing are very different from those existing in light articles. Heat penetrates thin rubber sheets so quickly that they may be said to cure at constant temperature. Heavy articles, however, are heated very slowly, so that their cure may generally be divided into periods of rising temperature, approximately constant temperature, and falling temperature. During August, 1926, the writer developed a method of evaluating and comparing cures made under such variable temperature conditions. The principle is applicable to all cases of variable temperature cures-as, for instance, shoe-curing schedules, etc. Two papers presenting methods of estimating the curing effect of variable temperature schedules have recently appeared. Sheppard and Wiegand2 have developed equations and charts whereby curing effect may be calculated and expressed mathematically. Their method is based on the empirical relation that the intensity of curing action doubles with every rise in temperature of A” F., where A is a selected constant (in the example given, 15” F.). The method is therefore limited, in exact application, to compounds for which the temperature interval ( A ) during which the rate of cure (corresponding to intensity of curing action of the schedule) doubles is actually constant. Tests show that for many stocks the interval is not constant over the range of curing temperatures. The procedure is also limited to schedules where the rate of rise of temperature is constant. Sherwood3has developed a means of predicting the temperature rise during the cure of heavy articles, and both his and Sheppard and Wiegand’s papers present graphical methods of calculating curing effect which are not subject to the limitations mentioned in the preceding paragraph. The graphical methods have the advantage of presenting curing effect pictorially as well as mathematically. They are open to the objection that, instead of plotting the known quantity, temReceived December 5, 1928. Sheppard and Wiegand, IND.END.CHEM..20, 953 (1928). a Sherwood, Ibid., PO, 1181 (1928). 1 2
perature, one must calculate the intensity of curing action corresponding to the temperature, and plot that value. Principle of Area Diagram
The writer’s method of evaluating the curing effect of variable temperature schedules makes use of a chart of special form, termed the “area diagram.” A horizontal time scale having uniform graduations is first laid out. Any desired law connecting temperature of curing with time for optimum cure may be selected as the basis of a temperature scale. T h e vertical temperature scale is then constructed so that the distances of the temperature lines above the base line (time axis) are inversely proportional to the corresponding curing times. Then if any lines of time and temperature representing optimum cure are drawn on the chart, the rectangular area enclosed between them and the axes of the diagram will be a constant. Since the vertical distances to the temperature lines are inversely proportional to the corresponding optimum curing times, they are directly proportional to “rate of cure,” and the area then represents the product of rate of cure by time, which in any particular case indicates the state of cure of the stock. If referred to the schedule as distinct from the stock to which it is applied, the area may be regarded as the product of intensity of curing action by time, which equals curing effect. The above statement makes no reference to variable temperature cures, but the principle is easily seen to apply tothem, since if any variable temperature schedule is plotted on the chart, the area under the curve may be divided into any desired number of thin vertical strips, which may be regarded as rectangles. The sum of these small areas represents the curing effect of the schedule. In use, then, the temperature schedule under consideration is plotted on the area diagram. The resulting curve presents, graphically, the curing effect of the schedule, or the state of cure of the stock subjected to that schedule, and the area under the curve, which may best be determined by the planimeter, gives a mathematical expression of these properties. Since the known area representing.
