UNIVERSITY OF CALIFORNIA 
 
 COLLEGE OF AGRICULTURE 
 
 AGRICULTURAL EXPERIMENT STATION 
 
 BERKELEY, CALIFORNIA 
 
 THE TANK-MIXTURE METHOD 
 OF USING OIL SPRAY 
 
 RALPH H. SMITH 
 
 BULLETIN 527 
 MAY, 1932 
 
 UNIVERSITY OF CALIFORNIA PRINTING OFFICE 
 BERKELEY, CALIFORNIA 
 
CONTENTS 
 
 PAGE 
 
 Introduction 3 
 
 Brief history of the use of oil sprays 4 
 
 Origin and development of the tank-mixture method 7 
 
 Major qualities of oil spray 11 
 
 Study of agitation in commercial spray practice 17 
 
 Experiments on spray-tank agitation 23 
 
 Power required to operate agitators 32 
 
 Study of mixtures during passage through spray hose 35 
 
 Size of oil globules 37 
 
 Factors governing quantity of oil deposited 40 
 
 Methods for determining the quantity of oil deposited 42 
 
 Oil deposited on sections of glass by proprietary emulsions 44 
 
 Oil deposited on orange leaves by proprietary emulsions and tank mixtures... 46 
 
 Orchard tests on quantity of oil deposited 48 
 
 Function of spreaders and emulsifiers in oil sprays 54 
 
 Experiments with oil sprays in control of black and citricola scales 68 
 
 Experiments with oil sprays in control of red scale 73 
 
 Advantages and shortcomings of the tank-mixture method 77 
 
 Recommendations for tank-mixture spray 82 
 
THE TANK-MIXTURE METHOD 
 OF USING OIL SPRAY" 
 
 RALPH H. SMITHS, 4 
 
 INTRODUCTION 
 
 Tank-mixture spray 5 is one in which the water, emulsifier or 
 spreader, and oil are added separately to the spray tank and a uni- 
 form mixture is produced and maintained by the agitators. This 
 method of using oil spray has been employed for five years at the 
 Citrus Experiment Station in experimental tests in comparison with 
 several leading brands of proprietary emulsions, and in regular 
 control work on the Station property. It has been tried out in more 
 than 300 experimental orchard tests. In the majority of these tests 
 the spray was applied by commercial spray operators. During the 
 years 1928 to 1930, inclusive, it received practical testing by growers 
 in the spraying of approximately 4,500 acres of citrus trees. It is 
 +imated that about one-third of all spraying of citrus trees in the 
 hern counties in 1931 was done with tank-mixture spray. 
 
 ing the past ten or fifteen years the trend of recommendations 
 nitrol has been away from the use of homemade sprays, 
 and ; horticultural industry has come to rely almost entirely upon 
 comn prepared spray materials. Owing to this fact the 
 
 decision ( *. m end the tank-mixture method has been delayed 
 
 in order the numerous factors of a technical, practical, and 
 
 industrial nature i t be studied with particular care. The evidence 
 
 i Eeeeived for pu] r arch 30, 1932. 
 
 2 Paper No. 260, Uni of California Graduate School of Tropical Agricul- 
 ture and Citrus Experiment . Riverside, California, 
 
 3 Entomologist in the Citr uent Station. 
 
 4 The author desires to acknowled the assistance rendered by J. P. La Due, 
 who, as laboratory assistant, has Lb Vently in carrying out a vast amount 
 of routine work in connection with ; ^"iments reported in this bulletin. 
 
 s There are many patented proc 3 to insecticides. Nothing pub- 
 
 lished herein is intended to be taken c . nice that processes, materials, 
 
 or means of employment thereof which are ■> <?in described or discussed, are free 
 of coverage by patent. Of necessity the ser ice which the University can render 
 in the matters dealt with in this bulletin is directed solely to advice of a technical 
 nature as to the efficacy of the processes and materials under consideration, and 
 as to what experience has indicated are appropriate and practical means for their 
 employment. 
 
4 University of California — Experiment Station 
 
 at hand shows that the highly refined oil emulsions now in use vary 
 widely in oil-depositing qualities. There is reason for believing that 
 this fact accounts for much of the irregularity in insect control and 
 injurious effects which have been experienced in the spraying of 
 citrus trees. A definite need exists, therefore, for an oil spray of 
 known composition which may be regarded as standardized. Tank- 
 mixture spray appears to meet this need satisfactorily. 
 
 BRIEF HISTORY OF THE USE OF OIL SPRAYS 
 
 Beginning of Oil Sprays. — Practically nothing was known con- 
 cerning the insecticidal value of petroleum until about 1860, or soon 
 thereafter, when kerosene began to be generally used as an illuminant. 
 From that time to the present, much attention has been given to 
 determining the most satisfactory means of applying petroleum oils 
 to trees infested with insects. In the early attempts to utilize 
 kerosene as an insecticide the undiluted oil was sometimes applied 
 directly to trees, but the results were often disastrous because, in 
 order to cover all parts of a tree, certain parts would receive such a 
 heavy coverage that serious injury would result. However, the pre- 
 ferred method was to apply the oil in a mixture with water. Since 
 soap had been used as an insecticide prior to the advent of kerosene, 
 it was logical that the two should come to be used together on the 
 assumption that the mixture would be more effective than either used 
 alone. Applying kerosene in mixture with soapy water was recom- 
 mended during the period 1870-1880. If those making the rec- 
 ommendation observed that the soap simplified the work of keeping 
 the oil mixed with the water, the fact does not appear to have been 
 recorded in the literature of that period. 
 
 Origin of Oil Spray Emulsions. — The principal objection to the 
 use of kerosene as an insecticide was the difficulty experienced in 
 keeping it dispersed in the water while applying the spray. In 1880 
 the discovery was made that a stable emulsion could be produced by 
 mixing the oil with milk and vigorously agitating the mixture. During 
 the succeeding two years much experimenting was done in the making 
 of emulsions, and in the year 1883 the Kiley-Hubbard formula for 
 kerosene emulsion, which has remained practically a standard to the 
 present time, was published. The formula is as follows: Dissolve % 
 pound of soap in 1 gallon of hot water, stir in 2 gallons of kerosene, 
 and pump the mixture through a spray nozzle one or more times to 
 produce a thick emulsion. 
 
Bul. 527] The Tank-Mixture Method of Using Oil Spray 5 
 
 Mechanical Mixtures. — Although the emulsifying of oils proved 
 to be a marked improvement over the method of mixing the oil directly 
 with the water, it was not by any means a perfect solution of the 
 problem; for much trouble was experienced from improperly made 
 emulsions and from the tendency of the oil to float out of the spray 
 mixture during the application of the spray. In 1888, E. S. Goff of 
 the New York Experiment Station reported experiments with a spray 
 device which was provided with separate chambers for containing the 
 oil and water and effected the mixing of the two substances at the 
 nozzle. A few years later, sprayers incorporating the principle sug- 
 gested by Goff were placed on the market. The pump cylinder con- 
 tained a large intake valve through which water was admitted and a 
 small valve through which oil was admitted, the mixing of the oil and 
 water being effected in the cylinder. 
 
 The development of power sprayers during the period from 
 1900 to 1910 resulted in marked improvements in agitating equip- 
 ment. This contributed materially to the stimulation of interest in 
 mechanical-mixture sprays, particularly in California. In the citrus 
 districts, where the use of emulsions had not been regarded as suc- 
 cessful as elsewhere, "mechanical mixtures" attained considerable 
 preference for many years. This type of spray is the same as the 
 present tank-mixture, except that in the latter the mixing is effected 
 entirely in the tank, no attempt is made to produce an emulsion, and 
 a spreader is used for the specific purpose of governing the safety 
 and effectiveness of the spray. The term "tank mixture" was coined 
 by W. M. Mertz of Ontario in 1928, and gradually came into 
 general use. 
 
 MisciMe Oils. — The introduction in 1904 of miscible oils, or 
 soluble oils as they are sometimes called, resulted in important changes 
 in concepts and practices relating to the use of oil sprays. The 
 principal shortcoming of oil emulsions had been that of instability. 
 Miscible oils were especially stable. They were particularly suited 
 for preparation and marketing as proprietary products and, as a 
 result, within a few years many brands were on the market. 
 
 Since miscible oils compared favorably with other oil sprays in 
 insecticidal value, mixed readily with water, and were aggressively 
 exploited by commercial enterprise, they soon largely displaced emul- 
 sions and mechanical mixtures. The idea gradually came to prevail 
 that stability was an indispensable quality for oil sprays and, also, that 
 commercially made preparations were much more dependable than 
 homemade emulsions. Emulsions continued to be used to some extent, 
 but the mechanical mixing idea was finally completely abandoned. 
 
6 University of California — Experiment Station 
 
 Lubricating -Oil Emulsions. — Two important factors were respon- 
 sible for bringing about a renewal of interest in oil emulsions. One 
 was the alarming increase in the damage caused by the San Jose scale 
 to deciduous fruit trees in certain sections of the United States and 
 the tendency to believe that the pest could not be satisfactorily con- 
 trolled by lime-sulfur spray, the remedy which had been in use for 
 many years. The other factor was the failure of fumigation with 
 hydrocyanic acid to control satisfactorily the California red scale, 
 Chrysomphalus entrant ii (Mask.), and the black scale, Saissetia oleae 
 (Bern.), in certain districts of California because the insects had 
 developed resistance to that gas. 
 
 The immediate stimulus arousing interest in emulsions was the 
 wide publicity in 1922 and 1923 given to a formula for boiled 
 lubricating-oil emulsion, sponsored by the United States Department 
 of Agriculture, and formulas for cold engine-oil emulsions, emanating 
 from the Missouri Experiment Station. These formulas, and the 
 method of emulsification, were essentially the same as those originally 
 suggested in 1880-1883 and used during the following twenty-five 
 years, with the exception that lubricating oil was specified instead of 
 kerosene, crude oil, and distillates. Lubricating-oil emulsions had 
 been described as early as 1907, and used to a limited extent in 
 certain parts of the country, especially in the spraying of citrus 
 trees in Florida, continuously up to 1922. However, it was not until 
 the latter year that the lubricating type of oil was generally recognized 
 as having an insecticidal value superior to that of the distillate oils 
 previously used. 
 
 Highly Refined Oil Emulsions. — The emulsions generally used 
 at present in spraying fruit trees of all kinds during the summer 
 are known as quick-breaking emulsions of the highly refined, 
 lubricating-oil type. 
 
 The term " quick-breaking " indicates that the emulsions are gen- 
 erally made with a minimum amount of emulsifier, and are unstable 
 in that when a drop of spray falls on a leaf, for example, the globules 
 of oil instantly rise to the surface and a high percentage of the oil 
 is deposited as the drop rolls off. This type of spray is more efficient 
 than one in which the globules float out slowly, as in a stable emulsion. 
 The emulsions now in use are not materially different in the quick- 
 breaking property from those originally made in 1880 and many 
 which have been used during the last fifty years. However, it was not 
 until the year 1925 that particular attention was called to the 
 important relation between stability and insecticidal efficiency. 
 
Bul. 527] The Tank-Mixture Method of Using Oil Spray 7 
 
 Up to 1900 kerosene and crude oil were the principal oils used 
 for spray purposes. Neither of these had been regarded as being 
 particularly satisfactory in California. In 1900 attention was directed 
 to the excellent success obtained with the use of "untreated distil- 
 late" by F. Kahles, manager of the Crocker-Sperry ranch at Santa 
 Barbara, California. In the following two years distillates came to 
 be used very extensively in California and elsewhere, and they con- 
 tinued to be used almost exclusively until the advent of oils of the 
 lubricating type, referred to in the preceding section. For a period 
 of many years, at least, the spray distillates consisted of the raw 
 products, untreated and without purification, just as they came from 
 the stills. 
 
 It was the findings of the Insecticide Laboratory of the University 
 of California which showed that the safety of an oil depends upon 
 the extent to which it has been purified subsequent to distillation, and 
 those findings formed the basis for adopting the present type of 
 highly refined spray oils. 
 
 ORIGIN AND DEVELOPMENT OF THE TANK-MIXTURE METHOD 
 
 Oil-Spray Experiments in 1926 and 1927. — As noted in the fore- 
 going discussion, sprays consisting of unemulsified oil and water, 
 known as mechanical mixtures, were recommended and used to a 
 greater or lesser extent for many years in citrus spraying in 
 California. However, this type of spray was finally abandoned. 
 
 When the author began oil-spray experiments on the control of 
 the California red scale at the Citrus Experiment Station in the 
 summer of 1926, he assumed that oils had to be emulsified in order 
 to be dependably utilized for spray purposes. Four grades of oil 
 had been obtained from refineries and the plan of the experiments 
 called for emulsifying them with calcium casemate spreader, according 
 to a formula originally suggested by A. M. Burroughs of the Missouri 
 Experiment Station. The formula is as follows : Dissolve 4 ounces 
 of calcium casemate in 1 gallon of water, stir in 2 gallons of oil, and 
 force the mixture through a spray nozzle to produce a thick emulsion. 
 
 At the outset of the experiments it was evident that no two batches 
 of emulsions were identical. The plan was to place 3 gallons of water, 
 12 ounces of calcium casemate, and 6 gallons of oil in the 300-gallon 
 spray tank and to force the mixture twice through the spray pump 
 and nozzle. In some cases, however, it was necessary to force it 
 through three or four times in order to have all of the free oil 
 incorporated in the emulsion. In many cases, on the other hand, 
 
8 University of California — Experiment Station 
 
 this procedure could not be followed because the emulsion became so 
 thick it could not be drawn through the pump. It was supposed that 
 the composition of the emulsion, particularly the size and number of 
 the oil globules, would be markedly affected each time the mixture 
 was forced through the nozzle. 
 
 In addition to these irregularities, instances occurred in which 
 the operation of the sprayer was interrupted, the interruption result- 
 ing in the floating out of varying proportions of the oil. The experi- 
 ment under way would have to be completed with an imperfect 
 mixture, or the spray thrown out and a fresh mixture prepared. 
 Furthermore, the last trees sprayed with each tank of emulsion showed 
 a distinctly heavier coating of oil than other trees, indicating that the 
 mixture in the spray tank was not uniform. Investigation showed 
 that in the case of the particular sprayer used, the agitators could be 
 speeded up sufficiently to effect a uniform mixture of oil, water, and 
 emulsifier when the ingredients were added separately to the spray 
 tank. As a result of this finding, the first experiment was repeated, 
 using the spray in the form of a tank mixture with no attempt to 
 produce an emulsion. 
 
 In 1927 a sprayer was built for experimental use at the Citrus 
 Experiment Station. It was provided with sufficient agitation to 
 permit the use of oil spray in the form of a tank mixture. The per- 
 formance of the sprayer in experiments that year and the functioning 
 of the spray, from the standpoint of insect control and safety, were 
 satisfactory. 
 
 Inception of Plan to Standardize Oil Sprays. — During the years 
 1926 and 1927, many extensive series of laboratory tests were made on 
 the control of the red scale. The data obtained presented incongruities 
 so marked as to show almost conclusively that the functioning of 
 oil-spray mixtures in general was much more variable and much less 
 understood than had been recognized. The results indicated that 
 further progress in determining the insecticidal efficiency of oils 
 depended upon obtaining a more definite knowledge of the 
 physiochemical nature of oil-spray mixtures. 
 
 Various perplexities confronted the citrus grower as a result of 
 the unprecedented exploitation of oil emulsions. Wide variations 
 occurred in the control efficiency and injurious effects of emulsions, 
 and in the majority of instances the cause remained a matter of 
 speculation and, often, controversy. During the year 1928 there were 
 about 35 brands of emulsions on the market, representing the products 
 of 17 manufacturers. The orchardist was besieged by salesmen who 
 dispensed information which, as would be expected, favored the par- 
 
Bui,. 527] The Tank-Mixture Method of Using Oil Spray 9 
 
 ticular emulsion in which each was interested and, in many instances, 
 was derogatory to all other emulsions. During' 1929 there were about 
 50 brands on the market. As a result of several conferences attended 
 by large numbers of growers, urging that something be done to remedy 
 the situation, the decision was made to initiate an investigation with 
 the object of standardizing oil sprays. 
 
 Developments During the Year 1928. — A survey of spraying con- 
 ditions at the beginning of the spray season in 1928 revealed the fact 
 that in many cases emulsions containing large amounts of free oil 
 were being used. This led to a study of the uniformity of mixtures 
 in spray tanks with the resultant discovery that the agitation in many 
 tanks was inadequate. 
 
 An extensive series of experiments was made to measure the range 
 of effective agitation in the use of oil emulsions. The interesting 
 discovery was made that it is very simple and entirely practicable to 
 provide tanks with sufficient agitation to assure a uniform mixture 
 regardless of the stability or instability of the emulsion used. More- 
 over, the experiments showed that in the case of modern sprayers it is 
 practicable to produce and maintain a uniform mixture of nnemulsified 
 oil and water even under the most adverse conditions. 
 
 Through the interest of W. M. Mertz of Ontario, and Earle 
 Baughman of Pomona, about 100 acres of citrus trees were sprayed 
 during the latter part of the spray season in 1928, using the tank- 
 mixture method. Many experiments were also made on the control 
 of red, black, and citricola scales, the spraying being done with the 
 Experiment Station sprayer. In all cases the results were as satis- 
 factory as those obtained with the prepared emulsions which were 
 used for the purpose of comparison. 
 
 Developments During the Year 1929. — An extensive series of 
 orchard tests, using the tank-mixture method, was made during 1929 
 for the purpose of obtaining further information concerning the 
 practicability of the method and to obtain dependable data on the 
 percentage of oil of given types required to control red, black, and 
 citricola scales. As a result of further interest by certain growers, 
 about 300 acres of citrus trees were commercially sprayed. The larger 
 percentage of this acreage was in Orange County, where the spraying 
 was done for red scale and red spider. Approximately 110 acres in 
 the Ontario, Pomona, and Claremont districts were sprayed for black 
 and citricola scales and red spider. 
 
 Developments During the Year 1930. — The results obtained in 1929 
 showed that the method was worthy of being given a more extensive 
 trial. The opportunity to make such a trial was afforded by the 
 
10 University of California — Experiment Station 
 
 cooperation of R. B. Denny, manager of the Indian Hill Citrus 
 Association at Pomona. Mr. Denny invited the members of his associa- 
 tion to meet on June 8, 1930, at which time the results of the investi- 
 gations of 1929 were explained, and the proposal for a commercial 
 trial was presented. As a result of the interest of growers in the 
 Pomona district and elsewhere, upwards of 4,000 acres of citrus trees 
 were sprayed by the tank-mixture method in 1930. Fifty-six 
 commercial spray operators participated in applying the spray. 
 
 Use of Tank-Mixture Spray During the Year 1931. — In the spring 
 of 1931 a careful study of the various data was made. The conclusion 
 was reached that the practicability of the tank-mixture method had 
 been amply demonstrated and that it satisfactorily met the existing 
 need for a standardized oil spray of known composition. A mimeo- 
 graphed circular containing concise directions and recommendations 
 was made available the first of July. A survey made at the close 
 of the year indicated that about one-third of all citrus spraying in 
 the southern counties was done with tank-mixture spray. 
 
 Comparative Tests at the Orange County Farm. — Early in 1926, 
 A. A. Brock, Agricultural Commissioner of Orange County, initiated 
 a project to determine in a practical manner the effect of various 
 oil emulsions on trees. As a result several leading brands of pro- 
 prietary emulsions were applied to orange trees on the Orange County 
 Farm, under his supervision, for a period of five years. From Sep- 
 tember, 1926, to April, 1929, the tests regularly included also the 
 application of a light, a medium, and a heavy oil by the tank-mixture 
 method. Applications were made monthly during the first year, 
 bimonthly during the second year, and at five-month intervals begin- 
 ning in the third year. Studies of the general reaction of the trees, 
 as indicated by leaf-drop, fruit-drop, coloring of fruit, and effect on 
 the amount of blossoming and set of fruit were made by the author. 
 Studies of effects on the composition and quality of the fruit were 
 made under the supervision of C. P. Wilson of the Research Depart- 
 ment of the California Fruit Growers' Exchange. Studies on the 
 keeping qualities of the fruit were made by C. W. Mann of the United 
 States Department of Agriculture. In addition, certain studies on 
 the rate of growth and size of fruits were made by D. D. Way nick of 
 the Association Laboratory at Anaheim. The various studies men- 
 tioned were made chiefly during the period from 1926 to the early 
 part of 1928. The merits of the tank-mixture method were not 
 specially evaluated at that time because the idea that the method 
 might be of practical value was not conceived until the summer of 
 1928. It is particularly significant, therefore, that the data obtained 
 
Bul. 527] The Tank-Mixture Method of Using Oil Spray 11 
 
 in the studies showed that, as concerned the factors evaluated, oils 
 applied as tank mixtures were equal in results to the leading brands 
 of emulsions containing corresponding" grades of oils. 
 
 MAJOR QUALITIES OF OIL SPRAY 
 
 The insecticidal efficiency of oil sprays and the harmful effects 
 of oil sprays on trees are governed, so far as the spray is concerned, 
 primarily by (1) the purity or degree of refinement of the oil, 
 (2) the heaviness of the oil as indicated by distillation range, and (3) 
 the quantity of oil deposited on the insect and tree by the spray 
 mixture. 
 
 A brief statement concerning the process by which oil is refined 
 will enable the reader to understand more fully the significance of the 
 terms "purity" and "heaviness." The refining of petroleum com- 
 prises two principal processes, distillation and purification. In simple 
 distillation the crude oil is placed in stills, where it is heated to 
 successively higher temperatures. The more volatile constituents, 
 such as gasoline, are driven off first, and these are followed in order 
 by less volatile constituents, such as kerosene, gas oil, and lubricating 
 oil. Heavy lubricating oil is given off at the highest temperature. 
 In some modern refineries the separating of the heavier fractions is 
 accomplished by means of fractioning towers operating under partial 
 vacuum. 
 
 The purification process can be explained by using kerosene as an 
 example. The kerosene distillate has a strong odor as it comes from 
 the still, produces an excessive amount of smoke when burned in a 
 lamp, and soon becomes dark. These undesirable qualities are largely 
 due to the presence of certain constituents known as unsaturated and 
 aromatic hydrocarbons, which are regarded as impurities. The puri- 
 fication of the distillate is accomplished by treating it with liquid 
 sulfur dioxide and, in the case of the more highly refined spray oils, 
 subsequently treating it with strong sulfuric acid. The unsaturated 
 and aromatic compounds dissolve in the sulfur dioxide and sulfuric 
 acid, forming a heavy dark sludge. The sludge separates to the lower 
 part of the treating tanks, where it is drawn off. The purified oil 
 is neutralized by washing with an alkaline solution, and is then 
 thoroughly washed with water. 
 
 Purity or Degree of Refinement of Spray Oils. — In the course of 
 an investigation of spray oils in 1915 and 1916 by the Insecticide 
 Laboratory of the University of California, it was found that the 
 unsaturated and aromatic hydrocarbons are particularly injurious 
 
12 
 
 University of California — Experiment Station 
 
 to trees and that the safety of an oil depends on the extent to which 
 these compounds are removed in the refining processes. The purity of 
 spray oils is determined, therefore, by the sulfonation test or sulfuric 
 acid test for these compounds, Purity is expressed in terms of the 
 percentage of oil that remains unchanged when subjected to the 
 sulfonation test. For example, an oil having a sulfonation of 90 
 
 Fig. 1. — Illustrating the sulfonation test or the effect of strong sulfuric acid 
 on spray oils of various grades of purity. Five cc of oil and 3 or 4 times that 
 quantity of strong sulfuric acid (37 N) are placed in the bottle and vigorously 
 agitated. Sufficient acid is then added to bring the oil into the graduated 
 portion of the bottle, this portion having a capacity of 5 cc. The bottles are 
 known as 50 per cent cream-test bottles and are so graduated that multiplying 
 by 2 gives the percentage of oil which does not dissolve in the acid. The 3 oils 
 shown in these test bottles are 100 per cent, 94 per cent, and 90 per cent 
 unsulfonatable. 
 
 per cent is one containing 10 per cent of the impurities mentioned 
 above ; that is, 90 per cent will remain unchanged when treated with 
 strong sulfuric acid, and the oil is said to be 90 per cent unsulfonatable 
 or to have an unsulf onated residue ora" sulfonation ' ' of 90 per cent. 
 The sulfonation test is illustrated by figure 1. 
 
 The oils used at present in spraying citrus trees in California, and 
 also in spraying deciduous trees during the summer, have ranged 
 
Bul. 527] The Tank-Mixture Method of Using Oil Spray 
 
 13 
 
 between approximately 85 and 100 per cent in snlfonation. This is 
 in marked contrast with the spray oils formerly used, which were 
 relatively unpurified. The more highly refined the oil, the less chance 
 there is of injurious effects on the trees; but, also, the more highly 
 refined the oil, the greater the cost, There is reason, therefore, to 
 compromise in the degree of refinement between the cost and the 
 possibility of injurious effects, 
 
 Fig. 2.— Saybolt Universal viscosimeter, the apparatus used for determining 
 the viscosity of spray oils and other oils of the lubricating type. The oil is heated 
 to 100° F by means of the electric heater. At that temperature a cork at the 
 bottom of the central cylinder is pulled out and the oil permitted to flow through 
 a small aperture into the flask underneath. The viscosity of an oil is the number 
 of seconds required for 60 cc to flow through the aperture. 
 
 The information obtained by experimentation and by observations 
 over a period of six years indicates that in the case of light and light- 
 medium spray oils a sulfonation of 90 to 92 per cent is reasonably 
 satisfactory. In the case of medium and heavy oils the factor of 
 injury presents a more difficult problem. Because of this fact the 
 tentative recommendation of the Citrus Experiment Station is that 
 oils falling within the medium grade should have a sulfonation not 
 lower than 93 per cent, and those falling within the heavy grade 
 should have a sulfonation not lower than 95 per cent. 
 
14 
 
 University of California — Experiment Station 
 
 Heaviness of Spray Oils. — Spray oils have been classified as light, 
 light-medium, medium, and heavy, on the basis of viscosity and also 
 on the basis of volatility or distillation range. Viscosity pertains to 
 the flowing quality of an oil. It is expressed in terms of the number 
 of seconds required for 60 cubic centimeters (approximately 2 ounces) 
 at a temperature of 100° F to flow through a small orifice in an 
 instrument known as the Saybolt Universal Viscosimeter (fig. 2). 
 
 Fig. 3. — Standard apparatus for making distillation tests of spray oils. The 
 required quantity of oil is placed in the flask, the top of which can be seen 
 bearing a thermometer in the compartment on the left. A gas burner is lighted 
 under the flask. As the oil vaporizes it passes into the condenser on the right, 
 from which it drips into the graduated cylinder at the extreme right. The 
 temperature rises gradually as the distillation proceeds, the light fractions being 
 driven off at lower temperatures than the heavier fractions. The temperature is 
 recorded at 25° F intervals, or it may be recorded each time the level of the oil 
 in the cylinder indicates that a 10 per cent portion of the oil has distilled. 
 
 Distillation range indicates the minimum and maximum temperatures 
 between which the distillation of an oil takes place, and the per- 
 centage of oil distilling at points within the range. It is determined 
 by the use of the apparatus shown in figure 3, and affords a very 
 dependable index to the volatility of oils. 
 
 The two systems of classification are not entirely consistent because 
 the viscosity of spray oils of a given volatility varies according to 
 the nature of the crude oil from which they are produced, and, also, 
 according to the manner in which they are produced. For example, a 
 certain spray oil produced from Pennsylvania crude oil, and used 
 
Bul. 527] The Tank-Mixture Method of Using Oil Spray 
 
 15 
 
 to a limited extent in spraying- citrus trees in California, has a 
 viscosity of 70 seconds ; but its volatility is nearly the same as spray 
 oils of 100 seconds viscosity produced from California crude oil. When 
 two types of oils are blended, as is commonly done in producing' spray 
 oils, the viscosity of the resultant oil may be out of line with its proper 
 rating on the basis of volatility. 
 
 It is now generally agreed that distillation range affords the most 
 satisfactory basis for grading spray oils according to the heaviness, 
 
 TABLE 1 
 
 Distillation Ranges of the Oils Contained in Two Brands of 'Light' 
 
 Emulsions, and the Series of Spray Oils Used in the 
 
 Experiments and the Commercial Trial of the 
 
 Tank-Mixture Method in 1930 
 
 
 Emulsions 
 
 Spray oils 
 
 Degrees 
 Fahrenheit 
 
 Brand No. 1 
 
 Brand No. 2 
 
 Number 1 
 
 Number 2 
 
 Number 3 
 
 Number 4 
 
 Number 5 
 
 
 Per cent distilled 
 
 550 
 
 6 
 
 33 
 
 3 
 
 1 
 
 
 
 
 
 
 
 575 
 
 24 
 
 43 
 
 21 
 
 14 
 
 9 
 
 3 
 
 1 
 
 600 
 
 48 
 
 54 
 
 46 
 
 38 
 
 27 
 
 13 
 
 4 
 
 625 
 
 67 
 
 62 
 
 70 
 
 59 
 
 50 
 
 36 
 
 19 
 
 650 
 
 78 
 
 72 
 
 86 
 
 75 
 
 69 
 
 56 
 
 43 
 
 675 
 
 90+ 
 
 77 
 
 90+ 
 
 86 
 
 82 
 
 73 
 
 59 
 
 700 
 
 
 85 
 
 
 90+ 
 
 89 
 
 84 
 
 77 
 
 725 
 
 
 90+ 
 
 
 
 90+ 
 
 90+ 
 
 86 
 
 750 
 
 
 
 
 
 
 
 90+ 
 
 because the results of research and practical experience show that the 
 insecticidal value of oils in the control of scale insects and the 
 deleterious action of oils on trees correspond most closely to the 
 volatility of the oils. The lower the volatility, the more effective is 
 the oil in destroying scale insects and the more deleterious it is to 
 the tree. Viscosity or flowing quality, in itself, does not appear to 
 be particularly important. However, grading oils on the basis of 
 viscosity has some merit in comparing oils produced from the crude 
 oil of a particular region; within such a group viscosity may be 
 regarded as a general though not a very reliable, index to volatility. 
 For example, the viscosity ranges of spray oils produced in California, 
 falling within the various grades of heaviness, are roughly as follows : 
 light, 50 to 60 seconds; light-medium, 60 to 70 seconds; medium, 70 
 to 80 seconds ; heavy, 100 to 110 seconds. 
 
16 University of California — Experiment Station 
 
 Distillation range reveals the composition of an oil as regards 
 lightness or heaviness. This point is made clear by the examples of 
 the distillation ranges of various oils shown in table 1, particularly 
 the ranges of the oils contained in the two brands of emulsions. Each 
 of these brands was sold under the designation "light emulsion." 
 The oil in No. 1 appears to be a particularly narrow-cut oil and is a 
 very desirable type for a light oil. The oil in brand No. 2 may be 
 regarded as an exceptionally wide-cut oil, but the more probable 
 interpretation is that it was produced by blending a very light oil 
 with a heavy oil like No. 5. It is not a suitable type of oil because a 
 large percentage of it, that distilling below 550 degrees, is too light 
 to be of much value in the control of scale insects ; and, furthermore, 
 the fraction distilling above 700 degrees is heavier than is necessary 
 or desirable for doing the work properly required of a light oil. Oils 
 No. 1 to No. 5, inclusive, represent those used in the commercial trial 
 of tank-mixture spray in 1930. Taken in order, they represent a 
 gradual increase in heaviness and afford a series of grades well 
 adapted to meeting the various requirements of citrus spraying. 
 
 Considering the welfare of the tree, it is desirable to use the 
 lightest oil that will effectively control the particular pest for which 
 the spray is applied. Recommendations covering the use of oils of the 
 various grades are given at the end of this bulletin. 
 
 Quantity of Oil Deposited by Spiny Mixtures. — The principal 
 consideration in the preparation of oil emulsions during the fifty 
 years in which they have been used has been to make them in such a 
 way that they will not break down prior to use ; that is, the quality 
 of an emulsion has been judged largely by its stability and the ease 
 with which it is mixable with water. Except for differences in 
 stability and mixability, the tendency has been to regard any par- 
 ticular emulsion as being essentially the same as every other emulsion. 
 The conception that oil must be emulsified in order to be utilized for 
 spray purposes has been universal. The research upon which the 
 tank-mixture method is based, and which is reported in this bulletin, 
 proves this conception to be largely erroneous and shows that in the 
 spraying of citrus trees, one of the most important characteristics of 
 an oil-spray mixture is that relating to the quantity of oil the mixture 
 deposits on the tree. 
 
Bul. 527] The Tank-Mixture Method of Using Oil Spray 
 
 17 
 
 STUDY OF AGITATION IN COMMERCIAL SPRAY PRACTICE 
 
 Throughout the history of oil sprays much emphasis has been 
 placed on the danger that the oil may rise to the surface of the water 
 because of improperly made emulsions and on breaking of emulsions 
 when mixed with water in the spray tank. In view of the fact that 
 the emulsions used in citrus spraying are relatively unstable, it was 
 supposed at the outset of the present investigation that the irregu- 
 larities experienced in insect control and injury to trees might be 
 caused, in part at least, by imperfect mixtures in the spray tank. 
 The subject of spray-tank agitation was, therefore, one of the first 
 phases of the problem to be investigated. 
 
 The efficiency of agitation depends on the capacity, shape, and 
 dimensions of the spray tank; the number and position of the 
 agitators ; the size, shape, pitch, and number of blades on the agitators ; 
 the position of the agitator shaft; and the speed at which it turns. 
 The efficiency is sometimes affected to a marked extent by braces, 
 supports, and cooling pipes which operators occasionally place in their 
 tanks. The uniformity of the spray mixture is also influenced by the 
 character of the emulsions used and by the manner in which they 
 are placed in the tank. 
 
 Description of Spray Tanks and Agitator Equipment. — Spray 
 tanks represent two types according to the form of the bottom : half- 
 round and elliptical. The elliptical-bottom tanks range from those 
 in which the bottom is uniformly rounded to those in which the 
 bottom is nearly flat along the middle portion and abruptly shouldered 
 at the sides. A few cylindrical tanks are in use, but they do not 
 represent what may be called standard equipment. Among sprayer 
 tradesmen, tanks are sometimes classified as horizontal, and transverse 
 or underslung. Horizontal tanks are those mounted parallel with 
 the frame of the truck. Transverse tanks are those mounted on a 
 low support, usually between the rear wheels of the truck. In a 
 general way, tanks are also classified as long tanks and short tanks. 
 
 Spray tanks present a wide range in dimensions. The greatest 
 range occurs in the length, and the least in the depth. The range 
 in dimensions of factory-made tanks of four sprayer manufacturers, 
 taken as a group and based on data supplied by them, is as follows : 
 
 Capacity 
 
 Range in length 
 
 Range in width 
 
 Range in depth 
 
 gallons 
 
 200 
 
 inches 
 iiV 2 to 50% 
 44% to 63% 
 43^ to 77% 
 
 inches 
 < 33 to 42 
 37 to 45 
 38% to 58 
 
 inches 
 29 to 36J^ 
 
 300... 
 
 33 to 39 
 
 400 
 
 34 to 39H 
 
 
 
18 
 
 University of California — Experiment Station 
 
 Agitators of various makes, occurring on sprayers in southern 
 California, are shown in figure 4, and data pertaining to each are 
 given in table 2. The agitators represent two types : two-bladed and 
 three-bladed. The total blade-area per agitator for those in group 1 
 ranges from 19 to 45 square inches. The length of the blades is 
 approximately 6% inches. Pitch indicates the number of degrees in 
 the angle formed by the blade and a plane at right angles to the 
 agitator shaft. The blades of agitator F (fig. 4) have a pitch of 90 
 degrees and are commonly referred to as flat blades. In the case of 
 the other agitators the pitch of the blades ranges from 30 to 60 degrees. 
 
 TABLE 2 
 Specifications or the Agitators Shown in Figure 4 
 
 
 Make of 
 
 Number of 
 
 Total area 
 
 Length of 
 
 Pitch of 
 
 
 agitator 
 
 blades 
 
 of blades 
 
 blade* 
 
 blade 
 
 
 
 
 square inches 
 
 inches 
 
 degrees 
 
 
 
 A 
 
 3 
 
 45 
 
 6H 
 
 60 
 
 
 
 B 
 
 2 
 
 19 
 
 5% 
 
 30 
 
 
 
 C 
 
 2 
 
 31 
 
 VA 
 
 60 
 
 
 
 D 
 
 2 
 
 42 
 
 6H 
 
 35 
 
 
 
 E 
 
 2 
 
 24 
 
 5H 
 
 30 
 
 
 
 F 
 
 2 
 
 28 
 
 6 
 
 90 
 
 
 
 G 
 
 2 
 
 35 
 
 6H 
 
 50 
 
 
 
 , H 
 
 2 
 
 23 
 
 6 
 
 35 
 
 Group 2 
 
 fl 
 
 2 
 
 22 
 
 5H 
 
 30 
 
 
 J 
 
 2 
 
 24 
 
 VA 
 
 30 
 
 
 u 
 
 2 
 
 45 
 
 9A 
 
 30 
 
 * Length is measured from center of shaft to tip of blade. 
 
 A study of figure 4 and the data in table 2 shows that certain 
 agitators are much more efficient than others. Agitators B, E, and H 
 are not satisfactory for use with oil sprays. Agitators A, C, D, and G 
 are particularly suitable for use with oil sprays. Agitators 7 and K of 
 group 2 are recommended for underslung tanks of 300 and 400-gallon 
 capacity in the Friend sprayer, when the agitator speed is 200 r.p.m. 
 
 The agitator shafts of the Bean, Deming, Hardie, Karth, and 
 Warlo sprayers are approximately 7% inches above the bottom of 
 the tanks. A few tanks are in use in which operators have installed 
 an additional agitator shaft in the upper part of the tank. In the 
 underslung tank of the Friend sprayer the agitator shaft extends 
 transversely and downward across the tank and is regularly equipped 
 with two agitators. 
 
 The speed of the agitator shaft, in the case of sprayers sold in 
 the citrus districts of California, has ranged from 110 to 240 r.p.m. 
 
Bul. 527] The Tank-Mixture Method of Using Oil Spray 19 
 
 During the past two or three years the speed has been more or less 
 standardized at approximately 200 r.p.m., except that the sprayers 
 regularly provided with higher speeds have retained those speeds. 
 
 Investigation of the Agitation Efficiency of Commercial Sprayers 
 in Operation. — During the summer of 1928, a study was made of the 
 
 Fig. 4. — Types of agitators used on sprayers in the citrus districts of Cali- 
 fornia, Group 1 represents agitators for horizontal tanks. Group 2 represents 
 agitators used on underslung tanks. Agitators B, E, and H are not satisfactory 
 for use with oil sprays. 
 
 agitation efficiency of 29 spray tanks. The agitators occurring in 
 these tanks, indicated according to letter as shown in figure 4, were 
 as follows : 2 tanks had five B agitators each ; 6 tanks were equipped 
 with four B agitators each; 2 tanks were equipped with four E 
 agitators each; 5 tanks had four D agitators each; 4 tanks each 
 had a set of three agitators consisting of one F and two H agitators ; 
 5 tanks had three A agitators each ; 2 tanks had homemade agitators ; 
 
20 
 
 University of California — Experiment Station 
 
 and 3 were underslung tanks, each tank having" one I and one J 
 agitator. The agitator speeds ranged from 62 to 220 r.p.m., the 
 average being about 140 r.p.m. 
 
 In most cases the agitation was decidedly unsatisfactory, judging 
 by the fact that there was only a gentle movement at the surface of 
 the spray when the tanks were full. Analyses made of samples of 
 spray taken from the 29 tanks showed that with 3 of them the 
 
 Fig. 5. — Taking samples of oil spray from nozzle (left) and determining 
 agitator speed (right), in the investigation of the agitation efficiency of sprayers. 
 The agitator speed was determined by placing one hand near the agitator 
 sprocket so that the head of the set-screw or the end of a wire fastened to the 
 sprocket struck the hand, and counting the number of revolutions per minute. 
 
 concentration of the oil in the upper part of the tanks was approxi- 
 mately twice that in the lower part. In all these tests emulsions which 
 appeared to be in fairly good condition were used and the agitators 
 were run continuously from the time the emulsions were added until 
 the tanks were emptied. 
 
 Observations on the Condition of Emulsions and the Way in Which 
 They Are Used. — During the years 1927 to 1929, inclusive, it was a 
 very common occurrence to see drums of emulsion being used in which 
 a considerable portion of the oil had separated out. This situation 
 
Bul. 527] The Tank-Mixture Method of Using Oil Spray 
 
 21 
 
 was particularly serious during the summer of 1928. During the 
 last week in September of that year, 22 spray rigs in operation were 
 
 Fig. 6. — Stirring oil into broken emulsion. During the years 1927 and 1928 
 spray operators commonly found it necessary to have stirring paddles as a part 
 of their equipment, and many cases were observed in 1929 and 1930 in which 
 broken emulsions were stirred up and used. 
 
 Fig. 7. — Drums of emulsion delivered to a grove and left in the sun several 
 days before being used. The products of three manufacturers are represented. 
 A layer of free oil from 2 to 4 inches in depth occurred at the top of the drums. 
 
 visited. Each drum of emulsion being used contained unemulsified 
 oil. The amount of unemulsified oil in different drums was estimated 
 to range from a fraction of a per cent to 30 per cent. Only two 
 
22 University of California — Experiment Station 
 
 samples were obtained which were considered to be satisfactory for use 
 in laboratory tests. Spray operators followed the practice of stirring 
 the oil into the emulsion by using long paddles which would reach 
 to the bottom of the drums (fig. 6). It appeared that the poor 
 condition of the emulsions was largely the result of their being 
 delivered to groves and left in the sun several days before they were 
 used (fig. 7). However, in several instances the emulsions were 
 badly broken when they were delivered to the groves, In same cases 
 it was asserted that the breaking took place during transportation. 
 In some instances labels on containers advised that the contents 
 should not be used if unemulsified oil was present. 
 
 Observations on the way emulsions were placed in the spray tank 
 by different operators showed that in the majority of cases the 
 endeavor was made to add the emulsion when the tank was about 
 half filled with water. However, owing to irregularities which can 
 scarcely be avoided in the operation of spray outfits, the emulsion 
 in many cases was not added until the tank was nearly full. Some- 
 times the emulsion was diluted with water and stirred thoroughly, 
 in which condition it was added directly to the tank or left in the 
 measure and added to the succeeding tank. Sometimes the emulsion 
 was washed through the screen into the tank but usually it was 
 added in mass directly to the water. A few operators had special 
 mixing devices for churning the emulsion thoroughly before placing 
 in the tank. Almost invariably the agitator was run from the time 
 the emulsion was added until the tank was filled. In about 20 per cent 
 of the cases the agitation was discontinued when the tank was full 
 and was not resumed until the sprayer had reached its place of 
 operation in the grove. When the emulsion was added in mass to 
 tanks having inefficient agitation, it sometimes did not become 
 thoroughly broken up and dispersed in the water. 
 
 Orchard Observations on the Use of Emulsions with Hard Water. — 
 Data obtained in experiments indicate that most emulsifying sub- 
 stances used in emulsions undergo chemical reactions with the salts 
 in hard water, resulting in partial de-emulsification of the oil. Such 
 reactions usually are especially pronounced in the case of soap emulsi- 
 fiers. Under certain conditions the reaction is accompanied by a 
 flocculation of the emulsifying substance and the oil globules, which 
 causes the oil to rise to the surface very quickly. A few instances have 
 been observed in which, owing to the reaction mentioned and to 
 inadequate agitation, the concentration of oil in the upper part of 
 the tank was much greater than that in the lower part. 
 
Bul. 527] The Tank-Mixture Method of Using Oil Spray 
 
 23 
 
 EXPERIMENTS ON SPRAY-TANK AGITATION 
 
 Method of Studying Spray -Tank Agitation. — The greater part of 
 the experimental work of a technical nature on spray-tank agitation 
 was done with an experimental sprayer having a 200-gallon tank, 
 built at the Citrus Experiment Station (fig. 8). The results obtained 
 with this tank were checked by tests with 300 and 400-gallon tanks 
 whenever it seemed advisable, in order to determine if the results 
 were applicable to standard sprayer equipment. A power take-off 
 from the truck motor and an extra set of gears on the agitator shaft 
 made it easy to obtain agitator speeds of from 100 to 300 r.p.m. The 
 
 Fig. 8. — Sprayer built especially for experimental use at the Citrus Experiment 
 Station. A power take-off from the truck motor and an extra set of agitator 
 gears make it possible to operate the agitators at speeds of 100 to 300 r.p.m. 
 The capacity of the tank is 200 gallons. 
 
 tank is the usual half-round type. The dimensions are as follows: 
 length, 45 inches ; width, 36% inches ; depth, 33 inches. 
 
 Oils and emulsions were colored with an oil-soluble red dye, known 
 as Oil Soluble Red. The dye rendered the oil globues readily visible 
 in the spray mixture. Certain brands of emulsions could be colored 
 readily by adding the dye to the emulsion, but in some cases the 
 coloring was accomplished by first diluting the emulsion with a small 
 amount of water and then stirring in the powdered dye. 
 
 In certain studies the oil and emulsions were placed in the tank 
 when starting to fill, and the agitator was kept running continuously 
 until the tank was filled and emptied. In other studies the oil was 
 poured on the surface of the water when the tank was full. The 
 agitator was then started and after agitating for 1 minute the spray 
 
24 University of California — Experiment Station 
 
 outlet was opened. The spray was permitted to discharge for 1 minute 
 in order to let the fresh mixture in the tank reach the discharge 
 opening before the first sample was taken. Samples were then taken 
 at intervals during the emptying of the tank. It was found advisable 
 to take the last sample just as the drop in pressure began to take 
 place, in order to avoid slight irregularities due to the emptying 
 of the pump. 
 
 The speed of the agitator shaft was determined by fastening a 
 piece of wire to the agitator sprocket, with one end of the wire 
 projecting to the side of the sprocket. With the forefinger of one 
 hand extended so as to strike against the wire, and a watch in the 
 other hand, counts were made of the number of revolutions per 
 minute. In some tests a speed indicator was used. 
 
 Method for Determining the Percentage of Oil in Spray Mix- 
 tures. — In the studies on spray-tank agitation made in 1927 the 
 method followed was that of filling a 16-ounce bottle at the spray 
 nozzle and simultaneously filling another in the spray tank with the 
 mouth of the bottle held about 2 inches below the surface of the 
 spray mixture. The uniformity of the spray mixture was judged 
 by comparing the thickness of the layers of oil a few days after 
 taking the samples. This method was fairly satisfactory for practical 
 purposes. 
 
 At the beginning of the studies in 1928 the practice of taking the 
 samples from the spray nozzle in 8-ounce bottles at intervals during 
 the emptying of the tank was adopted. An attempt was made to 
 determine the percentage of oil by using the Babcock milk-test method. 
 However, it was found impracticable to use a pipette to withdraw 
 measured quantities of spray from the bottles because of the rapidity 
 with which the oil globules floated out and the variable amount of air 
 contained in the mixtures. As a result of a considerable amount of 
 experimentation, the method described in the succeeding paragraph 
 was finally adopted and found to be very satisfactory. The equipment 
 used in making the determination is shown in figure 9. 
 
 At the time of taking the samples the bottles were filled approxi- 
 mately three-quarters full. Concise directions covering the technique 
 in the laboratory are as follows : Stopper the bottle with a cork having 
 a small tube through the middle. Place the forefinger over the end 
 of the tube and shake vigorously until the oil is dislodged from the 
 walls and uniformly dispersed in the water. While continuing the 
 shaking, with the bottle upside down, lift the finger and jet 20 cc of 
 the mixture into a test tube of 25 cc capacity, with pouring lip, 
 
Bul. 527] The Tank-Mixture Method op Using Oil Spray 
 
 25 
 
 graduated to 20 cc. A large cork reamed out to form a funnel and 
 supporting the test tube at the mouth simplifies the technique of 
 jetting the mixture into the tube. Set aside for a few minutes while 
 the air bubbles rise to the top and then add more mixture to bring 
 to the graduation, taking into account the probable amount of oil 
 and water in the supernatant layer, which sometimes is composed 
 largely of enmeshed air bubbles. Pour the mixture into an 18-gram, 
 8 per cent Babcock milk-test bottle. Fill the test tube with warm 
 
 "v 
 
 
 
 
 ^B^r<< * ^SJS) >!"^HHi 
 
 j*£.J? 
 
 A.t\' ' ,.t '*' ; ■': "* 
 
 I*?**- - -^Jf 
 
 &4 ar^flF jt 
 
 
 **; 
 
 
 ABC 
 
 D 
 
 E 
 
 ^^^^^ 
 
 Fig. 9. — Equipment used for determining the percentage of oil in oil-spray 
 mixtures. A, Sulfuric acid; B, washing bottle filled with hot water; C, eight- 
 ounce bottle containing sample of spray mixture. The layer of dyed oil shows 
 distinctly. D, Gage holding 25 cc test tubes. A cork reamed out at the top is 
 slipped over the test tube in order to facilitate the jetting of the mixture into the 
 tubes. The cork is shown on one of the tubes at the left. E, Babcock milk-test 
 bottles, 18 gram, 8 per cent. F, Centrifuge. 
 
 commercial sulfuric acid, allow to stand for a few minutes in order 
 to permit the oil on the walls of the tube to rise to the surface of the 
 acid, and pour the acid into the test bottle. Then rinse the test tube 
 with hot water and pour the rinsings in the test bottle. Shake the test 
 bottle thoroughly until any emulsifier that is present is broken down 
 and dissolved as much as possible in the acid. Add sufficient hot 
 water to bring the contents nearly to the top graduation. Centrifuge 
 for 1 minute and make readings immediately. 
 
 Agitation Tests with Prepared Emulsions and Tank Mixtures. — 
 Table 3 gives the results of certain tests which were made for the 
 purpose of determining the effect of an emulsifier on the mixability 
 of spray oils used as tank mixtures and the relative mixabilities of 
 tank mixtures and proprietary emulsions. In each test the spray 
 
26 
 
 University of California — Experiment Station 
 
 contained 1 per cent of actual oil, but, owing" to the fact that a 
 pellicle of emulsifier carrying a certain amount of oil was excluded 
 in making the readings, the determinations do not show an average of 
 1 per cent of oil. The proprietary emulsions were the brands most 
 widely used during" the year 1928. In each test the spray ingredients 
 were placed in the tank when starting to fill and the agitator was 
 kept running continuously until the tank was filled and emptied. The 
 oil used in the tank-mixture test had a viscosity of 80 seconds and was 
 
 TABLE 3 
 
 Eesults of Agitator Tests Made with Tank Mixtures and Proprietary 
 
 Emulsions, Using Two Small Agitators at 150 r.p.m. 
 
 in a 200-Gallon Tank 
 
 
 Spray mixture 
 
 Number of gallons in tank when samples were taken 
 
 Test 
 
 200 
 
 150 
 
 100 
 
 50 
 
 10 
 
 Last 
 
 
 Per cent of oil in samples 
 
 1 
 
 
 30 
 0.70 
 0.70 
 
 0.80 
 
 0.90 
 90 
 0.70 
 0.85 
 
 0.40 
 
 70 
 
 0.75 
 
 0.85 
 95 
 0.95 
 0.80 
 0.85 
 
 0.80 
 
 0.90 
 
 0.75 
 
 0.85 
 0.95 
 0.95 
 95 
 0.9 
 
 1.10 
 
 0.90 
 
 95 
 
 0.95 
 0.95 
 0.95 
 0.95 
 0.95 
 
 1.70 
 
 1 20 
 
 1.10 
 
 1.00 
 1.00 
 1.00 
 1.00 
 1.00 
 
 2.20 
 
 2 
 
 Oil, water, calcium caseinate % pound to 
 100 gallons 
 
 1 20 
 
 3 
 
 Oil, water, calcium caseinate 1 pound to 
 100 gallons 
 
 1 00 
 
 4 
 
 Oil, water, calcium caseinate 2 pounds to 
 100 gallons 
 
 90 
 
 5 
 
 
 1.00 
 
 6 
 
 
 1.00 
 
 7 
 
 
 1.00 
 
 8 
 
 
 1.00 
 
 
 
 
 98 per cent unsulfonatable. The calcium caseinate was dissolved in 
 a bucket several minutes before using in order to insure complete 
 dissolving of the casein. The tests were made with two small, type B 
 agitators, shown in figure 4. The purpose of using only two small 
 agitators was to bring out more distinctly than would otherwise be 
 possible the small differences existing in the mixability of the various 
 mixtures. The agitator speed was 150 r.p.m. 
 
 A study of table 3 shows that in the case of the mixture of oil 
 and water only (test 1) the last spray from the tank contained 
 several times as much oil as the sample taken when the tank was full. 
 When calcium caseinate was used at the rate of % pound to 100 
 gallons, the uniformity of the mixture was greatly improved, the last 
 sample showing less than twice as much oil as the first. Increasing 
 the amount of spreader resulted in further slight improvement in the 
 
Bul. 527] The Tank-Mixture Method of Using Oil Spray 
 
 27 
 
 uniformity of the mixture. The proprietary emulsions, with the 
 exception of No. 3, resulted in very uniform mixtures, Emulsion 
 No. 3 showed about the same degree of mixability as the tank mixture 
 in which calcium casemate was used at the rate of 1 pound to 100 
 gallons. 
 
 The conclusions to be drawn from the tests are (1) that a small 
 amount of emulsifying or spreading agent greatly facilitates the 
 producing and maintaining of a uniform mixture, and (2) that when 
 oil, water, and emulsifier are agitated during the filling of the tank 
 
 TABLE 4 
 
 Results of Tests on Agitator Speed Made with 200-Gallon Tank, Using 
 Oil and Water Only 
 
 Number and kind of agitators 
 
 Agitator 
 speed 
 
 Number of gallons in tank when samples were taken 
 
 200 
 
 150 
 
 100 
 
 50 
 
 10 
 
 Per cent of oil in samples 
 
 2 small. 
 2 small. 
 2 small. 
 
 2 large... 
 2 large .. 
 2 large .. 
 
 4 small 
 
 4 large.. 
 4 large... 
 
 2 large* 
 
 r.p.m. 
 100 
 200 
 300 
 
 100 
 200 
 300 
 
 200 
 
 100 
 200 
 
 200 
 
 3 
 0.5 
 10 
 
 3 
 10 
 1.0 
 
 0.9 
 
 0.6 
 1.0 
 
 1.0 
 
 20 
 
 2 
 
 0.2 
 
 0.70 
 
 1 
 
 1.1 
 
 1.0 
 
 1.0 
 
 1.0 
 
 0.7 
 
 9 
 
 0.7 
 
 1.0 
 
 1.0 
 
 1.0 
 
 1.0 
 
 1.0 
 
 1.0 
 
 0.9 
 
 1.1 
 
 1.1 
 
 0.6 
 
 0.8 
 
 8 
 
 10 
 
 10 
 
 1.0 
 
 1.0 
 
 10 
 
 1.0 
 
 7.5 
 1.4 
 10 
 
 2.7 
 1.3 
 1.0 
 
 1.1 
 
 1.4 
 1.0 
 
 1.0 
 
 * Oil added when tank was filled, and agitator run for 2 minutes before taking first sample. 
 
 and the agitation is continued until the spray is applied, the resultant 
 spray mixture, even under conditions of inadequate agitation, com- 
 pares favorably in uniformity with mixtures in which the oil is 
 emulsified previous to placing it in the spray tank. 
 
 Number and Speed of Agitators in Relation to Efficiency of 
 Agitation. — Table 4 gives the results of agitator tests made with the 
 200-gallon tank (fig. 8) in the year 1928. Two gallons of kerosene 
 were used with 198 gallons of water, making 1 per cent of oil in the 
 mixture. No spreader or emulsifier was used. Except as otherwise 
 noted, the oil was added when starting to fill the tank and the 
 agitator was run continuously until the tank was filled and emptied. 
 
28 University of California — Experiment Station 
 
 The agitators used in the tests are shown in figure 4, the small agitators 
 being those designated B and the large agitators D. The data show 
 that with only two small agitators in the 200-gallon tank a uniform 
 mixture was produced and maintained by a speed of 300 r.p.m. In 
 regular sprayer equipment there would be four such agitators in a 
 200-gallon tank. The test with the four small agitators shows prac- 
 tically a uniform mixture at a speed of 200 r.p.m. Two large agitators 
 produced insufficient agitation at a speed of 100 r.p.m., but they gave 
 a uniform mixture when the speed was increased to 200 r.p.m. It is 
 interesting to note that even four large agitators failed to produce a 
 
 Fig. 10. — Sprayer with 400-gallon tank, used for making' the agitation 
 tests reported in table 5. 
 
 uniform mixture at a speed of 100 r.p.m., indicating that increased 
 speed is more important than an increase in the number of agitators. 
 The last test in the table indicates that the use of oil sprays can be 
 made very safe indeed so far as concerns the uniformity of the 
 mixture of the oil and water in the spray tank. In this test, using 
 two large agitators, the oil was poured on the surface when the tank 
 was full, and a uniform mixture was produced by running the 
 agitators for 2 minutes at a speed of 200 r.p.m. 
 
 Table 5 gives the results of certain tests made with the sprayer 
 of 400-gallon capacity shown in figure 10. The dimensions of the 
 tank are as follows: length, 68 inches; width, 44 inches; depth, 34 
 inches. Except in test 6, the tank was filled with water and 4 gallons 
 of dyed kerosene were poured on the surface. The first sample was 
 taken after the agitator was started and run for 2 minutes. Other 
 samples were taken at intervals until the tank was emptied. One 
 series of these tests was made with four, six, and eight large agitators 
 (fig. 4D) turning at a constant speed of 150 r.p.m. The results 
 
Bul. 527] The Tank-Mixture Method of Using Oil Spray 
 
 29 
 
 given in the table show that the mixture produced by eight agitators 
 was decidedly unsatisfactory and that it was but slightly more uni- 
 form than that produced by six agitators. Six agitators produced a 
 mixture which was slightly more uniform than that produced by four 
 agitators. At a speed of 220 r.p.m., on the other hand, four large 
 agitators resulted in practically a uniform mixture, as shown by 
 test 4. The results of these tests have been verified by observations 
 
 TABLE 5 
 
 Ebsults of Agitator Tests Made with 400-Gallon Tank, Using 
 
 Oil and Water Only 
 
 
 Number and kind 
 of agitators 
 
 Agitator 
 speed 
 
 Number of gallons in tank when samples were taken 
 
 Test 
 
 400 
 
 300 
 
 200 
 
 100 
 
 Last 
 
 
 Per cent of oil in samples 
 
 1 
 
 
 r.p.m. 
 150 
 150 
 150 
 220 
 200 
 150 
 
 20 
 25 
 
 25 
 0.90 
 
 1 00 
 50 
 
 80 
 0.85 
 
 85 
 
 1 00 
 1.00 
 90 
 
 1 20 
 1 05 
 1 20 
 1 05 
 1 00 
 1 00 
 
 1 20 
 1 20 
 1 20 
 1 05 
 1 00 
 1.10 
 
 1 20 
 
 2 
 
 
 1.20 
 
 3 
 4 
 
 8 large 
 
 1 20 
 
 1 05 
 
 5 
 
 
 1.00 
 
 6 
 
 
 1 25 
 
 
 
 
 * Oil placed in tank when starting to fill, and agitator run continuously until tank was filled and 
 emptied. 
 
 made on a large number of commercial sprayers, proving that a com- 
 paratively high agitator speed is essential for efficient agitation in the 
 use of oil sprays. The explanation for this fact is that the oil tends to 
 concentrate at the surface of the spray mixture and this lighter 
 portion of the mixture can be effectively drawn to the bottom of the 
 tank only by violent agitation ; and violent agitation can be produced 
 only by rapidly revolving agitators. 
 
 Capacity and Dimensions of Spray Tanks in Relation to Agitator 
 Requirements. — Special attention has been given to testing a few 
 privately constructed spray tanks which are exceptionally large, in 
 order to determine the limit of size which might be permissible in the 
 use of tank-mixture spray. The most unusual tank thus far observed 
 is shown in figure 11. The capacity of the tank is 465 gallons. The 
 dimensions are as follows : length, 53 inches ; width, 40 inches ; depth, 
 54 inches. The depth exceeds by 14 inches that of any standard 
 make of spray tank of the horizontal type. The agitator has a speed 
 of 210 r.p.m. 
 
30 
 
 University of California — Experiment Station 
 
 The results of a series of tests with this tank are given in table 
 6. In tests 1, 2, and 3 the tank was filled with water and 4 x /2 gallons 
 of oil were poured on the surface of the water. The agitator was 
 
 Pig. 11. — Spray tank of unusual capacity and depth, used for making 
 agitation tests shown in table 6. 
 
 TABLE 6 
 
 Kesults of Agitation Tests Made with Sprayer Shown in Figure 11, with 
 
 Agitator Speed of 210 r.p.m. 
 
 
 Manner in which tests 
 were made 
 
 Number and kind 
 of agitators 
 
 Approximate amount of spray in tank 
 when samples were taken 
 
 Test 
 
 Full 
 
 M full 
 
 Yi full 
 
 M full 
 
 Last 
 
 
 Per cent of oil in samples 
 
 1 
 
 4J/2 gallons oil poured on surface 
 of filled tank. Agitated for 2 
 minutes before taking first 
 
 7 small 
 4 large 
 4 large and 3 small 
 
 Same as in test 3 
 
 0.2 
 6 
 0.6 
 
 10 
 
 0.4 
 0.9 
 8 
 
 1.0 
 
 0.9 
 1.0 
 
 10 
 
 10 
 
 1.5 
 12 
 1.2 
 
 1.0 
 
 1.5 
 
 2 
 
 
 1.2 
 
 3 
 
 
 1.2 
 
 4 
 
 2 pounds calcium caseinate and 
 4H gallons oil* 
 
 1.0 
 
 * Placed in tank when starting to fill, and agitator run continuously until tank was filled and emptied. 
 
 then started and samples were taken at the nozzle at intervals during 
 the emptying of the tank. Tests 1 and 2 show that four large agi- 
 tators (fig. 4Z>) were more efficient than seven small agitators (fig. 
 
Bul. 527] The Tank-Mixture Method of Using Oil Spray 31 
 
 4 2£). In the tests with seven small agitators the last sample of spray 
 contained about seven times as much oil as the first sample, while in 
 the test with four large agitators the last sample showed only two 
 times as much oil as the first sample. In test 3, using four large and 
 three small agitators, the mixture was slightly more uniform than that 
 produced by only four large agitators. In test 4, 2 pounds of calcium 
 casemate and 4% gallons of oil were placed in the tank when starting 
 to fill and the agitator was run continuously until the tank was filled 
 and emptied. This procedure resulted in a uniform mixture. 
 
 Test Recommended for Determining Agitator Equipment Required 
 for Oil Sprays. — The complete standardization of agitator equipment 
 by sprayer manufacturers would materially simplify the problem of 
 the orchardist. However, even though a standard agitator were 
 adopted, the difference in dimensions existing among spray tanks, 
 necessitated by different types of assemblage, would make it impos- 
 sible to lay down one set of specifications for agitator equipment 
 which would be equally suitable for all tanks. An equipment which 
 would give satisfactory agitation in one tank might give less satisfac- 
 tion in another, the agitation being either more than required or less 
 than required. 
 
 The fact is obvious, therefore, that spray-tank agitation cannot be 
 standardized, except within broad limits, on the basis of specifications 
 for agitator equipment. The most satisfactory solution is for sprayer 
 manufacturers and spray operators to adopt a standardized test by 
 means of which the proper agitator equipment for their tanks can 
 be determined. Such a test is suggested herewith, and it is believed 
 every tank used for applying oil spray should satisfy this test. 
 
 Method of Making Agitation Test. — The method of making the 
 recommended test is as follows : Fill the tank with water and pour 
 on the surface 2, 3, or 4 gallons of dyed kerosene, the quantity of 
 kerosene depending on whether the tank is 200, 300, or 400-gallon 
 capacity. Then start the agitator and after 1 minute open the spray 
 nozzle and allow sufficient time for the pumps and spray line to 
 become filled with the fresh mixture from the tank. Take samples at 
 the nozzle, preferably in bottles holding 8 ounces or more, at intervals 
 until the tank is emptied. In order to ascertain the exact percentage 
 of oil in the samples, determinations can be made according to the 
 method described on a preceding page. The uniformity of the spray 
 mixture may be determined roughly by filling the bottles to a. given 
 level, three-quarters full for example, when taking the samples, and 
 comparing the thickness of the layers of dyed oil on the samples 
 (fig. 12). If, when taking a sample, the bottle is filled beyond the level 
 
32 University of California — Experiment Station 
 
 desired, the quantity can be reduced by placing the finger over the 
 mouth of the bottle and, while shaking vigorously, allowing some of 
 the mixture to jet out past the finger. 
 
 It is important that the motor be thoroughly warmed up and that 
 the samples be taken from the nozzles under working pressure in 
 order that the agitator shaft shall turn steadily at the speed which is 
 normal for the sprayer under operating conditions. 
 
 W) ^ w * * 
 
 Fig. 12. — Samples of oil spray taken in test 5, table 5, made with the sprayer 
 shown in figure 10. From left to right the bottles represent samples taken when 
 the spray was at levels of 400, 300, 200, and 100 gallons, and the bottle on the 
 end at the right was filled with the last spray from the tank just when the 
 pressure began to drop. The uniformity in the thickness of the layer of dyed 
 oil in the bottles shows that a uniform mixture existed in the tank. 
 
 The agitation should be sufficient to produce and maintain a 
 mixture that is uniform but it need not be materially greater than 
 required to give this result, Excessive agitation which might interfere 
 with the filling of tanks should be avoided. 
 
 POWER REQUIRED TO OPERATE AGITATORS 
 
 Experiments on the Power Consumed in the Operation of Agu 
 tators. — The studies on spray-tank agitation indicated that an agitator 
 speed of approximately 200 r.p.m. is desirable in the use of oil sprays 
 in general and particularly in the use of oil by the tank-mixture 
 method. The question arose as to whether or not the operation of 
 agitators at that speed would involve an excessive consumption of 
 power. In order to obtain definite information on this question, a 
 series of power-consumption tests, using a 300-gallon tank, was made 
 by Kenneth R. Frost, Assistant Engineer in the Division of Agri- 
 cultural Engineering, in cooperation with the author. These tests 
 were made with the tank full of water, except in the case of series 5, 
 in which tests were made with 100, 200, and 300 gallons of water in 
 the tank. The results of the experiments are given in table 7. 
 
Bul. 527] The Tank-Mixture Method of Using Oil Spray 
 
 33 
 
 In the tests of series 1, made with four large agitators of the type 
 shown in figure 4 D, the blades of adjacent agitators were at right 
 angles to one another. This arrangement of the agitators is com- 
 monly referred to as a right-angle position, and is illustrated in 
 figure 13 A. The power consumed at 100, 200, and 300 r.p.m. was 0.08, 
 0.43, and 1.76 hp., respectively. In the tests of series 2, made with 
 
 TABLE 7 
 
 Horsepower Required to Operate Agitators in Tests Made 
 
 with a 300-Gallon Tank 
 
 Series 
 of 
 test 
 
 Approxi- 
 mate 
 speed* 
 
 Kind and 
 number of 
 agitators 
 
 Position 
 
 of 
 agitator 
 
 Quantity 
 
 of water in 
 
 tank 
 
 Power 
 
 required 
 
 to operate 
 
 agitator 
 
 
 r.p.m. 
 [ 100 
 \ 200 
 [ 300 
 
 [ 100 
 \ 200 
 [ 300 
 
 f 100 
 -j 200 
 [ 300 
 
 [ 100 
 \ 200 
 [ 300 
 
 f 300 
 •| 300 
 [ 300 
 
 4 large 
 
 
 gallons 
 300 
 300 
 300 
 
 300 
 300 
 300 
 
 300 
 300 
 300 
 
 300 
 300 
 300 
 
 100 
 200 
 300 
 
 horsepower 
 0.08 
 
 1 
 
 
 
 43 
 
 
 
 
 1.76 
 
 
 4 large 
 
 4 large 
 
 4 large 
 
 Parallel 
 
 15 
 
 2 
 
 Parallel 
 
 56 
 
 
 Parallel 
 
 2 00 
 
 
 Parallel 
 
 06 
 
 3 
 
 4 small 
 
 4 small 
 
 1 flat, 2smallt 
 
 1 flat, 2 small 
 
 Parallel 
 
 15 
 
 
 Parallel 
 
 65 
 
 
 Parallel 
 
 09 
 
 4 
 
 Parallel 
 
 40 
 
 
 1 flat, 2 small 
 
 Parallel 
 
 1 48 
 
 
 4 large 
 
 4 large 
 
 4 large 
 
 Parallel 
 
 0.92 
 
 5 
 
 Parallel 
 
 1.92 
 
 
 Parallel 
 
 1.98 
 
 
 
 
 * An endeavor was made to employ speeds of 100, 200, and 300 r.p.m. but owing to imperfections in 
 the testing equipment slight variations in speed occurred in different tests. The range in the three speeds 
 was as follows: 108 to 114 r.p.m., 192 to 198 r.p.m., and 296 to 302 r.p.m. 
 
 t The flat and small agitators are shown as E and F respectively, in figure 4. 
 
 the same agitators, the axes of the blades were parallel and the agi- 
 tators were paired according to the pitch of the blades, the agitators 
 of each pair throwing the water toward each other. This arrangement 
 is shown in figure 13 B, and is known as a parallel position. One pair 
 of agitators was forward of the center of the tank and the other pair 
 was to the rear of the center of the tank. The power consumed at 
 speeds of 100, 200, and 300 r.p.m. was 0.15, 0.56, and 2.00 hp., respec- 
 tively. The parallel position of the agitators provides more efficient 
 agitation and, therefore, involves a greater power consumption than 
 the right-angle position. 
 
34 
 
 University of California — Experiment Station 
 
 At speeds of 200 and 300 r.p.m. the four small agitators (fig. 41?) 
 consumed roughly about 25 per cent of the power that was required 
 for the four large agitators, indicating that they were much less 
 effective in producing agitation than the large agitators. The one 
 flat and two small agitators which comprised the standard equipment 
 for the model of sprayer used for making the tests, as shown by the 
 
 Fig. 13. — The arrangement of the agitators in the tests of series 1 and 2. 
 A, Right-angle position; B, parallel position. The parallel position provides more 
 efficient agitation than the right-angle position. 
 
 results of series 4, consumed about 25 per cent less power than the 
 large agitators in parallel position and were, therefore, about 25 per 
 cent less effective. 
 
 The tests in series 5, made with four large agitators in parallel 
 position, at a speed of 300 r.p.m., show a power consumption of 1.98 
 hp. with 300 gallons of spray in the tank; 1.92 hp. with 200 gallons 
 in the tank; and 0.92 hp. with 100 gallons in the tank. It appears, 
 therefore, that the power consumption does not materially decrease 
 until the tank is about half empty. 
 
Buk 527] The Tank-Mixture Method of Using Oil Spray 35 
 
 Horsepower of Sprayer Motors. — Information obtained through 
 the cooperation of sprayer manufacturers reveals that in the citrus 
 districts of California the motors on sprayers average 15 hp. A large 
 percentage of the large-capacity sprayers have 20 hp. motors. A small 
 percentage of the smaller-capacity sprayers have motors ranging as 
 low as 8 hp. It is believed that very few, if any, sprayers are in use 
 which have motors with less than 8 hp. Manufacturers find the trend 
 of demand is for the higher-powered motors. 
 
 Returning to the question of whether or not increasing the agitator 
 speed would be likely to overtax the motor, it may be said that, as 
 indicated by the results of the test in series 2, increasing the speed 
 from 100 r.p.m. to 200 r.p.m. involves an increase in power con- 
 sumption from 0.15 hp. to 0.56 hp., or a net increase of 0.41 hp. 
 Sprayer manufacturers and engineering authorities consulted agree 
 that an increase of 0.41 hp. in power consumption is relatively 
 negligible in the case of motors of 8 hp. and above. 
 
 STUDY OF MIXTURES DURING PASSAGE THROUGH SPRAY HOSE 
 
 The results of the studies on spray-tank agitation showed that it 
 was a very simple matter to produce and maintain a uniform mixture 
 of oil and water in the spray tank. Samples of mixtures dipped from 
 the tank showed the oil to be dispersed in the form of minute globules, 
 but the globules floated to the surface rather rapidly. There was a 
 possibility that during the passage of the mixture through the spray 
 hose the floating out of the globules might take place to such an 
 extent that by the time the stream of mixture reached the spray nozzle 
 it would consist of pure oil along the upper portion and water below 
 it. In order to obtain data on this question, a piece of heavy-walled 
 glass tubing, 3 feet in length, was attached to each end of a 50-foot 
 spray hose. With this arrangement the mixture could be observed 
 as it came from the spray pump and as it entered the spray gun. 
 The oil and emulsions used in these tests were dyed red in order to 
 make the globules readily visible to the eye. The set-up of the 
 equipment used in making the study is shown in figure 14. 
 
 In order to study the mixture to the best advantage the pressure 
 was reduced to about 30 pounds and a disk having an orifice % 4 inch 
 in diameter was used in the nozzle. This resulted in the mixture 
 moving slowly through the hose, the rate of discharge through the 
 nozzle being approximately 1 gallon a minute, or about one-sixth of 
 the usual rate in orchard spraying. With mixtures of oil and water 
 only there was a distinct tendency for the oil globules to become 
 
36 
 
 University of California — Experiment Station 
 
 concentrated in the upper portion of the stream, but the floating 
 out was not sufficient to result in the formation of a layer of pure oil. 
 When the rate of discharge through the nozzle was speeded up 
 to 5 gallons a minute, no floating-out of the globules could be observed. 
 This was due to the fact that the spray pump was operated at a 
 higher speed, which probably caused the oil to be broken up into much 
 smaller globules than those occurring in the mixture in the spray 
 
 *£*.*, 
 
 mS^--mm 
 
 
 A !-- — • 
 
 Fig. 14. — Set-up of equipment used in determining the extent that oil globules 
 float out of spray mixtures during passage through spray hose, showing the 
 sections of heavy-walled glass tubing inserted near the spray tank and near the 
 spray gun. 
 
 tank, and to the fact that, at the higher rate of discharge the mixture 
 passed five times as rapidly through the hose as it did when the 
 rate of discharge was 1 gallon a minute. 
 
 In experiments made with proprietary emulsions, and in tank 
 mixtures consisting of oil, water, and spreader, no visible floating-out 
 of the globules occurred even in tests in which the mixture passed 
 through a hose 100 feet in length and the rate of discharge was 1 
 gallon a minute. 
 
 The results of the experiments indicate that the floating-out of oil 
 globules during passage through the spray hose is a factor of wholly 
 negligible importance in the use of oil sprays, whether with emulsions 
 or with tank mixtures. 
 
Bul. 527] The Tank-Mixture Method of Using Oil Spray 37 
 
 SIZE OF OIL GLOBULES 
 
 Size of Globules in Spray Mixture in Tank. — During the past 
 several years certain data have been published which tend to show 
 that an important relation exists between the size of the oil globules 
 in emulsions and the insecticidal efficiency of oil sprays. In view of 
 this fact studies were made of the size of the oil globules in tank 
 mixtures and in sprays of proprietary emulsions. 
 
 Owing to the fact that the spray nozzle has a marked disrupting 
 effect on the globules, it was desirable to determine their size in the 
 mixture in the tank and in the spray after passing through the 
 nozzle. The studies of the globules in the tank were made with the 
 experimental sprayer shown in figure 8. The tank was equipped 
 with four large agitators. The oils and emulsions were dyed in the 
 manner previously described. The globules could be studied rather 
 satisfactorily in the tank when the agitators were operated at a 
 speed of about 100 r.p.m. but when the speed was 200 r.p.m. they 
 were best studied by dipping the mixture from the tank with white 
 porcelain pans. Globules ranging in size up to about % inch in 
 diameter occurred in nearly all sprays of proprietary emulsions. This 
 indicated that a considerable quantity of unemulsified oil is present 
 in most emulsions. This oil is probably produced in most cases by 
 the partial breaking of the emulsions during transportation and 
 storage or while waiting to be used at the orchard. 
 
 In tank mixtures of oil, water, and spreader, in which the oil and 
 spreader were placed in the tank when starting to fill and the agitator 
 was run continuously at a speed of 200 r.p.m. until the tank was 
 filled, the largest globules were on the whole no larger than the largest 
 globules in the sprays of proprietary emulsions. As regards size 
 frequency, however, or the number of globules of different sizes, the 
 majority of the globules in the tank mixtures were sufficiently large 
 to be visible to the unaided eye, while they were predominantly 
 microscopic in size in the sprays of proprietary emulsions. 
 
 Size of Globules in Spray Issuing from Spray Nozzle. — Extensive 
 investigations on the homogenization of milk and ice cream by forcing 
 these substances through small apertures under high pressure, have 
 been made by creamery specialists. It appears, however, that no 
 studies of a similar kind had ever been made on the disrupting action 
 of the spray nozzle in the application of oil spray. Investigators of 
 
38 
 
 University of California — Experiment Station 
 
 oil sprays have apparently overlooked the fact that the size of the 
 globules occurring" in an emulsion or in a spray mixture in the tank 
 may be greatly affected when passing through the spray nozzle. 
 
 The results of a series of experiments on the homogenizing action 
 of the spray nozzle are given in table 8. The average diameter, in 
 microns, of the 15 largest globules in three samples of spray taken 
 at the nozzle on a microscope slide is given for each test. The experi- 
 
 TABLE 8 
 
 Diameter of Oil Globules in Spray Mixture in Tank and in Spray 
 
 Issuing from Nozzle 
 
 
 Type of spray mixture 
 
 Spray 
 from tank 
 
 Pressure under which spray was 
 forced through nozzle 
 
 Test, 
 
 10 pounds 
 
 50 pounds 
 
 150 pounds 
 
 
 Diameter of globules 
 
 1 
 
 Tank Mixtures: 
 
 microns 
 575 
 327 
 143 
 
 204 
 118 
 
 microns 
 311 
 135 
 140 
 
 171 
 
 79 
 
 microns 
 129 
 67 
 70 
 
 70 
 56 
 
 microns 
 58 
 
 2 
 3 
 
 Oil, water, and calcium caseinate H 
 pound to 100 gallons 
 
 Oil, water, and saponin x /i ounce to 
 100 gallons 
 
 42 
 46 
 
 4 
 
 Proprietary Emulsions: 
 No. 35 
 
 58 
 
 5 
 
 No. 33 . 
 
 49 
 
 
 
 
 ments were made with the precision sprayer shown in figure 16, using 
 a nozzle of the Vemorel type with a disk having an orifice % inch 
 in diameter. 6 The microscope slide was exposed to the spray and 
 instantly covered with a cover glass. Samples of spray were taken 
 from the nozzle at pressures of 10, 50, and 150 pounds. A set of 
 samples was also taken from the tank. 
 
 In the case of the samples taken from the tank, the globules in 
 the mixture of oil and water averaged 575 microns in diameter; those 
 in the mixture of oil, water, and calcium caseinate averaged 327 
 microns ; and those in the mixture of oil, water, and saponin averaged 
 
 6 The results presented in table 8 are taken from data obtained by J. B. Corns 
 who, in the summer of 1930, completed a thesis for his Master of Science degree, 
 in work at the Citrus Experiment Station, on the subject, "A Study of the 
 Factors Affecting the Size of Oil Globules in Oil Sprays." 
 
 During the summer of 1931, Norman A. Donges made further investigations, 
 using orchard spraying equipment, in completing a thesis for his Master of 
 Science degree. 
 
Bul. 527] The Tank-Mixture Method of Using Oil Spray 39 
 
 143 microns. These data indicate that the character of the emulsify- 
 ing' substance has a marked effect on the extent to which oil is 
 dispersed in the process of agitation. Saponin was much more con- 
 ducive to the dispersing action than was calcium casemate. It is 
 interesting to note that the globules from the tank in the test with 
 
 Fig. 15. — Photom'erographs showing oil globules in spray forced through 
 spray gun under pressure of 300 pounds. A and B are sprays of leading brands of 
 proprietary emulsions. C is a tank mixture of oil and water only. D is a tank 
 mixture of oil, water, and calcium casemate, % pound to 100 gallons. 
 
 proprietary emulsion No. 35 average 204 microns in diameter, which 
 was larger than those of the tank mixture of oil, water, and saponin. 
 The data show that the greater the pressure with which the spray 
 is forced through the nozzle, the smaller the globules. With the 
 oil-and-water mixture the average diameter of the globules at pressures 
 of 10, 50, and 150 pounds was 311, 129, and 58 microns, respectively. 
 At the same pressures the diameter of the globules in proprietary 
 emulsion No. 35 was 171, 70, and 58 microns, respectively. When the 
 
40 University of California — Experiment Station 
 
 spray was forced through the nozzle under a pressure of 150 pounds, 
 the globules of the tank mixtures were practically the same size as 
 those of the proprietary emulsions. 
 
 From the standpoint of size frequency, the globules of small size 
 predominated in the sprays of proprietary emulsions. However, 
 studies made of samples of spray taken from the nozzle of a spray 
 gun under 300 pounds pressure showed that the size frequency of the 
 globules in tank mixtures was not materially different from that of 
 the globules in mixtures of proprietary emulsions. This fact is 
 indicated by the photomicrographs in figure 15. 
 
 FACTORS GOVERNING QUANTITY OF OIL DEPOSITED 
 
 The purpose underlying the search for a method of emulsifying 
 kerosene fifty years ago w T as to provide a practical way to obtain a 
 uniform mixture of oil and water, and that purpose has continued to 
 be a dominant consideration among insecticide manufacturers up to 
 the present time. Inasmuch as the studies on spray-tank agitation 
 have shown that with modern sprayer equipment, such as is used in 
 the citrus districts of California, it is practicable to produce and 
 maintain a uniform mixture of oil and water when the oil is added 
 directly to the water in the spray tank, the questions arise : What 
 reason is there for continuing to use emulsions, and what is the 
 advantage of using an emulsifier or spreader 7 in the tank mixture? 
 
 The questions relate to two principal factors: (1) the quantity 
 of oil deposited on the tree and insect and the uniformity of the 
 deposit, as effected in the practical application of sprays, and (2) the 
 covering qualities of spray mixtures. The usual conception has been 
 that the amount of oil placed on the tree is adequately controlled by 
 the percentage of oil used in the spray mixture, and that any given 
 emulsion of a class is essentially the same as all other emulsions of 
 that class. Thus, the standard treatment for the red scale calls for 
 2 per cent of a heavy emulsion, and for black and citricola scales the 
 treatment is 1% to 2 per cent of a light, light-medium, or medium 
 emulsion, irrespective of brand. In the case of homemade emulsions 
 entomologists commonly have given more than one formula, per- 
 mitting a choice of emulsifying agents, but invariably a definite 
 
 7 In the usual meaning, an emulsifier is a substance which, when dissolved in 
 or suspended in water, facilitates the work of dispersing oil in minute globules 
 through the water and tends to hold the oil in an emulsified condition. A 
 spreader is a substance that tends to cause the spray to wet and to produce a 
 film instead of collecting in drops on the sprayed surface. Many emulsifiers are 
 ineffective as spreaders. In tank-mixture spray the element of emulsification is 
 not so important as that of wetting or spreading. 
 
Bul, 527] The Tank-Mixture Method of Using Oil Spray 41 
 
 percentage of oil has been recommended irrespective of the formula 
 or the kind and amount of emulsifying agent used in making the 
 emulsion. 
 
 The importance of the subject under discussion is emphasized by 
 the fact that experiments reported herein have shown that, in the 
 case of oil emulsions in general, the deposit of oil tends to build up 
 as spray is applied in excess of the amount required to produce a 
 film, and that the quantity of oil deposited in the film, as well as 
 the building-up tendency, varies greatly among brands of emulsions. 
 
 The following outline of factors pertaining to the quantity of 
 oil deposited will indicate the scope of the investigation that has 
 been made : 
 
 A. The spray mixture 
 
 1. Uniformity of oil-and-water mixture in spray tank 
 
 2. Percentage of oil in spray mixture 
 
 3. Viscosity of oil 
 
 4. Sulfonation of oil 
 
 5. Kind and amount of emulsifier 
 
 6. Amount of emulsifier in relation to the percentage of oil in 
 
 spray mixture 
 
 7. Hardness of spray water 
 
 8. Size of oil globules in spray mixture 
 
 9. Surface tension and interfacial tension 
 10. Electrokinetic phenomena 
 
 B. The application of the spray 
 
 1. Pressure with which spray is applied 
 
 2. Size of orifice in disk in spray nozzle 
 
 3. Force with which spray strikes surface and distance of 
 
 surface from nozzle. 
 
 4. Quantity of spray applied 
 
 5. Manner of applying spray 
 
 6. Rate of discharge of spray through nozzle 
 
 C. The character of the surface sprayed 
 
 Each of these factors has been studied. Special attention has 
 been given to experiments on the kind and amount of emulsifier 
 because it was evident at the outset that, with the quick-breaking 
 type of emulsions generally used in citrus spraying, differences in the 
 oil-depositing and covering qualities of oil sprays are due chiefly to 
 differences in the kind and amount of emulsifier contained in the spray. 
 
42 University of California — Experiment Station 
 
 METHODS FOR DETERMINING THE QUANTITY OF OIL DEPOSITED 
 
 Use of Sections of Glass for Determining Quantity of Oil De- 
 posited. — The methods employed in determining the quantity of oil 
 deposited by various mixtures included laboratory tests in which 
 weighings were made of the oil deposited on sections of glass and on 
 citrus leaves, orchard tests in which the amount of leaf-drop and 
 the percentage of insects killed were regarded as an index of the 
 quantity of oil deposited, and extractions of the oil from the leaves 
 of sprayed trees. 
 
 Owing to the speed and accuracy of work which they permit, 
 sections of light-weight window glass, each 3y 2 by 7 inches in size, 
 the area of one surface being approximately 25 square inches, were 
 used as a standard in the oil-deposit studies. The sections were 
 numbered consecutively and their weights recorded. One section at 
 a time was placed on a support, resting at an angle of 20 degrees 
 with the vertical front of the support, and sprayed in the manner 
 described later. When the water had evaporated after spraying, the 
 section was again weighed. The difference between the original weight 
 and the weight after spraying represented the weight of the oil 
 deposited by the spray. A series of four sections was used in each 
 test and many replications of tests were made in order to obtain 
 dependable data and to determine the range of variability due to 
 experimental error. 
 
 Use of Leaves for Determining Quantity of Oil Deposited. — It was 
 important to learn whether or not the quantity of oil deposited on 
 glass is comparable to that deposited on foliage. The results obtained 
 with the glass sections were checked, therefore, by spraying citrus 
 leaves. The orange leaf, being thick and heavily cutinized, is well 
 adapted to being sprayed and handled in a manner similar to the 
 method used with sections of glass. However, the continuous decrease 
 in weight due to evaporation and transpiration resulted in a relatively 
 high degree of error, which made the use of leaves less satisfactory 
 than sections of glass for routine work. The method requires the 
 services of two persons, one of whom does only the weighing and 
 recording, while the other does the spraying, drying, and handling. 
 The procedure in brief is as follows : A leaf is weighed and the weight 
 and time are recorded. The upper side is then sprayed and the leaf 
 placed on a support to dry. When the water has evaporated, the leaf 
 is again weighed and this second weight and the time of making the 
 
Bul. 527] The Tank-Mixture Method of Using Oil Spray 
 
 43 
 
 weighing are recorded. The leaf is then placed on the support and 
 reweighed at the end of 10 minutes. The rate of loss of weight due 
 to evaporation and transpiration can then be determined, and the 
 amount of oil deposited calculated. 
 
 Leaf-Drop and Insect Control as an Index of Quantity of Oil 
 Deposited. — Data of much importance relating to the oil-depositing 
 qualities of mixtures were obtained by orchard spraying experiments, 
 Two methods were used. One was that of spraying trees with oils 
 sufficiently low in purity to result in a pronounced dropping of 
 leaves, and judging the amount of oil deposited by the amount of 
 
 Fig. 16. — Precision sprayer used in experiments to determine the 
 quantity of oil deposited by oil sprays. 
 
 leaf -drop. The other method involved spraying trees heavily infested 
 with red, black, and citricola scales, and judging the amount of oil 
 deposited by the percentage of insects surviving the treatments. 
 
 Extraction of Oil from, Sprayed Leaves to Determine Quantity of 
 Oil Deposited. — At the beginning of the studies on the quantity of 
 oil deposited an attempt was made to extract the oil from sprayed 
 leaves with petroleum ether, sulfonate the extract, and make volu- 
 metric determinations of the oil by the use of Babcock milk-test 
 bottles. It was found, however, that the particular technique employed 
 did not give data which were satisfactorily reliable. Through the 
 research of P. W. Rohrbaugh, working at the Citrus Experiment 
 Station on the effect of oil sprays on citrus trees, the method has 
 recently been perfected to the point where it gives promise of being 
 of much value for future studies on the oil-depositing quality of 
 oil spray. 
 
 Application of Spray with a Precision Sprayer. — The spraying 
 equipment shown in figure 16 was designed and built with the 
 
44 University of California — Experiment Station 
 
 object of using spray in small quantities and applying it in a manner 
 closely approximating that accomplished in the use of orchard spray- 
 ers. The equipment consisted of a spray chamber capable of with- 
 standing 300 pounds pressure and fitted with an agitating device. 
 The latter was operated by an electric motor, with suitable gear- 
 reducing units. The pressure was provided by air-compressor 
 equipment. Pressure regulators enabled the operator to adjust the 
 pressure readily, the range used in the tests being from 50 to 175 
 pounds. The spray nozzle was held in a fixed position 24 inches 
 distant from the surface sprayed. When sections of glass were 
 sprayed, a flattened funnel immediately beneath the lower edge of 
 the glass collected the run-off and carried it to a graduated cylinder. 
 In this manner the quantity of run-off, as well as the quantity of oil 
 deposited, was determined. The application of the spray was governed 
 by the operator who, with a stop watch in hand, regulated the exposure 
 by turning a cut-off near the nozzle. 
 
 OIL DEPOSITED ON SECTIONS OF GLASS BY PROPRIETARY 
 
 EMULSIONS 
 
 Table 9 shows the amounts of oil deposited by proprietary emul- 
 sions in 1929 and 1930, in tests in which the spray was applied under 
 a pressure of 50 pounds. The samples tested were taken from con- 
 tainers in orchards where spraying was in progress. Only emulsions 
 in good condition were sampled. In the tests of 1929, brand No. 38 
 showed the highest deposit of oil, the amount being 21.5 mg. This 
 was more than five times the amount deposited by brand No. 13, which 
 ranked lowest in oil-depositing quality. In the tests of 1930, using 
 emulsions without spreaders, brand No. 17 ranked highest, the amount 
 deposited being 20.9 mg. This was slightly more than seven times the 
 amount deposited by brand No. 11, which ranked lowest. 
 
 Manufacturers No. 4 and No. 6 marketed spreaders to be used 
 with their emulsions. In the case of manufacturer No. 4, the spreader 
 was a liquid product. The data show that in 1929 the use of the 
 spreader resulted in a decidedly heavier deposit of oil than that which 
 occurred when the emulsions were used without the spreader. The 
 spreader in 1930 had no significant effect on the oil-depositing quality 
 of the spray. Its composition was apparently not the same as in 
 1929. In the case of manufacturer No. 6 the spreader consisted 
 principally of casein and hydrated lime. This spreader very greatly 
 accentuated the oil-depositing quality of the emulsion, the amount of 
 oil deposited when the spreader was used being more than twice the 
 
TABLE 9 
 
 Quantity of Oil Deposited oisr Glass Sections 25 Square Inches in Area, 
 by Spray Containing 2 Per Cent of Oil 
 
 Brands of emulsions grouped 
 according to manufacturers 
 
 1929 
 
 1930 
 
 Manu- 
 facturer 
 
 Brand of 
 emulsion 
 
 Sample 
 
 1 
 
 Sample 
 2 
 
 Sample 
 3 
 
 Aver- 
 age 
 
 Sample 
 1 
 
 Sample 
 2 
 
 Sample 
 3 
 
 Aver- 
 age 
 
 
 
 
 mg 
 
 8.8 
 4.5 
 7.5 
 
 mg 
 6.0 
 
 mg 
 
 mg 
 8.8 
 4.5 
 6.8 
 
 mg 
 8.8 
 
 mg 
 6.0 
 
 mg 
 7.8 
 
 mg 
 
 1 
 
 2 
 
 7 5 
 
 
 3 
 
 
 
 4 
 
 
 
 
 
 8.0 
 
 
 
 8.0 
 
 2 
 
 / 6 
 
 5.5 
 
 8.8 
 
 
 7.2 
 
 6.8 
 
 7 
 
 
 6.9 
 
 
 1 7 
 
 8.5 
 
 8 3 
 
 
 8.4 
 
 
 
 
 
 
 
 ' 9 
 
 
 
 
 
 4.8 
 2 5 
 
 3.5 
 
 
 4 8 
 
 
 10 
 
 3.0 
 
 3 
 
 
 11 
 
 5 3 
 
 
 
 5.3 
 
 2.8 
 
 
 
 2 8 
 
 
 12 
 
 
 
 
 , 13 
 
 4 2 
 
 3.5 
 
 
 3.9 
 
 4 3 
 
 3 5 
 
 
 3 9 
 
 
 
 f 15 
 
 18 
 
 16.8 
 
 
 17.4 
 
 19 
 
 15 5 
 
 19.5 
 
 18.0 
 
 
 
 16 
 
 17.0 
 
 
 
 17.0 
 
 18.3 
 
 18.0 
 
 
 18.2 
 
 
 
 17 
 
 17.8 
 
 
 
 17.8 
 
 23 3 
 
 18.5 
 
 
 20.9 
 
 
 
 18 
 
 
 
 
 
 19 3 
 
 
 
 19.3 
 
 4 
 
 
 19 
 
 
 
 
 
 17.5 
 
 
 
 17 5 
 
 
 < 
 
 15* 
 
 26 
 
 
 
 26 
 
 21 
 
 17.8 
 
 
 19 4 
 
 
 
 16* 
 
 27.8 
 
 
 
 27.8 
 
 19 3 
 
 
 
 19 .3 
 
 
 
 17* 
 
 
 
 
 
 18 5 
 
 
 
 18.5 
 
 
 
 , 18* 
 
 24 5 
 
 
 
 24.5 
 
 16.3 
 
 
 
 16.3 
 
 
 
 ' 19 
 
 
 
 
 
 7.0 
 
 
 
 7.0 
 
 
 
 20 
 
 8.8 
 
 8.8 
 
 
 8.8 
 
 12 5 
 
 13.8 
 
 
 13 2 
 
 
 
 21 
 
 10 2 
 
 
 
 10.2 
 
 12 .8 
 
 15 
 
 
 13.9 
 
 5 
 
 
 22 
 
 9.3 
 
 8 
 
 10.7 
 
 9.3 
 
 11 5 
 
 
 
 11.5 
 
 
 < 
 
 23 
 
 8.2 
 
 10 .3 
 
 11.7 
 
 10.1 
 
 12.3 
 
 
 
 12.3 
 
 
 
 24 
 
 9.3 
 
 
 
 9.3 
 
 3.8 
 16 .8 
 
 13.3 
 
 
 3.8 
 
 
 25 
 
 15.0 
 
 
 
 [ 26 
 
 6 7 
 
 10 5 
 
 
 8.6 
 
 12.0 
 
 16.8 
 
 15.5 
 
 14 8 
 
 
 
 ' 27 
 
 9.0 
 
 9 
 
 8.5 
 
 8 8 
 
 8.3 
 9.0 
 
 12 
 
 8.9 
 
 8 3 
 
 6 
 
 28 
 
 10.0 
 
 
 1 28t 
 
 26.3 
 
 25.0 
 
 
 25.7 
 
 21.0 
 
 
 
 21.0 
 
 
 
 [ 29 
 
 7.5 
 
 9 
 
 
 8.2 
 
 
 
 
 
 
 
 30 
 
 11.0 
 
 
 
 11.0 
 
 19.5 
 
 
 
 19.5 
 
 7 
 
 . 
 
 31 
 
 12.7 
 
 
 
 12 7 
 
 14 .3 
 
 19.3 
 
 18.5 
 
 17 4 
 
 
 
 32 
 
 13.7 
 
 
 
 13.7 
 
 
 
 
 
 
 
 33 
 
 13 .7 
 
 
 
 13.7 
 
 18.5 
 
 
 
 18.5 
 
 8 - 
 
 .34 
 
 9.0 
 
 9 
 
 
 9.0 
 
 6.8 
 
 5.0 
 
 
 5.9 
 
 
 
 f 36 
 
 
 
 
 
 13.5 
 
 19 
 
 
 16.3 
 
 9 
 
 
 37 
 
 20.5 
 
 
 
 20 5 
 
 15.5 
 
 
 
 15.5 
 
 <-■'"" - ; 
 
 
 . 38 
 
 21 5 
 
 21 5 
 
 
 21 5 
 
 14 5 
 
 16 .3 
 
 
 15.4 
 
 10 
 
 39 
 
 4.2 
 
 
 
 4.2 
 
 8.0 
 
 
 
 8.0 
 
 11 
 
 
 40 
 
 
 
 
 
 8.5 
 
 9.5 
 
 
 9 
 
 • ' . • • 
 
 
 
 * Manufacturer No. 4 marketed a liquid spreader to be used with the emulsions. In these tests this 
 spreader was used at the rate of 3^ pint to 100 gallons. 
 
 t Manufacturer No. 6 recommended the use of a calcium caseinate spreader with brand 28. In these 
 tests this spreader was used at the rate of X A pound to 100 gallons. 
 
46 University of California — Experiment Station 
 
 amount deposited by the emulsion alone. Presumably, the object of 
 using the spreader was to affect the oil-depositing quality of the spray 
 in such a manner that the deposit would not be excessive. The data 
 indicate that the opposite result occurred. These emulsions, used 
 with the spreaders recommended, deposited larger amounts of oil 
 than any one of the thirty-five other emulsions tested, except that 
 the emulsions and spreader of manufacturer No. 4 in 1930 did not 
 deposit as much oil as certain other brands. 
 
 It may be noted that the products of certain manufacturers con- 
 sistently rank low in the amount of oil deposited and others rank 
 high. The emulsions of manufacturer No. 3 ranked lowest, the 
 average deposit for the two years being approximately 4.0 mg. In 
 1929 the emulsions of manufacturer No. 9 ranked highest with an 
 average of 21.0 mg, and in 1930 the emulsions of manufacturer No. 4 
 ranked highest with an average of 18.8 mg. 
 
 The differences in the amount of oil deposited by various samples 
 of a given brand in 1929 are not significant. The differences among 
 samples of given brands in 1930 were greater than occurred in 1929, 
 but they are not regarded as being particularly significant. 
 
 The spraying of the sections in the tests in 1929 was standardized 
 on the basis of spraying each section for 3 seconds, while in the tests 
 in 1930 the spraying was standardized on the basis of 7 cubic centi- 
 meters of run-off per section, the time interval averaging more than 
 3 seconds. Although these differences in the manner of spraying 
 existed, a study of all of the data obtained seems to indicate that the 
 emulsions of perhaps six manufacturers in 1930 were different in 
 oil-depositing quality from the same brands in 1929. 
 
 OIL DEPOSITED ON ORANGE LEAVES BY PROPRIETARY 
 EMULSIONS AND TANK MIXTURES 
 
 Table 10 gives the results of experiments made to determine the 
 amount of oil deposited on orange leaves by certain proprietary 
 emulsions and by tank mixtures. The spray was applied to the upper 
 surface of the leaves. The quantity of oil deposited has been calculated 
 on the basis of the number of milligrams of oil per 25 square inches 
 of leaf surface in order to permit direct comparisons with the amount 
 deposited on the sections of glass. The amount deposited on sections 
 of glass by the emulsions concerned is also given in the table. The 
 spray was applied with the precision sprayer under a constant 
 pressure of 50 pounds. The oil used in the tank mixtures had a 
 viscosity of 50 seconds and a sulfonation of approximately 95 per 
 
Bul, 527] The Tank-Mixture Method of Using Oil Spray 
 
 47 
 
 cent. Four leaves were used in each test. Replications of the tests 
 yielded data which indicated that the factor of experimental error 
 in each test amounted to approximately ± 5 mg. 
 
 The composition of the blood albumen spreader used in tank mix- 
 ture test 4, and in various experiments reported on the following 
 
 TABLE 10 
 
 Quantity of Oil Deposited on Orange Leaves and Sections of Glass 
 
 by Spray Containing 2 Per Cent of Oil 
 
 Emulsion 
 or tank 
 
 Kind and amount of emulsifier 
 
 Amount of oil deposited on 25 
 sq. in. of surface, in milligrams 
 
 Ratio of deposit 
 on leaves to 
 
 mixture 
 No. 
 
 Leaves 
 
 Glass 
 
 deposit on glass 
 
 Proprietary emulsions 
 
 2 
 
 
 15 6 
 38.3 
 48.5 
 
 50 7 
 196 
 41 7 
 38.7 
 33 4 
 
 47.8 
 
 66.3 
 49.5 
 
 7.5 
 6.9 
 19 4 
 
 18 2 
 
 7 
 11 5 
 14 8 
 10.0 
 
 21 
 17.4 
 
 2.1 
 
 1 
 
 6 
 15 
 
 None 
 
 Liquid spreader 
 
 5.5:1 
 2 5:1 
 
 16 
 
 
 2.8 
 
 2 8 
 
 3 6 
 
 2 6 
 
 3 3 
 
 2 3 
 
 1 
 
 19 
 
 
 1 
 
 22 
 
 
 1 
 
 26 
 
 
 1 
 
 28 
 28 
 
 None 
 
 Calcium caseinate Yi pound to 100 
 
 1 
 1 
 
 28 
 31 
 
 Calcium caseinate, 1 pound to 100 
 
 gallons* 
 
 None 
 
 2.8 
 
 1 
 
 Tank mixtures 
 
 Test 1 
 Test 2 
 
 Test 3 
 Test 4 
 
 None 
 
 Calcium caseinate, Yi pound to 100 
 
 gallons* 
 
 Saponin, Yi ounce to 100 gallons 
 
 Blood albumen spreader, 6 ounces to 
 
 100 gallons 
 
 32 2 
 
 45.9 
 49 3 
 
 30 4 
 
 5 4 
 
 8.5 
 9 6 
 
 5.9:1 
 
 2.5:1 
 5.8:1 
 
 3.2:1 
 
 * The liquid spreader and calcium caseinate were the same products as were used in the tests reported 
 in table 9. 
 
 pages, is given in detail in the section, "Recommendations for 
 Tank-Mixture Spray," at the close of this bulletin. 
 
 It will be noted that the data agree with those presented in table 9 
 in showing that important differences exist among oil sprays in regard 
 to their oil-depositing qualities. Brand No. 2 ranked lowest, the 
 deposit being 15.6 mg. Brands 16 and 31 each deposited approxi- 
 
48 University of California — Experiment Station 
 
 mately 50.0 mg. The use of calcium casemate with brand No. 28 
 resulted in increasing the deposit of oil, the spray without the spreader 
 depositing" 33.4 mg, that with the spreader used at the rate of % 
 pound to 100 gallons depositing 47.8 mg, and that with the spreader 
 used at 1 pound to 100 gallons depositing 66.3 mg. The use of 
 calcium casemate also produced a marked increase in the deposit of 
 oil in the case of the tank mixtures, the deposit resulting from oil 
 and water only being 32.2 mg, while the deposit resulting from oil, 
 water, and calcium casemate used at % pound to 100 gallons was 
 45.9 mg. The use of saponin resulted in a deposit of 49.3 mg. 
 
 The ratios given in the right-hand column of table 10 show that 
 the amount of oil deposited on the leaf surface was approximately 
 three times that deposited on the glass. With certain exceptions 
 the sprays which deposited large amounts on the glass deposited 
 correspondingly large amounts on the leaves. The exceptions include 
 brand 6 and oil-and-water mixtures 1 and 3, each of which deposited 
 almost six times as much oil on the leaves as they deposited on the 
 glass. Eliminating from consideration these three sprays, the eleven 
 remaining sprays show an average ratio of 2.7 :1 between the amount 
 of oil deposited on the leaves and the amount deposited on the glass. 
 
 ORCHARD TESTS ON QUANTITY OF OIL DEPOSITED 
 
 Oil Deposited as Indicated by Leaf-Drop on Orange Trees. — In 
 order to obtain additional data on the relation between the kind and 
 amount of emulsifier and the quantity of oil deposited in the use of 
 tank-mixture sprays, eight series of orchard tests were made in which 
 orange trees were sprayed and the amount of leaf -drop regarded as an 
 index of the quantity of oil deposited. Three rows of trees uniform 
 in size and in excellent state of vigor were used for the experiments. 
 One row is shown in figure 17. The trees were approximately 9 feet 
 high and 10 feet in spread. Alternate trees were sprayed so that each 
 sprayed tree stood between two unsprayed trees used as controls. The 
 control trees were protected by tarpaulin covers while the spray was 
 being applied, as shown in figure 17. In order to accentuate the 
 dropping of the leaves and to bring out differences which would not 
 be apparent with ordinary spray oil, oils low in purity (80 and 85 
 per cent unsulfonatable) were used in the tests. The viscosity of the 
 oils was 100 seconds. In certain tests 15 gallons of spray was applied 
 per tree, which was sufficient to spray the trees thoroughly from the 
 inside and from the outside. In other tests each tree received 20 
 gallons of spray. The spray was applied under a pressure of 400 
 
Bul. 527] The Tank-Mixture Method of Using Oil Spray 49 
 
 Fig. 17. — Applying spray to alternate trees in orchard tests in determining 
 the relation of the kind and amount of emulsifier to the quantity of oil deposited. 
 
 Fig. 18. — Counting leaves dropping from trees in experiments on the relation 
 of the kind and amount of emulsifier to the quantity of oil deposited. 
 
50 
 
 University of California — Experiment Station 
 
 pounds. The spray nozzle had a discharge of 3 1 /? gallons per minute 
 and the time required to spray each tree was approximately 4 minutes 
 when 15 gallons was applied, and 6 minutes when 20 gallons was 
 applied. These conditions tended to greatly accentuate the building 
 up of the oil deposit and to bring out differences in the oil-depositing 
 qualities of the various sprays. 
 
 The amount of leaf -drop was determined by counting the number 
 of leaves dropping during a given period (fig. 18) and also by making- 
 frequent ratings of the condition of the trees as determined by observa- 
 tion. Although the trees were uniform in size and were sprayed in 
 a particularly systematic manner, sufficient variation occurred in 
 
 TABLE 11 
 Eating of Sprays According to Amount of Leaf-Drop Produced* 
 
 Kind and amount of emulsifier 
 
 Oil and water only 
 
 Blood albumen spreader: 
 
 4 ounces to 100 gallons... 
 
 6 ounces to 100 gallons .. . 
 
 8 ounces to 100 gallons... 
 Calcium caseinate: 
 
 Y% pound to 100 gallons.. 
 
 1 pound to 100 gallons... 
 
 2 pounds to 100 gallons.. 
 
 Number of test 
 
 2 3 4 5 6 7 
 
 Ratings 
 
 6 
 
 7 
 
 6 
 
 5 
 
 5 
 
 7 
 
 7 
 
 5 
 
 4 
 
 2 
 
 2 
 
 2 
 
 3 
 
 3 
 
 2 
 
 2 
 
 3 
 
 -t 
 
 -t 
 
 2 
 
 2 
 
 1 
 
 1 
 
 1 
 
 1 
 
 1 
 
 1 
 
 1 
 
 4 
 
 5 
 
 4 
 
 3 
 
 4 
 
 6 
 
 5 
 
 7 
 
 6 
 
 7 
 
 4 
 
 3 
 
 5 
 
 6 
 
 3 
 
 3 
 
 5 
 
 -t 
 
 -t 
 
 4 
 
 4 
 
 Average 
 
 3 3 
 2 3 
 11 
 
 4.4 
 5 
 
 4.1 
 
 * The smallest amount of leaf-drop is indicated by 1 and the largest amount is indicated by 5, 6 or 7, 
 depending on the number of trees used in the particular test, 
 t No test made of the particular spray. 
 
 the number of leaves and in the application of the spray to produce 
 considerable variation in the results obtained with a given spray. The 
 results of the tests are shown in table 11. 
 
 The data indicate that the heaviest deposit of oil was produced 
 by the spray of oil and water only. The sprays containing calcium 
 caseinate at the rate of V 2 , 1, and 2 pounds to 100 gallons each 
 deposited a larger amount of oil than blood albumen spreader at the 
 rate of 4 ounces to 100 gallons. In the case of the blood albumen 
 spreader the amount deposited consistently varied inversely with the 
 quantity of spreader used, that is, 4 ounces deposited more than 6 
 ounces, and 6 ounces deposited more than 8 ounces. This fact is 
 illustrated by figure 19. With the calcium caseinate, however, there 
 was a considerable degree of inconsistency. The averages for the 
 
Bul. 527] The Tank-Mixture Method of Using Oil Spray 51 
 
 Fig. 19. — Condition of trees 6 weeks after being sprayed with a. low-purity 
 oil, in experiments on the relation of the kind and amount of emulsifier to the 
 quantity of oil deposited. The trees on the right are controls. The spray applied 
 to the trees on the left was as follows: A, oil and water only; B, oil, water, and 
 blood albumen spreader at the rate of 4 ounces to 100 gallons; C, oil, water, and 
 blood albumen spreader at the rate of 8 ounces to 100 gallons. 
 
52 
 
 University of California — Experiment Station 
 
 tests indicate that calcium casemate at the rate of 1 pound to 100 
 gallons deposited a larger amount of oil than y 2 pound, and also a 
 larger amount than 2 pounds. 
 
 Quantity of Oil Deposited as Indicated by Amount of Leaf -Drop 
 on Lemon Trees. — -Through the cooperation of J. M. Barnett of Long 
 Beach, California, the opportunity was afforded of carrying out an 
 orchard experiment on the quantity of oil deposited, as determined 
 by leaf -drop and the effectiveness of insect control, on an unusually 
 extensive scale and in a particularly satisfactory manner. The orchard 
 was located near Yorba Linda, California, and consisted of approxi- 
 mately 10 acres of lemon trees of the type shown in figure 20. The 
 
 Fig. 20. 
 
 ying lemon trees in experiments in J. M. Barnett grove 
 at Yorba Linda, California. 
 
 trees were fairly uniform in size and shape and were well pruned, 
 which facilitated the work of spraying them uniformly. The spray 
 was applied in a systematic manner by two workmen who had become 
 particularly proficient in the technique of applying spray to meet 
 the requirements of experimental work. Approximately 10 gallons 
 of spray was applied per tree, which was sufficient to thoroughly 
 drench the trees. The spray nozzles were fitted with disks which gave 
 a discharge of 3y 2 gallons a minute. This made it possible to spend 
 about 3 minutes in spraying each tree. About one-third of the 
 spraying was done beneath the tree in order to insure a thorough 
 coverage of the surface of the leaves and fruit facing the center of 
 the tree and a coverage of all interior parts of the tree. The trees 
 were, on the whole, heavily infested with red scale. 
 
 The experiment included the use of oils having viscosities of 80 
 seconds and 100 seconds, and sulfonations of 98-100 per cent, 90 
 
Bul, 527] The Tank-Mixture Method of Using Oil Spray 
 
 53 
 
 per cent, and 86 per cent. The oils were used at iy 2 , 2, 2 1 /2, and 3 
 per cent, and blood albumen spreader was used in amounts of 4 
 ounces and 8 ounces to 100 gallons of spray. The tests with IVo and 
 2 per cent of oil also included sprays of oil and water only. 
 
 The amount of leaf -drop resulting from 39 treatments, shown by 
 figure 21, was determined by counting the number of leaves on a 
 given sector beneath each of 10 trees in each test plot and on the 
 basis of these counts estimating the average number of leaves dropping 
 per tree. The spray was applied September 28 to October 1 and 
 the leaf counts were made October 16 and 17. The data on the 
 amount of leaf -drop as shown by the counts agreed with ratings made 
 
 SULFONAIION OP OIL 100 £ 
 VISCOSITY OP OIL 
 
 Fig. 21. — Graphic representation of the quantity of oil deposited on lemon 
 trees by 3 types of sprays, as indicated by the average number of leaves dropping 
 per tree. The types of sprays were (1) oil and water only; (2) oil, water, and 
 blood albumen spreader at the rate of 4 ounces to 100 gallons; and (3) oil, 
 water, and blood albumen spreader at the rate of 8 ounces to 100 gallons. 
 
 The figure also shows the relation of the purity and heaviness of oils to the 
 amount of leaf-drop. 
 
 by several persons who, in company with the author, inspected the 
 grove with the particular object of noting the effect on leaf -drop. 
 A study of figure 21 shows that with a given type of oil used at a 
 given percentage, the heaviest leaf -drop was produced by the spray 
 of oil and water only, and the lightest drop by the spray containing 
 blood albumen spreader at the rate of 8 ounces to 100 gallons. These 
 results agree with the laboratory tests and with the orchard 
 experiment in spraying orange trees. 
 
 Oil Deposited as Indicated by Degree of Scale Insect Control. — 
 Since the killing efficiency of an oil spray containing a given oil 
 
54 University of California — Experiment Station 
 
 depends upon the quantity of oil deposited, the percentage of insects 
 killed can be regarded as an index to the quantity of oil deposited. 
 The results of experiments on the control of black and citricola scales 
 given in table 14 show that the sprays of oil and water only, and oil, 
 water, and calcium casemate at the rate of % pound to 100 gallons 
 were more effective than the spray containing blood albumen spreader 
 at the rate of 6 ounces to 100 gallons. The spray with blood albumen 
 spreader at the rate of 6 ounces was more effective than the spray 
 with this spreader used at the rate of 12 ounces to 100 gallons. These 
 results agree with those obtained in the orchard tests in which the 
 quantity of oil deposited was determined by the mount of leaf -drop. 
 Further information on the relation of spreaders to the amount of 
 oil deposited is provided by the experiments on the control of the red 
 scale in the J. M. Barnett grove, reported in table 17. The treatments 
 included sprays of oil and water only, and sprays containing blood 
 albumen spreader at the rate of 4 ounces and 8 ounces to 100 gallons. 
 While the data are not accepted as being conclusive, they indicate 
 that the spray of oil and water gave about the same degree of control 
 as the one containing blood albumen spreader at 4 ounces to 100 
 gallons. This result, when compared with the results of other tests, 
 suggests that the performance of sprays as regards oil-depositing 
 quality varies according to the character of the surface sprayed, a 
 point that was brought out by the laboratory tests. The data indicate 
 very definitely that the spray containing 4 ounces of blood albumen 
 spreader was much more effective than that containing 8 ounces. In 
 the tests with the 100 viscosity oil used at 2 per cent, 15.27 per cent 
 and 27.78 per cent of the insects survived the sprays containing 4 
 ounces and 8 ounces of the spreader, respectively, and when the oil 
 was used at 2% per cent the percentage of insects surviving the 
 sprays was 4.28 per cent and 11.78 per cent, respectively. Results 
 similar to these were obtained in the use of the 80 viscosity oil. 
 
 FUNCTION OF SPREADERS AND EMULSIFIERS IN OIL SPRAYS 
 
 Spreaders in Relation to Covering Quality of Oil Sprays. — The 
 covering qualities of oil sprays depend upon the wetting and spread- 
 ing quality of the water phase of the mixture. A spray of oil and 
 water only will produce a film on the upper surface of many old 
 citrus leaves. In order to produce a film on the less senile leaves and 
 new leaves, which comprise the majority of the leaves on a tree, a 
 spreader is required. Spreading and the forming of a film of spray 
 mixture on the leaf is complicated by the fact that the leaves become 
 
Buu 527 j The Tank-Mixture Method of Using Oil Spray 55 
 
 more or less completely coated with oil while the spray is being 
 applied. An effective spreader is a substance, therefore, which has 
 the ability to cause water to wet and form a film on a surface partially 
 coated with oil. The investigation of many substances in the present 
 study has indicated that powdered blood albumen is particularly 
 efficacious in meeting this requirement. 
 
 The speed and thoroughness of the work of spraymen are governed 
 to a marked extent by the wetting and spreading quality of the spray. 
 The presence of a film of spray on the foliage is satisfying evidence 
 to the sprayman that a good coverage has been effected. In using a 
 spray which forms in drops as soon as it hits the foliage the evidence 
 of a thorough coverage is less definite. 
 
 An opportunity to study the reaction of spraymen to sprays of 
 various covering qualities was afforded by experiments on the control 
 of black and citricola scales, made in 1930. Twelve spray crews par- 
 ticipated in the tests. Three tank -mixture sprays were applied. One 
 consisted of oil and water only; another consisted of oil, water, and 
 blood albumen spreader at 6 ounces to 100 gallons ; and the third con- 
 sisted of oil, water, and blood albumen spreader at 12 ounces to 100 
 gallons. It was the plan of the experiments that the quantity of spray 
 applied per tree would be uniform in each test, and a supervisor was 
 present to see that the. plan was carried out. Without exception, how- 
 ever, the spraymen spent more time and applied more spray per tree 
 when using the oil and water mixture than when using the spray 
 containing the blood albumen spreader. 
 
 Other factors being equal, a spray which spreads well is decidedly 
 preferable to one which does not spread or which spreads poorly. 
 Spraymen are not as likely to overspray trees when using a spray 
 which spreads well as when using one which spreads poorly. A spray 
 having good spreading quality will go farther and, therefore, is more 
 economical than one that covers poorly. Data obtained in various 
 experiments and commercial tests during 1930 indicated that the 
 average sprayman will cover 10 to 20 per cent more trees with a spray 
 containing blood albumen spreader at the rate of 6 ounces to 100 
 gallons than he will with a spray of oil and water only. The covering 
 quality of some emulsions in 1930 was about the same as that of oi] 
 and water only. 
 
 Spreaders in Relation to Building Up of the Oil Deposit. — In order 
 to effect a coverage of oil on all parts of a citrus tree, drenching 
 quantities of spray must be applied. The principal facts pertaining to 
 the mechanism of the covering and oil-depositing processes can be 
 made clear by analyzing the conditions attendant upon the spraying 
 
56 University of California — Experiment Station 
 
 of an orange tree such as one of those used in the orchard tests on 
 the quantity of oil deposited, shown in figures 18 and 19. The spray 
 was 2 per cent oil. Twenty gallons was applied to each tree and the 
 time required for the application was 6 minutes. Observation showed 
 that some leaves received only a single light shower of droplets of 
 spray, some received several showers, and others, particularly those 
 near the center of the tree, were showered continuously during the 6 
 minutes. A large proportion of the leaves on the periphery of the 
 tree repeatedly received the full force of the spray as the nozzle was 
 played back and forth across the tree. 
 
 When the quantity of spray falling upon a leaf is not sufficient to 
 produce a run-off, all of the oil contained in the droplets or in the film 
 of spray is deposited on the surface. When the quantity is sufficient 
 to produce a run-off, however, only a, portion of the oil contained in 
 the spray is deposited. The results of experiments given on preceding 
 pages show that marked differences occur in the quantity of oil depos- 
 ited by oil sprays. Certain factors which appear to relate to the 
 differences observed require brief consideration. 
 
 For the sake of clearness the terms "initial deposit" and "second- 
 ary deposit" are introduced. The initial deposit refers to the oil that, 
 apparently, is deposited on the surface the instant the spray strikes 
 the surface. The secondary deposit refers to the oil that is deposited 
 as a result of the evaporation of the water in droplets of spray, or in 
 a film of spray, or as a result of the run-off of droplets from the sur- 
 face. The study has shown that certain emulsions, and tank mixtures 
 containing certain spreaders, result in particularly heavy initial 
 deposits. This fact is illustrated by the photomicrographs reproduced 
 in figure 22. 8 The samples of spray were obtained by exposing a 
 microscope slide to spray issuing from a nozzle under 300 pounds 
 pressure and instantly covering the slide with a microscope cover 
 glass. Photomicrographs A, C, and E in figure 22 were made with 
 the microscope focused on the globules or masses of oil in contact 
 with the microscope slide, and photomicrographs B, I), and F with 
 the microscope focused on the globules or masses of oil in suspension 
 or in contact with the lower surface of the cover glass. 
 
 A study of the photomicrographs reveals marked differences in 
 the initial deposit of oil among the three sprays In the spray of oil 
 and water only, the globules in contact with the microscope slide (fig. 
 22 A) are small in size and few in number. They represent but a small 
 
 s The photomicrographs shown in figures 22, 23J!, 25, and 26 were made with 
 a photomicrographic camera and a microscope fitted with a 16 mm objective and 
 a lOx ocular containing an ocular micrometer. 
 
Bul. 527] The Tank-Mixture Method of Using Oil Spray 57 
 
 Fig. 22. — Photomicrographs of three oil sprays showing the globules or masses 
 of oil in contact with the microscope slide, and the globules suspended in the 
 mixture. The photographs on the left (A, C, and E) were made witfc the 
 microscope focused on the surface of the slide ; those on the right (B, D, and F) 
 were made with the microscope focused just beneath the cover glass. 
 
 A, B, Tank-mixture spray of oil and water only; C, D, tank-mixture spray 
 of oil, water, and calcium casemate at the rate of 1 pound to 100 gallons of spray; 
 E, F, a proprietary emulsion which ranked high in oil-depositing quality. 
 
58 University of California — Experiment Station 
 
 fraction of the total amount of oil contained in the spray as can be 
 seen by comparing' photomicrograph A with B. In the case of the 
 spray of oil, water, and calcium casemate, however, by far the greater 
 proportion of the oil is in contact with the microscope slide (fig. 22C). 
 In photomicrograph D of figure 22, the spherical masses in contact 
 with the cover glass are in sharp focus, while the large masses form- 
 ing" the initial deposit are out of focus. The heavy initial deposit 
 characteristic of spray containing calcium casemate is also shown in 
 figure 15D, which is a photomicrograph of a tank mixture containing 
 this spreader at the rate of V* pound to 100 gallons. Photomicro- 
 graph E of figure 22 shows the initial deposit of oil produced by 
 proprietary emulsion No. 38 (table 9), which ranked highest in oil- 
 depositing quality in the tests of emulsions made in 1929. 
 
 The amount of oil in the initial deposit is apparently governed, in 
 part at least, by electrostatic phenomena. The globules in sprays 
 which give light initial deposits seem to bear strong negative charges. 
 They tend to repel one another and are perhaps repelled by most wet 
 surfaces. With sprays which give heavy initial deposits, the globules 
 exhibit a strong tendency to cluster, indicating that their charges 
 have been neutralized or otherwise altered. 
 
 The studies have shown that mixtures which produce heavy initial 
 deposits rank high in oil-depositing and building-up quality. The 
 initial deposit does not, however, account for heavy deposits and 
 building up in all sprays which rank high in oil-depositing quality. 
 A spray of oil and water only, as shown by figure 22A, produces a 
 very light initial deposit; yet the orchard tests on the amount of oil 
 deposited, previously related, indicate that the spray of oil and water 
 deposited more oil on the trees than was deposited by the spray con- 
 taining calcium casemate at V2 pound to 100 gallons and blood 
 albumen spreader at 4 ounces to 100 gallons. 
 
 It appears that the high oil-depositing quality of oil-and-water 
 spray and many sprays which do not produce particularly heavy 
 initial deposits, can be explained in part at least by the wetting quality 
 of the sprays. As mentioned in the preceding section, it is probable 
 that the majority of the leaves on a tree are repeatedly showered in 
 the process of spraying. The example may be taken of a spray of oil 
 and water only. When the spray nozzle is passed across a portion of 
 a tree, each leaf in the path of the nozzle is bombarded and washed 
 by thousands of particles and droplets of spray. As a result a deposit 
 of oil is effected over the surface of each leaf. Instantly, the water 
 forms in droplets and the interspaces among the droplets present an 
 exposed, oil-covered surface. Each time the spray nozzle passes over 
 
Bul, 527] The Tank-Mixture, Method of Using Oil Spray 59 
 
 the same portion of the tree an additional deposit of oil is made. It 
 is apparent, therefore, that a spray which does not spread permits the 
 oil deposit to build up. The building up is apparently due to the fact 
 that the oil comes into contact with the surface as the drops of spray 
 run off. In using a spray containing blood albumen spreader at the 
 rate of 6 ounces to 100 gallons, however, a film of spray mixture is 
 produced on the leaves the first time the nozzle passes across the tree. 
 A small proportion of the oil makes direct contact with the leaf in 
 the form of an initial deposit, but by far the larger proportion rests 
 in the form of globules at the surface of the film. Each time the 
 spray nozzle is passed over the same portion of the tree the particles 
 and droplets of spray fall upon the film of spray mixture, which 
 serves as a protection against a further deposit of oil on the leaf. 
 This fact is illustrated by figure 23. Figure 23A shows the globules 
 
 Fig". 23. — A, Photomicrograph showing the globules of oil on the surface of a 
 film of spray of oil, water, and blood albumen spreader at the rate of 6 ounces to 
 100 gallons. B, Photomicrograph of low magnification showing the margin of 
 the film of spray at which the last trace of water was evaporating. The oil 
 globules were merging into the continuous film of oil shown at the lower, 
 right-hand portion of the photomicrograph. 
 
 of oil highly magnified, floating on the surface of the aqueous film. 
 Probably 95 per cent of the oil occurs as globules floating on 
 the surface and only a small percentage is in contact with the 
 microscope slide. Additional spray falling upon the film tends to run 
 off but a surface layer of globules always remains. As the water 
 evaporates, the globules are brought into contact with the surface of 
 the leaf and break, forming a continuous film of oil as shown in figure 
 231?. This figure is a photomicrograph of a much lower magnifica- 
 tion than 23 A, and shows the process by which the oil film is formed. 
 
60 
 
 University of California — Experiment Station 
 
 On the lower right-hand portion of the field the water has evaporated 
 and the oil occurs as a continuous film. Toward the upper left-hand 
 portion of the field sufficient water remains to support the globules. 
 Near the central portion the last trace of water is disappearing and 
 the globules are breaking and merging into the continuous film of oil. 
 
 IV 
 
 B 
 
 Fig. 24. — The mechanism of oil depositing and building up. A, A very stable 
 oil spray; B, a quick-breaking type of spray which does not spread; C, a quick- 
 breaking type of spray containing an effective spreader. 
 
 The mechanism of depositing and building up is further illustrated 
 by figure 24, which indicates diagrammatically what takes place when 
 the surface of a leaf is showered with droplets of spray. A of figure 
 24 represents a very stable spray such as one made with a miscible 
 oil. The globules are much smaller than those in tank-mixtures and 
 in emulsions generally used in spraying citrus trees. Owing to their 
 small size and to the nature of the emulsifier, the globules remain dis- 
 persed through the droplets of water. A very small proportion of 
 the oil borne by each droplet is deposited as the droplet strikes the 
 surface and rolls off. B of figure 24 represents a quick-breaking type 
 
Bul. 527] The Tank-Mixture Method of Using Oil Spray 61 
 
 of spray which does not spread, such as oil and water. Some globules 
 make contact with the surface the instant the droplet strikes, as shown 
 in I, and the other globules, or most of them, are deposited when the 
 droplet rolls off, as shown in II. In the same manner, succeeding 
 droplets deposit most of their oil as shown in III, causing the building 
 up of a heavy oil deposit as indicated in IV. C of figure 24 represents 
 a quick -breaking type of spray which contains an effective spreader. 
 A film of spray is formed on the surface as shown in II. Succeeding 
 droplets strike this film and, since the oil globules float on the sur- 
 face, no pronounced building up of the oil deposit occurs. The deposit 
 finally produced, as shown in IV, represents the initial deposit and the 
 secondary deposit resulting when globules on the film are brought 
 into contact with the surface through the evaporation of the water. 
 
 The discussion up to this point has related to the behavior of 
 spray on the upper surface of the citrus leaf. The lower surface is 
 very difficult to wet. There is no emulsion on the market, so far as 
 the author knows, which effectively wets and produces a film on the 
 under surface of the leaf. Blood albumen spreader used at the rate 
 of 8 ounces to 100 gallons does so very effectively. Calcium casemate, 
 used at the rate of 2 pounds to 100 gallons with water low in hard- 
 ness, will also produce a film on the under surface. These statements 
 pertain to the average leaf. The under surface of senile leaves can 
 be wet rather easily. Owing to the fact that sprays spread so poorly 
 on the under surface, the oil deposit builds up to a much greater 
 extent on this surface than on the upper surface. 
 
 Data regarding the way oil is deposited on the bark is very lim- 
 ited. There is evidence, however, that sprays vary in their ability to 
 deposit oil on the bark and that those which deposit large amounts 
 on the leaves may not deposit proportionately large amounts on the 
 bark. The oil deposit apparently builds up to a much less extent on 
 the rough bark than on the leaves. This is probably due to the fact 
 that the rough bark wets readily even with sprays which spread 
 poorly on the leaves. It becomes covered with a heavy film of spray 
 and this film causes additional spray to run off without adding to the 
 oil deposit. 
 
 Spreaders in Relation to Character of the Oil Deposit. — The idea 
 appears to have prevailed universally that a droplet of oil placed on a 
 surface will spread and creep indefinitely, forming a thin film. The 
 present study has shown this conception to be erroneous, in part at 
 least, and that one function of a spreader or emulsifier is to cause the 
 oil to spread. The more important facts can be made clear by referring 
 to figures 25 and 26. 
 
62 University of California — Experiment Station 
 
 Figure 25 is a photomicrograph of a droplet of spray of oil and 
 water only, taken under low magnification. A considerable portion 
 of the water had evaporated when the picture was taken. The dark 
 area near the center of the droplet represents numerous oil globules 
 floating on the surface of the water. The instant the droplet fell upon 
 the microscope slide it assumed a convex form and the globules of oil 
 became massed at the highest point on the dome-shaped body of water. 
 As the globules coalesced they migrated to the edge of the droplet and 
 were deposited on the surface of the slide. 
 
 Fig. 25. — Photomicrograph of a droplet of spray of oil and water only. The 
 outline of the droplet is marked by globular masses of oil. Globules of oil also 
 occur in the field surrounding the droplet. The dark area at the center of the 
 droplet is produced by numerous oil globules out of focus on the dome-shaped 
 body of water. 
 
 The outline of the droplet is marked by globular masses of oil at 
 the edge of the water. Masses of oil deposited by smaller droplets, 
 from which the water had evaporated before the picture was taken, 
 are shown in the field surrounding the droplet. 
 
 Figure 26 A shows the masses of oil deposited on a microscope 
 slide as a result of the evaporation of the water from a droplet of 
 spray of oil and water only. The outline of the original droplet is 
 marked by a continuous line of oil masses. Within this line of masses 
 are less distinct lines which were formed as the margin of the droplet 
 
Bul. 527] The Tank-Mixture Method of Using Oil Spray 63 
 
 receded during 1 the evaporation of the water. The water receded in 
 the direction of the upper left-hand part of the droplet, and the large 
 number of oil masses in that part were deposited by the last water to 
 evaporate. The photograph was taken several hours after the water 
 had evaporated. It will be observed that there was practically no 
 tendency for the oil masses to spread and form a film. Even when 
 the slide was heated to a temperature of 165° F no appreciable 
 spreading of the oil occurred. Figure 265 shows the oil film resulting 
 from a droplet of spray of oil, water, and blood albumen spreader 
 
 Fig. 26. — Photomicrographs showing the character of the oil deposits produced 
 by droplets of oil spray: A, oil deposit resulting from a droplet of spray of oil 
 and water only; B, oil deposit resulting from a droplet of spray of oil, water, and 
 blood albumen spreader at the rate of 6 ounces to 100 gallons. 
 
 at the rate of 6 ounces to 100 gallons. The uniform film of oil pro- 
 duced by the spreader is due to three phenomena: (1) The droplet 
 of spray flattened out or spread the instant it fell upon the slide. 
 
 (2) The globules of oil were held enmeshed at the surface of the film, 
 as shown in figure 23, and did not migrate to the edge of the droplet. 
 
 (3) When the water evaporated the albumen laid down a coating on 
 the glass, producing a surface over which the oil spread in a uniform 
 film. 
 
 Character of Sprayed Surface in Relation to Type of Oil Deposit. — 
 The discussion and data presented up to this point have dealt with 
 the types of oil deposits observed on the surface of clean glass. The 
 fact may now be considered that the character of the deposit varies 
 with the nature of the surface sprayed. This point is illustrated 
 by the photomicrographs in figure 27. Photomicrograph 27 A shows 
 the type of oil deposit produced by spraying a clean piece of glass 
 continuously for 3 seconds. The oil tended to build up, forming large 
 
64 University of California — Experiment Station 
 
 globular masses, and there was only a slight tendency for the masses 
 to spread. Photomicrograph 275 shows the oil deposit produced on a 
 piece of glass which was coated with a thin film of inorganic material. 
 This film was produced by dipping the glass in hot tap water and 
 permitting the water to evaporate. It will be observed that spreading 
 of the oil took place to a marked degree, apparently due to a type of 
 capillarity provided by the film. 
 
 The deposit shown in photomicrograph 27 A is fairly typical of 
 that which is produced on the lower surface of citrus leaves and the 
 upper surface of the newer leaves when sprayed with oil and water 
 
 Fig. 27. — Photomicrographs illustrating the relation of the character of the 
 surface sprayed to the type of oil deposit. The spray applied was oil and water 
 only. A, Deposit produced by spraying a clean piece of glass ; B, deposit pro- 
 duced on a piece of glass coated with a thin film of inorganic matter. 
 
 only. Various emulsions have also been observed to give this type of 
 deposit. The deposit shown in photomicrograph 21B is typical of 
 that produced on the upper surface of citrus leaves by a spray of oil 
 and water only. The roughened character of the leaf surface and the 
 covering of particles of dust, which may not be washed off when the 
 spray is applied, account for the spreading of the oil. 
 
 Discussion Regarding the Use of Spreaders. — Knowledge of the 
 functioning of oil sprays in the control of scale insects on citrus trees 
 is far from complete. This discussion is for the most part, therefore, 
 a tentative statement. The final answer to many of the questions 
 which have been raised must be sought through more extensive orchard 
 experiments than have yet been made. The experiments made in the 
 present investigation have been extensive, and the results have been 
 carefully checked. However, the factors of heterogeneity encountered 
 in orchard experiments are so varied that it is extremely difficult to 
 
Bul. 527] The Tank-Mixture Method of Using Oil Spray 65 
 
 evaluate a particular factor which may affect the control efficiency of 
 a spray to the extent of a difference, for example, of % P er cent ; and 
 in the control of scale insects a difference of this magnitude is of 
 much importance in the spraying of heavily-infested groves. 
 
 The discussion under the preceding topics and the data presented 
 may have led the reader to suppose that the film type of oil deposit is 
 more efficacious than the droplet type in the control of scale insects. 
 This supposition, however, is not borne out by the results of orchard 
 experiments made during 1930 and reported in table 14. The data 
 show that the spray of oil and water only consistently gave the highest 
 degree of control of black and citricola scales. The greater efficacy 
 of this spray is probably explained largely by the fact that more 
 spray was applied per tree and the oil deposit built up, resulting 
 in a heavy coverage ; but there may be grounds for surmising that 
 the particular type of oil coverage produced by the oil and water was 
 also more efficacious than the film coverage produced by the spray 
 containing the spreader. 
 
 Inasmuch as there is a definite correlation between the percentage 
 of oil in a spray and its effectiveness, there is reason to believe, other 
 factors being equal, that the most efficient spray is the one ranking 
 highest in oil-depositing quality. In the orchard tests on the amount 
 of oil deposited there was evidence that the spray of oil and water 
 only, and the one containing calcium casemate at the rate of 1 pound 
 to 100 gallons of water, both deposited on the leaves nearly twice as 
 much oil as was deposited by the spray containing blood albumen 
 spreader at the rate of 6 ounces to 100 gallons. The question arises : 
 Why would not 1 per cent of oil in a spray of oil and water only, or 
 in one of oil, water, and calcium casemate at the rate of 1 pound to 
 100 gallons, give as effective control as 2 per cent of oil in a spray 
 containing blood albumen spreader at the rate of 6 ounces to 100 
 gallons? The results of the experiments on the control of black and 
 citricola scales, reported in table 14, show that with a given per- 
 centage of oil, the sprays of oil and water only, and of oil, water, and 
 calcium casemate, gave better control than the spray containing blood 
 albumen spreader. However, as is explained in the following para- 
 graph, the differences in the degree of control are not sufficiently 
 large to warrant the supposition that 1 per cent of oil in tank mixtures 
 of oil and water only, or oil, water, and calcium casemate, will give 
 as effective control as 2 per cent of oil in a tank mixture of oil, water, 
 and blood albumen spreader at the rate of 6 ounces to 100 gallons. 
 In fact, the results given in table 14 indicate that 0.32 per cent of 
 the insects survived the spray of oil and water containing iy 3 per 
 
66 University of California — Experiment Station 
 
 cent of oil, while only 0.08 per cent survived the spray containing blood 
 albumen spreader at 6 ounces to 100 gallons and 2 per cent of oil. 
 
 The data obtained in the experiments on the control of black and 
 citricola scales in 1929 and 1930, reported in tables 13 and 14, in 
 which oil was used at %, 1, 1%, 1%, 1%, and 2 per cent in tank 
 mixtures, with calcium casemate and blood albumen spreader, suggest 
 that l 1 /^ per cent of oil of the grade used is about the minimum 
 percentage that will give effective control with a spray application 
 that is average in thoroughness. The explanation of this fact appar- 
 ently is that a portion of the surface of the tree is covered only by 
 minute particles and droplets of spray. A droplet that is 2 per cent 
 oil will deposit on an insect twice as much oil as a droplet of the 
 same size that is 1 per cent oil. In the one case the amount of oil 
 deposited might be sufficient to kill the insect and in the other the 
 insect might survive. 
 
 With leaves that receive a sufficient quantity of spray to become 
 covered with a film of spray or that are washed to such an extent 
 that a film of oil is produced on the surface, the amount of oil 
 deposited depends largely on the kind and amount of emulsifier. If 
 it were practicable to produce this type of coverage on the entire 
 surface of a tree, 1 per cent of oil in a spray of oil and water only, 
 or a spray of oil, water, and calcium casemate, might give as effective 
 control as 2 per cent of oil in a spray of oil, water, and blood albumen 
 spreader at the rate of 6 ounces to 100 gallons. In fact, as shown in 
 table 13, orchard experiments have been made in which an excep- 
 tionally high degree of control of citricola scale has been obtained 
 by using y 2 per cent of oil with calcium casemate, and applying the 
 spray in sufficient quantity and with sufficient thoroughness to wash 
 each leaf and cover it with a deposit of oil. 
 
 The preceding discussion has dealt with the function of spreaders 
 as related to the efficiency of the spray in controlling scale insects. 
 Safety to the tree is equally important. As regards safety, the prin- 
 cipal object of using a spreader is to avoid the excessive building up 
 of the oil deposit. The ideal spray is one which will lay down just 
 enough oil in an initial coverage to kill the insect, but will not permit 
 the oil to build up as spray is applied in excess of the quantity 
 required to produce the initial coverage. This ideal is approached by 
 increasing the amount of spreader, but in order to maintain the effect- 
 iveness of the spray, a corresponding increase must be made in the 
 percentage of oil, which means added cost. It is necessary, therefore, 
 to strike a compromise among the factors of effectiveness, safety, 
 and cost. 
 
Bul. 527] The Tank-Mixture Method of Using Oil Spray 67 
 
 As far as is practicable, the safety of the spray mixture should 
 be varied according to the tolerance of the tree and also according 
 to the heaviness of the oil used. Experience over a period of thirty 
 years or more has shown that lemon trees will stand a larger amount 
 of oil and a heavier oil than will orange trees. 
 
 Since the extent of the building up of the oil deposit is propor- 
 tional to the quantity of spray applied, the safety of the spray, 
 theoretically at least, should also be varied according to the degree 
 of the thoroughness of the application. A spray of oil and water, 
 or one ranking equally as high in oil-depositing quality, m / be used 
 satisfactorily provided the application is light ; but it is not considered 
 safe to use such a spray when the thoroughness of the application is 
 average. In the case of heavy applications, it is advisable to use a 
 spray which ranks relatively low in oil-depositing quality. 
 
 The data obtained in the experiments reported in lis bulletin and 
 the results of the commercial use of tank -mixture f\^ay during 1931 
 indicate that when the percentage of oil in the spray is the same, 
 tank-mixture spray containing 4 ounces of blood albumen spreader 
 to 100 gallons corresponds within narrow limits to the average of 
 emulsions in oil-depositing quality. The oil deposit appears to be 
 satisfactorily within the tolerance of orang" trees where the oils used 
 are grade 1 and grade 2 (table 19) in heaviness, and the degree of 
 thoroughness of the application is average. In the coastal district, 
 however, where oils of grades 3 and 4 are used in spraying oranges 
 to control red, purple, and off-hatch black scales, and red spider, 
 experience has shown that the safety margin of the average spray, 
 as determined by oil-depositing quality, is so narrow that pronounced 
 fruit-drop, leaf-drop, and other injurious effects may often result, 
 particularly if the application is heavier than average or the trees 
 are in a subnormal condition physiologically. With these numerous 
 factors relating to the safety of the spray to take into consideration, 
 it is evident that no one spray meets all the requirements, and that 
 a considerable element of risk may be involved in using a spray that 
 is average in oil-depositing quality. At the present stage of progress 
 it seems necessary to be contented with a spray that may be slightly 
 low in effectiveness and also imperfect as regards safety. 
 
 In spraying lemon trees for the red scale, it seems permissible 
 and desirable to use a spray which ranks high in oil-depositing 
 quality. It is particularly desirable to effect a heavy deposit of oil 
 on the rough bark, since it is on this part of the tree that oil sprays 
 are the least effective. The data presented in table 17 and figure 21 
 tend to indicate that blood albumen spreader, used at the rate of 4 
 
68 University of California — Experiment Station 
 
 ounces to 100 gallons, exhibits a differential action as regards its 
 ability to deposit oil on leaves and the rough bark. It appeared to 
 give about the same degree of control of the insects on the bark as 
 did the spray of oil and water only ; but, as determined by the amount 
 of leaf-drop, it apparently produced a distinctly lighter deposit on 
 the leaves than the spray of oil and water only. 
 
 EXPERIMENTS WITH OIL SPRAYS IN CONTROL OF BLACK 
 AND CITRICOLA SCALES 
 
 Experv,n(.nts in 1928 and 1929. — The object of the experiments on 
 the control of black and citricola scales was to determine the lightest 
 oil that will give effective control, used at a given percentage in a 
 given type of .spray mixture. It was evident that the unfavorable 
 fruit and tree- eactions experienced with oil sprays in the navel dis- 
 tricts could be argely avoided provided control could be obtained 
 with lighter oils. 
 
 The experiments in 1928 involved the use of oils ranging from 
 kerosene (viscosity 32 seconds as determined by the Saybolt Universal 
 Viscosimeter) to a medium spray oil having a viscosity of 75 seconds. 
 The oils were applied as tank mixtures, using calcium casemate at 
 the rate of y 2 pound to 100 gallons as a spreader. The sprays were 
 applied at intervals from July 24 to February 14. The results indi- 
 cated definitely that it was not necessary to use a medium oil to control 
 these insects, as had been generally practiced up to that time. 
 
 The experiments were continued in 1929, using light oils having 
 viscosities of 50 and 55 seconds and a medium oil having a viscosity 
 of 75 seconds. The distillation ranges of the oils are shown in table 12. 
 
 The tests made in the Covina district of Los Angeles County were 
 of particular interest, since it had been contended that owing to the 
 "resistant" nature of the black scale in this district, and the tendency 
 to hatch unevenly, in some years at least, a heavier oil would be 
 required than in the Riverside district where the tests of 1928 were 
 made. 
 
 All together, 54 tests were made in which extensive counts were 
 taken to determine the percentage of insects surviving the treatments. 
 In addition, 28 tests were made in which the effectiveness of the treat- 
 ments was roughly determined by inspection. A summary of the 
 results of the 54 tests first mentioned is given in table 13. The per- 
 centages are based on counts made of the total number of insects 
 and the number alive on 20 scale-bearing leaves selected at random 
 oil each of 10 trees in each test. In some tests counts were made of 
 
Bul. 527] The Tank-Mixture Method of Using Oil Spray 
 
 69 
 
 50 leaves per tree. The live insects included those which survived 
 because the oil deposit was too thin or the oil too light, and also those 
 which survived because they were not covered when the spray was 
 applied. Therefore, the percentages pertain to the thoroughness of the 
 spray application as well as to the effectiveness of the particular 
 sprays. Since twelve spray crews participated in the application of 
 the spray, a considerable degree of variation among the results in 
 different groves was probably caused by variation in the thoroughness 
 of the spray application. 
 
 TABLE 12 
 
 Distillation Ranges of Oils Used in Experiments on the Control 
 of Black and Citricola Scales, 1929 
 
 
 Viscosity 
 
 Degrees 
 Fahrenheit 
 
 50 seconds 
 
 55 seconds 
 
 75 seconds 
 
 
 Per cent distilled 
 
 550 
 575 
 
 20 
 35 
 
 5 
 
 22 
 
 
 
 7 
 
 600 
 
 52 
 
 46 
 
 22 
 
 625 
 
 67 
 
 65 
 
 40 
 
 650 
 
 77 
 
 78 
 
 56 
 
 675 
 
 85 
 
 85 
 
 68 
 
 700 
 725 
 
 90+ 
 
 90+ 
 
 79 
 
 87 
 
 750 
 
 
 
 90+ 
 
 It is believed that the efficacy of the tank-mixture sprays can tje 
 judged fairly well by comparing the percentage of insects surviving 
 those sprays with the percentage surviving the proprietary emulsion 
 with which the remainder of each grove was sprayed. Using this 
 criterion, the data indicate that distinctly unsatisfactory results were 
 obtained with 1 per cent of the 50 and 55 viscosity oils and V> per 
 cent of the 75 viscosity oil. The excellent control obtained with 1 
 per cent of the 50 viscosity oil in the Gage grove was due to the 
 unusually thorough manner in which the trees were sprayed. The 
 trees received nearly twice the quantity of spray applied in the other 
 tests. The excellent control obtained with y 2 per cent of the 75 
 viscosity oil in the tests made August 1 in the Pitze/* grove is also 
 explained by the fact that the trees were purposely sprayed unusually 
 thoroughly in order to secure data on the relation between the normal 
 efficiency of the spray and the thoroughness of the spray application. 
 
70 
 
 University of California — Experiment Station 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
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Buk 527] The Tank-Mixture Method of Using Oil Spray 71 
 
 Only three tests were made with 1 per cent of the 75 viscosity oil. 
 The data indicate that the control was not satisfactory. 
 
 The control obtained with the 50 and 55 viscosity oils used at 
 IV2 and 1% per cent compared very favorably with the control 
 obtained with the proprietary emulsions. The latter contained oils 
 of the light-medium grade of heaviness. The oil content of the 
 emulsions ranged from 83 to 85 per cent; therefore, when they were 
 used at 1% per cent the spray contained only about 1.4 per cent 
 actual oil. 
 
 There was evidence that the poor control of citricola scale obtained 
 in the Henry grove with 1% per cent of the 55 viscosity oil was due 
 to some irregularity in the application of the spray. For example, 
 the counts revealed 65 live insects, 47 of which occurred on 5 leaves 
 which evidently were missed when the spray was applied. Inspections 
 showed this condition to be quite general through this test. In the 
 case of the two tests with proprietary emulsion No. 4, duplicate 
 counts of 50 scale-bearing leaves per tree were made in order to 
 determine whether or not the poor control was due to irregularity 
 in the spray application. The counts indicated that the application 
 was satisfactory. 
 
 Experiments in 1930. — The principal purpose of the experiments 
 in 1930 was to test the use of blood albumen spreader and to determine 
 the relation between the effectiveness of the spray and the amount of 
 spreader used. The tests were made in cooperation with growers who 
 sprayed their groves with tank mixtures in connection with the 
 commercial trial of the tank-mixture method. All together 88 tests 
 were made in 16 groves. Twelve spray crews participated in the 
 application of the spray. The experiments were not entirely satis- 
 factory because the infestation of scale in many of the groves was 
 too light for experimental purposes, and since each grove was sprayed 
 entirely with the tank-mixture there was no opportunity to make 
 direct comparisons of the effectiveness of the test sprays with the 
 effectiveness of proprietary emulsions. The oil, which was the same 
 as that used in the commercial trial in 1930, had a viscosity of 60 
 seconds and a sulfonation of 90 per cent. The distillation range 
 was as follows: 
 
 "Degrees Per cent 
 
 Fahrenheit distilled 
 
 550 3 
 
 575 21 
 
 600 46 
 
 625 70 
 
 650 86 
 
 675 93 
 
72 
 
 University of California — Experiment Station 
 
 The tests included the use of the oil at 1%, 1%, 1%, and 2 per 
 cent, with blood albumen spreader at the rate of 6 ounces and 12 
 ounces to 100 gallons and calcium caseinate at the rate of % pound 
 to 100 gallons. A spray of oil and water only was also applied in each 
 series of tests. The effectiveness of the treatments was determined by 
 counts made in the same way as in the experiments in 1929. 
 
 A summary of the results of certain tests is given in table 14. 
 The data indicate that the most effective spray was that of oil and 
 water only. The spray containing calcium caseinate at the rate of 
 % pound to 100 gallons ranked second, the one containing blood 
 albumen spreader at the rate of 6 ounces to 100 gallons ranked third, 
 
 TABLE 14 
 
 Summary of Results of Experiments in Spraying for Black and 
 Citricola Scales in 1930 
 
 
 Per cent of oil in spray 
 
 Kind and amount of 
 
 iy 3 
 
 m 
 
 m 
 
 2 
 
 emulsifier 
 
 Num- 
 ber 
 of 
 tests 
 
 Per cent 
 
 of 
 insects 
 alive 
 
 Num- 
 ber 
 
 of 
 
 tests 
 
 Per cent 
 of 
 
 insects 
 alive 
 
 Num- 
 ber 
 of 
 
 tests 
 
 Per cent 
 
 of 
 
 insects 
 
 alive 
 
 Num- 
 ber 
 of 
 
 tests 
 
 Per cent 
 
 of 
 
 insects 
 
 alive 
 
 
 7 
 
 5 
 
 6 
 
 3 
 
 0.32 
 
 1.39 
 2.69 
 
 0.29 
 
 8 
 
 7 
 6 
 
 6 
 
 0.19 
 
 0.89 
 1.34 
 
 0.22 
 
 9 
 
 9 
 6 
 
 9 
 
 0.07 
 
 36 
 1.22 
 
 0.20 
 
 3 
 
 3 
 3 
 
 0.03 
 
 Blood-albumen spreader: 
 
 6 ounces to 100 gallons 
 
 12 ounces to 100 gallons 
 
 0.08 
 0.21 
 
 Calcium caseinate: 
 Yi pound to 100 gallons 
 
 
 
 
 and blood albumen spreader at 12 ounces to 100 gallons gave the 
 poorest control. The degree of effectiveness was proportional to the 
 percentage of oil in the spray. These results are in accordance with 
 the theoretical expectation as explained under the heading, "Function 
 of Spreaders and Emulsifiers in Oil Sprays," The high degree of 
 effectiveness of the spray of oil and water is explained in part by the 
 high oil-depositing quality of the spray and in part by the fact that, 
 owing to the poor covering quality of the spray, the spraymen applied 
 more spray per tree than was applied in the tests with blood albumen 
 spreader at 6 ounces to 100 gallons. The spray containing the calcium 
 caseinate also ranked high in oil-depositing quality and much lower 
 in covering quality than the sprays containing blood albumen spreader. 
 
Bul. 527] The Tank-Mixture Method of Using Oil Spray 73 
 
 EXPERIMENTS WITH OIL SPRAYS IN CONTROL OF RED SCALE 
 
 Experiments Prior to 1930. — Orchard experiments with oil sprays 
 in the control of the red scale were started in August, 1926. The 
 tests that year were made chiefly in the groves of C. D. Holmes and 
 C. D. Brown at Tustin, California. Tests were also made in 1927, 
 1928, and 1929. The variation in the degree of control obtained in 
 various groves was of such magnitude that it obscured differences in 
 the control efficiencies of the sprays tested. Although a given experi- 
 ment using a 50 viscosity oil and a 100 viscosity oil, for example, 
 might show that the heavier oil was more effective than the lighter 
 oil, the differences between an 80 viscosity and a 100 viscosity oil, or 
 between iy 2 per cent and 2 per cent of a given oil, were too obscure 
 to warrant basing conclusions on them. The variations revealed by 
 the data were due to the fact that the tests were not replicated a 
 sufficient number of times and the counts were not sufficiently exten- 
 sive to yield an average result that would outweigh the factors of 
 heterogeneity and experimental error. It was believed that these 
 factors presented a more difficult problem in experimenting with 
 sprays in the control of the red scale than in experimenting with 
 sprays in the control of black and citricola scales, owing to the fact 
 that the latter insects have but one generation a year and occur only 
 on the leaves and green bark. For this reason the experimental work 
 on developing a standardized oil spray was done chiefly in spraying 
 for the black and citricola scales. 
 
 Experiments in 1930. — Arrangements were made in 1930 to make 
 an extensive series of experiments on the control of the red scale. 9 
 Eleven spray crews participated in the application of the sprays. It 
 was not possible to make counts in all of the groves owing to the 
 limited assistance that was available. 
 
 The results of experiments made in 10 groves are given in table 16. 
 Oils of two grades of heaviness were used, namely, 100 seconds and 80 
 seconds viscosity. The oils had sulfonations of 86 and 90 per cent, 
 except in two tests in which the sulfonation was 100 per cent. The 
 distillation ranges are shown in table 15. 
 
 9 In order to accomplish this work Walter Ebeling was employed as Junior 
 Entomologist in May, 1930. He was located at Anaheim to devote his entire 
 time to the red scale investigation. The experiments reported in this section 
 were carried out by Mr. Ebeling and the author. The data given in tables 16, 17, 
 and 18 are derived from accounts made by Mr. Ebeling. 
 
74 
 
 University of California — Experiment Station 
 
 TABLE 15 
 
 Distillation" Kanges of Oils Used in Experiments 
 on the Control of Eed Scale, 1930 
 
 Degrees 
 
 80 seconds viscosity 100 seconds viscosity 
 
 Fahrenheit 
 
 Per cent distilled 
 
 550 
 
 
 
 
 
 575 
 
 3 
 
 1 
 
 600 
 
 13 
 
 4 
 
 625 
 
 36 
 
 19 
 
 650 
 
 56 
 
 43 
 
 675 
 
 73 
 
 59 
 
 700 
 
 84 
 
 77 
 
 725 
 
 90+ 
 
 86 
 
 750 
 
 
 90+ 
 
 TABLE 16 
 
 Summary of Kesults of Experiments in Spraying Lemon Trees for Control 
 
 of Eed Scale; Blood Albumen Spreader Used at Bate of 4 
 
 Ounces to 100 Gallons in Tank Mixtures 
 
 Owner of grove 
 
 Bushnell 
 
 Emde 
 
 Honey 
 
 Martin 
 
 Morris 
 
 Rowe 
 
 Smith 
 
 Todd 
 
 Utley 
 
 Webber 
 
 Average, all groves 
 
 W* 
 
 27.88 
 56 18 
 
 20.32 
 32 18 
 
 31.99 
 11.06 
 
 29.19 
 
 Tank mixtures 
 
 Oil viscosity 
 100 seconds 
 
 Oil viscosity 
 80 seconds 
 
 Per cent of oil in spray 
 
 2H 
 
 Per cent of insects alive 
 
 13.13 
 17 43 
 
 13 49 
 6.31 
 
 26.92 
 
 14 58 
 5.39 
 
 21.79 
 5.95 
 
 14 48 
 
 4 84 
 7.71 
 
 4 
 
 20 
 
 3 
 
 23 
 
 9 
 
 03 
 
 7 
 
 21 
 
 2 
 
 81 
 
 14 
 
 03 
 
 1 
 
 78 
 
 5.79 
 
 15.29 
 28 00 
 21 15 
 18.72 
 13.22 
 11.84 
 17.89 
 14 05 
 32.59 
 15.76 
 
 19.80 
 
 21.39* 
 7 12 
 4 92 
 
 12.83 
 
 10 87 
 7.53 
 9.91 
 8.26 
 
 11.36 
 
 9.75 
 
 Proprietary 
 emulsions 
 
 15.04t 
 35.57 
 17.95 
 36 35 
 9.52 
 52.89 
 16.03 
 12.98 
 36.37 
 12. 05* 
 
 26.60 
 
 * Spray contained V/i per cent of oil. 
 
 t Spray contained 2H per cent of a medium emulsion. 
 
 \ Percentage of emulsion in spray not known. 
 
Buu 527] The Tank-Mixture Method of Using Oil Spray 75 
 
 The 100 viscosity oil was used at 1%, 2, and 2y 2 per cent, and the 
 80 viscosity oil was used at 2 and 2% per cent. Blood albumen 
 spreader was used at the rate of 4 ounces to 100 gallons in the tank- 
 mixture sprays. Proprietary emulsions were applied in each of the 
 groves. Except in the Bushnell and Webber groves, the emulsions 
 represented the heavy types most generally used in spraying for the 
 red scale. The effectiveness of the treatments was determined by 
 making counts of the full-grown and nearly full-grown insects at 20 
 points on the bark on each of 10 trees in each test. 
 
 The wide range in the degree of control of a, given spray in the 
 different groves may be disconcerting to many readers. This matter 
 has been touched upon in preceding sections. In the tests with 1% 
 per cent of the 100 viscosity oil, the percentage of insects alive varied 
 from 56.18 to 11.06 per cent; with 2 per cent of the oil the per- 
 centage alive ranged from 26.92 to 5.39 per cent; and with the 2% 
 per cent of the oil the percentage alive ranged from 14.03 to 1.78 per 
 cent. These variations in different groves and among tests are prob- 
 ably due to many factors. It is believed, however, that the number of 
 groves was sufficiently large so that the average result shown at the 
 bottom of table 16 gives a dependable indication of the efficiencies of 
 the various treatments. 
 
 The data indicate that the 100 viscosity oil was distinctly more 
 effective than the 80 viscosity oil and that the degree of control was 
 directly proportional to the percentage of oil in the spray. The poor 
 control given by the proprietary emulsions may be accounted for by 
 the fact that the emulsions were about 83 per cent oil, and the sprays 
 of the emulsions, therefore, contained only 1.66 per cent of oil. 
 
 Table 17 gives the results of the extensive experiment made in the 
 Barnett grove, previously referred to. The spraying was done in a 
 particularly thorough manner, the object being to produce a film of 
 oil on the entire surface of the bark and on each leaf and fruit. Two 
 grades of oil were used as regards heaviness, namely, 100 viscosity 
 and 80 viscosity. The sulfonation ranged from 86 to 100 per cent, 
 The 100 viscosity oil was used at IV2, 2, 2%, and 3 per cent, and the 
 80 viscosity oil was used at 2, 2%, and 3 per cent. The tests included 
 sprays of oil and water only, and sprays containing blood albumen 
 spreader at the rate of 4 ounces and 8 ounces to 100 gallons. 
 
 The percentages of insects alive are based on counts made at 20 
 places on the bark on each of 10 trees in each test. The places on 
 which the insects were counted were selected at random. The extent 
 of the discrepancies due to experimental error in sampling is not 
 
76 
 
 University of California — Experiment Station 
 
 known. Regardless of the variations due to factors of heterogeneity 
 and experimental error, the results appear to indicate very definitely 
 that spray containing' blood albumen spreader at the rate of 4 ounces 
 
 TABLE 17 
 
 Summary of Eesults of Experiments in Spraying for Bed Scale in the 
 
 J. M. Barnett Lemon Grove, Showing Number of Insects 
 
 Counted and Percentage Surviving on Rough Bark 
 
 Specifications 
 of oil 
 
 
 
 No spreader 
 (oil and water only) 
 
 Blood albumen spreader 
 4 ounces to 100 gallons 
 
 Blood albumen spreader 
 8 ounces to 100 gallons 
 
 Vis- 
 cosity, 
 
 Per cent 
 
 unsul- 
 
 fonat- 
 
 able 
 
 Per cent 
 
 of oil 
 in spray 
 
 Insects counted 
 
 Per 
 
 cent of 
 
 insects 
 
 alive 
 
 Insects counted 
 
 Per 
 cent of 
 insects 
 alive 
 
 Insects counted 
 
 Per 
 cent of 
 
 in 
 seconds 
 
 Total 
 
 Alive 
 
 Total 
 
 Alive 
 
 Total 
 
 Alive 
 
 insects 
 alive 
 
 
 100 
 90 
 
 86 
 
 98 
 90 
 86 
 
 { m 
 
 \ 2 
 
 I 3 
 
 if 
 
 3,860 
 2,323 
 
 
 25 21 
 13 13 
 
 37.00 
 18.55 
 
 968 
 
 21.10 
 
 14.00 
 
 2,868 
 3,161 
 
 2,592 
 2,388 
 2,118 
 
 3,334 
 3,753 
 2,953 
 
 3,158 
 2,769 
 2,700 
 
 3,018 
 2,883 
 5,364 
 
 3,285 
 2,177 
 2,457 
 
 735 
 196 
 
 1,092 
 
 328 
 50 
 
 25.72 
 6.19 
 
 42.11 
 13 75 
 2.36 
 
 2,927 
 3,355 
 
 2,930 
 
 2,278 
 2,680 
 
 924 
 367 
 
 31 51 
 
 100 
 
 
 10 93 
 
 
 973 
 305 
 
 1,024 
 623 
 
 
 100 
 
 816 
 
 293 
 
 95 
 
 27.84 
 12.87 
 
 
 2,773 
 3,306 
 
 3,766 
 
 3,739 
 
 2,971 
 
 3.54 
 
 
 1,192 
 313 
 106 
 
 561 
 214 
 166 
 
 765 
 385 
 439 
 
 289 
 
 179 
 
 79 
 
 35.77 
 8.35 
 3 59 
 
 17.82 
 7.73 
 6 15 
 
 25.36 
 13.35 
 
 8.00 
 
 8.78 
 8.23 
 
 3.22 
 
 
 100 
 
 3,992 
 3,368 
 3,834 
 
 2,543 
 3,207 
 1,826 
 
 3,104 
 2,811 
 2,990 
 
 2,887 
 2,730 
 3,144 
 
 996 
 400 
 254 
 
 386 
 508 
 290 
 
 942 
 539 
 396 
 
 634 
 442 
 351 
 
 24 94 
 11.88 
 6 63 
 
 80 
 80 
 80 
 
 365 
 789 
 416 
 
 15.14 
 15.84 
 15.87 
 
 30.34 
 19.08 
 13,24 
 
 21.91 
 16.20 
 11.14 
 
 Average 
 with 100 
 
 viscositj 
 
 , all oils 
 seconds 
 
 2 
 
 ] 2H 
 [3 
 
 
 
 30.17 
 16.49 
 
 
 
 3954 
 15.27 
 4.28 
 
 
 
 27.78 
 11.78 
 
 
 5.36 
 
 Average 
 with 80 
 
 viscosit 
 
 , all oils 
 seconds 
 
 
 ' 2 
 3 
 
 
 
 14.99 
 
 
 
 16.89 
 994 
 6 50 
 
 
 
 22.99 
 17 02 
 13.03 
 
 
 * 
 
 
 to 100 gallons is distinctly more effective than spray containing the 
 spreader at 8 ounces to 100 gallons. The average results for all tests, 
 given at the bottom of the table, indicate that the spray containing 
 blood albumen spreader at the rate of 4 ounces to 100 gallons may 
 
Bul, 527] The Tank-Mixture Method of Using Oil Spray 
 
 77 
 
 have about the same degree of efficiency as the spray of oil and 
 water only. 
 
 Effectiveness of Oil Spray on Branches, Twigs, Leaves, and 
 Fruit. — Counts were made of the insects on 20 green twigs, 20 leaves, 
 20 lemons, and on 20 places on the rough bark of branches on each of 
 10 trees in various tests in order to determine the effectiveness of 
 oil sprays in killing v red scale on different parts of the tree. The 
 results of counts made in the Lee Utley grove are given in table 18. 
 
 TABLE 18 
 
 Per Cent of Bed Scale on Branches, Twigs, Leaves, and Lemons 
 Surviving the Application of Oil Sprays 
 
 Unit 
 
 Oil viscosity 
 100 seconds 
 
 Oil viscosity 
 80 seconds 
 
 Per cent of oil in spray 
 
 2V 2 
 
 Per cent of insects alive 
 
 lYi 
 
 Branches 
 
 Twigs 
 
 Leaves 
 
 Lemons.. 
 
 31 99 
 3.69 
 83 
 3.62 
 
 21.79 
 
 14.03 
 
 32.59 
 
 0.79 
 
 41 
 
 4.89 
 
 25 
 
 0.16 
 
 0.39 
 
 3 94 
 
 7 31 
 
 3 69 
 
 11.36 
 1 71 
 0.33 
 1.11 
 
 The data show that the spray is least effective on the branches and 
 most effective on the leaves. The insects on the twigs and fruit are 
 much more easily killed than those on the bark. A large proportion 
 of those found alive on the twigs and fruit were obviously missed 
 by the spray. 
 
 ADVANTAGES AND SHORTCOMINGS OF THE 
 TANK-MIXTURE METHOD 
 
 The Question of Standardization. — The principal advantage of 
 the tank-mixture method is that it provides a spray of known com- 
 position at a marked saving over the cost of emulsions. In regard 
 to standardization, the data presented on the preceding pages indicate 
 that under like conditions some brands of emulsions may deposit 
 several times as much oil as other brands. This means that when 
 used in the usual proportions of 1% or 2 per cent, some brands 
 probably produce a lighter coverage than will give effective control 
 of the insects, and other brands produce a heavier coverage than is 
 necessary or desirable. The more important facts relating to varia- 
 
78 University of California — Experiment Station 
 
 tions among emulsions can be made clear by the following example : 
 An emulsion such as the orchardist uses can be made by dissolving 
 2 ounces of soap in y 2 gallon of water, stirring in 2 gallons of oil, and 
 forcing the mixture through a spray nozzle. As regards appearance 
 and general consistency, the emulsion would be the same if 4, 6, 8, or 
 even 16 ounces of soap were used instead of 2 ounces. However, 
 emulsions made with different amounts of soap would give decidedly 
 different results when diluted in the usual manner and sprayed on 
 trees. If the spray water were soft, like rain-water, the spreading 
 efficiency would vary directly with the amount of soap, that is, 2 
 ounces of soap would spread better than a spray of oil and water only, 
 4 ounces would spread better than 2 ounces, 6 ounces would spread 
 better than 4 ounces, etc. The amount of oil deposited would vary 
 inversely with the amount of soap used, that is, 2 ounces would 
 deposit less oil than a spray of oil and water only, 4 ounces would 
 deposit less than 2 ounces, 6 ounces would deposit less than 4 ounces, 
 etc. If the spray water were hard, a certain amount of soap would 
 be used in the reaction with the salts causing the hardness. In this 
 case an emulsion made with 8 ounces of soap might spread no better 
 than a mixture of oil and water only, and the amount of oil deposited 
 might be as large as would be deposited by a mixture of oil and 
 water only. 
 
 Soap is but one of many substances used in oil emulsions. Certain 
 compounds of casein, particularly ammonium casemate and potassium 
 casemate, are used to a considerable extent. Mixtures or solutions 
 of two or more emulsifying substances are used in some emulsions. 
 Obviously, there is no standardization in the kind of emulsifying 
 agent or the proportion used in the manufacture of emulsions, and 
 this fact largely accounts for variations in the performance of sprays 
 of different brands of emulsions. 
 
 The function of an emulsiner or spreader in the spray is three- 
 fold : (1) to make it easy to maintain a uniform dispersal of the oil 
 through the water in the spray tank; (2) to cause the spray mixture 
 to spread over the surface of the tree,, thereby facilitating the appli- 
 cation of the spray; and (3) to govern the amount of oil deposited 
 and the uniformity of the deposit. From the standpoint of the. manu- 
 facturer another very essential function of an emulsiner is to hold 
 the oil in an emulsified condition during transportation and storage 
 and until it is used by the grower. 
 
 The investigation tends to indicate that, as regards the performance 
 of the spray, nothing is gained by emulsifying the oil. When an 
 emulsion of 2 ounces of soap, % gallon of water, and 2 gallons of oil, 
 
Buu 527] The Tank-Mixture Method of Using Oil Spray 79 
 
 for example, is placed in 97% gallons of water, making a spray of 2 
 per cent oil, the 2 ounces of soap become evenly diluted in the water 
 and the globules of oil become uniformly dispersed through the water 
 by the action of the agitators. From the standpoint of spreading, 
 oil-depositing quality, and practical results in insect control, this 
 spray mixture is essentially the same as one in which the 2 ounces 
 of soap and 2 gallons of oil are added separately to the tank and a 
 uniform mixture of the oil and water produced and maintained by 
 the agitators. 
 
 Most emulsifying substances used in emulsions are affected by the 
 hardness of the spray water. Calcium casemate was used largely in 
 the commercial trials of the tank-mixture method in 1928, 1929, and 
 1930. Although the results were satisfactory on the whole, it was 
 noted that in some cases the spreading and oil-depositing quality of 
 the spray was markedly affected by the hardness of the spray water. 
 This spreader was found to be distinctly unsuited for use in certain 
 districts. In the search for a suitable spreader for oil sprays, powdered 
 blood albumen proved to be particularly satisfactory. The data 
 obtained indicate that it is not affected by the hardness of spray 
 water and possesses excellent spreading quality. During 1930 it was 
 tried out in approximately 200 tests in the control of black, citricola, 
 and red scales, and also was used in extensive commercial trials. It 
 was used entirely in tank-mixture spray during 1931. 
 
 The Question of Cost. — It was estimated that the growers who 
 participated in the commercial trial of the tank-mixture method in 
 1930, in which about 4,000 acres were sprayed, saved over $35,000 
 in the cost of spray material. The majority of them paid 26 cents a 
 gallon for the oil. The cost of the spreader amounted to 7 cents for 
 each 100 gallons of spray. The prevailing cost per gallon of emulsion 
 was approximately as follows : heavy emulsion, 90 cents ; medium 
 emulsion, 70 cents; light-medium and light emulsion, 50 cents. 
 
 As a result of the low cost of tank-mixture spray, the price of 
 the various grades of emulsions dropped during 1931 from 10 to 15 
 cents a gallon below the prevailing prices of the preceding year. The 
 cost of the oils specified for tank-mixture spray varied somewhat 
 during the year and among districts, but the average cost per gallon 
 was approximately as follows: heavy oil, 34 cents; medium oil, 28 
 cents; light-medium and light oils, 24 cents. The cost of the blood 
 albumen spreader was 5 cents for each 100 gallons of spray. Con- 
 sidering the lower cost of the oil and the fact that 1% gallons of oil 
 is equivalent to 2 gallons of emulsion, owing to the water contained 
 in the emulsion, it appears that in general the cost per 100 gallons of 
 
80 University of California — Experiment Station 
 
 tank-mixture spray was from one-third to one-half of the prevailing 
 cost of emulsions during 1930 and 1931. This meant a saving to the 
 growers of $10 to $20 an acre in the cost of spray material. 
 
 Even though emulsions are 15 to 20 per cent water, they apparently 
 cannot be manufactured and marketed at as low a cost per gallon as 
 the pure spray oil. 
 
 The Question of Quality. — The orchardist uses the oil in the same 
 form in which it is produced at the refinery. The question arises : 
 Can he depend on the quality's being what it is represented to be? As 
 explained under the topic, "Major Qualities of Oil Spray," the speci- 
 fications for spray oils cover the qualities of purity (sulfonation) and 
 distillation range. These qualities are accurately measured by tests 
 adopted by the American Society for Testing Materials, and are 
 regularly used by all oil-refining companies. In view of the fact that 
 the large oil companies producing spray oils have efficient control test- 
 ing laboratories where each run or batch of oil is systematically tested 
 as it is produced, it would appear that the variations in spray oils 
 would be no greater than in commercial insecticides, including oil 
 emulsions, Firms manufacturing and selling oil for spray purposes 
 will, of course, be required to operate under a state license, as are 
 other insecticide manufacturers. 
 
 It appears that there is at present but one firm in this country 
 regularly manufacturing blood albumen in large quantity. The 
 product is known as Grade A Powdered Blood Albumen. It is approxi- 
 mately 96 to 98 per cent water soluble, has a moisture content of 
 approximately 5 per cent, and from 90 to 95 per cent will pass through 
 a 100-mesh screen. Any product meeting these specifications is satis- 
 factory. The possibility of variation in 'quality would probably be 
 no greater than in other commercial products with which insecticides, 
 including oil emulsions, are compounded. In order to make it dissolve 
 readily in water, 1 part of the blood albumen is mixed with 3 parts of 
 fuller's earth. The quality of the fuller's earth used in the spreader 
 is not particularly important, inasmuch as its function is that of a 
 diluent only. Samples of the spreader put up in Kraft paper bags 
 and kept for eight months under average warehouse conditions, showed 
 no deterioration. It should be kept dry, since the absorption of 
 moisture will cause deterioration; owing to this fact glassine-lined 
 bags are more suitable than ordinary Kraft paper bags. 
 
 The question of the quality of tank-mixture sprays and that of 
 their practicability, discussed in the succeeding topic, necessarily 
 involve a comparison with emulsions, and in this connection certain 
 shortcomings of emulsions may be mentioned. Most emulsions are 
 
Bul. 527] The Tank-Mixture Method of Using Oil Spray 81 
 
 composed of oil and water in the proportions of about 80 per cent 
 oil and 20 per cent water, in which the emulsifier is dissolved. Emul- 
 sions tend to undergo change. The change is usually physical, but it 
 may be both physical and chemical. The nature of the change 
 depends upon the kind of emulsifier, the physical character of the 
 emulsion^ the period of time elapsing between the time the emulsion 
 is manufactured and the time it is used, and the temperature and 
 treatment to which the emulsion may be subjected before being used. 
 When emulsions are properly made and properly handled these 
 factors on the whole are not particularly important. However, despite 
 careful handling, much wastage is inevitable. Emulsions left over in 
 drums in the grove very commonly break down to the extent of 
 being unusable, and stocks of emulsions left on hand in warehouses 
 either must be regarded as unusable or be sold with more or less 
 uncertainty as to whether or not they will give the same results as 
 freshly made emulsions. Instances are certain to occur in which 
 emulsions will remain at the grove for several days before use, and 
 owing to the high temperature usually prevailing during the spraying 
 season they may undergo marked de-emulsification. The continued 
 vibration and jarring to which emulsions are subjected during trans- 
 portation by train and truck sometimes cause pronounced de-emulsifi- 
 cation. Spray operators find emulsions messy to handle because the 
 thick mass adheres to the sides of the drums, to the utensil used for 
 dipping, and to the sides of the measure. 
 
 Tank -mixture sprays involve none of these shortcomings of emul- 
 sions. Oil kept in tight drums does not undergo material change 
 regardless of temperature or duration of storage. This statement is 
 based on tests with spray oils kept for a period of four years. There 
 is no wastage. The oil is delivered to the grove in 50-gallon drums. 
 The spray operator draws the oil through a faucet and can accurately 
 fill his measure to the desired level. 
 
 The Question of Practicability. — The practicability of the tank- 
 mixture method hinges chiefly upon the question of spray-tank 
 agitation. The subject of agitator equipment and efficiency of agita- 
 tion has been investigated with special thoroughness. The data 
 obtained show that practically the only limiting factor is that of the 
 horsepower of the motor. In the case of most 300-gallon and 400- 
 gallon tanks, three (fig. 4A) or four (fig. 4:C,D,G) large agitators 
 turning at a speed of 200 r.p.m. will provide sufficient agitation to 
 produce and maintain a uniform mixture of oil and water, and 
 approximately y 2 hp. is consumed by the agitators. According to 
 information obtained through the cooperation of sprayer manufac- 
 
82 University of California — Experiment Station 
 
 turers, the sprayers in the citrus districts of California are equipped 
 with motors ranging from 8 to 24 hp. The average is about 15 hp. 
 and comparatively few are as low as 8 hp. It is the opinion of 
 sprayer manufacturers that in the case of sprayers with 8 hp. motors, 
 % hp. applied to agitation is not excessive and is relatively negligible 
 in the case of the average sprayer motor. 
 
 The question arises as to whether or not trouble might be experi- 
 enced with tank mixtures owing to loss of power through use, which 
 might result in such a decrease of agitation that a uniform mixture 
 could no longer be produced and maintained. Concerning this point 
 it may be said that, as shown by the experimental data, the agitation 
 specified for tank-mixture sprays provides for a wide margin of 
 safety. Furthermore, inasmuch as a decrease in the speed of the 
 motor results in a lowering of pressure, only indifference on the part 
 of an operator would cause him to continue to use a motor when it 
 was seriously inefficient. During the commercial trial of the tank- 
 mixture method in 1930 careful inspections were made on the agitation 
 of 78 sprayers. No motor was found which was not handling the 
 agitation satisfactorily. In the course of spraying one grove, the 
 agitator chain of the sprayer broke. The trouble was immediately 
 discovered but the particular tank of spray was applied without 
 agitation, resulting in poor control on the first trees and injury to 
 the last two. Sprayer manufacturers now equip their machines with 
 steel roller chains and steel sprockets, and a large number of spray 
 operators have installed this modern type of chain and sprocket. No 
 complaints of agitator trouble or poor agitation were reported during 
 1931. However, there may have been grounds for complaint in some 
 cases. It is believed that the chief possibility of trouble lies in the 
 danger that some operators will attempt to apply tank-mixture spray 
 without first making sure that their agitator equipment is in order 
 and meets the requirements specified. It is advisable, therefore, for 
 growers to require operators to produce satisfactory evidence that their 
 sprayers have been inspected and passed as meeting the requirements 
 for tank-mixture spraying. 
 
 RECOMMENDATIONS FOR TANK-MIXTURE SPRAY 
 
 Specifications for Blood Albumen Spreader. — The blood albumen 
 spreader consists of 1 part of powdered blood albumen intimately 
 mixed with 3 parts of fuller's earth, or a similar form of neutral 
 earth. The blood albumen should be 96 to 100 per cent water soluble, 
 should have a moisture content of not more than 6 per cent, and 90 
 per cent should pass through a 100-mesh screen. It is probably not 
 
Bul, 527] The Tank-Mixture Method of Using Oil Spray 
 
 83 
 
 advisable for the individual grower to attempt to make the spreader 
 since reliable firms are better equipped to compound it and pack it in 
 accurately weighed bags. 
 
 The spreader is used at the rate of 4 ounces to 100 gallons of spray. 
 
 Specifications for Oils. — During the past few years oil emulsions 
 have been grouped into four general classes of heaviness : light, light- 
 medium, medium, and heavy. Each of these classes, however, has 
 included oils of a wide variety, some being narrow-cut and some 
 wide-cut, or blends of various grades of heaviness ranging from very 
 light oils to heavy oils. It is believed that the specifications given in 
 table 19 afford a fairly satisfactory basis for grades of heaviness: 
 
 TABLE 19 
 
 Specifications of Oils for Tank-Mixture Spray 
 
 
 Maximum 
 percent* 
 distilled 
 at 575° F 
 
 Minimum 
 per cent* 
 distilled 
 
 at 700° F 
 
 Sulfonation 
 
 
 20 
 15 
 10 
 5 
 
 
 95 
 90 
 85 
 80 
 70 
 
 per cent 
 90 
 
 Grade 2 
 
 91 
 
 Grade 3 
 
 92 
 
 
 93 
 
 
 95 
 
 
 
 * The object of the specifications for distillation is to limit the 
 percentage of light fractions and also the percentage of heavy 
 fractions for the various grades. In grade 1, for example, not 
 more than 30 per cent of the oil shall distill at 575° F, while not 
 less than 94 per cent shall distill at 700° F. 
 
 These specifications are founded on the fact that the most practical 
 and economical way for refiners to produce oils of the various grades 
 of heaviness is to make a straight-run light oil of the specifications 
 of grade 1, and a straight-run heavy oil of the specifications of grade 
 2; and to blend these grades in suitable proportions to produce the 
 intermediate grades. They also are founded on the fact that com- 
 mercial use and the orchard experiments reported on preceding pages 
 show that grades of oil produced in this manner are well adapted to 
 meeting the requirements of citrus spraying. 
 
 On the basis of present knowledge, it appears that five grades of 
 heaviness are needed to meet the various conditions of citrus pest 
 control effectively. In order to promote the cause of standardization, 
 and to simplify the problem of the grower who desires to order an 
 oil of a definte grade of heaviness, the grades are designated by 
 number, No. 1 being the lightest, and No. 5 the heaviest. Approx- 
 
84 University of California — Experiment Station 
 
 imately, grade 2 contains 25 per cent heavy oil, grade 3 contains 40 
 per cent heavy oil, and grade 4 contains 60 per cent. 
 
 Grade 1 specifies a rather narrow-cut oil and falls strictly in the 
 light class. It has a wide margin of safety, as regards volatility, and, 
 therefore, is particularly useful for off-season spraying for red spider 
 and scale insects. It is the preferable grade to use in the interior 
 districts where red spider is not a problem and where impaired bloom- 
 ing and coloring of fruit are important factors of consideration in 
 spraying navel oranges. The dosage recommended for citricola and 
 black scales is iy 2 to 1% per cent. For winter and spring treatment 
 of red spider, a thorough application, using iy 2 per cent, has given 
 satisfactory results, 
 
 Grade 2 falls in the light-medium class and corresponds to the 
 grade designated as "light-medium 65" in the recommendations for 
 tank-mixture spray during 1931. Its commercial use that year and 
 the results of experiments indicate that it meets the needs for black 
 scale and red spider control, and provides a relatively safe spray for 
 oranges in the districts intermediate between coastal and interior. 
 The dosage recommended is 1% to 1% per cent. 
 
 Grade 3 also falls in the light-medium class, It was extensively 
 used during 1931 in the coastal districts in spraying oranges for red, 
 purple, and black scales, and red spider. On the whole, the results 
 were very satisfactory, although the control was not as high as was 
 obtained with grade 4. The dosage recommended is 1% to 1% per cent. 
 
 Grade 4 corresponds to the oils contained in the leading brands 
 of medium emulsions which have been used extensively in spraying 
 oranges in the coastal district. It will give a higher degree of control 
 of scale insects, particularly red scale, and a better hold-over control 
 of red spider than grade 3. It is the heaviest oil that should be applied 
 to orange trees. The dosage recommended is 1% to 1% per cent, 
 
 Grade 5 is to be used only in spraying lemon trees for the red 
 scale. The dosage may be gauged within limits by the degree of 
 infestation and the degree of control desired, bearing in mind the 
 fact that 1% per cent of this oil in tank -mixture spray is equivalent 
 to 2 per cent of the heavy emulsions which were widely used prior 
 to the year 1931. It is estimated that more than half of all spraying 
 of lemons for the control of the red scale during 1931 was done with 
 tank-mixture spray, using this grade of oil. The prevailing dosage 
 was 2 per cent. 
 
 With grades 1 and 2 particularly, iy 2 per cent is adequate for', 
 average conditions of infestation. 
 
Bul. 527 J The Tank-Mixture Method of Using Oil Spray 85 
 
 Sprayer Equipment. — Spray tanks should have sufficient agitation 
 to meet the requirements of the agitation test described in the section, 
 "Method of Making Agitation Test." This necessitates an agitator 
 speed of approximately 200 r.p.m. and the use of large-sized agitators. 
 
 Directions. — No particular directions need be followed in placing 
 the oil and spreader in the tank, but the preferable procedure is to 
 add the oil when starting to fill, and then to sift in the spreader. 
 The agitator should be kept running continuously from the time the 
 oil is added until the spray is applied. This requirement eliminates 
 the possibility of the use of imperfect mixtures and also the possibility 
 of splashing out the oil while the sprayer is being hauled from the 
 filling station to the spraying point in the grove. 
 
 Effectiveness of Control Versus Safety. — In the use of oil sprays 
 it is necessary to take into consideration effectiveness of control, 
 safety to tree, and cost. These factors relate to a wide variety of 
 conditions and possibilities which, in a very large measure, the 
 grower must evaluate on his own responsibility. 
 
 The most effective oil for the control of scale insects is the heaviest ; 
 but the heavier the oil the greater the risk of injurious effects. The 
 safest oil of a given heaviness is the highest in sulf onation ; but the 
 higher the sulfonation the greater the cost. Weak trees are more 
 susceptible to injury than trees in good condition, yet experience 
 has shown that trees appearing to be in good condition may be 
 subnormal physiologically and may suffer more serious injury than 
 some trees which are apparently weak. 
 
 Other things being equal, the degree of control varies directly 
 with the quantity of spray applied ; but the more spray applied the 
 greater the cost and the greater the possibility of injurious effects. 
 Satisfactory control may be obtained in lightly infested groves by a 
 light application of spray. The heavier the infestation the greater the 
 quantity of spray and the greater the degree of thoroughness required. 
 
 The most effective spray appears to be that of oil and water only, 
 but this spray ranks lowest in safety. The safest spray is the one 
 which builds up to the least extent; but it is the most expensive 
 because a higher percentage of oil must be used in order to obtain a 
 satisfactory degree of control. The use of blood albumen spreader at 
 the rate of 4 ounces to 100 gallons gives a spray that is about average 
 in oil-depositing quality. This means that when the proper grade of 
 oil is used at 1% to 1% per cent, and the degree of thoroughness of 
 the spray application is average and the physical condition of the 
 tree is normal, effective control may be obtained without particular 
 
86 University of California — Experiment Station 
 
 risk of excessive fruit-drop, leaf -drop, or other unfavorable effects. 
 However, observations on the use of oil sprays during' the past several 
 years indicate very clearly that a certain element of risk is involved 
 even when the spraying- is done under conditions which may seem to 
 be optimum. There is no means of definitely knowing in advance 
 whether or not a tree will react unfavorably as a result of having its 
 leaves coated and partially filled with oil. The most that can be done 
 to guard against such reactions is to endeavor to use the lightest oil 
 and to place no more oil on the tree than is required to control the 
 pests concerned. 
 
STATION PUBLICATIONS AVAILABLE FOR FREE DISTRIBUTION 
 
 BULLETINS 
 
 in the 
 Cali 
 
 Fruit 
 
 No. 
 
 253. Irrigation and Soil Conditions in the 
 
 Sierra Nevada Foothills, California. 
 263. Size Grades for Ripe Olives. 
 279. Irrigation of Rice in California. 
 283. The Olive Insects of California. 
 310. Plum Pollination. - 
 331. Phylloxera-Resistant Stocks. 
 343. Cheese Pests and Their Control. 
 
 348. Pruning Young Olive Trees. 
 
 349. A Study of Sidedraft and Tractor 
 
 Hitches. 
 
 357. A Self-Mixing Dusting Machine for 
 Applying Dry Insecticides and Fun- 
 gicides. 
 
 361. Preliminary Yield Tables for Second- 
 Growth Redwood. 
 
 364. Fungicidal Dusts for the Control of 
 Bunt. 
 
 369. Comparison of Woods for Butter Boxes. 
 
 370. Factors Influencing the Development 
 
 of Internal Browning of the Yellow 
 Newtown Apple. 
 
 371. The Relative Cost of Yarding Small 
 
 and Large Timber. 
 
 373. Pear Pollination. 
 
 374. A Survey of Orchard Practices 
 
 Citrus Industry of Southern 
 
 fornia. 
 379. Walnut Culture, in California. 
 386. Pruning Bearing Deciduous 
 
 Trees. 
 389. Berseem or Egyptian Clover. 
 
 392. Fruit Juice Concentrates. 
 
 393. Crop Sequences at Davis. 
 
 394. I. Cereal Hay Production in California. 
 
 II. Feeding Trials with Cereal Hays. 
 
 395. Bark Diseases of Citrus Trees in Cali- 
 
 fornia. 
 
 396. The Mat Bean, Phaseolus Aconitifolius. 
 404. The Dehydration of Prunes. 
 
 406. Stationary Sorav Plants in California. 
 
 407. Yield. Stand, and Volume Tables for 
 
 White Fir in the California Pine 
 Region. 
 
 408. Alternaria Rot of Lemons. 
 
 409. The Digestibility of Certain Fruit By- 
 
 products as Determined for Rumi- 
 nants. Part I. Dried Orange Pulp 
 and Raisin Pulp. 
 
 410. Factors Influencing the Quality of Fresh 
 
 Asparagus After It is Harvested. 
 
 416. Culture of the Oriental Persimmon in 
 
 California. 
 
 417. Poultry Feeding: Principles and Prac- 
 
 tice.. 
 
 418. A Study of Various Rations for Fin- 
 
 ishing Range Calves as Baby Beeves. 
 
 419. Economic Aspects of the Cantaloupe 
 
 Industry. 
 
 420. Rice and Rice By-Products as Feeds 
 . for Fattening Swine. 
 
 421. Beef Cattle Feeding Trials, 1921-24. 
 423.. Apricots (Series on California Crops 
 
 and Prices). 
 
 425. Apple Growing in California. 
 
 426. Apple Pollination Studies in California. 
 
 427. The Value of Orange Pulp for Milk 
 
 Production. 
 
 428. The Relation of Maturity of California 
 
 Plums to Shipping and Dessert 
 Quality. 
 
 431. Raisin By-Products and Bean Screen- 
 
 ings as Feeds for Fattening Lambs. 
 
 432. Some Economic Problems Involved in 
 
 the Pooling of Fruit. 
 
 No. 
 
 433 
 
 435 
 439 
 
 445 
 
 446. 
 447. 
 
 448. 
 
 449. 
 
 450. 
 
 452. 
 454. 
 
 455. 
 
 456. 
 
 458. 
 
 459. 
 
 462. 
 464. 
 
 465. 
 466. 
 
 467. 
 468. 
 
 469. 
 470. 
 
 472. 
 473. 
 
 474. 
 
 475. 
 476. 
 
 477. 
 
 479. 
 
 480. 
 
 481. 
 
 482. 
 483. 
 484. 
 
 485. 
 487. 
 
 , Power Requirements of Electrically 
 Driven Dairy Manufacturing Equip- 
 ment. 
 
 The Problem of Securing Closer Rela- 
 tionship between Agricultural Devel- 
 opment and Irrigation Construction. 
 
 The Digestibility of Certain Fruit By- 
 Products as Determined for Rumi- 
 nants. Part II. Dried Pineapple 
 Pulp, Dried Lemon Pulp, and Dried 
 Olive Pulp. 
 
 The Feeding Value of Raisins and 
 Dairy By-Products for Growing and 
 Fattening Swine. 
 
 Economic Aspects of the Apple In- 
 dustry. 
 
 The Asparagus Industry in California. 
 
 A Method of Determining the Clean 
 Weights of Individual Fleeces of Wool. 
 
 Farmers' Purchase Agreement for Deep 
 Well Pumps. 
 
 Economic Aspects of the Watermelon 
 Industry. 
 
 Irrigation Investigations with Field 
 Crops at Davis, and at Delhi, Cali- 
 fornia, 1909-1925. 
 
 Economic Aspects of the Pear Industry. 
 
 Rice Experiments in Sacramento Val- 
 ley, 1922-1927. 
 
 Reclamation of the Fresno Type of 
 Black-Alkali Soil. 
 
 Yield, Stand and Volume Tables for 
 Red Fir in California. 
 
 Factors Influencing Percentage Calf 
 Crop in Range Herds. 
 
 Economic Aspects of the Fresh Plum 
 Industry. 
 
 Prune Supply and Price Situation. 
 
 Drainage in the Sacramento Valley 
 Rice Fields. 
 
 Curly Top Symptoms of the Sugar Beet. 
 
 The Continuous Can Washer for Dairy 
 Plants. 
 
 Oat Varieties in California. 
 
 Sterilization of Dairy Utensils with 
 Humidified Hot Air. 
 
 The Solar Heater. 
 
 Maturity Standards for Harvesting 
 Bartlett Pears for Eastern Shipment. 
 
 The Use of Sulfur Dioxide in Shipping 
 Grapes. 
 
 Adobe Construction. 
 
 Economic Aspects of the Sheep In- 
 dustry. 
 
 Factors Affecting the Cost of Tractor 
 Logging in the California Pine 
 Region. 
 
 Walnut Supply and Price Situation. 
 
 Poultry Houses and Equipment. 
 
 Improved Methods of Harvesting Grain 
 Sorghum. 
 
 I. Irrigation Experiments with Peaches 
 in California. II. Canning Quality 
 of Irrigated Peaches. 
 
 The Use, Value, and Cost of Credit in 
 Agriculture. 
 
 Utilization of Wild Oat Hay for Fat- 
 tening Yearling Steers. 
 
 Substitutes for Wooden Breakpins. 
 
 Utilization of Surplus Prunes. 
 
 The Effects of Desiccating Winds on 
 
 Citrus Trees. 
 Drying Cut Fruits. 
 
 Asparagus (Series on California Crops 
 and Prices). 
 
BULLETINS— (Continued) 
 
 No. 
 
 488. Cherries (Series on California Crops 
 
 and Prices). 
 
 489. Irrigation Water Requirement Studies 
 
 of Citrus and Avocado Trees in San 
 Diego County, California, 1926 and 
 1927. 
 
 490. Olive Thinning and Other Means of 
 
 Increasing Size of Olives. 
 
 491. Yield, Stand, and Volume Tables for 
 
 Douglas Fir in California. 
 
 492. Berry Thinning of Grapes. 
 
 493. Fruit Markets in Eastern Asia. 
 
 494. Infectious Bronchitis in Fowls. 
 
 495. Milk Cooling on California Dairy 
 
 Farms. 
 
 496. Precooling of Fresh Fruits and Tem- 
 
 peratures of Refrigerator Cars and 
 Warehouse Rooms. 
 
 497. A Study of the Shipment of Fresh 
 
 Fruits and Vegetables to the Far East. 
 
 498. Pickling Green Olives. 
 
 499. Air Cleaners for Motor Vehicles. 
 
 500. Dehydration of Grapes. 
 
 501. Marketing California Apples. 
 
 502. Wheat (Series on California Crops 
 
 and Prices). 
 
 503. St. Johnswort on Range Lands of 
 
 California. 
 
 504. Economic Problems of California Agri- 
 
 culture. (A Report to the Governor 
 of California.) 
 
 No. 
 
 505. The Snowy Tree Cricket and Other 
 
 Insects Injurious to Raspberries. 
 
 506. Fruit Spoilage Disease of Figs. 
 
 507. Cantaloupe Powdery Mildew in the 
 
 Imperial Valley. 
 
 508. The Swelling of Canned Prunes. 
 
 509. The Biological Control of Mealybugs 
 
 Attacking Citrus. 
 
 510. Olives (Series on California Crops 
 
 and Prices). 
 
 511. Diseases of Grain and Their Control. 
 
 512. Barley (Series on California Crops 
 
 and Prices). 
 
 513. An Economic Survey of the Los 
 
 Angeles Milk Market. 
 
 514. Dairy Products (Series on California 
 
 Crops and Prices). 
 515.. The European Brown Snail in Cali- 
 fornia. 
 
 516. Operations of the Poultry Producers 
 
 of Southern California, Inc. 
 
 517. Nectar and Pollen Plants of California. 
 
 518. The Garden Centipede. 
 
 519. Pruning and Thinning Experiments 
 
 with Grapes. 
 
 520. A Survey of Infectious Laryngotrache- 
 
 itis of Fowls. 
 
 521. Alfalfa (Series on California Crops 
 
 and Prices). 
 
 CIRCULARS 
 
 No. 
 
 115. Grafting Vinifera Vineyards. 
 
 178. The Packing of Apples in California. 
 
 212. Salvaging Rain-Damaged Prunes. 
 
 230. Testing Milk, Cream, and Skim Milk 
 
 for Butterfat. 
 232. Harvesting and Handling California 
 
 Cherries for Eastern Shipment. 
 
 239. Harvesting and Handling Apricots and 
 
 Plums for Eastern Shipment. 
 
 240. Harvesting and Handling California 
 
 Pears for Eastern Shipment. 
 
 241. Harvesting and Handling California 
 
 Peaches for Eastern Shipment. 
 
 244. Central Wire Bracing for Fruit Trees. 
 
 245. Vine Pruning Systems. 
 
 248. Some Common Errors in Vine Pruning 
 
 and Their Remedies. 
 
 249. Replacing Missing Vines. 
 253. Vineyard Plans. 
 
 257. The Small-Seeded Horse Bean (Vicia 
 
 faba var. minor). 
 
 258. Thinning Deciduous Fruits. 
 
 259. Pear By-Products. 
 
 261. Sewing Grain Sacks. 
 
 262. Cabbage Production in California. 
 265. Plant Disease and Pest Control. 
 
 269. An Orchard Brush Burner. 
 
 270. A Farm Septic Tank. 
 
 No. 
 
 279. The Preparation and Refining of Olive 
 
 Oil in Southern Europe. 
 282. Prevention of Insect Attack on Stored 
 
 Grain. 
 288. Phylloxera Resistant Vineyards. 
 290. The Tangier Pea. 
 292. Alkali Soils. 
 
 294. Propagation of Deciduous Fruits. 
 296. Control of the California Ground 
 
 Squirrel. 
 301. Buckeye Poisoning of the Honey Bee. 
 
 304. Drainage on the Farm. 
 
 305. Liming the Soil. 
 
 307. American Foulbrood and Its Control. 
 
 308. Cantaloupe Production in California. 
 310. The Operation ef the Bacteriological 
 
 Laboratory for Dairy Plants. 
 
 316. Electrical Statistics for California 
 
 Farms. 
 
 317. Fertilizer Problems and Analysis of 
 
 Soils in California. 
 
 318. Termites and Termite Damage. 
 
 319. Pasteurizing Milk for Calf Feeding. 
 
 320. Preservation of F.ruits and Vegetables 
 
 by Freezing Storage. 
 
 321. Treatment of Lime-induced Chlorosis 
 
 with Iron Salts. 
 
 322. An Infectious Brain Disease of Horses 
 
 and Mules (Encephalomyelitis). 
 
 13m-6,'32