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INDUSTRIAL A-VD ENGINEERING CHEMISTRY
Vol. 17, No. 5
Selenium Compounds as Spray Materials'3' By F. Marion Lougee with B. S. Hopkins UNIVERSITY OF ILLINOIS, U R B A N AILL. ,
H E object of the present investigation was to study lurium. Nemec and Kas" have made a study of the influthe relative toxicities of selenium and selenium ence of selenium on the metabolism of certain molds. compounds in order to determine their suitability The effect of selenium on plants has recently become for use as insecticides, fungicides, herbicides, and the like. a subject of cohsiderable interest. TurinaI2examined the acInasmuch as selenium and sulfur are strikingly alike in their tion of selenites and selenates as well as other salts, on properties, except that compounds of selenium in general the germination of barley, mustard, and Lepidium plants, are more toxic than those of sulfur, it was believed possible and on the mature plants. He concluded that these salts that selenium may find successful application along these entered the plant system by way of the root-cap. Stoklines. 1asal3 undertook to deterThe physiological effects mine the influence of seleof selenium and its comnium on vegetable growth in Sulfur is the basis of many of our more important pounds have been the subthe presence and in the absprays. Since selenium is more toxic than sulfur, ject of rather extensive insence of radioactivity. He it should be more efficient in destroying parasitic vestigations. I n the living found that selenites were forms of life. Many solutions containing selenium in organism selenates are reinvariably more toxic than a variety of forms have been tried as spray materials duced to selenites and the selenates and that the toxagainst apple scab and bitter rot. Leaf injury is too latter to metallic selenium, icity of selenium compounds great to permit the successful use of selenium for these which is subsequently transwas inhibited by. radium purposes, but there is prospect of success in their use formed, according to Maasemanations. as dormant sprays against such pests as pear blight and s e q 3 into selenium ethyl, Such in brief is the hisoyster-shell scale. The most promising use of these Se (C2Ha)2, in the case of tory of selenium from the selenium solutions is for the eradication of broadanimals, or into selenium biological standpoint. Alleaved plants such as dandelions and plantain from though the toxicity of selemethyl, Se(CH3)2, in the fields and lawns. nium and its compounds has case of microbes. Chabri6 and L a p i c q ~ e , ~ been studied in considerable CzaDek and WeiL6 Jones.6 detail, no attempts have Woodruff and Gies,7 and Lehman,8 who have made careful apparently been made to apply either selenium or its comstudies of the effect of selenium and its compounds on the pounds along horticultural lines as spray materirtls. Such animal organism, were unable to demonstrate any direct toxic attempts were made in the present investigation. action on the cells. They conclude that selenium compounds Preliminary Experiments of 1920-21 act poisonously on the animal body as a whole and that selenites are more poisonous than selenates, whereas elementary Assuming that the principal chemical reaction involved selenium is nonpoisonous. in the manufacture of lime-sulfur is represented by the Some attempts have been made to find applications of selenium compounds in medicine, especially as remedies for equation 3Ca (OH)z 12s --.c 2CaSs Cas08 3Hz0 cancer, but the utility of selenium for this purpose is extremely selenium'4 analogs were prepared, using the proportions doubtful and Keyssergmaintains that selenium compounds are called for by the following equations: not true curative agents for cancer. Numerous investigators have studied the effects of sele3Ca0 12Se 2CaSe6 CaSezOs 6NaOH 12Se --.c 2NazSe6 NaZSezOa 3Hz0 nium compounds on widely divergent types of bacteria. Because of their ease of reduction, selenites are coming Since the lime and selenium did not unite readily when into rather extensive use for the detection of bacterial life. cooked up according to the ordinary rules for lime-sulfur, The particular effects vary with the bacterial species. the lime-selenium was prepared by fusing the materials A few studies have also been made of the effects of sele- together in a covered crucible. The resulting product, nium compounds on fungi. In 1902, Maassen and Rosen- on treatment with boiling water, dissolved to a wine-red heim10 called attention to the fact that analogous organic solution, leaving considerable residue. compounds of arsenic, selenium, and tellurium are formed The soda-selenium was easily obtained by evaporating by the action of fungi and bacteria, and that it is therefore down on a steam bath aqueous sodium hydroxide and selenecessary, in applying the biological test for arsenic, to take nium in the proper proportions. The product was, when into consideration the possible presence of selenium and tel- freshly prepared, completely soluble in water t0.a mahoganyred solution, but the solubility decreased on standing, owing 1 Received September 27, 1924. to the separation of elementary selenium. 2 Submitted by Miss Lougee to the faculty of the Graduate School of the University of Illinois in partial fulfilment of the requirements for the degree These materials were subjected to a series of laboratory
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of doctor of philosophy. a Arb. kais. Gesundh., 1 8 8 , 475 (1902). 4 Compl. Yend., 110, 152 (1890). 6 Arch. e r p . Path. Pharmakol., 32, 438 (1893). 6 Biochem. J . , 4, 405 (1909). 7 A m . J . Physiol., 6 , 29 (1902). 8 Biochem. Z., 134, 390 (1922). 9 Z . Chemolhcrapie, 11 Orig., 188 (1914). 10 Proc. Chem. Soc. (London), 18, 138 (1902).
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Compl. rend., 171, 746 (1920). Biochem. Z., 129, 507 (1922). Compl. rend,, 174, 1075 (1922); 174, 1256 (1922), Biochem. Z . ,
130, 604 (1922). I4 The selenium used in all experiments, unless otherwise specified, was the gray, metallic selenium supplied by the Baltimore Copper Smelting and Refining Company. Selenious acid from the same source was also used in the later experiments.
I N D U S T R I A L AI1‘D E S G I S E E R I N G CHEMISTRY
May, 1929
and field tests in the horticulture department of the university. The laboratory tests with lime-selenium showed that this material was toxic, but field tests failed to confirm the favorable results, because great difficulty was experienced in getting the lime-selenium into solution and the toxic powers of the spray did not measure up to expectations. The soda-selenium could not be criticized on grounds of insolubility, but any possible advantages were counterbalanced by its extremely caustic properties which defoliated the trees and caused the fruits to drop. Field tests were also made with atomic selenium-finely powdered, gray, metallic selenium-but the indications were that this material was altogether too coarse to be of any value as an insecticide or fungicide. Colloidal red selenium was used in the next field tests. This was prepared by boiling selenium with aqueous sodium sulfite solution, diluting and acidifying with a few drops of dilute sulfuric acid according to the method of Julius Meyer’5 who represents the chemical reactions as follows :
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sodium selenite were sufficiently promising to warrant furt’her tests in the field. Accordingly, trees infected with the fungus causing apple blotch were sprayed with these solutions a t the rate of 7.6 liters ( 2 gallons) per tree. Each solution was made up in such a way that the concentration of selenium was 6304 parts per million, since this corresponded to the concentrations used in the laboratory experiments. These sprays gave good control of the apple blotch fungus but the foliage of the trees was severely injured. Experiments of 1922-23
In view of the foregoing results it was thought best to conduct a series of laboratory and field experiments to determine the upper and lower limits of the toxicity of selenium compounds. This work was done with the assistance of H. W. Anderson, assistant professor of pomological pathology. The considerations governing the choice of spray materials for the laboratory tests were ease of preparation and stability of compounds; hence the decision to use selePu’aaSOa Se + NaZSeSOs nious acid and sodium selenite. Owing to the few difficulNalSeSO:, HzSOa Se SO2 H20 NazSO, ties offered in the way of propagating and maintaining a This material was tried out on a single tree against Vien- satisfactory supply of spores, the fungus chosen was the turiapomi, the fungus causing apple scab, and the first se- organism causing bitter rot, Glomerella cingulatu (Stoneries’of applications apparently gave as good results as those man) Spaulding and Von Schrenk. obtained with lime-sulfur and lead arsenate, the standard LABORATORY WoRK-Six slides were sprayed by means of spray, as there was a heavy infection of scab on the fruit of an atomizer with a standard solution of selenious acid, and the trees used as checks. Unfortunately, however, serious six other slides with sodium selenite. After the spray had injury to the trees later developed. dried, five drops of water in which spores were held in suspension were placed on each slide, which was then put in a Experiments of 1921-22 Petri dish along with a check in the form of an unsprayed Since the results of the earlier experiments were by no slide also bearing five drops of water holding suspended spores. means conclusive and the necessity of testing the sprays The Petri dishes were kept in a 20” C. incubator and counts under a variety of conditions was recognized, it was deemed of the germinated spores made a t regular intervals. In the advisable to cooperate with the department of horticulture standard solutions of selenious acid and sodium selenite the in carrying out a series of laboratory and field tests to estab- concentration of selenium was 6304 parts per million. These lish more definitely the i possibilities of selenium sprays. solutions were used a t different dilutions ranging from 6304 During the fall and winter of 1921-22, Emil Guba, research to 63.04 parts per million. Repeated experiments showed that the minimum strength assistant for W. A. Ruth, assistant professor of pomological pathology, carried out a series of laboratory tests against of selenious acid that permitted no germination of spores Phyllosticta solitaria, E & E, the fungus causing apple blotch, was one-third that of the standard solution, while none of using solutions of 200-mesh lime-selenium, freshly prepared the concentrations of sodium selenite used gave complete soda-selenium, potassium polyselenide, and sodium selenite, inhibition. The next step was to test the sprays under field conditions with the corresponding sulfur compounds to serve as checks. The potassium polyselenide was designated in the ear- in order to determine whether or not the strength that prelier experiments as “potassium selenosulfocarbonate,” be- vented germination of spores in the laboratory would show cause it was made by passing hydrogen selenide in excess equal efficiency in the orchard without any accompanying into the calculated amounts of strong potash solution and injury to the trees. FIELDWORK-Before application of the sprays on the large carbon disulfide in the expectation of obtaining a solution of K1CSeS2, analogous to potassium sulfocarbonate, K2CS3, scale, preliminary tests were made by spraying separace which is used to destroy the phylloxera of grapevines. That branches with the solutions, using an atomizer. I n this way such a compound was not formed, however, and that the dark it was found that the concentration that prevented germinawine-red liquid obtained was a solution of potassium poly- tion of spores in the laboratory experiments injured the oliselenide became apparent later when it was found that the age of the trees in every case. Hence the sprays were furvolume of carbon disulfide remained unchanged after the ther diluted for application on the large scale. The conhydrogen selenide was passed into it. The true chemical centration of selenium in the selenious acid used was 350 parts per million; in the sodium selenite, 500 parts per milreactions, therefore, may be represented as follows: lion; and in the potassium polyselenide, which was also H2Se 2KOH K2Se 2H20 used in the field tests, 2100 parts per million. A power spray 2H&e 0 2 2Se 2H20 rig was used for the application of the materials and two K2Se (X - 1) Se -,KZSe, The sodium selenite was made by neutralizing commercial Ben Davis trees were sprayed with each solution, allowing selenious acid with caustic soda in accordance with the 56.7 liters (15 gallons) per tree. A seventh unsprayed tree served as a check. equation The first spray applied was the calyx spray, May 14, 1923. H~Se03 2NaOH + NanSeOa 2H20 A heavy rainstorm followed about an hour after applicaThe laboratory tests with the lime-selenium and soda- tion so that it was impossible to determine the effects of the selenium indicated that the toxicity of these compounds solutions. The next spray was put on a little over a week was comparatively low, but the potassium polyselenide and later, on May 25. The trees were subsequently kept under: 1b 2. Elektrochem., 25, SO (1919). observation and it was soon evident that considerable in-
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jury was developing. As approximately half of the leaf surface turned brown, it was considered wise not to apply the full number of sprays, as it seemed highly probable that concentrations weak enough to insure against injury to the foliage would not be strong enough to prevent the growth of the undesirable fungi. Experiments of 1923-24
In spite of these rather discouraging results, it was still believed possible that the toxicity of selenium might find some useful applications. Inasmuch as selenium compounds had shown themselves injurious to the foliage of trees as well t as to fungi, it seemed likely that these compounds might prove effective as dormant sprays, or as sprays to be applied to the trunks or branches of trees, which are comparatively resistant. Furthermore, consideration of the fact that the intensity of injury from the selenium compounds corresponded roughly to the amount of leaf surface presented, suggested the possibility of using these compounds for the eradication of weeds. I n order to test the correctness of this theory, rather extensive experiments were carried out in the summer and fall, using selenium compounds as sprays against various obnoxious weeds. Selenious acid and sodium selenite in varying volumes a t concentrations of selenium ranging from 791 to 19,180 parts per million in the case of the selenious acid and 791 to 18,978 parts per million in the case of the sodium selenite, were applied to plots of known area on which dandelions, plantain, burdock, grass, and clover were growing and observations were made a t regular intervals. The stronger solutions attacked and injured all the vegetation, but with selenious acid a t a concentration of 791 parts of selenium per million applied a t the rate of 1.2 liters per square meter (1 liter per square yard), the dandelions, plantain, and burdock were completely shriveled, while the grass and clover suffered very little injury. A second series of experiments made in early spring, using a concentration of selenious acid equivalent to 614 parts of selenium per million applied a t the rate of 1350 cc. per square meter (125 cc. per square foot), resulted in severe injury to the grass and clover as well as to the dandelions, plantain, and burdock. These results, which failed to harmonize with the results of the earlier experiments, might possibly be explained on the basis of the relatively greater susceptibility to injury shown by all young vegetation. An application of 100 cc. of selenious acid containing 6140 parts of selenium per million to individual dandelions destroyed these without any attendant injury to the surrounding vegetation. I n pursuance of the idea that selenium compounds might prove effective as dormant sprays, or as sprays that would not of necessity involve application to the leafy parts of the trees, it was thought possible that pear blight might be combated successfully by means of selenium preparations. Hence a pure culture of Bacillus amylovorus (Burr) Trev. was secured and a series of laboratory tests made in order to determine which compounds would be effective. A loopful of a beef broth culture of the organism causing pear blight was transferred to 5 cc. of each of the various solutions, and after the bacteria had been exposed to the action of the chemicals for a definite number of minutes, a loopful was removed from each test tube, introduced into sterile beef broth, and left for incubation a t room temperature or in the 30" C. incubator. Growth of bacteria was indicated by turbidity of the medium. The solutions used were sodium selenite, selenious acid, alcoholic selenious acid, furfural and selenious acid, furfural alone, and ammoniacal zinc selenite made by dissolving precipitated zinc selenite in concentrated ammonium hydrox-
Vol. 17, No. 5
ide. The inclusion of the last-named compound in the test materials was prompted by recollection of the experiments of Hayward Reed, of Sacramento, Calif., who attained some degree of success in his experiments with zinc chloride against the pear-blight bacillus.l6 The most promising of all the materials tested was selenious acid. This acid at a selenium concentration of 6140 parts per million caused the death of the organisms in the case of cultures 1, 2, and 3 months old, whereas 24-hour cultures were killed by a concentration of 682 parts of selenium per million, as shown by the following table: Effect of Selenious Acid on 24-Hour Cultures
Concn of selenium
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6140 3070 2146 1535 1228 1023 877 767 682 614 55s 512 472 438 409 384 361 34 1 323 317
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Inasmuch as bacteria of various ages would be encountered under field conditions, it was deemed advisable to adopt selenious acid containing 6140 parts of selenium per million as the standard solution for subsequent field work on pear blight. Accordingly, in preparation for the field tests, an attempt was made April 16, 1924, to inoculate twigs of pear trees in one of the university orchards by means of the laboratory cultures. The field tests were never carried out, however, owing to the failure of the attempted inoculation, which might have been due to a lack of virulence on the part of the cultures, or to very unfavorable weather conditions. A few minor experiments were carried out against oystershell scale, Lepidosaphes ulmi, with the idea that the same concentration of selenious acid that had proved effective under laboratory conditions against the organism causing pear blight might also be effective in this case. Two small willow trees about 1 and 1.7 meters (3 and 5 feet) high, respectively, were sprayed March 27, 1924, with the standard selenious acid a t the rate of 1.9 liters (0.5 gallon) per tree, 3.78 liters (1 gallon) of the spray were also applied April 5 , 1924, to a white lilac bush about 2 meters (7 feet) high, which was badly infested with the scale. A week later the scale was dry, showing a tendency to slough off, and observations made on the lilac bush at various times during the spring indicated that it was in a healthy condition. More extensive experiments with the selenious acid against pear blight and oyster-shell scale could not be undertaken at the time, but it is hoped that the investigation can be continued at a later date. Conclusions
1-The selenium sprays so far tested are unsatisfactory for application to the leafy parts of trees, because the concentrations that prevent germination of fungal spores of such diseases as apple blotch and bitter rot are injurious to the foliage of trees. 2-The caustic properties of selenium compounds which make them undesirable for spraying trees in leaf may not prevent their possible usefulness as dormant sprays or sprays to be applied to the more resistant parts of trees or other 18
A m . Fruit Growers' Mag., June, 1923
INDUSTRIAL A N D ENGISEERIiL'G CHEMISTRY
May, 1925
plants. -4mong the diseases or insect pests which might be combated successfully by means of such sprays are pear blight, oyster-shell scale, blister canker, crown-gall, and the like.
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3-Selenium compounds are deleterious to certain plants such as dandelions, plantain, burdock, etc., while the injury to grass and clover is less severe; hence these chemicals may prove useful as weed eradicators.
The Determination of Cyanamide' By L. A. Pinck FIXEDNITROGEN RESEARCH L,4BORATORY, ~ ' A S H I N G T O Z I ,D.
ET'ERAL methods and many modifications have been proposed for the quantitative determination of cyanamide. Nearly all of them are based on the precipitation of cyanamide as a silver salt, and the determination of the cyanamide on the basis of nitrogen or silver.
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Previous Methods
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low in others, That the solubility of the silver cyanamide, either in the solution from which it was precipitated or distilled water, was not in part responsible for the unsatisfactory results was soon demonstrated, and hence attention was directed to the effect of the presence of various quan& ties of cyanamide deriua-1 tives.
Perotti2 first developed Experimental In the course of an investigation at this laboratory a titration method consiston cyanamide and some of its derivatives, unsatisfacA serieb of cyanamide ing in the addition of an amtory results were obtained in the quantitative deterdeterminations was theremoniacal extract of calcium mination of cyanamide, particularly in the presence of fore made on crude calcium c y a n a m i d e to a definite relatively large amounts of derivatives, such as dicycyanamide extracts to which quantity of silver nitrate anodiamide, urea, guanylurea, and guanidine. A study varying amounts of urea, solution, the filtration of the was therefore made of the effect of various concentraguanylurea sulfate, guanisilver cyanamide precipitions of these compounds on the determination of dine nitrate, and dicyanotate, and the titration of the cyanamide in the two most promising analytical diamide were added. To excess sil\,er nitrate with methods. The results of this study are briefly presented each 50-cc. aliquot of crude standard thiocyanate solutogether with a description of an analytical procedure calcium cyanamide extract, t i o n . K a p p e n 3 modified for cyanamide which was developed and has been found containing approximately this method by acidifying to be very satisfactory in the work at this laboratory. 50 mg. of cyanamide nitrothe cyanamide solution to convert the calcium into 1; 11 gen, ,: 25>50, and 100 mg. a neutral s a l t a n d t h e n of t h e a b o v e substances adding a slight excess of ammonia. He also stipulated the were added. The results are given in Table I. Since use of dilute solutions. Grube and Kriiger4 modified the the first set of results on the extracts containing dicyanodiKappen method by adding the silver nitrate to an acid solu- amide was divergent, that set was repeated. tion and then making it ammoniacal. In the Caro methodb of Various Cyanamide Derivatives on Determination the precipitation was made with an ammoniacal silver ace- Table I-Effectof Cyanamide by t h e Caro-Brioux Method tate solution and the cyanamide was determined by kjel- Material added P E R CENT CYANAMID€ N A S DETERMINED I N PRESENCE OF t O 0.25 gram dahling the silver cyanamide precipitate. BriouxG modicrude CaCNz Guanylurea Guanidine rDicyanodiamideGram Urea sulfate nitrate 1st set 2nd set fied the Caro method by using silver nitrate instead of the 19.12 18.97 18.87 18.95 18.87 None acetate and titrating silver in the silver cyanamide. Anot'her 1 9 . 7 6 19.58 0,005 19.09 18.97 18.92 \20.86 21.59 method, consisting in the hydrolysis of cyanamide to urea 0.025 19.13 19.15 19.07 20.38 21.66 and the determination of the latter, had been proposed by a 120.65 21.66 21.70 21.48 number of investigator^,^ but the writer did not find that 0.050 19.20 19.24 19.29 method quantitative. Marquerol and co-workers8 made a 20.20 22.90 comparative study of most of the methods and found them 0.loo 19.24 19.29 19.44 22.55 22.08 22.54 22.37 all to be inaccurate: however, the Car0 method gave the best results. These results show that the method is not reliable for samThe method employed in the early work of this laboratory ples containing large amounts of cyanamide derivatives, was a combination of the Car0 and Brioux methods (hereafter referred to as the Caro-Brioux method), consisting of dicyanodiamide interfering most. The development of a volumetric method in which cyanthe addition of silver nitrate solution to an ammoniacal solution of cyanamide and t'he determination of the nitrogen amide derivatives would not interfere was then undertaken. in the silver cyanamide by the Kjeldahl-Gunning method. To a 50-cc. aliquot of crude calcium cyanamide extract there The results were unsatisfactory, being high in some cases and were added 1 cc. of concentrated ammonium hydroxide and varying amounts of ammoniacal silver nitrate solution. 1 Received March 7. 1925. The silver cyanamide precipitate was filtered off a t the end Gas. chim. ita2., 36, 11, 230 (1905). of 2 hours. The silver was determined either in the filtrate 3 Landw.Vers.- Sla., 70, 455 (1909). or in the precipitate by means of potassium thiocyanate 4 Z . angew. Chem., 87, I, 326 (1914). ' Ibid., 8 3 , 2405 (1910). in acid solution. The Caro-Brioux method was used as a ' A n n . sci. agron., April, 1910. check. Table I1 shows the results obtained with different 7 Monnier, Chem. Z l g . , 86, 601 (1911); Fosse, et a l . , c ' o m p f . r e n d . , 179, samples of calcium cyanamide (or mixtures containing cyan408 (1924). amide) and with varying amounts of silver nitrate. 6 .Ann. chim. anal., [2] 2 , 164 (1920).
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