“ , ey fi One Pe: Tt hy i . Y a : : fax an 6, 1910. : L 4\z, Be . DEPARTMENT OF AGRICULTURE, | BUREAU OF CHEMISTRY —BULLBTIN No. 134 pang H. W. WILEY, Chief of Bureau. eager - LEAD ARSENATE. ea i Composition of lead arsenates found on the market. -. Bog a Home-made’? lead arsenate and the chemicals entering into ane its manufacture. Ir. Action of lead arsenate on foliage. a Ne Bi; 4 BY i se . ee ot | J. K. HAYWOOD, - 7 hg Chief, Miscellaneous Division, Pe Seo GumcDONNELE, m __, Chief, Insecticide and Fungicide Laboratory, Miscellaneous Division. ened bs MY By ia ged a IN COOPERATION WITH THE BUREAU OF ENTOMOLOGY, 4 + mal\s f ( ‘ ay Ba, ; GOVERNMENT PRINTING OFFICE. Dee een eo OA. oi: “.) -. WASHINGTON: ~ Sees wb yeah ya ‘a 1% My | ae) (ee! fl i mrs cae * Die i? ‘ Pri ” ‘Gl if A Issued April 6, 1910, U. S. DEPARTMENT OF AGRICULTURE, BUREAU OF CHEMISTRY—BULLETIN No. 131. H. W. WILEY, Chief of Bureau. 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. < . BY file aN Jo KY HAYWOOD, Chief, Miseellaneous Division, AND C. C. McDONNELL, Chief, Insecticide and Fungicide Laboratory, Miscellaneous Division. IN COOPERATION WITH THE BUREAU OF ENTOMOLOGY. WASHINGTON: GOVERNMENT PRINTING OFFICE. OOK LETTER OF TRANSMITTAL. U.S. DEPARTMENT OF AGRICULTURE, BuREAU OF CHEMISTRY, Washington, D. C., October 16, 1909. Str: I have the honor to submit for your approval a report on the composition of commercial and ‘‘home-made” lead arsenates, together with the results of two years’ experimental work on the action of this insecticide on foliage, especially that of the peach tree. The problems and conditions discussed are of vital interest to all orchardists and farmers, and I recommend the publication of the report as Bulletin 131 of the Bureau of Chemistry. The work was performed in the insecticide and fungicide laboratory of the Miscel- laneous Division of this Bureau, with the cooperation of the Bureau of Entomology. ; Respectfully, H.W... Witanye Chief of Bureau. Hon. JAmEs WILSON, Secretary of Agriculture. APR 14 1910 B. OF B. CONTENTS: Iimtrodutetion'.....cecase- occcs- 3+ I. Composition of lead arsenates found on the market...............-.------ Scope of the investigation. .-. Methods of analysis-.......-- - Results of analyses..........- DISC USHOME so steec oss. es. Methods of analysis......... - Weadtsallitsie. sass 05-2se Sodium arsenate......... Wom PosLiOnyOLteagtaeCebatel< a. os. 454.2 ci isan shea ss ha oak eos Results of analyses. ...-.- Discussions: (2-5-2550 - C sition of 1 i ‘omposition of lead nitrate. - Results of analyses. .....- WAISCUESION: 3.2. 5.<00' 5-52 Conmmpositiom.ol sodium arsenate... .......05 5... 2402-520 eu ee cases nase Results of analyses....... Discussions 2 5... ese 2 Theoretical composition of lead arsenate..............-.....-.-.---- Published formulas.......-.... Directions for preparing lead arsenate... -.....5 02. s.se25c.c2 2s. Comparative merits of lead acetate and lead nitrate.................. Physical properties of lead arsenate. ._..............--2:--.-.0-005- III. Action of lead arsenate on foliage General discussion. ......... Preparation‘or the lead arsenate Used -2..<..8. 4.2 - 6.0.00. elo. eb ese - Experimental work of 1907... Description of experiments. Record of observations... Weather conditions. .-.- Summary for 1907........ Experimental work of 1908... Description of experiments Record of observations. .- Notes made on July 29 on condition of fruit Notes made on August 13 on condition of fruit Weather conditions. .... Summary for 1908........ ae @/eia se seis ee ele ielea lee ele jale sie ae ois \=.s) ioc = lee «= Hm He CO as bo b> bo bt bt bb bo f=) [o.) 4 CONTENTS. III. Action of lead arsenate on foliage—Continued. Page. — Summary of results for the two years’ experiment. ......-..-..-..... 42 General discussion of problems involved in the investigation........- 43 Lead nitrate vs.‘lead acetate..922 2.7... 22.42 6.5. +2 2: ee 43 Susceptibility of peach foliage to injury.........-..-....------.- 44 Cause of the decomposition of lead arsenate...............--.---- 45 Experiments on the action of the carbon dioxid of the air..... 45 Experiments on the solvent action of water used in spraying. 46, Conclusions: 2.383020 ee ee ee eee 48 List Of tables:.oj2 2500. 2 oka eee ee ee eee ee 50 ILLUSTRATIONS. PLATES. Page. Puate I. Effect of different treatments on the settling oflead arsenate. Fig.l1— 24 After standing two minutes. Fig. 2.—After standing fifty minutes. — II. Peach leaves showing injury from lead arsenate. Fig. 1.—Leaves from trees in Experiment 3. Fig. 2.—Leaves from trees in Ex- periment 120 5. sec. ac aot ee eos eee a ae 34 III. Check plot, not sprayed, showing normal, healthy foliage of peach [2 2) ee a Me RA Se eRe SU Seca io lois ioc 5 3c. 36 IV. Peach tree in Experiment 12 sprayed with lead arsenate and show- ing partial defoliation: 232-22. sass sce eee ae ee 36 TEXT FIGURE. Fic. 1. Injured peaches from trees sprayed with lead arsenate ....-.-----..- 37 LEAD ARSENATE. INTRODUCTION. It is onlyin more recent years that lead arsenate has been used as an insecticide for spraying purposes. Its use was first suggested by Mr. F. C. Moulton in 1892, while acting as chemist for the gypsy moth commission of Massachusetts, after having made a study of numerous materials to be used as insecticides for the extermination of the gypsy moth. It was found that Paris green could not be used successfully for this purpose, principally because it could not be applied in sufficient quantity to kill the caterpillars without seriously injuring the foliage. While lead arsenate was not found entirely satisfactory in destroying this pest,it possessed several advantages over Paris green, and this has resulted in its replacing the latter material for spraying purposes to a very large extent, in fact, almost entirely in some of the Rocky Mountain and Pacific Coast States. Some of these advantages are: (1) It is not so injurious to foliage when applied thereto, on account of its being less soluble in water. (2) When sprayed upon leaves it forms a thin film, which is quite adhesive and is not so easily washed off by rains. (3) It remains in suspension much better, thereby requiring less effort to keep the mix- ture agitated, and thus insuring a more uniform application. (4) Being white, it forms a visible coating and is easily distinguished when it has been applied. The initial cost of this material is slightly greater than that of Paris green, owing to the fact that it contains a smaller percentage of arsenic than the latter, and therefore more of it must be used to produce the same effect. Because of its greater adhesive qualities, however, it remains on the foliage better, requiring less frequent application, and thus in the end lead arsenate is no more expensive than Paris green; in fact, it may be even cheaper, as the greatest expense in spraying is the cost of applying the material to the trees. The use of lead arsenate has increased very rapidly during the last few years, as is shown by the fact that less than ten years ago no one was manufacturing it to any large extent, while at the present time there are at least eighteen manufacturing chemists in the United States making it in greater or less quantities, and a number of other firms are preparing to doso. An attempt was made to determine the total amount sold in the United States for the years 1907 and 1908 by writing to the various manufacturers for figures showing their sales. 5 6 LEAD ARSENATE. Many of these very cheerfully gave the information asked for, but several refused, and a few others did not have the data available. Judging from the information which has been obtained, the total amount sold in 1908 was approximately 2,500 tons, the value of which was more than half a million dollars. In addition, a great quantity of the home-made material has been used, but this quantity can not be estimated. It was on account of the great importance which lead arsenate is assuming for spraying purposes and in view of certain variable results which have been reported, that this study was begun by the Bureau of Chemistry two years ago, principally for the purpose of determin- ing, if possible, the conditions which cause it to be injurious to foliage in some cases. The experiments have been conducted for two suc- cessive years, as it was considered impossible to arrive at any trust- worthy conclusions in a shorter period. At the same time a study of the composition of the lead arsenates found on the market and also that of ‘‘home-made” lead arsenate was made, including analyses of such of the chemicals entering into its manufacture as could be pro- cured from druggists and other sources. This work, therefore, has been divided into three parts, as follows: 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. The work has been carried out in cooperation with the Bureau of Entomology, Mr. A. L. Quaintance, in charge of deciduous-fruit insect investigations, having furnished the larger number of the sam- ples herein reported and cooperated in the carrying out of the spraying experiments outlined in the third section. I. COMPOSITION OF LEAD ARSENATES FOUND ON THE MARKET. SCOPE OF THE INVESTIGATION. The object of this investigation was to determine by chemical analysis the quality or grade of the leading lead arsenates as found on the open market and supplied to the trade. To this end samples were obtained at many points in different sections of the United States by various collectors, and, while the products of a few manu- facturers are not represented, all of the leading brands, representing about 98 per cent of the total output, are included in the list. Ina number of instances several samples of the same brand, purchased at different times and places, have been analyzed in order to deter- mine whether the output of the same firm is of uniform composition. As the purpose of the investigation was to show the general condition of the trade during 1907-8, more particularly as a preliminary to other studies, the names of the manufacturers are not given, but all of the samples from one firm are designated by the same letter, that they may be compared. COMPOSITION OF LEAD ARSENATES ON THE MARKET. 7 METHODS OF ANALYSIS. The samples were analyzed according to the provisional methods of the Association of Official Agricultural Chemists %, as follows: PREPARATION OF SAMPLE. In case the sample is in the form of a paste, as it usually is, dry the whole of it to constant weight at the temperature of boiling water and calculate the results as total moisture. Grind the dry sample (which will gain a small amount of moisture by so doing) to a fine powder and determine the various constituents as follows: MOISTURE. Weigh 2 grams of the sample and heat in a water bath for eight hours or in a hot air bath at 110° C. for from five to six hours, or till constant weight is obtained. TOTAL LEAD OXID. Dissolve 2 grams of the sample in about 80 cc of water and 15 cc of concentrated nitric acid on the steam bath; transfer the solution to a 250 cc flask, and make up to the mark. To 50 cc of the solution add 3 cc of concentrated sulphuric acid, evapo- rate on the steam bath toa sirupy consistency, and then on the hot plate till white fumes appear and all nitric acid has been given off. Add 50 ce of water and 100 cc of 95 per cent alcohol. Let stand for several hours and filter off supernatant liquid, wash about ten times with acidified alcohol (water 100 parts, 95 per cent alcohol 200 parts, and concentrated sulphuric acid 3 parts), and then with 95 per cent alcohol till free of sulphuric acid. Dry, remove as much as possible of the precipitate from the paper into a weighed crucible, and ignite at low red heat. Burn the paper in a sepa- rate porcelain crucible and treat the residue first with a little nitric acid, which is afterwards evaporated off, and then with a drop or two of dilute sulphuricacid. Ignite, weigh, and add this weight to the weight of the precipitate previously removed from the paper for amount of the lead sulphate. If preferred, the lead sulphate may be filtered and weighed in a porcelain Gooch crucible. TOTAL ARSENIC OXID (MODIFIED GOOCH AND BROWNING METHOD b), Transfer 100 ce of the nitric acid solution of the sample, prepared as in the above determination of lead, to a porcelain dish, add 6 cc of concentrated sulphuric acid, evaporate to a sirupy consistency on water bath and then on hot plate to the appear- ance of white fumes of sulphuric acid. Wash into a 100 cc flask with water, make up to mark, filter through dry filter, and use a 50 cc aliquot for further work. Transfer this to an Erlenmeyer flask of 400 cc capacity, add 4 cc of concentrated sulphuric acid and 1 gram of potassium iodid, dilute to about 100 cc and boil until the volume is reduced to about 40 cc. Cool the solution under running water, dilute to about 300 cc, and exactly use up the iodin set free and still remaining in solution with a few drops of approximately tenth-normal sodium thiosulphate. Wash the mixture into a large beaker, make alkaline with sodium carbonate and slightly acidify with dilute sulphuric acid; then make alkaline again with an excess of sodium bicarbonate. Titrate the solution with a twentieth-normal iodin solution to the appearance of a blue color, using starch as indicator. WATER-SOLUBLE LEAD OXID. Place 2 grams of the sample in a flask with 2,000 cc of carbon-dioxid-free water and let stand ten days, shaking eight times a day. Filter through a dry filter (being sure a clear filtrate is obtained) and use aliquots of this for determining soluble lead and arsenic oxids and soluble solids; determine lead as described above for total lead, @U.S8. Dept. Agr., Bureau of Chemistry Bul. 107, Revised, p. 239. b Amer. J. Sci., 1890, 40: 66. 8 LEAD ARSENATE. using the same relative proportions of sulphuric acid, water, and alcohol, but keeping the volume as small as possible. WATER-SOLUBLE ARSENIC OXID. For this determination use 200 to 400 cc of the water extract obtained under the determination of soluble lead oxid. Add 0.5 ce of sulphuric acid and evaporate it to a sirupy consistency, then heat on a hot plate to appearance of white fumes. Adda very small amount of water and filter off lead through the very smallest filter paper, using as little wash water as possible. Place this filtrate in an Erlenmeyer flask, and determine arsenic as described under total arsenic oxid, using the same amount of reagents and the same dilutions. SOLUBLE SOLIDS OR IMPURITIES. Evaporate 200 cc of the water extract obtained above to dryness in a weighed platinum dish, dry to constant weight at the temperature of the boiling water bath, and weigh. The soluble solids so obtained represent principally any sodium acetate or sodium nitrate present, with a very small quantity perhaps of lead acetate or nitrate and some soluble arsenic, probably in the form of lead arsenate, or sodium arsenate. These methods were not followed exactly in all cases, owing -to peculiarities of some of the samples. Those which were moist and in the form of a paste were heated at about 85° C. till dry enough to powder, and the loss noted. The analysis was then carried out on this dried sample and the results calculated to the material in its original condition. The moisture on the dried sample was calculated to the original material and added to the loss obtained on the first drying for ‘‘total moisture.”’ Insoluble matter was that remaining from the treatment with nitric acid and was removed by filtration, washed, ignited, and weighed. In case calcium is present in the sample, it may be separated from the lead by treating the precipitated sulphates with water (acidified with sulphuric acid) to which no alcohol has been added and filtering, or by the following method, which is the one used in this work: Precipitate the lead from a solution slightly acidified with nitric acid, with hydrogen sulphid in the cold; filter off the precipitate containing the lead sulphid, wash, dissolve in moderately strong hot nitric acid, treat this solution with 4 or 5 cc of concentrated sulphuric acid, carry down in a porcelain dish to expel nitric acid, treat with water and alcohol mixture, and proceed as before. Calcium is determined in the filtrate from the lead sulphid (after removing any arsenic remaining therein by hydro- gen sulphid) by precipitating with ammonia and ammonium oxalate in the regular way. In case the material was lead arsenite or contained this substance, it was determined as follows: t Boil 2 grams of the sample with 50 ce of dilute (1 to 5) sulphuric acid for about one hour, cool, make up to mark, filter through dry filter, and to 50 cc of the filtrate add sodium bicarbonate in considerable excess and titrate with standard iodin solu- tion, using starch as indicator. The arsenic equivalent of the iodin solution used is Peiegiaicd as arsenious oxid (As,O,). Tests were made on the water soluble impurities for acetates aie nitrates. This would indicate which lead salt had been. used in the manufacture of the sample. COMPOSITION OF LEAD ARSENATES ON THE MARKET. 9 RESULTS OF ANALYSES. TaBLE I,.—Composition of commercial lead arsenates. ANALYSIS OF ORIGINAL SAMPLE. Serial | num- Water- | Water- ber Total Total Water- and | Mois- | Acidin-| lead | arsenic | soluble soluble soe ectele 4 oe F purities | letter ture. soluble oe Aerts impuri- axid atl conta ano (PbO). | (AssOs). | ties. | (PHO). | (As:0s). : Per cent. | Per cent.| Per cent. | Per cent. | Per cent. | Per cent. | Per cent. 4535 61. 84 0.03 23. 06 12. 62 2.03 0.15 0.31 | Nitrates. 4629 44. 69 -05 35. 45 17.97 ati) - 06 .38 Do. 4656 59. 65 . 04 25. 27 13. 66 10 .09 .22 Do. 5084 47.91 : - 03 32. 50 17.13 . 80 -18 -33 Do. 5086 40. 63 .14 42.23 14. 49 1.34 «18 .50 | Acetates. 5087 52. 02 - 03 30. 06 15. 64 . 65 - 09 .25 | Nitrates. 5088 48. 21 . 04 32.11 16.99 99 | .16 .33 Do. 5089 45. 60 - 02 35. 53 16. 93 .o2 | -29 -43 Do. 5090 42.75 . 06 36. 07 17. 55 1. 42 | «25 -o0 Do. 5853 41 - 05 66.75 28. 91 . 66 | 1.06 1.06 | Acetates. 5854 48.05 . 04 32.75 16. 86 1.51 ol .32 | Nitrates. 6451 4 SOi | sees eens 37.79 17.38 . 76 .48 -82 | Acetates. B: 6456 AOE GIO Seas. Ses 39. 49 14. 44 1.06 .32 41 Do. Cc: a 5341 445.09) bee acces 41. 46 12.16 . 08 .28 Salil Do. 4633 36. 89 . 28 39.75 17.76 4.51 16 . 50 Do b 4651 46. 38 - 03 35. 03 14.65 3.71 17 .22 Do b 4652 37.76 ll 40. 66 17.23 3.20 18 . 30 Do 5085 37. 61 08 40. 92 17.76 1.27 2 36 Do. 5091 31. 54 . 06 48.09 15. 69 2.18 22 +22 Do. 5961 41.18 -05 35. 48 18. 81 4. 33 . 55 -20 | Nitrates. 6452 ZA Pee eso 46. 80 22.11 5. 68 . 67 06 Do. c 4720 45. 60 3. 42 26. 97 12.08 7. 54 1.19 2.42 | Acetates. 4291 BOS SOU eetad fee ree 36. 46 19. 60 1.04 .37 .33 b 4301 48.29 04 33. 89 15. 46 2.23 .29 230 Do. 4533 28. 39 . 04 49. 67 20. 49 2.03 .49 1.01 Do 5611 Slots!) Bee onasene 43. 88 14. 87 77 .10 a3 Do 5855 1.89 05 64. 54 28. 06 3. 80 1.04 1.08 Do. 5856 45. 60 03 37. 93 14. 33 . 64 . 30 -41 Do. 6454 Be ye ee eee ee 45. 64 16. 90 75 . 58 - 90 Do. 4534 87 .09| 72.57| 24.01 1.14 AT 51 Do. 6453 CeO Xt Re eae 36. 88 11.98 1.04 44 .04 Do. 4296 AS OSM Eee ecs nee 38. 81 15. 22 2.32 . 22 .23 | Nitrates. 4631 45. 84 - 03 35. 25 16.76 1.34 sali .24 | Acetates. 4632 45.12 -29 35. 82 16.70 44 -12 . 26 Do. b 4648 45. 20 04 36. 58 16. 24 . 68 .19 .30 Do. 4657 40. 38 hl 40. 04 17.83 . 65 36 BBP Do. 4721 . 59 . 03 67.14 28. 87 2.01 A At ~44 Do. 4830 46. 34 .07 34. 44 16. 56 93 -13 . 26 Do. 5852 - 67 . 67 65. 24 26. 42 1.39 . 60 .58 | Nitrates. 5959 47. 56 03 35. 06 15.98 .74 35 .39 Do. ae Al OS.n|eoateat sey 38. 46 16. 24 | 1.45 .44 aril Do. d aan 2.00 . 05 51.35 43. 81 2.27 44 5.45 | Acetates. 6455 Boro. |Eeaseecee 44. 64 16. 43 . 67 -40 . 87 Do. e 4532 35. 43 - 06 44.73 18.04 . 88 . 63 2.12 Do. F 6458 AGH ayers ae 45. 62 6. 03 3.35 1.61 OQ ee ae ere 4624 .76 alt 60. 06 28. 52 5. 40 .38 | .30 | Nitrates. 4571 61.03 -23 23.31 12.89 2.03 .19 | 21 Do. 4630 22.18 . 09 50. 55 20.15. 83 . 29 .80 | Acetates. 4870 38. 81 oa 37.98 20, 91 = RO ies lls) .45 | Nitrates. 5960 43. 26 03 36. 02 19. 36 - 40 - 42 | 53 Do. aSample had distinct odor of ammonia; on determination gave 0.14 per cent on original sample. b Sample had decided acid reaction; strong odor of acetic acid. cContained 2.48 per cent of CaO, 1.75 per cent of COs; calculated to moisture-free basis, 4.56 per cent of CaO, 3.22 per cent of COs. d Mostly lead arsenite. Total arsenic reported as AseO3, 43.81 per cent; of this, 3.37 per cent (<>-3.91 per cent As2QOs5) is pret as arsenate; soluble arsenic reported as As2O3. ¢Sample labeled ‘lead arsenite;”’ a mixture of lead arsenite and lead arsenate. Arsenic as arsenite 6.52 per cent of AsgO3 (<>-7.57 per cent of AsOs); as arsenate 10.47 per cent of AsgQs. Calculated to moisture- free basis As2O3= 10.01 per cent; AszO;=16.31 per cent. Water-soluble arsenic reported as As2Q3. / Contains an excess of lead as carbonate. 23904—Bull. 131—10 2 10 LEAD ARSENATE. Tasie I.—Composition of commercial lead arsenates—Continued. CALCULATED TO MOISTURE-FREE BASIS. Serial num- ber and letter indi- cating firm. A: 4535 4629 4656 5084 5086 5087 = Water- Total W ater- Acid Total arsenic Water- soluble soluble “ lead oxid . soluble & arsenic insoluble. oxid ; sen lead oxid ° (PbO). (As20s) impurities. (PbO) oxid - 4 (As205). Per cent. Per cent. Per cent. Per cent. Per cent. Per cent. 0. 08 60. 43 33. 07 5. 32 0.39 0. 81 .09 64. 09 32.49 .99 ali . 69 .10 62. 63 33. 85 1. 86 a7) - 55 - 06 62. 39 32. 89 1. 54 2300 . 63 .24 71.13 24. 41 2.26 1.26 . 84 07 62. 65 32. 60 ses) 19 -O2 -08 62. 00 32. 81 1.91 31 . 64 . 03 65. 31 31.12 . 59 . 53 -79 pili 63. 00 30. 66 2.48 44 . 65 05 67.03 29.03 . 67 1.06 1. 06 . 08 63. 04 32. 45 2.91 . 60 . 60 ER cca 64. 44 29. 64 1.30 . 82 1.40 BS ieee 68. 80 25.16 1.85 . 56 Atal pee So soe okt 74. 97 21.99 14 ail . 20 .44 62.99 28.14 7.15 .25 .79 - 06 65. 33 27.32 6.91 .32 -41 .18 65. 33 27. 68 5.14 .29 . 48 -13 65. 59 28. 47 2.04 . 34 . 58 .09 70. 25 22. 92 3.18 sou BPA .09 60. 32 31.98 7.36 . 94 .34 eee eS, 59. 54 28.13 1.22 .85 . 08 6.29 49. 58 22.21 13. 86 2.19 4.45 aeons eves 61. 68 33.16 1.76 . 63 . 56 Bene ay Se 65. 54 29. 90 4.31 . 56 . 64 . 06 69. 36 28. 61 2. 83 . 68 1.41 eee Ae ae 70. 65 23.94 1.24 .16 wall -05 65. 78 28. 60 3.87 1.06 1.10 . 06 69. 72 26. 34 1.18 Sta) niltl AES eee 69. 40 25. 69 1.14 . 88 1.37 . 09 72.99 24.15 1.15 -47 -51 ee Pe te Mea 71.39 23.19 2.01 -85 .08 Pena SneBee 68.18 26.74 4.08 . 40 . 40 . 06 65. 08 30.95 2.47 .20 .44 700 65. 27 30. 43 . 80 22 47 . 07 66. 75 29. 64 1.24 .35 300 .18 67.16 29.91 1.09 . 60 .54 . 03 67. 54 29. 04 2.02 aA .44 518} 64.18 30. 86 15783 .24 . 48 B67 65. 68 26. 60 1.40 . 60 . 58 . 06 66. 86 30. 47 1.41 . 67 .74 |bSecbsasscne 65. 20 27. 54 2.47 .75 1.20 05 52. 40 44.70 2.32 . 45 5. 56 ok cecais ere 69. 48 25. 57 1.04 . 62 1.35 . 09 69. 27 27.94 1.36 .98 3. 28 IE sieve ont swiss 77.93 10. 30 §.72 2.75 .03 Fall 60. 52 28.74 5. 44 . 38 .30 . 59 59. 82 33. 08 RAL . 50 . 54 -12 64. 96 32.32 1.07 -o0 1.03 . 34 62.07 34.17 .74 .24 .74 .05 63. 48 34. 12 .70 .74 .93 COMPOSITION OF LEAD ARSENATES ON THE MARKET. ait DISCUSSION. Some of the samples examined had dried out considerably before they were received, as was evident from their mechanical condition, weight of package, etc. Insuch cases the per cents given on the origi- nal sample are based on the goods as received and will not represent the correct composition of the material as placed on the market, on account of this decrease in the moisture content, making the per cent of the other constituents as given higher than they were originally. In making lead arsenate from lead acetate and disodium arsenate a certain amount of acetic acid is formed. This had not been com- pletely washed out in all cases, as was shown by the fact that several of the samples had a strong odor of acetic acid. No quantitative determination was made of the amount, but as it would be driven off at the temperature of drying, the term ‘‘moisture’’ not only includes water, but any other material volatile at from 105° to 110° C, One of the samples examined was lead arsenite and another was a mixture of the arsenate and arsenite in about equal proportions. Several others contained small amounts of arsenic as arsenite, but usually only traces were present. In such cases the water-soluble arsenic reported as arsenic oxid (As,O,) contained some arsenious oxid. As soluble arsenic is injurious in either form, the two have not been determined separately, except in the cases noted, where it was present entirely as arsenite. On inspecting the analyses given in Table I, the first striking fact that will be observed is the great variation in the composition of the different samples. The content of arsenic oxid ranges from 6.03 to 43.81 per cent (the latter as As,O,); lead oxid varies from 23.06 to 72.57 per cent; moisture from 0.41 to 61.84 per cent; water-soluble arsenic from 0.02 to 5.45 per cent (As,O,); and water-soluble impur- ities from 0.08 to 7.54 per cent. In order to secure a more uniform basis for comparison all of the determinations have been calculated to moisture-free material. A much greater uniformity is shown when this is done, but there is still a considerable variation. Arsenic oxid ranges from 10.30 to 44.70 per cent (the latter As,O,); lead oxid from 49.58 to 77.93 per cent; water-soluble arsenic oxid from 0.03 to 5.56 per cent (As,O,); and water-soluble impurities from 0.14 to 13.86 per cent. Evidently in some cases the salts formed as by-products in the manufacture have not been washed out, or at most the material has simply been run through the filter press to remove the super- fluous liquid, as is shown by the high per cent of water-soluble mate- rial in a number of samples. Lead arsenate is recommended for spraying purposes mixed with water in various proportions. A standard formula and one fre- quently recommended is 2 pounds to 50 gallons. It is easy to see 12 LEAD ARSENATE. from the analyses of these samples that if they were made up accord- ing to this formula there would be in some cases eight times as much arsenic applied as in others. As a consequence the spraying might be condemned as inefficient in certain cases, owing to too weak an application, while in others, using the very same formula, severe injury to the tree might result from too strong an application. An- other and even more serious condition may result from a high per cent of soluble arsenic, due to the lead arsenate being carelessly or improperly made. Where sufficient care is exercised in the making the soluble arsenic should certainly not exceed 0.75 of 1 per cent, calculated as arsenic oxid (As,O;) on a 50 per cent moisture basis, or 1.5 per cent on a moisture-free basis. Lead arsenate should be packed in air-tight packages, in order to keep it in a moist condition until ready for use. After it has once been dried it is much more difficult to keep it in suspension during spraying, which often results in an unequal application. This is the main reason for putting it up in a moist condition instead of in the dry state. Forty to fifty per cent of moisture is sufficient to preserve it in good condition, if it is kept in air-tight receptacles until used. In case a package is opened and only partly used, that remaining may be held over in good condition for the next spraying, by covering it with an inch or more of water. Lead arsenate should always be bought in original packages, which are plainly labeled; when purchased from a broken package, more or less risk is run of not getting true lead arsenate. Three instances have been found in which supposed ‘‘lead arsenate’? was purchased from drug stores, which on analysis proved to be white arsenic (arsenious oxid). The result of spraying this material on the peach or any other fruit tree would be disastrous. While some of the firms are making a good product, this can not be said of all. It was not to be expected, however, that a perfect product would be produced in all cases, especially as the material has not been manufactured until recently and evidently some have taken up the business without proper knowledge of the subject. The product will no doubt be improved as its use and preparation become better understood. II. ‘‘HOME-MADE”’ LEAD ARSENATE AND THE CHEMICALS ENTERING INTO ITS MANUFACTURE. INTRODUCTION. As has been previously noted, arsenate of lead was first proposed as an insecticide in 1892, but it was several years before it was used to any great extent. This was not a product that could be obtained on the market at that time and it was therefore necessary for those using it to prepare their own supply. These conditions no longer HOME-MADE LEAD ARSENATE. 13 exist, as there are at the present time twenty or more firms in different parts of the United States which manufacture it, and it is possible to procure it in almost any section of the country. Only those brands should be accepted, however, which bear the guaranty of a reliable manufacturer on the package. When such can not be obtained at a reasonable price, or if only a small amount is needed, it may be advantageously made at home by following the directions which are given herein. Again, in some cases where a large quantity is to be used and the proper chemicals can be purchased at a reason- able price, a considerable saving might result by making it at home, but this would probably not be advisable as a general rule. In the making of such a product there is always some risk due to poor chem- icals, an incorrect formula, or carelessness in making. The chemicals used in its preparation are sodium arsenate and either lead acetate or lead nitrate. All of these can be easily obtained from druggists and are the cheapest compounds containing the necessary elements in a suitable form. The wholesale prices of the technical grades of these chemicals at the present time are: Lead acetate, 7}? to 8 cents per pound; lead nitrate, 7? to 8} cents per pound; sodium arsenate, 54 to 6 cents per pound. These salts all show some variation in their composition and at times this may be very great, particularly in the case of sodium arsenate, which is the salt used to supply the arsenic. Samples of these chemicals have been obtained in various parts of the country from druggists and other sources and subjected to analysis. In the lead salts the total amount of lead oxid has been determined and in the sodium arsenate total arsenic oxid and chlorin. These are the only substances which it is necessary to consider, as they are the ones that enter into the reaction. METHODS OF ANALYSIS. LEAD SALTS. Total lead oxid.—This may be determined as sulphate by precipi- tating with sulphuric acid, or as oxid by precipitating with ammonia and ammonium carbonate and converting into the oxid by ignition. The details of these methods are given in works on quantitative anal- ysis and both give satisfactory results. SODIUM ARSENATE. Total arsenic oxid.—Dissolve 2 grams of the sample in water and make volume up to 250 cc. Heat 50 ce of this solution to about 80° C., add 3 grams of potassium iodid and 50 ce of concentrated hy- drochloric acid. Let stand fifteen minutes, cool, add approximately tenth-normal sodium thiosulphate solution just to disappearance of color caused by free iodin. (The end point is easy to obtain without the use of starch.) Add immediately sodium carbonate until most of the acid is neutralized, then after all the sodium carbonate has 14 LEAD ARSENATE. been dissolved complete the neutralization with sodium bicarbonate, adding it in considerable excess. Add a few drops of starch indicator (made by boiling 1 gram of pure starch in 100 ce of water) and run in standard iodin solution till all arsenite has been oxidized to arsenate as will be shown by the appearance of the blue color. Calculate the amount of arsenic present in terms of arsenic oxid (As,O;) from the volume of the standard iodin solution required for the oxidation. The strength of the standard iodin solution is determined by titrating against a solution containing a known amount of arsenious oxid, in the same manner. Chlorin (Volhard’s method).—Acidify with nitric acid 50 ce of the solution used for determining total arsenic, then add an excess of standard silver nitrate solution and make up to 200 cc. Filter through a dry filter and determine the excess of silver in 100 cc of the filtrate by titrating with standard ammonium sulphocyanate solution, using solution of ferric alum as indicator. Twice the amount of silver in this 100 ce portion, subtracted from the total amount added, will give the amount of silver equivalent to the chlorin in the 50 ce of the solu- tion originally taken, from which the per cent of chlorin present may be calculated. COMPOSITION OF LEAD ACETATE. RESULTS OF ANALYSES. In Table IT are given the analyses of the samples of lead acetate examined. In column four is given the equivalent of the lead oxid found in crystallized lead acetate, Pb(C,H,O,),3H,O, in order to show more clearly the relative value of the various samples for the purpose of making lead arsenate. TaBLE II.—Composition of lead acetates. lea oes X ead calculated Serial A = to number. Grade: ( EO) \erystallized Oe lead | acetate.a Per cent. | Per cent. 4546 White cs. che ose eee eee 58. 84 100. 11 4650 Wihites=eneee Sate 59. 29 100. 88 4626 | Commercial. Be 66. 43 113. 03 4719 White.... 59. 93 101. 97 4718 Browse see. eas 60. 94 103. 69 4538. | Pure pranulatedjc.c--pe-o-- -— 59. 97 102. 04 4544 | Pure granulated...........--- 60.76 103. 38 4545) |) Pureleranulatedies 2 =... --4-/- 60. 67 103. 23 4627 | Purified granulated....*.-..-.- 66. 77 113. 61 4645) | (Commercial/#=. s-e--— sae ee 59. 00 100. 39 4539 | Purified granulated. --......--- 58. 76 99. 98 4540 | Purified granulated.........-- 60. 76 108. 38 A645. (Pe unified ass5-5ac2e5sess eee 60. 34 102. 67 4647 CP. powderedis- coe. aoe = 65. 24 111. 00 A543) 3| Ce ePoenystallizediesssneeseeeee 58.83 100. 10 4537 UTIMER Ee cee sere cee eee 59. 37 101. 02 4642) || \Commerciall sence aeeee oe 63. 59 108. 20 4832 "| Commercials=.-..2-22s---22- = 61. 43 104. 52 a Formula, Pb(C2H 302): 3H20. HOME-MADE LEAD ARSENATE. 15 DISCUSSION. Pure crystallized lead acetate contains theoretically 58.81 per cent of lead oxid and 14.25 per cent of water of crystallization. A number of these samples have lost much of their water of crystallization, as is shown by the high lead content. The commercial ‘‘brown”’ acetate of lead is cheaper than the pure crystallized salt and the samples examined contained more lead. For these reasons the technical gerade is to be preferred rather than the pure salt for the preparation of lead arsenate. None of the samples examined contained impuri- ties which would in any way decrease their value for this purpose. One hundred pounds of samples Nos. 4626 and 4627 would be equiva- lent to over 113 pounds of the crystallized salt for this purpose, in addition to being cheaper per pound. COMPOSITION OF LEAD NITRATE. RESULTS OF ANALYSES. The results for total lead oxid in the samples of lead nitrate analyzed are as follows: TaBLe II1.—Composition of lead nitrates. Calculated Serial Lead oxid to lead number. (PbO). nitrate Per cent. Per cent. a 4541 67. 09 99. 60 @ 4550 67. 03 99. 51 b 4628 66. 33 98. 48 b 4654 66.19 98. 27 a 4646 67.10 99. 62 @ Oop b ‘*Commercial.’’ DISCUSSION. The theoretical per cent of lead oxid in pure lead nitrate is 67.35. It will be seen that all of these samples contain very ‘close to this amount. The composition of lead nitrate is more uniform than lead acetate, and it also contains more lead, though some of the partially dehydrated samples of the acetate contain nearly as much. * COMPOSITION OF SODIUM ARSENATE. RESULTS OF ANALYSES. Pure crystallized sodium arsenate, or, chemically, disodium hydro- gen arsenate, has the formula Na,HAsO,7H,O, and contains theo- retically 36.84 per cent of arsenic oxid (As,O,). One authority states that this salt has the composition Na,HAsO,12H,O, and gives direc- 16 LEAD ARSENATE. tions for making lead arsenate based on this formula. This is mislead- ing, as such a salt forms below 18° C.4 (above this temperature it loses water rapidly) and it is not the ordinary sodium arsenate of commerce. The pure crystallized salt, however, is too expensive for the purpose in question and it is necessary to employ the technical grades. These are very cheap and if we can be assured of the absence of objectionable impurities they are just as good as the pure salt for making lead arsenate. In fact they usually contain more arsenic oxid than the crystallized salt, owing to the fact that they have been fused and do not contain water of crystallization, which theoretically amounts to 40.4 per cent in the pure salt. Frequently, however, they contain large amounts of impurities, usually sodium chlorid, which lowers the per cent of arsenic oxid. Sodium arsenate sold for technical purposes comes in varying degrees of purity, concerning which there has been much confusion. Two grades commonly on the market are the 50 per cent and the 65 per cent grades, which figures refer to the arsenic oxid (As,O,) content. In only one sample examined was the arsenic oxid over 45 per cent. In Table IV is given the total arsenic oxid and chlorin in the sam- ples of sodium arsenate examined. TaBLE I1V.—Composition of sodium arsenates. Serial ae Chlorin number. (AsgOs). (Cl). Per cent. | Per cent. 4547 44.65 0.43 4649 68. 07 .39 4625 44. 59 12. 58 4717 42.74 15.17 4548 37.39 . 00 4623 37. 23 00 4831 37.08 . 00 4549 37.29 . 00 4653 39. 33 17. 72 4643 BY Grall 15. 28 4542 37.11 11 DISCUSSION. All of the samples were tested for arsenic present as arsenite, but none was found except traces in two or three of the commercial samples. Nos. 4542, 4548, 4549, 4623, and 4831 are samples of the pure crystallized salt, and all of them have effloresced to a slight extent, which accounts for the arsenic content being a little above the theoretical amount. No. 4547 is comparatively pure and con- tains nearly 8 per cent more arsenic oxid than the crystallized salt, owing to partial dehydration. Nos. 4625, 4643, 4653, and 4717 are technical samples and are very impure, containing large amounts a Fresenius, J. prakt. Chem., 1852, 56:30. HOME-MADE LEAD ARSENATE. alee of sodium chlorid, as shown by the high chlorin content. On account of this, none of them is desirable for making lead arsenate. Sample No. 4649 is a technical sample and is unusually high in arsenic oxid. It is probably composed largely of sodium dihydrogen arsenate (NaH,AsO,). . The analyses here reported show that there is little or no risk in buying the technical grades of the lead salts, but sodium arsenate is much more variable, and when chlorin is present sufficient lead must be added to combine with this as well as with the arsenic. This is a waste of the lead salt, as lead chlorid is not considered of value as an insecticide and therefore the presence of chlorids is objectionable, particularly in amounts greater than 3 or 4 per cent. The presence of arsenious oxid (As,O,) or sodium arsenite is also objectionable, as by uniting with lead it forms lead arsenite, which is more soluble than the arsenate, does not remain in suspension as well, and, as shown by Kirkland and Burgess,? is less poisonous to insects. THEORETICAL COMPOSITION OF LEAD ARSENATE. As has been pointed out by others, arsenate of lead may mean any of the various lead arsenates, but the most common ones are the tri-plumbic arsenate and the plumbic hydrogen arsenate, rep- resented by the formulas Pb,(AsO,), and PbHAsO,, respectively. Most of the commercial samples consist of a mixture of these two, the one predominating depending upon the method used in its manufacture. As has been shown by Smith © and Haywood,° when lead acetate and di-sodium arsenate are used for its preparation the following reaction takes place: 3Pb(C,H,0,),3H,O + 2Na,HAsO,7H,0 = Pb, (AsO,), + 4NaC,H,0,3H,0 + 2HC,H,O, + 11,0. Using nitrate of lead and di-sodium arsenate, Smith? gives the reaction thus: 5Pb(NO,), + 4Na,HAsO,(H,O)" = Pb, (AsO,), + 2PbHAsO, + 8NaNO, +2HNO, +n(H,0). Haywood ¢ found the reaction to be mainly as follows: ' Pb(NO,), + Na,HAsO,7H,O = PhHAsO, + 2NaNO, +7H,0. @ Agriculture of Massachusetts, 1897, p. 379. b Acriculture of Massachusetts, 1897, p. 364. cU.S. Dept. Agr., Bureau of Chemistry Bul. 105, p. 165. doc. cit., p. 365. €Loc. cit., p. 166. 23904—Bull. 181—10——3 18 LEAD ARSENATE. 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, Pb,(AsO,),. This contains theoretically 74.40 per cent of lead oxid (PbO), and 25.60 per cent of arsenic oxid (As,O,). 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 As,O,;) 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, PbHAsO,, contains theoretically 64.26 per cent of lead oxid (PbO); 33.15 per cent of arsenic oxid (As,O,), 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 As,O;) 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 to 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 i FE s ee aii oe pipe pad Pty 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. MEAD 6 Teeth Dee errns Mido ho bs PN 3h asc 10 (1) LA) See Ree yal: CEI) Se a en ae 12) () tapes le a 0 8 LN I neg 7h (1) Co SPOR Ai tert ee os ee bBo se ee 181) eee en Bo ee Fe es! Se ee Oe eres meal PREPS | fy) ce 24 (3) 1 eee ene ee Ss 2 ere 25. (1) Ty a em tr mers. ©) 24 (5) Formulas using arsenate of soda and nitrate of lead have been given as follows: Arsenate of soda. Nitrate of lead. Oz. Oz. DoW elbeals 6 o0 ccthles Ger ae eee pen, eae ee 10 (4) Whew efi ay S< d/o oa a ae I Cee 183 (1) NOME + eee ae ee le ee 2413) 4 Agriculture of Massachusetts, 1893, p. 282. 5 Massachusetts Hatch Exper. Sta., Bul. 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 (As,O,). 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. o1 precipitate of lead chromate will be formed. If to a nltered 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. Pouuunarsenate (bo: Per COHL) =. 226 4-2kreS-ccccices seons eens sss 8 Mend meetane, (Hear OLtead))22 2 coc stcehe cc eas osa.- See lo ee Be Formula LB: Vaan Sau ei kha! kN a Ie Ra eh ag Oe en Sia ee ee ee 18 If the sodium arsenate employed is 50 per cent strength, use 104 ounces instead 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 contamed 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,’ which will turn a bright yellow if lead is inexcess. If the paper does not turn yellow, add more of the lead salt slowly, stirring con- stantly, and test from time to time. When the solution turns the paper yellow sufficient lead salt is present, but if it should occur that the paper does not turn yellow after all the lead salt has been added dissolve a little more and add until an excess is indicated. The @ The solution of lead acetate may havea milky appearance. This will be no objec- tion, and it need not be filtered. > 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 saturating filter paper or blotting paper with this solution. After the paper has dried, cut into strips and keep dry until needed. 29 LEAD ARSENATE. great advantage of this test is that it is not necessary to filter 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 slight 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 discardit. 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- plumbie 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. a 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 which are to be applied as a spray are very important. [Freshly precipitated 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 which it has been made. If it has once been dried, on mixing with water 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 } lead nitrate was used instead of the acetate; tubes c and d are the same as tubes a and b, respectively, except that they have been dried out and then mixed with water again. All of the samples represent the same amount of actual lead arsenate and the column of water 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 @ about one-third of the way down, tube c nearly to the 94 LEAD ARSENATE, bottom, and tube d about halfway down. Some of the finer particles still remain in suspension in tubes ¢ and d, and the distinguishing line between the water and the main body of the precipitate is indistinct. After fifty minutes tube 0} 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 foliage 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 150 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, Bul. 24, p. 7. Z b Agriculture of Massachusetts, 1897, p. 355. Bul. 131, Bureau of Chemistry, U. S. Dept. of Agriculture. PLATE |. Fic. 2.—AFTER STANDING FIFTY MINUTES. EFFECT OF DIFFERENT TREATMENTS ON THE SETTLING OF LEAD ARSENATE. a, Lead acetate used; 6, lead nitrate used; cand d, same as a and 0, but have been dried out and again mixed with water. y aK ee rd he) by J “fa, & e, 4 PAN ty 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 applied to peach foliage and on conifers.’ Stene:/ ‘“‘Tt has the great advantage over most of our insecticides that it is entirely harmless to all plants in any strength.’ Bentley:9 “Ar- senate of lead will not burn foliage.” Taft and Shaw:* ‘“‘* * * 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 would result in burning. In view of the analyses reported in Table I, page 9, it would appear that this 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 fungicides 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- aU.S. Dept. Agr., 1898, Farmers’ Bul. No. 19, p. 6. 6 Proc. Seventh Ann. Meeting, Assn. Econ. Ent., 1897, p. 24. ¢Seventh Ann. Rep., Vermont Agr. Exper. Sta., 1893, p. 124. @ Economic Entomology, 1896, p. 437. ¢ New Jersey Agr. Exper. Sta., 1903, Bul. 169, p. 8. / Rhode Island Agr. Exper. Sta., 1904, Bul. 100, p. 138. 9 Tennessee Agr. Exper. Sta. Bul., 1905, vol. 18, No. 4, p. 36. h Michigan Board of Agriculture, 1908, p. 397. 7 Ohio Agr. Exper. Sta., 1908, Bul. 199, p. 94. 23904— Bull. 181—10——4 26 LEAD ARSENATE. age in some States may be used with safety in others. The injury to foliage 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: Taste V.—Analysis of lead arsenates prepared in the laboratory. ’ , Water-sol- | Water-sol- Total lead | Total ar- | Water-sol- | Fiieibecl (fives son Number of sample. Moisture. oxid senic oxid | ubleim- | =: é 2 (PbO). (As205). | purities. | (PO). eae | | Per cent. Per cent. Per cent. Per cent. Per cent. Per cent. eS Er ion oete me ar Bese Ee 0: 10 67. 44 29.76 1.07 0.56 0. 40 Dogan ON see eee eae parca ae | . 09 64. 02 32. 64 NPY B53) .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 (Pb,(AsO,),) and plumbic hydrogen arsenate (PbHAsO,), 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 14 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.—TYo 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 14 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 14 pounds of dry lead arsenate, using lead nitrate and assuming that plumbic hydrogen arsenate is formed. 98 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 14 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 14 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 14 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 application 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 11B, 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 ARSENATE 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 to fungus diseases. No fungi- cide had been applied, and the season was favorable to the growth of fungi. August 7. No further injury was shown than that recorded in the preceding 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 11A and 11B, to which lead nitrate had been applied. August 27. 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 sprayed 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 thirty-seven years. TaBLeE VI.— Monthly meteorological data, March to August, 1907, Washington, D. C. MARCH. Temperature. es -- Precipi- aT ee * ’ | Possible Date. Le ae Raton Character of day. RaeRinicl 2 Mean. mum. | mum. ene ge ae was Inches. Per cent. i Waa 40 31 | 36 OS 2On IGlowd eves. . Ree es Lae ee 92 26 83 ory Ol 49 See Cops Po See eee 75 isco 61 46 Partly iclowdyoeesse 2 =-see ee 69 ra eee 59 48 Cloudy. . ete este ee oe 22 29 71 52 Partl cloudy alee oe okies ea 55 30 78 55 Wloudlyer sie eater eorees 53 Mean 58.0 38.8 48.4 3.61 or to- tal. MAY. eae 68 51 60 OXGIS | Cloudya= = -sen ase eee 6 eee 60 48 54 00) Pee 2 Owais. cescetseces sie ssce 9 Baesee | 65 49 57 Trace. | Partly cloudy=---.-2- 5.----- 49 Avie 70 46 58 nile He |G eth Bee eee ac dee 69 Ditess 62 39 50 $009) 55528 (6 (0 eee re eee ee erg he 100 (eases 71 51 61 HO 2 NiClOUG Yee .c sees eee oseeeeiass 10 eeerr 62 57 60 Tracey ieee eter. - Seaokeapeneuaa st 0 Bssece 71 52 62 748) || Clear. coe 2222. --e ec emece ae | 70 eee 67 54 60 E24 | Cloudlyz: ss sncts- aoeeeiseeee 18 10 78 52 65 Trace, | Clears. ve .=snice cts tee eer 85 LSS 5 62 42 52 SOS bee GOs cea eee eee 75 12 59 39 49 OOM Ee orns Got 6.2. ete eee 100 13 | 73 44 58 OO Geer OO). cena sone eee’ 100 14. 85 51 68 00) | Frese (6 oe RES Sense a 100 Deere 83 59 71 201) Bar tlyicloudyerees ee eeee 73 16S 225 70 57 64 2395 | Cloudyeeeecene = oe cera ae 0 AW ace 70 54 62 S003 PRanthy;cloudiypeere cannes 51 NB terre 83 53 68 Tracey (Clears. Bis. oe ete sins = sis 76 Sees 84 62 73 1.10 oy Cloudiveem crests... 51 20 67 50 58 SLOP ete Ones eee siete ee ainla 34 21 60 41 50 . 00 Cis bcectao 2 sea denoaueaooes 100 22 70 39 54 O08 Bases Ose at ane sae telecine si 86 23 74 56 65 MOM hCloudiyaeerse se eenane-=e == - 20 24 66 56 61 23 |eene= Os. saboues bee Soaaaaerar 12 25 58 46 52 He a eae GOSS eee cece Sai oe 4 Peer 61 46 54 200 eee GON e merase occas nc 0 ier 72 51 62 -58 | Partly cloudy...-.--.- Bee 35 2B ose 64 44 54 ZOO) |((Cleaniie - cee sees 11 21a 46 25 36 NOOSE Cleary A. Sees Se a. el eee 100 QDi cs 56 32 44 Trace. | Partly cloudy 75 23... - 56 47 52 S825 CCloudiyse ets mec aes 0 Dare 65 46 56 -00 | Partly cloudy 65 201255 57 41 49 OOH See GOs ae Soe 68 26 75 40 58 00: - Clears. 2h: Oesbvoe sec eStecars 88 istxs 80 58 69 UO eases GOs se a ee oa ae 90 28 73 62 68 05 Ni Cloudyisse so ee ane see 6 2057.2 73 43 58 568) eeose Of eee ca a renee 18 30 §2 40 46 (WO Serres GO Near ok oie oot See 41 31 50 42 46 SOR eae GOs Aiea eis ive oae ates 0 Mean or to- tal .. 56.8 38.0 47.4 2. 45 APRIL. eee! 51 44 48 ONOSs Goudy seisaseteceie cece see 0 OA 63 38 50 21 partly: cloudy 45 Saoae 41 32 36 Traces)|-- << sdOs2~ sc cos= ee nese 59 1 ae a ge 51 33 42 OOK Sa32 a Ste sreatne ae Usain Sree 95 Gpee 53 29 41 508) lesaoe Os. sere eet ao ees 7 (eee 69 48 58 1007)! Cléar 22228) 25222. asceseee ne 91 sae 77 44 60 SU] eae Ose Seese'ss soo eee 88 aa 75 58 66 aon ClOUd Waser en eaer see AEISE 12 eae 70 43 56 .07 | Partly cloudy aaa 86 10 e532 53 40 46 2 15|P Cloud yess oe eee a seee eee 0 Uh Soi 69 46 58 -01 | Partly cloudy. 74 ee 62 41 52 (OO) | Cleat co. 5 3 een oe te eee 100 ISissc6 78 40 59 OOH S2ee2 (0 he et er ee Soe 91 14 60 40 50 BOO eae ee COE Soest ee See eee 91 LOM ee 64 47 56 2eul Clowdiyarrtaeeaeetase terse cele 0 Gees 63 38 50 01 || Clean tes See oe eee 82 Wf eee 57 35 46 008|\s2282 GO Ee a eee ese inne 100 ISR 60 44 52 2101/2 Cloudiy sate eee nears 4 19s 72 51 62 Trace. | Partly cloudy 57 20 eee 80 44 62 100) RGlearie ease nesce sae se oct ee 100 Ae 60 43 52 J008|'S5a>2 COM re se os as,- 100 Weses 76 39 58 = O0u Sees GO ere ai rce Renesas ='s-205 100 23 83 55 69 OOM Ear CO eee ulna? avele 94 Pee ae 87 54 70 OO} Peer GO see aeret ess cces seas 92 25. 76 57 66 02 | Partly cloudy 47 26nae 85 58 72 OOW Clear eer eae ee: in nee nas 100 fe Se 85 65 75 03 Partly cloudy 64 28... 71 56 64 600) ges sO b.4- She soeeemanee a5 65 29. 76 46 61 . 00 Clear, LE BORER EE Eeee eee 93 oO Sae 68 42 55 .17 | Partly cloudy 44 Mean or to- tal .. 67.8 45.0 56.5 1.59 ACTION OF LEAD ARSENATE ON FOLIAGE. 39 Tapie VIII.— Monthly meteorological data, March to August, 1908, Washington, D. C.—- Continued. MAY. Temperature. . Precipi- f Possible Date. : istion Character of day. sunshine. Maxi- | Mini- | yrean mum. | mum : eH ovis oH: Inches. Per cent. 3 eae 56 39 48 Ol OOm R@lear see sens sola elect tele ae, 92 ies 66 44 55 204) Barth yicloudys-.-5----eo. 4 82 eee 62 44 53 008 || Sae (6 0) ee ees Br eres 84 A 52 42 47 OOH ECloudyeeeee eater eee 3 Dtnees 55 45 50 Sb Ya leaaae 0) Sete a ea eea aoe ace 9 Gis 50 46 | 48 ae) Eecae GOS acess ee eetn nes 0 Usissos 64 47 56 ISON eae GO eek cs eee s 2 SEen i. 64 51 58 Trace. eae Cloudy tees essa see 42 ORm 22 60 49 54 OA re AC Oe estan tet ences cele 55 10-- 64 44 54 . 00 Clear. oinlaoaisie OK Sais bse oaee 100 1 tee 82 42 62 SOOn eee GOsae sce sek ect see 100 1 88 63 76 Trace. Paty cloudy Seem Sets oe 52 Gee 87 61 74 MTACe | Rasa GOMM each neat oper ean 83 14.. 88 58 ta} SOG) Saas GOSS Ae eee tee eee Sc kes cists 55 Ge 58 52 55 Ssh tCloudivieeccerctsssanesceneee ol 0 16.. 63 51 57 OL Eantly Cloudy ahaa sere see 7 ive 80 58 69 OOK |Wsha sO Ona as celeae ei apha sao, a10 56 18.. 78 60 69 race see ae Bie ean Oe area we 69 1959 74 | 61 68 TOO} CO lord yee ees 12 20). - 81 | 61 71 W586 emcee GOW Se nee sie Ses 40 7 Nase 75 | 64 70 Trace. pony Gloudiy2r so.) Sse 24 22. - 84 64 74 races tee. COs acsccc cnt asses 69 23... 81 66 74 oar eaeee: ae Lie sleicie mice iniopsatepe eete ath 54 24.. 85 63 74 Ali) eee! Goa eset See eee, 81 25. . 87 64 76 HOON Clear Ms cgsaaceus soasenciack 82 24 Dey 88 68 78 JOON EE eae GOS sete mec oein eee 79 Zee 89 69 79 aOO UN WE ers GOs Sees aet ee eee 87 28... 92 67 80 - 00 ACG Ko) see eee ee Pcs 99 29... 82 70 76 00 Partly cCloudyars sie oases: 60 30.. 83 66 74 .74 ME Omen ne ee eee eee 59 Ses 85 64 74 a OO erate GOES ee ae ae 86 Mean or to- tal... 74.3 56. 2 65. 2 6.10 JUNE WR ao 72 59 66 OX00" | Clears. cta-c stn asetes ee ee 97 econ 80 56 68 AD Weeeed ose ee ee ee dee 99 OscaeE 74 58 66 O09) barthyicloudy==s-sen-- ses 66 Beare: 67 58 62 BAGH SW ClOUG Ye cine ae eee rai 9 Onaeee 78 57 68 OOP Cleary sees Se mle eee hee 72 Giese 68 59 64 S00) Cloudy acini ee ace ses 7 Mieco 81 52 66 200) sRanthy‘cloudiy.e- 4-6-0 -- 82 Boece: 85 59 72 00 Lene SE SET eR ae eae 99 Oe eee 87 64 76 OZ) | Seer Omer ce er rs oaee 82 il( DEE 82 65 74 Trace. Partly Cloudy) ae eee 74 1ale 73 61 67 GUO a es it (0) At ee a 30 12. 82 56 69 - 00 Clear. Ce Ar Aree ee een ee) GIES 84 58 71 OOM teers GOP ee ee ee 100 14.. 84 66 75 SOOM eee GOR eee ek menos 99 Oe 78 58 68 HOON RClOUGiy eerste er ae 29 1Gee 74 | 54 64 OO} P Clean ar So ee eee sae caine cee 99 (ee 75 52 | 64 SOON ber tlyselouclyarrme see 100 1827 78 58 | 68 500) aan CU aat ea 7 ee rie, Sera ae 70 ORs 88 60 74 S OOH Clonee tee lee ae hee che 99 20... 89 70 80 2005) Barthyicloudys95-5) 5 seo - 60 PAS 89 70 80 Mraces||seee Om esters oes ate ae 83 22... 89 68 78 AUD) jee GORE eet eee asec ae Sociales 91 23. . 94 68 81 .00 clean. EPL et AS OY. oh a 88 24. 97 76 86 B11 ie eae (oe A ee Se a ee 88 25... 85 71 78 -O1 Partly Clotdy wee aceeere n= 64 26... 80 64 72 S008 Res ome sane eee eee 85 27... 83 57 70 08 Clear. A afer Bree ee ahs 76 28. . 85 57 (fil ZOOM oS Onme chins oacee aot eneeue 93 29.. 92 67 80 .00 Partly cloudyspeee Soro 99 30... 87 71 79 AUG OFS ca 8 Serta i ea eee aes 72 | | Mean or to- taliez|) 8250 61.6 71.8 LB} 40 LEAD ARSENATE. Taste VIII.— Monthly meteorological data, March to August, 1908, Washington, D. C_— Continued. JULY. Temperature. Precipi- Possible Date. z A Tati Character of day. sanchinel Maxi- | Mini- Meni mum. | mum. ; 70s ae ooh. Inches. Per cent. eee 90 69 80 0. 01 Harily Gloudye ae ae 86 hee es 90 72 81 B05 Td (eee, 0 C0 oP ie ier SPS ees salle 78 aioe 86 71 78 Tracers |eeece de Be reper a eer ee a eee 58 Auees 88 73 80 BPA ty (ete OBA sere aeteiss Sees 43 ee se 86 71 78 races seas Gots. 2 ee eee 56 Barer 94 72 83 m0, Oo ee (Oto) Gene meee cet ie 82 eases 94 72 83 HOAs Clears was sas. cate rem eerers 98 Soar 22 81 64 72 TOO) | PParthyicloudiyata. ses ees 66 Qeoce 80 59 70 100 Wee GO Sets ee oe eee 67 10 79 60 70 JOON Se aee GO Sra aee eee eee 59 11 90 61 76 BOB | Clear. sue wee ple Cee. 92 12) oe 99 68 84 HOS we Partly eloudiyecsseeee sass 69 ieee 96 70 83 S00) Cleartos inset ocean se ne neees 93 ie 96 74 | 85 OG) Partlyaclotdiye Sterne sceee 64 15 87 LM 79 O00)" Clearacere. 2 Reese Sees 78 16 81 62 | 72 OOM ae Bier 6 Sinan eee 98 ily (Seer 87 57 72 | OOo Sd Oe eee See bes ren 78 18: =... 91 72 | 82} Trace. | Partly clotidy. 2 ee ates 56 19 | 91 76 84 | OON Le dO cece. tee 71 20325] 90 71 80 S00) aace ab Foe ee ee ace eee 67 21 88 69 78 On BCLOUG YAS s fa hineeee eee 57 22 | 87 70 78 V3} lene CO sine Six ota Ss eee 38 POR 89 71 80 | (iC Ree OBE aaa aaeanescicsy, 41 24 88 69 78 LS eye dO! cas gecb ee eee eee 46 MABE 88 70 79 On| zeae OOo eases eee one 38 eeen|| 81 71 76 SSuieeee (Ohm Ecaar Aen oe erase 19 27 78 68 73 G5) a eee GO 3 ceade peepee 3 28 84 68 76 00 Eauuly cloud ya) ne 48 29 85 66 | 76 ADPACR Le G0 Moose a cemece coerce 62 30 84 68 | 76 CON Saar. de SE Ree ae 73 31 80 72 76 SOLS OlOUd Wg eee Sees ree 0 | Mean | | | or to- | | tal . 87.4 68.6 | 78.0 3. 29 Oe Bes oi 89 59 74 SO0G Oleane: ees ac 8 senate. 100 Sass | 92 66 79 HOON eeeee dO. ceeee see ee eee eee 89 Bec: lisyi a Ob 70 82 OD es ae GLO Sess Neneh ee cee 91 ERA OAl 89 72 80 1024 Cloudive sees eaten 36 Olsiee 85 71 78 MOGN|eeee Oreck vedere peer 16 sna | 87 69 78 BO) aes GOs .cc.e eee ee ee 26 82.252] 78 65 2) eeDTACO ene mene Cit ee See Pete Sree Ses 31 Qee eas 70 62 66 SO re ciae GOiz.s2 sce eee eee 1 Wo 3.4) 84 60 72 00) | (Clean. 7 Js ssc 2 eee eee 92 11 86 68 77 A On eecee Oisabssoeseiebis See oaeeee 85 12 92 65 78 HOON Zac 52 Oso 2 cee ee eS 72 IBY eal 93 73 83 YOO) Ese 2 Ot. 25 pee pe eee 99 14.. 93 72 82 - 00 Early Cloud ys ee -asee eee 75 15ee 88 74 81 O00) |222 ed Oks ce ae ohana nemacar 57 OSE 84 68 76 Trace Cioindy poe ose ase reece 28 Wie 87 68 78 I Lill ed [ee CO retereverneraerteetaree = ae 18 18.. 86 70 78 -18 Partly Cloudiyi.222 2-22-22 =- 38 TORE 89 70 80 (00) || (CWE te ees Sopot desc eciggeae 68 20 77 59 68 Trace. Early Cloudy reese ea 61 21... 80 53 66 OOM PREG Oe tecce cena saat = s/s 74 22 || 84 69 76 | Trace. Cloudy Todnecedacs. cape oaeees| 20 2de==| 79 71 75 Nracennlaeeee Qatar eeeRia 2 < 2558 15 24... 74 66 70 OOS soe OOo aceetesetes ce. eess5% 5 25 68 56 62 845 5one0 ORS Seo es Soe 0 26 61 57 59 TORR |Seeee (nc on cae anes eee 0 27 63 56 60 OLN eens Ogee st een oss cee 0 28 67 58 62 00) | Beas GOme ee eee ee ke ss tee 6 29 76 52 64 S00) (CLE ceo gotiobneemepceeadcs 89 30 81 52 66 (00) |23532 CSe: . Saseeee meh aiac= 98 tal..| 82.0 64,3 73.2 5.14 ACTION OF LEAD ARSENATE ON FOLIAGE. 41 Tapie IX.— Comparison of monthly meteorological data for 1908 with the average for thirty-eight years. : Temperature. Rainfall. & a eee | Monthly | eeceee or SAY Month. Mean eee deficiency | Total ara conceney ioe | ‘etant | a6m,| fee | elght | pared with ri years. aalennit aye tae years. mean for ait es thirty-eight thirty-eight | = years. | Deate: i 5 ES | 2 Sele wae elt Inches. | Inches. Inches. March 47.4 42.3 +5. 1 2. 45 3. 93 —1. 48 April. 56. 5 53. 0 +3.5 1.59 3.14 —1.55 May.. 65. 2 64.0 +1.2 6. 10 3. 81 +2. 29 JUNe= S-sa52 71.8 72. 6 —0.8 1.73 4.08 —2.35 Juliy--< 78. 0 77.0 +1.0 3. 29 4. 61 —1.32 August..... 13.2 | 74.6 —1.4 5. 14 | 4. 43 +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 which 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- fallwas 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 application 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 foliage the injury would probably have been noticeable several days previously, but no obser- 49 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 applications of lead arsenate, made from sodium arsenate and lead acetate, or sodium arsenate and lead nitrate, when applied at the rate of 14 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 14 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 foliage in 1907 from two or three applications of lead arsenate (made by the two methods) at the rate of 14 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 quality 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, Bul. 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 14 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—tnat 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 following may be mentioned: Gillette, Galloway,® Galloway and Woods, °¢ Fairchild,? Sturgis, © Bain,’ and Hedrick. 9 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, ‘‘foliage 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 Towa Agr. Exper. Sta., 1890, Bul. 10. b U.S. Dept. Agr., Div. Veg. Path., 1892, Bul. 3; 1894, Bul. 7. ¢ Proc. Soc. Prom. Agr. Sci., 1895, p. 42. @U.S. Dept. Agr., Div. Veg. Path., 1894, Bul. 6. e Connecticut Agr. Exper. Sta., Ann. Rep., 1900, Pt. III, p. 219. f Tennessee Agr. Exper. Sta., 1895, Vol. 8, No. 3; 1902, Vol. 15, No. 2. g New York Agr. Exper Sta., 1907, Bul. 287. h Towa Agr. Exper. Sta., 1890, Bul. 10, pp. 402-403. ‘California Agr, Exper. Sta., 1899, Bul. 126, pp. 10-11. ACTION OF LEAD ARSENATE ON FOLIAGE. 45 which compound, under the usual conditions, is more injurious to foliage 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 OF 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 lead arsenate, made from sodium arsenate and lead acetate, was treated with 1,000 cc of cold distilled water which had been previously 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 2.—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.) 4 New York Cornell Agr. Exper. Sta., 1899, Bul. 164. bAnn, 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 As2Os5.] Carbon-dioxid-free water: Per cent. Hixperimient L... /..g2seeees 2-5 eee eae eee ee v2 cls er 0. 40 Bxperiment 2... 22). o2 2eeee 22 SIS eee deen os 2s es ee 49 Water with carbon dioxid added: Experiment 3. «203 )42 Swi. 22 oe ee ee ees . 25 Experiment 4... .2.0o<.2.tideiox sG08 ft sce ee 39 Water with carbon dioxid added and warmed to 50° ©.: Experiment 5.2.2.4 -22a0s. S65 be hn b ecko oa on ee ee noo Experiment 6.2.2... 05.50.00. esuiass Sek tcdee ee 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 ce 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 8.—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 ce 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 ARSENATE ON FOLIAGE. 47 Taste XI.—Results of experiments to determine solvent action of water constituents on lead arsenate. [Arsenic in solution expressed as As20s.] eee Arsenic in solution. Per cent Kind of lead arsenate and water treatment used. based on Per cent weight of of total lead arsenic arsenate present. taken. Water used in spraying experiments: Used cold— Per cent. Per cent. Experiment | (lead arsenate made from TER GEACELALC)beecses tees ant winiccciceme 5. 24 17. 61 Experiment 2 (lead arsenate made from IWeeval sain pits) 5 Seo ab SmceS anor obec 3. 61 11.06 Heated to 50° C.— Experiment 3 (lead arsenate made from lead acetate)............--.--------- 8. 42 28. 29 Experiment 4 (lead arsenate made from lead nitrate).......-..-...--.------- 8. 27 25. 34 Water containing 0.2 per cent of sodium chlorid: Experiment 5 (lead arsenate made from lead acetate)...........--------------- 9, 20 30. 91 Experiment 6 (lead arsenate made from lead nitrate). ........-....------..---- 11.22 34. 38 Water containing 0.2 per cent of sodium carbonate: Experiment 7 (lead arsenate made from lead acetate).........-..--.--.-------- 9. 56 32.12 Experiment 8 (lead arsenate made from lead nitrate).........-..-------------- 11. 82 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: Taste XII.—Analysis of water used in spraying experiments. [Water Laboratory, Miscellaneous Division.] Parts | Grains Parts | Grains Constituent. per per Constituent. per per million. | gallon. | million. | gallon. SHOR (SiO) Seno nenesaeaeneeecaes 23. 2 15:353)|| Magnesinmit@Me) 5222-5... 2 4.3 0. 251 Sulphuric-acid radicle (SO4)-.-...-- 7.4 243251 OCASSIUMN GKS) nena nets -i- s 1.0 . 058 Biearbonic-acid radicle(HCOs3)....| 37.5 2a 87a Sodium (ING) elses ee anes once eee. 20.9 1.219 Nitric-acid radicle (NO3)-...-..--.-.-- 13.5 . 787 || Oxygen (to form Fe2O3)-......---- 2 - 012 Cleon (Cl) Re oenesecsoereesec a 20.5 1.195 Tron and aluminum (Feand Al).-- 6 - 035 Motalyaee oceans sae 382 134.6 7. 850 Chilishivonn (Cb) See eee 5.5 . 321 | HYPOTHETICAL COMBINATIONS Potassium chlorid (KCl).......... 1.9 0.111 || Caleium bicarbonate (CaHCQOs). . 2728 1.301 Sodium chlorid (NaCl)...........-. 32.3 1. 884 || Ferric oxid (Fe2O3)...........-.--. 8 . 047 Sodium nitrate (NaNOg)........-- 18.5 TROZOD esiliea(SiOs were sas seenese eee ne 23: 2 1.353 Sodium sulphate (Na2SO,4).......- 9.9 Dud Magnesium sulphate (MgSQ,)....- 9 . 052 Totalem asc. em cesseseess 334.6 7. 850 Magnesium bicarbonate (MgHCOs3), 24.8 1. 446 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 high, 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. Hesays: “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 4Colorado Agr. Exper. Sta., 1908, Bul. 131, p. 22. ACTION OF LEAD ARSENATE ON FOLIAGE. 49 that the arsenic had gone into solution 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, 14 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 applied 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 defoliated. (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 foliage was almost entirely pre- vented. / LIST OF TABLES. Page. TaBLE I. Composition of commercial lead arsenates.......................-- 9 II; Gomposition of lead acetates... <-.222...20 sense eee 14 IIT. Composition of lead nitrates:<..-5.<2+2.2+ 23.222 25- 9) see ee 15 IV... Composition of sodium arsenates--......2.---:2.2....2-5-e=e= eee 16 V. Analysis of lead arsenates prepared in the laboratory.............- 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... 2. /.4.4-+4.diee. e504 ee eee 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-...<:. 22 5..¢...24.5.5-02 $28 ee 41 X. Results of experiments with carbon dioxid.......-..-.-------:---- 46 XI. Results of experiments to determine solvent action of water con- stituents on-lead arsenate... 2:45, 5202.-24 5.4252 \ ae XII. Analysis of water used in spraying experiments......-...........- 47 50 O a fin! Boe ; Sea ares a Wut P, i omens nn ( in han a) ea p res 1) De i leh ‘ my