Spreading and Adherence
_ of Arsenical Sprays

A THESIS

PRESENTED TO THE FACULTY OF THE GRADUATE SCHOOL
OF CORNELL UNIVERSITY FOR THE DEGREE OF

DOCTOR OF PHILOSOPHY

BY
WILLIAM MOORE

; Reprinted from University of Minnesota Agricultural Experiment Station
Technical Bulletin 2, ie 1921

Spreading and Adherence
of Arsenical Sprays

A THESIS

PRESENTED TO THE FACULTY OF THE GRADUATE SCHOOL
OF CORNELL UNIVERSITY FOR THE DEGREE OF

DOCTOR OF PHILOSOPHY

BY
WILLIAM MOORE

Reprinted from University of Minnesota Agricultural Experiment Station
Technical Bulletin 2, June, 1921

TABLE OF CONTENTS

Page

Ginieia dogsepeasemordnoonoe one ood G oo odoebananonclaccacasounosnanoOee 3
IGeXaqo(s (bree (e)| Pe ee a aT ENA Users, m.cariiine Sana cM Orde Gpoletwole d O.d toward o'r 4
IDG Un MARee ORE Goons ao ues. nucomiccucnoboogdoocogsc 5
Historicallconsideration on spread mpi operetta ete oie sheter ellie otek ote taltse tel oettele ner 5
abhestheoryot spreading. ae tcetacirerect sree tae eee ric aren te ed iene ee iS;
Sprays that will spread on cabbage leaves..........-.- 2222-2 2s eee seer eeeeees 18
Sprays that will spread on other leaves........ 22... 2-2-2 -seeecersceceeseaee 20
Conclusion regarding the phenomenon of spreading.............-.+-+eeeeee eee 22
Historicalyconsiderationvof adherence! ae cme teeter eienen ieee ietiene iekonete ete 22
Use of organic materials with fungicides. \.. 0.02. 0.00 523 eee eee ene 22

Use of organic materials with insecticides................--.- 2 ede ree 24
Wserof inoreanicysulstancesi: myers ey etors ete ter Revere hey elon sire rete eR telnet 26
(Atnewatheoryjot adherences rience ee eekerie ero eit icon ike et ate tere 29
Electric charge exhibited by the common arsenical preparations ...............-- 30
Electrie’charge exhibited by the leaf ‘sutkace ss <.o7 ac © 6 seit ine helen tod ee etc 31
Preparation of an electrically positive arsenical substance...............-.2+---- 32
Iieldstestsiotadherences\-1... seuss erat ie ech e hereto insite etna eck ietetars 34
Preparation of positively charged ferric arsenate........-..-+-002+s2eceeeeee eee 36
Comparative toxicity of different arsenical preparations ............--2--++ee0e- 39
Methods) of determining: comparative tOxicttyse.)nre itll ke eee ete 40
Comparative tests Of tOXICity ns 17) a eee eter eel ere eee ire seater gL
Aemethodrof expressing a toxicity ricci icteric ieleleiet tase nerf eye 43
Influence of ferric hydroxide on toxicity.................-- POST Os 43
Conclusion regarding the phenomenon of adherence...........-..--.5..5------=- 44
Heiteraturewcite diac\c.: aterm tusuiencusis nes neperr: Etcueverel baveliee Feline rere Laer nnenetonedeneneeas 46

SPREADING AND ADHERENCE OF ARSENICAL
: SPRAYS

By Wict1AmM Moore

SUMMARY 5

>]

The addition of material similar in chemical constitution to the leaf
‘surface causes the spray mixture to form a film of liquid over the leaf.
The positive adsorption of the added material at the leaf-spray inter-
face, resulting in a lowering of the interfacial tension, appears to offer
the best explanation of the results.

Different types of leaves naturally require different materials. Thus
organic compounds such as beechwood creosote, carvacrol, or amyl alco-
hol, soluble in fats and waxes and but slightly soluble in water, produce
good spreading over waxy leaves, such as cabbage. ;

Various proteins and plant infusions give good spreading on leaves
with surfaces of cellulose, even when they are strongly cutinized, as in
the case of plum and citrus leaves.

Suspensions containing small-sized particles adhere better than those
with larger particles.

An even distribution of the spray over the leaf tends to increase the
adherence.

The leaf surface, when wet, exhibits a negative electric charge.

The common compounds of arsenic, such as lead arsenate, paris
green, calcium arsenate, and others, have particles carrying negative
electric charges.

Arsenic compounds of aluminum, chromium, and iron may be pre-
pared so that the particles carry a positive charge.

Ferric arsenate appears the most promising and is more toxic than
lead arsenate.

Field tests show that electrically positive arsenical preparations ad-
here more strongly to the leaf surface than do those which are negatively
charged.

Ferric oxide, or hydroxide, by adsorbing compounds of arsenic,
lower their toxicity to insects.

The ratio of the amount of the arsenic compound in the body to that
in the excreta is a better basis of comparing toxicity of different arsen-
ical preparations than tests based on the food consumed or the time re-
quired to produce death.

1 The writer wishes to acknowledge the assistance of Dr. R. A. Gortner, of the Uni-

versity of Minnesota, on certain phases of the problem, particularly the studies of cataphoresis
and endosmosis.

4 TECHNICAL BU LEE IN 2

INTRODUCTION

The successful use of arsenical sprays for the control of various in-
jurious insects depends upon a number of factors. The simple recom-
mendation of paris green or lead arsenate is not sufficient, since the re-
sults will vary greatly according to the character of the plant or insect.
If the plant is particularly sensitive to arsenic, care must be taken to
use an arsenical material with a very low percentage of soluble arsenic.
In spraying plants subjected to moist conditions resulting from frequent
light rains or fogs, the stability of the arsenical preparation becomes of
prime importance. Many compounds of arsenic are decomposed by the
action of water and carbon dioxide.

Leaves require a spray mixture of such a character that the film pro-
duced at the time of spraying will persist and will not tend to collect
in drops and roll off. This is particularly true of waxy leaves, such
as those of cabbage, or strongly cutinized leaves, such as those of the
citrus fruits. Such spray mixtures are not only more economical but
are also of great importance in the control of insects, which, like the
plum curculio, feed on isolated portions of the plant.

Not only the nature of the plant but also that of the insect must be
considered. Some insects are easily destroyed by arsenical poisons,
while others require large quantities to produce the desired results.
When the plant to be treated is not sensitive to soluble arsenic, a resist-
ant insect may be destroyed by the use of a compound containing a rather
high percentage of free arsenious oxide, or one which readily decom-
poses with the liberation of soluble arsenic. In most cases, however, the
use of a very stable and insoluble arsenical substance is required. Only
a small percentage of such a poison is absorbed by the alimentary tract
of some insects, the major portion being excreted. The excreta in such
cases may be white in color owing to the’presence of lead arsenate, and
chemical analysis will frequently show that more than fifty per cent of
the poison consumed was not absorbed. By greatly increasing the quan-
tity of the arsenical material applied to the leaves, the death of such in-
sects may be produced, but such an increase is not always justified from
an economic standpoint. Smaller quantities of the poison may be suc-
cessfully used, providing it remains on the leaves long enough for the
insect to consume a killing dose. The adherence of the dried material
of the spray, that is, its ability to withstand the washing effect of rain
and dew, thus assumes much importance. Plants subject to the attack
of an insect over a long period of time must be treated with a very ad-
herent spray, or the treatment must be repeated several times.

The present investigation is a study of the principles governing the
uniform distribution of the spray material over the plant, and the adher-
ence of the dried particles when subjected to rain, dew, wind, and other

_ SPREADING AND ADHERENGE OF ARSENICAL SPRAYS 5

influences. The object of the study is general, and no effort has been
made to apply the results to the control of any particular insect.

DEFINITION OF TERMS

Many attempts have been made, in the use of insecticides and fungi-
cides, to insure even distribution of the spray over the foliage of the
treated plant. In many of the papers dealing with this matter it is not
clear whether the investigator is considering the spreading of the spray
over the foliage or the adherence of the dry materials. Statements that
the spray did not “stick” or adhere well to the plant are frequent. In
some cases, from the context, it is apparent that reference is made to
spreading, the drops of the spray having failed to adhere to or spread
over the leaves. The term “wetting” is frequently used as a synonym of
spreading. Throughout this paper the word “spreading” will be used
to denote the formation or the maintenance after being formed, of a
continuous film over the surface of the leaf, and ‘‘adherence” will apply
to the resistance to the action of rain, dew, and wind exhibited by the
spray material after it dries. The term “wetting” may be considered as
the slight chemical or physical affinity between the liquid and the solid,
which is one of the factors in the formation of a continuous film.

HISTORICAL CONSIDERATION OF: SPREADING

One of the earliest records of the use of a material which tends to
produce the spreading of a spray over the leaves is contained in the
Rapport au Ministre de L’ Agriculture (1885). This report deals with
the treatment of the mildew of the vine, and Davis, an investigator, is
reported to have used 6 kilos of glue to 800 liters of copper sulphate
solution, thinking that the glue increased the efficacy of the remedy.
Whether the increased value of the spray was caused by a more even
spreading or by a better adherence is not mentioned. The following year,
Millardet and Davis (1885) said that the addition of glue to bordeaux
did not appear to be of notable advantage.

Soap or soapsuds was early used in contact sprays with tobacco and
other materials in order to insure the spreading of the insecticide over
the body of the insect. Altho the earliest applications of paris green
were in the form of dust, the use of suspensions of paris green or lon-
don purple in water soon developed. Gillette (1890) used soapy solu-
tions with paris green and london purple, but found that these mixtures
were more injurious than a suspension containing no soap. The addition
of flour at the rate of half an ounce to a gallon was. tried, but this
preparation also proved more injurious. The increased injury, it was
thought, was due to the greater adhesiveness of the mixture. Resin in
the form of a soap, sodium resinate, was successfully used without in-
creasing the amount of injury to the foliage. Washburn (1891) used

6 TECHNICAL BULLE TRIN 2

whale oil soap, 6 pounds to 50 gallons of a paris green suspension,
thereby producing an even spread of the mixture over the fruit and
leaves, and apparently rendering the poison more tenacious. Galloway
(1892) used soap with different fungicides to increase spreading.
Swingle (1894) recommended the use of soap with bordeaux mixture.
No definite quantity was specified, it was said merely that sufficient soap
should be added to give a good permanent foam. This result was usu-
ally obtained by using a quantity of soap equal to one half the com-
bined weight of the copper sulphate and lime in the bordeaux mixture.
Fairchild( 1894) used soap with eau celeste, obtaining excellent spreading
even on leaves with a heavy cuticle, such as those of the pear. Galloway
(1894) used a resin soap with bordeaux mixture, finding it just as
effective in producing a continuous film on the leaf as Ivory or whale oil
soap. Lowe (1896) encountered considerable difficulty in spreading a
lead arsenate spray evenly over the surface of willow leaves. Glue used
at the rate of 2 quarts to 45 gallons of spray gave satisfactory results.

The indefiniteness encountered in the use of soap as a spreader for
various spray mixtures was shown by the analysis of various soaps by
Van Slyke and Urner (1904). They showed that in the different makes
of whale oil soap the water content varied from 11.15 to 54.85 per cent
and the amount of actual soap from 14.90 to 59.27 per cent. The nature
of the alkali present varied greatly, as did also the quantity of fatty
acids and resins. Other common soaps showed a similar variation. The
addition, therefore, of a definite amount of soap to a spray may or may
not cause an even distribution of the material over the leaves.

Mausier (1908) studied the spreading of a number of liquids over
different solids. He realized that spreading is dependent on the nature
of the solid and of the liquid, but considers this difference as due to the
surface tension of the liquid. A liquid which will spread over a par-
ticular solid must possess a certain definite surface tension value. If
it has this value it will spread regardless of the nature of the liquid.
A spray containing 30 grams of soap to Io liters of water with either 50
grams of oil of tar or 10 grams of formaldehyde is considered as meet-
ing the surface tension requirements of the leaf.

Vermorel and Dantony (1910) state that a body is wetted by a
liquid, 1.e., the liquid spreads over it when the cohesion of the molecules
of the liquid, the one for the other, is less than double their adhesion for
the solid. They distinguished between the surface tension of a fresh
surface of a soap solution, dynamic surface tension, and the surface
tension of an old surface, static surface tension, considering that there
was a direct relationship between the static surface tension of a soap
solution and its ability to spread over an insect. Measurements of the
surface tensions, by means of a stalagmometer, of several organic
compounds were made, and it was found that none possessed as low a

SPREADING AND ADHERENCE OF ARSENICAL SPRAYS 7

surface tension as a soap solution. Since no mention is made of the
time allowed for the formation and breaking away of the drop from the
tip of the stalagmometer, it is doubtful whether sufficient time was al-
lowed for the concentration of the soap in the surface layer, thus insur-
ing a true measurement of the static surface tension. In a second paper,
Vermorel and Dantony (1911) take up the addition of soap to fungi-
cides to increase their spreading, showing, that the results obtained de-
pend largely upon the method used in the preparation of the mixture.
A method is mentioned for the preparation of a colloid copper soap
which exhibited good spreading properties.

Parker (1911) found that the addition of 2 or 3 bars of common
laundry soap to each 50 gallons of a lead arsenate spray retarded the
settling out of the suspended particles. The use of soap with arsenical
sprays to retard settling and to increase spreading, when tried under or-
chard conditions by certain growers, was frequently accompanied by an
increased injury to the foliage of the sprayed plants. These results
caused Tartar and Bundy (1913) to investigate the action of soap on
lead arsenate. They showed by chemical analysis that the addition of
different soaps had little influence on the neutral lead arsenate
Pb,(AsO,)., but that the addition of soap to the acid lead arsenate
PbHAsO,, rendered soluble a considerable quantity of the arsenate.
Since the acid lead arsenate is more generally used than the neutral, the
addition of soap to cause spreading can not be safely recommended.
Edwardes-Ker (1913) also studied the addition of soap to lead arsena‘e
sprays, obtaining results opposed to those of Tartar and Bundy. He
found that the addition of 1 per cent of soap, either home-made or com-
mercial, did not influence the solubility of lead arsenate suspensions.
Both home-made lead arsenate, formed by the reaction of lead acetate
and sodium arsenate, and commercial lead arsenate were used in the ex-
periment. No distinction is drawn between the different kinds of lead
arsenate. The mixtures of lead arsenate and soap were filtered half an
hour after being made up, and the arsenic in the filtrate was determined
gravimetrically as magnesium pyroarsenate. Tartar and Bundy used
less soap, 4.8 grams to 1,000 cubic centimeters of water, but the mixture
was allowed to stand six hours before filtering. They used the iodine
titration method of Gooch and Browning in the determination of the
quantity of soluble arsenic. As the lead arsenate and soap would gen-
erally be mixed for periods longer than half an hour, and even after
spraying would have an opportunity for chemical reactions, it appears
that the results of Tartar and Bundy more nearly represent the effect of
adding soap to lead arsenate sprays.

Gastine (1912) recommended the use of saponin to reduce the sur-
face tension of spray materials and hence to insure spreading. One of
its advantages is said to be that, unlike soap, it is not precipitated by acids

8 DECHNICAL BULEE ELN 2

or metallic solutions, and will not cause injury to the plants. Saponin
can therefore be added to either fungicides or insecticides without dan-
ger of any decomposition resulting. It may be used instead of soap in
the formation of emulsions. Used with beechwood creosote or coal-tar
creosote the surface tension of the mixture was lower than that of the
pure saponin solution.

Weinmann (1912) prepared a cupric spray with calcium polysul-
phide and soap, finding that this combination gave a very high drop num-
ber and spread well. The drop number of the cupric spray with soap,
but without the polysulphide, was much lower. The substitution of
saponin in place of soap also gave inferior results.

Vermorel and Dantony (1912), continuing their investigations, con-
cluded that the surface tension of a spray solution is not ‘an index of
its spreading power. Solutions with different surface tensions may
have the same ability to spread, or the spreading power may vary ac-
cording to the nature or physical state of the material to be treated.
Two distinctions are made: (1) Where the liquid is able to touch the
surface, when it may spread as water on a potato leaf or may collect in
a drop as water on a vine (grape) leaf; (2) where the liquid rests on
the surface without touching it, as in the case of a drop of water on a
cabbage leaf, a film of air being interposed between the leaf and the
water. A solution of sodium oleate giving a stalagmometer reading of
142 drops may spread over a cabbage leaf and fail to spread on the leaf
of a vine. They believed that the surface tension of the spray in-
fluenced its spreading less than did its surface viscosity. Whereas the
sodium oleate solution giving 142 drops from the stalagmometer failed
to spread over the leaves of the vine, a saponin solution giving only ro1
drops, and therefore apparently possessing a higher surface tension,
spread readily. This difference is thought to be explained by the
higher surface viscosity of the saponin solution, so that when spread in
a thin film over the leaf, surface concentration rapidly took place, thus
increasing the surface viscosity to such an extent that the solution was
unable to collect in a drop. A gelatin solution of I part in 10,000 parts
of water, possessing a surface tension nearly equal to water, caused
spreading when applied to the leaves of a vine. Gelatin in solution was
more effective than either saponin or soap and had the further advantage
of being uninfluenced by either acid, neutral, or basic materials.

In this as in the preceding paper (Vermorel and Dantony, 1910), no
mention is made of the speed of formation or the rate of detachment of
the drops from the tip of the stalagmometer. Concentration of the ma-
terials in the surface layer reduces the surface tension, and since dif-
ferent materials may vary as to the time required to concentrate in the
surface layer, these measurements of surface tension are not comparable.
Further, if surface concentration takes place so rapidly as to cause the

SPREADING AND ADHERENCE OF ARSENICAL SPRAYS 9

film to become so viscous that it can no longer collect in a drop, a de-
cided lowering of the surface tension should be apparent in the stalag-
mometer readings. No consideration is taken of the possibility of a
concentration of the materials at the interface of leaf and spray which
would result in a lowering of the surface tension at the interface and
tend to produce spreading.

Chappaz, G., (1913) recommends the use of saponin in preparing
sprays which will spread well and considers it superior t6 soap. Chapaz
(1913) reviews the recent work with spreaders, discussing soap, gelatin,
glue, and saponin. He recognizes a general but not a mathematical rela-
tionship between spreading and the drop number determined by means
of a Duclaux pipette (stalagmometer). Vermorel and Dantony (1913)
recorded several methods of preparing fungicides with casein. A solu-
tion of casein is prepared by dissolving it in a solution of roo grams of
sodium carbonate to a liter of water. Parker (1913) used from 4 to 10
pounds flour paste with lime sulphur and nicotine sulphate to each 100
gallons of liquid. The spray was used primarily for red spider and was
tried on several different plants. Altho it was an effective spreader on
many plants, it failed when used on carnations, sweet peas, and green-
house roses. The possibility of its use as a “sticker” for lead arsenate
suspensions was considered. Glue and miscible oil mixed with lime sul-
phur was used for the control of red spider by Jones (1913). Excellent
spreading was reported on all parts of plum and peach trees and it is be-
lieved that similar results would be obtained on citrus trees. Neuls
(1913) confirmed the results of Parker (1913) on the spreading prop-
erties of lime sulphur and flour paste and the value of this spray for the
destruction of red spider.

Lafforgue (1913) points out that spreading and adherence are two
entirely different phenomena. The addition of saponin to the spray
mixture gives good spreading but not good adherence, while gelatine
spreads well and also improves the adherence.

Lefroy (1913), working in India, had determinations made of the
surface tension of the solutions used for controlling psylla attacking in-
digo. Soap solutions showed a very much lower surface tension than
water, but soap emulsions of oil or creosote exhibited a higher surface
tension than the soap solution alone. These results are opposed to the
work of Gastine (1912), who found that a saponin emulsion of beech-
wood creosote or coal-tar creosote possessed a lower surface tension than
the saponin solution. However, since no mention is made by Lefroy of
the method employed in determining the surface tension, and in view of
the fact that in one case soap and in the other saponin was used to emul-
sify the creosote, no conclusion can be reached as to the accuracy of the

results.

10 PECHNICAL BULLETING2

Astruc (1913) divides spreaders into four types: (1) Soaps; (2)
saponins; (3) albuminous substances, such as albumin, gelatin, milk,
dried blood, and casein; (4) organic salts of more or less limited pro-
duction. No mention is made as to the nature of these organic salts.
Issleib (1914) extracted 2 kilograms of ‘“‘carrangeen,” or pearl moss
with 100 kilograms of water. The extract, a thick slimy liquid, when
sprayed over the leaves formed a thick continuous coating which on
drying cracked and scaled off, carrying with it the larvae or eggs of in-
sects infesting the plant. These results are comparable to those re-
corded by Parker (1913), using flour paste, and no doubt this prepara-
tion would give similar spreading.

Del Guercio (1914), in Italy, recommended the use of 1 to 2 per
cent of flour paste, fish glue, or other colloidal substance, with potas-
sium or calcium polysulphide to give an even distribution of the spray
over citrus trees to control Chrysomphalus dictyospermi var. pinnuli-
fera. Rye flour is preferred, but spoiled wheat flour or the flour of
other grains may be used. An even distribution was obtained regard-
less of the degree of maturity or the position of the treated portions.
Arnal (1914) mentions that “soluble caseins,”’ for use with bordeaux
mixture, are being manufactured in France and put on the market. It
may be that these preparations are similar to the casein glue being sold
in the United States.

Vermorel and Dantony (1915) prepared rapidly a calcium caseinate
by stirring a liter of milk of lime into a suspension of 100 grams of
casein powder in a liter of water. The milk of lime may contain from
50 to 200 grams of lime without influencing the results. One liter of
this solution is added to a hectoliter of alkaline bordeaux mixture to
give spreading and adherence.

The most important paper, following the papers of Vermorel and
Dantony, dealing with the spreading of sprays, is that of Lefroy
(1915). The fact that spreading depends not only upon the value of
the surface tension of the spray, but also upon the surface tension of
the leaf? and the surface tension at the interface of the spray and the
leaf, is presented by Lefroy for the first time in entomological literature.
Unfortunately Lefroy becomes confused in his terms, and draws the
incorrect conclusion that if the surface tension at the interface between
the spray and the leaf is greater than the sum of the surface tension
of the spray and that of the leaf, spreading will occur. Realizing that
the surface tension of the leaf and the surface tension at the interface
of leaf and spray can not be readily determined, he recommends the
determination of the surface tension of the spray, which should be as low
as possible. Using the term “wetting” to denote the specific attraction

2 Solids are usually considered as possessing a surface tension altho it has not been
demonstrated.

SPREADING AND ADHERENCE OF ARSENICAL SPRAYS II

or slight chemical affinity existing between the spray and the leaf, the
statement is made that “spreading of a liquid over a surface it never
wets” may occur. This conclusion does not appear to be justifiable,
since if no wetting occurred the surface tension at the interface would
be so high that spreading would be impossible. The theory of spread-
ing of both sprays and dips is presented in a very interesting paper by
Cooper and Nuttall (1915). First pointing out the value of having
sprays and dips which will spread over the treated plant or animal,
they give the principles of spreading established by Quincke (1877).
QOuincke studied the capillary rise of liquids in tubes of different ma-
terials, the spreading of one liquid over another liquid or a solid, and
the angles formed by the liquid at its point of contact. From this
study he formulated the conditions necessary for spreading to occur.
These conditions in terms of sprays may be expressed by the statement
that if the surface tension of the solid (leaf) is greater than the sum
of the surface tension of the spray and the surface tension at the inter-
face of spray and solid, spreading will occur. Cooper and Nuttall
believe that in general this statement holds, but believe that there
may be certam exceptions. Two factors are thought to be able to upset
entirely this relationship. The first of these is the solvent action of the
liquid on the solid, particularly in those cases where the solid is coated
with wax or grease. This solvent action of the spray is believed to be
independent of the surface tension at the interface of solid and liquid,
but as will be shown later in this paper the solvent action of one liquid
on another liquid or a solid, results in the lowering of the surface ten-
sion at the interface. Sprays, therefore, which spread because of their
solvent action, are not exceptions but actually fulfil the surface tension
conditions necessary for spreading to occur.

The second factor considered as vitiating the surface tension equa-
tion is the phenomenon of surface concentration. The experiments of
Vermorel and Dantony are cited as showing that a spray with a high
surface tension spreads well owing to its high surface viscosity resulting
from a rapid surface concentration of the solute.

Since these experiments have already been discussed and will be
taken up later they will not be considered further here, tho it may be
said that in the opinion of the writer, they do not invalidate the surface
tension relations already expressed.

Having presented the problem, Cooper and Nuttall take up the possi-
bility of measuring the spreading power of dips and sprays. The work
of Vermorel and Dantony is thought to show that the measurement
of surface tension alone is insufficient to determine the spreading quali-
ties of the liquid. The ability of the spray to produce a foam, since it
depends upon surface tension and does not express the surface tension
at the interface of the liquid and solid, can not be used as an index to

WZ IMR ETEUN COAL, TE(CULILIGIPIUIN| 2

spreading. The weight of the quantity of liquid adhering to a solid
dipped into it is largely influenced by viscosity, and is therefore not
considered an accurate method of determining spreading. Spreading
may be conveniently expressed by the formula 8 s> 41+ &ls where “3”
represents surface tension; ‘‘s’’, solid; “1”, liquid; and “ls”, the liquid-
solid interface. Then %s—(3&14+ %ls)= the spreading power of the
liquid expressed in dynes. Cooper and Nuttall, being chiefly inter-
ested in dips where the solid is represented by the skin of the animal,
usually oily in character, adopted castor oil or liquid vaseline as a
liquid substitute for the solid. This substitution simplified the prob-
lem, as the surface tension of the oil and of the liquid (dip) could easily
be measured and expressed in dynes. Using a modification of the drop
pipette method for determining the emulsifying action of soap solutions,
they measured the surface tension at the interface of the oil and the
dip. Substituting the values of the different surface tensions in the
above formula, a definite value for spreading, expressed in dynes, was
obtained. It is pointed out, however, that this method is applicable
only to soap solutions and will not give results with gelatine, saponin,
or similar solutions.

This method, based on the use of an oil as a substitute for the
solid, may be used only when the solid is oily or greasy, and can not
be used to determine the spreading power of sprays on leaves which
possess an entirely different surface.

From the results of their experiments they conclude that for com-
parative values the interfacial tension alone may be considered. Since
this is inversely proportional to the number of drops produced by a
given volume of the oil, and since the spreading varies inversely as the
interfacial tension, it is directly proportional to the drop number. This
conclusion, however, is based on the assumption that the liquid has a
low surface tension, which, altho correct in the case of soap solutions,
is not always true of spray materials which will spread. Of the two
surface tensions, they consider the surface tension of the solid-liquid
interface more important.

A new material and one well adapted for use in certain countries
was suggested by High (1915). Fifteen pounds of cactus leaves sliced
and soaked in 50 gallons of water over night is recommended as a
spreader. Cactus extract gave excellent results when used with zinc
arsenite, and paris green and lime, but with lead arsenate the results
were unfavorable, owing to the formation of a precipitate. Cactus
grown near water contains a lower percentage of the desired material
and hence larger quantities were required to give the desired results.

Smith, L. B. (1916), using the method of finding the surface ten-
sion at the liquid-solid interface suggested by Cooper and Nuttall, deter-
mined the spreading power of various combinations of fish oil soap

SPREADING AND ADHERENCE OF ARSENICAL SPRAYS 13

and nicotine sulphate. No effort was made to determine the surface
tension of either the oil or the spray. The sprays were tested with
Acyrthosiphum pisi Kalt. on garden peas, Myszus persicae Sulz. on spin-
ach, and Tetranychus sp. on strawberries. The maximum killing was
reached with certain concentrations of soap or soap and nicotine sul-
phate. Further additions of soap failed to increase the efficacy of the
spray. Using a fixed concentration of soap and increasing the concen-
tration of nicotine sulphate reduced the spreading and also the killing
power of the spray. This result was undoubtedly due to the reaction
between nicotine sulphate and soap.

Lees (1917) tested the spreading of paraffin (kerosene) emulsion
on cloth surfaces previously painted with boiled linseed oil and dried.
A drop of the emulsion was rolled about on this surface and arbitrary
values from one to three were used to express the degree of spreading
of the kerosene and similar values for the aqueous phase. Based upon
these preliminary tests, further experiments were made on the spread-
ing of water solutions of gelatin, casein, soap, and paraffin emulsions
on the leaves of gooseberry and sea kale and on goosebrry mildew. All
the preparations gave complete spreading on gooseberry leaves but only
certain of the emulsions gave complete spreading on kale leaves and
gooseberry mildew. No attempt is made to explain the results.

Altho not directly bearing on the spreading of sprays on foliage,
the experiments of Gray (1918) in preparing “wettable” sulphurs are
of interest. An ounce and a half of powdered glue dissolved in 3 gal-
lons of water thoroly wets, or spreads over, powdered sulphur, thus
making possible the formation of a suspension.

Lovett (1918) studied spreaders for arsenate sprays. Spreading is
thought to be caused largely by surface tension and specific gravity.
It is stated that the ability of the liquid to hold the arsenate in suspen-
sion is a very fair indication of its ability to spread. This is not al-
ways true, for altho some spreaders which increase the viscosity of the
medium also reduce the rate at which the suspended particles settle, this
characteristic in itself can not be considered an index of spreading.
Soap, glycerine, glue, casein, and an infusion of sage were tes’ed as to
spreading ability and also as to the degree of injury they produced on
bean foliage. An infusion of sage made by steeping Artemesia triden-
tata, Nutt, for twelve hours gave very encouraging results. The oils
and other ingredients present in the infusion were no‘ determined but
were considered as probably similar to those found in Artemesia frigida,
Willd. by Robak (1906). This species was shown to contain an es-
sential oil composed primarily of borneol camphor and cineol. From
4 to 8 ounces of casein converted into calcium caseinate and added to
each 100 gallons of spray gave good spreading.

14 TECHNICAL BOLE TN ae

Stearns (1920) experimented with the “Irish” moss which is simi-
lar to that used by Issleib (1914), as a spreader of arsenical substances
over peach foliage. Issleib’s proportion of 4 pounds to 20 gallons was
found to be too thick for spraying purposes, but when used at the rate of
4 pounds to 50 gallons gave good results. Calcium caseinate at the rate
of 1 pound to 50 gallons also gave good results on peach foliage.

The most recent paper dealing with spreaders is that of Lovett
(1920). In discussing the suspension test as an index of spreading, he
says that altho not a definite criterion of spreading it “does indicate a
physical quality in the solution much to be desired in a spreader.” His
belief that increased viscosity is accompanied by increased spreading is
shown in the experiments where phosphates and sulphates are added
to aqueous solutions of glue and of calcium caseinate to increase the
viscosity and therefore the spreading. Increased spreading was not
ob‘ained.

A number of different materials were tested, not only colloids such
as saponin, sage tea, gelatin, glue, calcium caseinate, corn, potato, wheat,
arrowroot, and starch, but also inorganic substances such as aluminum
sulphate with lime, kaolin, barium sulphate with lime, chromium fluoride
wiih lime, calcium chromate with lime, and lead chromate with lime.
None of the inorganic materials gave the desired results. On the basis
of compatability, efficacy, availability, cost, and ease of preparation, he
arranges the colloids in the following order of merit : Calcium caseinate,
glue, gelatin, soap bark (saponin), and oil emulsion.

A new method for testing spreading in the laboratory is presented.
Tubes lined with a coating of wax obtained from the surface of Ben
Davis apples were used to determine the capillary rise of the different
solutions. The numerical value of 3.5 (probably millimeters) is given
for water, while 2 per cent gelatin had a value of 11.8, 2 per cent soap
bark 2 8, 2 per cent caseinate 10.11, and 2 per cent glue 7.8. Lovett be-
lieves that the height to which the liquid rises in the capillary tube is a
measure of spreading power. This is not strictly true, as only those
liquids which will spread over or “wet” the surface of the tube (in this
case the wax of the apple) will rise in it, and the height to which they
rise is determined by the surface.tension of the liquid and the angle of
contact of the liquid to the wall of the tube. The use of a capillary tube
will merely show whether the liquid will or will not spread. If it rises
at all, spreading will occur; and if no spreading will occur there will be
no rise.

Summarizing briefly the work of the various investigators, it is
apparent that various colloidal substances, such as casein, gelatin, flour,
glue, and soaps modify the spray mixture to such an extent that it
will remain spread out over the leaf surface in the form of a film. The
surface tension relationships of the leaf and spray offer the best ex-
planation, but in certain cases other factors are thought to influence the

SPREADING AND ADHERENCE OF ARSENICAL SPRAYS 15

results. These various colloidal ‘substances have given good spreading
on leaves with a thin cellulose epidermis, and even on leaves more or
less strongly cutinized, such as those of apple, peach, grape, pear, and
the citrus fruits. Results on waxy surfaces, such as the waxy bloom on
the fruit of apple or plum and the leaves of cabbage, have not been at-
tained except by the use of soap or soap emulsions. Soap will produce
spreading on such surfaces, but, owing to the reaction between the soap
and the arsenical materials, its use may result in injury to the foliage.
Other disadvantages of the use of soap are its varying composition, its
reaction with hard water, and the difficulty of dissolving it without the
use of heat. The following experiments were therefore undertaken to
find a new material for use on waxy surfaces, and to obtain a better
understanding of the causes governing spreading.

TEE; TEEBORY ‘OF SPREADING

The manner in which surface tension is related to spreading is
shown by the following illustration. Upon a liquid, B, with a surface
exactly two square centimeters in area, place a drop of an immiscible
liquid, A, so that its area is exactly one square centimeter. The area of
the surfaces of A, B, and the surface at the interface AB is then
exactly one square centimeter in each case, and the surface tension of
the entire system is expressed by the equations A+ 3 B+ &8 AB, in
which 8 represents the surface tension. Now assume that A is spread
out until it completely covers B, then the area of the surface of A and
the surface at the interface AB is in each case two square centimeters,
while B no longer has an exposed surface. The surface tension of the
system then becomes 243 A+2¥%AB. Subtracting the second equation
from the first gives the equation § B— § A—¥& AB as the difference be-
tween the surface tensions of the system under the two conditions.
Since a system will always arrange itself so as to reduce its surface
tension, if the surface tension of the system in the second state is less
than in the first case, spreading will occur and the equation will be posi-
tive. If the surface tension under the original arrangement is the low-
est, then the equation is negative and spreading will not occur. The
surface tension conditions favorable to spreading may then be repre-
sented by the equation § B> 8 A+ 8 AB, while conditions unfavorable
to spreading may be expressed by the equation §B<8A+¥8AB. An
excellent example of these conditions is the system benzene and water. A
drop of pure benzene placed on the surface of pure water immediately
spreads out, forrning a thin film®.

8H,O>%8C,H, + 8 (H,O—C,H,).
O—J2:05, 0 —=25, 17 0 — 34.00,

3 The surface tension values given are those of Harkins, Brown, and Davies (1917).

16 TECHNICAL BUGLE TIN 2

In a few minutes the water becomes saturated with benzene and the
benzene becomes saturated with water. The surface tension of each is
lowered, while the surface tension at the interface is increased. The
value for the equation becoming :
8 Sat. H,O< 8 sat. C,H,+ 8 (H,O—C,H,).
0 60:10 <5 —2 700 so eens

The benzene which had previously been spread out in a thin film now
collects in the form of a drop. In this case, at least, there is no doubt
that spreading or lack of spreading may be explained on the basis of
surface tension.

Unfortunately it is at present impossible to measure the surface ten-
sion of a solid, or even to prove conclusively that a solid possesses sur-
face tensiom. Since the surface tension of a liquid increases as the tem-
perature is lowered, even to the freezing point, it does not appear rea-
sonable that surface tension completely disappears in the solid. It
seems more reasonable to believe that a solid has a high surface ten-
sion which can not be demonstrated because of the immobility of the
molecules. The surface tension at the interface of the solid and liquid
is also impossible of measurement. With two of the surface tensions
unknown, it is useless to measure the surface tension of the spray
liquid, and it becomes necessary to find some other method of solving
the problem.

From a consideration of the above formula, it appears that spread-
ing can be obtained only by lowering the surface tension of the liquid or
the surface tension at the liquid-solid interface, since the surface ten-
sion of the solid (leaf) can not be increased. The problem, therefore,
resolves itself into this: How may the surface tension of the spray
and the surface tension at the spray-leaf interface be lowered? It is
well known (Willows and Hatschek, 1915) that the adsorption of a
solute in the surface layer will result in the lowering of the surface ten-
sion, while if it is negatively adsorbed, the surface tension will be in-
creased. Thus soap or saponin dissolved in water is adsorbed or col-
lects at the surface and the surface tensign lowered. Sodium chloride dis-
solved in water concentrates in the interior of the liquid and is therefore
negatively adsorbed and the surface tension is increased. In a similar
manner a dissolved substance adsorbed in the surface at the interface of
the liquid and solid will lower the surface tension at this interface. The
next question then is to determine what substances will be positively
adsorbed in the liquid-air surface and the liquid-solid surface.

Data on this problem have been given in three different papers which
are too long to be completely reviewed here. Altho the papers deal
with a different problem, certain facts given in them may be directly
applied to the present problem. Harkins, Brown, and Davies (1917),
considering the work done when water and some other liquid come

SPREADING AND ADHERENCE OF ARSENICAL SPRAYS 17

together to form an interface, have shown that at the interface of the
two liquids the molecules in the surface of the liquid orient themselves
so that the active group is in contact with the water. The decrease in
the free energy, i.e., the surface tension at the interface, when the sur-
face of a second liquid approaches that of water, depends primarily
on the most active group present in the molecules and secondarily on
the shape and size of the molecules. The solubility in water is related
to this decrease in free energy which more or less perfectly measures the
attraction of the active group for the water molecule. The presence of
such active groups as COOH, CO, CN, OH, or CONH, is sufficient
to make the molecule of an organic substance soluble in water, providing
the active group does not have to pull into the solution a slightly less
active group, which is too long or too large.

In a second paper Harkins, Davies, and Clark (1917) show that in
the surface of a liquid the molecules are so oriented that the least active
group is toward the vapor phase, that is, the vapor above the liquid. At
any surface or interface, the orientation of the molecules is such as to
make the transition to the adjacent phase—that is, the vapor, liquid, or
solid in contact with it—least abrupt. At the interface of two liquids
their like parts come together in conformity with the above law. In
two liquids, A and B, the portion of the molecules of A like B turn
toward B and those of B like A turn toward A. If a solute is present
in either of the liquids, A or B, which collects at the interface, the mole-
cules of the solute will so arrange themselves that the parts of the mole-
cules which are like A will turn toward A, while those like B will be
attracted to B. In such a case the free surface energy, that is, the
surface tension at the interface, will be reduced. An aqueous solution
of a solute which is active like water but to a lesser degree, will be posi-
tively adsorbed in the surface and the least active portion will be turned
toward the outside.

The third paper by Langmuir (1917) approaches the problem from
a slightly different angle. Studying the spreading of oleic acid on water,
the conclusion is reached that the active carboxyl groups are actually
dissolved in the water but the long hydrocarbon chains have too much
attraction for each other to be dissolved, hence the acid spreads out into
a thin film. Oils without this carboxyl group should not spread, and in
fact pure paraffin oil, which lacks an active group, fails to spread at all.
Results show that the spreading of films on surfaces is determined by
the shape of the molecules and by the relative activities of the different
portions of the molecule. In a similar manner a substance, such as a
soluble fatty acid, dissolved in water, is adsorbed in the surface layer
and lowers the surface tension. Adsorption of a liquid on a solid is
considered as similar to the spreading of oil on water, i.e., the portion

18 TECHNICAL BULLET IN=2

of the liquid similar to the solid is attracted by the molecules of the
solid forming a molecular layer upon it.

Considering the data presented in these papers, the investigation be-
came a search for those substances which possess an active group to
render them soluble in water and an inactive group which will cause
their adsorption in the surface layer. If the inactive group should be
similar to the surface of the leaf or soluble in it, then adsorption at the
spray-leaf interface would occur and would result in a lowering of the
interfacial tension. A substance fulfilling one or the other of these
conditions, preferably the latter, should cause spreading.

SPRAYS THAD Wii Ss FR AD.ON CABBAGE LEAVES

An effort was made by the author in the earlier experiments to de-
termine whether a given solution would spread or not, by means of cap-
illarity. Altho this method might be used in considering waxy sur-
faces, it could not be adapted to the study of leaves with a thick cuticle.
To obtain comparable results, nothing but a capillary tube possessing
walls exactly similar to the leaf surface would suffice. Tests in all the
experiments were therefore made by spraying the solution on the sur-
face of the leaf by means of an atomizer.

The first efforts were directed toward producing spreading of the
spray on cabbage leaves. A saturated solution in water of several or-
ganic compounds was tested. Solutions of kerosene, methyl salicylate,
benzaldehyde, chloroform, camphor, and salicylic acid failed to-give the
desired results. Amyl alcohol and benzyl alcohol gave good results but
were too expensive for actual use. Crude phenol produced spreading but
since a I per cent solution of pure phenol failed, the results with crude
phenol must have been due to impurities. Phenol possesses an active OH
group, while resorcinol possesses two such OH groups. A I per cent
solution of resorcinol failed to give spreading. It appeared therefore
necessary to introduce such groups in the phenol as would decrease its
solubility in water and increase its solubility in the wax of the cabbage
leaf, thereby increasing its adsorption at the leaf-spray interface and
lowering the interfacial surface tension. A saturated solu‘ion of
beechwood creosote consisting of a mixture of cresols, C,H,(OH)CH,,
and guaiacol, C,H,(OH)OCH,, gave excellent results. So concen-
trated a solution of beechwood creosote is not necessary, since a good
spreading accompanied the use of a one-third and even a one-fourth
per cent solution. One-fourth per cent is about the lower limit and one-
third is a safer proportion. A saturated solution of carvacrol,
C,H,(OH (CH, )C,H,,. containing about one-twelith of 1 per cent
and a saturated solution of eugenol, C,H,(OH)(OCH,)CH,: CH;
CH., containing only about one-fifteenth to one-twentieth of 1 per

SPREADING AND ADHERENCE OF ARSENICAL SPRAYS 19

cent, gave good spreading, each being less soluble in the water and more
soluble in the wax of the leaf.*

Most of these substances are adsorbed in the surface layer and re-
duce the surface tension of the solution. The question naturally arises
whether the spreading is not caused by the lowering of the surface ten-
sion of the liquid itself rather than the lowering of the surface tension
at the interface of the leaf and the solution. Surface tension determina-
tions were therefore made by means of a stalagmometer. Harkins and
Brown (1918), in studying this method of determining surface tension,
pointed out that if the formation of the drop is too rapid, some of the
liquid streaming from the tube seems to force its way into the falling
drop during the time of detachment, hence increasing its weight. From
the figures given, this error is not very large and can be ignored in
these relative determinations. It is also stated that when dilute aqueous
solutions of long chain organic molecules are used, it is often necessary
for the drop to hang for half an hour to obtain the value of the static
surface tension. In spraying it is really the surface tension of the so-
lution at the moment it is sprayed over the leaf that is desired, hence a
determinatin of dynamic surface tension is more important than static
surface tension. .

A one-third per cent solution of creosote allowed to drop at the
rate of one drop per minute showed a surface tension of 49.27 dynes.
One-fourth of a pound of sodium oleate to 100 gallons of water pos-
sessed a surface tension of 42.42 dynes. The soap solution, altho it
possessed a lower surface tension than the creosote solution, failed to
spread over cabbage leaves. A soap solution with a surface tension of
24.28 dynes gave spreading. It is therefore apparent that the spread-
ing of the creosote solution is not owing to its low surface tension but
to the lowering of the surface tension at the leaf-solution interface.
Further confirmation of this statement is found in the fact that none of
these solutions would spread over the leaves of citrus, guava, or other
plants possessing strongly cutinized leaves but lacking the waxy
surfaces.

The possibility that the results of Lovett (1918) with sage infusions
may have been due to some organic principle in the essential oil of the
sage, at once suggested itself. Robak (1912) has shown that another
species of sage possessed an oil rich in cineol, hence a saturated solu-
tion of cineol was tried and gave good results. Since this experiment
was conducted, Lovett (1920) has stated that sage infusions did not
spread well over the waxy surface of apples, hence his results may
have been due to some other ingredient of the infusion.

4A saturated solution of a mixture of xylenols sold under the name of cresylic acid
(straw-colored) by the Barrett Co. will cause spreading on cabbage leaves.

20 TECHNICAL BU ERIN <2

No doubt a very large number of organic compounds will give simi-
lar results. Apparently all that is needed is a chemical containing an
active group to make it slightly soluble in the water, and an inactive
portion soluble in wax. With this principle as a base, it should be a
simple matter to select the compound best suited for each particular set
of conditions. The practical application of these results has been left
for future investigation.

SPRAYS THAT With SP READ ON @i EE Ree Aare

It has been stated that these organic solutions failed to spread on
leaves which did not possess a waxy coating. Other investigators have
obtained good spreading on such leaves by means of various colloids,
such as soap, casein, glue, and gelatin. Sodium oleate, 2 pounds to 100
gallons, gave spreading on citrus leaves, while a smaller quantity failed.
Commercial casein was dissolved in water containing a very small
quantity of sodium hydroxide (2 ounces to 5 pounds of casein). Sucha
solution containing only one-fourth pound of casein to 100 gallons of
water gave very good spreading on citrus leaves, but failed on cabbage
unless applied with such force that the liquid penetrated between the
wax particles, reaching the epidermis below. Gelatin used at the same
rate also gave favorable results on citrus leaves. Acidifying the solu-
tion did not destroy its spreading properties.

Flour paste has often been used as a spreader, but much of the
protein in the flour is insoluble in water and is therefore not utilized.
If about one ounce of sodium hydroxide is added to 5 pounds of flour
when the paste is being prepared, all of it goes into solution. Prepared
in this way, one-fourth pound of flour to each 100 gallons of the spray
produces a film when sprayed over citrus leaves.

Saponin gives good results but is too expensive for general use.
Jacobson (1919) has shown that alfalfa hay contains a saponin quite
soluble in water. About one per cent of pure saponin was recovered
from air-dried alfalfa. Alfalfa hay should therefore serve as a spreader.
One hundred grams of hay was heated in 3 liters of water and allowed
to stand twenty-four hours. Two and a half liters were recovered on
straining. This solution was diluted until it represented only six-
tenths of rt per cent of alfalfa hay, and at this dilution gave good
spreading. Five pounds of dry alfalfa would be sufficient for 100 gal-
lons of the spray.

The question arose as to whether these results were due to the
lowering of the surface tension of the liquid, to the increased surface
viscosity suggested by the work of Vermorel and Dantony, or to a con-
centration of the materials at the leaf-spray interface, resulting in a
lowering of the interfacial tension as suggested by the experiments with
waxy leaves. A creosote solution with a surface tension of 49.27 dynes

SPREADING AND ADHERENCE OF ARSENICAL SPRAYS 21

failed to spread, as did also a soap solution of 38.36 dynes, while one
with a surface tension of 24.28 dynes gave good spreading. A solution
of gelatin of I part in 10,000 which will produce spreading had a surface
tension of 72 dynes. Casein in solution, alkaline to litmus, had a sur-
face tension of 64.4 dynes, while when acid to litmus the surface tension
was lowered to 57.74 dynes. These values were obtained by allowing
one minute for the drop to fall from the tip of the stalagmometer, and
therefore represent the dynamic rather than the static surface tension.
Since the spreading occurs on the leaf at once, it is apparent that the
results are not due to a low’surface tension.

Vermorel and Dantony (1912) explained similar results on the
basis of a very rapid surface concentration of the colloid resulting in
an increase in the surface viscosity so great that the film was prevented
from collecting in a drop. If such a rapid concentration occurred, it
should make itself manifest by its influence on the surface tension.
The number of drops produced from a given volume of liquid when
measured by allowing one second for each drop, compared with the
number obtained when one minute was allowed, should be a fair test
of the rapidity of the surface concentration which might occur on the
leaf surface quickly enough to make the surface so viscous that the
film could not collect in drops. Water measured at the rate of one
drop per second gave 45.5 drops while at the rate of one drop per
minute 46 drops were produced. Gelatin, I part in 10,000, gave 46
and 46.5 drops; while casein, 3 parts to 10,000, gave 46 and 52 drops
when alkaline to litmus and 50 and 58 drops when acid to litmus. This
increase does not appear sufficient to produce as high a surface viscosity
as Vermorel and Dantony considered possible. Harkins and Brown
(1918) found that the surface concentration is so slow in such solutions
that a half hour must be allowed each drop to insure the maximum
surface concentration and a true measurement of the static surface ten-
sion. Further, if the spreading is due to surface viscosity it should be
possible to produce the -film on any surface, but this can not be
accomplished.

Like material has been shown to attract like, and there is a strong
similarity between the colloids used and the cellulose and cutin of the
leaf surface. This similarity should cause a concentration in the sur-
face at the interface of the leaf and spray, thus reducing the interfacial
tension. On the cabbage leaf the contact is with the wax, different
in character from the proteins, and spreading is not obtained. Only
when the spray is delivered with sufficient force to drive the liquid
between the wax particles and bring it into contact with the epidermis
will results be obtained.

TECHNICAL BULEETING2

bo
bo

CONCLUSION REGARDING THE PHENOMENON OF
SPREADING

On the basis that substances of like nature attract each o her,
materials were selected which, while soluble in water, would be attracted
to the leaf surface and concentrate in the leaf-spray interface. Using
materials similar in character to the wax of the cabbage leaf produced
spreading but failed with leaves which did not possess the waxy coat-
ing. Protein and similar materials produced spreading on leaves with
a surface of cellulose or cutin but failed to give good spreading on
waxy leaves. It appears possible that an infusion of nearly any plan‘
would serve to give spreading to a spray for use on wax-free leaves,
but this statement requires confirmation.

The viscosity of some of the sprays was increased, but in the case
of carvacrol, beechwood creosote, and eugenol it was not materially
altered. Viscosity, therefore, is not related to spreading. Surface con-
centration appears not to take place rapidly enough to increase the
surface viscosity to such an extent as to prevent the film from collecting
into drops. The surface tension of the leaf was not altered and the
values for the surface tension of the liquids did not agree with the
results obtained in spreading. The reduction of the interfacial tension
appears to be the most reasonable explanation of the facts. Unfor-
tunately this surface tension has not yet been measured, nor has the
concentration of the material at the leaf-spray interface been dem-
onstrated. However, with this theory as a basis, sprays that will
spread on the different types of leaves may be produced.

HISTORICAL CONSIDERATION OF ADHERENCE
THE USE OF ORGANIC MATERIALS WITH FUNGICIDES

The adherence of spray materials was studied very early in the
history of spraying. In one of the earliest papers, Millardet and Davis
(1886) drew attention to the fact that cupric steatite powder possesses
remarkable adherence, owing to its extreme fineness. When it was
demonstrated that plant diseases might be controlled by means of
copper compounds, an effort was made to form on the leaf a coating
of copper which would adhere well and serve as a barrier to the fungus.
Crouzet (1899) recommended copper caseinate, prepared by adding
raw milk to a solution of copper sulphate, as a very adherent spray. .
Galloway (1891) used molasses and also glue to give adherence to a
mixture of copper sulphate and sodium carbonate. In the experiments
of Girard (1892), molasses actually diminished the adherence of
bordeaux mixture. Lavergne (1896) tested a “tannocuprique” spray,
possibly copper tannate, bordeaux and sugar, and bordeaux mixture

SPREADING AND ADHERENCE OF ARSENICAL SPRAYS 23

alone, for the control of black rot. Bordeaux mix‘ure applied six days
earlier than the other sprays gave the most satisfactory results.

'. Cazeneuve (1898) published a paper on albuminous bordeaux mix-

tures, the original of which is not available. Bourcart (1913) men-
tioned the use by Cazeneuve of three types of albuminous bordeaux,
one containing milk, one made with dried egg white, and one with dried
blood. The bordeaux casein did not adhere better than bordeaux and
sugar, but the other two types persisted on the foliage throughout
the season. Bourcart cited only the name, hence it is not certain that
he is referring to Cazeneuve (1898). Guillon and Guirand (1898)
tested the adherence of different preparations to glass slides. They
showed that the adherence of bordeaux mixture decreased with its age.
The addition of 1 per cent molasses or three-tenths per cent gelatin
increased adherence, while larger quantities decreased it. They also
used 3 per cent soap with 2 per cent copper sulphate, a combination
which must have resulted in the formation of a colloidal copper soap.
In a second paper published the same year they give results of studies
on the adherence of these materials to grape leaves. Bordeaux mixture
with 2 per cent soap showed the greatest adherence, while gelatin or
molasses gave poor results. Perraud (1898) studied the adherence to
the fruit rather than to the leaves of the vine. Starch, dextrine, egg
powder, and dried blood failed to increase the adherence of bordeaux
mixtures. Resin, soap, potassium silicate, molasses, gum tragacanth,
and glue increased the adherence in the order named. In a second
paper Perraud (1898) recommends the use of resin dissolved in boiling
sodium carbonate. This material was added when cool to copper sul-
phate to increase its adherence. Similar results were claimed for a
mixture of 2 per cent of copper sulphate and 3 per cent of soap. An
actual decrease in the adherence of bordeaux mixture due to the addi-
tion of turpentine was noted by Ravaz and Bonnet (1903). Resin
slightly increased the adherence, but the difference in both cases was
considered unimportant. In many of these investigations, the organic
material was added to give both adherence and spreading and many
workers believed that a spray which would spread would also adhere
better. Vermorel and Dantony (1913) clearly distinguished between
these two properties, pointing out that a spray may spread without
showing any remarkable adherence, while excellent adherence may
occur even if the spray does not spread well. Lafforgue (1913) also
distinguishes between spreading and adherence.

These papers represent the development of one method of making
fungicides adhere. In many cases the added material reacted with the
copper, forming such compounds as copper saccharate, copper stearate,
copper resinate, copper caseinate, and copper albuminate. Some of
these compounds, colloidal when freshly prepared, gave an increased

24 TECHNICAL BUIELE iN 2

adherence as a result of the fineness and insolubility of their particles.
The copper, being formed into a stable and insoluble compound, lost
much if not all of its fungicidal value. This fact coupled with the
physiological effects produced by coating the leaves with an insoluble
preparation similar to varnish, resulted in the discontinuance to a ee
large extent of the use of such materials.

THE USE OF ORGANIC MATERIALS WITH INSECTICIDES

In early experiments with arsenic preparations for the control of
insect pests, investigators feared that the material might adhere too
long. Spraying for the gypsy moth developed the use of lead arsenate,
a slow-acting poison which could be applied in large quantities without
injury to the foliage. Because of its low toxicity, it was necessary
that it should adhere for a longer period. Fernald (1894) stated that
it is highly desirable to add 2 quarts of glucose or molasses to each 150
gallons of water to increase the adherence. The idea of using glucose
to cause adherence was possibly the result of the use of sugar with
fungicides, but lead arsenate gave no reaction with glucose. Lowe
(1896) pointed out that the use of glucose did not increase the adher-
ence of lead arsenate but that glue at the rate of 2 quarts to 45 gallons
gave satisfactory results. Kirkland (1898) showed clearly by means
of general observation, chemical analysis, and physiological tests on
caterpillars, that the addition of glucose did not increase the adherence
of lead arsenate. The glucose was washed off the leaves by the first
shower.

Washburn (1891) found that the addition of whale oil or soft soap
to the spray increased the adherence of paris green, probably because
of its more even distribution. A finely divided solid is more adherent,
but Marlatt (1897) showed that paris green when very finely pulverized
was more injurious to the foliage. Sirrine (1898) recommended the
use of a resin-lime mixture to cause paris green and bordeaux mixture
to adhere to the leaves of cabbage and cauliflower. This mixture 1s
really a resinate of lime prepared by making a stock solution of resin,
fish oil, and lye, to which, after proper dilution, the lime and paris
green are added. The paris green adheres to the particles of the
calcium resinate and these in turn adhere to the leaves. Volck (1913)
used flour paste made of 4 pounds of wheat flour to 100 gallons of
water to increase the adherence of sulphur. Larger quantities of flour
caused the dry film to scale off, while smaller quantities were insufficient
to “stick” the sulphur.

Surface (1905) lists the materials used to increase adherence.
These are resin-lime mixture, ee resin added to kerosene and used
in kerosene emulsion, molasses, glue, flour, and salt when used with

SPREADING AND. ADHERENCE OF ARSENICAL SPRA eS 25

lime sulphur. The use of salt is now generally recognized as having
no influence on the adherence of lime-sulphur sprays.

Paste lead arsenate was shown by Astruc, Couvergue, and Mahoux
(1911) to be more adherent than a freshly prepared suspension of dry
lead arsenate. The age of the diluted spray did not appear greatly to
influence its adherence.

Parker (1913) pointed out the possibility of using flour paste with
lead arsenate to increase the adherence as well as to produce spreading.

A new method of rendering arsenical materials rainproof or more
adherent is given in U. S. Patent No. 1166387. The arsenical substance
is coated with an insoluble metallic soap, copper stearate in the case of
paris green and lead stearate in the case of lead arsenate. These
products were marketed for a few years by the International Color
Company, generally as a dry powder for dusting purposes, altho they
also manufactured a paste form for general spraying.

Lees (1915), interested in lime preparations as cover washes for
trees in late winter and early spring, tried to increase the adherence by
the addition of various substances. Glue, flour, and farina (potato
flour) gave good results. The best results were obtained with a mix-
ture of whiting, starch, glue, and potassium bichromate. In a second
paper (1916) he modified the formula, leaving out the starch. The
potassium bichromate was added to the mixture because on exposure
to light it reacts with glue, rendering it insoluble.

O’Kane, Hadley, and Osgood (1917), in a study of the arsenic
retained by fruit after spraying with lead arsenate, give some data as
to the actual adherence of lead arsenate. Altho not directly concerned
with adherence, the percentage of arsenious oxide was determined on
fruit picked from three to five days after spraying and before a rain
had occurred. The fruit on other trees was not picked until much
later, thus giving data for a comparison of adherence. Fruit picked so
carefully that none of the lead arsenate was rubbed off, showed an
average of 0.37 milligram of arsenious oxide per apple, from three to
five days after spraying and before rain occurred. An average for
twenty-five apples, selected as showing the maximum amount of lead
arsenate, was 0.77 milligram per apple. Fruit from other trees sprayed
at the same time but picked seventy-five days later had 0.08 milligram
and those picked after seventy-six days later had 0.11 milligram
per apple. These trees were subjected to a total rainfall of 5.01 inches
The average amount of arsenious oxide present on the fruit was 25.6
per cent. Fruit sheltered by the leaves would no doubt show a much
higher percentage of arsenic than would normally be the case.

Gray (1918) found that the addition of glue to sulphur increased
its adherence. The fact that dry lead arsenate was not so adherent
as lead arsenate paste and also that the addition of molasses or sugar

26 TECHNICAL BULELE RING?

reduced the adherence, was confirmed by the experiments of Hartzell
(1918). Stearns (1920) showed that the addition of Irish rock moss
or calcium caseinate to the spray increased its adherence. Lovett
(1920) considers that in general those substances which increase the
spreading of a spray will also increase the adherence of the spray
material.

THE USE OF INORGANIC SUBSTANCES

The fact that certain inorganic substances adhere to the leaves
better than do others was early noted. This fact led to the use of
certain inorganic materials to increase the adherence of the spray
materials. Compounds of chromium, aluminum, and more particularly
iron, have been tried. Kilgore (1911) combined london purple and
paris green with ferrous sulphate and ferric chloride, but the mixture
was not a success. Arsenious oxide combined with ferrous sulphate
or ferric chloride gave a rather soluble mixture which proved injurious
to the foliage. In these experiments adherence was not sought but
rather a combined insecticide and fungicide. Girard (1892) added
aluminum sulphate to bordeaux mixture to produce a greater adherence.
The use of aluminum sulphate suggested itself to Girard because of
its mordant character, but the results were not satisfactory. Fairchild
(1894) noted the remarkable adherence of ferrous ferrocyanide. This
led to experiments with iron borate, ferric hydrate, and iron sulphide
but no such remarkable adherence was noted. Smith (1907) tested
an iron arsenate said to be a by-product in the preparation of ore. It
contained 45 per cent of arsenious oxide. Used at the rate of 1.25
pounds to too gallons it killed the larvae of the elm leaf beetle without
injury to the foliage. The plants were sprayed July 17 and on the
18th a heavy rain occurred and another lighter rain on the 2oth. Little
trace of the material was found on the 22d. Selby (1908) proposed
a modified formula for bordeaux mixture in which the amount of
copper sulphate was reduced and a large quantity of iron sulphate was
added to serve the purposes of a “sticker.” The formula was

Copper sulphate sha ces pup eianetemet inet area 2 pounds
Tron) isulphate wees coer aca eile pe riteeiee e 4 pounds
Omicldlime Jessi seme ee ee ocean eee eee 6 pounds

Water to make 50 gallons.

The spray was rust colored and showed great adherence. He
considered that the iron sulphate (probably ferrous) was precipitated
by the lime in the form of iron hydroxide. Pickering (1907), how-
ever, has shown that the reaction of ferrous sulphate and lime forms
a precipitate of a basic iron sulphate, evidently of the formula Io
FeO.SO,. Volck (1909) prepared an iron sulphide spray by adding
ferrous sulphate to lime-sulphur solution. The addition of 20 pounds
of iron sulphate to 200 gallons of lime-sulphur spray mixture gave a

SPREADING AND ADHERENCE OF-ARSENICAL SPRAYS 27

black muddy precipitate of sulphur, iron sulphide, and calcium sulphate.
This spray proved very effective for powdery mildew of apple.

A definite ferrous arsenate was prepared by Vermorel and Dantony
(1909). A solution of 4oo grams of ferrous sulphate in 1o liters of
water was added and stirred into a solution of 400 grams of sodium
arsenate in Io liters of water, until a test paper impregnated with po-
tassium ferro- and ferricyanide became a clear‘ blue color. Diluting
this mixture to 100 liters, it contained 200 grams of ferrous arsenate to
the hectoliter. On exposure to the air, as in spraying, the ferrous
arsenate forms ferroso ferric arsenate and the ferrous hydrate becomes
ferric hydroxide. It is pointed out that ferric hydroxide is an antidote
for arsenic poisoning, which fact may explain why very large amounts
of this preparation were not injurious to the foliage of plants. Vines
were not injured by a proportion of 500 grams to a hectoliter; while
pears, apples, and prunes were not injured by a spray containing 2
parts in 100. Used at the rate of 100 to 200 grams to 1 hectoliter,
ferrous arsenate successfully controlled the codling moth, Carpocapsa
pomonella, in experiments extending over three years. Vermorel and
Dantony (1909), in another paper, point out that ferrous arsenate can
not be successfully combined with bordeaux mixture because of the
formation of cupric arsenate, which is injurious to the foliage. They
also say that ferrous arsenate alone shows great adherence, but that
this adherence is reduced if glucose or molasses is added to the spray.
Dalmasso (1910) used ferrous arsenate prepared according to the
formula of Vermorel and Dantony for grape spraying in Italy,
finding it not quite so effective as lead arsenate. No particular adherent
properties are recorded. In America, Smith (1910) used a similar
ferrous arsenate, successfully controlling the potato beetle and the elm
leaf beetle. No special mention is made of the adherence. About
this time several insecticide manufacturers put ferrous arsenate on the
market in the United States. One of these, analyzed by Bradley
(1910), showed 84.25 per cent of water, only 7.37 per cent of arsenic
oxide, and 5.51 per cent of ferrous oxide. The dry ferrous arsenate
contains from 50 to 55 per cent of arsenic oxide and from 4o to 45
per cent of ferrous oxide. Melander (1911) tested both home-made
and commercial ferrous arsenate for the control of the codling moth.
One pound to 125 gallons of water was used, the trees having 0.37 per
cent of wormy apples compared with 0.16 per cent for those sprayed
with lead arsenate, and 21 per cent for unsprayed trees. Melander
said that ferrous arsenate may be successfully combined with lime
sulphur. Scott. and Siegler (1915) tested ferrous arsenate in both
laboratory and field experiments. It was found to be a slow-acting
poison requiring fairly large doses to insure success. On the other
hand, it was considered a safe arsenical substance for use on sensitive

28 TECHNICAL BULLETIN 2

plants, even 2 pounds of chemically pure ferrous arsenate to 50 gal-
lons of water being used on beans and peach without injury. High
(1915) considered ferrous arsenate a very desirable spray, since it
remains in suspension for long periods and shows no injury on delicate
foliage. Ferrous arsenite did not show these desirable qualities. Fer-
rous arsenate was successfully combined with the cactus extract used
for spreading.

Howe (1910) tested the iron sulphate-bordeaux mixture recom-
mended by Selby (1908), finding it a less effective fungicide than
standard bordeaux mixture, but more adherent and less injurious to the
foliage. Waite (1910) used two fungicides containing iron sulphate ;
One a 3-3-50 bordeaux with 2 pounds of iron sulphate, and the other
self-boiled lime sulphur plus 3 pounds of iron sulphate. It was
observed that iron sulphide spray adhered so strongly as to give the
plants a brownish appearance which did not wear off until picking
time. It increased the greenness of the foliage and fruit to such an
extent that the fruit was late in ripening. Ballard and Volck (1914)
pointed out that the chief value of iron sulphide spray as a fungicide
is due to the presence of precipitated sulphur, no claim being made of
superior adherence. Stewart (1915) mentions the addition of iron
sulphate to lime sulphur to reduce the injury to the plants and to
increase the “sticking’’ quality of the spray. Lees (1915) used alum-
inum sulphate, iron sulphate, and potassium bichromate with lime to
increase its resistance to rain. Aluminum sulphate was introduced
because of the gelatinous character of precipitated aluminum hydroxide.
In some cases fair results were obtained but they were not equal to
those obtained by the use of organic materials such as glue and flour,

and hence are not recommended.
In recent years in a few places in the United States a rain-proof

arsenical material has been placed on the market. This preparation
contains chromium and arsenic, possibly a chromium arsenate, and when
mixed with water forms a bluish-green suspensoid. Great adherence
is claimed for this product by the manufacturers.

Summarizing the review of the literature it is found that in general
a finely divided material will adhere better than a coarse material. The
use of organic materials to cause spreading of the spray will increase
the adherence, apparently owing in part at least to the more even dis-
tribution of the material over the leaf surface. Some investigators have
found the use of certain inorganic salts or elements, particularly iron,
greatly to increase the adherence of the spray material, while others
have failed to obtain these results.

SPREADING AND ADHERENCE OF ARSENICAL SPRAYS 29

A NEW THEORY OF ADHERENCE

A survey of the literature fails to show any definite theory or any
attempt to explain why the adherence of one material to the leaf
surface is superior to that of another. It appeared necessary as a point
of departure to obtain some idea as to the causes of adherence between
different substances. One of the best examples of adherence suggested
was that existing between the particles of two oppositely charged
colloids. If a colloid exhibiting a negative electric charge is added in
the proper proportions to one possessing a positive electric charge, the
particles are attracted to each other, forming masses which separate
out as a precipitate. An example is the precipitation of a negative
arsenious sulphide sol, a colloidal solution, by a positive ferric oxide
sol. The colloidal particles of arsenious sulphide adhere strongly
to those of ferric oxide. Suspensoids of dye substances also exhibit
either positive or negative electric charges, and when two oppositely
charged sols are mixed in the proper proportions, a precipitate is formed
without any chemical reaction taking place. The question arises as
to whether solids when not of colloidal dimensions possess such electric
charges. Glass ground to colloidal dimensions exhibits a negative elec-
tric charge, and if added to a positive sol in the proper proportions will
produce a precipitate. A glass beaker should therefore be negative
if it possesses an electric charge. A positive sol placed in a clean glass
container will have some of its colloidal particles deposited upon the
glass and these adhere so thoroly that they can be removed only
by acid. Another example is that of filter paper dipped into a positive
sol such as methyl violet. It will be observed that altho the water rises
on the filter paper the dye particles do not extend above the surface of
the liquid. This is due to their precipitation on contact with the negative
filter paper. The paper can be placed in running water and the dye
particles will not be washed away. On the other hand, if the paper
is placed in a negative indigo sol, the dye rises with the water far above
the surface of the liquid and is readily removed by washing in running
water.

King (1917), after a general review of all the theories of dyeing,
reached the conclusion that the reaction between the fabric having one
electric charge and a dye oppositely charged furnished the best expla-
nation of the results obtained in the dye industry. The various nega-
tively charged fabrics are easily dyed by positive dyes; but if a
negative dye is to be used, the cloth must be rendered positive by means
of a mordant. The mordant is positive and precipitates itself on the
negative surface until a new surface with a positive charge is produced.

he negative dye will then readily color the cloth. The mordant
may be added to the dye in such quantity that the sol becomes positive,
when it will give the desired results.

30 TECHNICAL BULLETING 2

If these electric forces are of sufficient magnitude to cause a dye
to adhere to a fabric and withstand numerous washings, then if similar
electric charges exist on the leaf and the arsenical materials, they could
be u‘ilized to increase the adherence of the spray materials. The first
question is, do the leaf and the common arsenical materials in use at
present possess electric charges, and, if so, are they the same or opposite
in character?

Apparatus Used in Determining the Migration of Particles in the Electric Field

A, electrodes; B, zinc sulphate solution; C and D, tap water; E, suspension to be tested.

ELECTRIC CHARGE EXHIBITED BY COMMON ARSENICAL
PREPARATIONS

Methods of testing the charge on the common arsenical preparations
found on the market were considered. The first method taken up was
the study of the precipitation of sols of known electric charge by suspen-
sions of various arsenites and arsenates. This method, however, may
give erroneous results, owing to chemical reactions between the various
constituents or to the mutual adsorption of particles with like electric
charges. The only method considered free from such objections is the
determination of the migration of the particles in the electric field.
Sols of the common arsenical materials were prepared by reducing the
particles to colloidal dimensions by grinding them with water in an
agate mortar. A sol to be tested was placed in a U-tube as shown
in the drawing. The stop cocks were closed and the upper end of
each arm was washed out and filled with tap water. The tube was then
clamped into position and connected with tubes of zinc sulphate, con-
taining the electrodes, by means of small pieces of glass tubing filled
with tap water. The level of the liquids was adjusted by connecting

SPREADING AND ADHERENCE OF ARSENICAL SPRAYS 31

the zinc sulphate containers by means of another piece of tubing contain-
ing water. When the level had been established this piece of tubing
was removed, the stop cocks were carefully opened, and the current was
turned on. It was found possible to use a 220-volt direct current with-
out the introduction of any resistance apparatus. Within half an hour
the position of the suspensoid, indicated by its milky or opalescent
appearance, was altered by the migration of the particles toward the
oppositely charged electrode. Since all these materials carried negative
charges, they migrated toward the positive electrode, the level of the
suspensoid being raised in the positive arm of the tube and lowered in
the negative arm. The rate of migration was faster on one side because
of the pull of gravity on the particles, while the rate was retarded on
the other side. In each case the position of the electrodes was changed
and the direction of migration reversed. Lead arsenate, paris green,
zine arsenite, tri calcium arsenate, and magnesium arsenate were all
found to be negative. The addition of calcium hydroxide did not alter
the negative charge of calcium arsenate. Which arsenical substance
possesses the strongest charge could not be determined by the experi-
ment, since the rate of migration is governed not only by the magnitude
of the charge but also by the size of the particles. The rain-proof
colloidal preparation containing chromium and arsenic, previously men-
tioned, was tested, but no definite migration occurred even in two
hours’ time. This electric neutrality may be due to the presence of
dextrin, which acts as a protective colloid.

PREC Ric ChAnRGE EXHIBLIED BY THE LEAF SURFACE

Having definitely proved by cataphoresis that the common arsenical
preparations possess, when wet, an electric charge negative in character,
the next question was the demonstration of an electric charge on the
leaf surface. Empirically, the leaf should be negative, since filter paper
made of cellulose is negative. Cotton, a plant product, is also negative.
Stains, which give good results with leaf tissues, either are positive
or are prepared with aluminum compounds so that the finished stain is
positive. The epidermis of a plant stained with eosin, which is nega-
tively charged, readily washes out in water; while Delafield’s Haema-
toxylin, prepared so that it undoubtedly is positive, is not removed by
washing. These statements, however, do not furnish positive proof of
the negative character of the leaf. The possibility of determining the
charge on the leaf by migration of its particles, after grinding in water,
was discarded, because such a test would merely show that the cellulose
and proteins of the leaf tissue are negative.

If gelatin in the form of a sol is placed in the electric field, the
particles of gelatin migrate toward the electrode opposite in character
to the charge carried by the gelatin particles. If a concentrated sol

32 TECHNICAL BUGLE TiN <2

of gelatin is placed in the bottom of the U-tube and allowed to set to
a gel, thus forming a semi-solid barrier, the passage of a current of
electricity across the field will no longer be accompanied by a migration
of gelatin particles. Under these conditions a flow of water will take
place through the gelatin toward the pole with the same sign as the
charge carried by the gelatin. The flow of water may be explained
by the fact that when a solid takes on a certain electric charge, the
water at its surface assumes the opposite sign. This phenomenon,
known as electric endosmosis, is well known and is utilized in several
industrial processes.

If water could be made to migrate across a leaf surface or through
a leaf by endosmosis, it would give positive proof of the presence of an
electric charge on the leaf surface. After several unsuccessful attempts
the following method gave good results. A bean leaf was bound tightly
over one end of a glass tube and the tube partially filled with water.
It was then clamped into’ positicn with the leaf end immersed in a
beaker of water. One electrode was inserted into the tube and the
other was placed near the leaf in the beaker. When the current was
turned on, the water passed through the leaf, moving in the direction of
the negative electrode. Changing the position of the electrodes changes
the movement of the water, about half a cubic centimeter passing
through the leaf in half an hour. A few minute holes having been
pricked in the upper epidermis of a citrus leaf, it was arranged in a
similar manner, and the results obtained were even better, since more
than a cubic centimeter of water was transferred in half an hour. The
better results appeared to be due to the tougher texture of the citrus
leaf, which made possible a tighter union with the tube. These experi-
ments show that the leaf surface, when wet, exhibits a negative electric
charge.

PREPARATION OF AN ERE CTRICALEY POs
ARSENICAL SUBSTANCE

Having shown that the arsenates and arsenites in use at the present
time are electrically negative in character and that the leaf surface shows
a similar negative charge, the question is presented as.to how a positive
material may be prepared. Most solids ionize in such a manner that
they become negative, and of those which are positive and might be
utilized in sprays, only three can be considered.* Sols of aluminum,
chromium, and iron oxides show the desired positive charge. Of these
aluminum and iron appeared the most promising. Two methods of

5 Besides the three mentioned in this paper, positive arsenicals of lead, zinc, calcium,

magnesium, copper, and barium have been made and a patent has been granted on these
products.

SPREADING AND ADHERENCE OF ARSENICAL SPRAYS 33

their utilization were suggested: (1) spraying the leaves with the posi-
tive material, followed by the application of the negative arsenical ma-
terial; and (2) the addition of sufficient positive material to the arsen-
ical suspension to make the whole mixture positive in character. The
first method is impractical, as it would require two sprayings of the
plant. Aluminum hydroxide was precipitated by adding ammonium
hydroxide to aluminum chloride, care being taker that not all of the
chloride was converted into the hydroxide. A precipitate of aluminum
hydroxide is readily peptized by aluminum chloride forming a positive
sol. By filtering the precipitate, but not washing it, enough chloride
remained to make the material electrically positive. In a preliminary
test, a quantity of this aluminum hydroxide was mixed with lead
arsenate and sprayed on young citrus trees in the greenhouse. To
serve as a check, similar trees were sprayed with lead arsenate alone.
After drying, some of the plants from each set were washed by a strong
stream of water from a hose for five hours. A macroscopic examina-
tion showed practically none of the spray material on the leaves sprayed
with the lead arsenate alone, while the leaves of those sprayed with the
lead arsenate—aluminum hydroxide mixture were similar in appearance
to the check plants which had not been washed. Similar results were
obtained by addition of ferric hydroxide to lead arsenate. The substi-
tution of geranium plants for citrus trees gave comparable results.

It would be difficult to make an estimate of the exact quantity neces-
sary to give the desired results. The reactions taking place are more
easily demonstrated by two colloids possessing opposite electric charges.
An illustration would be the reaction of a negative sol of arsenious
sulphide with a positive sol of ferric oxide. One particle of the ferric
oxide carrying three positive charges would tend to neutralize the
charges of three arsenious sulphide particles, since these carry only
one negative charge. When a quantity of the ferric sol is added to an
arsenious sulphide sol in such proportions that all the negative charges
are not neutralized, no precipitation occurs and the mixture is negative.
If the number of positive and negative charges is equal or nearly equal,
the mixture produces electric neutrality and a precipitate is formed.
If enough ferric oxide is added to produce an excess of positive charges,
the mixture remains clear and is positive in character. This latter con-
dition is the one sought when aluminum hydroxide or ferric hydroxide
is added to lead arsenate to increase its adherence.

Owing to these difficulties, an effort was made to prepare an arsenical
substance which would itself be positive. Grimaux (1884) showed
that the precipitate formed when ferric chloride is added to sodium ar-
senate or sodium arsenite may be peptized, forming a sol which on
dialysis gave a basic ferric arsenate, Fe, (AsO,). Recently, Holmes

34 TECHNICAL BULLETIN 2

and Rindfusz (1911), Holmes and Arnold (1918), and Holmes and
Fall (1919) have studied the preparation of ferric arsenate sols and
gels. It is possible to prepare similar preparations of aluminum and
chromium. In none of these papers is there any mention of the char-
acter of the electric charge carried by the particles of the ferric, alum-
inum, or chromium arsenate. Sols of ferric arsenate and arsenite,
aluminum arsenate and arsenite, and chromium arsenate prepared in a
similar manner were found to be electrically positive. Ferric arsenate
precipitated by adding go parts of a one-fifth molar solution of sodium
arsenate to 100 parts of a one-fifth molar solution of ferric chloride
was centrifuged, washed, and the paste dried. This material, ground
to colloidal dimensions, showed a migration of the particles toward the
negative poles, demonstrating that they carry a positive electric charge.
Aluminum arsenate similarly prepared showed a slight migration toward
the negative pole. These and several other arsenical materials were
used in a field test of adherence.

FIELD-TEST SOF ADHERENCE

The test of the adherence of different preparations was made on
potato plants. The potatoes were in an open field exposed to wind,
dew, and rain. During heavy showers, soil was splashed over the plan‘s
and washed off again, actually tending to scour the leaves. In the
cultivation of the plants, soil was frequently thrown over the leaves,
thus tending to remove the spray materials.

The following preparations were used in the proportions given, the
amount of each material being figured on a dry basis.

TABLE I
Pounds to Gallons

ead warsenate® powder amt crete ot pert roiern ames Catce he SCS aT ee ae ee 1.5 50
Galcium* arsenate) powder scyisrccce cats ties wel ere a eee En Gee 15 50
ZANC mALSEHIEEG SNOW CEL =, starcerorc merece eat haere casieseme tel he SheP A inA Se S 1.5 50
Magnesium tarsenate spowder nica. crasr want nee coe ae ee CE Te5 50
Paris p SreEne POW MEL isons wratso sisted Ae sre praise wale ORE ee eee 1.5 50
Lead arsenate powder, 1.5 lbs. + ferric hydroxide paste, 0.4 Ib. (dry

uta) ly earn eA ori Oe TOM OrOe he oho GSC LOGoC eat ams ohonece 50
BErric 'ArSenateMpaste » s\2rckevel ajo isieidisy cle te\sureco eS Dee ae eee oe ee 2.0 50
Bernice parsenibe! {paste ciercie sb. cjae ofavencun cockatiels ieveteraeie soca ay eT a Te ee 2.0 50
Mernous: arsenater Paste Acsiemasmic ee stoi mio ee Oe ne AOS es 2.0 50
Aluminium “arsenate pastes icici ide eee chet oe ee ner eee eee 1.0 50

The materials were applied to one or two rows of potatoes and
several rows throughout the plot were left unsprayed to serve as checks.
When the sprayed plants were dry, ten representative leaves were col-
lected from each set to be analyzed for arsenic. There was no rain for
six days after the sprays were applied and then only 0.06 inch fell,
hence all the compounds had an excellent opportunity to destroy the
potato beetle larvae. Nine days after spraying the check plants were
completely stripped of leaves and a count of larvae on the sprayed
plants gave the results shown in Table II.

SPREADING AND ADHERENCE OF ARSENICAL SPRAYS 35

TABLE II

Average

per plant
LEDE]” GRRAMNTD ES ReaD ies ance ae =e ac ne ee Ae 2a3
Orit CLUES SIA EC ey MRM EAST AT C0 SS pah a iatou cans ah gavel al sR ats Noman leds RNa tee ee ed 0.7
UCM IS CLLU COL Me ct ae RIC TR ty Meyectctee rie: Pvothec Shay Alclave a: crigrs.se\arlare rel aoa le ancteVOn eee IEE CRS ee Bt ae 0.4
MIO Mes IEE AL SEH AUG ie! clsineieie cae éreiciee as niche cielsit ee oe RASS Goinriootrottncnak optoce.t 0.3
IE ZyAIS) GRASS 5 Gee Bia. prota ghee SABIE Cee Oo ERE Rone ae aI Ie a are Becker ee I 1.0

Werdgarsenare.=— ferric HY ATORIGEs eet. 2,0 'c.06 ciel < eic.e c cicn aden aalee Sen ave Padua tobatencrere over 9.6

IPGiPGD ERAREINEIGSS GU Gs Suaeachcls OEICRCIC SCENE EIA TER RE eR naa Leola PO ek Sn RA La IE 2.4

Beis U ot auehan ele) eii¢ihene'la ies 10) jake; (waite) si/myiavie: s¥iee\'s.9\ isceliw \e/ie aie apelie fejtareie: sy shale isl este Kanmleliayict nis velisi (ellis 0.2
Ear SEMA C pet ie gmat atates ate te techs; chine 2io io fe ave yd uss so biaie we avaes ee tebeenpel an comet cee eater ee aero 1.6

=Ungey Mist alietsl. a *alleiteVeira\eyn\e\e 0, loljste!e:s)>,/e)is'(a) ai 8[-e.-eheiw ape \elalecie: abn, efi toleeserelsl spahearcie chee 2-1

Some of these averages are high, owing to the proximity of check
rows where the larvae, having stripped the plants, were migrating to
adjacent rows. A count on part of. the lead arsenate row next to a
check row showed an average of four larvae per plant, while that part
not adjoining the check row had an average of one larva per plant.
This condition existed in the rows sprayed with ferric arsenate, ferrous
arsenate, and aluminum arsenate, but not in the row treated with lead
arsenate—ferric hydroxide mixture.

In. the preparation of the lead arsenate-ferric hydroxide mixture
there was a decided tendency for the particles to form masses which
were extremely difficult to hold in suspension. The first six plants in
the row obtained a very heavy dose of the spray materials while the
rest of the row received very little. For this reason in the analysis of
the plants, the first six plants in this set were kept separate from the
others. In the analysis of the plant material for arsenic, the organic
material was oxidized by boiling with nitric and sulphuric acids. The
arsenic was determined by the Gutzeit method (Scott, 1917). The
leaves of the plants, taken immediately after the spray had dried, repre-
sented 100 per cent of the spray material. Other determinations were
made on leaves collected seven, eleven, and seventeen days after spray-
ing, the average amount per leaf in terms of arsenious oxide being
recorded in Table III. In this table is also given a record of the
rainfall during this period.

Reviewing the field test, a relationship between the adherence and
the electric charge is quite apparent. Lead arsenate, which adhered
best of those possessing a negative electric charge, showed only 6.6 per
cent at the close of the experiment. Aluminum arsenate tested in the
electric field was only very slightly positive, since only a slight migra-
tion of the particles occurred. Ferrous arsenate was negative, but on
the plant decomposition would produce ferric arsenate and ferric
hydroxide according to Vermorel and Dantony (1909). The decom-
posed material would then no doubt be positive. No definite data are
available concerning the charge possessed by particles of the lead
arsenate-ferric hydroxide mixture, but it was mixed in proportions

36 PECH NICAL BULLER IN <2

which should form a positive material. Ferric arsenate was considered
the most promising of the entire set, but its use requires further
investigation.

TABLE III
| Per Per | Pens
| After | cent cent | cent | Total
| spray-| 6 7a On DON | ee TE of 16 | 17 of rain-
| ing | days | days | total | days | days total | days | days | total | fall
Mg. Mg. | | Mg. | | Mg.
Lead arsenate. .....:-. I VOEzS dee 0.10 | 40.0 pretey |LOS2ZOOu| 2080 amie |LOL05 0 | 6.6
Calcium arsenate..... 1.00 et OSLO OLO) vee 0.05G) 5.0 Sa OOO SKON ||) Selo)
ZAC) ALSemIcemeretertaehe= 1.40 0:35 || 25:0 Ses ORNS 8.9 Se lioKovras |e Gast
Magnesium arsenate... was, sain || eons |) BAX) eee | 0.075-| 6.0 | 0.025 | 2.0
Panis Seen tel aeaieerrs 1.60 Ser OStON| Ns Sone Mier |(KOLOus 4.6 | | 0.025] 1.5
Lead arsenate + fer- | |
ric hydroxide |

inst 6) platatsrr ri. ery Ni toc || aaah || "A@kOal|! noe bts ines | ad 1.400 | 17.5

Other plants...... | 0.65 BeeaO220 | ezoe7 Ni meee aul 0.100 | Ne Bae 0.100 | 15.3
Ferric arsenate....... mere Ih, Goo |, CNG) ROLE ...|0.400| 33.3| ... | 0.200] 16.6
Eerric arsenite.....-.. 2.40 | «+. | 0.75] 31-2 |... |"0.600))| 25-0))/) F.. /O-400 | 12.5
Ferrous arsenate...... | 2.80 eo lle teers | 44.6 | tsetse 0.750 20ST AN ekerseg O23 50 | 12.5
Aluminum arsenate... | 0.75 Healosnsa|" azoronll| (eee | 0.075 | 10.0| ... | 0.075 | 10.0 erate

In. | In. Genta es) | Baty In.

IRewrapielll SA sosodeonges ae 0.06) 0.03 | 0.80 hate. se sey |) 22h | Rome Bel sey?

* This record represents one severe storm.

The poor adherence of calcium arsenate is of particular interest.
Graham (1918) found it to adhere better than lead arsenate, while
Wilson (1919) also considered it equal in adherence to lead arsenate.
Graham’s tests were conducted in the greenhouse and hard water was
used to wash off the arsenical materials. Owing to the presence of the
common calcium ion, the presence of calcium carbonate in the tap water
would reduce the solubility and the rate of decomposition of the calcium
arsenate. Wilson applied the calcium arsenate with lime and a similar
effect was obtained. In these experiments, the calcium arsenate was
used alone, and apparently rapidly dissolved, decomposed, and disap-
peared from the leaves.

PREPARATION OF POSITIVELY CHARGED FERRIC
ARSE MA is

In further investigations with ferric arsenate it was found that it
did not always possess a positive electric charge, in fact it was often
neutral or even negative. An effort was made to discover under what
conditions the best material could be prepared. Grimaux (1894)
considered the first precipitate formed by the addition of sodium
arsenate to ferric chloride as represented by the formula (AsO,H),Fe,.
When this material was peptized by ferric chloride, a reaction was
obtained represented by the following equation:

SPREADING AND ADHERENCE OF ARSENICAL SPRAYS Sv

2(AsO,H),Fe,+Fe,Cl,=3 (AsO,H), Fe,Cl,

Upon dialyzing this sol a basic compound of ferric arsenate was
retained by the membrane while hydrochloric acid passed through.
Holmes and Arnold (1918) noted that the appearance of the gel
obtained on dialysis depended upon the proportion of ferric chloride
used in the peptization of the ferric arsenate precipitate. If a large quan-
tity was used the gel obtained was reddish or reddish-brown, while if
only a small quantity was used the gel was a dirty yellowish color. A
study of these materials and the character of the charge carried by
their particles should throw light upon the problem,

Three different sols were prepared, the first, which will be referred
to as the 50-45, was made by adding slowly to 50 cubic centimeters
of a one-fifth molar solution of ferric chloride, 45 cubic centimeters
of a one-fifth molar solution of disodium arsenate, the precipitate being
peptized as rapidly as it formed. The second was similarly prepared,
but only 35 cubic centimeters of the arsenate was added, while 25 cubic
centimeters was added to the third. These were known as the 50-35
and the 50-25 sols. The 50-45 sol was light yellow with greenish tints
and somewhat clouded. The 50-35 and 50-25 sols were perfectly clear
and of a deep yellow: color with greenish tints. The three different
sols were dialized in separate containers by means of collodion sacs.
Only distilled water was used and all the wash water was saved for
analysis. Having determined the amount of Cl, AsO,, and Fe present
in the original sols, a fairly accurate knowledge of the composition of
the gel was obtained by the analysis of the wash water.

Hydrogen sulphide was first passed through the solution to
remove the arsenic. This required considerable time to insure its com-
plete removal. The arsenious sulphide was filtered off, redissolved,
and the quantity of arsenic finally determined by iodine titration. The
filtrate was made up to 1,000 cubic centimeters and a portion used for
the determination of the ferrous iron by titration with potassium
permanganate. The chlorine was titrated with silver nitrate, using
potassium chromate as an indicator. Considerable difficulty was ex-
perienced with this method since the indicator did not indicate the end
point, more chlorine being found than had existed in the original sol.
A double titration method using an excess of silver nitrate and then
determining this excess by titration with ammonium thiocyanate using
ferric sulphate as an indicator gave better results. The three different
sols may be represented by the following equations based upon the
results of the analyses.

38 TECHNICAL BUBEE TiN ss

50-25 Sol
Cl }
50 FeClg+25 NasH(AsOy-+XHeO=Fe-Fe(AsO,) +Cl \ Fe-Fe(AsO,) +25 HCl+5o0NaCl
Cl
Fe.=0.60256 g. : Fe=0.1344 g. J
@ll=1-0476<2: AsO4=0.1530 g. Fe=0.46816 g.
AsOy=0.7006 g. (Colloid) AsOs=0.5476 g.
Cl==1.0415 “2.
(Passed through membrane
crystalloid)
50-35 Sol
Cl}
50 FeCl,+35 NasH(AsOy+XHsO=Fe-X FeAsO, +Cl | Fe-FeAsOu+ 35 HCl+70 Na€l
Gl
Fe=0.60256 g. Fe=0.22624 g. roa g.
Cl=1.0476 g. AsOs=0.50064 g. AsOg=0.4802 g.
AsO,=0.98084 g. (Colloid) Cl=70437/"2:
(Crystalloid)
50-45 Sol
Cl
50 FeClz=45 NasH(AsOy) +XH20=Fe-XFeAsO, get eels HCl+90 NaCl
Gl
Fe=0.60256 g. Fe=0.56566 g. Fe=0.0369 g.
Gi=1-0476) 2 AsO.,=1.20703 g. AsOy=0.05405 g.
AsO,=1.26108 g. (Colloid) Cl=s203143) ie.

(Crystalloid)

From these equations it appears that there is a compound of ferric
arsenate and ferric chloride formed which is capable of passing through
a dialyzing membrane.® The proportions in all three cases show that
this compound is made up of one molecule of ferric chloride and one
of ferric arsenate, Cl,Fe Fe (AsO,). The proportions of ferric arsen-
ate of iron in the colloid, however, vary. In the 50-25 it apparently may
be represented by the formula Fe FeAsO,, while in the other gels a
larger quantity of ferric arsenate is present and the formula may be.
represented by Fe X Fe (AsO,).. The 50-25 formula appears to be
ferric oxide with an adsorbed molecule of ferric arsenate. The 50-35
and 50-45 may contain ferric oxide with an X number of adsorbed
ferric arsenate molecules or it may consist of Fe-FeAsO, with a num-
ber of unadsorbed ferric arsenate molecules. The 50-45 sol set to a
eel when dialyzed from ten to fifteen hours, and was a rather opaque
dirty yellow mass. The 50-35 and 50-25, after two to three days dialy-
sis, finally formed a clear reddish gel.

The three gels were carefully dried, and after grinding to colloidal
dimensions their migration in the electric field was determined. Both
the 50-45 and the 50-35 migrated toward the positive pole and therefore
possessed a negative charge. The 50-25 sol, being positive, migrated
toward the negative pole. All three sols before dialyzing had particles
carrying positive charges.

® Arsenic acid may be liberated by the stronger hydrocloric acid, and the material which
passes through the membrane may consist of a mixture of ferric cloride and arsenic acid. If
such is the case, it is not apparent why this arsenic acid should be reduced in quantity by the

addition of sodium arsenate.

SPREADING AND ADHERENCE OF ARSENICAL SPRAYS — 39

From these results it would appear that the pure or nearly pure
ferric arsenate was negative, while if ferric chloride or ferric oxide is
present with it, the particles possess a positive charge. Ferric arsenate
prepared from equal molecular portions of disodium arsenate and ferric
chloride was filtered, washed, dried, and prepared as a suspensoid by
grinding. This material was negative. The addition of ferric chloride
equal in weight to the ferric arsenate present in the. suspensoid, caused
it to take on a strong positive charge. Holmes and Fall (1919) have
shown that the amount of ferric chloride necessary to peptize a given
quantity of ferric arsenate increases rapidly with the age of the pre-
cipitate up to one or two days, with only a smaller further increase
being noted with older precipitates. This was found to be due to a
decrease in the hydration of the precipitate and in the formation of
larger aggregates with a consequent decrease in the external surface of
the particles. In the present investigation it was found to be impos-
sible to peptize with ferric chloride a precipitate which had been thoroly
dried. However, as already shown, the ferric chioride is able to give
the particles a positive charge, due apparently to a reaction with the
surface of the particles. The amount necessary to give the desired
results will vary with the surface area of the particles. The quantity
necessary to produce a positive charge on the surface of large particles
such as are present in the spray suspension, will be much less than is
required where the surfaces are greatly increased by reducing the size
of the particles to colloidal dimensions. The minimum quantity that
may be used to give the desired adherence to a ferric arsenate spray,
remains to be determined by further tests in later investigations.

Holmes and Rindfusz (1916) showed that ferric arsenate may be
peptized by ammonium and other hydroxides, apparently a ferric oxide
with an adsorbed arsenate being produced. This method has been tried
and gives a positive material but is undesirable, since the presence of
large quantities of ferric oxide reduces the toxicity of the mixture.

COMPARATIVE TOXICITY OF DIFFERENT ARSENICAL
PREPARATIONS

_ Freshly precipitated ferric hydroxide is a well-known antidote for
arsenical poisoning in higher animals (Sollmann, 1917). The reaction
between ferric hydroxide and arsenious oxide was first thought to be
due to the formation of a basic ferric arsenate, but Biltz (1904) has
shown that the ferric hydroxide adsorbs the arsenious oxide and does
not form a definite compound. Vermorel and Dantony (1909) stated
that ferrous arsenate on the plant was decomposed with the formation
of ferric hydroxide. Scott and Siegler (1915) found ferrous arsenate
low in toxicity. In view of these facts it was considered advisable to

40 TECHNICAL. TBIQICTE TE Talis

obtain some idea of the toxicity of these new preparations in com-
parison with other common arsenical compounds.

METHODS OF DETERMINING COMPARATIVE TOXICITY

A short review of the literature dealing with toxicity presents sev-
eral methods of obtaining a comparison of toxicity. Marlatt (1897)
studied the toxicity of paris green, london purple, and copper arsenate,
using as a basis of comparison the time required to kill the insects and
the total number killed. Holloway (1912) attempted to express the
toxicity numerically. Paris green at the rate of two milligrams per
leaf was taken as a standard. The toxic value was expressed in the
period of time required to kill. If a given poison required twice as
long as paris green to produce death, then its toxic value would be
expressed as 0.5, while a poison killing more quickly than the standard
would be represented by a number greater than 1. This value was
called the poison exponent. Mention is made of iron arsenate having
a poison exponent for Heliothus obsoleta of 0.5 for the first instar,
0.33+ for the second, 0.81 for the third, and 0.47-++ for the fourth, fifth,
and sixth instars. Scott and Siegler (1915) compared the killing
values of various arsenical compounds by measuring in square inches
the amount of leaf surface consumed by the fall webworm, Hyphantria
cunea (Drury), feeding on black cherry, Prunus serotina. The time
required to produce death was also taken into consideration. They
consider lead arsenate as the best arsenical compound, but the triplumbic
form is a slow acting poison. No attempt is made to arrange the prep-
arations in the order of their toxicity and such an arrangement would
be difficult, owing to the variation in quantity of the poisons used.
Tartar and Wilson (1915) studied the comparative toxicity of lead
hydrogen arsenate and basic lead arsenate. An arsenic analysis was
made of the tissues of the dead insects, showing that those killed by
the acid lead arsenate contained more arsenic. This was considered
due to the more rapid adsorption of the chemically reactive diplumbic
form, while the triplumbic lead arsenate was passed through the intes-
tinal tract without much ‘absorption taking place. Sanders and Brit-
tain (1916) based their comparison of toxicity upon the percentage of
larvae dead after feeding on sprayed foliage for a certain arbitrary
number of days. Lovett and Robinson (1907), continuing the investi-
gations started by Lovett and Wilson (1915), take into consideration
the time required to kill, the approximate amount of the arsenical com-
pound necessary to produce death, and the ratio of arsenic pentoxide
in the tissues to that in the excrement. The ratio of lead hydrogen
arsenate is given as I to 0.544, calcium arsenate I to 0.70, and basic
lead arsenate 1 to 1.51.

SPREADING AND ADHERENCE OF ARSENICAL SPRAYS 41

COMPARATIVE TESTS OF TOXICITY

In the present work, locusts, Melanoplus femur-rubrum, were fed
upon a standard mixture composed of I gram of bran to 0.5 gram of
sugar, 1.5 cubic centimeters of water, and 0.04 gram of the poison to be
tested. When the mixture became dry it was moistened with a few
drops of water. Large glass cylinders covered with cheese-cloth at
the top were used as feeding cages. Each cage coftained ten insects.
Numerous observations were made, and the number of dead locusts
was recorded. When all were dead in any experiment their bodies and
their excreta were separately collected, dried, and preserved for analysis.
The experiments with each poison were repeated five times, hence the fig-
ures given represent the average for fifty locusts. The relative merit of
the different methods of comparing toxicity may be judged from the
data presented, which are based upon the time required to kill, the
amount of bran mash consumed, and the ratio of the poison found in
the body and in the excreta. The organic matter was destroyed by
boiling with nitric and sulphuric acid and the arsenic determined by the
Gutzeit method. (Scott 1917). The data have been compiled in the
following tables, where the materials are arranged. in order of their
toxicity, the most toxic substance being placed first.

These tables show clearly that the best basis of comparison is the
ratio of the quantity of the chemical found in the body to that found
in the excreta. This point is confirmed by feeding mixtures containing
different quantities of the same chemical.

TABLE IV
Toxicity Bas—Ep on Numper or Grams oF Bran MasH ConsumMep BeForeE DeatH*
CO eal oe titntteecd oS EERE ey opel csenie teticresch oy oY en cheiiais ef cts selees, cl aie cieie eyovera muciavonsrace’ ehele etekeeiaee hate 0.0045060
SOG RIMM IGS EMAL) sa cver srs treteze(elerolcia aie.e.0.o\erele a milst e, drSyere ahah ol taiene ekenevetiile oleimretemeke 0.0051975
Oem arts ar SET Crags tee roi cs ere. e) Dice) aiieyecctaice aici os apa gible ou elehei ers evceutyal enehs/ sjsehe at oletetpis 0.0052730
Eeinal Sem EET era ey overseas cue ote rotors ore vahancsatiava: Gus ayia o- ete eth waren erers ote sve etveliavel elevaasitelenelateds 0.0056700
EESatal SMD TES LULL teteyel reir erever sie! a) ef cece. aier<fele ei eLeliei stele) sein eraretehe le tele cele er aueler sivtareveleiece 0.0058905
CG ental mpc ATEY ATS ET ALC sacl ai oa! 0) svncsie sie) evorweei=) asopsienelie| nicllera ra) alm cveleteuellehet sia 0.0060705
PAIN OammecT SEMEN UCC NeteMer pay sy iials eile er aiererey oho wae ai vestayel sie et ole llevevale ciemeiensy av evelere erslin evareione re 0.0061905
Crpliised all mare trl ema TSEN abet inveleels ors clalcleielelele sere leis sucdovers aiatoietsharsietstorerel areains 0.0063370
Meron ets I AETMR CUES ELNALE cpavare ie sna, sxeye, sie) ora sare aileherer eielenels! acslspeleiolermucte ere aaeuslereuchelois 0.0077400
PLACE Cm ATISS GOGEEM hese na loaeretuie 51 wer oial-stai.aleelleielel's eat cvepeber smenisiey atch ener Crepsravatas 0.0077400
eS ACME T SCT AUG iF foilere sor stsusis) ole: a. eh ele avauallareia, eee.» «i aicsl ey enélefejlatsleperslsraakouniel al Giaeale 0.0078000
PSO CITI ALS GELATO iett arc ic eihelev-aire/vo lanfenty ous ri yous Ain a,.s fale el averaneh cle vsebetel oinudienrevelaveretes ate oiaue 0.0078000
PU rrairta Tal SELL AL Gly stars oer eV avesel ol afiny a's) s vo Woxolte) oa (olroteh slavekeisiesaperooccrehsieiein euarcon ee 0.0083610
ENrsivionics Gas tles te tealo cit Or OFLC ECan OmIcIOL DECC DOT.CO DIDS OcO.COOIGr 0.0116700
ERE OI SMARSE Mt DeiN tetas face cistaraiere ia: 20: qyeielerorer ceveloy spelen sino otakenalenente alicverate emcuerone 0.0120000
NGAI RAT SENATE « cyte itete eta G oie ce elas eis a -crono nis sr, l6;"eue lara oantasehalege rats rererevarerorsbat re 0.021T0000

* Calculated from the sum of the arsenic recovered from the bodies and excreta and
the proportion of arsenic present in the mash.

42 TECHNICAL BULLE ETN: 2

TABLE V
Toxicity BasED ON THE AVERAGE NuMBER OF Hours NEceEssary TO Propuce DEATH
Soditim, \ARSENIte so.) cys, a's /arens! eocean ost wrote cute, GU ee eee aE Lee eon ee Tete 20.1
Caleitim: ‘arsenite 22 55 Ss bist ono aere an la tee Seaa te eats enero ret pate Srna een EE ee Een 25.5
Stearated paris: iGreen si hc.<,c:eirere-ccei cre Mlanwls, 1 sien seve Teens eee nee eae set ce eae ete 30.3
Arsenious: ‘OXides'.... 6.8). als «rotons oe oe eR OIA Oe ens ee EE ore 33-0
Sodium ‘arsenate 7 <<... 2:ssvra ce tetas ale marcetete on eh nioko sheet oeione Rector aeaaaee tetas 3725
Paris: i@TOGIs ¢ isis, oat ods vassals outhesuatatete puckerele tetehelo Cease aeolian CURTIS io teen Me teteretore ne 38.1
Magnesium arsenate, %iccimalcrevaee crore ere aaioreote © Olea eaitn Rela ie eae tere 44.7
Galeium “arsenate «5 2.32.50) f toss ie Bee onsen Ie eR eho ee baie eel ee nee ee 45.2
Ferric... ArS@N at :d oFiacors egeraitie, ois 0 Plcve Ruste tere ie ie aia etedeteNeaal ata ele oven eval wane Tavnieretene hentia 46.7
ZANE » | ATSENILSs wc edn ote eoegoseane OREO ours le Oe eIAS OMIM a elert O mere ee eer eter aenoe 46.7
Colloidal aluminum arsenate cscs cree eee tele neleten st ool dsloust eliccsrsiclere staueaate 57.2
Colloidal : ferric. arsenate crass hecesoke cht eavevees Cai iate tesaieen Siero ero ere Gi REE 57.9
Ferrie’ arsenite). occ accte sroteles ore eater neh hae Ore re Rete Sos eel one 60.6
Misr baLb ray | GhalseeNisinn Codon Oooo dO 4 SUC AS oOo OUaOGONA TAS ooo aoS aH SSapnoDS 67.2
Ferrous! ; "ATSEMALEE FA. aks oce ater o SES sha oa a Posty cee une at ere a aioe tal elatiepommes covet east eactctemrane 70.0
Lead arsenate’s:. ayer stenneteie tides eciars cies ene heen s Di ee tg RU En es Serene ters 92.2

TABLES. Vil

Toxicity BasEp oN THE RATIO OF THE CHEMICAL IN THE Bopy AND IN THE EXCRETA

Excreta

Chemical | Milligrams | Milligrams Ratio
in excreta | in body Body
AESEDLOUS: > OXIGER A). sielwicis evade eine eae we 0.005600 | 0.15000 | 0.037334
Sodium arsenite iiss see csiaielee Fe 0.004330 O.IIIIO 0.039000
Colloidal aluminum arsenate........ 0.006051 | 0.15130 0.039995
SOGhiveak ar SNWA, CaGadoe ooo ddp ooo 0,010000 0.25000 0.040000
Magnesium’ “arsenate... 2....0...+.- | 0.006400 0.16000 0.040000
Calcitimgsansenate elem ricimnties er 0.005290 0.13200 0.040077
Gollordal ferrie arsemate yar. 1e- os 0.011440 0.21440 0.053360
Calenuint gansenitece eee eee 0.006100 0.11000 0.055455
Stearated panis: (greenj..0...0.+00006 0.010900 0.16000 0.068130
GEEIC GAGSENILE su.uapersiee reat ete aioe | 0.010578 | 0.13210 0.080077
FANG. ALSENICES sale Omea.S Qo ier re coed ares 0.017800 | 0.13210 0.134750
PAariss Oreen. scleiels mete oo con ei nse ere tele 0.015000 0.11000 0.136370
Merrie’ “arSenatecs1is. sieracisiawe sare cre se 0.048000 0.16060 0.300000
Aluminiim, arsenate sc) sity 'o eters’ eke 0.047160 | 0.13830 0.341240
errous arsenate cy. = cite ste cheiierere | 0.120900 0.20000 0.600000
beads tarsenaeyancscic cose thet yerueee oe | 0.486660 | 0.44333 1.097700
TABLE VII
Grams of lead Grams of bran Excreta
arsenate added to consumed before | Hours required Ratio
bran mash death | _ kill Body

0.02 | 0.0300 66.5 1.0000

0.04 0.0210 92.2 1.0998

0.10 0.0108 69.5 1.2005

0.20 0.0090 5505 1.2502

58.0 0.9092

0.30 0.0070

The hours required to produce death vary greatly while the quan-
tity consumed is reduced rapidly. On the other hand, the results are
affected but slightly by great differences in the quantity of the poison
fed to the locusts.

SPREADING AND ADHERENCE OF ARSENICAL SPRAYS 43

A METHOD OF EXPRESSING TOXICITY

Incidentally this method opens up a possibility of directly comparing
-arsenical compounds, giving them a definite numerical value in com-
parison with some standard compound of arsenic. In the present
investigation, the object was merely to obtain an idea of the relative
toxicity of certain new arsenical materials compared with those in use
at the present time. By taking the reciprocal of the number obtained
by dividing the quantity of the chemical in the excreta by that found
in the body, the most toxic chemical becomes the one with the highest
numerical value, as is shown in Table VIII.

, TABLE VIII

Reciprocal Value when

of the ratio | lead arsenate=1
PAGS ELIS KORG Catecsiay cyelcleieishaliel revere) bis Sip GE cisiale « oiSleie Biseoie e 26.78500 29.4010
SOMMrats era SEMI Oe wetcte rye cre bierearevarn ccsaitvevalece se sve eelevrelsnarnis:s 25.64100 28.1460
CollosdalWaltumuneamyarsenatesiscers eral ieeleitiereisieie # ce od oiters 25.00000 27.4430
OMIUMIM AUS GLALE Le Marirrcitetclotte late iets ral tus niere nes aahoiare, ole Reserere 25.00000 27.4430
Midomestum™= (arsenateria cis acs cielcrrs (oie ate oroais syestsje sie die: aires 25.00000 27.4430
Cal erumbvarsematece ee recvcle site acire ee lelolene Grays aes te .cnshels ans 24.95200 27.3890
Colloidal Piernic, varsenates pics asics en os lelsveueicl ave latevos teen 18.74000 20.5710
Cal critmimanSemite ann 5 tater ieueverse oar oeresers ene Gis chain o¥e- ew eisia ee 18.03200 19.7940
Stearated! | paniSer SEEeMcrss aiuisyeve ssc os cuakeisielee waves acta e-areve 14.78000 16.1120
Blennic) arsenite rn snvevrevs octewers ans siclere eyare:arese avs vielevelelsverelaye'e 12.48800 13.7070
FMC ALS CLIUBLE okey aravetten shane teas seve arene eis (arava lara, siehe aie cls) © afhay seis, aveve 7.42110 8.1462
PAT ISHERTCE Weta ie mianctebewiels custeustalctbelete sialic ae eieusiainrs (ocnefelalaeheG 7.33330 8.0494
MEI Ca ARS eta berrars cralnintaroere is 5 /enaverelarchsrcfasave.a erSleaie o epol as anaes 3.33330 3.6590
CAM iy Gierle AGS EMAL ele tox ccsyatay oi afeysisl sicten ne eietosevclale.c «lave she @iehiuenens 2.93050 3.2169
Grr OUMSe AGS Ghlaba nan aeyioneve a cbae drarcinie te tevepeis olerele: ie devie.efc) susie o6!6 . 1.66660 1.8295
USAC MISSILE tice nan, seen ater cteka reve eer etewelota Saute in areaace ee anctelatacenets | 0.91099 1.0000

Assuming the value of the lead arsenate to be 1 instead of 0.91099
it is simple to express the toxicity of any of the other arsenical com-
pounds in terms of lead arsenate. Ferric arsenate would then have a
value of 3.659, or in other words, would be more than three times as
toxic as lead arsenate, while paris green would be eight times, and
arsenious oxide more than twenty-nine times as toxic as lead arsenate.
Selecting absolutely pure lead arsenate as a standard, several common
insects could be fed under definite conditions and a numerical value
applied to any compound of arsenic placed on the market.

The values presented in this paper can not be used in this manner,

as the lead arsenate used was a commercial product and not chemically
pure.

INFLUENCE OF FERRIC HYDROXIDE ON TOXICITY

The results obtained by the addition of ferric hydroxide to arsenious
oxide are recorded in Table IX.

44 TECHNICAL BE UE Baia

TABLE IX
Ratio
Chem. in excreta
Chem. in body
ATSENIOUS/ SOXIGE (OLO4 STAM. - Nels cise) telelesetone eres J -sPeteyesepasr state totes tvalioh one cliadctarene fate te 0.037334
Arsenious oxide 0.04 g. + stale ferric hydroxide paste containing 0.1614 g.
Cryo’ wy C1 Hts ire jsiale we Biola eo-nasts fe opehia olleuete aes Une tore poreiaas keboners) te aye oestrone ae etoile 0.056000
Arsenious oxide 0.04 g. + colloidal ferric oxide containing 0.0647 g. of
dirny material (pir ts.s< crate sree sotto ooh okevorevettaete levenekafevensrsrencionetelel oretcueha role ercelstekers 0.133333

Arsenious oxide 0.04 g. + fresh ferric hydroxide paste containing 0.1714

SMALYAPWEISME. riasrejoicls bats nalsuslerenaueralisietel ici ake tat epancotadereheraeeteiVetens(cbet otcaekeraievae 0.333333
Arsenious oxide 0.04 g. + fresh ferric hydroxide paste containing 0.1714 g.

dry weight, but allowed to stand mixed for 48 hours before feeding.... 0.600060

The data show clearly that the addition of ferric hydroxide which
adsorbs arsenious oxide reduces the toxicity of the mixture. Calcium
hydroxide mixed in the same way gave a ratio of 0.05 compared with
calcium arsenite with a ratio of 0.055455. In this case the two reacted,
giving calcium arsenite with a ratio checking with the ratio of calcium
arsenite previously tested. None of the figures given in the table
check with ferric arsenite having a ratio of 0.080077. This compound
is apparently not formed.

The addition of ferric hydroxide to other arsenical compounds gave
similar results. Sodium arsenate with a ratio of 0.039 was reduced
by the addition of ferric hydroxide to 0.1333, while paris green 0.13637
became 0.74834.

These experiments explain the cause of the low toxicity of ferrous
arsenate. Ferric arsenate is not so low in toxicity, but the addition of
ferric hydroxide in any large quantity to increase the positive electric
charge would no doubt reduce its toxicity. The adsorption of arsenic
preparations by ferric hydroxide may be the explanation of the lack
of injury to bean and peach foliage recorded by Scott and Siegler
(1915). It has not been possible to investigate this phase of the
subject at the present time.

CONCLUSION REGARDING THE PHENOMENON OF
ADHERENCE

In that portion of the present investigation dealing with the adher-
ence of spray materials to the leaf, it has been demonstrated that the
leaf surface assumes, when wet, a negative electric charge and that
suspensoids of the common arsenic compounds ionize in such a way
that their particles are also negative. Based upon the results obtained
in the dye industry, the assumption is made that spray materials carry-
ing positive electric charges would adhere to the negatively charged
leaf surface better than materials exhibiting negative charges. Field
tests have confirmed this assumption. Positive arsenic preparations

SPREADING AND ADHERENCE OF ARSENICAL SPRAYS 45

of different elements were prepared and tested, ferric arsenate being
considered the most promising material The presence of ferric
hydroxide in the spray material is not desirable since, owing to its
adsorption of arsenic, it lowers the toxicity of the preparation.

Many phases of the problem remain to be solved by future ‘nvesti-
gations. One of the most important questions is the successful com-
bination of a positive ferric arsenate with a spreader to give the mixture
both spreading and adherent properties. Organic materials which pro-
duce a film of the spray on the surface of waxy leaves should have
no influence on the electric charge, but the protein type of spreader may
have a decided effect. Since most emulsoids, such as gelatin, casein, and
proteins, act as protective colloids, their addition to the spray might
result in the complete loss of the electric charge. On the other hand.
a mutual precipitation may occur (Bancroft, 1920), or if the positive
charges are in excess the material may retain its positive character.
Only field tests will solve these problems.

46 TECHNICAL, BUELE MIN 2

LITERATURE CITED

Arnal, A. Préparation des bouillies cupriques mouillantes et adhérents par 1’addi-
tion de caséine. Jn Rev. Maladies des Plantes, v. 2, No. 2, p. 9-10, 1914.
Abst. Rev. App. Ent. v. 2, ser. A, pt. 12, p. 681, 1914.

Astruc, H. Bouillies mouillantes. Jn Prog. Agr. et Viticole, v. 59, No. 24, p. 746-
753; No. 25, p. 780-782. 1913.

, Couvergne, A., and Mahoux, J. Sur 1’ adhérence des bouillies
insecticides a 1’ arseniate de plomb. Jn Compt. Rend. Acad. Sci. v. 152, p.
1860-1862. I09II.

Ballard, W. S. and Volck, W. H. Apple Powdery Mildew and Its Control in
Pajaro Valley. U.S. Dept. of Agr. Bul. 120, 1914.

Bancroft, W. D. Mutual Action of Sols. Jn Jour. Phys. Chem. v. 24, No. 1.
p. 21-29. 1920.

Biltz, W. Ueber die Einwirkung arseniger Saure auf “frisch gefalltes Eisen-
hydroxyd.” In Berichte der Deut. Chem. Gesell. Ja. 37, v. 3, p. 3138-3150.
1904.

Bourecart, E. Insecticides, Fungicides, and Weed-Killers. Scott, Greenwood and
Son, London, 1913. Translated by D. Grant.

Bradley, C. E. Commercial Fertilizers and Insecticides. Ore. Agr. Exp. Sta.
Buleero7a0 1010:

Cazeneuve, —. An Albuminous Bordeaux Mixture. Jn Vigne France, No. 4,
p. 51-53. 1808. Cited from Exp. Sta. Rec. v. 10, No. 5, p. 457. 1808.

Chapaz, G. Les bouillies mouillantes. Bul. Agr. Algerie et Tunise, v. 19, p. 187-
10%), LOF3:

Chappaz, G. Les bouillies mouillantes. Jn Prog. Agr. et Viticole, v. 59, No. 16,
p. 487-491. 1913.

Cooper, W. F. and Nuttall, W. H. The Theory of Wetting and the Determina-
tion of the Wetting Power of Dipping and Spraying Fluids Containing a
Soap Basis. Jn Jour. Agr. Sci. v. 7, pt. 2, p. 219-239. I9QI5.

Crouzet, E. Bouillie Lacto-cuprique. /n La Messager Agricole v. 4, ser. 10, Pp.
306-307. 1809.

Dalmasso, G. La lotta contro le Tignuole dell ’uva. Jn Stazioni sperimentali
agrarie Italiane, v. 43, No. 7-9, p. 503-645. 1910.

Del Guercio, G. I resultati delle prime esperienze tentate con i Polisolfuri colloi-
dati contro la “Bianca-rossa” delgi Agrumi. Jn Rivista di Patologia Vegetale,
Van NOs 5. Ds 120-135. LOLA:

Edwardes-Ker, D. R. The Addition of Soft Soap to Lead Arsenate for Spray-
ing Purposes. Jour. South East Agr. College (Wye, Kent). No. 22, p.
359-362. 1913.

Fairchild, D. G. Experiments with Fungicides to Prevent Leaf Blight of Nursery
Stock. Jour. Mycol. v. 7, No. 4, p. 338-353. 1894.

Fernald, C. H. A New Insecticide. Arsenate of Lead. Mass. Agr. Exp. Sta.
(Hatch) Bul. 24, p. 3-7. 1804.

Galloway, B. T. Report on Experiments Made in 1891 in the Treatment of
Plant Diseases. U. S. Dept. of Agr., Div. Veg. Path. Bul. 3, 76 pp. 1891.

Field Work of the Year in Treating Plant Diseases. Jn Rept.
U. S. Sec. of Agr. p. 216-234. 1892.

SPREADING AND ADHERENCE OF ARSENICAL SPRAYS 47

Some Observations on New and Old Insecticides and Their Com-
bination with Fungicides. Jn Insect Life, v. 7, No. 2, p. 126-132. 1804.

Gastine, G. Sur 1’ emploi des Saponines pour la préparation des émulsions insecti-
cides et des liqueurs de traitements insecticides et anticryptogamiques. Compt.
Rend. Acad. Sci., v. 152, p. 532-534. IQII.

Le Progrés agricole et viticole, v. 33, No. 14, p. 427-429. IQII.

Gillette, C. P. Experiments with Arsenites. Iowa Agr. Exp. Sta. Bul. 10, p.
401-420. 1890.

Girard, Aime. Recherches sur 1’ adhérence aux feuilles des plantes, et notamment
auz feuilles de la pomme de terre, des composés cuivriques destinés a combattre
leurs maladies. Jn Comp. Rend. Acad. Sci., v. 114, No. 5, p. 234-236. 1892.

Graham, S. A. Potato Spraying in Minnesota. Jn 17th Rept. State Ent. of
Minn. p. 21-31. 1918.

Gray, G. P. Wettable Sulfurs. Jn Monthly Bul. St. Comm. of Hort. Calif., v. 7,
No. 4, p. 191-192. 1913.

Grimaux, E. Sur des sels ferriques colloidaux. Compt. Rend. Acad. Sci., v. 98,
No. 25, p. 1540-1542. 1884.

Guillon, G. M. and Gouirand, G. Sur l’adhérence des bouillies cupriques utilisées
pour combattre les maladies cryptogamiques de la Vigne. Compt. Rend. Acad.
Sci., v. 127, No. 4, p. 254-256; No. 11, p. 423-424. 10918.

Harkins, W. D. and Brown, F. E. The Determination of Surface Tension
(Free Surface Energy), and the Weight of Falling Drops: The Surface
Tension of Water and Benzene by the Capillary Height Method. Jour. Amer.
Chem. Soc., v. 41, No. 4, p. 499-524. 1918.

Harkins, W. D., Brown, F. E., and Davies, E. C. H. The Structure of the
Surfaces of Liquids, and Solubility as Related to the Work Done by the
Attraction of Two Liquid Surfaces as They Approach Each Other. Jour.
Amer. Chem. Soc., v. 39, No. 3, p. 354-3604. 1017.

Harkins, W. D., Davies, E. C. H., and Clark, G. L. The Orientation of Molecules
in the Surface of Liquids, the Energy Relations at Surfaces, Solubility, Ad-
sorption, Emulsification, Molecular Association, and the Effect of Acids and
Bases on Interfacial Tension. Jn Jour. Amer. Chem. Soc., v. 39, No. 4, D.
541-5900. IIQI7.

Hartzell, F. Z. The Influence of Molasses on the Adhesiveness of Arsenate of
Lead. Jn Jour. Econ. Ent., v. 11, No. 1, p. 62-66. 1918.

High, M. M. Cactus Solution as an Adhesive in Arsenical Sprays for Insects.
U. S. Dept. of Agr. Bul. 160. 1915.

Holloway, T. E. The Poison Exponent: A Symbol of the Toxicity of Chemicals
in Their Relation to Insects. Jn Jour. Econ. Ent., v. 5, No. 6, p. 452-456.
1912.

Holmes, H. N., and Arnold, R. The Peptization of Ferric Arsenate and Phos-
phate and the Formation of Their Gels. Jn Jour. Amer. Chem. Soc., v. 40,
No. 7, p. IOI4-1019. 1918.

, and Fall, P. H. The Influence of the Age of Ferric Arsenate on
Its Peptization. Jn Jour. Amer. Chem. Soc., v. 41, No. 5, p. 713-717. 1919.

, and Rindfusz, R. E. The Colloidal Arsenates and Phosphates of
Iron. In Jour. Amer. Chem. Soc., v. 38, No. 10, p. 1970-1982. 1916.

Howe, R. G. Results of Spraying Experiments, 1909. Ill. Agr. Exp. Sta. Circ.
D3 7e lOO:

48 TECHNICAL, BULLETIN 2

Issleib, —. Die Beseitigung der Insekten, welche den Wein- und Obstbau schadi-
gen, durch Verklebung mit Hilfe von Moosschleim. Jn Zeitschr. ftir
Pflanzenkrankheiten, v. 24, pt. 2, p. 78-79. 1914.

Jacobson, C. A. Alfalfa Saponin. Alfalfa Investigation VII. Jn Jour. Amer.
Chem. Soc., v. 41, No. 4, p. 640-648. 1919.

Jones, P. R. Machine Gun Work with a New Formula on Red Spider in Tulare
County. In Monthly Bul. St. Comm. Hort., Calif., v. 7, No. 7, p. 455-457.
1913.

Kilgore, B. W. On the Cause and Prevention of the Injury to Foliage by Arsen-
ites Together with a New and Cheap Arsenite and Experiments on Combining
Arsenites with Some Fungicides. N. C. Agr. Exp. Sta. Bul. 77b, Tech. Bul.
IN), 2, ulstoyr,

King, P. E. General Review and Bibliography of Dyeing. Ist Rept. on Colloidal
Chem. and Its Indust. App., British Assoc. Adv. Sci., p. 20-38. 1917.

Kirkland, A. H. On the Value of Glucose in Spraying. Jn Mass. St. Bd. of Agr.
46th Ann. Rept., p. 478-481. 1808.

Lafforgue, G. Les bouillies cupriques mouillantes. Jn La vie Agricole, v. 3, p.
611-614. I9QT3.

Langmuir, I. The Constitution and Fundamental Properties of Solids and
Liquids. II Liquids. Jn Jour. Amer. Chem. Soc., v. 39, No. 9, p. 1848-1906.
1917.

Lavergne, G. Rapport sur le black-rot dans l’Armagnac en 1895. Jn Bul. Min.
Agr., France, v. 15, No. 2, p. 285-201. 1806.

Lees, A. H. Winter Cover Washes. In Ann. App. Biol., v. 1, No.-3-4, p. 351-
364. IOTS.

Winter Cover Washes. Jn Ann. App. Biol., v. 2, No. 4, p. 245-
249. 10916.

Accessory Wetting Substances with Special Reference to Paraffin
Emulsions. Jn Ann. App. Biol., v. 3, No. 4, p. 141-149. 1917.

Lefroy, Maxwell H. The Psylla Disease of Indigo in Behar. Jn Agr. Jour.
India, v. 8, pt. I, p. I-26. 1913.

Insecticides. Jn Ann. App. Biol., v. 1, No. 3-4, p. 280-298. 1915.

Lovett, A. L. Spreaders for Arsenate Sprays. In Jour. Econ. Ent., v. 11, No. 1,
p. 66-69. 1918.

Insecticide Investigations. Ore. Agr. Exp. Sta. Bul. 169. 1920.
and Robinson, R. H. Toxic Values and Killing Efficiency of the
Arsenates. Jn Jour. Agr. Res., v. 10, No. 4, p. 199-207. 1917.

Lowe, V. H. Combating the Cottonwood Leaf Beetle. In N. Y. Agr. Exp.
Sta.- 15th Ann. Rept. p. 543-544. 1806.

Mausier, —. Principles d’aprés lesquels doivent étre composés les insecticides. In
Bul. Soc. des Agr., France, v. 63, p. 86-93. 1908.

Marlett, C. L. Comparative Tests with New and Old Arsenicals on Foliage and
with Larvae. U. S. Dept. of Agr. Div. of Ent. Bul. 6, new series, p. 30-35.
1897.

Melander, A. L. The Control of the Codling Moth. Wash. St. Coll. of Agr.
Bul. 103, p. 4-55. IQII.
Millardet and Davis. Résultats de divers procédés de traitement sur le developpe-
ment du mildiou. Jn Jour. Agr. Pratique, v. 2, No. 50, p. 761-770. 1886.

SPREADING AND ADHERENCE OF ARSENICAL SPRAYS 49

Neiils, J. D. The Use of Flour Paste in Lime Sulphur Solutions in the Con-
trol of the Citrus Red Spider. Jn Monthly Bul. St. Comm. Hort. Calif.,
v. 2, No. 6, p. 557. 1013.

O’Kane, W. C., Hadley, C. H., and Osgood, W. A. Arsenical Residues after
Spraying. N. H. Agr. Exp. Sta. Bul. 183. 1917.

Parker, J. R. The Use of Soap to Retard the Settling of Certain Arsenicals.
Mont. Agr. Exp. Sta. Bul. 86, P. 35-45. IQII.*

Parker, Wm. B. Flour Paste as a Control for Red Spiders and as a Spreader
for Contact Insecticides. U. S. Dept. of Agr. Bur. of Ent..Circ. 166. IQI3.

Perraud, Joseph. Recerches sur quelques moyens permettant d’augmenter 1’ad-
hérence des bouillies cupriques. Jn Comp. Rend. Acad. Sci. y. 1274) Now225
p. 876-879. 1808.

Sur une nouvelle bouillie cuprique, plus spécialement destinée A
combattre le black rot. Jn Compt Rend Acad. Sci., ‘v. 127, No. 23, p. 978-980.
1808.

Pickering, S. U. The Interaction of Metallic Sulphates and Caustic Alkalies. In
Jour. Chem. Soc., v. 91.92, p. 1981-1988. 1907.

Quincke, G. Ueber den Randwinkel und die Ausbreitung von Fliissigkeiten auf
festen K6rpern. Jn Wiedemann’s Annalen der Physik und Chemie, neue
Folge, Band II, No. 10, p. 145-194. 1877.

Rapport au Ministre de L’Agriculture. Sur le traitement du mildiou dans le
médéc. Jn Jour. Agr. Pratique, v. 2, No. 49, p. 659-662. 1885.

Ravaz, L., and Bonnet, A. Expériences sur le traitement du mildiou. Jn Ann.
de !’Ecole Nationale d’Agri. de Montpellier, n. ser., v. 3, No. 2, p. 157-168.
1903.

Robak, F. Wild Volatile-Oil Plants and Their Economic Importance. I Black
Sage; II Wild Sage; III Swamp Bay. U. S. Dept. of Agr. Bur. Plant
Indust. Bul. 235. 1912.

Sanders, G. E., and Brittain, W. H. The Toxic Value of Some Common Poisons
Alone and in Combination with Fungicides, on a Few Species of Biting In-
sects. In Proc. Ent. Soc. Nova Scotia, No. 2, p. 55-64. 1016.

Scott, E. W., and Siegler, E. H. Miscellaneous Insecticide Investigations. U. S.
Dept. of Agr. Bul. 278. 1015.

Scott, W. W. Standard Methods of Chemical Analysis. Van Nostrand Co.,
N.Y. 1917:

Selby, A. D.. Spraying for Apple Scab in 1908. In Ohio Agr. Exp. Sta. Circe.
87, p. 4-8. 1908.

Sirrine, F. A. A Spraying Mixture for Cauliflower and Cabbage Worms. N. Y.
Agr. Exp. Sta. (Geneva) Bul. 144. 1808.

Smith, John B. Insecticides. Rept. of Ent. Jn 28th Ann. Rept. N. J. Agr. Exp.
Sta., p. 350-373. IQI0.

Insecticides. Rept. of Ent. Jn 31st Ann. Rept. N. J. Agri. Exp.
Sta. p. 359-373. I9QI0.

Smith, Loren B. Relationship Between the Wetting Power and Efficiency of
Nicotine-Sulphate and Fish-oil Soap Sprays. Jn Jour. Agr. Res., v. 7, No, 0;
p. 389-399. 1016.

Sollmann, T. A Manual of Pharmacology, 1917.

50 TECHNICAL BULLETIN 2

Stearns, L. A. Experiments on the Control of the Oriental Fruit Moth. Jn
Quart. Bul. Va. St. Crop Pest. Comm, v. 2, No. 1. 1920.

Stewart, V. B. Some Important Leaf Diseases of Nursery Stock. Cornell
Agr. Exp. Sta. Bul. 358, p. 167-226. 1915.

Surface, H. A. Calendar for 1905 for Treating Insect Pests and Plant Dis-
eases. Monthly Bul. Div. Zool. Pa. v. 3, No. 1, p. 8-30. 1905.

Swingle, W. T. An Improved Method of Making Bordeaux Mixture. In Jour.
Mycol., v. 7, No. 4, p. 365-371. 1804.

Tartar, H. V. and Bundy, L. A. Arsenic Soluble in Mixtures of Lead Arsenate
and Soap. Jn Jour. Indust. and Engin. Chem., v. 5, No. 7, Pp. 561-562. 1913.

and Wilson, H. F. The Toxic Value of the Arsenates of Lead. In

Jour. Econ. Ent., v. 8, No. 5, p. 481-486. 10915.

U. S. Patent No. 1166387. Dec. 28, 1915.

Van Slyke, L. L., and Urner, F. A. The Composition of Commercial Soaps in
Relation to Spraying. N. Y. Agr. Exp. Sta. (Geneva) Bul. 257. 1904.
Vermorel, V., and Dantony, E. De l’emploi de l’arséniate ferreux contre les
insects parasites des plantes. Compt. Rend. Acad. Sci., v. 148, No. 5, p. 302-

304. 1900.

Arséniate ferreux et bouillies cupriques. Jn Progres Agricole, v.
51, Pp. 423-424. 1900.

Des principes généraux que doivent présider a 1’établissement des
formules insecticides. Jn Compt. Rend. Acad. Sci. v. 151, p. 1144-1146.
IQI0.

Sur les bouillies anticryptogamiques mouillantes. Jn Compt. Rend
Acad. Sci., v. 152, p. 972-974. IQII.

Bouillie anticryptogamique au savon de cuivre colloidal. Jn Compt.
Rend. Acad. Sci., v. 152, p. 1263-1265. 10911. ;

Tension superficielle et pouvoir mouillant des insecticides et fongi-
cides. Moyen de rendre mouillantes toutes les bouillies cupriques ou insecti-
cides. In Comp. Rend. Acad. Sci., v. 154, No. 20, p. 1300-1302. I912.

Preparation des bouillies alcalines mouillantes. Jn Prog. Agr. et
Viticole, v. 59, No. 24, p. 745-746. 1913. ~~

Pouvoir mouillant et adhérence des bouillies. Jn Prog. Agr. et
Viticole, v. 59, No. 25, p. 778-780. 1913.

Préparation rapide des bouillies a la caséine. Jn Progres Agricole,
vi 163, 9Ps.500; LOTS!

Volck, W. H. Sulphur Sprays for Red Spider. Cal. Agr. Exp. Sta. Bul. 154. °
1903.

The Apple Powdery Mildew in Pajaro Valley. Office of County
Ent. for Monterey and Santa Cruz Counties, Cal. Special Bul. 1, 19009.

Waite, M. B. Experiments on the Apple with Some New and Little-known Fungi-
cides. U.S. Dept. of Agr. Bur. Pl. Indus. Circe. 58. 1910.

Washburn, F. L. Practical Work with the Codling Moth and with a Combined
Insecticide and Fungicide. Ore. Agr. Exp. Sta. Bul. 10. 1891.

Weinmann, J. Bouillies mouillantes. Jn Progrés Agricole, v. 57, p. 700-712.
IQI2.

Willows, R. S. and Hatschek, E. Surface Tension and Surface Energy and
Their Influence on Chemical Phenomena. J. and A. Churchill, London.
IQI5.

Wilson, H. F. Common Insecticides. Wis. Agr. Exp. Sta. Bul. 303. 1919.

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