■ ' > ' \ ■ / ' . A STUDY OF SOME OF THE TOXIC COMPOUNDS OF SELENIUM BY FLORA MARION LOUGEE A. B. Bates College 1914 THESIS Submitted in Partial Fulfillment of the Requirements for the Degree of MASTER OF ARTS IN CHEMISTRY IN THE GRADUATE SCHOOL OF THE UNIVERSITY OF ILLINOIS 1921 \t£\ u'S'S.B Csi Ol~ UJ CO QC r*) UNIVERSITY OF ILLINOIS THE GRADUATE SCHOOL June 2, 192L I HEREBY RECOMMEND THAT THE THESIS PREPARED UNDER MY SUPERVISION BY TOIL LQUGKE — ENTITLED A. .STUDY Off SOME, QJ 1 THE TCLKIC , COMPOUNDS Off BE ACCEPTED AS FULFILLING THIS PART OF THE REQUIREMENTS FOR THE DEGREE OF Master o£- Arts irnCneir, jjstry Recommendation concurred in* Committee on Final Examination* ^Required for doctor’s degree but not for master’s Digitized by the Internet Archive in 2015 https://archive.org/details/studyofsomeoftoxOOIoug An Acknowledgement . (The experimental work described in this thesis was carried out under the direction of Dr. B.S. Hopkins, Head of the Division of Inor- ganic Chemistry, whose ever ready interest and advice were an unfailing source of inspiration and encouragement . Thanks are also due Dr. W. A. Ruth, assistant Professor of Pomology, for his kindly assistance in the matter of field tests for the materials prepared. 1 Table of Contents. page I. Introduction . A. Nature of Research Problem 1. Object. 2. Origin 3. Limitation of field of investigation B. Preparation for Experimental Work 1. Study of literature relative to lime-sulfur a. Preparation b. Chemical composition c. Properties d. Uses II. Description of Experimental Work A. Lime-Sulfur 1. Preparation 2. Analysis B. Lime-Selenium Solution 1. Unsuccessful experiments, using a. Gray selenium (1) Use of a modified lime-sulfur formula (2) Fusion of selenium and calcium b. Red Selenium (1) Use of a modified lime-sulfur formula 2. Successful experiments, using a. Gray selenium (1) Use of a modified lime-sulfur formula (a) Attempts at analysis (b) Effect of varying proportions O) to ' (c) Properties 2 pages (x) Lab tests ( y ) Field tests C. Soda-Selenium Solution 12 1. Preparation 2. Properties D. Atomic Selenium 13 1. Field tests E. Ammonium Polyselenide 13 1. Preparation 2. Properties P. Colloidal Selenium 14 1. Preparation 2. Properties a. Lab tests b. Field tests III. Conclusions 15 A. Significance of results 15 B. Future possibilities 15 1. Modifications of earlier experiments 2. Extension of previous work 3. Pests with ammonium polyselenide 4. Tests with carbon diselenide IV. Summary 16 A Study of Some of the Toxic Compounds of Selenium. 3 I Introduction. A. Nature of Research Problem: The object of the research here described was an investigation of selenium compounds which gave promise of exhibiting toxic powers, The idea for this problem grew out of a careful consideration of the close analogy between the physical and chemical properties of selenium and sulfur and a realisation of the limitations of the sul- fur compounds at present employed as insecticides and fungicides. It is a well-known fact that selenium and its compounds are, in general, more toxic than sulfur and its compounds, and this tox- icity of selenium has been the subject of considerable investiga- tion in biological and physiological fields; but no attempts have apparently been made to try the effect of substituting selenium for sulfur in the insecticides and fungicides now in use. In the re- search here described, the effect of such a substitution was studied in the hope that selenium might prove superior to sulfur in appli- cations of this kind. Since the properties of selenium and sulfur are very closely allied, as previously stated, it will not be necessary to discuss the history of selenium and its compounds. Y/e will merely note in passing that selenium, like sulfur, occurs in three allotropic forms: (1) Liquid selenium, of which there are three varieties, -- viz., the vitreous, the amorphous and colloidal selenium; (2) cry- stalline, red selenium; and (3) crystalline, gray or metallic selen- ium, which was the material that constituted the basis of the pres- ent experiments. i • . - r ■ . - . . 4 B. Preparation for Experimental Work: The first selenium preparation to be attempted was a lime- selenium solution corresponding to the commercial 'lime-sulfur.” In order to understand Just what experimental conditions would be most desirable, a study of the methods of preparation, the chem- ical composition, the properties and uses of lime-sulfur was un- dertaken. The formulas for the preparation of the lime-sulfur sprays now on the market are numerous, the ratio of lime to sulfur vary- ing from 1:2 to 1:2.25. There is a like variation in the direc- tions as to proper methods of mixing, length of boiling, etc.; but we will here confine our attention to the procedure followed in the preparation of one of the standard commercial lime-sulfurs. Water is added to fifty pounds of quicklime in sufficient quantity to start vigorous action and before the heat of slaking is dissipated, a hundred pounds of sulfur are stirred in. More water is then added to make the volume up to fifty gallons and the mixture is boiled for about forty-five minutes, the water lost by evaporation being replaced from time to time as needed. The re- sulting solution on dilution to one hundred gallons, is ready for spraying purposes. Although the literature on the general subject of lime- sulfur is voluminous, the real chemical investigations have been few. Perhaps the men who have contributed most to our meager knowledge of the chemistry of lime-sulfur, are Avery (Bull. 90, Bureau of Ghem. , U.S. Dept, of Agr. ) ; Haywood (Jour. Amer. Chem. Soc. 27, 244 and Bull, 101, Bureau of Ghem., U.S. Dept, of Agr.); Thatcher (Bulls. 56 and 76, Wash. Agr. Exp. Sta. ; Jour. Amer. Chem. Soc. * . < 5 30, 63); Giboney (Cir. no. 1., Virginia State Crop Commission); Wellington (Bull. 116, Mass. Agr. Exp. Sta. ) ; Van Slyke (Bull. 329, U.Y.Agr. Exp. Sta., Geneva); Stewart (Bull. 99, Penn. Agr. Exp. Sta.); Harris (Tech. Bull. 6, Mich. Agr. Exp. Sta.); Shafer (Tech. Bull, no 11, Mich. Agr. Exp. Sta.); Thompson and Whittier (Bull, 105, Delaware Agr. Exp. Sta.); Tartar and Bradley (Jour. Ind. Eng. Chem. 2, 271); Tartar (Research Bull. no. 3, Oregon Agr. Exp. Sta.); Chapin (Bull. no. 451, U.S.Dept. ox Agr.); and Winter (Jour. Ind. Eng. Chem. 10, 545). In the earlier investigations here referred to, there is con- siderable disagreement as to the exact nature of the chemical re- actions involved in the manufacture of lime-sulfur solution; but among the more recent investigators, Tartar, Thompson and Whittier, and Chapin, the differences of opinion are few. According to these men, the primary reaction that occurs when the ratio of lime to sulfur is 1:2, is represented by the following equation: 3Ca( OH )g 4 10S - — > 2CaS4 4 CaS 2 0^ 4 SH^O. When the ratio of lime and sulfur is 1:2.25, the main reaction is: 3Ca( OH) g 4 IPS * 2Ca3205 4 3HgO. In most cases it is probable that the lime-sulfur solution contains a mixture of the tetra- and penta-sulfides . The valuation of lime-sulfur as an insecticide has been made the subject of an exhaustive investigation by Shafer. (Tech. Bull, no. 11, Mich. Agr. Exp. Sta.). His work strongly indicates that the insecticidal value of lime-sulfur solution is due principally to the following properties: (l)Its power to take up large amounts of oxygen, thus causing the insects treated to suffer from an in- sufficient supply of this element. (2) Its ability to soften the newly secreted wax (a property which is probably intimately connected with the poly sulfides present). (3) The amount of free sulfur formed in its decomposition. If these conclusions are correct, the value of lime-sulfur as an insecticide is largely dependent upon the following reactions: CaSg 4 30 — > CaSsOg 4 33 CaS4 + 30 » CaS^Qg + 23 CaS£0g — > CaSOg + S CaSOg 4 0 - ■ CaS 04 Besides its use against scale insects such as the San Jose / scale, lime-sulfur is now employed in a wide variety of ways. It has given good results against aphis, blight, apple scab, larvae of fall webworm, caterpillars, etc. It has also been used quite expensively as a sheep and cattle dip. II. Description of Experimental Work. A. Lime -Sul fur Solution: Preparation. In order to become acquainted with the technique that is re- quired in the preparation of insecticides in general, a sample lime- sulfur solution was prepared in accordance with the formula previous- ly given. Analysis . The solution was analysed by a combination of the methods em- ployed by Tartar and Harris. In preparing the samples for the ti- trations, lOcc of the filtered lime-sulfur solution was diluted to lOOcc, and lOcc aliquots used for the analyses. Each aliquot v;a 3 diluted with 30cc of distilled water before the titrations were - 7 made. The determination of the "poly sulfide sulfur" was made by titrating with decinormal HG1, using methyl orange as indicator; the "sulfide sulfur" was determined by titrating with ammoniacal zinc chloride, usinp: nickel sulfate as indicator; and the "total sulfur” was determined by oxidising with UagOg and precipitating and weighing as barium sulfate. As the results of the foregoing analyses agreed in every par- ticular with the composition consigned to lime-sulfur by Tartar and others, the chemical reactions previously given, as the most probable primary reactions between lime and sulfur, were accepted as correct and we re made the basis of the formula to be used in the x :I * e P a 't a 'ti° n of an analogous lime -selenium solution. B. Lime-Selenium Solution: Unsuccessful Experiments. Acting on the assumption that lime and selenium under condi- tions analogous to those observed in the preparation of a lime-sul- fur solution, whould react in accordance with the following equa- tion : 3Ca( OH ) 0 + lOSe — * 3CaSe4 f GaSegOg f 3HgO. 11.35 gms. of quicklime, 56 gms. of gray selenium and lllcc of wa- ter were boiled together in an open vessel over a Bunsen flame, for one hoar without any apparent chemical reaction. Only amechanical mixture of selenium and lime was left in the vessel. In the next attempt at preparation of a lime-selenium solution, quicklime (made by calcining calcium carbonate), gray selenium and water in the same proportions as before were refluxed over a Bunsen flame for twelve hours without any apparent effect. Gray selenium, and metallic calcium in the right proportions •« . \ 8 for the formation of calcium pentaselenide Ca: 5gms. Se ) were next fused in a covered crucible. The product was a hard st 6 el-gray substance of metallic luster, suggestive of a calcium- selenium alloy. The solubility of this product was very slight as it was apparently unaffected by long-continued boiling with water. When dropped red-hot into cold water, it assumed the form of di- minutive pellets which were slowly decomposed on long standing with water on a closed flask, as shown by the mulberry shade developed by the water and the disagreeable odor resembling that of CSg which was evolved whenever the flask was uncorked. The next variation from the original procedure consisted in the substitution of red selenium for the gray. The red selenium for this purpose was prepared by passing chlorine gas into a water- suspension of gray selenium; adding strong HC1 to reduce the selen- ic acid thus formed to selenious acid; and precipitating red selen- ium from the solution, by means of sulfur dioxide. The red selen- ium was filtered, washed thoroughly with distilled water, and dried in a desiccator over sulfuric acid. This red selenium, which had become plum-colored after standing for several days, was mixed in the usual proportions with water and lime (prepared by calcining CaCO 3 ) and heated on a steam bath for exactly one hour. The only apparent change was a reversion of the red selenium to the gray va- riety. No lime-selenium solution was formed. Successful Experiments. In the meantime, a better grade of quicklime was procured, and one of the earlier attempts at preparation of a lime-selenium solu- tion by use of gray selenium and the modified lime-sulfur formula was repeated. One gram of the quicklime was fused for about an hour 9 with 5.65 gras, of gray selenium, the resulting product finely po - d6red, and about 50 cc of boiling water poured upon it. A deep wine-red solution was immediately produced, indicating that the lime and sulfur had reacted at last. Analysis . Some attempts were made to analyse the lime-selenium solution by the methods previously used in the analysis of lime-sulfur; but the lime-selenium solution was much less stable than the correspon- ding solution of sulfur and lime, and its composition changed so rapidly, owing to the deposition of elementary selenium, that the results of the analyses were very unsatisfactory. The degradation of the solution was especially noticeable after dilution of the samples preliminary to their use in the titrations, and the selen- ium that settled out from the solution although red at first, had changed to gray by the time it had collected in a layer on the bot- tom of the beaker. During the titrations with HG1 , the odor of hydrogen selcnide was very distinct. Effect of Varying Proportions. The proportions used in the first lime-selenium preparation were those required for the formation of the penta-selenide . The correct proportions for production of the tetraselenide were now used. One gram of CaO was fused with 4.7084 gms. of 3e. The re- sulting product when dissolved in water gave&solution which was ap- parently as deep in color as the preceding preparation. For preparation of the triselenide, 1 gm. of CaO was fused with 3.7614 gms. of Se . The color of the solution obtained from this was red, but much paler than before. When the right proportions for the formation of calcium disel- 10 enici.6 (1 gm. Ca0:2.825 gms. of Se ) were used; the aqueous solution of the product was only slightly colored. In case of each of the above four solutions, a considerable amount of gray sludge remained after the hot water extraction, and the proportion of undissolved material noticeably increased in go- ing from the pentaselenide to the diselenide. Properties. Sinc6 a "lime -selenium solution" had evidently been actually prepared the next step was to try out its toxic powers. A possi- ble index of its promise along this line was determined by means of a simple laboratory test. Lab Pests. Half a dozen small, rectangular glass plates were equipped with rubber rings glued on at each end of the plate and over these rings the sprayed and unsprayed slides were placed after inocula- tion with viable spores. In order to determine the strength of the lime-selenium solu- tion that would be necessary to make it correspond approximately with the strength of lime-sulfur at the time when it is ready for application to the trees, the following reasoning was applied: It is commonly accepted that, for practical pur oses, .344 lbs. or 156.176 gms. of sulfur per 5 gals, of w ter are required as a spray for one tree. The necessary amount of selenium would then be found by solving for x in the following proportion: 156.18: x : :32.06:79.2. This value, 385.822 gms., would represent the quantity of selenium required per 22,634 liters of water; or 17.046 gms. would be neces- sary for every liter of water. Since 84.962 %, by weight, of lime- 11 selenium is selenium, 20.063 gins, of lime -selenium would be re- quired for each liter of water. Accordingly, for spraying the slides, approximately 2 gins, of dry lime-selenium were placed on a filter-paper and dissolved as completely as possible by pouring over it 100 cc of boiling hot wa- ter in lOcc portions. The wine -red solution thus obtained was placed in an atomiser and tiny square glass plates were sprayed with the solution. The sprayed slides were subjected to atmospher- ic conditions for 24 hours, in order to approximate the conditions that prevail in the field. The spores used in this particular experiment were the peni- cillium glancum and the aspergillius niger. Just before use, the bottles containing the spores were shaken in a shaking-machine for ten or fifteen minutes in order to ensure an even distribution of the spores, thus rendering counts unnecessary. A drop of. water from one of the bottles was then placed in the middle of each of three sprayed and three unsprayed slides and these slides were seal- ed face down over the rubber rings on the glass plates previously prepared, in such a way that the drop of water was in the center of the ring. Each of the three glass plates thus carried a sprayed slide at one end and an unsprayed slide at the other end to serve as a check. In exactly the same way , the three other glass plates were inoculated with the other variety of spores and all six plates were placed in petri dishes and set away for 48 hours. At the end of that time, the slides were examined carefully under a microscope. The spores on the unsprayed slides showed con- siderable germination, while in every instance the sprayed slides showed either no germination at all or only a slight swelling. Field Tests. 12 . These results were somewhat encouraging, hut realising the un- reliability of a single laboratory test where it would be impossi- ble to duplicate natural conditions very closely, it was decided to give the lime-selenium a trial on a larger scale. Dr. W. A. Ruth, assistant Professor of Pomology very kindly consented to subject the lime-selenium to a field test, Accordingly, two bottles, each containing 454 gms. of finely powdered lime -selenium, were turned over to Dr. P.uth, The results of the field tests were much less encouraging. In the first place, considerable difficulty was ex- perienced in getting the lime -selenium into solution; and secondly, the toxic powers of the spray, did not measure up to expectations. G. Soda-Selenium Solution: Preparation. Thinking that these difficulties might possibly be obviated if caustic soda were substituted for lime in preparing the spray, a "soda-selenium" solution was made by the simple device of evaporat- ing down on the steam bath, with frequent stirring, 97.5 gms. of HaOH, 306 gms. of gray selenium and 785 cc. of water, as required by the equation: GIIaOH + 12Se ^ 2Ha 2 Se 5 + Na 2 SeOg + 3HnO. Properties. The soda-selenium, in accordance with expectations, could not be criticised on grounds of insolubility as it dissolved readily and completely in water to a clear mahogany-red solution; but this advantage, couple 1 with any possible advant s of insecticidal or fungicidal pov/ers were rendered nil by the fact that the caustic properties of the solution were so grea as to defoliate the trees and cause the fruit to drop D. Atomic Selenium: xh6 next field tests were those made with "atomic selenium" , -- i.e., the finely powdered gray, metallic selenium; hut the indica- tions were that this material w :s altogether too coarse in its na- ture to he of any value as an insecticide or the like. E. Ammonium Polyse lenide : Believing that an ammonium polyse lenide prepared after the an- alogy of ammonium polysulfide might possess some of the properties of the latter which render it efficacious against powdery mildews, an attempt was madG to produce such a solution. Preparation. Iron selenide was first prepared hy fusing together in the proper proportions iron filings and gray selenium. A current of hydrogen selenide, produced hy dropping dilute sulfuric acid upon the iron selenide, was th6n passed through a mixture of lOcc of strong ammonia solution, 5 cc of distilled water and 9.9gms. of e- lemantary selenium, until all of the selenium was dissolved. The resulting dark red solution, after the addition of strong ammonium hydroxide, constituted the stock solution from which the diluted wash wa3 to he prepared by dissolving . o5 lh. of soft soap in .995 gals, of water and stirring into this. 005 gal. of the stock solu- tion. Properties. The toxic properties of the ammonium polyselenide were never determined through lack of facilities at the time for making the proper tests; hut the appearance and general behavior of the solu- tion would lead one to suspect that it might find applications very 14 similar to those of the corresponding ammonium poly-sulfide. F. Colloidal Selenium: The last and most promising of the selenium preparations is the colloidal red selenium which is now undergoing field tests. Preparation. In the preparation of this spray in quantities sufficient for application to one tree, 38 gms. of gray selenium were boiled fear half a minute or more with approximately fifty-gram portions of crystallised sodium sulfite and about lOOcc of water until 349 gms. of Ua 2 S 03 were used up and practically all of the selenium was dis- solved, in accordance with the equation: ITapSOg 4 Se > NagSeSOg. The resulting straw-colored solution was - filtered , diluted with water to 5 gals., stirred, 35cc of dilute H 0 SO 4 added, and the solu- tion stirred again vigorously. The chemical reaction here invol- ved is represented thus: IlagSeSOg 4 HqS 04 ^ Se 4 30g + HgO 4 UagSOq. Properties . The yellowish-red solution of colloidal selenium thus produced was applied immediately as a spray. The results of a single test with this material appeared sufficiently encouraging to warrant the preparation and application of two more samples. The latest re- ports from hr. Ruth, dated May 17th, state that the colloidal selen- ium from its behavior in the tests now being conducted is promis- ing. This spray, along with several other materials, is being tried out on a small scale in the commercial orchard on the University South Farm. Each of the sprays is applied to one tree. The col- loidal selenium, according to the statement by Dr. Ruth, SGems to . . - < 15 have given as good results in controlling apple scab as lime-sul- fur and lead arsenate which is the standard spray. There was a heavy infection of scab on the foliage of the checks. III. Cone lusions . Significance of Results. Of course the above results, no matter how encouraging, cannot be taken too seriously. Before it would be possible to pass judg- ment definitely with regard to the value of colloidal selenium as a spray, it would be necessary to subject it to field tests for more than one season, in different localities, and under varying climatic conditions, Future Possibilities. Perhaps the foregoing description of experimental work will serve better as an index of the possibilities for the future devel- opment of selenium and its compounds than as a record of actual achievement. It is evident that only a beginning has been made a- long the line of determining ways of utilising selenium in the ag- ricultural world. It is not inconceivable that some variation in the methods of preparation or application of the "lime -selenium" and "soda-selen- ium" described in this thesis, might make all the difference between success and failure in their utilisation as insecticides or fungi- cides. For example, "soda-selenium", although too caustic for many purposes, might prove effective as a dormant spray. It is possible also that the colloidal selenium, on more ex- tensive investigation, may reveal valuable properties at present en- tirely beyond our ken. V ■ * * r *\ f- 16 The ammonium polyselenide should he tested out thoroughly as a substitute for ammonium polysulfide against powdery milde~;s, as its success along this line would open up an entirely new field of possibilities. Carbon diselenide might also be tried out as a weapon against weevils and the like, because of the similarity of its properties to those of carbon disulfide. These are but a few of the possibilities suggested by the re- sults of the present experiments, but they will serve to illustrate the lines of investigation that are as yet untouched. IV. Summary . 1. A lime-sulfur solution was prepared and analysed and the results of the analyses were found to agree with those of recent chemical investigators of lime-sulfur. 2. An analogous lime-selenium solution was prepared and its analy- sis attempted, but the results were unsat isfact ory because of the unstable character of the solution. 3. The toxicity of the lime-selenium was tested both in the labora- tory and the field. 4. Laboratory tests indicated that the lime-selenium solution was strongly toxic. 5. Field tests failed to confirm the favorable results of the lab tests because of the difficulty experienced in getting the lime-se- lenium into solution. 6. A soda-selenium solution was prepared and found unsatisfactory as a spray because of the strongly caustic properties of the solu- tion 17 7. Field tests indicated that atomic selenium is too coarse a ma- terial to he of value as an insecticide or fungicide. 8. Ammonium poly selenide was prepared but its tonic powers were not tested. 9. Colloidal red selenium was prepared and subjected to field tests. 10. Latest reports indicate that the colloidal red selenium is giv- ing as good results against apple scab as lim6-sulfur and lead ar- senate, which is the standard spray.