The great value of arsenic in the forms of Paris green and London purple for the destruction of leaf-eating insects has long been recognized. As pure white arsenic in solution is occasionally recommended to take the place of the above named arsenites, and as I have been repeatedly urged to recommend its use on account of its greater strength and cheapness, the following experiments were mailed for the purpose of determining whether or not it can be safely used in this way for insecticidal purposes:
One part of arsenic is soluble in 10 parts of boiling water and in 100 parts of cold water, the solution being as clear as the water used and remaining for an indefinite length of time without any sediment forming.
In order to have solutions of known strength throughout, one ounce of arsenic was in each case dissolved in a gallon of boiling water for a standard solution, and from this solutions of desired strengths were mad

Gillette, C. P.

English

The great value of arsenic in the forms of Paris green and London purple for the destruction of leaf-eating insects has long been recognized. As pure white arsenic in solution is occasionally recommended to take the place of the above named arsenites, and as I have been repeatedly urged to recommend its use on account of its greater strength and cheapness, the following experiments were mailed for the purpose of determining whether or not it can be safely used in this way for insecticidal purposes:
One part of arsenic is soluble in 10 parts of boiling water and in 100 parts of cold water, the solution being as clear as the water used and remaining for an indefinite length of time without any sediment forming.
In order to have solutions of known strength throughout, one ounce of arsenic was in each case dissolved in a gallon of boiling water for a standard solution, and from this solutions of desired strengths were made</p

Gillette, C.

Digital Repository @ Iowa State University (ISU)

Arsenic Experiments.By C. P . Gil l e t t e .The great value of arsenic in the forms of Paris green and London pur­ple for the destruction of leaf-eating insects has long been recognized. As pure white arsenic in solution is occasionally recommended to take the place of the above named arsenites, and as I have been repeatedly urged to recom­mend its use on account of its greater strength and cheapness, the following experiments were maile for the purpose of determining whether or not it can be safely used in this way for insecticidal purposes:One part of arsenic is soluble in 10 parts of boiling water and in 100 parts of cold water, the solution being as clear as the water used and remaining for an indefinite length of time without any sediment forming.In order to have solutions of known strength throughout, one ounce of arsenic was in each case dissolved in a gallon of boiling water for a standard solution, and from this solutions of desired strengths were made.On June 23d solutions o f various strengths ranging from 1 pound of ar­senic in 200 gallons of \yater to 1 pound in 800 gallons were applied to the foliage of various plants and trees. June 2<5th a heavy rain set in, and for nearly twenty-four hours the leaves received a constant wash. On June 27th the following notes were taken :A p p le  Foliage. One to 200 and 1 to 250 have scorched at least, one-half of the leaf surface; 1 to 400 has scorched only the tips and edges of the leaves.P lu m  Foliage. One to 200 and 1 to 350 have hardly left a green le a f ; I to 400 and 1 to 500 have scorched badly the entire fo liage; and 1 to 800 has damaged the leaves too badly to allow this strength to be recommended.Or ape  Foliage. One to 200 has spotted the leaves b a d ly ; 1 to 250 has damaged the foliage almost as much as the preceding; 1 to 400 and I to 500 have damaged the foliage but little, the latter almost none.B ox E lder. One to 200 and 1 to 250 have burnt about one-half of the foliage to a crisp ; 1 to 400 has burned the leaves b a d ly ; 1 to 500 has spotted and scorched the edges but l it t le ; 1 to 800 hardly shows any effect at all.H oney L ocust. One to 350 is turning all the leaves brow n; 1 to 400 and 1 to 500 are both burning the leaves badly.31A m eric a n  E lm . One to 200 and 1 to 350 have browned the edges o f th e  leaves a little , and the weaker strengths do not show at all.P o p la r  Foliage. One to 800 scorched the leaves badly.S ilve r M aple. One to 200 and 1 to 250 have each destroyed about one- half o f the fo lia g e; 1 to 400 has burnt ihe leaves too badly to be recommended ; X to 500 has injured the foliage som e but not seriously; and 1 to 800 has done no perceptible harm.R aspberry . One to 500 has destroyed about one-half o f the surface of the leaves.G arden W eeds. A s it  was convenient to do so, some of the solutions were applied to a luxurient growth of weeds in  a garden, among which were red-root, pig-weed, burdock and plantin. The effects o f the same strength  on the different weeds were so  similar that I  w ill give them together. One to- 200 and 1 to 250 caused nearly all o f the leaves to droop and d ie ; 1 to 400 and 1 to 500 scorched the plants b ad ly; and 1 to 800 showed its effects, although it  damaged the plants but little.Before giving other experiments, it should be mentioned that when the  above notes were taken the arsenic had not yet completed its damaging effects on the trees and plants above mentioned. Notes taken two weeks later showed  the damage fully  double in many cases. For example, 1 to 200 did not leave a green leaf on plum and destroyed more than 90 per cent, o f apple fo liage; 1 to 400 destroyed about one-half o f the foliage of box elder, entirely de­stroyed the leaves o f honey locust, hardly left any green leaves on raspberry, and spotted and scorched the edges of the leaves of the elm  a good d e a l; 1 to 800 on plum destroyed at least 75 per cent, o f the foliage.On July 7th another series of applications were made on plum and apple foliage, in  which the dilutions were carried to one pound of arsenic in 1,200 gallons of water. These trees were selected for two reasons: first, because it  is on these two trees that arsenic solutions have most often to be app lied ; and second, because plum leaves are among the m ost susceptible and apple leaves among the least susceptible o f all foliage to injury from arsenic solutions. So  that a solution of arsenic that w ill not injure plum can be safely recommended on very delicate foliage, and a solution that w ill injure apple leaves cannot be recommended on even the m ost hardy leaves without first experimenting to  find out whether or n o tit  is safe.A s the second series o f experim ents runs so nearly parallel w ith the first, I w ill economise time and space by summarizing the results.The proportions of pounds of arsenic to gallons o f water used are as fol­low s : 1 to 200, 1 to 300, 1 to 400, 1 to 600, 1 to 800 and 1 to 1,200.32The applications were made between one and three in the afternoon, and tjefore the next morning a heavy rain set in that lasted through the greater portion of the day.P lu m . Twenty-four hours after the treatment plum leaves showed plainly the effect of the treatment; three weeks after the application there was scarcely a green leaf on plum trees where the strength exceeded 1 to 600; and 1 to 200 not only took all of the leaves, but killed all of the small tw igs as w e ll; 1 to 1,200 took off about half of the leaves and left the remainder looking sickly and somewhat burned.A p p le .  The three weakest dilutions, 1 to 600, 1 to 800 and 1 to 1,200 differed little in their effects. In any of these cases it is difficult to find a leaf not damaged, the amount of harm varying in  each case from a small spot to  more than half o f the leaf, and some of the leaves, on 'account of the -treatment, have fallen to the ground. The stronger solutions did much more harm, 1 to 200 leaving but a few  scattering leaves and they with a large por­tion of the surface burned to a crisp.Two other series of experim ents were made, but the results 'coincide so perfectly with the preceding that I w ill not take space to enumerate them.Effects on  Insects. Deem ing it thoroughly proven that arsenic could not be used in solution stronger than one pound to 1,200 gallons of water, a por­tion of an apple tree was thoroughly sprayed w ith this solution, and the leaves gathered daily and fed to larvse of Datana ministra. After feeding on the poisoned leaves for five days the worms gave no signs of failing health  and the experiment was discontinued.W HY SOLUBLE ARSENIC BU R N S FOLIAGE.It may seem strange at first that dissolved arsenic in so small quantities should injure foliage when London purple or Paris green, which are nearly one-half as strong in arsenious acid, can be used in the proportion of one pound to 150 gallons of water on the most delicate foliage without doing per­ceptible harm. The reason seems evident, however, on a second thought. It is certain that only that part of the arsenic that is in a soluble condition can act on the leaves to corrode them. Paris green and London purple do not dis­solve in water, except in very minute quantities. Their finely divided par­ticles are simply held in suspense in the water and when the latter evaporates these particles remain in an insoluble condition on the surface of the leaves where they may be plainly seen by the aid of a microscope.The white arsenic, on the other hand, is so perfectly soluble in the pro­portions used that it  is able to pass quickly by tjsmosis into the substance of •the leaves, and produce its evil effects.33A N A L Y SIS OF LEAVES.For the purpose of determining whether or not the soluble arsenic does penetrate the substance of the leaves, and whether the arsenic would all be  washed off by the lirst heavy rain, several tests for arsenic were made. For these tests I am indebted to Professor G. E. Patrick, the Station Chemist.On the morning of July 9th tw igs from apple and plum trees were gath­ered that were treated July 7th w ith the solution 1 to 200, It w ill be remem­bered, as before stated, that this application was followed in the night by a rain fall that lasted for nearly tw elve hours. The apple and plum leaves were taken separately and thoroughly washed, the water being changed many times, and in each case the first wash water and the leaves were saved to be examined for arsenic by the Marsh test.The water from the plum leaves gave only a faint trace of arsenic. The  water, in  which the apple leaves were washed gave a somewhat better te st in  dicating that the fuzzy exterior of the latter leavas enables them to retain  more of the poison on their surface. The leaves were then examined and suf­ficient tests to ensure the presence of artenic, were obtained in either case, but the amount was exceedingly small. Supposing the poison to have been entirely washed from the surface of the leaves, this would be sufficient proof that the arsenic did enter the substance of the leaf. To make surei that this was the case, other leaves were sprayed and treated as fo llo w s: F ifteen  hours after spraying, leaves were picked, and thoroughly washed in  hydrate of soda, which is a ready solvent of arsenic, in order to remove all traces o f  the poison from the surface. This wash was then poured off and saved and the leaves washed many times in pure water. The soda wash, the last tw o  wash waters, and the leaves were then tested for arsenic, which resulted as fo llo w s: The soda wash gave abundant tests. The last two waters combined gave no trace whatever. The leaves gave abundant tests, but there seemed not to be as much arsenic present as in the first wash. This I beleive to be sufficient proof, that the arsenic did enter the substance of the leaves and that very quickly after being applied.W hether white arsenic can be advantageously applied in cold water, is a subject still open for investigation. But in this case the application would  have to be made before the arsenic had time to become thoroughly dissolved, and before solution takes place the arsenic is so heavy that it settles rapidly to the bottom of the vessel, which necessitates constant stirring.W hen we add to these facts the increased danger to human life , that is incurred by having in the house so deadly a poison that cannot be distinguished  in color from flour, saleratus, baking powder, and other materials used incooking, and the other fact that London purple, which is also a waste product, can be had almost as cheap as arsenic, it would be unwise in the extreme to recommend the latter, especially if  it be in solution, for insecticidal purposes.HOW TO SPRAY,There is an opinion more or less prevalent that the arsenites when thrown with much force, w ill be driven into the surface of the leaf so as to do more harm than if applied in a gentle spray. To test this point four apple trees of the same age and variety standing side and side were sprayed with the same pre­paration of London purple. The pump used was Nixons Barrel Machine, In  the first case a number 3 nozzle, complete, was used which threw a very gentle spray that was directed on all parts of the foliage of two of the trees until every leaf seemed thoroughly wet above and below. In the other case the gauze on the end of the nozzle was removed and the direct stream thrown upon the two remaining trees with all the force that could be had, especial pains being taken to hit the underside of the leaves. The strength of the mixture was one pound of the Londen purple to one hundred gallons of water, In both cases the foliage was somewhat burnt but not seriously and I could not see that the damage was more in the latter case than in the former.Other experiments were tried by throwing a fine spray so as to have it fall only on the upper surface of the leaves and then again so as to have it fall on both surfaces. W herever this was done, the damage sustained by the leaves that were wet on both sides was fully  double that sustained by those wet only on the upper surface. Twigs were also dipped in arsenic solutions and the effect compared with those that were thoroughly and forcibly sprayed but no difference could be seen in the amount of damage to the folige.That forcible spraying does, in ordinary cases, damage foliage worse than gentle sprajing I have no doubt, but I believe the reason for it  to be found in  the fact that the leaves are more thoroughly treated in the former case than in  the latter.LONDON PURPLE AND PARIS GREEN.In this connection it w ill be w ell to state the proportions in which the arsenites, Loddon Purple and Paris green, can be safely applied to foliage.The maximum strength in which London, purple should be applied to apple foliage I would put at 1 tb, to 100 gallons and I do not think it advisable to apply it weaker than 1 to 160.Paris green, which contains a little larger percent of arsenious acid, should not be applied to apple foliage stronger than 1 to 120 nor weaker than 1 to 180 ; and on plum not stronger than 1 to 160 nor weaker than 1 to 200.:)435Although weaker resolutions than any above mentioned might often prove efficient, I do not think it advisable to use them as a few  heavy dews, or a light rain would remove a sufficient amount of the poisons to make a second application necessary, and either of these arsenites can now be purchased very cheaply.

Arsenic Experiments

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Arsenic Experiments

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