Bulletin STATE OF ILLINOIS DEPARTMENT OF REGISTRATION AND EDUCATION DIVISION OF THE NATURAL HISTORY SURVEY STEPHEN A. FORBES. Chef Vol. XVII. BULLETIN Article V. Some Properties of Oil Emulsions Influencing Insecticidal Efficiency BY L. L. ENGLISH PRINTED BY AUTHORITY OF THE STATE OF ILLINOIS URBANA. ILLINOIS March. 1928 STATE OF ILLINOIS DEPARTMENT OP REGISTRATION AND EDUCATION A. M. SiiELTON, Director BOARD OF NATURAL RESOURCES AND CONSERVATION A. M. Sheltox, Chairman William Trllkase. Biology John W. Alvord. Engineering Henry C. Cowles. Forestry Charles M. Thompson. Representing EnsoN S. Bastin, Geology the President of the University of WiLi.iAjr A. NoYES, Chemistry Illinois THE NATURAL HISTORY SURVEY DIVISION Stephen A. Forues, Chief SciixEPP & Babxes. Printers Springfield, III. 1928 S2S73—2M FOREWORD The first sprays used for combatting San jose scale when it became estaljHshed in the United States were made mainly from Hght oils, such as kerosene. Kerosene emulsion, one of the principal insecticides in use at that time, was first recommended for the control of San Jose scale by John B. Smith, of the New Jersey Agricultural Experiment Station, in ISilT. During the next few years, when oil sprays were being tried for this pur]M>se in many parts of the country, little attention was given to the standardization of the emulsion, and in some cases kerosene and water were a])]jlieil in the form of a mechinical mixture made by forcing the two materials through a spray pump and mixing them in two jets discharged from the spray nozzle. Much injury resulted and many trees were killed, so that oil sprays as a class were more or less in disrepute for a number of years. Since li)!^, however, there has been a marked increase in the use of oil sprays, due largely to the work of Federal and State entomol- ogists with the so-called lubricating oil emulsions. These emulsions, made by several different formulae, have proved very effective and have large- ly taken the place of lime-sulfvu" in dormant si)raying for the control of San Jose and other scale insects. Entomologists and horticulturists generally have recognized that oil sprays as a class, while very effective, are dangerous to use imless prop- erly prepared. In order to be sure that a spray is safe, we need to know its exact effect on insects and plants. This means that we must recognize differences in oils and diilerences in emulsifying agents, so as to learn what kind of emulsion to use for the result desired. In the hope of throwing some light on these important cjuestions con- cerning the use of oil sprays, the investigation herein rejjorted by Mr. English was undertaken in February, IStSo, on a Crop Protection Institute fellowship established by the Standard Oil C(imi)any of Indiana. The project was directed by a committee composed of W. P. Flint, J. S. Houser, J. J. Davis, and W. C. OTvane, and the work was done at Urbana, Illinois, in cooperation with the Illinois State Natural History Survey. December, 1927. W. P. Flint. CONTENTS PAGE Foreword by W. P. Flint 233 Introduction 235 Theory of wetting 236 Angle-of-contact measurements 238 Relation between wetting ability and toxicity to aphids 240 Relation of chemical property of oil and stability of emulsion to effective- ness against aphids 244 Relation between wetting ability and toxicity to San Jose scale and oyster- shell scale 246 Relation of volatility and viscosity of oil to effectiveness against scale insects 248 Relation of chemical property of oil and stability of emulsion to effective- ness against scale insects 249 Injury to plants 253 Conclusions 255 Acknowledgments 256 Bibliography 256 Appendix A : Definitions of terms 258 Appendix B : Experimental methods 259 Appendix C: Analysis of tap water used in experiments 259 Volume XVII Article V SOME PROPERTIES OF OIL EMULSIONS INFLUENCING INSEGTIGIDAL EPFIGIENGY* L. L. English An insect's initial experience with an oil emulsion is physical. After the contact or the physical reaction, there may be chemical action. Oil. the killing agent used in emulsions, is not highly active chemically, and the oil globules are given a "coat" of material which usually is even less active chemically. As Woodman ('24) points out: "The failure of a spray is not usually dvie to a lack of toxicity but rather to the absence of certain desirable physical properties." These properties have been con- sidered in the investigations of Cooper and Nuttall ('15), Moore and Graham ('18), and others, but their importance has not been given suffi- cient attention in actual spray practice. The term "oil emulsion" is often used with the incorrect inference that all oil emulsions are alike. Some emulsions are suitable for applica- tion to foliage, while others are not. Some are more effective than others on scale insects, and those that are elifective on scale insects may not be effective on aphids. The more the subject is investigated, the greater becomes the variety of oils and the larger the number of emulsifying agents encountered. Each oil, each emulsifier, and each class of insect pest introduces factors that must be considered more or less separately. It is very difficult to isolate any one property of an emulsion and determine separately its action on insects. The physical and chemical properties of the oil, the kind and amount of emulsifying agent, and the stability of the emulsion are all so closely interlocked that one property usually cannot be varied without changing the others. There is good reason for believing that no two emulsions—and, very likely, no two lots of an emulsion made by the same formula—are exactly alike. The "in- dividuality" of any emulsion will depend upon the way in which it is put together, the manner and duration of manipulation, the type and amoimt of emulsifying agent, the kind of oil. the quality of water, and the tem- perature at the time of dispersion. Ordinarily, with the same amount of * This paper was submitted as a thesis foi- the degree of doctor of philosophy in entomology at Iowa State College of Agriculture. 1027. [235] 236 Illinois Natir^vi. History Svrvky Billetin emulsifying agent, and the same treatment, an oil of 80 to 100 viscosity* is easier to emulsify than one of ;!() to 40 viscosity. Hence, the latter more nearly approaches the unstable, "quick-breaking" ty])e of emulsion. Gen- erally, the inert emulsifying agents, such as gums, calcium caseinate, glue, etc., at the usual concentrations, give less stable emulsions than iish-oil soaps or petroleum soaps. Everything else being equal, a reduction in the amount of emulsifier reduces stability. The relative size of the globules of oil is an indication of the sta- bility of an emuLsion, and for lack of a better criterion this is used in correlating stability with efficiency. Very minute (1 micron or less), uni- form globules, exhibiting pronounced Brownian movement, indicate a very stable emulsion. But a wide range in the size of the globules (from 1 micron to 30 or 40 microns) indicates a relatively unstable emulsion. The homemade, boiled emulsion of fish-oil-soap and lubricating oil is of this latter type. Such an emulsion may be less stable than one having relatively large (10 to 15 microns), uniform droplets. Two emulsions that look identical under the microscope may differ in stability : one may be more stable than the other because of an excess of emulsifier, a differ- ent emulsifier, or the kind of water used for dispersion. The properties of oil emulsions which have been found to be import- ant and which will be discussed are: L Physical properties — (1) \\'etting ability of the emulsifying agent. (8) Volatility and viscosity of the oil. (3) Stability of the emulsion. II. Chemical properties — (1) Saturated oils.* (2) Unsaturated oils.* Theory of Wetting Various efforts have been made to establish criteria of wetting. j Robinson ('25) was unable to find a definite relation between the surface tension of the liquid and its spreading ability. Neither did he find the interfacial tension of an oil-water system to be a suitable indication. The same idea was used by Smith ('16) and by Cooper and Nuttall ('20). As there is no satisfactory technique for measuring the interfacial tension of a liquid in contact with a solid, these workers substitute a heavy oil for the solid. Measurements of this kind certainly give some indication * See definitions, Ai)peiidix A. t There are differences of opinion, especially among entomological workers, as to the distinction between wetting and spreading. Indeed, there is some doubt whether or not there is a real difference between the two phenomena. Conse- quently, there is no agreement as to what criterion should be used in deterniining the wetting ability of a spray. Woodman ('24) does not regard wetting and spreading as synonymous terms. He treats the contact-angle theory of wetting, but uses the amount of spray adhering to a glass slide as the measure of wetting. He states, however, that this is somewhat unsatisfactory. Moore ('21) and Nut- tall ('20) also make a distinction between the two terms. But neither of the terms is well defined, and it is difficult to separate the two ideas, even if there is a real difference between them. For practical purposes, then, it may be just as well to continue to use both terms, although there seems to be no fundamental distinction. Vreundlich ('22) uses the term "spreading" in speaking of liciuid-liquid systems and tne term "wetting" in speai \ ]f tlic euiKition is transposed, ///////////////// T- ' Pk;. 1. DiAGR.^nr (if Pokces Tii.vr Cos = . DkTERJII-NE the AlUI.lTY OF A LiQi-iD TO Wet the Svuface of A SOLTD. T, Thus it will be seen that the angle is a function of all three forces. For a condition of non-wetting, the angle of contact would be 1S0° and, theoretically, the drop of liquid would touch the solid at one jioint. For perfect wetting, the angle would be zero and the liquid would lie flat over the solid. Between zero and 180° there is partial wetting; and the smaller the angle of contact, the greater the wetting ability. For example, in Figure 'lA where the system is in equilibrium at 60°, the wetting ability is about twice as great as in Figure 2B, where the angle is 120°. A B Pig. 2. Di.\GRAJis Coxtrastixg the Wetting Aiiii.itie.s of Two Lujuids. 238 Illinois Natural History Survey Bullktin Angle-of-contact Measurements In practice it is difficult to measure the angle of contact of a drop of liquid. The force of gravity will flatten the drop somewhat ; it is difficult to get drops of the same size ; and the evaporation of small drops is rather rapid. Because of these difficulties it is not feasible to reflect the drop into a binocular microscope with a protractor in one barrel and measure the angle of contact. This method was tried and discarded for the simple method used by Stellwaag ('2-i).* The apparatus is simple, and the method is quite rapid and entirely practical. The necessary pieces of equipment are: (1) a container for the liquid, (2) a device for holding the object to be tested, so that it can be turned, raised, and lowered into the liquid, and (3) a protractor etched on a mirror. For this particular work a museum jar (8x15x13 cm.) was used, and a device for holding the object was made from an old microscope stand. (See Figure 3.) The jar should be perfectly level, and its rim should be coated with paraffin, so that the liquid will stand flush with the top or a little above it. Before testing, the surface of the liquid should be freshly cleaned with a glass rod. Leaves and other objects to be tested should not be handled, of course, and should be placed in the holder in a manner that will give as uniform a surface as possible. The liquid should be kept at a constant temperature. As the object is slowly lowered, the liquid either will be depressed by it or will rise to it, forming a meniscus. The object is turned until the surface of the liquid is exactly horizontal at the point of contact. Then the angle of contact is read by means of the protractor, care being exer- cised to see that the bottom of the protractor coincides with the surface of the liquid and that the midpoint coincides with the point of intersection of the liquid by the object. Suppose the liquid meets the leaf perpendicularily as in Figure 4A, the angle of contact is 90°. If, however, the liquid is depressed (Figure 4B), the angle is greater than 90°, and the leaf must be rotated to the left until the liquid meets it horizontally (Figure -iC) . The leaf should be inserted at an angle smaller than the proi)er angle of contact and slowly rotated until the liquid meets it on a horizontal * So far as known, Stellwaag is the first entomologist to use the angle of con- tact for measuring wetting- ability, and much credit is due him for pointing out the action of liquids on plant leaves of different kinds and structures, and the im- portance of wetting in the control of aphids. This method was also used by Adam and Jessop ('2.5) in determining the polarity of various solids. Trappman ('26) criticizes Stellwaag's method and prefers surface tension meas- urements. It is quite true that the determination of the angle of contact on leaves and twigs, no two of which are exactly alike, is subject to more variability than sui'face tension measurements in which nothing biological is involved. An- other di.sadvantag:e of Stellwaag's method is that the surface of the liquid must be kept uncontaminated. Also, this method is not well adapted for use with coarse suspensions. But it is fundamentally correct, and, by careful and repeated observa- tions, it affords a means of working out some of the underlying principles of spray practice. SoirE Propertiks ok On. Emui.sioxs 239 Pig. 3. Apparatus Used in Making Axglbi-op-contact Measlrements. (Photo by K. F. Auden.) 6 = 30° "mr^^- B Pig. 4. Diagrams Showing Insertion ok a Le:af into Liquids at Different Angles in Order to Measure Wetting Ability. In A, where the liquid is neither elevated nor depressed at the point of con- tact, the angle is 90°. In B. where the liquid is depressed, the angle of contact is greater than 90°, and the leaf must be rotated to the position shown in C. D represents the position to which the leaf must be rotated when the liquid is ele- vated at the point of contact, the angle being less than 90°. 240 Iii.ixois Natural History Sirvky Bullktin plane. Tliis may necessitate several trials, especially if the angle is con- siderably smaller than !)0°. Figure 4D shows the position at an angle of 40°. It is difficult to make angle-of-contact measurements with oil emul- sions because of the very thin film of oil which persistently appears on the surface; consequently, it was thought better to make a study of the emulsifying agents that were used in several emulsions. The objects to be tested were always selected fresh, and the measurements were carried out as soon after collection as possible. The liquids were kept at a tem- perature of 25° C. throughout the tests. From three to ten observations were made of each object in contact with the liquids at each dilution. The dilutions ranged from 1 per cent to 1/16 of one per cent. (For analysis of the water used for dilution, see Appendix C.) It is not to be supposed that data thus obtained on the angles of con- tact represent fixed values, but they do represent relative conditions from which reliable deductions can be made. No attempt was made to study the effect of time or repeated contact on the value of the angles. Indeed, it may be that the determinations which were made should be regarded as indications of the initial wetting ability. The hysteresis of liquid-solid systems is a study within itself. Figure 5 shows the results obtained in tests with corn, oat, and cab- bage leaves. These leaves were chosen because the hair-like structures on the corn and oat leaves and the waxy covering of the cabbage leaf make them difficult to wet ; and the angle-of-contact measurements for each emulsifying agent against these three kinds of leaves were averaged in preparing the graphs of Figure 5. From these graphs it will be noted that the soaps give much lower angles than calcium caseinate or glue. This is to be expected, after reviewing the work of Harkins, Davies and Clark ( 'IT) ; for glue, calcium caseinate, and such materials are not strong- ly polar, and are not as readily adsorbed as soaps, nor are they thrown into an interface as easily. So far as wetting ability is concerned, the soaps are in a class by themselves, both theoretically and practically, unless the spray mixture is of such composition as to destroy the soap. Rel.-xtion between Wetting Ability AND Toxicity to Aptiids That aphids are not readily killed by a spray that does not wet them, is well known. One of the reasons for adding soap to nicotine sulfate is to give the spray wetting ability. Stellwaag states that the effectiveness of a spray on aphids is almost entirely dependent on its wetting ability. The curve for soap No. 15 in Figure 5 shows almost the same angle of contact at all the dilutions used. With potash-fish-oil soap and soap No. 55, the angle begins to increase quite rapidly at dilutions of 3-2 and '4 per cent, as these soaps begin to precipitate out with hard water ;* and at * See analysis of water, Appendix C. Some Propkrtiks of On, Emilsioxs 241 weaker dilutions there is insufficient soap left to give good wetting. Di- lution causes no appreciable change in the angle of contact with calcium caseinate and glue. The angles with these materials are not much below those oljtained with water. I/U /60 /SO /40 %/20 c \ 242 Illinois Natural History Survey Billktin Table I. Summary of 17 Tests on Aphids, Showing the Relative Effectiveness OP Various Oh. Emulsions. SoMK Properties of Oil Emulsions 243 emulsion and soluble oil No. 5G, which are made with soaps that precipi- tate out with hard water, also show inefficiency. It is quite striking that soluble oil No. 56 shows a kill of only 65 per cent, while its emulsifying agent (Soap No. 55), alone, shows a kill of 88 per cent. Soluble oil No. 56 consists of about 30 per cent of soap No. 55 and 80 per cent oil ; hence, the spray contains only one-fifth as much soap as No. 55 at the same dilutions. From Figure 5 it will be seen that soap No. 55 at a dilution of 1 per cent still shows a low angle of contact. But soluble oil No. 56, being so much weaker, has soap precipitated from it quite rapidly and, hence, is low in wetting ability. Soap No. ]5, by contrast, does not precipitate out so readily, and its soluble oils maintain their efficiency. In view of the fact that fish-oil soap and soap No. 55 precipitate out in hard water, it would be logical to predict a higher per cent kill if these soaps were dispersed in distilled water instead of tap water. This pre- diction is borne out by Table II. While there are varying increases with all of the soaps, the increase from ."^i.e per cent to 73.3 per cent with fish-oil soap is particularly noteworthy. Calcium caseinate shows very little dift'erence, as would be expected. Since the soaps are more eft'ective with distilled water, it seems that the emulsions made from them should be more efifective. This, however, is not true, as will be seen in Table III. where the per cent kill for distilled water is in no case higher than the per cent kill for tap water. Here the effect of the water on the type of emulsion is introduced. If tap water precipitates out some of the soap, an enuilsion dispersed in it naturally is not as stable as one dispersed in distilled water. With the exception of emulsion No. S15 there is very little difference in stability of those diluted with tap water and those diluted with distilled water, as de- termined by centrifuging. There is no perceptible difterence in the size of the globules of the tap water emulsions and the distilled water emul- sions. If, however, the dihited emulsions are allowed to stand in cylin- ders for a few days, those made with tap water show a distinct separation of oil. Soluble oil No. 90 is very stable, and the dift'erence in stability with tap and distilled water is insufficient to be preceptible in a photo- graph. If drops of the emulsions are compared under a binocular micro- scope, those diluted with tap water seem to have more oil at the surface of the drop than the corresponding emulsions diluted with distilled water. This adsorption of oil may be a factor in the wetting of aphids and the retention of spray by them. Drops of a poor wetting spray bounce oft' the aphids, and very little is retained. Much additional work is needed to clear up the relation of wetting ability and stability to the possible concen- tration of the oil on plants and insects. 244 Illinois Naturai. Histoky Si'rvky Bvllf.tin Relation of Chemical Propektv of Oil AND Stability of Emulsion to Effectiveness Against Apiiids The kind of oil and tlie amount of emulsifying agent in an emulsion produce differences in efficiency, as sliown in Table IV. (See Figure (i.) The emulsions under items 1 and 3 in this table are relatively ineffective. These emulsions are of the quick-breaking type, but they do not have the necessary wetting ability. The emulsions under items 3, 4, 5, and (5 have the necessary wetting ability, but vary in stability. Soluble oil No. 18, an extremely stable emtilsion, the globules of which cannot be seen with the ordinary high power of the microscope, is the least effective of these four, its per cent kill being only 86.8. Soluble oil No. !)l), the globules of which can barely be seen in the photograph, gives a kill of 88.4 per cent. When the amount of emulsifying agent is reduced as in No. 17, making a less stable emulsion, the kill is 94.6 per cent. Soluble oil No. 16 has the same amount of emulsifying agent as No. 90, but it is made from a saturated oil, which in this case gives an emulsion having about the same stability as No. 17, and the kill is in very good agreement. That emulsions having globules of different sizes woidd have different properties was indicated by Moore ('23 j, and the size of globules has been correlated with toxicity to aphids in recent work by Griffin, Richardson, and Burdette ('27). As to instability, this theory is offered : The less stable the emulsion, the greater the amount of oil thrown to the surface of the spray drops, or adsorbed by them ; and a very unstable emulsion thus ap]:iroaches a water-in-oil type of spray, with a consequent increase in the amount of oil adhering to the plant or insect. The chemical difference between the saturated and unsaturated oils in these emulsions appears to be of minor importance. The dominating factors are the wetting ability and the instability of the emulsion. The experimental data indicate that the most eft'ective emulsion on aphids Table IV. SujniARY OF Tfsts ox Three Species of Aphids (T. ambrosiae. H. setariae. axd A. pomi). Showing Infltjence of Chemical Pkopebty of Oil axd Stability OF Emulsion. Item Some Propektiks of On. Ejh-i.sioxs 245 A. Stock emulsion No. 5. b:>^:.^'^'^:''^' -J?- B. Homemade lubricatingoil emul- sion. C. Soluhl.' oil .\ O "J ',. , .^' V9 /', Soluble oil No. 17. E. Soluble oil No. 16. Fii;. I). Mil lioriKiTdcit.M'iis of E.aii'i.sio.ns Used in Exi'Eiumext.s. (X 290) 246 Ii.T.iNoi.s Natiiral History Survey Bili.ktin would be one that is relatively unstable and has high wetting ability. But antagonistic factors are encountered ; for the emulsions that have high wetting ability are injurious to foliage, and chemically inert emulsions do not have high wetting ability. Relation between Wetting Ability and Toxicity to S.\x Jose and 0^STER-SHELL Scale (in the Dormant Stage) Good wetting ability, which was shown to be an important requisite of emulsions for use on aphids (Table I), is not so important in the case of oyster-shell scale and San Jose scale. In this case, the emulsions that certainly have poor wetting ability are just as effective as those having good wetting ability. This can be seen from a series of laboratory ex- periments on oyster-shell scale* (Table V) and a typical field test on San Jose scale* (Table VI). It is not necessary to discuss this point at length or to present a great many data, for similar results have been obtained by Table V. Summary of Tests ox Oyster-shell Scale, Showing Influence of Wetting Ability'. 1 Item ! Emulsion Some PRori'.KTiKs of On, Emilsioxs 247 Taui.k VII. Angles of Contact (Mean Values), Suowing Rel^vtive Ease of Wetting Various Leaves and Twigs. Object 248 Illinois N.M'ru.vi. Histouy STitvi-.v Bii.i.ktin Relation of Volatility and Viscosity of Oil TO Effectivenes.s against Scale Insects. The theory formulated by deOng from his work on citrus scales may be applied also to oyster-shell and San Jose scales. The data in Table VIII demonstrate that a spray containing an oil of 60 viscosity and 5.3 per cent volatility is not as effective against oyster-shell scale as a corre- s])onding spray containing an oil of .slightly higher viscosity and lower volatility. Likewise, a refined kerosene of 32 viscosity and 35.1 per cent volatility, emulsified with potash-fish-oil soap, is very ineffective. If the toxicity were due to penetration alone, a light oil of this nature should be more effective than heavier oils. With this in mind, a series of laboratory tests were run with oyster-shell scale to determine the action of unemulsi- fied, or "straight", oifs on the scale (Table IX). Neither the refined nor the unrefined kerosene was effective. Oil No. 31, of 60 viscosity and 5.3 per cent volatility, which was run as a check, gave practically a perfect Table VIII. Showing Relatiox of Vol.vtility akd Viscosity of Oil to Effectiveness on Oystek-shell Scale.—Dormant. Item Some Propeuties of On, Eju'esioxs 249 kill. An hour or two after twigs are treated with these light oils, there is no evidence of oil present ; whereas a distinct residue of the heavier oil persists for a week or more. Analogous results were obtained on San Jose scale, as will be seen from Table X. The light oil of high volatility was not effective when emulsified with fish-oil soap or with an inert agent or when incurjiorated in a soluljle oil. There may be a wide range of viscosity (from SO up to "JjO or 300) without any appreciable change in volatility. When the viscosity drops as low as GO, there is a rise in volatility and a decrease in effectiveness. It is believed that a suitable oil for scale control should not fall below SO viscosity and should not have a volatility of over 1 per cent. TAliLE X.* Siiowi.Mi Relation of Volatility and Viscosity of Oil to Effectiveness ox San Jose Scale. 250 Illinois Natural History Sirvey Bvllktin cent less emulsifying agent than No. 16, is a very unstable emulsion, and the difference in kill at a dilution of 5 per cent is very striking: 97.7 per cent kill for the unstable emulsion against 26.3 per cent for the stable one. Nos. S9 and SlO, although made from different oils, are both quick- breaking emulsions. Here, apparently, the unsaturated oil seems to be slightly more effective than the saturated oil. If reference is made to Table IX. showing the toxicity of undiluted volatile oils to oyster-shell scale, it will be noted that the saturated oil gave kills of 4.0 per cent and 52.7 per cent in two separate experiments, whereas the unsaturated oil gave kills of 41.7 per cent and 67.7 per cent in the same experiments. The data under items 5 and 6 in Table XI also indicate that the unsaturated Table XI. Showing Relation op Choiical Property op Oil and Stability of Emilsion Some Propertiks of Oil Emulsions 251 -1. S(,lublp nil Xi ^:^' C. Soluble oil No. 16. E. stock emulsion No. S9. 5J^; '0^^':x..v .il X. Zl. Soluble oil No. 4.-.. '« F. Stock emulsion No. SIO. Fig. 7. MKiiOPHOTOGK.\rHs of Emulsions Used i.x Experime.nts. (X 290) 252 Illinois Natural History SrRVF;Y Bulletin *i . '"fir A. Soluble oil No. 90. B. Soluble oil No. 16. C. Soliil)l(. nil No. 17. n. stock emulsion No. 210. E. Stock emul.sion No. 200. Fig. S. MicROPHOTOGRAPHS OF EiiULsioxs Used in Experiments. (X 290) Some Properties ok Oil E.mulsioxs 253 The re>ults on scale insects corroborate deOng's work hv indicating that the action of an oil emulsion in prodncing death is largely a physical one, cansing suffocation. If the action is due to penetration alone, then the oils of low viscosity shotild be more effective, because of their greater mobility. But high volatility is usually associated with low viscosity, and if death is to be effected by penetration, the oil should persist. The in- effectiveness of light volatile oils has been demonstrated by Moore and Graham (TS), who state that such oils maj' evaporate too quickly to cause Table XII. Showing Relation of Chemical Property of Oil axp Stability of Emulsion TO Effectiveness on San Jose Scale. On Peacli 254 Illinois Natural History Survey Bltlletin order to insure safety to foliage. Wherever a persistent residue is required, therefore, the difference between saturated and unsaturated oils is the most important consideration with respect to plant injury. In tests on apple foliage it has not been found necessary to use an oil of medicinal quality, i. e., an oil that shows no loss to 97 per cent sulfuric acid. An oil having a loss of 1 per cent to sulfuric acid and a viscosity of 83 has been found quite safe on apple foliage at dilutions as high as 4 per cent when emulsified with some inert material. But the incorpora- tion of a saturated oil, even of medicinal quality, in a soluble oil did not prove safe, nor did it apparently decrease the injury below that of the corresponding unsaturated oil. Although the saturated oil itself and the petroleum soap were relatively innocuous when applied separately, a safe combination of the two could not be worked out. Replacing sodium with potassium in the soap did not reduce injury ; neither did an entire change of emulsifying agent. The incorporation of a highly volatile saturated oil in a soluble oil did reduce injury considerably, but the combination was not entirely safe and was not of satisfactory insecticidal efficiency. (Tables VIII, IX, X.) In the early stages of the work, various oils were applied undiluted, or "straight", to apple twigs in order to determine their liability to cause injury. The results of a typical test are seen in Table XIII. Table XIII. Some Properties of Oil Eiivlsions 255 Conclusions Emulsifying agents used in making oil emulsions for spray purposes vary in wetting ability, as measured by Stellwaag's angle-of-contact method, and consequently cause variations in the effectiveness of the emul- sions. This is especially important in the control of aphids. The stability of oil emulsions, which is indicated to some extent by the size of the globules, is one of the principal factors in insecticidal ef- ficiency. The type of oil emulsified, the kind and amount of emulsifying agent, the quality of water used for dilution, and other factors commonly considered unimportant, are capable of causing changes in stability and consequent fluctuations in efficiency. Increased effectiveness may or may not be accompanied by an in- crease in the size of globules. Increased size of globules is the result of desirable qualities in an emulsion rather than the cause of effectiveness. For use against aphids, the most effective emulsion is one that has high wetting ability coupled with instability. Either of these factors may vary so as to be dominant. A relatively "])oor-wetting", unstable emul- sion may be more eft'ective on aphids than a "good-wetting", stable ennil- sion. If the stability of two emulsions is about the same, then the one with the greater wetting ability is the more effective on aphids. In the control of scale insects, the instability of the emulsion is the primary consideration. The less stable the emulsion, the greater its ef- ficiency. High wetting ability is not necessary for the control of San Jose scale and oyster-shell scale, because of the comparative ease with which their host plants are wetted. The emulsions used for the control of these insects should release qtiickly an oil of sufficiently high viscosity and low volatility to give a persistent residue. A saturated oil, because of its influence in some cases on the stabil- ity of the emulsion, may be more effective than an unsaturated oil. The amount of oil adhering and taking proper effect on the insect is dependent upon both the wetting ability and the instability of the emul- sion. Inadequate wetting is a common cause of inefficiency, but excessive wetting, which results in some of the emulsion running oft' from objects that are easily wetted, is also a possible cause of inefficiency. These con- ditions are dependent on the kind of emulsion and the insect involved. In order to be innocuous to plant foliage, an emulsion should be as inert chemically as possible. Soaps and unsaturated oils tend to injure foliage. Each oil emulsion should be considered as a particular iiidiz'idiial in- secticide, having properties peculiar to itself and giving results that other emulsions nia\- not. 256 Illinois Natur.u. History Survey Billktin Acknowledgments The writer hereby expresses his gratitude to Air. W. P. Flint, of the Illinois State Natural History Survey, for arranging many of the experi- ments and for suggestions and assistance from time to time; to Dr. B. A. Porter, of the U. S. Bureau of Entomology, for assistance, particularly with the San Jose scale experiments ; and to Dr. W. A. Ruth, of the Hor- ticultural Department of the University of Illinois, for the use of equip- ment and orchards, and for most friendly cooperation in every way. For a careful criticism of the manuscript, the writer is grateful to Dr. F. W. Sullivan and Dr. E. W. Adams of the Standard Oil Company (Indiana). Thanks are due, also, to these chemists and other members of the Technical De])artment of the Standard Oil Company for assistance and cooperation at all times. Most of the emulsions used in the various experiments were prepared by the laboratories of the Standard Oil Com- pany. Bibliography AnAM, Neil K., and Jessop, Gilbert 1925. Angles of contact and polarity of solid surfaces. Jovr. Chem. Soc. 127: 1863-1868. Chandler, S. C, Flint, W. P., and Hvher, L. L. 1926. Recent insecticide experiments in Illinois with lubricating oil emulsions. III. State Nat. Hist. Surv. Bull. 16: 103-126. Cooper, W. F., and Nuttall, W. H. 1915. The theory of wetting, and the determination of the wetting power of dipping and spraying fluids containing a soap basis. Joui\ Agr. 8c. 7: 219-239. deOng, E, R. 1926. Technical aspects of petroleum oils and oil sprays. Jour. Econ. Ent. 19: 733-745. deOng, E. R., Knight, H., and Chambeelin, J. C. 1927. A preliminary study of petroleum oil as an insecticide for citrus trees. Hilgardia. Calif. Agr. Exp. St a. 2: 351-383. Flint, W. P., and Bigger, J. H. 1926. The fruit-tree leaf roller and its control under Illinois conditions. III. State Nat. Hist. Surv. Ent. Circ. 9. Feeundliiii, H. 1922. Colloid and capillary chemistry. Translation by Hatfield from the third German edition. Pub. by E. P. Button Co., New York. Griffin, E. L., Richard.sox, C. H., and Burdette, C. 1927. Relation of size of oil drops to toxicity of petroleum oil emulsions to aphids. Jour. Agr. Res. 34: 727-738. Harkins, W. D., Davies, E. C. H., and Clahk, G. L. 1917. The orientation of molecules in the surface of liquids, etc. Jour. Amcr. Chem. Soc. 39: 541-96. Some Properties of Oil Emulsions 257 Hawlev, I. M. 1926. The fruit-tree leaf roller and its control by oil sprays. Utah Agr. Exi). Sta. Bull. 196. List. G. M. 1924. The oyster-shell scale. Kith Ann. Rcpt. of the State Entomologist ofColo.. 25-31. JlEi..\xi)Ei!. A. L., Spiler, a., and Greex, E. L. 1924. Oil sprays—their preparation and use for insect control. ^.Vash. Atir.Exp. Sta. Bull. 1S4. MooKE, W.. and Grah.vji. S. A. 1918. Physical properties governing the efficacy of contact insecticides. Jour. Agr. Res. 13: 523-537. Moore. W. 1921. The spreading and adherence of arsenical sprays. Univ. Minn. Teeh. Bull. 2. 1923. The need of chemistry for the student of entomology. .Jour. Econ. Ent. 16: 172-176. NlTTALI.. W. H. 1920. Wetting power and its relation to industry. Jour. Soe. Cliem. Ind. 39: 67-77. Roliixso.x, R. H. 1925. Spreaders for spray materials, and the relation of surface tension of solutions to their spreading qualities. Jour. Agr. Res. 31: 71-81. RfTH, W. A. and Kelley, V. W. 1922. Recent advances in spraying. Trans. III. Hort. Soe. (n. s.) 56: 90-103. Smith. Lorex B. 1916. Relationship between wetting power and efficiency of nicotine- sulphate and fish-oil-soap sprays. Jour. Agr. Res. 7: 389-399. Stellw.\ag. p. 1924. Die Benetzungsfahigkeit fliissiger Pflanzenschutzmittel und ihre direckte Messbarkeit nach einem neuen Verfahren. Zeits. Anyeic. Ent. 10: 163-176. Svlmax, H. L. 1920. A contribution to the study of flotation. Trans. Inst. Min. Met. (London) 29: 44-208. Trappmaxx, W. 1926. Methoden zur Priifung von Pflanzenschutzmitteln. I. Benetz- ungsfahigkeit. Arb. Biol. Anst. 14: 259-266. Wakelani), Claude. 1925. The fruit-tree leaf roller — its control in Southern Idaho by the use of oil emulsion sprays. Idaho Ayr. Ej:i>. Sta. Bull. 137. WOGLIJI, R. S. 1925. The value of sprays and fumigation for resistant black scale con- trol. Bull. Caiif. Fruit Groirers Exch. (Los Angeles). 258 Illinois Naturai, History Survey Bulletin Woodman, R. M. 1924. The physics of spray liquids. I. The properties of wetting and spreading. Jour. Pom. Hort. Sci. 4: 38-5S. YOTHERS, W. W. 1924. Mixing emulsified mineral lubricating oils with deep-well waters and lime-sulphur solutions. U. S. Deiit. Agr. Dept. Bull. 1217. Appendix A DEFINITIONS OF TERMS A saturated hydrocarbon is a compound of hydrogen and carbon in which the normal valence of carbon (four) is entirely satisfied. H H I I Example : ethane H — C C — H ! I H H An unsaturated hydrocarbon is one in which the normal valence of carbon is not satisfied; hence, the compound is more active chemically than a saturated hydrocarbon. h H I I Example: ethylene C==C I I H H A saturated oil, or white oil, is one from which the unsaturated hydrocar- bons have been removed by treatment with sulfuric acid. A saturated oil is practically inert chemically. An unsaturated oil is not as highly refined as the white oils. While an oil of this kind may consist largely of saturated hydrocarbons, not all the un- saturated hydrocarbons have been removed in refining it. Loss to Sulfuric Acid.* The loss in volume of an oil as a result of treat- ment with sulfuric acid is an index to the unsaturated hydrocarbon content. The greater the loss, the more unsaturated the oil. There is a standard method of procedure for this test. Viscosity.* This is simply defined as resistance to flow, or negative fluidity. The standard of comparison used for oils is the Saybolt test. The units used are seconds, and they represent the time required for a given volume of oil to flow through a given orifice at a definite temperature. Volatility. t This is an arbitrary test which expresses as per cent by weight, the evaporation of a given quantity of oil at 212°F for S hours. "Soluble Oil" and "Stock Emulsion". For purposes of discussion, a dis- tinction is usually made between "soluble oil" and "stock emulsion", although there is no basic difference between them, both being oil emulsions. "Soluble oils," which are more or less transparent because of the extremely fine degree of dispersion of the oil phase, are compounded petroleum products which form milky-white emulsions when diluted with water. Dendrol and Sunoco are examples. The term "stock emulsion" is used with reference to a concentrated emulsion, such as Volck, Sherwin-Williams Free-mulsion, homemade lubricating oil emulsion, etc. * The determinations of loss to sulfuric acid and of viscosity were made by the Standard Oil Company (Indiana), according to United States Government Specifi- cations for Lubricants and Liciuid Fuels and Methods of Testing, U. S. Bureau of Mines, Technical Paper 323 A., March 18, 1924. t Refer to British Engineering Standards Association, Tentative British Stand- ard Specifications 148 (1923), pages 9-10, Section 14b. Some Properties of Oil Emulsions 259 Appendix B EXPERIMENTAL METHODS Tests on aphids. Aphis pomi De G. was obtained on the water sprouts of apple; Aphis spirnrcohi Patch on Spirara i^anhoutiei Zabel; Hesteroneura selariae Thos. on a grass (Echinichloa crus-gaUi L.): and Tritocienaphis am' Jirosiae Thos. on wild lettuce (Lacttira canadensis L. ). The infested shoots were cut from the plants a short time before spraying. Nearly all the leaves were removed so that the aphids would not be protected. The shoots were then placed vertically on a revolving stand and sprayed thoroughly with a hand sprayer having bottom feed. An excessive amount of spray on the aphids was insured, i. e., as much as would adhere. After treatment, the shoots were inserted in holes in the tops of pill boxes filled with water and Isolated on squares of paper bordered with tree tanglefoot. After approximately 24 hours, the aphids were carefully removed with a camel's hair brush and counted. Tests on oyster-shell scale. For the laboratory tests with oyster-shell scale, Lrpidosaphcs iilmi Linn., infested poplar (PopiiUis dcltoidcs Marsh) twigs were used. These were trimmed uniformly, and all scales were removed except 25 to 50. the number varying with separate experiments, but never within one experiment. Five of these twigs were treated with each material, and several untreated checks of five twigs each were carried through each experiment. After treatment, the twigs were placed in a moist sand bench to grow. A ring of tanglefoot around each prevented the escape of "crawlers" at the time of hatching. Throughout the hatching period, the twigs were examined daily with a binocular microscope, and the crawlers were removed as counted. The checks usually hatched very uniformly, and the hatch on the treated blocks was calculated to "check basis". About 3,000 to 3,500 eggs hatched from each check block of five twigs. Tests on San Jose scale. All of the tests of sprays on San Jose scale (Aspidiotus prrniciosiis Comstock) were conducted in the field. In some cases, large infested branches were treated; in others, several entire trees were used in each block. The usual procedure of taking San Jose scale data was followed. A month or six weeks after treatment, twigs were collected from the various blocks, and a count of 1,000 scales was made to determine the percentage of survival. In making the counts, the scale was turned over in order that the insect itself mlglit be seen. Robust, lemon-colored ones were recorded as "alive". Brown, black, shriveled, or "off color" ones were recorded as "dsad." Appendix C ANALYSIS OF TAP WATER USED IN EXPERIMENTS Illinois State Water Survey, Sample No. 5172S, June 2S, 1924 Determinations Parts per million Iron Fe 1.2 Manganese Mn 0.0 Silica SiO, 14.1 Nonvolatile 1.8 Alumina ALO3 0.0 Calcium Ca 66.9 Magnesium Mg 31.4 Ammonia NH, 5.3 Sodium Na 34.8 Potassium K 4.1 Sulfate SO, 1.2 Nitrate NO, 1.4 Chloride CI 4.0 Alkalinity as CaC03 Phenolphthalein 0.0 Methvl Orange 376.0 Residue 380.0