SB U) [a I Issued April ti, 1910. ^\4\% ^' ^' DEPARTMENT OF AGRICULTURE. ' ' ^' BUREAU OF CHEMISTRY— BULLETIN No. 131. ^' ' , H. W. WILEY, Chief of Hurmui. LEAD ARSENATE. I. Composition of lead arsenates found on the market. II. ''Home-made" lead arsenate and the chemicals entering into its manufacture. III. Action of lead arsenate on foliage. J. K. HAYWOOD, Chief, Miscellaneous Division, AND c. c. McDonnell, Chief, Insecticide and Fungicide Laboratory, Miscellaneous JHvision. IN COOPERATION WITH THE BUREAU OF ENTOMOLOGY. WASHINGTON: GOVERNMENT PRINTING OFFICE. 1910. Jtono graph, Book I.sstied April 0, 1910. U. S. DEPARTMENT OF AGRICULTURE, BUREAU OF CHEMISTRY - BULLETIN No. 131. H. W. WILEY, Chief of Biireiui. LEAD ARSENATE. I. Composition of lead arsenates found on the market. II. "Home-made" lead arsenate and the chemicals entering into its manufacture. III. Action of lead arsenate on foliage. rrei Agriculture of Massachusetts, 1897, p. 364. f U. S. Dept. Agr., Bureau of Chemistry Bui. 105, p. 1G5. rfLoc. cit., p. 365. «Loc. cit., p. 166. 23904— Bull. 131—10 3 18 LEAD AESENATE. In numerous trials with pure salts it was found that the latter reaction occurs almost theoretically, though a small amount of the tri-plumbic arsenate is usually formed. With lead acetate, however, there are other conditions which affect the .reaction, probably temperature, concentration, method of mixing, etc. In several cases when pure chemicals were used the resulting product was found to be principally the plumbic hydro- gen arsenate. Most of the samples examined in which the acetate was used in the preparation consisted mainly of the tri-plumbic arsenate, Pb3(AsOj2- This contains theoretically 74.40 per cent of lead oxid (PbO), and 25.60 per cent of arsenic oxid (AS2O5). As may be calculated from the reaction previously given, it will be found that by using pure crystallized lead acetate (58.81 per cent PbO) and crystallized sodium arsenate (36.84 per cent AS2O5) there will be required to make 1 pound of tri-plumbic arsenate 1.296 pounds of lead acetate and 0.695 pound of sodium arsenate, or 64.55 per cent of lead acetate and 35.45 per cent of sodium arsenate. Plumbic hydrogen arsenate, PbllAsO^, contains theoretically 64.26 per cent of lead oxid (PbO); 33.15 per cent of arsenic oxid (AS2O5), and 2.59 per cent of water of constitution. Calculating the amount of lead nitrate (67.35 per cent PbO), and sodium arsenate (36.84 per cent AS2O5) required to make 1 pound of this compound from the second reaction given, the following result is obtained: 0.954 pound of lead nitrate, and 0.900 pound of sodium arsenate, or 51.43 per cent of lead nitrate, and, 48.57 per cent of sodium arsenate. However, formulas can not be given based on technical or even on pure salts, for a number of reasons: (1) Pure salts are too expensive to use. (2) The technical grades show considerable variation in composition, as has been shown . (3) Allowance must be made for other salt-forming compounds in the sodium arsenate, notably chlorids, which use up some of the lead salt. (4) The lead salt should be in slight excess to insure rendering all of the arsenic insoluble. (5) Under the varying conditions which exist at the time of making, the reactions do not proceed as indicated by theory. In regard to the last reason, it may be said that even if the exact chemical composition of the salts were known and the correct propor- tions calculated tp satisfy the reaction were mixed together, it would seldom, if ever, result in a complete combination of the lead and arsenic radicals. The only way to proceed, therefore, is either to add lead salt considerably in excess of the theoretical amount, or to add the lead salt gradually and test from time to time to see when it is in excess. The latter method is much the better one. In a few of the published formulas attention is called to the necessity of having HOME-MADE LEAD ARSENATE. 19 the lead salt in excess, but in most of them no reference is made to this point. In the majority of the formulas, however, the amount called for is considerably in excess of the theoretical. This, of course, results in a waste of the lead salt, except in rare instances, where sodium arsenate containing an unusually high per cent of arsenic is being used. In such a case there might not be sufficient lead to combine with all of the arsenic, thus leaving the soluble arsenic salt in excess and yielding a product that would cause injury to most foliage to which it might be applied. PUBLISHED FORMULAS. A number of formulas for making lead arsenate have been pub- lished in the various experiment station bulletins, governmental reports, and works on economic entomology. These, as a rule, call for lead acetate as the lead salt and show considerable variation in the relative proportion of the lead and arsenic salts. The various proportions which have been recommended are given below, with the number of publications in which they have appeared placed in paren- theses. The original proportion given by Moulton '^ and which was followed for the preparation of the arsenate of lead used by the Mas- sachusetts gypsy moth commission, was sodium arsenate 29.93 per cent and lead acetate 70.07 per cent, or sodium arsenate 3 ounces and lead acetate 7 ounces. This formula has been repeated in thirteen publications. Another proportion, recommended by Fernald ** and found by the authors to have been more frequently recommended than any other (26 cases) is arsenate of soda 4 ounces and acetate of lead 11 ounces. The following formulas have also been found : Arsenate of soda. Acetate of lead. Oz. Oz. 4 10 (1) 4 12 (1) 2i 7H1) 6 18 (1) 8 : 24 (3) 10 25 (1) 10 24 (5) Formulas using arsenate of soda and nitrate of lead have been given as follows: Arsenate of soda. Nitrate of lead. Oz- Oz. 5 10 (4) 12 18f (1) 10 24 (3) a Agriculture of Massachusetts, 1893, p. 282. 6 Maspachusetts Hatch Exper. Sta., Bui. 24. 20 LEAD ARSENATE. The amount of water recommended to be added to these quantities varies from 16 to 200 gallons. In some cases one is directed to mix the chemicals, then add the water; in other cases to dissolve the chem- icals in separate portions of water and then mix the solutions. But in only a few cases is attention called to the necessity of having the lead salt in excess or a method given for determining when it is in excess. The grade of arsenate of soda to be used is sometimes given, but usually no reference is made to it. The 4 to 11 formula is based on arsenate of soda of 50 per cent strength and the 3 to 7 formula on arsenate of soda of 65 per cent strength; that is, 50 per cent and 65 per cent of arsenic oxid (AsjOj) . Some confusion seems to have arisen in regard to arsenate of soda and arsenite of soda, as some of the formulas call for the latter, though the other salt is no doubt intended. Arsenite of soda is not suitable for the purpose. In a few instances the objection to the presence of chlorids in the sodium arsenate is referred to, but usually this is not mentioned. It was the practice originally to add glucose or thick molasses at the rate of 2 quarts to 100 gallons for the purpose of increasing the adhesive qualities of the mixture. This practice has since been dis- continued, as it was found that these substances did not increase adhesion, nor was the material eaten any more readily when they were present. According to some of the published formulas there would be present in the prepared mixture less than one-half pound of actual arsenate of lead to 150 gallons of water. It is very doubtful whether the appli- cation of such a small amount would be of sufficient benefit to pay for the trouble of applying it. In all of the formulas the lead salt is present in large enough pro- portions, under ordinary conditions, to combine with all of the arsenic and still be in excess. In extreme cases, however, when sodium arsenate was used which contained an unusually large per cent of arsenic or of sodium chlorid this would not be true. It is necessary that a different formula should be used for different grades of chem- icals, and unless the person making the lead arsenate knows the grade of material he is working with he will be in the dark as to which for- mula to employ. This shows how necessary it is to apply some test to determine when sufficient lead has been added, instead of using definite amounts of the two salts. The following tests for this purpose have been given : After mixing the salts, filter a portion and to the clear filtrate add a few drops of dilute sulphuric acid, when, if lead is in excess, a white precipitate of lead sulphate will be formed. Instead of sulphuric acid, there may be added to the clear filtered liquid a few drops of chromate or dichromate of potash, when, if lead is in excess, a yellow HOME-MADE LEAD ARSENATE. 21 precipitate of lead chromate will he formed. If to a illtered portion of the solution a little of the lead acetate or lead nitrate solution is added and a white precipitate produced, it shows that the arsenic salt is still in excess and more lead should be added. The objection to all of these tests is that the liquid must either be filtered or allowed to settle before the test can be applied, either of which takes consid- erable time and extra utensils for the purpose. The test described in the following directions for making lead arsenate has proven reli- able and can be made instantaneously. DIRECTIONS FOR PREPARING LEAD ARSENATE. This method will give a good product, without any material waste of chemicals, and will require a minimum amount of time. For every pound of lead arsenate it is desired to make, use — Formula A : Ounces. Sodium arsenate (65 per cent) 8 Lead acetate (sugar of lead) 22 Formula 15: Sodium arsenate (05 per cent) 8 Lead nitrate 18 If the sodium arsenate employed is 50 per cent strength, use 10^ ounces instoatl of 8. Of the pure crystallized salt, 14 ounces would be required to furnish the same amount of arsenic oxid as would be fur- nished by the given amounts of the 50 and 65 per cent grades if they actually contained these per cents. In only one technical sample examined, however, was the arsenic oxid content over 45 per cent. The formulas are based on lead acetate containing 60 per cent of lead oxid and .lead nitrate containing 66 per cent of lead oxid. Dissolve each salt separately in from 1 to 2 gallons of water " (they dissolve more readily in hot water), using wooden vessels. After solution has taken place, pour slowly about three-fourths of the lead acetate or nitrate into the sodium arsenate. Mix thoroughly and test the mixture by dipping into it a strip of potassium iodid test paper,'' wliich will turn a bright yellow if lead is in excess. If the paper does not turn yellow, add more of the lead salt slowly, stirring con- stantly, and test from time to time. Wlien the solution turns the paper yellow sufficient lead salt is present, but if it should occur that the papei- does not turn yellow after all the lead salt has been added dissolve a little more and add until an excess is indicated. The o The solution of lead acetate may have a milky appearance. This will be no objec- tion, and it need not be filtered. b If potassium iodid test paper can not be obtained it may be prepared by dissolving a few crystals of potassium iodid in about a tablespoonful of water and satm-ating filter paper or blotting paper with this solution. After the paper has dried, cut into strips and keep dry until needed. 22 LEAD AKSENATE. great advantage of this test is that it is not necessary to fiher the solution or wait for it to settle. If the paper is not at hand, the test may be made by adding a few drops of a solution of potassium iodid, when, if lead is in excess, the instant the drops touch the solution a bright yellow compound, lead iodid, will be formed. It is very essential that the lead salt be added in sliglit excess, but a large excess should be avoided. If the material has been carefully prepared with a good grade of chemicals it will not be necessary to filter and wash the lead arsenate formed, though it would be a safe precaution to allow the lead arsenate to settle, then decant the clear solution and discard it. Approximately 1 pound of actual lead arsenate will be obtained by using the amounts of chemicals specified, which is equivalent to practically 2 pounds of commercial lead arsenate in the paste form. It may be made up to 50 gallons with water if a formula is being used which calls for 2 pounds of commercial lead arsenate to 50 gallons, or if a stronger application is desired add less water. As these chemicals are all extremely poisonous, vessels in which they have been dissolved or mixed should be plainly marked and not used for any other purpose. COMPARATIVE MERITS OF LEAD ACETATE AND LEAD NITRATE. As far as expense is concerned it makes little difference which of these lead salts is used, as their price per pound is practically the same. The nitrate may be slightly cheaper, as it contains a higher per cent of lead, though some of the commercial samples of lead acetate which are nearly free from moisture contain almost as much. A little less lead nitrate is required to make the same quantity of lead arsenate, since when made from this salt more of the lead hydrogen arsenate is formed, which contains a larger per cent of arsenic — on an average about 4 per cent more. This compound has also more desirable phys- ical properties, as it remains in suspension better. Kirkland " has shown that the lead hydrogen arsenate is slightly more poisonous than the tri-plumbic arsenate. This may be due to the fact that the former has a larger per cent of arsenic and therefore a smaller quan- tity of it would give the same effect. It is probable, however, that the lead would possess some poisonous properties in this compound, and therefore the larger amount of lead in the one may somewhat offset the excess of arsenic in the other. Some' have claimed that the lead hydrogen arsenate was more injurious to foliage than the tri- plumbic arsenate, but this was not found to be the case during the three years of the experiments here reported. Taking all of these a Agriculture of Massachusetts, 1897, p. 386. HOME-MADE LEAD ARSENATE. 23 facts into consideration, it would appear from our knowledge at the present time that the product prepared from lead nitrate is slightly more desirable. PHYSICAL PROPERTIES OF LEAD ARSENATE. The physical properties or characteristics of all insecticides wdiich are to be applied as a spray are very important. P'reshly jjrecipitated lead arsenate is a white, very light, flocculent compound, and it is hard to conceive of an insecticide possessing more desirable physical properties. When sprayed on foliage it forms a thin film over the leaf, and after once having been dried thereon it is with difficulty washed off by ordinary rains, and therefore need not be applied so fre- quently as some other insecticides. This is quite an important con- sideration, particularly as the greatest expense connected with spray- ing is the cost of applying the mixture. Another important point is the ease with which it may be kept in suspension in water. Such materials as Paris green, Scheele's green, and others which have a high specific gravity are with difficulty kept in suspension during spraying, and there is always great danger from the material becoming too concentrated in the bottom of the spray tank, thus causing too strong an application and resulting in the scorching of the foliage. Paris green is particularly objectionable in this regard, as it settles very rapidly unless thoroughly and constantly agitated. Lead arsenate shows considerable variation in the time of settling, depending upon the way in which it has been treated and also the chemicals from wdiich it has been made. If it has once been dried, on mixing w^ith w^ater again it settles out much more readily than if it has never been dried. It is for this reason that is is generally put on the market in the form of a paste. There is also a difference between that prepared from lead nitrate and that prepared from lead acetate. The former is more bulky and remains in suspension much longer. After drying there is very little difference in rapidity of settling between the products made from the different lead salts. Plate I shows graphically the variation in settling observed among prepara- tions of lead arsenate which have received different treatments. As stated in the legend, tube a is lead arsenate prepared from sodium arsenate and lead acetate; in tube h lead nitrate was used instead of the acetate ; tubes c and d are the same as tubes a and h, respectively, except that they have been dried out and then mixed with w^ater again. All of the samples represent the same amount of actual lead arsenate and the column of w^ater in each case is 12 inches high. All were thoroughly shaken and then photographed, fig. 1 after they had stood two minutes, and fig. 2 after they had stood fifty minutes. It will be noticed that after two minutes tube 6 had settled but very little, tube a about one-third of the way down, tube c nearly to the 24 LEAD ARSENATE. bottom, and tube d about halfway down. Some of the finer particles still remain in suspension in tubes c and d, and the distinguishing line between the water and the main body of the precipitate is indistinct. After fifty minutes tube h is scarcely more than halfway down while the others have practically all settled to the bottom. III. ACTION OF LEAD ARSENATE ON FOLIAGE. GENERAL DISCUSSION. The fact is well known to entomologists, fruit growers, and others that the foHage of the stone fruits is very susceptible to injury by' many substances used as insecticides and fungicides, notably arseni- cals and Bordeaux mixture, when applied as a spray in sufficient strength to destroy insects and fungi. This is particularly true in regard to the peach, which seems to be the most delicate and easily injured of them all. For this reason entomologists have been en- deavoring for many years to find an insecticide that would destroy leaf-eating insects and not injure the most delicate foliage. The list of substances which may be used is somewhat limited, because of the fact that whatever the material may be it must be comparatively cheap and in such a physical condition as to be easily and thoroughly applied. There is no effective insecticide of this class known at the present time which can be used on the peach without more or less risk of injury. As a result of this condition, many peach growers have given up the use of arsenicals, and, in fact, in some sections many orchards have been abandoned entirely. This is a serious problem, and if a successful method can be discovered of combating these de- structive insects without injuring the tree or fruit it will mean millions of dollars to the peach industry. When lead arsenate was first used it was thought that it possessed all of the necessary qualifications and would prove to be the ideal insecticide. It is of inestimable value and is extensively used on apple and other more hardy foliage, and even on the peach it is often used without injury, as shown by many reports on the subject and as personally, observed by the authors. Some of the statements in regard to this point which have appeared in several experiment station bulletins and other reports on the sub- ject are quoted as follows: Fernald states that "it [arsenate of lead] can be used in large proportions, if necessary, even up to 25 pounds to 1 50 gallons of water, without injury to the foliage. "'=' "It does not injure the foliage of the most delicate plants, even when used in as large a proportion as 25 pounds, or even more, to 150 gallons of water." ^ Marlatt: "It may be used at any strength from 3 to 15 a Massachusetts Hatch Exper. Sta., 1894, Bui. 24, p. 7. fc Agriculture of Massachusetts, 1897, p. 355. jl. 131, Burtaj of Chemistry, U. S. Dept. of Agricultur. Plate I. Fig. 1.— After Standing Two Minutes. Fig. 2.— After Standing Fifty Minutes. EFFECT OF DIFFERENT TREATMENTS ON THE SETTLING OF LEAD ARSENATE. a, Lead iiuetate u.sed; b, lead nitrate used; c and d, same a.s a and 6, but have been dried out and again mixed witli water. ACTION OF LEAD ARSENATE ON FOLIAGE. 25 pounds to the 100 gallons of water without injury to foliage. "'^ "It is totally without action on plants at any strength whatever, even when applied as a sirup." ^ Perkins:'^ "It does no injury to the foliage." Smith: "This combination has the advantage of being harmless to foliage, whatever the strength in which it is applied * * * . Its great advantage is its harmlessness to plant life of all kinds. "'^ "It is absolutely harmless to foliage at any strength * * * . It is the only effective poison of this character that can be safely ap])lied to peach foliage and on conifers."^ Stene:^ "It has the great advantage over most of our insecticides that it is entirely harmless to all plants in any strength." Bentley:^ "Ar- senate of lead will not burn foliage." Taft and Sliaw:'^ ';* * * it can be used upon the most tender foliage without injuring it, even though no lime is added." Green, Selby, and Gossard:* ''* * * if properly made from good materials, will burn foliage but little, no matter what strength is used." Others who have used and experimented with it have found that it frequently caused serious injury. In some of the cases reported peach trees to which it was applied were practically entirely defoliated. There are a number of causes to which this variation in the observa- tions of different investigators may be attributed. In the first place some of them are not based on experiments carried on for a sufficient length of time, or they have been conducted on apple or equally hardy foliage and the assumption made that the results would be the same on all foliage. No doubt, also, arsenate of lead of poor quality and containing an unnecessarily large amount of arsenic in a water-soluble form has been used in some cases, which woukl result in burning. In view of the analyses reported in Table I, page 9, it would appear that tliis might easily occur. Making allowance for all of these conditions, however, it is still evident that injury results at times from the use of properly made lead arsenate, while the same experiments carried out in the same way at a different time or place may not result in any injury. It is well known that the effect of insecticides and fimgicides in general on plants shows great variation in different parts of the United States, and even in the same place in different years, depending upon the temperature, moisture, and undetermined influences. Formulas that may be injurious to foli- alJ. S. Dept. Agr., 1898, Farmers' Bui. No. 19, p. 6. ^Proc. Seventh Ann. Meeting, Assn. Econ. Ent., 1897, p. 24. c Seventh Ann. Rep., Vermont Agr. Exper. Sta., 1893, p. 124. <* Economic Entomology, 1896, p. 437. « New Jersey Agr. Exper. Sta., 1903, Bui. 169, p. 8. /Rhode Island Agr. Exper. Sta., 1904, Bui. 100, p. 138. P Tennessee Agr. Exper. Sta. Bui., 1905, vol. 18, No. 4, p. 36. '« Michigan Board of Agriculture, 1908, p. 397. i Ohio Agr. Exper. Sta., 1908, Bui. 199, p. 94. 23904— Bull. 131—10 4 26 LEAD ARSENATE. age in some States may be used with safety in others. The injury to foHage from arsenicals in arid regions is less than in non-arid regions. Atmospheric conditions following spraying have a great influence on the action of the spray mixture on the foliage. As to why these conditions cause such variations in results no satisfactory explanation has ever been given. It is well known to chemists that pure arsenate of lead is practically insoluble in pure water, and it seems impossible that it can cause injury as long as it remains so. It has never been proven that leaves can absorb insoluble substances, but investigators have shown conclusively that they do absorb salts in solution. It would appear, therefore, that the lead arsenate must be acted upon by some solvent, rendering more or less of the arsenic soluble, before burning of the foliage will result. It was for the pur- pose of determining this important point, if possible, that this inves- tigation was begun. In order that the experiments may be carried out under the varying conditions presented by different seasons, it is the intention to conduct them for a number of years in succession, and while it is considered that the results obtained from the experi- ments conducted and reported herein are extremely suggestive they are not given as conclusive, but on account of the importance of the subject are presented as showing the progress that has been made. PREPARATION OF THE LEAD ARSENATE USED. That there might be no doubt of the purity of the lead arsenate used, it was prepared in the laboratory from pure chemicals and thoroughly washed. The product was then dried in order that it might be more conveniently handled and accurately weighed. No. 1 was made by adding a solution of crystallized lead acetate to a solution of crystallized sodium arsenate until the lead salt was in slight excess. The precipitated lead arsenate was allowed to settle, the supernatant liquid decanted, then the material was washed by decantation with pure water, and finally filtered and washed till the greater portion of the soluble impurities were removed, after which it was dried and powdered. No. 2 was prepared in the same way, except that pure lead nitrate was used instead of lead acetate. On analysis the samples showed the following composition : Table Y. — Analysis of lead arsenates prepared in the laboratory. Number of sample. Moisture. Total lead oxid (PbO). Total ar- senic oxid (AS2O5). Water-sol- uble im- purities. Water-sol- uble lead oxid (PbO). Water-sol- uble arsen- ic oxid (AS2O,). 1 Per cent. 0:10 .09 Per cent. 67.44 64.02 Per cent. Per cent. 29.76 1.07 32.64 1.57 Per cent. 0.56 .53 Per cent. 0.40 2 .49 ACTION OF LEAD ARSENATE ON FOLIAGE. 27 Sample No. 1 agrees closely in composition with a mixture, in about equal proportions, of tri-plumbic arsenate (Pb3(As04)2) and plumbic hydrogen arsenate (PbHAsOJ, while No. 2 corresponds very closely to the theoretical composition of plumbic hydrogen arsenate. EXPERIMENTAL WORK OF 1907. The experiments were carried out on trees in the Bureau of Ento- mology orchard on the Department farm at Arlington, Va. Two types of fruit trees were selected, namely, apple, which is one of the least susceptible to injury from arsenicals, and peach, which is the most tender and easily injured of all fruit foliage. The only apple trees available for the experiments were young trees about 6 feet high, which had not reached the bearing age. The peach trees were large and had borne several crops of fruit. In applying the mixtures an ordinary barrel-sprayer outfit, fitted with a "Vermorel" double noz- zle, was employed. For each experiment there were used six apple and six peach trees. These were divided into two sections: A (three trees) received two applications and B (three trees) received three applications. DESCRIPTION OF EXPERIMENTS. Experiment 1. — To test the effect of pure lead arsenate made from sodium arsenate and lead acetate. Applied the material at the rate of IJ pounds of dry lead arsenate to 50 gallons of water. This is equivalent to about 2 pounds of a good grade of com- mercial lead arsenate to 50 gallons of water. Experiment 2. — Same as Experiment 1, except that freshly slaked quicklime was added at the rate of 4 pounds to 50 gallons of the spray mixture. (To determine to what extent the presence of lime would lessen or prevent burning of the foliage.) Experiment 3. — Same as Experiment 1, except that lead nitrate instead of the acetate was used in the preparation of the lead arsenate. (To show whether lead arsenate made from lead nitrate has a different action from lead arsenate made from lead acetate.) Experiment 4- — Same as Experiment 3, except that quicklime was added at the rate of 4 pounds to 50 gallons. Experiment 5. — To determine whether sodium acetate and acetic acid, which are formed as by-products when lead acetate acts on sodium arsenate, will scorch foliage. Applied a mixture of sodium acetate and acetic acid in the proportion of 9.6 ounces of crystallized sodium, acetate and 2.9 ounces of anhydrous acetic acid to 50 gallons of water. (These are the respective amounts of sodium acetate and acetic acid obtained in the making of 1^ pounds of dry lead arsenate, assuming that tri-plumbic arsenate is formed.) Experiment 6. — To determine whether the amount of sodium acetate used in Experi- ment 5, when used alone, will injure foliage. (Applied wash in the proportion of 9.6 ounces to 50 gallons.) Experiment 7. — To determine whether sodium nitrate, which is formed as a by- product when lead arsenate is made from sodium arsenate and lead nitrate, will injure foliage. This was applied in the proportion of 10.4 ounces to 50 gallons of water, the theoretical amount of sodium nitrate formed in making IJ pounds of dry lead arsenate, using lead nitrate and assuming that plumbic hydrogen arsenate is formed. 28 LEAD ARSENATE. Experiment 8. — To observe the effect of lead acetate on foliage to determine whether, if lead acetate were added in considerable excess, it would cause burning. Applied in the proportion of 2.7 ounces to 50 gallons of water. (This is 10 per cent of the theo- retical amount of lead acetate required to make 1^ pounds of dry lead arsenate.) Experiment 9. — To determine whether a still larger excess of lead acetate would burn when applied in the proportion of 5.4 ounces to 50 gallons of water. (This is 20 per cent of the amount required to make 1^ pounds of dry lead arsenate.) Experiment 10. — To prove whether a small excess of lead nitrate would cause burning when applied in the proportion of 2.1 ounces to 50 gallons. (This is 10 per cent of the theoretical amount of lead nitrate required to make 1^ pounds of dry lead arsenate.) Experiment 11. — Same as Experiment 10, except that the material was applied at the rate of 4.2 ounces to 50 gallons, which is 20 per cent of the theoretical amount of lead nitrate required to make IJ pounds of dry lead arsenate. A number of trees were left unsprayed in different portions of the orchard for comparison. The spraying was done on the following dates: April 18, first apphcation on peach A and B, Experiments 1 to 7, inclusive. The following day it rained, and on April 20 the appli- cation was made according to Experiments 8 to 11, inclusive. The foliage on the apple trees had not developed sufficiently at this date to be sprayed. The second application was made on peach A and B and the first application on apple A and B on April 29 and 30. April 29 applied the spray in Experiments 1 to 9, inclusive, and on April 30 in Experiments 10 and 11. On May 13 and 14 the third application was made on peach B and the second application on apple A and B. On May 13 applied spray in Experiments 1 to 4, inclusive, and finished on the following day. The third application on apple B was made on June 4. RECORD OF OBSERVATIONS. Observations were made on the condition of the foliage at intervals of one to two weeks, and a detailed record kept which it is not neces- sary to record here in full. It may be stated in the first place in regard to the apple that no noticeable injury whatever was caused to the foliage from any of the various mixtures, either in the case of two or three applications. The following notes apply only to the peach: June 4. On this date the last spraying was done and no evidence of any injury to the foliage was apparent which could be attributed to the materials previously ap- plied. A number of leaves showed split and ragged edges, but this was no doubt caused by a severe hailstorm which occurred on May 19. No scorching or burning of the foliage was noticeable. June 28. The foliage showed no injury except that on the trees in Experiment 11 B, which had been sprayed three times with the stronger solution of lead nitrate. This showed some spotting and the "shot hole" effect, though the injury was not serious. The amount of fruit on these trees was small, many of them did not have any at all, and, owing to the unfavorable weather conditions which had prevailed during the growing season, the fruit was all of inferior quality; however, that on the unsprayed trees was in a worse condition than on those to which lead arsenate had been applied. July 19. As far as the foliage was concerned, very little injury was apparent which could be attributed to the spraying mixtures. Experiment 3B showed slight leaf in- ACTION OF LEAD AKSENATE ON FOLIAGE. 29 jury, some of the leaves showing the "shot hole" effect, but not more than 2 or 3 per cent were so injured. As before noted, the small amount of fruit present was, as a rule, inferior, but this condition appeared to be due mainly lo fungus diseases. No fungi- cide had been applied, and the season was favorable to Ihe growth of fungi. August 7. No further injury was shown than that recorded in the i)receding obser- vations. A few peaches from trees sprayed with lead arsenate from either source had the appearance which arsenic injury frequently gives; that is, a dark, shriveled spot on the end, evidently where a drop of the spray had collected and concentrated. The greatest injury and in fact the only positive injury to foliage was shown in Ex- periments llA and llB, to which lead nitrate had been applied. August ^7. The fruit was just ripening at this date, but the crop was too small to draw any positive conclusions except in a general way. There was more fruit on the trees that had been sprayed with lead arsenate, and it was also in better condi- tion. That on trees s{)rayed with lead acetate and lead nitrate was in very good condition, but the amount was small. The main difference in the appearance of the fruit that had received the applications of lead arsenate, aside from the few cases noted, was its deep red color, which gave it a better appearance and, in this instance, in no way injured the quality. WEATHER CONDITIONS. Table VI shows the meteorological conditions for the period from March 1 to September 1, 1907, and Table VII gives a comparison between the temperature and rainfall for this season and the average data for tliirty-seven years. Table VI. — Monthly meteorological data, March to August, 1907, Washington, D. C. MARCH. Date. Temperature. Precipi- tation. Character of day. Possible sunshine. Maxi- mum. Mini- mum. Mean. 1 2 3 4 5 6 7 8 9 10.... 11.... 12.... 13.... 14.... 15.... 16.... 17.... 18.... 19.... 20.... 21.... 22.... 23.... 24.... 25.... 26. . . . 27.... 28. . . . 29. . . . 30.... 31.... Mean or to- tal. "F. 40 61 50 44 45 40 28 48 51 35 44 44 71 73 55 62 70 61 54 58 55 90 93 85 5() 66 80 83 92 74 56 "F. 31 35 28 26 30 28 22 28 33 29 27 20 43 40 36 31 38 44 40 42 32 40 50 48 39 37 46 54 55 56 41 °F. 36 48 ■ 39 35 38 34 25 38 42 32 36 35 57 56 46 46 54 52 47 50 44 65 74 66 48 52 63 68 74 65 48 Inches. 0.26 .19 Trace. Trace. .02 .00 .02 .08 Trace. .'.'0 Trace. .17 .03 .08 .01 .00 .00 Trace. .81 .01 .00 .00 .00 ,00 .00 .00 .00 .00 .00 .00 .21 Cloudy Per cent. 65 38 90 36 91 3 40 74 83 8 6 89 96 77 75 100 45 75 84 89 75 41 70 60 98 81 Partly cloudy do " Clear Partly cloud v Clear " Cloudy Partly cloudy do Cloudy Clear Cloudy do do.. .. Clear do do Partly cloudy Cloudy ....." Clear Partly cloudy do do Clear do Cloudy. . . do Partly cloudy Clear. " do Cloudy 60.] 37.5 48.8 2.79 30 LEAD ARSENATE. Table VI. — Monthly meteorological data, March to August, 1907, Washington, D. C- Continued. APRIL. Date. 10.. 11.. 12.. 13.. 14.. 15.. 16.. 17.. 18.. 19.. 20.. 21.. 22.. 23.. 24.. 25.. 26.. 27.. 28.. 29.. 30.. Mean or to- tal. Temperature. Maxi- mum. 'F. 45 48 65 72 74 45 40 59 49 47 53 46 49 44 51 65 48 57 48 54 58 65 61 65 79 83 61 59 71 7S 58.0 Mini- mum. Mean. 'F. 37 36 47 54 60 38 36 49 42 42 44 42 44 40 42 51 43 46 43 44 46 50 56 56 60 70 54 54 62 66 48.4 Precipi- tation. Inches. Trace. 0.00 .00 Trace. Trace. .12 .34 .07 1.06 Trace. .00 .01 .00 .00 .00 .00 .00 .00 .21 .00 .00 .00 1.23 Trace. .00 .49 .08 .00 Trace. .00 3.61 Character of day. Possible sunshine, Partly cloudy. Clear do Partly cloudy. do Cloudy do Partly cloudy. do do do Cloudy do Partly cloudy. Clear Partly cloudy. do ".. do Cloudy Partly cloudy. Clear Partly cloudy. Cloudy Clear do do Partly cloudy. Cloudy Partly cloudy. Cloudy Per cent. 100 100 88 57 3 41 34 62 79 33 33 47 100 54 83 66 100 71 4 100 92 75 69 22 55 53 MAY. 10.. 11.. 12.. 13.. 14.. 15.. 16.. 17.. 18.. 19.. 20.. 21.. 22.. 23.. 24.. 25.. 26.. 27.. 28.. 29.. 30.. 31.. Mean or to- tal. f)S 51 60 60 48 54 65 49 57 70 46 58 62 39 50 71 51 61 62 57 60 71 52 62 67 54 60 78 52 65 62 42 52 59 39 49 73 44 58 85 r,! 68 83 59 71 70 57 64 70 54 62 83 53 68 84 62 73 67 50 58 60 41 50 70 39 54 74 56 65 66 56 61 58 46 52 61 46 54 72 51 62 64 44 54 72 42 57 74 49 62 61 52 56 69.1 49.4 59.2 0.61 .00 Trace. .13 .00 .52 Trace. .48 .24 Trace. .05 .00 .00 .00 .01 .39 .00 Trace. 1.10 .10 .00 .00 .01 .23 .14 .20 .58 .00 .00 .00 .24 5.03 Cloudy do Partly cloudy. Clear do Cloudy do Clear Cloudy Clear do do do do Partly cloudy. Cloudy Partly cloudy. Clear Partly cloudy. do Clear do Cloudy do do do Partly cloudy. Clear do do Cloudy 49 69 100 10 70 18 85 75 100 100 100 73 51 76 51 34 100 86 20 12 4 35 87 79 100 ACTION OF LEAD ARSENATE ON FOLIAGE. 31 Table VI. — Monthly incleorological data, March to August, 1907, Washington, D. C- Continued. JUNE. 1 2 3 4 5 6 7 8 9 10.... 11.... 12.... 13.... 14.... 15.... 16.... 17.... 18.... 19.... 20. . . . 21.... 22.... 23.... 24.... 25.... 26.... 27.... 28.... 29.... 30.... Mean or to- tal. Temperature. Maxi- mum. °F. 85 75.1 Mini- mum. Mean. Precipi- tation. Inches. 2.20 .14 .00 Trace. .16 .00 .11 .21 .00 Trace. .81 .05 .09 .07 .00 .00 .00 .00 Trace. .00 .00 .00 .00 Trace. .01 .06 .00 .01 .94 .00 Character of day. Cloudy do Partly cloudy. Clear." Partly cloudy. Clear ". . do Cloudy Clear do Cloudy do do do Clear do do do Partly cloudy. do Clear do Partly cloudy. Clear." do do do Partly cloudy. Cloudy Partly cloudy. Possible sunshine Per cent. 53 65 62 80 69 20 100 69 1 3 64 100 100 66 48 40 100 78 52 65 79 69 87 64 70 32 JULY. 1.... 2.... 3.... 4.... 5.... 6.... 7.... 8.... 9.... 10... 11... 12... 13... 14... 15... 16... 17.... 18.... 19... 20... 21... 22... 23... 24... 25... 26... 27... 28... 29... 30.... 31.... Mean or to- tal. 86 85 77 81 81 86 90 93 85 91 93 82 80 84 82 88 85 91 87 90 83 87 88 91 92 86 80 83 72 86 85 59 65 58 52 57 63 66 73 72 68 70 08 03 61 64 72 73 74 72 74 66 62 71 69 71 09 61 62 65 65 63 72 75 68 66 69 74 78 83 78 80 82 75 72 72 73 80 79 82 80 82 74 74 80 80 82 78 70 72 68 76 74 0. 27 .00 .00 .00 Trace. .00 Trace. .00 Trace. .02 Trace. .04 .00 .00 .00 Trace. .31 Trace. Trace. Trace. .00 Trace. .00 .00 .02 Trace. .00 .00 .89 .00 .00 Clear 85 74 97 84 68 84 88 67 54 57 68 18 65 83 35 61 36 36 56 57 100 80 82 83 76 43 97 55 99 100 Clear do Partly cloudy Clear . do do Partly cloudy d"o " do Cloudy Partly cloudy do ." do.. .. Cloudy do .do. Partly cloudy do Clear . . . Partly cloudy Clear". " do Cloudy Clear Cloudy Clear do 85.5 66. 1 75.8 1.55 32 LEAD AESEKATE. Table W.— Monthly meteorological data, March to Augu.H, 1907, Washington. D.C. Continued. AUGUST. Date. Temperature. Precipi- tation. Character of day. Possible sunshine. Maxi- mum. Mini- mum. Mean. 1 2 3 4 5 6 7 8 9 10.... 11.... 12.... 13.... 14.... 15.... 16.... 17.... 18.... 19.... 20. . . . 21.... 22....' 23.... 24.... 25.... 26.... 27.... 28. . . . 29.... 30.... 31.... Mean or to- tal. 87 89 78 78 79 88 89 91 76 76 80 88 85 77 79 76 88 80 81 82 88 73 72 86 78 81 77 80 78 80 80 °F. 06 67 62 58 59 67 67 67 66 66 70 67 71 62 56 66 68 65 60 70 67 58 56 67 66 55 58 63 60 57 59 °F. 76 78 70 68 69 78 78 79 71 71 75 78 78 70 68 71 78 72 70 76 78 66 64 76 72 68 68 72 69 08 70 Incites. 0.00 .00 .79 .01 .12 .43 .00 .00 .67 .40 .00 .00 .09 .00 .00 Trace. Trace. .04 .00 .70 .20 Trace. .64 .25 .00 .00 Trace. .00 .00 Trace. .00 Partly cloudy Per cent. 42 84 24 100 20 59 75 81 9 36 72 61 74 100 7 57 6 99 34 55 39 79 99 98 10 34 100 21 66 Clear Cloudy Clear Cloudy Partly cloudy Clear " do Cloudy do do Clear Partly cloudy Clear ". . do Cloudy Partly cloudy Cloudy Clear Partly cloudy do ." do Cloudy Partly cloudy.. . Clear do Cloudy Partly cloudy. .. Clear Partly cloudy do 81.3 03.4 72.4 4.34 Table VII.- -Comparifson of monthly meteorological data for 1907 with the average for thirty-seven years. SUMMARY FOR 1907 Summing up tlie results for the season it can be stated that no injury resulted to the foliage of the apple from any of the mixtures applied, and only very slight injury to that of the peach, none of ACTION OF LEAD ARSENATE ON FOLIAGE. 33 which was of a decided enough character to attribute it with cer- tainty to the spraying. Some of the trees which had not been sprayed at all showed a condition which would have been attributed to spraying injury if it had not been known that no insecticide had been applied to them. The most positive results were shown on trees which had received the applications of lead nitrate, but the fruit on these trees did not appear to have been injured in the least. By referring to the meteorological report for the period several striking facts will be noticed. March, the month preceding spray- ing, was unusually warm, the mean being 6.6° higher than the average of the month for the preceding thirty-seven years, and also higher than for the month following. This caused the trees to put out their foliage very early. Following this the temperature was below normal for the entire growing season to the following extent: April 4.5°, May 4.8°, June 7.1°, July 1.1°, and August 2.6° below the daily average for these months for the preceding thirty-seven years. The rainfall for April, May, and June — the months when spraying was actually done — was considerably above the average, and the number of clear days for this period, was only about one in three. In every case rain fell on the same day or within two days after spraying. These abnormal conditions render the drawing of any satisfactory conclusions from this year's work impossible. The recorded experience of users of Paris green, other arsenicals, and Bordeaux mixture shows that greater injury has occurred following wet weather. This may be true in general, but when spraying is followed soon thereafter by heavy rain the material may be washed off to such an extent that injury would not result from the small amount remaining. Frequent rains which are just sufficient to thor- oughly wet the foliage would naturally produce conditions favorable to the maximum injury. EXPERIMENTAL WORK OF 1908. DESCRIPTION OF EXPERIMENTS. The results obtained in 1907 indicated that it was not necessary to continue experiments wdth two applications; therefore in 1908 three applications were made in all except one instance, to which attention is called later. The experiments were conducted on the same apple trees as in the preceding year, but conditions made it necessary to select peach trees in another orchard. These were young vigorous trees and were in their second bearing year. As they were not large, a five-gallon knapsack sprayer outfit was selected for the work as being more convenient. 34 LEAD ARSENATE. All of the experiments made in 1907 were repeated this year with the following in addition : Experiment 12. — ^To test the effect of applying lead arsenate made from lead acetate and sodium arsenate without removing any of the by-products formed; i. e., sodium acetate, acetic acid, and a slight excess of lead acetate. Experiment 13. — Same as Experiment 12, except that lime was added in the propor- tion of 4 pounds to 50 gallons. Experiment 14- — To test the effect of lead arsenate made from lead nitrate and sodium arsenate without removing the by-products formed; i. e., sodium nitrate and a slight excess of lead nitrate. Experivient 15. — Same as Experiment 14, except that lime was added at the rate of 4 pounds to 50 gallons. In these four experiments the lead arsenate was applied in the same proportion as in other experiments in which it was used; that is, on the basis of IJ pounds of dry material to 50 gallons of water. Four apple and four peach trees were used for each experi- ment. The first application was made on April 27 and the second on May 8. On May 20 the third application was made on the apple trees and Experiments 1 to 4 on the peach, when work was inter- rupted by a very heavy rain (1.86 inches), followed by several days of unsettled weather. On the 25th the remaining mixtures were ap- plied, and Experiments 1 to 4 were resprayed. The latter, therefore, had received four applications of lead arsenate, but as the third had not had sufficient time to dry completely on the leaves before rain fell it was undoubtedly largely washed off. The last application was followed by five days of very hot, clear weather without rain. RECORD OF OBSERVATIONS. When the last spraying was done, on May 25, there was no injury apparent from any of the apphcations previously made. June 4 no injury could be observed to any of the apple trees. The foliage of the peach, however, showed very decided injury in some cases, as noted below. NOTES MADE ON JUNE 4. Experiment 1. — Quite a number of leaves had brown, shriveled edges and showed the "shot hole" effect, the injury, however, not being severe. Experiments 2, 3, and 4 the same, accompanied in the latter case by slight dropping and yellowing of the leaves. Experiment r,. — Evidence of very slight injury; Nos. 6, 7, and 8, no injury. Experiment 9. — Slight injury, some "shot-hole" effect; no dropping of leaves. Experiment 10. — Same as No. 9. Experiment 11. — Same as Experiment 9, but more severe; some dropping of leaves. Experiment 12. — Showed some injury; leaves pretty badly spotted, and some had dropped. Experiment 13. — Same as Experiment 12, but not so severe. Bui. 131, Bureau of Chemistry, U. S. Dept. of Agriculture. Plate II. Fig. 1 .—Leaves from Trees in Experiment 3. (Natural vSize.) Fig. 2.— Leaves from Trees in Experiment 12. (Reduced.) PEACH LEAVES SHOWING INJURY FROM LEAD ARSENATE, ACTION OF LEAD ARSENATE ON FOLIAGE. 35 Experiment 14. — A few leaves had fallen, but the injury was less marked than in Experiment 12. Experiment 15. — Practically the same as Experiment 14. Plate II, fig. 1, shows the appearance of leaves on June 4, injured by lead arsenate. These were selected from trees in Experiment 3 as representative. Figure 2 shows some of the most severely injured leaves taken irom Experiment 12. NOTES MADE ON JUNE 9. Apple trees showed no injury. The notes on the peach trees were as follows: Experiment 1. — Considerable injury to foliage; a great maaiy leaves had fallen, as evidenced by the thin appearance of the foliage and the number of leaves on the ground. Experiment 2. — Injury very evident, but not so severe as in Experiment 1. A few leaves had fallen. Experiment 3. — Many leaves with "shot holes," but as a whole the injury appeared to be slightly less than in Experiment 1. Experiment 4- — Practically the same as Experiment 2, except that a few more leaves had fallen. Experiment 5. — A little "shot holing" of leaves, but none had fallen. As a whole the trees looked healthy and in good condition. Experiment 6. — No injury noticeable. Experiment 7. — Foliage in good condition; fine green color; no injury. Experiment 8. — No injury. Experiment 9. — Injury slight; a few "shot holes;" no fallen leaves. Experiment 10. — Same as Experiment 9. Experiment 11. — Some injury; many leaves with numerous "shot holes," but few had fallen. Experiment 12. — Quite severely injured. Many fallen leaves and foliage noticeably thin on tree. Many leaves were yellow and had numerous "shot holes." Experiment 13. — Considerable injury, but not so severe as in Experiment 12. Not many yellow leaves. Experiment 14- — Practically the same as Experiment 12. Experiment 15. — Same as Experiment 13. NOTES MADE ON JULY 29 ON CONDITION OF FRUIT. Apple foliage uninjured; no fruit. Notes on the peach trees were as follows: Experiment 1 . — Fruit nearing maturity, very much redder in color than that on trees not sprayed with arsenicals. Many peaches, approximately 40 per cent, showed the injurious effect of spraying by having a brown or black shriveled spot usually around or near the stem end or on the upper side. In some cases the injury showed on the small end, when the fruit was hanging down, presumably a drop of the liquid having collected there and concentrated. Experiment 2. — Same as Experiment 1; injury not so severe. 36 LEAD ARSENATE. Experiment 3. — Same as Experiment 1 ; no more severe. Experiment 4- — Same as Experiment 2. Experiment 5. — Fruit normal color (green); not injured from spraying. Experiments 6, 7, and 8. — Same as No. 5. Experiments 9, 10, and 11. — Fruit in good condition; normal color. Experiment 12. — Injury about the same as in Experiment 1 but not so severe; a smaller per cent of injured fruit, probably not over 30. Experiment 13. — Fruit deep red in color, as was all that sprayed with lead arsenate; not over 10 per cent showed injured spots and these were not so large nor deep as in Experiment 12. Experiment 14- — Injury i)ractically the same as in Experiment 12. Experiment 15. — Fruit not so red; injury about the same as Experiment 13. The presence of lime showed some beneficial effect by lessening the injury to the fruit as well as to the foliage. The fruit on unsprayed trees was still deep green in color and about one week behind that spraj^ed with lead arsenate as to maturity. All trees were in a healthy looking condition aside from the fact that Experiments 1 to 4 and 12 to 15, inclusive, were not so thickly foliated, owing to previous drop- ping of the leaves. The fruit on these trees, in addition to being a deep red, was more fully matured, and ripened about a week earlier than that unsprayed. Plate III shows the trees on the unsprayed plot with normal healthy foliage. Plate IV represents a tree in Experiment 12 sprayed with lead arsenate and showing partial defoliation, leaving the fruit largely exposed. Most of tlie leaves on the ends of the branches came out after the spraying was done, thus masking to a large extent the injury produced. NOTES MADE ON AUGUST 13 ON CONDITION OF FRUIT. These observations on the peach crop may be generalized. Experi- ments 1 to 4, inclusive, and 12 to 15, inclusive, in which lead arsenate had been applied, showed about 50 per cent of injured fruit when no lime was uSed and about 25 per cent injured when lime was applied. That showing the worst injury was somewhat shriveled and usually dropped before having fully matured. In other cases it showed a dark shriveled spot, usualh^ around the stem end, but frequently on the upper side or on the small end. This condition is brought out in fig. 1, which shows some of the most seriously injured fruit that remained on the trees. The per cent of insect injury, as shown by wormy fruit, was very small, in no case over 5 per cent of the total. Experiment 9, in which lead acetate was used, yielded more perfect fruit than any of the other trees sprayed; 90 per cent of it was sound, 80 per cent of which was of good size and practically perfect, while 10 per cent showed insect injury. Bui. 131, Bureau of Chemistry, U. S. Dept. of Agriculture. Plate III Bui. 131, Bureau of Chemistiy, U. S. Dept. of Agriculture. Plate IV. ACTION OF LEAD ARSENATE ON FOLIAGE. 37 The fruit from iill of the other sprayed trees was in practically the same condition as that from the unsprayed trees, none of tlie mix- tures having lessened insect injury except lead nitrate, which was effective to a slight extent. Fruit from the unsprayed trees was very much gummed; from 50 to GO per cent was wormy, and not over 30 ])er cent was sound and marketahle. Fig. 1. — Injured peaches from trees sprayed with lead arsenate. (Reduced.) WEATHER CONDITIONS. The tables following give the meteorological conditions for the period from March 1 to September 1, 1908, and a comparison of the average data for thirty-eight years with those for the season of 1908. 38 LEAD ARSENATE. Table VIII. — Monthly meteorological data, March to August, 1908, Washington, D. C. MARCH. Date. Mean or to- tal .. Temperature. Maxi- mum. 56. Mini- mum. Mean. °F. 32 44 40 36 34 36 50 44 39 40 47 55 51 56 60 52 44 46 52 34 36 44 52 56 49 58 69 68 58 46 46 Precipi- tation. Inches. 0.20 .02 .00 .00 .10 .59 .00 .00 .27 .00 .00 Trace. .00 Trace. .04 Trace. Trace. Trace. .21 .00 .00 Trace. .32 .00 .00 .00 .00 .05 .35 .00 .30 Character of day. Cloudy do. Partly cloudy. Clear Cloudv do Clear Partly cloudy. Cloudy Clear Partly cloudv. Clear ". . Partly cloudy. Clear ". . Cloudy Partly cloudy. do Cloudy Partly cloudy. Cloudy Clear Partly cloudy. Cloudy Partly cloudy. do Clear do Cloudv do do do APRIL. 1 51 44 48 0.08 2 63 38 50 .21 3 41 32 36 Trace. 4 51 33 42 .00 5 53 20 41 .03 6 69 48 58 .00 7 77 44 60 .00 8 75 58 66 .43 9 70 43 56 .07 10.... 53 40 46 .15 11.... 69 46 58 .01 12.... 62 41 52 .00 13.... 78 40 59 .00 14.... 60 40 50 .00 15.... 64 47 56 .28 16.... 63 38 50 .01 17.... 57 35 46 .00 IS.... 60 44- 52 .10 19.... 72 51 62 Trace. 20.... 80 44 62 .00 21.... 60 43 52 .00 22.... 76 39 58 .00 23.... 83 55 69 .00 24.... 87 54 70 .00 25.... 76 57 66 .02 26.... 85 58 72 .00 27.... 85 65 75 .03 28.... 71 56 04 .00 29.... 76 46 61 .00 30.... Mean 68 42 55 .17 or to- tal.. 67.8 45.0 50.5 1.59 Cloudj' Partly cloudy. do ....do ....do Clear do Cloudy Partly cloudy. Cloudy Partly cloudy. Clear do do Cloudy Clear do Cloudy Partly cloudy. Clear." do do do do Partly cloudy. Clear Partly cloudy. do Clear Partly cloudy. Possible sunshine. Per cent . 4 81 85 4 100 66 100 86 100 86 100 34 72 4 10 45 11 100 75 65 68 88 90 6 18 41 74 100 91 91 82 100 4 57 100 100 100 94 92 47 100 64 65 93 44 ACTION OP LEAD ARSENATE ON FOLIAGE. 39 Table Ylll. — Monthly meteorological data, March to August, 1908, Washington, D. C— Continued. MAY. Tei Date. Maxi- mum. 'F. 1 56 2 66 ^ 62 4 52 5 55 6 50 7 64 8 64 9 60 10.... 64 11.... 82 12.... 88 13.... 87 14.... 88 15.... 58 16.... 63 17.... 80 18.... 78 19.... 74 20.... 81 21.... 75 22.... 84 23.... 81 24.... 85 25.... 87 26.... 88 27.... 89 28.... 92 29.... 82 30.... 83 31.... Mean 85 or to- tal . . 74.3 Temperature. Mini- mum. Mean. 39 44 44 42 45 46 i 47 51 49 44 42 63 61 58 52 51 58 60 61 61 64 64 66 63 64 Precipi- tation. Inches. 0.00 .04 .00 .29 .32 .35 1.01 Trace. .04 .00 .00 Trace. Trace. .06 .13 .01 .00 Trace. 1.20 1.86 Trace. Trace. .05 .00 .00 .00 .00 .00 .00 .74 .00 Character of day. Clear Partly cloudy. do Cloudy do do do Partly cloudy. do Clear do... Partly cloudy. do do Cloudy Partly cloudy. do do Cloudy do. Partly cloudy. do do do Clear do do do Partly cloudy. do do JUNE. Possible sunshine, ■ cent. 92 2 42 55 100 100 52 83 55 7 56 69 12 40 24 69 54 81 82 79 87 99 60 59 1 2 3 4 5 6 7.... 8 9.... 10... 11... 12.... 13.... 14... 15.... 16... 17... 18... 19... 20... 21... 22... 23... 24... 25... 26... 27... 28... 29... 30... Mean or to tal. 72 80 74 67 78 68 81 85 87 82 73 82 84 84 78 74 75 78 88 89 89 89 94 97 85 80 83 85 92 87 59 56 58 58 57 59 52 59 64 05 61 56 58 66 58 54 52 58 60 70 70 68 68 76 71 64 57 57 67 71 66 68 66 62 68 64 66 72 76 74 67 69 71 75 68 64 64 68 74 80 80 78 81 86 78 72 70 71 80 79 0.00 .00 .09 .46 .00 .00 .00 .00 .02 Trace. .02 .00 .00 .00 1.00 .00 .00 .00 .00 .00 Trace. .00 .00 .00 .01 .00 .08 .00 .00 .05 Clear 97 99 66 9 72 7 82 99 82 74 30 99 100 99 29 99 100 70 99 60 83 91 88 88 64 85 76 93 99 72 .do.. . Partly cloudy Cloudy Clear. . ... Cloudy Partly cloudy. Clear do Partly cloudy. do Clear. . do .. .do Clear. . Partly cloudy do Clear Partly cloudy do do Clear. . do Partly cloudy. do Clear. . do Partly cloudy Clear.. 82.0 61.6 71.8 1.73 40 LEAD ARSENATE. Table VIII. — Monthly meteorological data, March to August, 1908, Washington, D . C. Continued. JULY. 9... 10.. 11.. 12.. 13.. 14.. 15.. 16.. 17.. 18.. 19.. 20.. 21.. 22.. 23.. 24.. 25.. 26.. 27.. 28.. 29.. 30.. 31.. Mean or to- tal Date. Temperature. Precipi- tation. Character of day. Possible Sunshine. Maxi- mum. Mini- mum. Mean. 1 2 3 4 5 6 7 8 9 10.... 11.... 12.... 13.... 14.... 15.... 16.... 17.... 18.... 19.... 20. . . . 21.... 22.... 23.... 24. . . . 25.... 26.... 27.... 28... 29... 30... 31... Mean or to tal. °F. 90 90 86 88 86 94 j 94 i 81 ! 80 1 79 90 99 96 1 96 87 81 87 91 91 90 88 87 89 88 88 81 78 84 85 84 80 °F. 69 72 71 73 71 72 72 64 59 60 61 68 70 74 71 62 57 72 76 71 69 70 71 69 70 71 G8 68 66 68 72 °F. 80 81 78 80 78 83 83 72 70 70 76 84 83 85 79 72 72 82 84 80 78 78 80 78 79 76 73 76 76 76 76 Incites. 0.01 .03 Trace. .24 Trace. .00 .04 .00 .00 .00 .00 .05 .00 .06 .00 .00 .00 Trace. .00 .00 .20 .13 .77 .17 .05 .88 .65 .00 Trace. .00 .01 Partly cloudy Per cent. 86 78 58 43 56 82 98 66 67 59 92 69 93 64 78 98 78 56 71 67 57 38 41 46 38 19 3 48 62 73 do do .do . ..do do Clear do do Clear Partly cloudy. . Clear Partly cloudy. Clear do do ..do .. ..do Cloudy ..do do do do . .do do do do Cloudy 87.4 68.6 78.0 3.29 AUGUST. 84 66 75 89 59 74 92 66 79 95 70 82 89 72 80 85 71 78 87 69 78 78 65 72 70 62 66 84 60 72 86 68 77 92 65 78 93 73 83 93 72 82 88 74 81 84 68 76 87 68 78 86 70 78 89 70 80 77 59 68 80 53 66 84 69 76 79 71 75 74 66 70 68 56 62 61 57 59 63 56 60 67 58 62 76 52 64 81 52 66 81 56 68 82.0 64.3 73.2 0.00 .00 .00 .00 .02 .06 .01 Trace. .86 .00 .00 .00 .00 .00 .00 Trace. 1.11 .18 .00 Trace. .00 Trace. Trace. .00 1.84 1.05 .01 .00 .00 .00 .00 Partly cloudy. Clear ....do ....do Cloudv ....do ....do ....do ....do Clear ....do ....do ....do Partly cloudy. do Cloudy do Partly cloudy. Clear Partly cloudy. do Cloudy do do do do do do Clear do do 65 100 89 91 36 16 26 31 1 92 85 72 99 75 57 28 18 38 68 61 74 20 15 5 6 89 ACTION OF LEAD ARSENATE ON FOLIAGE. 41 Table IX. — Comparison of monthly meteorological data for 1908 with the average for thirty -eight years. ♦ Month. March April May June July August Temperature. Rainfall. Mean for 1908. Mean for thirtv- eight years. Average daily e.xcess or deficiency as com- pared with mean for thirty-eight years. Total for 1908. Mean for thirty- eight years. Monthly excess or deficiency as com- pared with mean for thirty-eight years. 47.4 56.5 65.2 71.8 78.0 73.2 "F. 42.3 53.0 64.0 72.6 77.0 74.6 "F. +.5.1 +3.5 +1.2 -0.8 + 1.0 -1.4 Inches. 2.45 1.59 6.10 1.73 3.29 5.14 Inches. 3.93 3.14 3.81 4.08 4.61 4.43 Inches. -1.48 -1.55 +2.29 -2. 35 -1.32 +0.71 SUMMARY FOR 1908. The results on the apple trees were the same as in 1907, that is, the foliage was not injured in any case from applications of pure lead arsenate or any of the by-products naturally formed in its manu- facture. Rather severe injury was caused to the foliage and fruit of the peach by pure lead arsenate, made either from lead acetate or lead nitrate, and the same was true when the salts formed as by-products in the making were not washed out, whether applied with or without lime. The fruit was of a deep red color wliich generally extended throughout the flesh, and maturity was hastened about one week. Lead nitrate caused severe injury to the foliage but not to the fruit. Lead acetate in the stronger application caused slight injury to the foliage, but very materially protected the fruit from insect injury. Sodium acetate and acetic acid, acetic acid alone, and sodium nitrate produced no injurious effect on the foliage or fruit in the strengths applied. The meteorological conditions from March to August, 1908, were very different from those for the same period in 1907. In general the temperature was considerably above the normal, and the rain- fall was very much below normal except for May and August. One-half of the total rainfall for May (nearly as much as the normal average for the month) fell on two consecutive days. During June and most of July the rainfall was very light. No injury from previous spray- ing could be detected on May 25, when the final apphcation was made. Five hot, clear days, without rain, followed this application, and on June 4, ten days after the application, very decided injury was observed. From the appearance of the fohage the injur}^ would probably have been noticeable several days previously, but no obser- 42 LEAD ARSENATE. vations had been made. This would seem to indicate very strongly that practically all the injury resulted from this last application. SUMMARY OF RESULTS FOR THE TWO YEARS' EXPERIMENT. No injury resulted to apple foliage in either 1907 or 1908 from three apphcations of lead arsenate, made from sodium arsenate and lead acetate, or sodium arsenate and lead nitrate, when applied at the rate of IJ pounds (dry basis) to 50 gallons of water. No injury resulted to apple foliage in 1908 from the use of lead arsenate made by the two methods, from which the salts formed as by-products were not removed, when applied the same number of times and at the same rate. (This experiment was not tried in 1907.) No injury was caused to the foliage of the apple in 1907 or 1908 by three applications of lead acetate or lead nitrate in strength greater than would occur in any but the most carelessly made lead arsenate. No injury was caused to the foliage of the apple in 1907 or 1908 from three applications of sodium acetate and acetic acid, acetic acid alone, or sodium nitrate,** in strengths produced from the amounts formed in the preparation of IJ pounds of lead arsenate by the two methods, made to 50 gallons. These results were expected, as lead arsenate is being used in apple orchards very extensively in all parts of the country and with success. No noticeable injury resulted to peach fohage in 1907 from two or three applications of lead arsenate (made by the two methods) at the rate of IJ pounds (dry basis) to 50 gallons of water. The fruit from these trees was a bright red color, which was desirable rather than otherwise, as its quahty was not impaired. Three applications of lead arsenate of the same strength (made by the two methods) in 1908 caused very marked injury to peach foliage and also to the fruit. The same when applied with lime in the proportion of 4 pounds to 50 gallons produced considerable injury, but to a less extent. Injury to the fruit was decreased about 50 per cent by the use of lime. In 1908 three applications of lead arsenate, made from sodium arsenate and lead acetate, and from sodium arsenate and lead nitrate, without removing the salts formed as by-products, resulted in the same injury as from the use of the washed product. The same applied with lime at the rate of 4 pounds to 50 gallons produced about 50 per cent less injury to the fruit. Three applications of lead nitrate, in the proportion of 2.1 ounces and 4.2 ounces to 50 gallons of water, produced slight injury to peach a Lodeman reports injury to the foliage of apple and quince from the application of nitrate of soda at the rate of 2 ounces in 2 gallons of water. Cornell Agr. Exper. Sta., 1893, Bui. No. 60, p. 291. ACTION OF LEAD ARSENATE ON FOLIAGE. 43 foliage in 1907 from the stronger application and very marked injury in 1908 from both strengths. No injurious effect on the fruit could be detected. Three applications of lead acetate at the rate of 2.7 ounces to 50 gallons of water produced no injurious effect on fruit or foliage in either 1907 or 1908. Three applications of lead acetate at the rate of 5.4 ounces to 50 gallons produced no injurious effect in 1907 and slight injury to foliage in 1908. The use of the latter strength showed a very marked effect on the fruit in reducing the injury caused by insects. This material would probably prove very effective as an insecticide if applied frequently enough or if the applications were followed by a few days of dry weather. No injury was caused to the foliage or fruit of the peach in 1907 or 1908 by three applications of sodium acetate and acetic acid, acetic acid alone, or sodium nitrate of the strengths in which they would occur in making 1 ^ pounds of lead arsenate without removing these products and making up to 50 gallons. As far as the protection of the fruit from insect injury is concerned, the lead arsenate was a success. GENERAL DISCUSSION OF PROBLEMS INVOLVED IN THE INVES- TIGATION. Naturally, the first question asked will be, Why did no injury result to the peach in 1907 from the application of lead arsenate, while in 1908, when the applications were made in the same way and of the same strength, serious injury resulted? Though our present knowledge is not sufficient to give a positive answer to this question, some very interesting results bearing on this point have been obtained. LEAD NITRATE VS. LEAD ACETATE. Contrary to the opinion held by many, lead arsenate made from sodium arsenate and lead nitrate did not cause any more injury than that made from sodium arsenate and lead acetate. Cases reported in which it has been more injurious may have been due to the pres- ence of lead nitrate in considerable excess, for lead nitrate, as these experiments have shown, is considerably more caustic in its effect on foliage than lead acetate. Lead arsenate prepared from lead nitrate possesses several qualities which make it slightly more desirable for spraying purposes than that prepared from lead acetate. These have been pointed out in Part II. It would be more dangerous to use, however, if not properly made — that is, if the lead nitrate were present in any considerable excess over that sufficient to combine with all the arsenic. The injury to the foliage caused by lead acetate appeared to be local in character, as it did not cause the leaves to fall 44 LEAD ARSENATE. or turn yellow. In very minute quantities arsenic appears to exert a stimulating effect or act as a tonic, as it does on animals. It is probably this action which, by accelerating the functional activity of the leaf and producing more rapid assimilation, causes the excess- ive reddening and hastens the maturity of the fruit. On the other hand, if too large an amount is absorbed, it has a toxic effect, resulting in retarded assimilation, which in turn will cause the fruit to shrivel and drop before it has matured. SUSCEPTIBILITY OF PEACH FOLIAGE TO INJURY. It has not been satisfactorily explained why the stone fruits, the peach in particular, should be so susceptible to injury. Numerous investigators have carried on extensive experiments on this point with copper compounds, mostly Bordeaux mixture, and with Paris green, resulting in much valuable information on the subject and the advancement of several theories to account for it. Those who have given special study to the action of fungicides and insecticides on plants and foliage include numerous foreign investigators. Among those in this country the follomng may be mentioned: Gillette,'' Galloway,^ Galloway and Woods, '^ Fairchild,'^ Sturgis, « Bain,/ and Hedrick. o It has been shown that leaves formed in a moist atmosphere have a thinner and more easily permeable cuticle than those grown in a dry atmosphere, and that injury from Bordeaux mixture and arsen- icals is more severe in warm, damp weather. Gillette ^ says: "The oldest leaves are most susceptible to injury;" also, "foHage most exposed to dew and direct sunlight will be most injured by the arsenites, other things being equal. Leaves kept perfectly dry can hardly be injured by the arsenites." Woodworth and Colby:* "It has been demonstrated repeatedly that dry Paris green can be placed upon a leaf in any quantity and so long as the leaf remains dry no evil results will follow." No experiments have been made in this investigation with lead arsenate to determine whether or not injury would result to peach foliage in the absence of water. It was assumed that none would be caused, in view of the results obtained by others with Paris green, a Iowa Agr. Exper. Sta., 1890, Bui. 10. & U. S. Dept. Agr., Div. Veg. Path., 1892, Bui. 3; 1894, Bui. 7. c Proc. Soc.'Prom. Agr. Sci., 1895, p. 42. d U. S. Dept. Agr., Div. Veg. Path., 1894, Bui. 6. « Connecticut Agr. Exper. Sta., Ann. Rep., 1900, Pt. Ill, p. 219. /Tennessee Agr. Exper. Sta., 1895, Vol. 8, No. 3; 1902, Vol. 15, No. 2. g New York Agr. Exper Sta., 1907, Bui. 287. 'ilowa Agr. Exper. Sta., 1890, Bui. 10, pp. 402-403. » California Agr. Exper. Sta., 1899, Bui. 126, pp. 10-11. ACTION OF LEAD ARSENATE ON FOLIAGE. 45 which compound, under the usual conditions, is more injurious to fohage than lead arsenate. Duggar" reports an extreme case in which bright sunshine follow- ing rain caused the appearance of "shot holes" in peach foliage. Others have also reported injury under these conditions, and it has been attributed to the concentration of the sun's rays on one spot by means of the drops of water acting as a lens and causing burning. A disease of the peach, shown to be of bacterial origin, has also been reported,'' which produces "shot holes" in the foliage and which is much worse in wet seasons. The work here reported has shown that pure lead arsenate applied to tender foliage like the peach will, in some cases, cause serious injury, indicating, therefore, that there is some influencing condition not as yet satisfactorily determined which causes the material to be decomposed and the arsenic to go into solution. This fact led to other experiments in the effort to discover the cause of this decom- position. CAUSE OF THE DECOMPOSITION OF LEAD ARSENATE. EXPERIMENTS ON THE ACTION OF THE CARBON DIOXID OP THE AIR. The first idea that presented itself as a possible explanation for this decomposition of lead arsenate was that the carbon dioxid of the air might act on the lead arsenate, forming lead carbonate, and thus liberate the arsenic acid. This theory, however, did not seem to be very plausible from a chemical point of view and also owing to the lack of uniformity in the injury reported in different years and at different places, but it was decided to determine the point. In order to do so the following experiments were carried out : Experiment 1. — One gram of lend arsenate, made from sodium arsenate and lead acetate, was treated with 1,000 cc of cold distilled water which had been jireviously boiled to expel carbon dioxid. This was allowed to stand ten days, being shaken eight times each day, and was then filtered. At the end of ten days the amount of arsenic in the solution was determined. Experiment ,?.— One gram of lead arsenate made from sodium arsenate and lead nitrate was treated in the same way. Experiment 3. — Same as Experiment 1, except that unboiled distilled water was used and carbon-dioxid gas was run into the solution for about one-half hour each day for ten days. Experiment 4. — Same as Experiment 3, except that lead arsenate was used as in Experiment 2. Experiment 5. — Same as Experiment 3, except that the solution was kept at about 50° C. during the day. Experiment 6.— Same as Experiment 4, heating to 50° C. each day. (This is probably a higher temperature than the material would ever attain on the tree.) "New York Cornell Agr. Exper. Sta., 1899, Bui. 164. t>Anu. Rep. Conn. Agr. Exper. Sta., 1903, p. 337; Mycologia, 1909, 1: 23. 46 LEAD ARSENATE. Table X . — Results of experiments with carbon dioxid. [Arsenic in solution expressed as AS2O5.] Carbon-dioxid-free water: p„ cent. Experiment 1 0. 40 Experiment 2 49 Water with carbon dioxid added: Experiment 3 25 Experiment 4 39 Water with carbon dioxid added and warmed to 50° C: Experiment 5 33 Experiment 6 43 It will be seen from these experiments that lead arsenate is slightly less soluble in distilled water saturated with carbon dioxid, even when heated to 50° C, than in cold distilled water free from carbon dioxid. It would hardly be expected that the results could be otherwise on the tree. EXPERIMENTS ON THE SOLVENT ACTION OF WATER USED IN SPRAYING. It was then thought that possibly the water with which the lead arsenate was being mixed for spraying contained compounds that had a solvent action on the lead arsenate. To determine this and also at the same time to determine the action of dilute solutions of sodium chlorid and sodium carbonate (two salts occurring fre- quently in waters) on lead arsenate, the following experiments were made : Experiment 1. — One gram of lead arsenate, made from lead acetate, was treated with 1,000 cc of the water which was used in the spraying experiments, and allowed to stand at room temperature ten days, shaking it eight times each day. This was filtered and the amount of arsenic in the solution determined. Experiment 2. — Same as Experiment 1, except that lead nitrate was used in making the lead arsenate. Experiment 3. — Same as Experiment 1, except that the mixture was heated to about 50° C. each day for ten days. Experiment 4. — Same as Experiment 2, except that the solution was heated as in Experiment 3. Experiment 5. — Same as Experiment 1, except that the lead arsenate was treated with 1,000 cc of distilled water, carbon-dioxid-free, in which had been dissolved 2 grams of pure sodium chlorid. Experiment 6. — Same as Experiment 5, using lead arsenate prepared from lead nitrate. Experiment 7. — Same as Experiment 1, except that 1,000 cc of distilled water con- taining in solution 2 grams of pure sodium carbonate was used. Experiment 8. — Same as Experiment 7, using lead arsenate prepared from lead nitrate. The amount of arsenic in solution and the per cent based on the total arsenic present are given in the following table: ACTION OF LEAD AKSENATE ON FOLIAGE. 47 Table XI. — Results of experiments to determine solvent action of water constituents on lead arsenate. [Arsenic in solution expressed as AsjOs.] Arsenic in solution. Rind of lead arsenate and water treatment used. Per cent based on weight of lead arsenate taken. Per cent of total arsenic present. Water used in spraying experiments: Used cold— Per cent. 5.24 3.61 8.42 8.27 9.20 11.22 9.56 11.82 Per cent. 17.61 11.06 Heated to .50° C.— 28.29 25.34 Water containing 0.2 per cent of sodium chlorid: 30.91 34.38 Water containing 0.2 per cent of sodium carbonate: 32.12 36.21 It will be seen from these results that a very large amount of arsenic has been dissolved, not only by the solutions of the two salts tried, but by the sample of water tested. It would appear, therefore, that the frequent injury reported from the use of lead arsenate may be due to the solvent action of the water used in apply- ing it. To elucidate this point the composition of the water that had been used in the spraying experiments reported herein was determined. The results are given in Table XII: Table XII. — Analysis of water used in spraying experiments. [Water Laboratory, Miscellaneous Division.] Constituent. Silica (SiOj) Sulphuric-acid radicle (SO4) Bicnrbonic-acid radicle (IICO3). . . Nitric-acid radicle { N O3) Chlorin (01) Iron and aluminum (Feand Al).. Calcium (Ca) Parts Grains per per 1 million. gallon. 23.2 1.353 7.4 .432 37.5 2.187 13.5 .787 20.5 1.195 .6 .035 5.5 .321 Constituent. Magnesium (Mg) Potassium (K) Sodium (Na) Oxygen (to form FejOa). Total Parts per million. 4.3 1.0 20.9 Grains per gallon. 0.251 .058 1.219 .012 7.850 HYPOTHETICAL COMBINATIONS Potassium chlorid (KCl) Sodium chlorid ( NaCl) Sodium nitrate ( NaNOa) Sodium sulphate (NajSOi) Magnesium sulphate (MgSO<) Magnesium bicarbonate (MgHCOs) 1.9 0.111 32.3 1.884 18.5 1.079 9.9 .577 .9 .052 24.8 1.446 Calciiun bicarbonate (CaHCOg) . Ferric oxid ( FejOa) Silica (SiOj) Total. 23. 1.301 .047 1.353 48 LEAD ARSENATE. While the total amount of dissolved salts occurring in this water is small, it will be noticed that the sodium chlorid content is rela- tively liigh, and to this the solvent action which this water exerts on lead arsenate is no doubt largely due. It would appear from these results that if certain salts commonly occurring in waters are present in more than very small amounts they will exert a solvent action on the lead arsenate. CONCLUSIONS. Referring again to the fact that no injury resulted in 1907 from the lead arsenate, while in 1908 severe damage followed the use of the same water and chemicals, this may be explained by the differ- ence between the two seasons with respect to climatic conditions. In 1907 every application was followed by cool, cloudy weather and rain within forty-eight hours. In 1908 the first two applications were followed by cool days and light rains soon thereafter, but the last application, which caused practically all of the injury, was followed by five clear, hot days and no rain. The dews at night would be sufficient to moisten the material, and when hot sunshine followed the conditions would be just right to dissolve the maximum amount of arsenic, and therefore cause the maximum injury. The salts (sodium chlorid and sodium carbonate and no doubt others which have not been tried), which cause the lead arsenate to be broken up, are readily soluble in water, and if their application were followed by rain they would be washed out, and therefore no injury should result. Headden," in a publication which has recently been issued, calls attention to the danger that may result from using water containing certain salts. He says : " It has often been asked at meetings of these orchardists whether it was a safe practice to use their surface alkali water in applying the lead arsenate and I have stated that it was not a good practice, for one could easily conceive of conditions under which the whole of the lead arsenate could be converted into sul- phate of lead and sodic arsenate be formed in solution. This state- ment never seemed to be an acceptable one. I have in this case not depended upon any chemical laws, however evident their ade- quacy might be, but took well-washed lead arsenate, a sample which we found by rigid test to be free from soluble arsenic, suspended 1 gram of it in 2,000 times its weight of water and added 2 grams of Glauber's salt, allowed it to stand three days, filtered off a portion of it, concentrated by evaporation, and tested it for arsenic. I found o Colorado Agr. Exper. Sta., 1908, Bui. 131, p. 22. ACTION OF LEAD AESENATE ON FOLIAGE. 49 that the arsenic had gone into sohition in very considerable quan- tities. A parallel experiment was carried out with salt, in which only 1 gram of salt was used to the 2,000 grams of water. This was not allowed to stand quite three days when 1,500 grams were filtered off, concentrated and tested for arsenic. This concentrated solu- tion was found to be so heavily charged with arsenic that only a small part of it gave an unmanageable amount of arsenic when brought into an active Marsh apparatus." Still more exhaustive experiments than those here reported are being made in the orchard this year, which it is hoped will definitely settle this point. It was deemed best to report the progress that has been made before waiting for the final conclusions or for the results of other experiments along the same line, some of which have sug- gested themselves since this work was begun. The full data obtained from the 1909 experiments have not as yet been collated, but some interesting results have been obtained and may be briefly mentioned. Lead arsenate was applied to peach trees in the same proportions as in previous experiments — that is, I3 pounds (dry basis) to 50 gallons — and three applications were made. (1) When applied with spring water (analysis of which has been given), some injury to foilage resulted, but it was not nearly so marked as in the preceding year, and a longer time elapsed before the injury was noticeable. (2) When appHed with distilled water very slight injury occurred, noticeably less than when the spring water was used. (3) When applied with distilled water to which 10 grains per gal- lon of sodium chlorid had been added, rather serious injury resulted. When distilled water containing 40 grains of sodium chlorid per gal- lon was used, the injury was very much increased, practically 50 per cent of the foliage being affected. (4) When, applied with distilled water containing 10 grains of sodium carbonate per gallon, injury was noticeable fourteen days after the first application, and seven days after the third application the trees were almost completely defohated. (5) Applied with distilled water containing 10 and 40 grains of sodium sulphate per gallon, some injury resulted, but this was not so marked as that produced in the presence of sodium chlorid. In similar experiments where lime was added at the rate of 4 pounds to 50 gallons, injury to the fohage was almost entirely pre- vented. LIST OF TABLES. Page. Table I. Composition of commercial lead arsenates 9 II. Composition of lead acetates 14 III. Composition of lead nitrates 15 IV. Composition of sodium arsenates 16 V. Analysis of lead arsenates prepared in the lal)oratory 26 VI. Monthly meteorological data, March to August, 1907, Washington, D.C. 29 VII. Comparison of monthly meteorological data for 1907 with the aver- age for thirty-seven years 32 VIII. Monthly meteorological data, March to August, 1908, Washington, D.C. IX. Comparison of monthly meteorological data for 1908 with the aver- 38 age for thirty-eight years 41 X. Results of experiments with carbon dioxid 46 XI. Results of experiments to determine solvent action of water con- stituents on lead arsenate 47 XII. Analysis of water used in spraying experiments 47 50 o ^ ^ i Vk