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UNITED STATES
DEPARTMENT OF AGRICULTURE
LIBRARY

BOOK NUMBER Ag84B
no, 1126-1150

347954

aro 8—Z671

fate |
| CHEMICAL, PHYSICAL, AND INSECTICIDAL PROPERTIES
OF ARSENICALS

By

F. C. COOK, Physiological Chemist, Insecticide and Fungicide Laboratory -
Miscellaneous Division, Bureau of Chemistry
and
N. E. McINDOO, Insect Physiologist, Fruit Insect Investigations
Bureau of Entomology

SS ee

CONTENTS

Purpose of investigation Comparative toxicity of arsenicals
___ Arsenicals studied General properties of arsenicals --
Chemical properties of arsenicals Summary

Physical properties of arsenicals Literature cited

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WASHINGTON
GOVERNMENT PRINTING OFFICE
1924

s June 9, 1923
Washington, D. C. v Revised May, 1924

“CHEMICAL, PHYSICAL, AND INSECTICIDAL PROPERTIES OF ARSENICALS.

By F. ©. Coox, Physiological Chemist, Insecticide and Fungicide Laboratory, Miscel-
| laneous ’ Division, Bureau of Chemistry, and N. HE. MciInpoo, Jnsect
Physiologist, Fruit Insect Investigations, Bureau
of Entomology.

CONTENTS.
Page Page
» Purpose of investigation ..........-.....-.--- 1 | Comparative toxicity of arsenicals........... 24
Bemetsenicals ShUdIed..) 2. see wet ee - = 2 1 | General properties of arsenicals.............. 50
_ Chemical properties of arsenicals............- 27) NUMMARyVat CEE Gy Fete yy rie 53
Os iatera tune crtediesie nig Ue la eeiMc lc ete eas 55

i Physical properties of arsenicals............- 2

PURPOSE OF INVESTIGATION.

_ A study of the chemical, physical, and insecticidal properties of
-arsenicals on the market was undertaken in order to gain a better
“understanding of them, to be able, if possible, to improve them, and
to produce new arsenicals for insecticidal purposes. The results of
‘this investigation, which was conducted by the Bureau of Chemistry
and the Bureau of Entomology of the United States Department of
Agriculture, are here reported.

ARSENICALS STUDIED.

9 Paris green and lead arsenate, which have, been standardized and
found reliable for many years, have constituted the principal in-
‘secticides used against external chewing insects. However, during
, the past few years, the use of calcium arsenate has steadily in-
creased, owing in part to the discovery that itis effective in combating
_ the boll weevil. The manufacture of calcium arsenate, although well
‘beyond the experimental stage in most factories, probably will not
a completely standardized for several years. Because of the im-
‘portance and recent large-scale production of calcium arsenate, many
of the results in this bulletin deal with comparisons of calcium

a senate and acid lead arsenate.

_1The following assisted in this work: R. Elmer, W. A. Gersdorff, R. Jinkins, B. Neuhausen, and A.
§ hultz, Junior Chemists, Insecticide and Fungicide Laboratory, Bureau of Chemistry, and W. A. Hoff-
I man. Scientific Assistant, and W. B. Wood, Entomological Assistant, Bureau of Entomology.

100173 °—24—Bull. 1147——1

2 BULLETIN 1147, U. S. DEPARTMENT OF AGRICULTURE.

The arsenicals analyzed in this investigation, many of which were
used in the entomological tests (pp. 26-50), were obtained on the
market in 1916. The samples were used as purchased, with the
exception of the paste products which were dried before being used.
Samples of the following arsenicals were studied: Arsenious oxid
(4 samples), arsenic oxid (2 samples), acid lead arsenate (18 samples),
basic lead arsenate (2 samples), calcium arsenate (9 samples), zinc
arsenite (2 samples), Paris green (2 samples), mixture of calcium
and lead arsenates (2 samples), sodium arsenate (2 samples), potas-
sium arsenate (1 sample), London purple (1 sample), and mag-
nesium arsenate (1 sample). Several samples of acid and basic
lead arsenate and of calcium arsenate, and one of barium arsenate, one
of aluminum arsenate, and one of copper barium arsenate mixture
were prepared in the laboratory, analyzed, and tested on insects.

Various names are applied to the arsenicals here designated as
(a) acid lead arsenate, (b) basic lead arsenate, (c) arsenious oxid,
and (d) arsenic oxid. Some of these names are incorrect because

they are based on erroneous analyses or interpretations of composi- |

tion, for example, ‘‘neutral lead arsenate’’ for a basic lead arsenate.

Some are considered not to be in good usage, according to modern |
chemical writing, for example, ‘‘arsenious acid’’ for arsenious oxid. |
Arsenious oxid dissolved in water forms arsenious acid. The same ©

relation exists between arsenic oxid and arsenic acid. Other names,
although correct, are unnecessarily involved, for example, ‘‘hydroxy-
lead arsenate’’ for basiclead arsenate. The terms selected for use in

this bulletin are both scientifically correct and commonly applied to |

arsenicals. Their names, with the synonyms, are as follows:

(a) Acid lead arsenate (PbHAsO,). (6) Basic lead arsenate—Continued.
Ordinary lead arsenate. Trilead arsenate.?
Hydrogen lead arsenate. Nonacid lead arsenate.
Diplumbic arsenate. Hydroxy-lead arsenate.
Dilead arsenate. Lead ortho arsenate.?
Diplumbic hydrogen arsenate. (c) Arsenious oxid (As,Q,).
Bibasic lead arsenate. Arsenic.

(b) Basic lead arsenate (Pb,(PbOH) White arsenic.

(AsO,)3. HO). Arsenious anhydrid.
Triplumbic arsenate (T. P. arsen- (d) Arsenic oxid (As,O;).
ate).? Arsenic pentoxid.

Neutral lead arsenate.? Arsenic anhydrid.

CHEMICAL PROPERTIES OF ARSENICALS.
OXIDS OF ARSENIC.

Arsenious oxid (As,O,), commonly called white arsenic or simply
arsenic, is the basis for the manufacture of all arsenicals. In the
United States arsenious oxid is a by-product from the smelting of
lead, copper, silver, and gold ores, being recovered from the flue dust
and fumes. The arsenious oxid first sublimed is impure, owing to the
presence of carbon and sometimes of sand. The impure oxid may
then be resublimed to give a relatively pure oxid, consisting of
approximately 99 per cent of arsenious oxid and a trace of arsenic
oxid (As,O,). Between 11,000 and 12,000 tons of arsenious oxid were

produced in the United States in 1920, more than half of which was

2 These names are incorrect, having been used when basic lead arsenate was considered to be trilead
arsenic.

ARSENICALS. 3

used for insecticide purposes. Canada, Mexico, England, Germany,
pencee, Japan, and Portugal produce large quantities of arsenious
oxid.

There are three forms of arseniousoxid: (a) Theamorphous, vitreous,
or glassy form; (6) the ordinary crystalline (‘‘octahedral’’) form; and
(c) the orthorhombic crystalline form. The amorphous form changes
spontaneously into the crystalline form on standing. The trade
usually recognizes two grades of arsenious oxid, the light and the
heavy forms, although they are the same chemically.

The literature contains conflicting statements concerning the
solubility of arsenious oxid in water. Because of the slowness with
which arsenious oxid goes into solution, many weeks being required
to dissolve even a small sample of the solid, it is ee abanle that in
all of the reported results equilibrium had not been reached. The
varying percentages of crystalline and amorphous material present
in the samples tested, the amorphous form being more soluble than
the crystallme forms, may possibly help to account for these dis-
crepancies.

With the exception of Paris green, the arsenites are prepared by
combining arsenious oxid and the base.

As a rule, arsenates are made by the direct action of arsenic acid
in solution on a metallic oxid. The arsenic acid used for this purpose
is manufactured from arsenious oxid by oxidation, usually by means
of nitric acid, but sometimes by other oxidizing agents.

The analytical results here reported are based on the weights of
the original samples. The methods of analyses used were in general
those of the Association of Official Agricultural Chemists (1).8
. Table 1 gives the analytical results on the six samples of arsenious
and arsenic oxids selected to represent the arsenical materials used
in the manufacture of arsenicals.

TaBLE 1.—Composition of arsenious oxid (As,03) and arsenic oxid (As,0;) used in manu-
facturing arsenicals.

Water- | Water-
Total Total | soluble | soluble

Sample P : arsen- | arsenic F
No. Material analyzed. Moisture. iou@oxid Bedi Tersene P one
(As203). | (As205)- 1 45503).1| (AssOs).2
Per cent.| Per cent.| Per cent.| Per cent.| Per cent.
9 | Laboratory arsenious OXid.................-. 0. 20 99: 805/48. “F552 iV Gri) | ee Se
19 | Commercial arsenious OXid-._.....-......... -99 99/014). Vee ZAG Se. SPARE Rd:
Dy Nera YG ae PAN RG ee irae Gene yee oh baa re pues TER aD a7 | G0 20i Lo oh Ses 38: QOH ty bees
= bl Be Di pe tae arate Sen. vt atari pel ere Ane ee ya Oe 215 QO 22M te ieee SONZON see cea
10 | Laboratory arsenic oxid (solid arsenic acid).|.........-]....--.--- (0-0 Gl $8 ke Ge $46 11.27
16 Commercial arsenic oxid (dissolved arsenic

| CT) se ta ois ae wie cURL meee ok cae emi’ aan Ce pe he ae tie oe 66.10

1 Determined by the A. O. A. C. method for Paris green.

Attention is called to the wide variation in the data obtained for
water-soluble arsenious oxid in the different samples of arsenious oxid.
This is undoubtedly due to differences in the size and structure of .
the crystals present in the samples tested.

Traces of arsenious oxid (0.008 per cent) and nitric acid (0.02 per
cent) were found in the commercial sample of arsenic acid (No. 16).

3 Italic numbers in parentheses refer to literature cited.

4 BULLETIN 1147, U. S..DEPARTMENT OF AGRICULTURE.

All samples of commercial arsenic acid are likely to contain traces
of arsenious oxid and nitric acid. Arsenic acid solutions containing
from 56 to 66 per cent of arsenic oxid have a specific gravity of from
1.8 to 2. Solid arsenic acid containing from 75 to 80 per cent of
arsenic oxid has recently been placed on the market.

BASES USED IN PREPARING ARSENICALS.

The oxids of lead, zinc, calcium, and’ magnesium are the bases
most used in manufacturing arsenicals. Litharge is the commercial
lead oxid and lime the commercial calcium oxid. Zine oxid (ZnO)
and lead oxid (PbO), ordinarily employed in the manufacture of zine
arsenite and lead arsenate, are more expensive than calcium oxid
(CaO) (Gn the form of lime) and magnesium oxid (MgO) used in manu-
facturing calcium arsenate and magnesium arsenate. Table 2 gives
the results of the analyses of the five bases and the copper oxid
(CuO) ‘and barium hydroxid (Ba(OH).) which were iaee in this

investigation.

TABLE 2.—Composition of bases in arsenicals.

| | Undefer-
s 1 Carbon | mined

: Nee 4 Material analyzed. Moisture. Oxid. dioxid | material,
a (CO2). | by dif-
ference.

| Per cent. Per cent. Per cent. | Per cent.

11,1, Lime (sboratory).3 <<. cs. c2edecrc Pe. eles 6.54 | 84.00 (CaO)...... 9. 02 0. 44

2 | era ORIG (ia DOLaLOLy =~ oust seer eee .00 | 99.13 (PbO)..... Trace. . 87

20 | Lead. oxid (commercial). .../.....2..0.2-.--... .02 | 97.88 (PbO)..... 1, 64 | . 46

220) “Zine @x1d) (COMMOLCIah) sees. we eee .17 | 100.00(Zn0O).... 900. fis. ceeu ec

63 | Magnesium oxid (laboratory)......--...------ -99 | 77.16 (MgO)..... 21.89) $12 cae

65 | Copper oxid (laboratory). .-.-....-.---..--+--.--- .00 | 98.75 (CuO)....- « 1.15

67 | Barium hydroxid (laboratory)..........-..--- 14.58 | 66.73 (BaO)..... 14, 91 3. 78

ACID LEAD ARSENATES.

F. C. Moulton, chemist for the Massachusetts gypsy moth com-
mittee, is credited with the discovery in 1892 of the insecticidal
properties of lead arsenate. The use of arsenate of lead as an in-
secticide, first recommended in October, 1893 (2i), has greatly
increased during the past few years. Forty-two United States patents
relating to its production have been issued.

The principal lead arsenate is acid lead arsenate (PbHAsQ,), an
acid salt, so-called because of the presence of hydrogen (H) in its
molecule. It has the followimg theoretical composition, As,O;
(33.13 per cent), PbO (64.29 per cent), and water of constitution
(2.58 per cent).

In the early procedure for preparing acid lead arsenate, solutions of
lead acetate or of lead nitrate were precipitated by sodium hydrogen
arsenate (Na,HAsO,). The tendency is to produce acid lead arsenate
when lead nitrate is used and the more basic form when the acetate
is used. McDonnell and Smith (27) obtained acid lead arsenate of
eae theoretical composition by precipitating lead nitrate or
ead acetate by an excess of monopotassium arsenate. A method
frequently employed in manufacturing this arsenate is to mix arsenic
head (H,AsO,) and litharge (PbO) in the presence of a small amount
of nitric acid. Other processes, however, are used. The fact that
acid lead arsenate is a comparatively stable compound and is but

ARSENIGCALS., - 5

slightly soluble in water, offers an explanation as to why it burns
foliage only very slightly when properly applied: McDonnell and
Graham (26) found that long-continued exposure: to constantly
changing water brings about decomposition, both lead and arsenic
being dissolved, the arsenic, however, at a relatively greater rate,
leaving the residue more basic than the original acid lead arsenate.
According to McDonnell and Smith (27), the specific gravity of acid
lead arsenate crystals 1s 6.05.

The chemical data on 10 samples of powdered lead arsenates and
on 9 samples of paste lead arsenate, the latter being dried in the
laboratory before analysis, are reported’in Table 3. Of the powdered
arsenate samples 1 apparently was a basic lead arsenate and 9 were
acid lead arsenates. Of the paste lead arsenate samples, 1 appar-
ently was a basic lead arsenate and 8 were acid lead arsenates. These
samples, which were obtained from various manufacturers in this
country, include most of the leading brands. The results of the
analyses, therefore, are representative of the composition of the
commercial lead arsenates on the market in 1916. : el

- te

TABLE 3.—Composition of powdered and paste commercial lead and calcium arsenates.

Arsenic oxid

(Asi03). iy piteiedale
nay arbon } tion and
ee z le Material analyzed. pote : silanes oxi: dioxid | impuri-/

Motai, | Water- (CQz2). | ties by

otal. | soluble. differ-

ence.’
Per cent. | Per cent. | Per cent. Percent. | | Percent.| Percent.
1 | Powdered acid lead arsenate... - - 0. 32 30. 86 0.31 64.88 (PbO) |} 0.54 3.40:
7 ee CU te NO Mat ae pe ne 1.43 31.55 -24| 62.95 (PbO) 515 3. 92:
$34) 3.5. do. FT (ere ha BA I 32. 29 £32 | “64.23 (PHO) Ue. . FFT: 3527
14.)5F On RE ESN ae Bild 32. 00 0 Hi OSsAe GR DO) jor aoe 4.41
Fil pape OS sary andr cops pend eed 230 31. 24 Pash BOs oo Ces) Necee ee 4.11
BSAl. - tot Go2foe4y ernie Se ahir et: 32. 47 -45 | 64.29 eats ey aestas 3.10:
a eee Pa ee A ope ee Saf aa - 20 32. 93 $66 | 63242: CR DO) die wee 2. 95
40 Piss Wore OU Ne ea ao 2. 06 32.76 $4510 63. 7O@PbDO) HP FTIOOD F 1.48
70 |e 5. DE sere praere sires ohio 45 31.59 «224 || 163; 00. OPBQ). | FE 496
28 | Powdered basic lead arsenate... 230 24. 80 43 (iP TAY (Bol UG 8) oe ocr 2.62
3 | Paste acid lead arsenate, dried... -10 31.95 34] 6457 (PbO) | Trace. 3. 38
lo ees 3 ona psi Sree eee 12 32.30 «42 | 64.50 (PbO) |e. see. - 3.08
BAERS Fe oe Y Set SP Seber JE 19 30.38 £531 S56552E (PbO} 2 eS = 4,22
So ATES a a, eee we «lll 32. 07 ob) | .OoNOIe GE DQ) it se 2.81
os Oe ee he ee td: 33.17 22 O35 62) GEeDON lao ene 2. 90
474 Ate Ores at ta ral 32.51 | 22'3°64567; GPHO)|> 3. Foe 274
AR ats C0 La a ah ee 22 33.09 | s6% |i 63:41" @PDO), le... 3. 28
49 | ..le. GOs IS SRA EE AIG ma 32. 98 1.73 68.13 (PbO) fy. ot 3.77
21 | Paste basic lead arsenate, dried. 2114 § 23.00 DOs PiionQOLGb © )h i. uae 2.90
6 | Paste calcium arsenate, dried... .28 43.35 -70 38. 86 (CaO) 2.74 14.77
7 | Powdered calcium arsenate..... 1.58 43.35 -38 44.08 (CaO) | - 1.83 9.16
yA OE Re Tee ee. 1.33 49, 40 2.74 | 40.57 (CaO) ;98 ae,
SON ENS: lp EES SS a Oe ren PE ORES Se Ie -31 41. 82 -22| 42.61 (CaO) 1.64 13. 62
BA | coe. Cee SS oe ee eee oe 9. 56 38. 16 1,92 37. 38 628} 4534 10. 56
F al ea Wee ee en Hii 39.19 -55 | 42.79 (CaO 4, 04 6.27
bY (5 are doatet ssrttefetn! carry 11.30 40.49 -08 } 44.08 (CaO) 1.05 3.13
Cte ae GIS a SE EE etl a -99 47. 83 -25 | 46.16 (CaO) 1.70 3. 32
50k ae oe aie we Pe 6.07 45. 37 2.32 | 41.48 (CaO) 2. 43. 4.65

The results in Table 3 show that in most cases the chemical com-
position of the commercial samples of acid lead arsenates closely
approaches the theoretical composition. The manufacture of lead
arsenate has become standardized to such an extent that different
batches, or “‘runs,’’ of the product vary but little from the theoretical
figures. Acid lead arsenates are sold in both dry and paste form, the
paste containing usually from 45 to 50 per cent of water.

6 BULLETIN 1147, U. S. DEPARTMENT OF AGRICULTURE.

The two most important determinations to be made on lead ar-
senates are the total arsenic oxid and the water-soluble arsenic oxid.
The total arsenic oxid of an acid lead arsenate usually varies from
31 to 33 per cent, and the water-soluble arsenic oxid is less than 0.3
per cent in a good grade of commercial acid lead arsenate.

Robinson and Tartar (37) reported analytical results on commercial
lead arsenates and described various tests used to determine the
forms in which the lead and the arsenic are combined, as well as the
extent to which these forms exist in such substances.

In acid lead arsenate the ratio by weight of arsenic oxid to lead
oxid is theoretically 1 to 1.94. According to the results of the
analysis (Table 3), however, this ratio is somewhat lower in com-
mercial lead arsenates, showing that a slight excess of lead oxid
(litharge) had been used in their manufacture in order to make sure
that no uncombined arsenic acid would be left in the product. A
small amount of carbon dioxid, which had been introduced in the
litharge, was found in the acid lead arsenates tested. This is of no
practical significance. In all but three of the powdered samples the
moisture content was less than 0.35 per cent. The water of consti-
tution of acid lead arsenates is theoretically 2.58 per cent. The
results by difference show differences slightly greater than the theo-
retical figures, but in no case are they of any magnitude. The per-
centages of arsenic oxid and lead oxid, together with the low per-
centage of water-soluble arsenic oxid, indicate that the commercial
acid lead arsenates examined were good and stable products.

BASIC LEAD ARSENATE.

The early investigators recognized ‘basic,’ or ‘‘sub,”’ arsenate of
lead and applied the term ‘neutral lead arsenate” to PbHAsO,,
which is the present commercial acid lead arsenate. They also ap-
plied the term ‘‘neutral lead arsenates’”’ to lead pyroarsenates, which
are not commercial products, and therefore will not be discussed here.
McDonnell and Smith have printed a report on pyroarsenates (27).
‘As a result of another investigation on basic lead arsenates, these
authors (28) report the existence of a basic arsenate eens optical
and crystallographic properties similar to those of mimetite, from the
analytical data apparently hydroxy mimetite, containing one mole-
cule of water of crystallization. e or two manufacturers of in-
secticides sell, generally on special order, what is commercially called
“'T. P.” arsenate.

Basic lead arsenate may be prepared as follows: Produce basic lead —
acetate by the action of acetic acid on lead or lead oxid, usually
litharge. Then mix it with arsenic acid, thus forming basic lead ar-
senate. Basic lead arsenate may also be made by the reaction of
sodium arsenate, litharge, and nitric acid, or by the action of ammonia —
on acid lead arsenate. It has the following theoretical composition:
As,O, (23.2 per cent), PbO (75 per cent), and water of constitution and ©
crystallization (1.8 per cent). The specific gravity of this substance
was found by McDonnell and Smith (28) to be 6.86.

Only two samples (Table 3, Nos. 28 and 21) of commercial basic
lead arsenate (a powder and a paste) were secured on the market. —
While these showed somewhat greater variations from the theoretical —
than did the acid lead arsenates, both are relatively pure compounds,

ARSENICALS. 7

They have essentially the same composition except for the presence
of water in the paste.
CALCIUM ARSENATES.

It is not known who made the first sample of calcium arsenate.
Pickering (37) in 1907 stated that calcium arsenate had already been
used in the United States as an insecticide. He gave the proportions
of a calcium salt and an arsenate to be united in preparing calcium
arsenate, recommending the use of an excess of lime in order to pro-
duce a calcium arsenate with all the arsenic precipitated and there-
fore containing no appreciable amount of water-soluble arsenic.

As many of the early commercial samples of calcium arsenate
contained. excessive amounts of water-soluble arsenic, frequent
scorching of foliage resulted from its use, thus retarding its general
introduction. Since 1907, many experiments to devise a method
for making a commercial calcium arsenate have been performed.
It is now being produced by many American manufacturers and its
sale is constantly increasing. The quality of the commercial pro-
duct has been much improved during the past few years, but its
course of manufacture has not yet been standardized as has that of
lead arsenate. 3

Dicalcium arsenate (CaHAsO,H,O) contains theoretically 28.3 per
cent of calcium oxid and 58 per cent of arsenic oxid. It breaks down
easily in water, yielding a large quantity of water-soluble arsenic and
is not suitable for commercial spraying purposes.

Calcium meta-arsenate (Ca(AsO,),) was prepared according to
directions obtained from C. M. Smith, of the insecticide and fungicide
laboratory. Because of its extreme insolubility, it can not be used
for insecticidal purposes.

All the commercial calcium arsenates are made more basic than
tricalcium arsenate; that is, the molecular ratio of calcium oxid to
arsenic oxid is 4 to 1, rather than 3 to 1. The additional lime is
used in their manufacture in order to produce compounds relatively
free from water-soluble arsenic.

The following simple method of preparing calcium arsenate com-
mercially, as outlined by Haywood and Smith (18), calls for the
direct mixing of calcium hydroxid and arsenic acid, the only
by-product being water: Slake the lime to a smooth paste by usin
from 3 to 34 times as much warm water (by weight) as lime, and
allow it to stand until the lime is completely slaked. Then mix it,
add the cold arsenic-acid solution at room temperature as rapidly
as possible, and stir the mixture well until the liquid becomes alka-
line to phenolphthalein. Lastly, filter, dry, and grind the resulting
compound.

The lime and arsenic acid should be mixed in such proportion
that the actual weight of calctum oxid used will be equivalent to
that of the arsenic oxid employed. This method produces a reason-
ably light (bulky) material, which is easily pulverized. The finished
ae should contain approximately 44 per cent of calcium oxid,

rom 40 to 42 per cent of arsenic oxid, and from 14 to 16 per cent of
.water and impurities, which approaches the ratio, 4 CaO: 1 As,O,.
The excess of lime is used to keep any soluble calcium arsenate from
remaining in the product.

8 BULLETIN 1147, U. S. DEPARTMENT OF AGRICULTURE.

The analytical results on nine samples of calcium arsenate are
recorded in Table 3. Samples 6, 24, and 34 were not strictly com-
mercial products, but were made by the manufacturers as an experi-
ment. Sample 24 contains a higher percentage of arsenic than the
strictly commercial samples. Samples 6, 24, and 34 have a lower
lime content than the six commercial samples analyzed, and it is
probable that a portion of their arsenate is in the form of dicalcium
arsenate. The somewhat large amount of carbon dioxid found in
all of the samples of calcium arsenate comes from the lime, which
is always carbonated to a certaim extent. The water of the calcium
arsenates varies more than that of the lead arsenates. Analyses of
samples 56 and 57 showed, respectively, 11.75 per cent and 12.35
per cent loss on ignition, 0.35 and 0.5 per cent of ferric oxid and
aluminum oxid, 0.51 per cent and 0.74 per cent of magnesium
oxid, and 0.62 per cent and 0.51 per cent of sodium oxid. Sample
56 contained 0.35 per cent of antimony oxid. |

Lovett (23) in 1918, reported a high water-soluble arsenic content
in samples of commercial calcium arsenate. Since then the amount
of water-soluble arsenic in commercial calcium arsenate has been
reduced, as shown in Table 3. Lovett (24) in 1920 published graphs
showing the chemical features of calcium arsenate, apparently based
on the percentages of lime or on the ratio of lime to arsenic oxid
in the calcium arsenates. No consideration seems to have been
given to the percentages of total and water-soluble arsenic oxid
which are the generally recognized criteria for judging the quality of
calcium arsenates chemically.

Robinson (35), who tested the solubility of calcium arsenates
in water containing lime, reported that the lime prevents the arsenic
oxid from becoming soluble. He also studied the action of carbon
dioxid on calcium arsenates and found that carbonic acid has a
solvent action upon the calcium arsenates. Patten and O’Meara
(30) made a series of tests on the amount of soluble arsenic oxid
obtained from calcium arsenate in water containing carbon dioxid
and in water free from carbon dioxid. From their results, which
showed a great increase of soluble arsenic oxid when carbon dioxid
was present, they concluded that the burning of foliage, when
calcium arsenate is applied, is due to the arsenic made soluble by
the carbon dioxid of the alr.

The commercial calcium arsenates contain approximately one-
third more lime than is required by tricalcium arsenate. They con-
tain a higher percentage of total arsenic oxid than the lead arsenates;,
but they should be manufactured more cheaply per unit of arsenic
oxid because of the low cost of the base (CaO),

Coad and Cassidy (10) have recommended that calcium arsenate
for dusting cotton should contain not less than 40 per cent of arsenic
oxid and not more than 0.75 per cent of water-soluble arsenic oxid,
and ve it should occupy a volume of from 80 to 100 cubic inches a
pound.

PARIS GREEN.

Paris green, originally used as a paint pigment, is said to have first.

served as an insecticide|in the western United States. It is a com-
pound of arsenic, acetic acid, and copper, known as aceto-arsenite of
copper. The theoretical composition of Paris green is copper oxid

ARSENICALS.. =; <A! 9

(31.39 per cent), arsenious oxid. (58.55 per cent), and acetic anhydrid
(10.06 per cent).

The manufacture of Paris green,* which has become standardized,
may be briefly described thus: Solutions of soda ash (commercial
anhydrous sodium carbonate) and arsenious oxid are first heated
together, forming sodium arsenite. Crystalline copper sulphate is dis-
solved in warm water in a separate container. The sodium arsenite
mixture is poured into a mixing tank, the copper sulphate solution is
added, and the mixture is stirred. Acetic acid is added, and after a
little stirring the olive-colored mixture becomes green. The Paris
green is washed with water, after which it 1s allowed to settle and all
the water that can be drained off isso removed. This washing should
be repeated as often as necessary to remove practically all the sodium
sulphate. The Paris greenisthendried. The dried product is passed
through a ‘‘breaker” and finally through a. fine sieve or a bolting
machine.. The ‘‘tailings” are mixed with the next batch of Paris
ereen. The finely divided Paris green is now ready to be placed in
containers.

The color of Paris green varies with the details of manufacture and
the degree of fineness of the product. The composition of Paris green
on the market ranges from 54 to 57 per cent of total arsenious oxid,
from 1.5 to 4.5 per cent of water-soluble arsenious oxid, and from
29 to 30 per cent of copper oxid. |

Haywood (17) stated that-the impurities in Paris green include
small amounts of sand, sodium sulphate, and arsenious oxid, and
pie that the soluble arsenic in Paris green produces scorching of
foliage.

Paris green, when of a high grade, breaks down to some extent when
water is added, but when it has been improperly prepared much more
soluble arsenic is yielded on treatment with water. Avery and Beans
(2) found that high-grade Paris green was slowly attacked by water
and that the rate of decomposition was increased by grinding to a very
fine powder and suspending in water. They also found that the pres-
ence of carbon dioxid in the water increased the rate of decomposi-
tion. There are two sources of the soluble arsenic in Paris green, (a)
the soluble arsenic originally present in the sample, and (b) the
arsenic made soluble by water and carbon dioxid.after the material
has been applhed. The admixture of lime with Paris green when used
as a spray lessens its scorching properties. Analysis of a typical
Paris green (sample 64) is given in Table 4.

MISCELLANEOUS COMMERCIAL ARSENICALS.

Analyses-of samples of several miscellaneous arsenicals which were
tested against insects are given in Table 4.
eles of the manufacture of Paris green are given in 45 Ann. Rept. Sec. Mass. State Board Agr. (1897),
p. 357.
100173°—24—Bull. 1147-2

10 BULLETIN 1147, U. S. DEPARTMENT OF AGRICULTURE.

Zine arsenite is made by heating together arsenious oxid, zinc
oxid, and water. It is sold only as a powder. The arsenious oxid
content of the two samples (Nos. 23 and 33) analyzed is pipe
mately the same as the average arsenic oxid content of the calcium
arsenates on the market. The water-soluble arsenious oxid figures
are alittle higher than the results for the best grade of lead or calcium

TABLE 4.—Composition of miscellaneous arsenicals.

Total Total ares
Rample Material analyzed. Moisture, *7Senious | arsenic | arsenious
(Asi03). | (As:03). | (226)
: ‘ Per cent.| Percent. | Per cent Per cent
23 | Commercial zinc arsemite.............-eeeeeeeeee 0.15 41, 49: \ortcy <2 5.2... 0. 52
oe leew e NER ReE dt SHE Sec Re ee Oa eee et - 06 42: DS... pate oo we - 85
64 | Commercial Paris green... ... cc ccccecccccccseces -53 MOsU9) | ee 3 os 1.94
36 | Commercial calcium and lead arsenates........- SHLD: Le ctercea tea Gar oobe AG TEIN | aac ia
8 | Commercial calcium and lead arsenates plus
calcium carbonates.) Sik. ceeds. te ses oe HOS jsos22 secs. | 21.95 |...-..2..e00
62 | Commercial magnesium arsenate.............-. 2: 9G |bn0 teeta 3o.U0, locos aeeeeens
71 | Laboratory barium arsenate............2-.222-- S29 tS 332. SES SOLOS NS EE Re
74 | Laboratory copper and barium arsenate........ 1 Py 4:8) eee 14 36 ee ee
73 {| Laboratory aluminum arsenate................- HOS 294 | nonce e cere 31: Os tose ne fee
31 | Commercial sodium arsenate............-...-.-- 3/4019 2 pees 45. AGiic od Leceey
Ca ee BG 6.s be oe on Ode hod t cats os dutta devin ne oon CRS 7 RRS ae a eine htea el
25 | Laboratory sodium arsenate............-.-..--- S754 FERS. STOR. 5. . SERS
26 | Laboratory potassium arsenate. ..........-.---- So wee see 59.39 fre. 202 eee
90 | Commercial London purple...............------ 6. 41 31.10 ~ 25 1.41
alti Carb
soluble arbon
Sample Material analyzed. arsenic Oxid. dioxid | Undeter-
0. oxid (CO). p=
(As20s).
|
Per cent.| Per cent. Per cent. | Per cent.
Z3',| COMMEPCIAl ZINC ATSAMIGCs os sicanceeccee cee eclneeeseesee 56-30 (ANNOY [eo cconcsce
Sar leneee OLS SESE Ltd. SEIS BE SIRE: RIVES Eee 56. 46 (an0} es. Sess 94
64 | Commercial Paris green..........222--22-2eeeeee|ecceeceeee!| { . a (Caos \ wack ads 35.92
36 | Commercial calcium and lead arsenates......... 1.14 ny 'p C203 1. 50 5.75
8 | Commercial calcium and lead arsenates plus
calciumuear Donates crass se ox) nce edes caiaels « -53 e 3 (Pe9} \ 23. 23 5.31
62 | Commercial magnesium arsenate...............- 1.56 | 34.32 89} -55 28. 57
71 | Laboratory barium arsenate.-................... -21 | 64.96 ears 1.33 2.49
74 | Laboratory copper and barium arsenate........ -90 ip % (Bu0} \ 13 25. 08
73 | Laboratory aluminum arsenate................. -72| 16.84 (42093 SSSISS EEE 35. 22
31 | Commercial sodium arsenate...........---.-...- 45.16 | 45.76 (NasO) |.......... 5.68
13 I hie OO Ie aiene ceca sn bie eeee aeaaw inne ae ene 59.80 | 27.66 (NasO) |.......... 6. 22
25 | Laboratory sodium arsenate...........-.-----.- 37.99 | 19.35 (NasO) |.......... 5.12
26 | Laboratory potassium arsenate............-...- 59:30 | 750.00) (50) [ose cles 4. 26
90 | Commercial London purple............-.......- -25| 3488 (CaO 4. 37 22. 99

arsenates. For more detailed information, the publication of Schoene
(44) on zine arsenite should be consulted.

Magnesium arsenates.—It is theoretically possible to prepare
ortho, meta, and pyroarsenates of magnesium in the same manner
as the corresponding arsenates of lead. Practically twice as much
magnesium, calculated as magnesium oxid, was found in the sample
analyzed as is needed to combine with the arsenic oxid present.
Patten and O’Meara (30) give analytical results on a magnesium
arsenate containing 32.13 per cent of arsenic oxid and 1.25 per cent
of water-soluble arsenic oxid. They found 41.7 per cent of the
total arsenic to be soluble in water containing carbon dioxid. A
commercial magnesium pyroarsenate analyzed je them had a low

ARSENICALS. 11

solubility in water and yielded only 3.01 per cent of arsenic oxid
soluble in water saturated with carbon dioxid.

London purple, originally a by-product in the manufacture of
aniline dyes, is now made directly to a limited extent. It consists
of arsenite of lime and arsenate of lime, with the addition of a dye.
Table 4 gives the composition of the material used in the investigation.
The Tila of four additional samples showed the following varia-
tions: Arsenious oxid, 18.30 to 29.38 per cent; arsenic oxid, 0.07 to
11.49 per cent; water-soluble arsenious oxid, 0.48 to 5.30 per cent; and
water-soluble arsenic oxid, 0.07 to 2.46 per cent. One sample showed
24.91 per cent of calcium oxid, 2.70 per cent of magnesium oxid, and
11.25 per cent of ferric oxid and silicon dioxid. London purple,
therefore, is of uncertain composition and contains varying amounts
of water-soluble arsenious oxid and arsenic oxid. On account of its
variable character and its tendency to burn foliage, the addition of
lime is recommended when it is used as a spray.

Calcium and lead arsenates combined (samples 36 and 8) were
analyzed and tested on insects. The demand for a mixed calcium
and lead arsenate is limited. It is held by some that lead arsenate
adheres to foliage better than calcium arsenate, so that the presence
of a little lead arsenate in the mixture increases the adhesive pron
erties. The use of calcium carbonate in the mixture reduces the
percentage of arsenic present and permits the product to be sold
more cheaply.

Sodium arsenate was formerly on the market in two grades, a 45
per cent and a 65 per cent arsenic oxid product. During the past
three or four years it has been difficult to obtain sodium arsenate -
in commercial quantities. In preparing sodium arsenate contain-
ing 45 per cent of arsenic oxid, nitrate of soda (NaNO,), arsenious
oxid (As,O,), sodium carbonate (Na,CO,), and salt (NaCl) are
roasted together. In preparing the 65 per cent grade the salt is
omitted. The two commercial samples (Nos. 31 and 41) correspond
to these two grades, although sample 41 contains only 60 per cent
of arsenic oxid. Sample 31 contains 28.44 per cent of sodium
chlorid, sample 41, 6.14 per cent, and sample 25, 0.096 per cent.
Calculating the results for these two samples and for sample 25
(prepared in the laboratory) to a moisture-free basis, sample 25
contains 60 per cent, sample 31 about 47 per cent, and sample 41
about 64 per cent of arsenic oxid. All the arsenic present in sodium
arsenate is water soluble. Sodium arsenate is sometimes added to
Bordeaux mixture to produce a combined fungicide and insecticide.
The excess lime of Bordeaux combines with the arsenic oxid of the
sodium arsenate, forming insoluble calcium arsenate. The amount

of sodium arsenate added and the amount of the excess lime of the

Bordeaux are the factors which determine whether all of the soluble
sodium arsenate is converted into the insoluble calcium arsenate.

Potassium arsenate.—Sample 26 is a laboratory product contain-
ing 59.39 per cent of arsenic oxid, all of which is soluble in water.
No commercial samples of potassium arsenate are now available.

MISCELLANEOUS EXPERIMENTAL ARSENICALS.
The analytical results on three samples of lead arsenates and four

. om les of calcium arsenates made in the laboratory are given in
_ Table 5.

a

12 BULLETIN 1147, U. S. DEPARTMENT OF AGRICULTURE.

TABLE 5.—Composition of lead and calcium arsenates prepared in the laboratory.

Arsenic oxid Water of
As2Q35): . constitu-
Lead {Calcium} Carbon | tion and

i i ioxid | impuri-

ture {| 10 SIRF iAP Soma oxid 0
Water- | (PPO). | (CaO). | (COs). | ties, by

soluble.

Samnle Material analyzed. Mois-

Total. er-

ence.

Per ceni.| Per ceni.| Per cent.

17 | Acid lead arsenate. ...... 5.2... 0.0 33. 09 SOO 12 FF. we SHI LAG. 3.09
63 (2.6: OiIBe SOUP... an 5 i " © 00 d- 76546 Fe) aes oo ea ES 2.98
181, Basic lead arsenate... oscasl 000) nda SD ben, on Oh aude oecnageeiecoee see 1.88
45 | Calcium meta-arsenate 18. 0. 00 1,39
46 | Monocaleium arsenate 19. 92 Patt 10. 66
42 | Tricalclum arsenate.......... o 52. 46 40. 07 ~. 5.86
69 }.2.k. CDUMIBY 2Ltetiias rs 44, 89 yp 4, 24

Lead arsenates—The two samples of acid lead arsenate (Nos.
17 and 68) contained percentages of arsenic oxid very close to the
theoretical. (33.11).. They were prepared by mixing lead nitrate

and arsenic acid, according to the procedure of McDonnell and Smith |
(27). The percentage of lead oxid in the two samples is a little lower |

than the theoretical. Basic lead arsenate (sample 18) was prepared

by the action of ammonia on acid lead arsenate. There is slightly |
more arsenic oxid and slightly less lead oxid in this sample than 1s |
called for by the theoretical figures. Both the acid and basic lead |
arsenates were made from pure lead oxid and crystallized arsenic |

acid; consequently they are extremely pure.

. Calcium arsenates.—A_calcium meta-arsenate (Ca(AsO,),) (sample |
45) was prepared according to directions obtamed from C. M. Smith |
of the insecticide and fungicide laboratory. The theoretical per- |

centage. of arsenic oxid for,such a product is 80. No moisture or
carbon dioxid was preseyt in the sample, as the product had been
REP Although
t

calcium arsenate (CaH,(AsO,),) (sample 46) was also prepared
according to, Smith’s directions. Its theoretical composition is as
follows: Arsenic oxid (71.4 per cent), calcium oxid (17.41 per

cent), and water of crystallization and water of constitution (11.19 |
per cent). This compound is very soluble in water and can not be |

considered a commercial possibility as an insecticide. Two samples

of tricalcium arsenate were prepared. The composition of sample

42 approached the theoretical composition of tricalcium arsenate
(Ca,(AsO,),.2H,O) as determined by Robinson (35), 38.7 per cent of

calcium oxid, 53 per cent of arsenic oxid, and 9.3 per cent of mois- |
ture and water of constitution. Sample 69 was prepared by using —
equal weights of lime and arsenic oxid, which gave a compound with an |

excess of lime, having slightly more than 4 equivalent parts of calcium
oxid to 1 part. of arsenic oxid, and containing but 0.17 per cent
of water-soluble arsenic oxid. Calcium arsenate of this composition

was recommended by Haywood and Smith (78) as suitable for com-

mercial manufacture.

Barium arsenate seems to have been used first by Kirkland (20) in |

1896. The next year Kirkland and Burgess (?/) tested barium arse-
nate against certain insects. Smith (48) in 1907 also used a barium
arsenate. Its preparation is not described by any of these investi-

gh in arsenic oxid, the product is so insoluble |
at its. isecticidal properties would undoubtedly be low. A mono-

|

{
}

.

|

ARSENICALS. 13

gators. A sample of barium arsenate (sample 71, Table 4) was pre-

ared by adding a solution of arsenic acid to a solution of barium
A sinha) with constant stirrmg. The details were as follows:
Dissolve 546 grams of barium hydroxid (Ba(OH),.8H,O), containing
240 grams are acai in 3 liters of water to which 300 cubic centi-
meters of commercial arsenic acid, containing 0.4 gram of arsenic
oxid per cubic centimeter, has been added: After this mixture has
been thoroughly stirred, the precipitated barium arsenate soon settles.
Then wash the precipitate several times by decantation, filter it on
a Biichner filter, dry and pulverize it, and finally pass it through
a 100-mesh sieve. The theoretical composition of tribarium or-
thoarsenate (Ba,As,O,) is as follows: Barium (59.7 per cent) and
arsenic oxid (33.32 per cent); that is, the ratio of arsenic oxid to
barium is 1 to 1.8. The ratio for the sample made in the laboratory
was 1 to 1.9, showing the presence of a slight excess of barium. Its
insecticidal value is discussed on page 38.

Copper barium arsenate mixture (sample 74, Table 4) was made as
follows: A solution contaiing 360 grams of copper sulphate was mixed
with 275 grams of arsenic oxid. No precipitate resulted. <A dilute
solution of barium chlorid was added and then barium hydroxid un-
til the solution was but slightly acid. ‘The mixture of copper and
barium arsenate and barium sulphate was then thoroughly stirred
and allowed to settle. The precipitate was washed several times by
decantation and then was separated by filtermg on a Buchner filter.
The precipitate was finally dried, ground, and passed through a 100-
mesh sieve. Its adhesive and fungicidal properties have not been
tested, but its insecticidal powers are discussed on pages 38 to 46.

Aluminum arsenate (sample 73, Table 4) was prepared by mixing
a solution of aluminum sulphate with arsenic acid. The precipitate
was washed, filtered, and dried. The insecticidal esults of this
product are discussed on pages 38 to 42.

Copper arsenate was eee ae by mixing a solution’ of copper sul-
phate with arsenic acid and then adding ammonia. The percentage
of water-soluble arsenic oxid in this product was so high that no ad-
ditional tests were made with the sample.

Zine arsenate has been prepared by several investigators. The
sample prepared in this study was made by mixing a solution of zinc
chlorid with arsenic acid. Its physical properties did not seem to
warrant further study. 7

COMBINATIONS OF ARSENICALS WITH FUNGICIDES AND OTHER MATERIALS.

In order to reduce the cost of spraying, various combinations of
arsenicals with fungicides are frequently made. The arsenicals are
also mixed with other substances, like glue and casein, to increase the
leneth of time the arsenicals will adhere to the foliage or fruit.

While some of these combinations are frequently made, very little
exact knowledge as to the chemical changes which take place in them
is available. Accordingly, an investigation was undertaken to
obtain information on the changes which occur in some of the im-
portant combinations involving arsenicals. One pound of powdered
acid lead arsenate per 50 gallons of water is recommended as satis-
factory for most commerical spraying. Acid lead arsenate at

_ this rate and other arsenicals in corresponding amounts, depending

ee ee

on their arsenious or arsenic oxid contents, were used in the tests.

14 BULLETIN 1147, U. S. DEPARTMENT OF AGRICULTURE.

Thus amounts of the arsenicals containing equivalent percentages of
arsenious or arsenic oxid were taken in each case.

In all the tests the mixtures of the arsenicals and other material
were agitated in flasks by rotating in a water bath which was main-
tained at a constant temperature of 35° C.. All were made in trip-
hicate, but only the average figures are reported in the tables. The
soluble arsenic (that found in the filtrates) was determined by the
modified Gutzeit test (47) or by the Gooch-Browning method (1).

ARSENATES AND LIME-SULPHUR.

Ruth (38) made a study of the chemical changes resulting when
acid lead arsenate and lime-sulphur were mixed. He found (a) a
decrease of lime and sulphur in the solution, (6) an increase of
thiosulphate sulphur in the solution and in the residue, (c) an increase
of culphies in the solution, (d) formation of lead sulphid, and (e) the
formation of a compound containing arsenic and sulphur, but in-
soluble in the lime-sulphur solution. Robinson (35), after agitating
mixtures of lead arsenate and lime-sulphur for three days, allowed
them to settle and then poured off the clear liquid. He found that
25 per cent of the lime and more than 35 per cent of the sulphur had
been precipitated and that 5 per cent of the arsenic had become
soluble. Robinson and Tartar (37) tested mixtures of lime-sulphur
and lead arsenates (4.8 grams of arsenate per 1,000 cubic centimeters
of lime-sulphur, diluted 1 to 30). When basic lead arsenate was
used little change occurred, but when acid lead arsenate was used an
increase of soluble arsenic and a decrease of total soluble sulphur
and polysulphid sulphur resulted. They concluded that the efficiency
of ‘i ime-sulphur had been reduced 25 per cent, and that the
arsenic rendered soluble might injure foliage. Fields and Elliott
(15) present data showing that less than five parts per million of
arsenic oxid by weight was made soluble when solutions of lime-
sulphur were mixed with either acid or basic lead arsenates.

n the present investigation standard commercial lime-sulphur
solution was diluted (1 to 30) with recently boiled and cooled distilled
water. Control flasks (500 cubic centimeters volume), completely
filled with this diluted solution, were securely closed with stoppers
and paraffin and agitated for 1-hour and 91-hour periods. Other
flasks, filled with the diluted solution of Heel ees to each of
which 1.2 grams of powdered acid lead arsenate (sample 39) had been
added, were aivnilatly treated. Series of three flasks were removed,
and the solutions were filtered immediately on removal from the bath.
The results obtained with lead »rsenate are given in Table 6.

ARSENICALS. 15

TABLE 6.—Composition of lime-sulphur solution and of the filtrates from mixtures of
lead arsenate or calcium arsenute and lime-sulphur solution.

Composition (grams per 500 cubic centimeters).

After
Material analyzed eee Thio
EN Total | Total | Sulphid ~ | Sulphate| Arsenic
snake lime sulphur | sulphur sulprate rig oxid
(CaO). (S). (S). (8). (S). | (As20s).
SERIES 1:
Bese. 6a Gat 1 hour..... 1.9680} 4.9480} 4.5190 | 0.1960] 0.0035 0. 0002
Bee a wea 91 hours... 2. 0520] 4. 2290 4. 5060 +2030 - 0069 - 0902
] : 1 hour..... 8050 | 4.4770 ; 020 . 0029 . 0270
Te ae UTES PFI tations lei b os 5, 4.2670 | 4.0450) 1990] 10055 0205
Fnbiie eoliti AB Naurs 2 |an ese a: 4,2560 | 3. 9080 1980 . 0036 .0199
a : Be a ae is 2 91 hours 1.8030] 4.2790] 3.7110 1970 6 0200
ERIES 2:
hour..... 1.9800 | 5.2500} 4.7800 . 3200 0089 . 0002
Lime-sulphur solution.... ehours:.) oe gap 2 oan 7 lt 19200 50 One
BVSe eee : i . 5 5 :
Filtrates from mixtures of |{1 hour..... 2.0400 | 5.1000} 4.7500 . 3200 . 0089 . 0008
calcium arsenate and {421 hours 2. 0600 5. 0500 4. 6800 3300 . 0087 . 0005
lime-sulphur solution ...| (5 days..... 1. 9600 5. 1000 4. 7000 3600 0108 0010

Using the analytical data on the lime-sulphur solution as controls,
the analytical results on filtrates from a mixture of lead arsenate and
lime-sulphur solution show the following: (a) The total lime in
solution was reduced 10 per cent after having been shaken for either
1 hour or 91 hours; (0) ie total sulphur in solution was reduced 9.5
pes cent after 1 hour and 14 per cent after 19, after 43, and after 91

ours; (c) the sulphid sulphur was reduced 8 per cent after 1 hour and
18 Pe cent after 91 hours; (d) the thiosulphate sulphur remained
unchanged after each period; (e) the sulphate sulphur increased
slightly, although the same increase was observed in the control; and
(f) 5.2 per cent of the total arsenic oxid of the lead arsenate used was
rendered soluble. From these results, it is apparent that chemical
changes have occurred. The mixture is therefore chemically in-
compatible.» Some of the sulphur in lime-sulphur solution probably
united with the lead of the lead arsenate and produced lead sulphid,
which could be seen as black particles in the mixture. The arsenic
oxid group, liberated by the decomposition of the lead arsenate, was
then free to combine with the lime in the lime-sulphur solution,
probably forming calcium sulph-arsenate. The formation of in-
soluble tricalctum arsenate took place only to a limited degree.

Robinson (34) in examining mixtures of calcium arsenates and
lime-sulphur found that no reaction took place in such mixtures.
His tests with “dry lime-sulphur”’ mixed with calcium arsenate
showed the presence of no soluble arsenic, but those with “soluble
sulphur” mixed with calcium arsenate showed that it was present.
Lovett (24) also reported that no changes take place when calcium
arsenate is mixed with lime-sulphur solution.

Experiments similar to the lead arsenate tests were performed,
using calcium arsenate (sample 57) in place of the acid lead arsenate.
A series of 500 cubic centimeter flasks were filled with lime-sulphur
solution diluted 1 to 30. Nine of the flasks were used as controls;
to each of the others 1 gram of calcium arsenate was added. The
solutions were agitated for periods of 1 hour, 21 hours, and 5 days.
They were immediately filtered and the filtrates were tested.

—E

’ The term “‘compatible”’ is here used only in the chemical sense.

16 BULLETIN 1147, U. S. DEPARTMENT OF AGRICULTURE.

The data given in Table 6 (series 2) show that no detectable changes
took place when calcium arsenate and lime-sulphur were mixed.
The small amount of arsenic found in the filtrates was the water-
soluble arsenic originally present in the calcium arsenate and
amounted to 0.2 per cent of the total arsenic oxid in the calcium
arsenate.

In brief, it is evident that chemical changes take place when acid
lead arsenate and lime-sulphur are mixed: This mixture is therefore
incompatible chemically. When calcium arsenate is mixed with
lime-sulphur no soluble arsenic is formed in the case of high-grade
products. Therefore this arsenate, when mixed with lme-sulphur,
would seem to be a satisfactory insecticide. Field experience, how-
ever, shows that it often injures the foliage sprayed.

Such a mixture is chemically compatible and has been recommended
by Quaintance and Siegler (32), Sanders (40), and others, who, how-
ever, do not claim that it is always free from burning properties.

No experiments with basic lead arsenate and lime-sulphur were
performed. Bradley (4), in 1909, used basic lead arsenate in com-
bination with lime-sulphur, and found 0.28 and 0.43 per cent of
soluble arsenic. He considered that there was no danger of the
formation of excessive amounts of soluble arsenic in such mixtures.
Bradley and Tartar (6), who used both acid and basic lead arsenates
in combination with lime-sulphur, found eight times more soluble
arsenic with acid lead arsenate than with basic lead arsenate. Both
forms of lead arsenate were more soluble in saline water than in pure
water. Alkaline carbonates exerted a decomposing action, especially
on acid lead arsenate.

ARSENATES AND BORDEAUX MIXTURE.

Fields and Elhott. (1/5) stated that very little soluble arsenic is
present when Bordeaux mixture is combined with lead arsenate.
They found in both the acid and the basic lead arsenates only from
1 to 3 parts of soluble arsenic per million. |

Since combinations of arsenicals with Bordeaux mixture are fre-
quently made, it was considered important to determine whether or
not chemical changes take place in these combinations. ‘Tests were
therefore conducted in which 4—3.67—50 Bordeaux mixture was pre-
pared, dried, and passed through a 100-mesh sieve. Four-gram sam-
ples of the dry Bordeaux were placed in each of a series of 300 cubic
centimeter flasks and to each flask were added portions of one of the
four arsenicals in the following amounts: 0.8 gram of acid lead arse-
nate (sample 39); 0.667 gram of calcium arsenate (sample 57); 0.69
gram of sodium arsenate (sample 25); and 0.47 gram of Paris green
(sample 64). Mixtures of the various arsenicals alone and of Bor-
deaux alone in distilled water were prepared and tested under the
same conditions as the mixtures of the arsenicals and Bordeaux. The
flasks were agitated at a temperature of 35° C. for periods of 1 hour,
1 day, and 3 days. The mixtures were filtered immediately and the
filtrates were tested, for copper by the colorimetric test, with potas-
sium ferrocyanid (12) and for lead by the lead sulphid color test as
used by W. D, Lynch, of the insecticide and fungicide laboratory.
The analytical data are given in; Table 7.

No copper was found in any of the filtrates. The filtrates from the
acid lead arsenate Bordeaux mixtures contained the following per-

ARSENICALS. 17

centages of the total lead present in the sample: For the one-hour
period, 3 per cent; for the one-day period, 7 per cent; and for the
three-day period, 7.6 per cent. The results for water-soluble ar-
senic in the combinations are lower than those for water-soluble ar-
senic in the arsenicals alone. It is evident that the excess lime of the
Bordeaux combined with part of the soluble arsenic present in the
arsenates, forming insoluble calcium arsenate.

The results show that Bordeaux mixture and the arsenates of lead
and calcium, as well as Paris green, are compatible, that a soluble ar-
senate, such as sodium arsenate, may be used in quantities large
enough to act as an insecticide in combination with ordinary Bordeaux
mixture, and that the excess lime of the Bordeaux will combine with
the soluble arsenic to form insoluble calcium arsenate.

ARSENATES AND KEROSENE EMULSION.

As kerosene emulsion is occasionally used in combination with acid
lead arsenate and may be used with calcium arsenate, a series of
experiments was undertaken to determine whether detectable chemical
changes take place in these combinations.

A kerosene emulsion was prepared according to the following direc-
tions:® One liter of commercial kerosene oil and 1 ounce of sodium
fish-oil soap in water were mixed, and the resulting emulsion was
diluted to 10 liters.

A series of 300 cubic centimeter flasks were filled with this emulsion
and 0.8 gram of acid lead arsenate (sample 39) or 0.667 gram of cal-
cium arsenate (sample 57) was added to each of the flasks, with the
exception of the control flasks. Mixtures of the arsenates alone
and of the emulsions alone were used for controls. The mixtures
were agitated at 35° C. for periods of one hour, one day, and three
days. They were filtered immediately and the filtrates were tested
for arsenic. The average figures only are recorded in Table 7.

TaBLE 7.—Soluble arsenic in filtrates from combinations of arsenicals with Bordeaux
mixture and with kerosene emulsion.

Soluble arsenic (As) found | Percentage of total ar-

Totalar- after standing for— senic (As) found soluble
Sample Material analyzed senic (As) : ater standiae
No. ai in sample
taken.
lhour. | 1 day. | 3 days. | Lhour. | lday. | 3 days.

Grams. | Grams. | Grams. | Grams. |Per cent.| Per cent.| Per cent.
25 | Sodium arsenate...........- Qi4909 dieu 43 s¢ce% Lhe Oi1GhOs (isso Ekel bd... 96. 55
64.1 Pariserecna j.s2"55 020-24 2 | $4938 det Gexs war [OS sree Fu sO06Gislotsosszejeseole . - 3. 41
57 | Calcium arsenate............ zi (Soebasess 3 (eos dic S000S4 ilseisesealel iiss. : 0. 20
39 | Acid lead arsenate.......... 1709 eee e.f:-eSS [POA so Pteorce cee ie is Sites acute 2.81
61 | Bordeaux mixture ........- Seaserees = = eee See rere [Sas OODOG" Essent nia. er. oe ee

— | Sodium arsenate (25) plus
Bordedux (GDS 2.2 o.. .. - - 1709 | 0.00095 | 0.00001 00001 0. 56 0. 00 00

— | Paris green (64) plus Bor-
deamixa(Ghys <0. $k . 1938 00113 | .00053 | .00046 - 58 27 24

— | Calcium arsenate (57) plus
Bordeaux (61)-........... .1753 | .00003 | .00005 | .00000 02 03 . 00

— | Acid lead arsenate (39) plus
H ordeaue = Fk 22 2572. tht -1709 | .00051 | .00030 | .00018 30 18 siti

— | Calcium arsenate (57) plus |

kerosene emulsion........ 1753 | .0018 0095 | .0122 1.03 5. 42 6. 96

Acid lead arsenate (39) plus
— kerosene emulsion........ -1709 | .0332 0768 | .0740 19, 43 44, 94 43, 30

- § Taken from U.S. Dept. Agr. Farmers’ Bull. 958, p. 28.
100173°—24—Bull. 1147-3

18 BULLETIN 1147, U. S. DEPARTMENT OF AGRICULTURE.

The amount of arsenic made soluble was much larger when acid
lead arsenate was combined with kerosene emulsion than when cal-
clum arsenate was combined with it. The same amount of arsenic
was rendered soluble in one day as in three days in the case of the
acid lead arsenate. When calcium arsenate was used, 1.5 per cent
more of the total arsenic was made soluble the third day than the
first day. It is evident that the lead and the lime of the arsenates
combined with the fatty acids to produce soaps, leaving the corre-
sponding amounts of arsenic in a soluble condition. The results show
that less decomposition occurred in the case of calcium arsenate
mixed with kerosene emulsion than in the case of acid lead arsenate
and kerosene emulsion. Both mixtures are chemically incompatible.

ARSENATES AND FISH-OIL SOAP.

Combinations of acid lead arsenate with fish-oil soap are sometimes
made. Because of the large quantity of calcium arsenate now being
manufactured, it seemed advisable to test combinations of calcium
arsenate and of acid lead arsenate with fish-oil soap in order to deter-
mine how much arsenic might be made soluble.

Fish-oil soap solutions of two strengths, 1 and 2 pounds of soap
per 50 gallons, were prepared. The fish-oil soap was the same kind
as that used in making the kerosene emulsion. A series of 300 cubic
centimeter flasks were filled with the soap solution. No arsenical
was added to some of the flasks which were used as controls, but 0.8
gram of acid lead arsenate (sample 39) or 0.667 gram of calcium
arsenate (sample 57) was added to the others. A one-day period
was taken for agitating the solutions, because the results with kero-
sene emulsion showed that in one day the reactions were practically
-complete for the lead arsenate and much retarded in the case of the
calcium arsenate.

TABLE 8.—Arsenic rendered soluble on combining lead or calcium arsenates with fish-oil

soap.
Arsenic :
Arsenic (As) rendered
Sample Material analyzed. (As)present) “" soluble after standing
No. in sample for 1 da
taken. y-
Grams Grams. Per cent.
Bi Calcnimbarsonatenl. | sa 2c Se Se Lee oe ee eee . 0.17
39 i|-Acid lead arsenate :2.)..2-: ous cet. bo see ee an spared bk -1717 . 0032 1.86
— | Calcium arsenate plus fish-oil soap (1 pound to 50 gallons). . 1753 . 0503 28. 69
— | Acid lead arsenate plus fish-oil soap (1 pound to 50 gallons). - .1717 - 1475 85.90
— | Calcium arsenate plus fish-oil soap (2 pounds to 50 gallons). - .1753 . 0667 BS ie

Acid lead arsenate plus fish-oil soap (2 pounds to 50 gallons). -1717 - 1703

! Calcium arsenate at the rate of 0.93 pound per 50 gallons.
2 Lead arsenate at the rate of 1.11 pounds per 50 gallons.

The results obtained (Table 8) follow the trend of the results
secured with kerosene emulsion (Table 7) in that they show that
more arsenic was rendered soluble when acid lead arsenate was used
than when calcium arsenate was used. They also show that the
greater the quantity of fish-oil soap used the larger the amount of
soluble arsenic formed. All of the arsenic was made soluble when
acid lead arsenate was mixed with the soap at the rate of 2 pounds
‘per 50 gallons. The lead soaps are more readily formed than the

=~ - =F

F tas

eee

7
ES

ARSENICALS. 19

lime soaps, for which reason more arsenic was left in a free or soluble
form when acid lead arsenate was used than when calcium arsenate
was used. Based on the results of chemical analyses, both of these
mixtures are incompatible.

ACID LEAD OR CALCIUM ARSENATES AND NICOTINE SULPHATE SOLUTIONS.

Mixtures of acid lead arsenate and of calcium arsenate with a
solution of nicotine sulphate were prepared and analyzed. A 1-800
dilution of a 40 per cent solution of. nicotine sulphate was made. In
the first series 500 cubic centimeter flasks were filled with this dilute
nicotine sulphate solution and 1.2 grams of acid lead arsenate (sample
39) or 1 gram of calcium arsenate (sample 57), containing 13 per cent
of free calcium oxid was added to each of the flasks, with the ex-
ception of the controls. Results of the analyses of the lead and cal-
cium arsenates used are given in Table 3. After agitating the differ-
ent solutions for periods of one hour, one day, and three days they
were immediately filtered and the filtrates were analyzed for arsenic
and nicotine. Nicotine was determined by the official silicotungstic
acid method (/). A second series of tests, usmg two commercial
calcium arsenate samples (Nos. 32 and 59) and a pure tricalcium
arsenate prepared by C. M. Smith, was made. Sample 32 contained
9.99 per cent, sample 59, 5.23 per cent, and sample 464 no free calcium
oxid. In this series 0.6 gram of the calcium arsenate was placed in
each of a series of 300 cubic centimeter flasks, which were made to
volume with the dilute nicotine sulphate solution. These solutions
were agitated for one hour and for three days.

TABLE 9.—Results of combining acid lead arsenate or calctum arsenate with nicotine-
sulphate solutions.

Soluble nicotine after agi- Soluble arsenic oxid (As203)
tating for— after agitating for—

Material analyzed.
1 hour. 1 day. 3 days. | 1 hour. 1 day. 3 days.

500 cubic centimeter volume tests: Grams. | Grams. | Grams. | Per cent.| Per cent. | Per cent.
Nicotine-sulphate solution............ OF 2A4Sh Tse eee 0. 2820 OF00) |S. 2s 22S 0.00
Acid lead arsenate (39) plus nicotine

Shire eee ee ORE RR eS . 2748 0. 2780 . 2763 -45 0.34 - 60
Calcium arsenate (57) plus nicotine ;

Saiphates sees can se oes. en roe . 2778 . 2815 . 2815 -44 .52 -90
Acid lead arsenate (39)-:.............-. . 0000 . 0000 - 0000 SOOM aes scarier > eee sre
Calatum arsenate (57) -s22...5..02.--- . 0000 - 0000 . 0000 SaUR aecmows crs |aseseneeee

300 cubic centimeter volume tests:

Nicotine-sulphate solution............ RIAD PES ert RENEE eee oe BOO) Seas sees -00
Calcium arsenate (32) plus nicotine

Sil phatere eek eee tte ke = thon a rt W 65; Cod (Rae ai ss | Paeaoeret alas See a bes Se 1.09
Calcium arsenate (59) plus nicotine

Silphiath 22s 75 sos 656 bes b Seo -92555 ~ 1760 loess; cecbel sees. $4. 04 hee. . S5cus 11. 50
Calcium arsenate (464) plus nicotine

Syephatet 2 os. Ege Ee Re eT RET S740) ad ELON sss HOS SOs See 2 ocee 11. 36
alctenamrsenacen(Go) oer on sere ino alae coon de alc breencest loses ccedes OV hal), aac Sasi © .27
Caleurmassenatereng joe cosets seek as cel Ce a cc eea|ocebee + oc|aeces acces Ba O9) | Se Ses e ie te 2. 22
Calciumarsenate:(464) or lecrsas. sacises! = 43425) peta s|a-4e08 3. SSA as ser oss. 8 z BEY

The results (Table 9) show that acid lead arsenate (sample 39)
_ when combined with nicotine sulphate gives no increase of soluble
_ arsenic and that the amount of soluble nicotine is not altered. This
_ mixture is therefore chemically compatible.

20 BULLETIN 1147, U. S. DEPARTMENT OF AGRICULTURE.

When calcium arsenates are combined with nicotine sulphate |
solutions, soluble arsenic oxid may be produced, depending on the }
sample of calcium arsenate used and on the quantity of nicotine }

sulphate present in the mixture. The percentage of soluble arsenic |

oxid will be low if there is enough excess lime in the calcium arsenate —
to combine with the SO, of the nicotine sulphate. If sufficient excess
lime is not present, the SO, combines with some of the CaO of the
calcium arsenate, liberating soluble arsenic oxid. Calcium arsenate
(sample 57) contained 13.16 per cent of free calcium oxid, and when
combined with nicotine sulphate only 0.5 per cent of free arsenic
oxid was found. Calcium arsenate (sample 32) contained 9.99 per
cent of free calcium oxid, and when combined with nicotine sulphate
1.15 per cent of soluble arsenic oxid was found.

When the free hme in the calcium arsenates was low or absent
entirely there was a marked rise in the percentage of soluble arsenic
oxid. For example, sample 59, containing 5.23 per cent of free cal-
cium oxid, and sample 464, contaiming no free calcium oxid, gave
practically 12 per cent of soluble arsenic oxid. Sample 6 (3.68 per —
cent free calcium oxid) and sample 58 (9.06 per cent free calcium
oxid) gave, respectively, 6.67 and 2.28 per cent of soluble arsenic
oxid after being agitated for 1 hour with nicotine sulphate solution —
in the proportions given. These mixtures, therefore, are chemically —
incompatible, and the only way that such a combination should be ©
made is to use a high-grade calcium arsenate containing at least 10 —
per cent of excess calclum oxid and using a proportion of nicotine ©
sulphate no higher than that used in these tests.

The lime of calcium arsenate decomposes the nicotine sulphate, —
leaving free nicotine, but does not change the amount of nicotine
present. The results given in Table 9 show that the percentage of
soluble nicotine was not altered by the presence of calcium arsenates.

A few tests made in the insecticide and fungicide laboratory in
which free nicotine solution was mixed with acid lead arsenate or
with calcium arsenate showed that these combinations were chemi-
eally compatible. Results obtained on combining nicotine sulphate ~
solutions with Bordeaux mixture were reported ‘by Safro (39) and
Wilson (52), who claimed that such mixtures were compatible.

PHYSICAL PROPERTIES OF ARSENICALS.

A commercial calcium arsenate and a commercial acid lead arsenate —
were selected for a series of tests on the adhesive properties of these ©
substances on sprayed foliage, which was extended over three seasons
(1917, 1918, and 1919). For each 50 gallons of water 1 pound of —
powdered acid lead arsenate or an equivalent amount of calcium
arsenate, based on the arsenic oxid content, was used. The sprays
were applied to potato and apple leaves with a power sprayer. At
various periods after the sprays had been applied leaves were gath-
ered for analysis. The leaves were dried and samples of approxi-
mately 5 grams each were digested with nitric and sulphuric acids —
and analyzed for arsenic by the modified Gutzeit (47) method. The -
results (Table 10) by this method do not warrant in all cases the ex- —
pression to the degree of accuracy which the figures may imply, but —
this is the common way of expressing results where small amounts of —
a substance are present. |

|
|
|

ARSENICALS. . 21

TaBLE 10.—Arsenic on potato and apple leaves sprayed with lead or calcium arsenates.

Arsenic (As) found.

Average

Year and locality. Spray used. BunineE Per
quare | On ary
samples.| meter a
of leaf eS
surface.
1917. POTATO LEAVES. Milli-_ | Parts per
: : grams. | million.
Washington, D.C... i222... Acid lea Gs arsenate: xy 45 Nos eee apes 5 140
Cie Se er eee 2 Be Calcium arsenate. 531-5355 SR 8 3 50
Presque Isle, Me............- Acid: leadiarsenates 253s scone eee 2 80 1, 460
C2 ae ae § oh ely SA Calcium arseriates 3.525257 25250 Oe 2 56 1,270
Greenwood, Va..........--.- Acid: lead-arsenate:s3 5.225.223 5cess08s- 2 16 50
DOM ear ee ey Caleiumarsenatexss.ss255252 asses 2 19 70
1918
Washinetom sD: Cr25. e222: A Cidtlendsarsenate: ssn ssasae sae tscce ne ae Siileasreesepese 170
DQ ats ee Oe Caleinmiarsenatesss s55.5sso025255. eee sate es Shige 60
Greenwood! Val. 22.3.2 2ss22- Acid lead: arsenatersss 2525 35055325 ee Dae ee Ae 180
DONS ate Se he cee Se Walersmrarsenates ss oo eR ee ee | | a ns 270
1919.
ArinetOn) Vas. cnac <asccese ACidileadarsenate-< 225s ance ce neeen sees Layh) (eee See 260
[DY ae ee ee ee @alenimarsen ate ese ise sano aoe te oe ee ae 210
1917. APPLE LEAVES.
Greenwood, Va......:....... Aeidviead arsenate. 2s. 42 — 2% 2: #. . . 5 2se2% 2 40 510
DE ea 2 Se a eee Cal clanl ATSCHALG= ste a ene ee 2 9 120
1918
Greenwood; Was 232! 2:35. 32 Cid deadvarsenate: 2235 5s ses Ss SL ES ee 1 Se ae 130

ES OES jaa es Ae EEE Calerameparsen ate. = 4: =p =e ees 2s (edie: ates 260

The results of the tests for all three years show an average of 286
parts per million of arsenic on the dry leaves receiving the lead

_arsenate spray and an average of 219 parts per million of arsenic on

the dry leaves receiving the calcium arsenate spray. The 1917 and
1919 results show that a larger percentage of arsenic of acid lead
arsenate adhered to the leaves than of the arsenic of the calctum
arsenate. The 1918 results are practically the same for the two
arsenates.

Lime was used with certain of the arsenates in some of the 1918

tests (Table 11). Potato vines were sprayed with a commercial

4
£

K

calcium arsenate and a commercial acid lead arsenate alone and with
the addition of lime to each. Zine arsenite and calcium meta-
arsenate were used without the addition of lime. Two calcium

- arsenates, one with a molecular ratio of 3 CaO to 1 As,O; and the

other with one of 4 to 1, were tested, with and without the addition

of lime. In these two cases both 2 ounces and 4 ounces of lime per

rf

10 gallons of spray were used. The arsenious or arsenic oxid con-

tents of the sprays were made the same in all cases, with the exception
of calcium meta-arsenate. From the data in Table 11 it is evident
that the lime was of no advantage in increasing the amount of arsenic
adhering to the leaves.

22 BULLETIN 1147, U. S. DEPARTMENT OF AGRICULTURE.

TABLE 11.—Arsenic on potato leaves sprayed with arsenicals with and without the addition

of lime.+
Total
3 apeenie Apenuical Arsenic
m F oxi use A
ae Material used. (AsoO;) | per 10 se ae
in dry | gallons. | leaves.
arsenical.

Parts per

Per cent.| Ounces. | million.
24 | Calcium arsenaters: -. see osc canted aa ene anes eee Seen ee 49. 40 2 240
24A0| Sample 24 plus iisme (2 Ounces): == 33 ee Seren cee es 49. 40 2 340
40°} Acidlead arsenate. . 22. -.52- 2.0225 cine ee een se eee ee 32. 76 34 530
40A | Sample 40 plus lime (2 ounces) ........-.-.-----------s----=s--:- 32. 76 4 580
23} AINCIArSeNite 2 oe beans clon ia ei ae Se ee naa 241.49 24 540
86 | ‘Calcium meta-arsendte- ==. <2: <5 28% <2) 55a-0= ~ cso ee ee eee 79. 60 24 830
87. |: Calcium arsenate:. 23: 2th ec sets nae. pees Sa aan cess eee * 55.00 2 290
87A. ||) Sample 87plus lime (2'0unCeS) 2 nae - ae eos eae eee eee eee 55. 00 2 270
875) sample/87splusilime:(4 ounces) = 23-2 2 eo aa een ene eee ee 55. 00 2 290
88.|. Caletum arsenate. 5.63. 24..c45. 455. ese) 3) ee et ee 42. 80 24 360
S8A° | Sample 88 plusilime (Ziounees) os 22a ne eo eee eee 42. 80 v2" 280
88B_| Sample 88 plus lime) (4iounces))-2 22+ 4252-5 5- seee eee ee eee 42. 80 24 380

1 Raval percentages of As»O3 and As2Os; were used for all the sprays.
: AS» CS

During the season of 1920 potato plants were sprayed at Arlington,
Va., using (a) dry acid lead arsenate, (b) dry ‘‘suspender” ” acid lead
arsenate, (c) zine arsenite, and (d) Paris green. The sprays were
made to contain the same percentage of arsenious or arsenic oxid and
were applied four times during the season, using a power sprayer.
Nine duplicate sets of 50 leaves each were collected on the same days
throughout the season from each plot of the various sprayed vines.
These leaves (900 in ali from each plot receiving a differant spray)
were analyzed for arsenic, with the following average results, ex-
pressed as parts of arsenic per million of anid potato leaves: Paris
green, 155; ‘‘suspender”’ acid lead arsenate, 195; zine arsenite, 203;
and acid lead arsenate, 210.

The physical properties of arsenicals have been studied to some
extent since the time they were first prepared, but no complete study
has been reported. This may be due in part to the difficulties
encountered in measuring those physical properties which contribute
toward making a satisfactory product for dusting or spraying.
Wilson (53) in 1919 gave data on the burning, suspensibility, and
adhesiveness of Paris green, zinc arsenite, acid and baie lead arse-
nates, and calcium arsenate.

A series of tests was performed, using commercial powdered arsen-
icals (Table 12), to obtain comparative data on the apparent density
and suspensibility of these products. The apparent density of a
powder thers described is based on the number of grams occupying
a volume of 1,000 cubic centimeters and the suspensibility on the
volumetric readings of 30 grams of powder which had settled after
having been shaken for one minute with approximately 500 cubic
centimeters of water and having stood for 10 and for 60 minutes.

7 ““Suspender”’ lead arsenate is a trade name applied to a powdered lead arsenate containing some added
organic substance for the purpose of keeping the arsenate in suspension when mixed with water.

ARSENICALS. 93

TABLE 12.—Physical properties of commercial powdered calcium and lead arsenates and
zine arsenite.

Suspension proper-

Total nee eae stand-
arsenic ing lor
5 ample Material examined. oxid pbparent
: (As205) in y-
powders. 10 60
minutes. | minutes.
Cubic Cubic
centi- centi-
Per cent.| Grams. | meters. meters.

HON kK Calctunlarsenate 2-45 ocssiste sre es nee 45. 37 254 245 200
Shs see QO F. SSRR UREA, NIRS is ESSERE) od USAR ae 47. 83 257 188 115
O75 laces? GOP baa eS Be a stat ee fet on RTA) le 40. 38 364 365 145
OSA ee. CLO ee ee ee Oe ee nT, ee es 41. 40 365 380 120
DANES (COPS a hom SELES: ol Sat Oe ee aes re Pe ae ae 49. 40 422 170 140
GE AL ae (OO SR ae eee Rae eee Sere Lee te Ag net Oe 40. 49 532 245 57
DOReetee GOSSESR Ae Ras poe Veh e 2A TSS} by oe SAS A hee Bias Se 39.19 567 170 71
SOIRACIG T6adlarSenaies so se atisss ee ee ee 31.89 247 230 167
SOU eee (OK ye a ocala ae ea Nag eye eee A ie 32. 93 249 270 132
Soules OKC AR EH seh TURE OL DE GEN Bie Oe Rae kOe Se ey See 31.50 284 210 123
Sa as (BOVE re a Same ary rape hie ha te Sa Re ON a Sa rh 32.90 306 265 135
SSleeeee GOR ter TN Seo aC SER NE ae. PED YAS 32. 47 369 146 90
iy eee CON Ses a ate AUN em aint ee ARP NUS AL AA GOKU ER 2 RMU RUNEAT By 32. 75 TAT 88 60
DRA SATAN SASSY OC ee ack a Ae nate Oh aN Te aay ONE 341,49 355 165 77

1 Weight of powder occupying a volume of 1,000 ce. without being jarred.
4 Based on volumetric readings of 30 grams of powder, shaken with 500 cc. of waterand allowed tostand.
3 Arsenious oxid (As2Q3).

In Table 12 the calcium and acid lead arsenates are arranged
according to their apparent densities, the lightest ones first. The
lightest powders usually remained suspended for the longest time
(60-minute test) and the heavy powders settled most rapidly. More
than 90 per cent of all the arsenicals tested passed a 40-mesh sieve
after having been shaken for five minutes. These results are of no
value and therefore are not given. It is believed that the fineness
of powdered arsenicals, which are generally amorphous, can not be
correctly determined by this test, since fine powders pack in a 40-
mesh sieve. The fineness of relatively coarse arsenicals, such as
arsenious oxid, can be determined by sieving.

Microscopical examinations of the various arsenicals were made.
A large number of samples of powdered calcium and acid lead arse-
nates and one of zinc arsenite were blown from a dust gun. These
dusts, collected on six or more microscopic slides placed at varying
distances from the dust gun, were photographed. Then, using a
high-power lens of the microscope, drawings were made by the aid
of the camera lucida which made possible the determination of
shieht differences in the size of particles but did not give satisfactory
information on the dusting or spraying properties of these products.

Several samples of powdered lead arsenate and Paris green,
examined under a magnification of 100 diameters, appeared to be
amorphous. The samples of calcium arsenate contained a few
small crystals, although the samples on the whole appeared to be
largely without crystalline shapes. Four samples of arsenious oxid
were examined under the microscope. Samples 19 and 27 consisted
chiefly of small octahedral crystals; sample 37 contained somewhat
larger erystals.

24 BULLETIN 1147, U. S. DEPARTMENT OF AGRICULTURE.

COMPARATIVE TOXICITY OF ARSENICALS.
RESULTS OF PREVIOUS INVESTIGATIONS.

CALCIUM ARSENATE.

Bedford and Pickering (3) and Smith (48) appear to have been
the first to use calcium arsenate as an insecticide. In 1907 all three
of these men tried it as a substitute for lead arsenate. Bedford and
Pickering found it practically as efficient as acid lead arsenate on
fruit trees in England. Against the army worm in New Jersey,
however, Smith did not find it satisfactory.

Between 1907 and 1912, calcium arsenate apparently was not
further tested as an insecticide, but during the seasons of 1912, 1913,
and 1914, the office of fruit insect investigations of the Bureau of
Entomology, United States Department of Agriculture, began to
test it, as a result of which a commercial calcium arsenate was put
on the market. Since 1915 the use of this arsenate in the field has
steadily increased. In 1914 a commercial calcium arsenate in com-
bination with lime-sulphur gave very satisfactory control of the
codling moth (45).

Scott (46), who, during the seasons of 1913 and 1914, used calcium
arsenate, states that for spraying apple and shade trees, it may be
used with the same degree of efficiency and safety as acid lead ar-

- senate.

Sanders (40), using acid lead and calcium arsenates of equal ar-
senic contents, found the lead salt shghtly superior in killing power,
but the calcium salt more desirable for use with sulphid sprays.

Sanders and Kelsall (42) state that when calcium arsenate is
used alone it may under some conditions burn foliage, but that when
used in combination sprays with Bordeaux mixture or lime-sulphur,
it is as safe as any known arsenical. In sodium sulphid sprays it
is much the safest of all arsenicals. It adheres fairly well to foliage
and remains in suspension.

Coad (9) used various arsenicals, as dusts, against cotton boll
weevils. He found acid lead arsenate much more toxic than basic
lead arsenate and a high-grade calcium arsenate still more effective.
Coad and Cassidy (10 and 1/7) recommend a high-grade calcium
arsenate above all other arsenicals for controlling the cotton boll
weevil, and they enumerate some of the physical and chemical prop-
erties that such an arsenical should have.

Ricker (33), testing poison baits against grasshoppers, determined
that calcium arsenate, used in direct competition with Paris green
and crude arsenious oxid, gave equally good results.

BARIUM ARSENATE.

Barium arsenate seems to have been used first by Kirkland (20),
who tested it in Massachusetts against the larve of the gypsy moth, .
fall webworm, and Datana ministra, securing satisfactory results in
each case. Kirkland and Burgess (21) say:

The experiments with barium arsenate in 1896 gave so good results that we were
hopeful that this insecticide would prove superior to lead arsenate. Its killing effects
on larvee in confinement are certainly superior to those of arsenate of lead. In the
field spraying operations it was found that the poison did not adhere to the foliage
for a sufficiently long time to kill the larve.

ARSENICALS. 25

Smith (48) did not find barium arsenate satisfactory against one
species of army worm.

Brittain and Good (7) used barium arsenate in 1917 against the
apple maggot, but did not recommend it because of its tendency to
burn the foliage.

MISCELLANEOUS SPRAY MIXTURES.

Kirkland and Burgess (21) determined in field experiments on the
gypsy moth that acid lead arsenate is slightly better than basic lead
arsenate.

Wilson (51) reported that zine arsenite killed tent caterpillars
(Malacosoma erosa and M. pluvialis) more quickly and stayed in sus-
pension better than the basic lead arsenate. The basic lead arsenate,
while slow in its action, finally killed the insects. The same arsenic
content was not used for both sprays. Lime-sulphur mixed with
arsenicals retarded the action of the arsenicals. Lime-sulphur used
alone was not of much value as a stomach poison.

Robinson and Tartar (36) conducted tests with tent caterpillars
(M. pluvialis) on sprayed foliage in an open part of an insectary,
using an equal arsenic content. The acid Npad arsenate killed more
quickly than did the basic lead arsenate which, however, although
slow, proved satisfactory because it killed all the caterpillars tested.

Tartar and Wilson (50), also using tent caterpillars, determined
that acid lead arsenate (2-200) was more efficient than the basic
form (2-100). The acid lead arsenate had an arsenic content of
about 33 per cent, while the basic form had one of only 25 per cent.

Sanders and Brittain (4/1), reporting tests on the toxic value of
certain arsenicals, both alone and in combination with fungicides,
against the brown tail moth, tent caterpillar, cankerworm, tussock
moth, and fall webworm in the field, report that calcium arsenate
is inferior to both acid and basic lead arsenates, and that barium
arsenate is still more inferior. Basic lead arsenate is inferior to
acid lead arsenate in all combinations except with Bordeaux mix-
ture. They think that Bordeaux mixture does not inhibit the
action of the basic form as much as it does that of the other ar-
senicals used.

Lovett and Robinson (24 and 25) used the tent caterpillar (M.
plumialis) throughout their experiments to determine the toxic
values and killing efficiency of the arsenates. Instead of examining
all the larvee daily to determine the exact number dead, they counted
the dead ones that dropped daily from the sprayed foliage in the
laboratory. These men also carried on preliminary field experi-
ments with calcium arsenate. They summarize their results as
follows:

Lead hydrogen [acid lead] arsenate has a higher killing efficiency at a given dilu-
tion than either calcium or basic lead arsenate. It requires a longer period of time
to kill the nearly mature caterpillars than the small forms. All of the arsenic devoured
by the insects in feeding upon sprayed foliage is not assimilated, but a portion passes
through the intestinal tract in the excrement. The percentage amount of the arsenic
assimilated depends upon the arsenate used; lead hydrogen arsenate was assimilated
readily and most of the arsenic was retained in the tissues while much of the basic
lead arsenate was found in the excrement. It requires approximately 0.1595 milli-
_ gram of arsenic pentoxid to kill 1,000 small tent caterpillars, and approximately
_ 1.84 milligram of arsenic pentoxid to kill 1,000 nearly mature tent caterpillars, irre-
spective of the particular arsenate used asa spray.

100173°—24—Bull. 1147-4

26 BULLETIN 1147, U. S. DEPARTMENT OF AGRICULTURE.

Howard (19), experimenting with the spotted cucumber beetle |
in the field, used equal amounts (by weight) of several arsenicals. —
The average mortality on the fifth day, Baked upon the results of
two seasons’ work, is as follows: Zine arsenite, 24 per cent; acid
lead arsenate, 17 per cent; Paris green, 16 per cent; Bordeaux-
lead arsenate, 14 per cent; and calcium arsenate, 1 per cent.

Sanders and Kelsall (43) give comparative figures for the toxicity
of several arsenicals. On the basis of one-half pound of metallic
arsenic to 100 gallons of liquid, they obtained the following percent-
ages of dead fall webworms on the eighth day: Sodium arsenate, 52;
Paris green, 72; acid lead arsenate, 36; zinc arsenite, 60; calcium
arsenate, 44; and white arsenic (As,O,), 60. On the same arsenic-
content basis, but with the addition of Bordeaux mixture (10—10—100)
to the spray materials, they obtained the following percentages of |
dead tussock-moth caterpillars on the eighth day: Sodium arsenate,
60; Paris green, 64; calcium arsenate, 48; and white arsenic, 60.

Wilson (53), using five arsenicals against the potato beetle in the
field and laboratory, presents their rates of toxicity graphically as
follows: Paris green, 80 per cent; zinc arsenite, 65 per cent; acid ea
arsenate, 60 per cent; calcium arsenate, 50 per cent; and basic lead
arsenate, 20 per cent. He did not use the same arsenic content
in any two of them.

EXPERIMENTAL WORK.

In comparing the toxicities of the various arsenicals, fed to several
species of insects, equal percentages of the two oxids of arsenic
(As,O, and As,O,;) were used in the spray mixtures.

PREPARATION OF SPRAY MIXTURES.

Suspensions or solutions of each of the arsenicals used were pre-
pared on the basis of the presence of 0.076 gram of arsenious or
arsenic oxid per 100 cubic centimeters of distilled water. This
preparuion is at the rate of 1 pound of dry or 2 pounds of paste acid
lead arsenate to 50 gallons of water, it being assumed that 32 per
cent is the average arsenic oxid content of a dry acid lead arsenate.
On the basis of equal percentage, the mixtures made by using arseni-
ous oxid contained 16.2 per cent more metallic arsenic than did those
containing arsenic oxid. Hach mixture, however, had either an
arsenious or arsenic oxid content of 0.076 percent. All the laboratory
samples used in 1919 and 1920 were pulverized and passed through a
100-mesh sieve before being mixed with water, but the commercial
samples were used as purchased. When properly prepared, the
arsenical mixtures were placed in clean mason jars having rubbers
and tops. Each jar was then thoroughly shaken to dissolve, if
possible, and to distribute the arsenical, and subsequently the mix-
tures were sprayed on foliage which was eaten by insects.

APPLICATION OF SPRAY MIXTURES.

In all, seven species of insects were tested: Silkworms (Bombyx
mori L.), two species of fall webworms (Hyphantria cunea Dru. and
H. textor Harr.), and tent caterpillars (Malacosoma americana Fab.),
belonging to Lepidoptera; the Colorado potato-beetle larvae (Lepiti-
notarsa debe hatansaen Say), belonging to Coleoptera; grasshoppers

: APT

ARSENICALS. aT

(mostly Melanoplus femur-rubrum De G.), pelonging to Orthoptera;
and honeybees idipts mellifica Li.), belonging to Hymenoptera. An
atomizer was used in all the spraying experiments.

Silkworms.—Silkworm larve were fed leaves treated as follows:
Mulberry leaves were sprayed with the various mixtures, the con-
trol leaves being sprayed with tap water only. After having been
dried in the air the leaves were cut into small strips which were then
placed in small wire-screen cages. An effort was made to put ap-
proximately the same quantity of food in each cage, so that a rough
comparative estimate of that consumed could be made. In 1919
about 50 normal silkworms in the second instar (varying in length
from 7 to 12 millimeters, with an average of 10 millimeters, and not
ready to molt) were put in each cage, but in 1920 silkworms in the
third instar (18 to 30 millimeters long, average 25 millimeters) were
employed. Counts were made daily except on Sundays, the cages
being cleaned and treated food being renewed at the same time. No
disease was noticed among these larve.

Webworms.—The webs were collected in the fields from a variety of
plants on Monday. At the laboratory these webs containing web-
worms were kept in large cages with a small amount of food until
Tuesday noon, when the larve, which were then very hungry, were
well mixed according to size (all instars but first one). Tuesday
morning approximately the same quantity of mulberry foliage was
placed in each of several wide-mouthed bottles containing water.
It was then sprayed, and, when dry, a bottle with contents was placed
in a large battery jar, 8 inches in diameter by 12 inches high. Tuesday
afternoon approximately the same number of webworms were placed
in each jar, and thereafter the sprayed food was renewed daily.
Thus by starting each set of experiments on the same day of the week,
the days (Sundays) on which no records were taken always fell on
the fifth, twelfth, and nineteenth days of the tests. Very little
disease or parasitism was noticed among these larve.

Tent caterpillars.—The tents, collected in the fields on wild cherry
trees, were handled in the same manner as the webs of webworms.
Sprayed wild cherry foliage was placed in the jars daily and counts
were made daily. Owing to the prevalence of the “ wilt,” or polyhe-
dral disease, it was necessary to test these larve while in the earliest
instars.

Potato-beetle larvee.—Collected on potato plants, these larve were
placed in cheesecloth cages, 9 inches square by 12 inches high. They
were so well mixed before being placed in the cages that each cage

contained about the same number in the various instars. Sprayed

potato-plant foliage was given to them daily. Parasitism was com-

mon only in the last instar.

Grasshoppers.—The fourth, fifth, and sixth (adults) instars caught
in the fields were tested in the cheesecloth cages. Having been
unable to use the foregoing spray mixtures, bran mash, mixed with
some of the same powdered arsenicals, served as food. Using Paris
green (sample 64, containing 55.09 per cent As,O,) as a standard,
and the regular formula * as a basis, a modified formula was derived,
whereby a pint of poisoned bran mash containing each arsenical to

3 Bran, 25 pounds; Paris. green, 1 pound; lemons or oranges, 6; molasses, 2 quarts; and water, from
2 to 4 gallons.

28 BULLETIN 1147, U. S. DEPARTMENT OF AGRICULTURE.

be tested was prepared. A temporary preservative was added to |
the mash. The poisoned mash was so prepared that each pint had
- an arsenic content of 1.08 per cent. The grasshoppers were fed daily.
Parasitism was common, causing a high daily mortality among the
controls. The temporary preservative in the control food seems to
have increased the mortality about 4 per cent.

Honeybees.—To obtain bees of practically the same age for insec-
ticidal purposes, the brood chamber of a hive was moved 30 feet from
the old stand. On the followig day all the old bees had returned
to the old stand, leaving only young workers (nurse bees and wax
generators), the brood, and the queen in the brood chamber. Fifty
of these young workers were placed in each of many screen-wire
experimental cases and were fed the spray mixtures, diluted twenty
times, in the following manner: One cubic centimeter of a diluted
mixture was thoroughly mixed with 4 cubic centimeters of honey in
a small feeder which was so covered with wire that the bees could not
waste the food. ‘The 50 bees were given 0.038 milligram of arsenic or
arsenious oxid. If all consumed equal quantities, each one ate 0.0005
milligram of metallic arsenic when the arsenic oxid form was used,
or 0.00057 milligram when the arsenious oxid form was employed.
After the bees had eaten the poisoned honey they were given queen
cage candy. The number found dead was recorded daily. Great
care was taken to see that the bees always had plenty of food.

STATEMENT OF RESULTS.

Amount of food consumed.—Not having had time to calculate accu-
rately the amount of food consumed during all of these tests, an effort
was made to estimate it, but this was found possible only with the
food eaten by the webworms and tent caterpillars. The amount
consumed of the foliage placed daily in each jar of larve was estimated
in tenths and fractional parts of tenths, if necessary. On the twen-
tieth day the experiments were ended and the total amount of food
eaten during this period was used in calculating the amount consumed
per larva, counting one-hundredth of each daily feeding as a unit.

Criteria of toxicity.—In order to judge the value of these methods,
so that the results obtained by using them can be properly inter-
preted, the following uncontrollable factors should be mentioned:
(a) The insects always varied more or less in age and size. (6) The
immature insects molted irregularly, causing an irregularity in feed-
ing, as insects do not eat during the molting period, which may last
from one to three days. (c) Disease and parasitism were often dis-
covered several days after the experiments had been started.
(d) The temperature often varied, causing the caterpillars, which are
chiefly night “‘feeders,”’ to eat less on cool nights than on warm nights.
(ec) Some insects die soon after eating a dose of poison, while others
lie ‘‘sick” for several days before dying, which causes a great variation
in their mortality record. (f) The sensitiveness of insects to poisons
varies. (g) In applying the spray mixtures it was impossible to
spray two bunches of folage in ys a manner that equal amounts of
arsenicals adhered to all the leaves. Moreover, the metallic arsenic
in the arsenites and arsenates varied slightly. No two arsenicals ad-
here equally well to leaves, and all of them have a tendency to collect
in drops, causing an unequal distribution of the poison. Neverthe-

ARSENICALS. 29

less, this spraying was done more thoroughly than is possible in prac-
tical spraying. th) It was often difficult to separate the dead insects
from those apparently dead. This was accomplished in a fairly satis-
factory manner by placing these insects almost against the globe of an
electric light. If they exhibited no signs of life after being subjected
for five minutes to the heat from this hight they were considered
dead. (2) In these experiments it was impossible to feed definite
amounts of the arsenicals to individual insects. In a very limited
way it would be possible to feed insects singly, but it is almost impos-
sible to make them eat definite amounts of poisons. It would be
‘possible to feed definite amounts of arsenicals to individual bees. If
they remain isolated singly in cages, however, they live for only a
few hours, although when 50 or more are confined in one case they
freely feed one another and usually live for 9 or 10 days.

Because of these uncontrollable factors, a large number of insects
were used for each individual experiment and the experiments were
repeated several times, if possible. The results thus obtained are
only comparative and are based on the average time required to kill
the insects tested rather than on the absolute single lethal doses
required to kill them. It was assumed that the insects ate equal
amounts of the poisons, although this may never have been true.
In the light of these probable errors it is easy to explain the delayed
deaths of many of the insects poisoned and the great variation in
their daily mortality.

PRELIMINARY TESTS.

During the summers of 1917 and 1918, many preliminary tests
were performed on silkworms, tent caterpillars, and fall webworms.
While no conclusive data were obtained, the following indications
may be given.

The 14 commercial acid lead arsenates (samples 1, 2, 3, 4, 13, 14,
29, 38, 39, 40, 44, 47, 48, and 49) used showed no important differ-
ences in insecticidal properties. All proved efficient. The two basic
lead arsenates (samples 21 and 28) did not kill as quickly as did the
acid lead arsenates. Only two of the five commercial calcium
arsenates (samples 5, 6, 7, 24, and 34) tested proved efficient. The
insoluble calctum meta-arsenate (sample 45) prepared in the labor-
atory had no effect, while the laboratory sample of water-soluble
monocalcium arsenate (No. 46) killed quickly. The arsenious oxid
samples (Nos. 9, 19, 27, and 37), arsenic oxids (samples 10 and 16),
sodium arsenates (samples 25, 31, and 41), potassium arsenate
(sample 26), and zinc arsenites (samples 23, 30, and 33) were usually
efficient. One of these with a high percentage of water-soluble
arsenic, however, was not necessarily more toxic than another with
a lower percentage of water-soluble arsenic. The bases—lead oxid,
(samples 12 and 20), calcium oxid (sample 11), and zine oxid (sample
22)—had little effect when used alone. From the insecticidal
viewpoint, there seems to be no advantage in combining calcium
arsenate and lead arsenate (sample 8). When lime was added to the
laboratory sample of calcium arsenate (No. 42) the toxicity seemed
to be decreased. :

30 BULLETIN 1147, U. S. DEPARTMENT OF AGRICULTURE.

RELATIVE TOXICITY OF COMMERCIAL LEAD AND CALCIUM ARSENATES.

Since the preliminary experiments indicated that the commercial
acid lead arsenates do not differ greatly in toxicity, sample 39, one
of those first used, was selected as a standard by which to judge the
relative toxicity of other spray materials, because its arsenic oxid
content (32.93 per cent) approaches most nearly the theoretical
content (33.11 per cent).

In order to obtain comparable percentages of toxicity for the three
arsenates tested against five species of insects, it was first necessary
to place all the daily percentages of mortalities on the same basis.
This was hose St by subtracting the daily mortalities of the
control insects fed nonpoisoned food from the daily mortalities of
the insects fed sprayed food. Smee the daily mortalities on any
given day vary too much to serve as a fair percentage of toxicity,
the average of the mortalities on the third, sixth, and tenth days
have been taken. The records given in Table 13 under the twentieth
day show whether or not the insecticides used were efficient. To
test the effect of starvation on the insects, other controls without
‘food were used also. |

The results reported in Tables 13 to 21 are comparable only when
the same combination of data and the same number of sets of insects
have been used. Data on the number of sets tested and the varia-
tion and average number of insects used for each individual spray
material, other than those given in the tables, therefore, are stated.
For Table 13 these data are as follows: Silkworms, | set (variation
48-52, average 50); webworms (H. cunea), 2 sets (619-1224: 864);
tent caterpillars, 4 sets (711-1126: 897); potato-beetle larve, 3 sets
(132-157: 145); and grasshoppers, 3 sets (868-482: 420).

TABLE 13.—Relative toxicity of commercial lead and calcium arsenates on 5 species of
insects, after deducting mortality of control with food, 1919 and 1920.

Percentage of insects dead within—

3 days. 6 days.
& g § e
Arsenates and con- - = E . of E
trols. yy 1 = p y | _ }
= ¢ t= AS Zz 3 =| 2 :
é 4 my 6 rs af FI = R a
é E E 35 | 35) Bol aplifche apie 2.) Bulig
>) i} Cun 3 4 S Ps) 5 =) ae a 4 Pa Th)
rt B PES Sologuledehsome 186 bas| So paidue
8 4 j/os|818/8)}8 |4 ]se]1a}8|]e1e
Bg nm |e ela! o |< |aile ae |a|o |'a
39 | Acid lead arsenate. ...} 96.0 | 39.1 | 53.1 | 61.5 | 37.6 | 57.5 |100.0 | 91.7 | 86.5 | 72.3 | 31.1} 76.3
28 | Basic lead arsenate. ..| 61.3 | 8.5 | 53.6] 47.0 | 33.0 | 40.7 | 81.6] 45.0] 88.5 | 66.2] 31.6 | 62.6
5 | Calcium arsenate. ....- 96.0 | 12.5 | 54.3 | 67.5 | 63.6] 58.8 |100.0 | 69.1 | 89.6 | 66.9 | 32.6 | 71.6
(dpe GOs fee Bey es 14.3] 3.6] 49.7] 45.6 | 48.0 | 32.2] 28.6] 15.6] 85.2] 47.0] 32.6) 4L8
BO 12 24 ag Oe eee ae 59.6 4.3 | 51.8 | 54.8 | 62.4 | 46.6 | 94.3 | 33.7 | 87.6 | 54.9 | 32.6 60.6
Bi thzaste GO. as cigars 43525 64.0] 1.1 | 43.9} 60.5 | 61.6 | 46.2 | 86.0] 27.8 | 82.9 | 73.3 | 32.6] 60,5
1 a fa Me dd: oso cok ee 12.5 | 2.7} 45.1 | 50.6 | 42.6 | 30.7] 18.7] 18.7] 85.6 | 70.4} 32.6} 45.2
i) So Geilitis. 2a! 72.5} 3.8} 60.3 | 57.8 | 61.0} 51.1] 96.1 | 42.1] 81.4 | 60.8} 32.6 | 62.6
Control without food. .| 12.2 .0 Se SA PU apd HO a falc cy 61.2 28.6 i 15.3 faa. 8) ome eee
Control with food... .. .0 .O| 1.9] 14.6 | 35.5 | 10.4 OF OF 0r7' | CRE IES

|
|
|

SE ee Pee

ARSENICALS. 81

TABLE 13.—Relative toxicity of commercial lead and calcium arsenates on 5 species of
insects, after deducting mortality of control with food; 1919 and 1920—Continued.

Percentage of insects dead within— La
wn.
PEE
°o

10 days 20 days. 2S =

ae fe

. . ore

s : 8 & 3 8 aes

Arsenates and _con- = 03 > me S oi a bp |ago
trols. y a 3 ee Sy 3 3 ® ISo8

sce ers al halt ~ |2|2 18 |S3s

ro ° n S ~~ 1-3) & . n a ~ (o) Sud
z {RUN Eo Sigs Eee Shes
2 Boo | dh abi iene nator. be Sapa lh Soo Pree
a. a A ees res ase Fo A iy ee (a (ie Ce
: Fg ies rr ra ah = iW Ul oa a i
a PE gee eels nS elise waa ef Be te
39 | Acid lead arsenate..../.....-. SA Steot | Day Or ee |p Ok bye k All.| All.| All. 71.6 2.9
28 | Basic lead arsenate. ..} 96.0 | 74.8 | 87.5 | 47.0 | All| 76.3 100.0 | All.} All.} All.} 59.9 10.9
5 | Calcium arsenate. ..../....-- 84.0) 87.7 |r5s. 7s All.) $1.3 |. .-.-- All.| All.} All| 70.6 9.1
i) (ram OF Se ee eee 30.3 | 24.4 | 87.7 | 40.6} All| 45.8 | 44.9 | 20.7} All.| All.| 39.9] 66.0
An ae eee GO apse ne Saeki 98.1 | 52.4 | 86.8 | 48.8 | All} 70.3 |100.0 | 49.8] All.| All.| 59.2] 30.8
af i ee Ga SOx Eee irever, SERRA aio a St 98.0} 50.3 | 84.7] 51.5] All| 71.1 |100.0 | 45.7} All| All| 59.3 | 29.9
Desi se sae 0 (0 ay ame erases Bee 22.9 | 22.2 | 87.7 | 53.2 | All.) 46.5 | 29.2 | 20.5] All.| All.| 40.8] 69.1
it Pee Oe sey a oc hy 10020156954) |. 8656) 75223) |, ALL ob a. ee 51.9 | All.| All.| 63.6} 18.5
Control without food. .| 71.5 | 83.3 | 79.3 | 37.4 |...-.-.].....- OO: G2) SAT SATE Sa Oe Ate eae
Control with food... .. SOL 44 1253) (4205) [8.3 kde | O50 4158 1 5055 45701 12525 1 10050

Table 13 shows the following: The average percentages of toxicity
of the acid lead arsenate (sample 39) and of one sample of calcium
arsenate (sample 5) on five species of insects are practically the same;
the percentage of toxicity for another calcium arsenate spray (sample

_ 59) is a little lower; those for two other calcium arsenates (samples
56 and 57) and for basic lead arsenate (sample 28) are practically

the same; while those for the remaining calcium arsenates (samples
7 and 58) are very low. Samples 7 and 58 were not efficient against
all five species of insects tested. The basic lead arsenate acted much
more slowly on the silkworms and webworms than did the acid lead
arsenate, but, as a rule, only slightly more slowly on the tent cater-
pillars, potato-beetle larve, and grasshoppers. The quantity of food
consumed is inversely proportional to the toxicity, being least for
samples 39 and 5 and most for samples 58 and 7. The results in
this table also show that starvation had little or no effect on the in-
sects tested, but that the insects really died from the effects of the
arsenates.

EFFECT ON TOXICITY OF ADDING LIME TO ARSENICALS.

According to the preliminary experiments conducted in 1917 and
1918, the laboratory sample of calcium arsenate (sample 42) and the
same compound plus 0.3 gram of lime (sample 42A) killed 69 per cent
and 68 per cent, respectively, of the webworms counted on the
twelfth day. When the quantity of lime was doubled (sample 42B)
the mortality was 50 per cent, and when it was quadrupled (sample
42C), 40 per cent. In 1919 many other experiments, in which a
larger amount of lime was added to every 418 cubic centimeters of
another laboratory sample of calcium arsenate, were performed, using
silkworms, 1 set (variation 49-53, average 51) ; webworms (H. cunea),
2 sets (538-818: 622); tent caterpillars, 4 sets (785-1021: 943); web-
worms (H. textor), 1 set (181-325: 266); potato-beetle larve, 3 sets
(290-361: 339); and potato-beetle adults, 1 set (87-41: 39). De-

-

32. BULLETIN 1147, U. S. DEPARTMENT OF AGRICULTURE.

ducting the mortalities of the controls and basing the average per-
centages of toxicity on the mortalities of the chert sixth, tenth, and
twentieth days, the results for all these insects are: Sample 69, 45;
sample 69A (sample 69 plus 0.5 gram lime), 32.7; sample 69B (sample
69 plus 1 gram lime), 29.1; sample 69C (sample 69 plus 2 grams lime),
26.5.

TABLE 14.—E fect on toxicity of adding lime to arsenicals on 4 species of insects, 1919 and
1920.

Percentage ofinsects dead within—

3 days 6 days
Arsenicals and control. l ; = :
S Lashes PA ; ech cB
Z, A |ESiSs1 315 | 8 |BS|g21 31 s
e S |Ss/8e| 2/8) 8 |ss| 8a) e) &
S Bes bet ei Bib oe Tes lea toe 1
g 4 jon |g) 8 | 2] & lesis"1.8 1 eb
& Bo |BSle Hi-<¢a | @ | Bole Hi <
39 | Commercial acid lead arsenate.| 91.0 | 11.0 | 18.1 21.0 | 35.3 | 100.0 | 72.8 | 82.2 | 58.0 | 78.3
39C | Sample 39 pluslime(2grams)..| 69.0] 6.3 | 18.0 14.0} 26.8] 93.0 | 38.3 | 81.1 | 40.0) 63.1
69 | Laboratory calcium arsenate...} 32.7 | 5.4 | 42.3 | 12.0 | 23.1] 53.8 | 39.7 | 91.6 | 44.0 | 57.3
69C | Sample 69 pluslime(2grams)..| 9.4] 1.8 | 33.3 | 7.0/12.9) 15.1 | 14.4 | 91.2 | 23.0) 35.9
64 | Commercial Paris green........ 10050537302 7 [365.60 11550) be Oe = 85.2 | 99.0 | 62.0} 86.6
64C | Sample 64 pluslime (2grams)..| 57.0! 1.8! 23.4 8.0} 22.5] 79.0 | 44.2! 86.0 | 56.0| 66.3
39 | Commercial acid lead arsenate-}.....-- Pts pl bet SpE ms eae A Ons ee a Be (ol Ali & Pee 4 Re ee
39L | Sample39(leavessprayed with
samplodddimel: = orn inc: oe Mebane Rese: pee ae eet pig ag ey Ne eet
57 | Commercial calcium arsenate. .|......- ase? | a SP UEL SS. Sho Ss. SRS, Se SRO gs eg eT
57L | Sample 57 (leavessprayed with
Sample figima)=-. fe. cose leees eee PAG yt btiaaeer| Stet aon (Pace pent ttle Te Me
Control with food......--:.-... -0 -0 .6 Odea -0 50.1) 8381-12508. 22
Percentage ofinsects dead
within 10 days. bebe Li pan rp q
: :
. es nos res wm sh bo “
S Arsenicals and control. z 5 = $ - ; 4 5 2/8 3 s
© a O§ | og % = S 8a] 2 %
E & |25/8e| 2 | § |35/Be| 8 | 8
E a | Bole < @ |Flle Hj <
39 | Commercial acid lead arsenate...._]....... 99.3 | 100.0; 99.8} 97.0! 61.0} 66.8 | 39.5] 66.1
39C | Sample 39 plus lime (2 grams)..... 100.0} 82.9 100.0 | 94.3] 87.3 | 42.5] 66.4 | 27.0] 55.8
69 | Laboratory calcium arsenate...... 59.6 | 66.0] 98.8] 74.8 | 48.7 | 37.0] 77.6] 28.0] 47.8
69C | Sample 69 plus lime (2 grams)..... 22.6.|. 30.2} 100.0} 50.9} 15.7 |.15.5 | 74.8] 150]. 30.2
64 | Commercial Paris green. ....2....-}..-...- 100.0 | 100.0 | 100.0 | 100.0 | 72.0 | 88.2} 38.5] 74.7
64C | Sample 64 plus lime (2 grams)..... 100.0 | 99.4; 100.0} 99.8] 78.7 | 48.5] 69.8 | 32.0) 57.2
39 | Commercial acid lead arsenate.....|......- oN Gy Wg re A cs get: 64. 3:0. it aheoeceeeeee
39L | Sample 39 (leaves sprayed with
sample 1Tfimey2 etek A Sta eed OF. 19} 4 23-2 ee Po 6207 | he al ee
57 | Commercial calcium arsenate......|......- $6..000e-2 eee oi eat 34.6. }: 35.21) eee
57L | Sample 57 (leaves sprayed with
sample fl Hitie)? Ua) ee AI S6I4 FSA LAL SES ES: WWD (OITA
Controlwith food < ..2 5. dan oes psa .0 PS Rs Sp | eee ae ee! Some ger SEL Rs

1 Based on mortalities for third and sixth days only, because these controls, confined in small cases,
lived for only 8.4 days on an average.

In 1920 these experiments were repeated on a larger scale. The
following data are not given in Table 14: Silkworms, 2 sets (each of
50); webworms (H. cunea), 1 set (variation 136-194: 145); tent
caterpillars, 3 sets (198-385: 280); and honeybees, 2 sets (each of
50). The percentages given for samples 69 and 69C are taken from
the 1919 results, and should be compared only roughly with the other
percentages given in Table 14. Reference to this table shows that

ARSENICALS. 33

the addition of lime to the three arsenicals employed reduced the
toxicity in practically all cases.

There are two possible explanations for the reduction in toxicity
due to the addition of lime. The excess lime may unite with the
soluble arsenic and prevent it from functioning as a poison. This
explanation is supported by practically all the results recorded,
providing the excess lime did not decrease the percentage of arsenic
in the food or on the leaves eaten. It did not reduce the percentage
of arsenic in the poisoned honey, yet the lime in every case caused
a decrease in toxicity to honeybees. In the case of the leaf-eating
insects, the lime added theoretically reduced the percentage of
arsenic on the leaves, because 2 grams of lime were mixed with every
gram or less of the arsenical. Consequently, the dried spray material
on the leaves would be greatly adulterated and the percentage of
arsenic in it would be lowered. To determine the extent of the
decrease in the arsenic, many leaves were sprayed with samples
39, 39C, 69, 69C, 64, and 64C. After repeating these experiments
three times and analyzing the 18 samples of leaves sprayed, it was
found that the addition of lime had reduced the arsenic on the leaves
26.3 per cent, while the excess lime on other leaves similarly sprayed
had reduced the average toxicity of the same three arsenicals only
21.1 per cent.

In order to prevent the decrease of arsenic on the leaves, at the
same time retaining an excess of lime on them, the following experi-
ments were performed. Many leaves were sprayed, some with acid
lead arsenate (sample 39) and others with calcium arsenate (sample
57). When dry, half of each lot was again sprayed with lime (sample
11) (2grams of calcium oxid in 418 cubic centimeters of water). When
all the leaves were dry, half of them were prepared as samples to
be analyzed for arsenic and the other half were fed to fall webworms.
These experiments were repeated twice, using 8,888 webworms in
all. The results in Table 14 show that the hme (sample 39L) did
not affect the toxicity of the acid lead arsenate (sample 39), but it
(sample 57L) reduced the toxicity of the calcium arsenate (sample 57)
50 per cent. Analyses of the leaves sprayed with samples 39 and
39L showed that the lime reduced the arsenic 18 per cent, while in
those sprayed with samples 57 and 57L the arsenic was reduced
29.4 per cent.

EFFECT ON TOXICITY OF ADDING BORDEAUX MIXTURE AND LIME-SULPHUR TO ARSENICALS.
.

Sanders and Brittain (47) reported that Bordeaux mixture and
Wilson (51) reported that lime-sulphur, when added to arsenical
spray mixtures, decrease the killing power of the arsenicals. Many
experiments were performed by the writers in 1919 to determine ~
whether or not these statements were true. The following insects
were used: Webworms (#7. cunea), 1 set (variation 102-476, average
241); tent caterpillars, 4 sets (742-1187: 919); and potato-beetle
larve, 2 sets (130—-264:153). After deducting the mortalities of the
controls, the average percentages of toxicity of the three species of
insects used are as follows: Sample 68 (laboratory sample of acid lead
arsenate), 47.1; sample 50 (sample 68 plus lime sulphur), 40.1; sample
69 (laboratory sample of calcium arsenate), 55.6; sample 53 (sample 69

34 BULLETIN 1147, U. S. DEPARTMENT OF AGRICULTURE,

plus Bordeaux mixture), 42.8; sample 51 (sample 69 plus lme-
sulphur), 41.8; sample 23 (commercial zine arsenite), 51.4; and
sample 54 (sample 23 plus Bordeaux mixture), 46. From these
figures it seems that both Bordeaux mixture and lime-sulphur
decreased the toxicities of the arsenicals used. Since silkworms and
honeybees refuse to eat food containing lime-sulphur, the experi-
ments in which they were used are not reported. All the other larvze
enumerated ate only about 25 per cent as much food as did the con-
trols, while those that fed on foliage sprayed only with Bordeaux
mixture and lime-sulphur ate 83 per cent and 54 per cent, re-
spectively. Neither Bordeaux mixture nor lime-sulphur used alone
had much insecticidal value against the insects tested.

In 1920 these experiments were repeated. Different arsenicals
were tested, but the Bordeaux mixture (4—3.67—50) and lime-sulphur
(1-30) were of the same strengths. The Bordeaux mixture and
arsenicals were so mixed that each dry spray material consisted of
practically 22 per cent of arsenious or arsenic oxid, and when the
necessary amount of water was added, each had an arsenic or
arsenious oxid content of 0.076 per cent. Table 15 gives the ana-
lytical results on these spray materials before water was added.

TABLE 15.—Com~position of Bordeaux mixture alone and in combination with arsenicals.

Arsenious
(As2O3) or
arsenic Spode Gata
Sample Material analyzed. = ia a Base. dioxid
Water-
Total. soluble.
| (PS CE) Ee Ck Pte. Per cent. Pars:
61 ue sample of Bordeaux mixture \ 0.68 a 0 eaoy \ 3.52
-67-50). i ie ea oom ree eee a '
: | 5.60(CuO) |
91 | Sample 61 plus acid lead arsenate (39)........ 24 | 22.06 0.12 regs Sexes 4 1.17
42.5 )
92 | Sample 61 plus calcium arsenate (57).......-- .57 | 22.30 26 aa fo } i 5.29
55 | Sample 61 plus sodium arsenate (25).......... 15.64 | 22.16] 16.81 Bap {CuO} \ te
; 7 7.07 (CuO)
54 | Sample 61 plus zine arsenite (23)-.--......... -o0 pt 23.05 a28 ae (200) 1.95
| if: n
30 | Commercial Bordeaux and zinc arsenite mix- 30.55 (ZnO <
ture. } 46 | 24.33] 38 { eee (CnO} \ 56

-

Table 16 shows the average percentages of toxicity against web-
worms and tent caterpillars of lead arsenate and of calcium arsenate
alone, with Bordeaux mixture, and with lime-sulphur, and of sodium
arsenate and zinc arsenite alone and with Bordeaux mixture.

Ty

SaNGeE As

ARSENICALS.

35

TABLE 16.—Effect on toxicity of adding Bordeaux mixture and lime-sulphur to arsenicals
on four species of insects, 1920.

Sample No.

Arsenicals and control.

Silkworms.

Webworms (dH.
cuned )

Percentage of insects dead within—

Tent caterpillars.

3 days.

Sample No.

6
Sample 39 pluslime-sulphur (60)../....--

Commercial calcium arsenate. -....

(6
Sample 57 plus lime-sulphur (60)..|....--

Laboratory sodium arsenate......

ere 25plus Bordeaux mixture
GI)E sok. as ee SSPE. ZI.

Commercial zinc arsenite. .......-

Arsenicals and control.

Commercial acid lead arsenate..-.|......-

Sample 39 plus Bordeaux mix
ture (61

Sample 39 pluslime-sulphur (60).|.....--

Commercial calcium arsenate. ...
Sample 57 plus Bordeaux mix-
GLEE CL (OL) Bae oe eee SORIA
Sample 57 pluslime-sulphur (60).
Laborator i
Sample 25 plus Bordeaux mix-
BUT: (OD) ee
Sample 23 plus Bordeaux mix-
ture (61

1 Based on mortalities for third and sixth days only.

Four arsenicals without Bordeaux mixture and lime-sulphur f

57.0 (all four species).

Four arsenicals with Bordeaux mixture 1351 (webworms and tent caterpillars).

Silkworms.

00. 0
97.0

sodium arsenate.....|....-..

wit

10 days.

Webworms (H.
cunea)

a ae 3

Neo ss. sss Sess

—

Tent caterpillars.

So oo ood Ooo So

Percentage ofinsects dead
ithin

GENERAL AVERAGE TOXICITY.

6 days.
hy p
YY os}
n =|
Sle S |es| 8 | 2} &
Oo we fo} ~ © a
e/e|8 [3 |e] 8] 8
ss ial ae ae (i ea == er |i pee
21.0 | 35.3 | 100.0 | 72.8 | 82.2 | 58.0] 78.3
12.0 | 27.2 | 99.0} 40.0 | 88.1 | 46.0] 68.3
Pere 20 las se SOU sede lode eee eee
12.0 | 22.7 85.0 | 27.1 | 72.8 | 44.0] 5722
12.0 | 19.3 83.0 | 11.7 | 72.2 | 20.0} - 46.7
ores 3 202 She Ses 2H Or Osa a. Is seh ete
33.0 | 49.3 | 100.0 | 72.2 | 91.4 | 62.0] 81.4
20.0 | 33.6 | 99.0 | 43.5 | 94.2 | 53.0] 72.4
25.0 | 50.6 | 100.0 | 37.5 | 96.9 | 44.0] 69.6
18.0 | 44.5 95.0 | 30.0 | 98.4 | 54.0] 69.4
si] upp .0 -0 SeSiiice Ons ae
Average
Toxicity for— toxicity
for—
; F am a
BUTE ash eat:
ea eee 5 3
< — ie o “=
| 4/8! e | @ jeg l as
Seles! bes 1S. (1a gies
os Ss iS oS PB HS = oO
So eC MELO) SIO
4/a({s eae | m |} | BS
99.8 | 97.0 | 61.0 | 66.8 | 39.5] 66.1 63.9
95.7 | 92.3 | 44.8 | 66.5 | 29.0 | 58.2] 55.6
ce AY eae a Te ariel agheol Beason 4 63.0
87.5 | 79.3 | 33.6 | 62.4 | 28.0 | 50.8 | 48.0
81.5 | 77.3 | 20.8 | 60.8 | 16.0 | 43.7] 40.8
8820) |=. 22. SEP ero Dol (ee ee 5 55.3
98.9 | 99.7 | 65.9 | 76.0 | 47.5 | 72.3 | 71.0
97.1 | 92.0 | 46.2 | 76.0 | 36.5 | 62.7 | 61.1
87.0 | 98.7 | 37.0 | 88.6 | 34.5 | 64.7 | 62.8
90.3 | 92.7 | 36.7 | 88.8 | 36.0 | 63.5 | 62.7
63.5 (all four species}:
\61.4 (webworms and tent caterpillars).

Two arsenicals without lime-sulphur, 56.0 (webworms and tent caterpillars).
Two arsenicals with lime-sulphur, 59.1 (webworms and tent caterpillars).

36 BULLETIN 1147, U. S. DEPARTMENT OF AGRICULTURE.

The addition of Bordeaux mixture to the four arsenicals employed
reduced the percentages of toxicity against silkworms, webworms, and
honeybees, but reduced the toxicity against the tent caterpillars little,
ifany. The addition of lime-sulphur (sample 93) to the lead arsenate
(sample 39) reduced the toxicity against webworms, but seemed to in-
crease it against tent caterpillars. The addition of lime-sulphur (sam-
ple 94) to the calctum arsenate (sample 57) neither decreased nor in-
creased the toxicity against webworms, but appeared to increase it
against tent caterpillars. In the 1919 results, Bartienas mixture and
lime-sulphur reduced the rates of toxicity in all cases.

The followiie data are not given in Table 16: Silkworms, 2 sets
(each of 50); webworms (4. cunea), 1 set (variation 107-332, average
141); tent caterpillars, 3 sets (118-557: 301); and honeybees, 2 sets
(each of 50).

To determine the percentage of arsenic borne by leaves sprayed
with the foregoing spray mixtures, many apple and mulberry leaves
were sprayed at four different periods. The parts of arsenic per
million parts of the leaves were as follows: Sample 39, 1,200; sample
91, 800; sample 93, 800; sample 57, 1,000; sample 92, 800; sample
94, 900; sample 23, 1,650; sample 54, 1,300; sample 25, 1,100; and
sample 55, 1,100. The general average of those containing neither
Bordeaux mixture nor hme-sulphur (samples 39, 57, 23, and 25) is
1,238 parts of arsenic, while those containing these two fungicides
(samples 91, 93, 92, 94, 54, and 55) have a general average of 950
parts of arsenic. According to these figures, the fungicides reduced
the arsenic content 23.3 per cent, whereas they reduced the general
~ average toxicity only 11.5 per cent.

RELATIVE TOXICITY OF ARSENATES AND ARSENITES.

Toxicologists report that arsenites are more toxic than arsenates.
Furthermore, on the basis of equal percentage of arsenious oxid and
arsenic oxid, 16.2 per cent more metallic arsenic is present in the
arsenites than in the arsenates. To secure additional data on this
subject, a high-grade acid lead arsenate, a calcium arsenate, a sodium
arsenate, a zinc arsenite, and a Paris green were selected in 1919 for
comparison. The following insects were used: Silkworms, 1 set
(variation 49-54, average 51); webworms (H. cunea), 2 sets (818-
1725, average 1173); webworms (H. teztor), 1 set (189-310, average
251); potato-beetle larvee, 3 sets (282-404, average 345); and grass-
hoppers, 2 sets (181-302, average 242). After deducting the mortali-
ties of the controls, the average percentages of toxicity were as follows:
Acid lead arsenate (sample 39) 66, calcium arsenate (sample 5) 63.9,
and sodium arsenate plus Bordeaux mixture (sample 55) 61.7, an
average of 63.9 for the arsenates on five species of insects; zine
arsenite (sample 23) 57.6, and Paris green (sample 64) 65.5, an average
of 61.6 for the arsenites. Thus the Paris green tested is equal to
the arsenates in toxicity, and, as shown by the average, these two
arsenites are not quite as toxic to insects as are the three arsenates
employed, although the comparison is not fair in all respects. The
smallest number of units eaten were sprayed with Paris green.

~
9

ARSENICALS. 37

TABLE 17.—Relative toxicity of arsenates and arsenites on 4 species of insects, 1920.

Percentage ofinsects dead within—

3 days. 6 days
3 Arsenicals and control. od ; 3 F E
5 —~ | & n P|) es wn
yy q {838/32 gy . 4 |/fsi2 2 k
2 E /se(ee| 2) 6) E | se/e8) 2 | $
= = ony Be 5 2 = Opi aa = 5
39 | Commercial acid lead arsenate...} 91.0 | 11.0 | 18.1 | 21.0 | 35.3 | 100.0 | 72.8 | 82.2 | 58.0 | 78.3
25 | Laboratory sodium arsenate..... 99.0 | 28.8 | 36.6 | 33.0 | 49.3 | 100.0 | 72.2 | 91.4 | 62.0 | 81.4
Average for arsenates........-... 95.0 | 19.9 | 27.3 | 27.0 | 42.3 | 100.0 | 72.5 | 86.8 | 60.0 | 79.9
23 | Commercial zine arsenite........ 96.0 | 12.5 | 68.9 | 25.0 | 50.6 | 100.0 | 37.5 | 96.9 | 44.0 | 69.6
64 |} Commercial Paris green.......... 100.0 | 30.7 | 65.7 | 15.0 | 52.8 |....--- 85.2 | 99.0 | 62.0 | 86.6
SSilaes ce Oneal Sse meet. eae LOO Oi38. 9 59% 3) 25.001 588 |. ep 24. 86.7 | 97.5 | 55.0 | 84.8
Sout oF GOL EA iy ass orca Tike 98.0 | 18.5 | 53.9 | 22.0 | 48.1 | 100.0 | 72.3 | 97.6 | 57.0 | 81.7
Average for arsenites............. 98.5 | 22.7 | 61.9 | 21.8 | 51.8 | 100.0 | 70.4 | 97.7 | 54.5] 80.7
90 |Commercial London purple...... 98.0 | 24.1 | 34.7 | 11.0 | 42.0 | 100.0 | 57.1 ; 92.0 | 383.0 | 70.5
Conttolywith toodessas-- ss sceecee OHO 2 050: 2 O56: | O50b eee O50 20: Os “S8Streh2 Oileeer ee

Percentage of insects

dead within—
Toxicity for—

10 days >

Arsenicals and control. 3

° BYR i, mes | st me 4

Z q 5 S = n 5 q g S]s “A g s

2 5 |£s| Sa) & ] § [£8] Sa] 2] &

a irs ORI. Pata NE Ca ST A mt cane fe is

5 aS ae qa 2 = On | 8 a

a ao |e] eae < ate (nes mH | <
39 | Commercial acid lead arsenate.......]..-.... 99.3 | 100.0 | 99.8] 97.0 | 61.0] 66.8 | 39.5 | 66.1
25 | Laboratory sodium arsenate........]..-.--- 96.6 | 100.0} 98.9} 99.7 | 65.9 | 76.0 | 47.5 | 72.3
Average for arsenates..............-- 100.0 | 98.0] 100.0 | 99.3] 98.3 | 63.5 | 71.4 | 43.5] 69.2
23 | Commercial zinc arsenite............|....... 60.9 | 100.0 | 87.0] 98.7 | 37.0 | 88.6 | 34.5 | 64.7
64 | Commercial Paris green. ............)..-..-- 100.0 | 100.0 | 100.0 | 100.0 | 72.0 | 88.2] 38.5 | 74.7
S85} 12-2 OP eae Sees obese eee 100.0 | 100.0 | 100.0 | 100.0 | 75.2 | 85.6 | 40.0] 75.2
Soe CGI es i eR oe RR AE Pai ae [cy as 3 96.6 | 100.0} 98.9] 99.3 | 62.5 | 83.8 | 39.5] 71.2
Average for arsenites..............-. 100.0} 89.4] 100.0} 96.5] 99.5 | 60.8 | 86.5} 38.1] 71.5
90 | Commercial London purple.........|.....-- 94.7 | 100.0 | 98.2} 99.3 | 58.6 | 75.6 | 22.0} 63.9
Controlhwithtood= 2c. 22 FS 0.0 Dei Ole H doe keene ts| ner el ook oo ate e ese eee alle erelels

1 Based on mortalities for third and sixth days only.

In 1920 experiments similar to the preceding ones were performed,
using one lead arsenate, one sodium arsenate, one zinc arsenite,
three Paris greens, and one London purple (an arsenate and an
arsenite combined). The following data, which are not given in
Table 17, were obtained: Silkworms, 2 sets (each of 50); webworms
(H. cunea), 1 set (variation 90-136, average 120); tent caterpillars,
3 sets (207-507, average 288); and fneu bees 2 sets (each of 50).
Table 17 shows that the average percentage of toxicity of the arsenates
was 69.2, while that of the four arsenites was 71.5. The toxicity of
the arsenites should be 16.2 per cent more than that of the arsenates,
providing the toxicity is due to the arsenic, irrespective of its form
of combination. According to the preceding figures, the toxicity
of the four arsenites is only 3.3 per cent more than that of
the two arsenates. Comparing the toxicity of the four arsenites
with that of the lead arsenate, however, it is 7.8 per cent more,

38 BULLETIN 1147, U. S. DEPARTMENT OF AGRICULTURE.

and comparing the toxicity of the three Paris greens with that
of the lead arsenate, it is 11.5 per cent more. London purple
(sample 90) has an average percentage of toxicity of 63.9, being
ractically the same as that of zinc arsenite. While this sample
illed all of the webworms tested within 20 days, only about 90 per
cent of those fed zinc arsenite died during the same period of time.

RELATIVE TOXICITY OF NEW ARSENATES.

In making a comparison of the relative toxicity of new arsenates,
three commercial products and three pure laboratory products were
used. The commercial acid lead arsenate (sample 39) was taken as
a standard by which to judge the relative toxicity of the other

roducts. The two other commercial products (sample 70, acid
fead arsenate made by a new process, and sample 62, magnesium
arsenate) and the laboratory sample of barium arsenate (sample 71)
are practically new, while the laboratory samples of arsenates of
aluminum (sample 73) and of copper and barium (sample 74) are
totally new, as far as known.

In 1919 the following insects were tested: Silkworms, 1 set of 50;
webworms (H. cunea), 1 set (variation 124-195, average 152); web-
worms (Jf. textor), 1 set (189-514, average 314); potato-beetle larve,
2 sets (150-355, average 260); and grasshoppers, 2 sets (181-305,
average 265). After deducting the mortalities of the controls, the
following figures were obtained. When silkworms, webworms (H.
cunea), and potato-beetle larve were tested, the average percentages
of toxicity were: Sample 39 (acid lead), 58.2; sample 70 (acid lead,
new process), 57.3; and sample 62 (magnesium), 59.8. When silk-
worms, webworms (both species), potato-beetle larve, and grasshop-
pers were tested, the percentages were: Sample 39, 58.8; and sample
62, 54.2. When webworms (both species), potato-beetle larve, and
Boel. were tested, the percentages were: Sample 39, 55; sam-
ple 71 (barium), 43.6; and sample 74 (copper and barium), 48.9.
When webworms (both species) and potato-beetle larvze were tested,
the percentages were: Sample 39, 57.2; and sample 73 (alumi-
num), 34.6. -

In 1920 these experiments were repeated, with the results shown
in Table 18, as well as the following: Silkworms, 2 sets (each of 50);
webworms (H. cunea), 2 sets (variation 647-897, average 776);
webworms (H. textor), 1 set (189-514, average 314); honeybees, 2 sets
(each of 50); and tent caterpillars, 3 sets (240-556, average 337).

ia

Sample No.

ARSENICALS. 39

TABLE 18.—Relative toxicity of new arsenates on 5 species of insects, 1920.

Arsenates and control.

Percentage ofinsects dead within—

3 days. 6 days.
nay . Sais FA
— — ee —
5 4 a _~ Z 4 a
0 na n-~ wm ° nm aAnA~
a 3 Ba rs)
g\és/is| 2 | 5 alee (eSde Sle ane
5 oR | & = A? o§$|ex| & 3 2
° ES ER BS Oo oD fo) ES ER mal oO oo
BS S ~ iS) S *) ~ o mS ios)
Q Q S = B 2 2 q ra
fa o @o So =| o O 5 q
= Ce) > r ) >
a |~e |e Hla la)a |e le Hie |4

Sample No.

Commercial acid lead
arsenate...........--
Laboratory barium
arsenatesscsk ace ce
Laboratory copper
barium arsenate. .-...
Commercial magne-

91.0 | 29.9 | 47.6 | 21.0 | 18.1 | 41.5 |100.0 | 95.3 | 84.2 | 58.0 | 82.2 | 83.9
22.0 | 3.2 | 10.9 | 11.0 | 14.0 | 12.2 | 68.0 | 68.2 | 37.3 | 18.0 | 75.1 | 53.3
61.0 | 10.0 | 11.7 | 9.0] 18.1 | 22.0 | 98.0 | 67.5 | 57.0 | 28.0 | 83.2 | 66.7

sium arsenate........ SLOW A135 82 es 2e| 4 One caterers LOOSON 85920746750 eSts Ou ee ea aoe
Commercial acid lead
aearane (new proc-
Be pgs ed TOMS Oe Oia eee | rece mea emcee es OOS {Ut Seay cle, « metre | ieee ace ell ene eee
Danone aluminum
ATSONALO Geet e ore eee eeeoe 27 Te Sa? (on) st es el Pes asl een Pee ae SONS PoasOr rete alan ce| ae
Control with food...-... O00 O80) O85) | OsOCIROLG ae OOM O58) |e Szon lela Onlin rsacn | eee

Percentage of insects dead within—

Toxicity for—
10 days.

Arsenates and control. ss ss x ss ss 5 iS
wa : wa =| w : wy y = 3
a ee,| ce | 6 alesles|¢|8|8
ree alos al tan (eed Meee os cs ee eae
Ea oe Gee clte 10-8 toe, Eo LB imes deemalrts
epee ae Belo (oe). benalveen lee 1B
a |e es a < a lune mjal|-<

Commercial acid lead

ATSCMMUCs ee oe eee lence 100.0 | 100.0 | 100.0 | 100.0 | 97.0 | 75.1 | 77.3 | 39.5 | 66.8] 711

73

Laboratory barium
SISENAUE ss - = 5s
Laboratory copper
barium arsenate....-.
Commercial magne-

Commercial acid lead
areenete (new proc-

92.0] 88.2] 72.1] 99.0] 87.8 | 60.7 | 53.2 | 40.1 | 14.5 | 62.7 | 46.2
100.0} 95.2] 82.7] 100.0] 94.5 | 86.3 | 57.6 | 50.5 | 18.5 | 67.1 | 56.0

Beate eee = [awoken © QOD ea setcd eet a sl ora srotelelal MOM Om edad cl oeisat a cect acne ro) = aces
Papbeor aluminum
ALSCHALENSois Perea | Goce = 4 ORES) tte SOE OI Rt ers | REET rea tae ret GLSSHRAON Cees essence 3 | see
Control with food...... COSCON ele 2 22 fea ai Ca a | YT Ie PU arent ose eer Oe ee eee

1 Based on mortalities for third and sixth days only.

Sample 39, 72.2; sample 62,
Sample 39) 86. 0: sample 70,
Sample 39, 76. 2: sample 73, 51.0.

COMPARATIVE AVERAGE TOXICITY.

56.5.
85.2.
0

40 BULLETIN 1147, U. S. DEPARTMENT OF AGRICULTURE,
RELATIVE TOXICITY OF PURE ARSENIC OXIDS AND OF BASES.

In order to judge as accurately as possible the relative toxicity of
various bases when combined with the oxids of arsenic, the mate-
rials used are grouped in Table 19. In each mixture of the bases,
0.48 gram of the base was used in 100 cubic centimeters of water. At
this rate from three to five times as much base was used as is present
in the arsenical mixtures.

The following data are not given in Table 19: Silkworms, 1 set
(variation 47-54, average 50); webworms (H. cunea), 1 set (161-761
average 280); tent caterpillars, 4 sets (565-1030, average 805); an
potato-beetle larve, 2 sets (105-279, average 152).

TaBLE 19.—Relative toxicity of pure arsenic oxids and of bases on 4 species of insects after
deducting mortality of control with food, 1919.

Percentage of insects dead within—

3 days. 6 days.
2 Ss
Material and controls. s BI = 3
PA aS? = | ele
= ~ <
SSP A tae hye fete S35
S a 2 ay 3S a | p 3
Z B..| Bote eS 4 sob Be idel) peoihenbehans
2 3 tire PS: 4 52 re) = = 4 52
= Bits 2h heart E As se ae
5 Eye) ey ete a eee
a ms fa Ae Ur a oh gn ry Sey eee aes
9" Arsenious Oxid. 2< 2s = 5. ocken 40.0 | 21.6; 4.6 | 19.2 | 21.4 58.0 | 67.3 | 50.5 | 23.1 49.7
TOS; AATSCNIG OXid==. swe, Sere he 100.0 | 23.1 68.1 | 65.1 | | RS SE 77.6 | 85.2 | 65.0 | 82,0
1fi}-Caleium oxid:_. 2... >. S-icc ee 045 sO See) Geet 5p 017 cO ln eee 2
5} Calcium arsenate -. 2... =.t..f.- | 96.0 | 12.5) 54.3 | 64.8 | 56.9 | 100.0 | 69.2 | 89.6] 63.4 80.6
i? Gead oxid])o. . Sho Se 12.8 -0 .0/} 30.5]10.8)} 31.9! 0 1.5 | 46.3 19.9
39 | Aeidlead arsenate..............- 96.0 | 39.1 | 53.1 | 50.4 | 59.6 100.0 | 91.8 | 86.5} 51.2 82.4
22 DINO OXAG es oe cee eee -0 .0 sO\f i423 1 Say .0 -0 | 12.0 3.0
eBinl AARC ATSONILE 4 jaered aoe. Bee ee eee 85.7 | 4.8! 73.8 | 59.8 | 56.0} 98.0] 32.7 | 90.0] 58.9} 69.9
63 | Maenesinm oxid'.- -- 5-22 h oss .0 On Scere a hal (at See So 0 50" eae a Oe pe
62 | Magnesium arsenate.........-.-- Tee eg Pe ag bea TacSyl= ees 100: 0) S165). Tt ee
Gas COD DCH OMG — to. dee oe eer eee .0 —O Sees Oa sence Be i Ny pe ca ch i oe ees
G4) Paris Sree <2 x aon Soo cee be ts 10030.4 180712 ee 65. 7a) Poa 67.0 Janes Sp! om el Set
74 | Copper barium arsenate.........)..-...- 142 0) )5.5¢22 Gaol ot ctiee teen Cs 23 SS Ey
72)| SB abi Oxd@: sone oa’ be pe Cee Fi Sst bee Pa Val GR Pee) Se. a! BF Pedra’ eid Bee
74 | BAP STSGNHLG:- = oo Sonos ee eee AS 1) ee a S7eO! tote oue meee ry el hee s ine? fa oay
Control without food............ IPA -0 | Se ee 61.27) 25.6 ta boa ee
Control with: food 2) oe hae .0 0; 1.9] 14.6) 41 -0 oO) Go) ake 6.7

Control with food, omitting tent
caterpillars: S 2u.tsu eae bes ee-s a Soe

RGA
-

é
:
:
E
;

- ARSENICALS. pie: 2 |

TaBLeE 19.—Relative toxicity of pure arsenic oxide and of bases on 4 species of insects
after deducting mortality of control with food, 1919—Continued.

Percentage of insects dead within— 3

—-

10 days. 20 days. 3

a

oO. be
A ER a3 as.
¢ S$ ; $s | Bos aa
Material and controls. iS 8 = g jogs of
= > > = 3 Sig: : es
tla el © | 218 Bo8| 5 | 88

x a & = Pe a == ae =~ 0

= fl bil >| al asl 2 18

3 a w e 2 ; fo jeed! 6 lie

Z Basel omens Pe | Heeikoee Weiaer |e) [Saal Sele

£ 5 = 2 3 wm | 5 S Ga yee bs eer Pee ed

a Be eS ee Se Behe | Sagal ele

S Lf OW B= Selb oii aka = a.|. 2 |se2| 3S. |s

3 = o S > =| 3) o |Posl 5 q

a | fa | Bia | ma bs | eee fe < |p
{ an ae eS pre i | =F ie
9 | Arsenious oxid........| 70.0 | 95.6 | 78.9 | 23.9 | 67.1 | 86.0 | All.| All. | 35.1 | 94.6 | 46.1 | 9.6
10‘) Atsenic oxid. 3022-5. eee OF 251787. 6.|) Diet | Soe" eos 3. All. | All. | All. {100.0 | 76.5 | 3.5
ii} Calerum Oxid 2-2) == erect Pa ieee 9 ema | .0 -3 0 | 0.0} 1.7] 26.9] 0.2 [143.4
5 | Calcium arsenate...........- | 92.7 | 87.7 | BA. Bub830O (es. All. | All. | All. |100.0 | 73.5 | 7.4
42) | Aves GrOmid asec | 46.8! .0! 4.8! 45.7 | 24.3 |100.0!) 4.1) 0.0! All. | 65.3 | 18.3 |148.6
39 | Acid lead arsenate... ..- 1B PRES: SBN. |-Siso 4020s) Ol-0-| 222. —- All. | All. | All. }100.0 | 74.5 | 2.8
22 ZING OX1G 234 3 Oe | 2.0 .0 -0 | 13.3 | 3.8] 6.0 -0O, 0.0 | 24.1 | 35.0] 2.6 |119.8
23 | Zine arsenite.........../100.0 | 66.7 | 86.9 | 45.6 | 74.8 |...... 70.2 } All. | All. | 97.8 | 66.9 | 22.0
63 | Magnesium oxid....... Ji O48 453 Ea. AeA 8225.2 i fer2ean ieee 22 8:6 | 2956") 2.2 = 105.5
62 | Magnesium arsenate...|--...-- S47 Re Dose (eases joasute 14. 8: |S 3: ATI PIO7. OF 45 Se 14.2
65 | Copper oxid.-...2..... by Pe QaHtst es OF peers ee 30F Meson: 2:0 | 2.55 | 22 0503|-2730')3 tS) 106.9
64 | Paris green.........-.. [ate 253 ES al ake ge AT. Gels 325 =e tes AD. +2 All. |100.0 |....--. 3.9
74 | Copper barium arsenate -....- OT, 1 peek Gil Bee [EL enee ye ae All. |100.0 |....-. 10.8
#2 |\( Pari OxiG= 235. 221555. 2 | O24" (ats e ye foil | A ee [seen TOUS SS B27-| 4TI2 4 ee 70.3
71 | Barium arsenate.....-. [asesss1 OGeS foot Br72 Et Pee ocean abd Oca pods eee 28.0
Control without food. .| 71.5 | 93.6 | 79.3 |.....-|.-.-.- 1 AT: PAID RE Tio PU ees eee
Control with food.----. | .O} 4.1 | 12.3 | 42.5 | 14.7 | 0 | 21.0 | 50.5 | 57.1 | 32.2 | 8.5 |100.0

Control with food,
omitting tent cater- |

pillarse 252" 4s tess Jee | bbe micas ate J eos Pe ee Bae jeeehcklosescslhee ten bessess 2630) ,|5=1 46|-5-26

1 First 8 and next to the last figures to be compared; next 8 and last figures to be compared.
2 Based on webworms (4H. cunez) and tent caterpillars.

Comparing the mortality of the insects fed on the various bases
with that of the control insects (Table 19), it appears that calcium
oxid is beneficial to insects (sample 11, 26.9 per cent, and control,
32.2 per cent), that zine oxid (sample 22, 35 per cent, and control,
32.2 per cent), magnesium oxid and copper oxid (samples 63 and
65, 29.6 per cent and 27 per cent, and control, 26 per cent) are
slightly injurious, that barium oxid (sample 72, 47.2 per cent, and
control, 26 per cent) is moderately injurious, and that lead oxid
(sample 12, 65.3 per cent, and control, 32.2 per cent) is the most
effective of all the bases used.

Since the arsenious oxid (sample 9) used in the 1919 experiments
had a low toxicity, a commercial white arsenic (As,O,) was used in
the experiments conducted in 1920. Sample 9 contained only 17.77
per cent of water-soluble arsenious oxid, while sample 27 contained
38 per cent. To obtain its average toxicity on four species of insects
in comparison with the toxicities of pure arsenic oxid (sample 10)
and acid lead arsenate (sample 39), the following insects were used:
Silkworms, 2 sets (each of 50); webworms (H. cunea), 1 set (varia-
tion 100-136, average 120); tent caterpillars, 3 sets (221-446, aver-
age 292); and honeybees, 2 sets (each of 50). The average per-
centages of toxicity are as follows: Sample 27 (arsenious oxid),
62.4; sample 10 (arsenic oxid), 74.3; and sample 39 (acid lead arse-
nate), 71.2.

42 BULLETIN 1147, U. S. DEPARTMENT OF AGRICULTURE.

RELATION OF WATER-SOLUBLE ARSENIC TO TOXICITY OF ARSENICALS.

No perceptible differences in mortality which could be attributed
to the usually small differences in water-soluble arsenic oxid were
observed in the 14 commercial acid lead arsenates used in the pre-
liminary tests. Three of these arsenates which have high percent-
ages of water-soluble arsenic oxid, however, killed no more insects
than the others.

TABLE 20.—Relation of water-soluble arsenic to toxicity of arsenicals, 1919.

Insects tested.

Food
eaten
Water- per
soluble j Toxicity | insect
- ene be de- She
ample : . base uctin mate
N = Arsenicals and control. nortatad tse & eee
Number. | Species.1| arsenic | tality of | on web-
in control. | worms
sample. and tent
cater-
pillars
Per cent. | Per cent Units.
18 | Laboratory basic lead arsenate.......-...-.- 1184 \rsftl. < soe 1a by Jib 68.6
28 | Commercial basic lead arsenate.........---- 1,939 |e. :do-4:.- 1.73 60.9 10.9
68 | Laboratory acid lead arsenate.-.........---- 1,361 |..-do----- wy 59.6 17.6
9°| Punearsenious oxid.!-3. 5 -5-8.0--- .-.<-5-8- 1,529 |s..d0.8.2- 17.77 46.1 9.6
10] Purearseni¢ Oxid... 3. (en = ot. as. 2s 1 516: peado.s2-: 100. 00 76.5 3.5
23 | Commercial zinc arsenite..........-......2. 1,448 je edo..2-- 1,25 66.9 22.0
70 | Commercial acid lead arsenate (new
[DEQGEESS EA 2 oo. Rees eelon ease ee 422 | sfl......- 69 66.9 2.8
39 | Commercial acid lead arsenate....-......... 2,263 | sftlg..... -61 68.9 2.9
5 | Commercial calcium arsenate........-...... 2645 |r ed0-8:. - -41 70.0 9,1
(| esse GO’ cated S. Sen ance Sete eee cee 2,492 |_..d0-...-- .88 39.9 66.0
HO noes se (1S ee Se epee Sn Dae oS ee PIE | Bans (Smear 1.31 59. 2 30.8
Gel ee GON Es 525 8 ice ceo see nee ae 2,393 |..-do-..... - 20 60.1 29.9
HS kes CO 2b Se Uae ee Eee oe ean ee oe See A ALA, | 2 2dO- «2-2 -52 43.1 68.1
HOAIeecee DOM Sorc ns eee ct eee ee eee 2; 607 1=220022--- 5. 20 65.9 18.5
69 | Laboratory calcium arsenate.......---.....- 2.298.| 2 -GOs.o52 . 88 52.5 55.0
45 | Laboratory calcium meta-arsenate..-....... db 2d2q) ibscs-eiee . 04 3.6 99.9
46 | Laboratory monocalcium arsenate--........-. 1758 sfo5 dOsnce- 89. 26 81.2 2.0
55 | Laboratory sodium arsenate plus Bor-
deawx mixtiure..ctcse. bead. oes. io 2, 674)| isfigyiecote.. 82.2. - 61.7 5.0
64 | Commercial Paris green...............0..62 2; 059 "| -». -<@ 02... ~ 3. 52 65.5 3.2
62 | Commercial Magnesium arsenate..........- 1,651 | figy..... 4,64 50. 2 18.3
71 | Laboratory barium arsenate................ 1.706. 4.) .ap-2. - 68 43.6 22.2
74 | Laboratory copper barium arsenate..-....... 1,814 |...do-....- 6. 27 48.9 15.6
73 | Laboratory aluminum arsenate.-..-.-.....-. 1,482 | fly...... 1.91 39.3 16.1
= @Contgol with 100d. 2.22) 0-0 ose bod aden ds kl fated bate. aerate ns tele eeee ake aeons 100.0

1s, silkworms; f, webworms (H. cunea); t, tent caterpillars; 1, potato-beetle larvee; g, grasshoppers; and
y, webworms (H. tevtor).

Table 20 shows that those arsenicals which are readily water
soluble (samples 10 and 46) have extremely high percentages of
toxicity, but that some of those which are almost insoluble in water
(samples 5, 23, and 39) have percentages of toxicity nearly as high.
The toxicity of the insoluble arsenicals does not appear to be based
upon the water-soluble arsenic present, but upon the stability of
the compound and how readily it can be broken down in the bodies
of insects.

During all of these experiments no special study of the burning
effects of the many arsenicals sprayed on foliage was made. The
porgentage of water-soluble arsenic is generally taken as a criterion
or judging the burning effect on foliage. The following spray
mixtures badly burned wild-cherry foliage: Sodium and potassium
arsenates, sodium arsenate plus Bordeaux mixture, all the samples
of arsenious and arsenic oxids used, calcium arsenates (samples 5,

|
|

ARSENICALS. 43

34, 46, and 59), lead and calcium arsenates plus lime-sulphur (samples
50 and 51), and Paris green. The following slightly burned wild-
cherry foliage: Zinc arsenite (samples 23 and 33), zinc arsenite
plus Bordeaux mixture (sample 30), calcium arsenate (sample 32),
and barium arsenate (sample 71). Zine arsenite (sample 23) and
Paris green slightly burned mulberry foliage.

RELATION OF ARSENIC RENDERED SOLUBLE BY INSECTS TO TOXICITY OF ARSENICALS,

Kirkland and Smith (22), in 1897, found that the alimentary
tracts of the gypsy moth larve were alkaline to litmus. Analyses
of the dialysate from washed and macerated alimentary tracts
showed the presence of phosphorus and potash in balay suffi-
cient to form alkaline potassium phosphate, which is suggested as
the cause of the alkaline reaction. Because of the report of these
investigators, determinations of the hydrogen-ion concentration
(pH value) were made on the water extracts of the bodies of the
insects fed various arsenicals and also of the bodies of control in-
sects. The results thus obtained showed a comparatively uniform
acidity for all the insects tested. It is possible, however, that
lactic or other acids are formed in the dead tissues of the insects.
The buffer effect normally available may possibly have masked any
slight changes in the reaction caused by the arsenicals fed. It is
obvious that the pH data as here obtained, or ash determinations
on dialysates of intestinal tracts as made by Kirkland and Smith,
are inadequate to show the reactions (pH) of the living tissue of
the intestinal tracts of insects.

The following methods were employed to determine the total
arsenic and water-soluble arsenic in insects and also the hydrogen-ion
concentration of the water extracts from the insects. The weights
and number of the washed larve were recorded, after which the
insects, parts of insects, or feces (dried in an oven at 105° C.) were
macerated in a mortar containing about 20 cubic centimeters of dis-
tilled water. The macerated larvee were then transferred to flasks
and diluted to 500 cubic centimeters with distilled water. The solu-
tions were shaken every 5 minutes for an hour, at the end of which
they were filtered and aliquots were taken for the determination of
the hydrogen-ion concentration and for the water-soluble arsenic.
The rest of the solution, with the residue, was used for the total
arsenic determination. The hydrogen-ion concentration was deter-
mined by the indicator method outlined by Clark and Lubs (8). The
solutions used for determining the soluble arsenic and those with the
residues for determining the total arsenic were placed in large por-
celain casseroles, and nitric and sulphuric acids were added. They
were then warmed on the steam bath and finally heated on the hot
plate until the organic material was completely destroyed. Since
the acids used, particularly the nitric acid, were not totally free from
arsenic, a record of the quantities of acids used was kept. The
solutions were then freed from nitric acid by adding water and by
applying heat. Next enough water was added to make a volume of
100 cubic centimeters, and finally the arsenic was determined by the
Gutzeit method, revised by Smith (47).

As preliminary tests, the following experiments were performed in
1919. Both sides of several mulberry leaves were heavily sprayed

44 BULLETIN 1147, U. S. DEPARTMENT OF AGRICULTURE.

with acid lead arsenate (sample 39). After having been dried by an
electric fan, the leaves were fed to 50 large hungry silkworms. When
the silkworms had ceased eating, they were removed to clean cages
where the feces, contaminated as little as possible, were collected and
subsequently analyzed. The next more a sample of 34 dead and
dying silkworms was thoroughly washed for five minutes in running
tap water, then, one worm at a time, in six different washes, the first
four consisting of hydrochloric acid (2 per cent) and distilled water
and the last two of aauilled water alone. A pencil brush was used for
scrubbing them. Analysis of the sixth wash showed the presence of no
arsenic. These experiments were repeated five times. To determine
how much of the arsenic had passed through the intestinal walls, the
alimentary canals of three sets were removed by careful dissections.

The results of the analyses of these samples were as follows: 84
entire silkworms yielded 2.66 milligrams of arsenic oxid, being 54
per cent water-soluble; 72 silkworms with alimentary canals removed
yielded 0.89 milligram of arsenic oxid, being 36.7 per cent water-
soluble; the alimentary canals of these 72 silkworms yielded 1.03
milligrams of arsenic oxid, being 55.9 per cent water-soluble; and the
2.18 grams of dried feces from these 72 silkworms yielded 0.45 milli-
eram of arsenic oxid. According to the figures obtained from these
72 silkworms, 37.6 per cent of the total arsenic eaten had passed
through the walls of the alimentary canals, 43.4 per cent of it was
retained inside these canals, and 19 per cent of it was voided with the
feces. Reaction (pH) of water extract from the larve was neutral
(7); from the alimentary canals, slightly alkaline (7.1); from the
larve with the alimentary canals removed, slightly acid (6.2); and
from the feces, acid.

The foregoing experiments were repeated on a larger scale by feed-
ne 13 arsenicals sprayed on leaves to caterpillars of the catalpa-
sphinx moth (Ceratomia catalpe Bdy.). The results obtained in-
dicate the following: (a) As a general rule, the higher the percentages
of water-soluble arsenic in the larve and feces, the higher the rates of
toxicity of those arsenicals; (b) the percentage of water-soluble
arsenic in the arsenical ingested usually has little to do with the rate
of toxicity; (c) the amount of arsenic found per caterpillar is fairly
constant for all the arsenicals used; (d) the higher the ratio of total
arsenic (per 100 grams of larval material or feces) found in the larvee
to that found in the feces, the higher the rate of toxicity; (e) the
reaction (pH) of water extracts from the lary fed various arsenicals
seems to pans no relation to the rate of toxicity.

In 1920 the preceding experiments were repeated on a much larger
scale, using the following insects: Honeybees, 2 sets (each of 100) ;
silkworms, 3 sets (each of about 25); Ceratomza, 2 sets (each of about
25). The procedure followed was the same as that in the preliminary
tests, but, in order to determine the percentage of arsenic actually
made soluble by the juices of the insects, the percentage under
‘“‘control results”? in Table 21 was subtracted from the percentage of
arsenic found soluble in the bodies of insects. Since the solubility of
a minute quantity of arsenic in 500 cubic centimeters of water
proved to be greater than that of a larger quantity, an amount, of
arsenic approximating the average amount found in a sample of the
insects analyzed was employed as a control.

| yom ARSENICALS. A5

TABLE 21.—Relation of arsenic rendered soluble by insects to toxicity of arsenicals, 1919

and 1920.
Total Percentage of arsenic.
number
of bo
insects g oO : Petr
ana- 32 _ | Soluble in bodies of— ons eehuy® Bodies
lyzed as @
°o ec
Arsenicals. i < R
eds
“IE He
A Solio Seas gq | 3s 5 2 gs | 5
on # E = i= 3 Oo = be (<>) =S s
= 8) |) 285 | 8 5 | & | 8 s. (+e
a wm |, oP) 8} RD S < a D Ss <
39 | Commercial acid lead arse-
Naess 4s se eas! Leet 8 | 310 17.3 | 44.5 | 46.0 | 83.5-| 58.0 | 27.2 | 28.7 | 66.2 | 40.7
28 | Commercial basic lead arse-
nate. 2 Qf shine: Naas: 8 | 353 7.2 | 28.8 | 37.7 | 68.5 | 43.3 | 21.6 | 30.5 | 56.3 | 36.1
57 | Commercial calcium arse-
PEE eed ses eer cet 8 | 405 35.7 | 78.6 | 60.6 | 84.7 | 74.6 | 42.9 | 24.9 | 49.0 | 38.9
27 | Commercial white arsenic..-| 7 | 320 5.2 | 64.8 | 33.9 | 20.0 | 39.6 | 59.6 | 28.7 | 14.8 | 34.4
71 | Laboratory barium arsenate.| 8 | 360 30.5 | 69.4 | 30.3 | 64.0 | 54.6 | 38.9 -0 | 33.5 | 24.1
45 | Laboratory calcium meta-
ATSeEn ALCL. oe Seon saan 6 | 336 2.4 | 41.8 | 39.1 | 22.6 | 34.5 | 39.4 | 36.7 | 20.2 | 32.1
64 | Commercial Paris green. ...- 9 | 423 15.9 | 98.3 | 44.3 | 71.0 | 71.2) 82.4 | 28.4 | 55.1 | 55.3
as cample 6“ plusima? grams)| 7 | 321 11.0 | 91.8 | 37.4 | 61.2 | 68.5 | 80.8] 26.4 | 50.2 | 52.5
ommercia magnesium
arsenate! . sft eb). fit 9) 546 37.9 | 80.3 | 59.9 | 98.7 | 79.6 | 42.41 22.0 | 60.8 | 41.7
90 | Commercial London purple.| 6 | 293 33.2 | 84.3 | 48.4 | 95.1 | 75.9 | 51.1 | 15.2 | 61.9 | 42.7
23 acca zine ose ES 6h 14292 6.0 | 58.4 | 63.8 | 73.9 | 65.4 | 52.4 | 57.8 | 67.9 | 59.4
74 aboratory copper barium
ATSONATO He Sewie ene pee 10 | 570 6.2 | 74.6 | 59.2 | 58.8 | 64.2 | 68.4 | 53.0 | 52.6 | 58.0
10 | Pure arsenic Oxid...........- 7 | 331 100.0 | 88.4 | 70.9 | 89.6 | 83.0 |......).0- 22 2)o 2.2/2.2.
25 | Laboratory sodium arsenate.| 9} 515 MKD US UT MACE DSC Bad ach ae Hel Vite ly P53 J Pegs ee eng eaten el ene
Bollea atletiee ephalligels
E 26 | Average amount of arsenic per) ° 3
g . Se insect analyzed. are
ag ~4 q:
n | Ss fq
go g °
aan lke be
oo a} &
Arsenicals. 2 2 2 5 S3
S} Fi 5 5 B I S cree
a bo | Sa 2 | s ss be
2 See ie Eewk gothas & | S38
a oS 3 SS ® iS Ss SiS
g Fe rr d if 3 5 Bas
et S $a S = S > ped
wD ; = = fy nD S < <
f Per ct.| Mg. | Mg. | Mg. | Mo.
_ 39.| Commercial acid lead arsenate.......... 78.5} 2.03 | 0.0223 | 0.1212 | 0.0126 | 0.0520 6.0
hs 28 | Commercial basic lead arsenate.......... 61.7 1.73 0142 | .0803 0158 | .0368 6.0
M4 57 | Commercial calcium arsenate..........- 65.5 - 20 0099 | .1245 0189 } .0511 6.0
ie 27 | Commercial white arsenic. .............. 69.5 | 38.00 0091 | .0914 0285 | . 04380 6.0
, 71 | Laboratory barium arsenate.........--.- 51.0 - 68 0105 | .0694 0138 | .0312 5.8
45 | Laboratory calcium meta-arsenate...... 17.5 04 0120 0676 0110 | .0302 5.9
i 64 | Commercial Paris green. :..2-...2.....-. 79.5 3. 52 0087 1203 0143 | .0478 5.9
_ €4C | Sample 64 plus lime (2 grams).........-.. 66.7 3.52 | .0075 1157 0276 | .0503 5.8
62 | Commercial magnesium arsenate.-...-... 71.0 4,64 0120 1460 0173 | .0584 6.0
90 | Commercial London purple. -........-.-. 73.7 5,30 0068 | .1315 0305 | .0563 5.8
23 | Commercial] zinc arsenite ...-............ 77.5 1.25 0132 |} .1430 0220 | .0594 6.0
74 | Laboratory copper barium arsenate..... 66.0 6.27 0058 0675 0177 | . 0303 6.0
10+| sPurearsenic Oxide - Sys Tics pe... tse y 78.5 | 100.00 0165 | .1130 0600 |. .0632 5.9
aie lene eerie 82.4 | 100.00 0180 | .0968 0169 | .0489 5.9

= Ce oe Se ey oe eS
le!
©
on
jo)
5
r)
ct
g
5.
ro)
4
o
i]
)
ct
oO

The following deductions are made from the results shown in
Table 21:

(a) Samples 45, 27, 23, 74, and 28 are very stable in water (slightly
soluble as compared with control results); samples 64C, 64, and 39
are moderately stable in water; samples 71, 90, 57, and 62 are
unstable in water; and samples 10 and 25 are totally water soluble.

ES at Se ee

——

46 BULLETIN 1147, U. S. DEPARTMENT OF AGRICULTURE.

(b) Sample 45 is least soluble and sample 10 is most soluble in the
bodies of insects. Samples 10 and 25 were totally water soluble
before they were eaten, but after being eaten only about three-
fourths of the arsenic was obtained as soluble arsenic.

(c) While no general deductions can be made as to the average
percentages of arsenic found soluble in the bodies of insects, when
the figures under “‘control results’”’ are subtracted from these aver-
ages, as a general rule, the higher the percentages of arsenic made
soluble by the juices of the insects, the higher are the rates of toxicity.
Using lead arsenate (sample 39) as a standard, the last statement is
strongly supported by the results obtained with the first seven
arsenicals (samples 39, 28, 57, 27, 71, 45, and 64), but it is not so
strongly supported by the following five samples (64C, 62, 90, 23,
and 74).

(d) The percentages of water-soluble arsenic in the original samples
of arsenicals bear no relation to the toxicity of those arsenicals,
except in the case of those which are totally water soluble.

(ec) As a general rule, the larger the average amount of arsenic
in the insects analyzed, the higher is the rate of toxicity of that
arsenical. Using average weights of the undried insects fed on all
14 of the arsenicals and average amounts of arsenic per insect, a
bee weighing 98 milligrams contained 0.0119 milligram of arsenic,
a silkworm weighing 1,370 milligrams contained 0.1063 milligram,
and a Ceratomia weighing 1,620 milligrams contained 0.0219 milligram
of arsenic. Thus, although a silkworm is 14 times as large and a
Ceratomia is 16 times as large as a bee, the silkworm contained 9
times as much arsenic as did the bee and 5 times as much as did
the Ceratomia. ‘This difference in amount of arsenic probably may
be explained by the fact that for bees and silkworms the spray mix-
tures were used five times the usual strength, while for the Cera-
tomia the usual strength (1 pound to 50 gallons of water) was suffi-
cient to kill the insects within 24 hours.

(f) None of the water extracts of the bodies of the insects fed
on the various arsenicals showed an alkaline reaction, and the
highest acid reaction was 5.8 (pH value). As an average pH value
for the 14 arsenicals, the bees gave a value of 6; the silkworms, 5.7;
and the Ceratomia, 6.1; and as an average pH value for any arsen-
ical against all three insects, the only figures obtained are 5.8, 5.9,
and 6. Again it is shown that the pH value has nothing to do with
the percentage of arsenic rendered soluble by the insect juices.

Experiments like those performed on the three foregoing species
of insects were also performed on another large but easily killed
caterpillar (Datana integerrima G. & R.). As the number of these
caterpillars was limited, only samples 39, 57, and 64 were used against
this species, so that the results obtained could not be easily incor-
porated in Table 21. They are, however, similar in all respects
to those already discussed.

MINIMUM DOSAGE OF LEAD ARSENATE REQUIRED TO KILL SILKWORMS.

By means of a needle-pointed pipette, an acid lead arsenate (sample
39) was dropped upon fresh mulberry leaves. Upon evaporation
of the water from these drops, the portions of leaves bearing the
white spots were fed to large hungry silkworms in the last instar.

ed

ARSENICALS. 47

One drop would occasionally kill a large worm but more often two
drops were fatal. In almost every case three drops proved fatal
within 24 hours. Therefore, for these larve three drops may be
regarded as a minimum fatal dosage of acid lead arsenate. An
analysis of 100 drops (4 sets) from the same pipette gave 0.0091
milligram of metallic arsenic as an average per drop, making 0.0273
milligram of arsenic a minimum fatal dosage for fully grown silk-
worms.

An analysis of 59 of the dead silkworms, each of which had eaten
three drops of the arsenical, gave 0.0027 milligram of arsenic per
larva, indicating that 90 per cent of the arsenic eaten had been
voided in the feces before the larve died. Silkworms which had
received a maximum dosage of the same arsenical voided in the feces
only 19 per cent of the arsenic eaten, and Ceratomia, which had
received an average dosage of the same poison, voided 64 per cent of
the arsenic with the feces.

QUANTITY OF ARSENIC EATEN BY INSECTS IN FEEDING TESTS.

During the feeding tests many samples of dead larve were pre-
pared for analyses, but only those of webworms (4. teztor) and those
of potato-beetle larve were finally analyzed. The webworm is one
of the most difficult to kill by arsenic, while the potato-beetle larva
is one of the most easily killed. Some of the webworms were washed
as described on page 44, but most of them were not washed. Also
several samples of feces (more or less contaminated) were analyzed.
The percentage of toxicity, as shown in Table 22, is the average of
the mortalities recorded on the third, sixth, and tenth days for the
one species concerned.

TABLE 22.—Arsenic consumed by insects in feeding tests, 1919.

Num- per million) | icity
: - . Condition of | ber of | Arsenic wa after de-
Boece. uf ae Arsenicals and controls. | larve before | larve | per ductus
ib zi being analyzed. | ana- | larva. tality
lyzed. Larve.|Feces.| of
control.
Webworms (H. tez- Milili-
tor): . grams
OP eats enaceass Commercial acid lead | Washed and 163 | 0.0017 309) Oa@alescesnes
arsenate. dried.
Ae Rieno see bl eee Oe eee sane = Driedeas sa-ol.e 400 0025 385 {1,114 68.6
Diaesioues seeneoes Commercial calcium ar- | Washed and 200 0014 303)" 746) [ese onee ~
senate. dried.
Gy ein Wes Fe ae facRae hae be rae (ap AAs ET pc RL Dried. see 400} .0024 481 |1,125 59.1
Payee bee ae Er peery Commercial basic lead |..... dO SS 200 | .0040 691 0 48.9
arsenate.
69............°.| Laboratory calcium arse-|..... doz.cvca2 ot? 180 | .0033 436 | 851 15.1
nate.
69Be=.sios neces = Sample 69 plus 1 gram |..... ca (a es a 130 0040 674 | 355 6.3
lime per 418 ce.
CSR Ra vapaetary, barium arse- |..... GON hone o 2k 160 | .0027 399 | 365 3155
nate.
G2 ee escent eeupe Commercial magnesium |..... GOs. 2. oda 200 0050 747 | 539 36.5
arsenate.
Bi S23, BOIS. Laboratory sodium arse- |..... do..2si Riot 200 0016 303 | 818 59.3
nate plus Bordeaux
mixture.
Baie od dae Saetp Commercialzincarsenite.|..... Gz th cnj4-5 200 0055 917 | 903 63.6
Ls eety oy ae pe Commercial Paris green .|..... do..........-| 200] .0050 911 | 946 62. 6
BC aa seem Laboratory aluminum |..... Goss. chee 200 0028 383 | 840 32.0
arsenate.
Uf Se eee eee Laboratory copper |..... Cs | eee 200 0053 613 | 306
barium arsenate.
Controliieces.s. 0) saeaetnac tuo einn oueisedelescaeecelswacdwettucwenees Ui leesasece

48 BULLETIN 1147. U. S. DEPARTMENT OF AGRICULTURE.

TABLE 22.—Arsenic consumed by insects in feeding tests, 1919—Continued.

: ; Condition of | ber of | Arsenic EF ater
eds LCF oe Arsenicals and controls. | larvz before | larve | per |———————|ductin®
aoe ; being analyzed. | ana- | larva. tality
lyzed Larvee.|Feces.| of
control
Potato-beetle Milli-
larvee: grams.
5 pls scape eniait Se Commercial acid lead ar- |..... GO. Seen css 150 | 0.0017 4 62.1
senate.
aS ee eae Commercial basic lead |.-...-. do Len. 5. ¥- 125 | .0020 IGS; [oss 5. 53.4
arsenate.
683.0nf3-23:5, Laboratory acid lead |..... dosts. te. 15% 100 | .00388 B27 ts bse 57.9
arsenate.
BP. $3255 f2 76 ..! pecaenes calcium ar- |....-. Hol Bee , 150 | . 0026 205 Hh . 2.4 62.7
senate.
epi ot Fs Laboratory calcium ar- |..... doz SMe 110 | .0043 Bitsy 61.8
senate.
ELAS Vi eagae aah dtl a Sample 69 plus 1 gram |..... GOte55~ cence 80 | .0042 BOO. | anse 61.9
lime per 418 ec.
Th ee Rees LAD ery, barium arse- |....- €0.43- 4%. 110 | .0049 SSO h2 =. 50.9
nate.
G2 tne ees Commercial magnesium |..... da. -5.2542 130 | .0029 223 | .=..<. 57.1
arsenate.
GG ret aA ae ee Laboratory sodium arse- |....- dors. sk 100 | .0028 Viiv ih see, © 51.8
nate plus Bordeaux
mixture.
Do omc se. see eis ek poo ercial zine arse- |..... OOsc2-s2568e4 100 | .0018 isi bs -23 54.7
nite.
i UR RO ae Eee Gee Commercial Paris green..]....- dae tii 29 120 | .0024 206.113 3... 59. 5
Cc et A eh a Laboratory copper ba- |..-.-- dot. Sere 130 | .0051 AGO TE fan: 54.7
rium arsenate.

The following facts are evident from Table 22: About 40 per cent
of the arsenic (samples 39 and 5) found in the samples of webworms
was probably carried on the integuments of the larve. As a general
rule, the higher the average toxicity, the smaller is the quantity of
arsenic found in the larve. The ratio of arsenic found in the
webworms to that found in their feces is about 3 to 5 for those
arsenicals giving high toxicities, while for those arsenicals giving low
toxicities the ratio is about 1 to 1.

PHYSIOLOGICAL EFFECTS OF ARSENIC ON INSECTS.

Symptoms of arsenic poisoning in the various insects used in the
preceding experiments can not be fully described, because these
insects were usually too sluggish to permit observation of the later
symptoms, other than an occasional contortion of the body, the
voiding of soft, watery feces, spewing at the mouth, and finally the
complete loss of control of the legs.

Since honeybees are extremely active and are easily studied in
observation cases, they were fed arsenic acid (sample 10) in honey at
the rate of 0.00076 milligram of arsenic oxid or 0.0005 milligram of
metallic arsenic per bee, providing all consumed equal quantities of
the poisoned food: The poisoned bees lived for 5.4 days on an average,
while the controls lived for 8.4 days on an average. On the second
day after being poisoned many of these bees became more or less
inactive, a few died| and subsequently but few of them were seen
eating. By the third day they were dying rapidly, their abdomens

ARSENICALS. 49

were swollen, and they could not fly, although they could walk in a
staggering manner, dragging their abdomens on the table. The only
letonvs between the behavior of the bees subjected to nicotine
poisoning (29, p. 91) and that of bees subjected to arsenic poisoning
is that (a) nicotine acts more quickly, (6) its symptoms are more
pronounced, and (c) in arsenic poisoning the abdomen is always
more or less swollen, while in nicotine poisoning the abdomen is only
rarely swollen. From the symptoms observed, it may be concluded
that the bees fed arsenic might have died of motor paralysis, although
the paralysis may be only a secondary cause.

Blythe (4, p. 567) says that flies, within a few minutes after eating
arsenic borne on common arsenical fly paper, fall, apparently from
paralysis of the wings, and soon die. Spiders and all insects into
which the poison has been introduced exhibit a similar sudden death.

According to the textbooks on pharmacology by Cushny (14) and
Sollmann (49), arsenic is termed, among other things, ‘a capillary
poison.” These authors state that arsenic is toxic to all animals having
a central nervous system and also to most higher plants, but not to
all the lower organisms. In mammals arsenic is cumulative, bein
stored in various organs, and it is excreted very slowly by the usua
channeis—urine, feces, sweat, milk, epidermis, and hair. With oral
administration, the main part leaves by the feces, probably having
never been dissolved.

TRACING ARSENIC IN TISSUES OF INSECTS.

All attempts to trace arsenic fed alone to fall webworms (4. cunea)
by histological methods failed. The light-colored precipitate formed
by the union of arsenic and silver nitrate was either washed out of the
tissues or was obscured because the tissues were stained dark by the
silver nitrate.

In an endeavor to trace arsenic in both the soluble and insoluble
forms by stains and lampblack the following experiments were per-
formed, using the method for tracing nicotine outlined by McIndoo
(29, p. 106-109).

Four sets of fall webworms were fed leaves sprayed with an acid
lead arsenate (sample 39), mixed with stains or lampblack as follows:
First set ate arsenate mixed with indigo-carmine; second set ate
arsenate mixed with carminic-acid; third set ate arsenate mixed with
No. 100 carmine powder; and fourth set ate arsenate mixed with
No. 100 lampblack powder. A daylater those fed carmine were voiding
reddish feces, and two days after being fed all of those nearly dead
were fixed in absolute alcohol. The indigo-carmine and carminic-
acid were soluble in water, but they were partially precipitated by
absolute alcohol; the carmine was only slightly soluble in water, but
totally insoluble in absolute alcohol; and the lampblack was soluble
in neither water nor absolute alcohol.

Webworms fed indigo-carmine showed nostain. Thosefed carminic-
acid and carmine revealed pinkish intestines, those colored with the
carmine being almost red. The intestinal contents of these larvee
were pink, but no carminic-acid could be observed outside the
intestinal wall. In the larve fed carmine the stain was widely
distributed. The nuclei in the cells of the intestine were strongly

50 BULLETIN 1147, U. S. DEPARTMENT OF AGRICULTURE.

stained, while all the tissues outside the intestinal wall contained
more or less of the stain. In the larve fed lampblack much of the
powder could be observed inside the intestine, but very little (perhaps
none in reality) outside the intestinal wall.

GENERAL PROPERTIES OF ARSENICALS.

Used alone, arsenious oxid burns the most resistant foliage,
because of its high percentage of water-soluble arsenious oxid. T)
overcome this difficulty, Sanders and Kelsall (43) mixed a very finely
divided arsenious oxid with Bordeaux mixture, to serve as a sub-
stitute for sodium arsenate and Bordeaux mixture, to control the
potato beetle and late blight in Nova Scotia. Cooley (13) suggested
the use of white arsenic with Bordeaux mixture for dusting potato
vines and has successfully used white arsenic as a substitute for the
expensive Paris green in bran mash to control grasshoppers in
Montana. He considers crude arsenious oxid to be superior to the
refined product, as the particles are finer. Most authors think that
arsenious oxid possesses high insecticidal properties. The results of
the investigation here reported, however, indicate that the toxicity
of arsenious oxid varies greatly, depending on the degree of fineness
of the crystals which influences the percentage of water-soluble
arsenious oxid present. In no case did the toxicity equal that of an
equivalent amount of arsenic oxid present in acid lead arsenate.

Acid lead arsenate, a satisfactory insecticide material, is to be
recommended in general when an uncombined arsenical is to be used,
as it possesses excellent adhesive and insecticidal properties, and
burns foliage little if at all. Acid lead arsenate is compatible with
Bordeaux mixture and with nicotine sulphate solutions. Lime-
sulphur and acid lead arsenate are incompatible from a chemical
standpoint, some soluble arsenic being formed. However, it is well
recognized that acid or basic lead arsenates are used with lime-
sulphur without serious foliage injury in most cases. A powdered
acid lead arsenate contains about 32 per cent of arsenic oxid and
about 64 per cent of lead oxid, while powdered basic lead arsenate
contains about 23 per cent of arsenic oxid and about 73 per cent of
lead oxid. Also, basic lead arsenate is more stable and less toxic
than acid lead arsenate.

Paris green, a valuable insecticide on account of its high arsenic
content, is said to dust well in spite of its high apparent density, but
not to adhere well to foliage. Tt has no advantages over acid lead
arsenate, but has several disadvantages, the burning of foliage being
the principal one. The expensive copper sulphate and acetic aci
used in its manufacture do not increase its power as a poison.

The amount of soluble arsenic in an arsenical is reduced by mixing
it with Bordeaux mixture, and an unsafe arsenical may in certam
cases be made safe by mixing it with Bordeaux.

Soaps contain alkalies which decompose arsenicals. The more
soap used, the greater the decomposition. When calcium arsenate
was mixed with sodium fish-oil soap, a smaller amount of soluble
arsenic was formed than when acid lead arsenate was used in the
mixture. Both of these mixtures are incompatible.

When acid lead arsenate or calcium arsenate is used in a kerosene-
soap emulsion, soluble arsenic is rapidly formed. In the acid lead

.

f
4
i

ARSENICALS. 51

arsenate combination, six times as much arsenic is formed as in the
calcium arsenate combination. Acid lead arsenate, therefore, should
not be used in preparing kerosene-emulsion sprays, as the mixture is
chemically incompatible. Gray (16) reports that basic lead arsenate
is not affected by the alkali of soap.
When acid lead arsenate was mixed with solutions of nicotine sul-
phate, no chemical incompatibility was found. When calcium
arsenate was used with nicotine sulphate, however, the latter was
decomposed and free nicotine was formed. The SO, of the nicotine
sulphate combined with free lime (CaQ), if present, or with lime of the
calcium arsenate, and large amounts of soluble arsenic were formed
in certain mixtures. Free nicotine is present im all of these mixtures.
The free nicotine is not dangerous but the soluble arsenic is. These
mixtures are chemically incompatible. The findings in connection
with the chemical compatibilities and incompatibilities of the various
arsenicals, fungicides, and other materials tested are summarized in
Table 23. Gray (1/6) in 1914 published a summary of data on the
compatibilities of various spray materials which he had collected.

TaBLE 23.—Chemical compatibility of arsenicals combined with other spray materials.

Other spray materials used.
Arsenicals used. Bord = Sodium fish. Nicotine aut
t ordeaux erosene um fish- icotine-sul-
Lime sulphur. | “mmixture. emulsion. oil soap. phate solution.

LE Oe

Acid lead arsenate. -..| Incompatible...} Compatible . TCO BALD IO: 3: Incompatible...| Compatible.

Calcium arsenate. .--- Compatible... -}..:.. dQncses5|----- Made sssead Base GOS seca: Incompatible.
Paris green { 334j549e- |e: eS. CELL iS2 23) oese esc SER Lo hn sel Geil cera totes
Sodigmarsenaies: a sp| aoe sc anaonem esis oe COs dscse|boosses cos soseediGeresseonesodcasd he se4ckeebsstocs

Sanders and Brittain (41) tested the comparative insecticidal prop-
erties of the arsenates of calcium, barium, and lead, alone and in com-
bination with Bordeaux mixture, lime-sulphur, barium tetrasulphid,
and sodium sulphid (‘‘soluble sulphur’’), on one species of insects.
The results obtained showed that the presence of a fungicide had a
marked influence on the efficiency of the arsenical investigated. The
four arsenicals were 13 per cent more efficient when used with sodium
sulphid than when used alone. The toxicity of the arsenicals was
reduced when they were mixed with any of the other fungicides. The
explanation given by these authors for the increased toxicity resulting
from the use of sodium sulphid with an arsenical is that the sodium
increases the palatability of the sprayed leaves, which causes the
insects to eat ravenously for afew days. The insects thus take a large
amount of arsenic into their systems in a short time and death rapidly
ensues.

Mixing sodium sulphid with acid lead arsenate produces some lead
sulphid and sodium arsenate. The sodium arsenate is soluble and
therefore may be more active than the original acid lead arsenate.
The results in Table 21 indicate that the soluble arsenicals are more
toxic per unit of arsenic than are the insoluble ones, the greater
toxicity being due to the water-soluble arsenic present in the com-
pound or to the arsenic which is quickly rendered soluble inside the
insects. Data obtained during this investigation suggest that the
amount of arsenic present per unit of sprayed leaf is larger when a

52 BULLETIN 1147, U. S. DEPARTMENT OF AGRICULTURE.

soluble arsenical is used in combination with a fungicide than when
an insoluble arsenical is used. Accordingly it may be possible to
explain chemically the increased activity or efficiency when sodium
sulphid is used with arsenicals.

vidence seems to show that it.is not always true that an insecti-
cide containing a high percentage of arsenic is more toxic than one
containing less arsenic, for the reason that toxicity depends not alone
upon the amount of arsenic present, but also upon its form of combi-
nation. The insecticidal rdle played by the base itself is small and
sometimes nonexistent.

When lime or Bordeaux mixture was combined with the arsenicals
the toxicity of the arsenicals was reduced. The fact that the addi-
tion of lime or Bordeaux mixture to the arsenicals reduced the
toxicity of these insecticides to insects may be explained in two ways:
(a) Leaves sprayed with the arsenicals combined with lime or
Bordeaux usually contained less arsenic than those similarly sprayed
with the arsenicals alone; (0) the toxicity was greater in the tests
with honeybees fed honey containing the arsenicals alone than in
tests in which bees ate honey containing the arsenicals with lime or
Bordeaux mixture. These results support the theory that the cal-
cium present prevents or counteracts the formation of soluble or
more toxic arsenic compounds.

Based on the reported results, it would appear that if all seven
species of insects used had been tested under similar conditions,
their susceptibility to an acid lead arsenate would probably be in
the tollowimg order, beginning with the insect most susceptible:
Honeybees, silkworms, grasshoppers, potato-beetle larve, tent
caterpillars, webworms (H. textor), and webworms (H. cunea).

The arsenious oxid (‘‘white arsenic”) samples were crystalline;
the other commercial arsenicals generally lacked crystal outline and
were probably for the most part amorphous. The calcium arsenates
used contained some small ‘“‘octahedral”’ crystals, but were largely
composed of apparently amorphous material. The arsenious oxid
samples gave variable results in the toxicity studies and wide varia-
tions were found in the results when calcrum arsenates were used.
On the other hand, the amorphous acid lead arsenates and the
amorphous Paris green samples gave uniform toxicity data. The
data show a relation between the uniformity of the products and
uniformity of toxicity. Where the products were not uniform |
variations in toxicity were found. a

Commercial arsenicals used for spraying or dusting purposes are
usually judged chemically on the basis of the total arsenious or arsenic |
oxid contents and on the percentages of the total amount of these
oxids which go into solution under certain conditions. The per- |
centage of base present is also determined. Soluble arsenic oxids
or arsenic rendered soluble after the application of arsenicals will
burn foliage, the extent of the injury depending mainly on the
amount of soluble oxid present or formed in the spray or solution |
applied. The results here reported indicate that it is the soluble
arsenic or the arsenic rendered soluble by the insects that causes ©
death. ‘The rapidity with which arsenicals are made soluble in the |
bodies of insects seems to be the most important factor in connection
with their toxicity. What happens to the soluble arsenic inside the
insects is not known, except that part of it passes through the in-

ARSENICALS. 53

testinal walls into the blood and is distributed to all parts of the
body. A small portion of it reaches the nervous system, where it
apparently kills by paralysis. The way arsenic affects the various
tissues is not known, although Sollmann (49) reports that it is now
generally believed that the arsenicals hinder protoplasmic oxidation
in an unknown way. A successful insecticide must be sufficiently
stable to be applied to foliage without injury and sufficiently unstable
to be broken down in appreciable amounts in the bodies of the insects
ingesting it.
SUMMARY.

Arsenious oxid, commercially known as white arsenic, or simply
as arsenic, is the basis for the manufacture of all arsenicals. Samples
of commercial arsenious oxid vary in purity, fineness, apparent
density, and in the rate of solution in water (soluble arsenic), which
accounts for the diverse chemical and insecticidal results reported
in the literature. Arsenites are prepared by combining arsenious
oxid with a base. Arsenates are produced by first oxidizing ar-
senious, oxid to arsenic oxid (arsenic acid) and then combining the
material with a base. Except for their water content of approxi-
mately 50 per cent, the paste arsenicals have the same general com-
position as the powdered arsenicals.

The usual lead arsenate on the market, acid lead arsenate
(PbHAsO,), is well standardized and stable. Basic lead arsenate
(Pb,PbOH(AsO,),), also well standardized and stable, is_ being
manufactured at present only to a limited extent. Chiefly because
of its low arsenic and high lead contents, basic lead arsenate is more
stable and therefore less likely to burn foliage than acid lead arsenate.
It possesses weaker insecticidal properties and is somewhat more
stable in mixtures than acid lead arsenate.

Commercial calcium arsenate (arsenate of lime), the manufacture
of which is rapidly becoming standardized, contains more lime than
is required to produce the tribasic form.

Paris green, an old and well standardized arsenical, is less stable
and ‘contains more ‘‘soluble arsenic’? than commercial arsenates of
lead or lime.

Laboratory samples of aluminum arsenate, barium arsenate, and a
copper barium arsenate mixture, in the powdered form, were tested.
The last named gave excellent insecticidal results.

The following combinations of insecticides and fungicides were
found to be chemically compatible: Lime-sulphur and. calcium arse-
nate; nicotine sulphate and lead arsenate; and Bordeaux mixture with
calcium arsenate, acid lead arsenate, zinc arsenite, or Paris green.
The following combinations were found to be chemically incompat-
ible: Soap solution with either calcium arsenate or acid lead arsenate;
kerosene emulsion with either calcium arsenate or acid lead arsenate;
and lime-sulphur with. acid lead arsenate. Combined with nicotine
sulphate, calcium arsenate always produces free nicotine, and unless
a decided excess of free lime is present soluble arsenic is produced.

The combination of sodium arsenate with Bordeaux mixture as
used in the experiments here reported gave no soluble arsenic.

4 a According to the Bureau of Entomology, this combination in large amounts is used successfully in the
d.

54 BULLETIN 1147, U. S. DEPARTMENT OF AGRICULTURE.

Of all the arsenicals tested, acid lead arsenate and zinc arsenite
were the most adhesive and Paris green the least adhesive on potato
foliage. The use of lime with arsenicals applied to potato foliage did
not increase their adhesiveness.

The suspension properties of the powdered arsenicals are of value
in differentiating Hight” from “‘heavy”’ powders, as determined by
their apparent densities. :

The physical properties of the commercial powdered arsenicals
could not be satisfactorily determined by sieving, as they are generally
amorphous and pack in the sieve on shaking. enious oxid samples
sometimes contain or consist of relatively coarse crystals, so that
sieving may provide valuable data.

Microscopic examination gave little information concerning the
desirable physical properties of the amorphous or seemingly amor-
phous powdered arsenicals. Differences in size of crystals present in
the arsenious oxid samples were detected under the microscope.

The toxicity findings are based on the use of equivalent quantities
of arsenious and arsenic oxids. Higher percentages of toxicity were
found for acid lead arsenate than for basic lead arsenate. The differ-
ent samples of calcium arsenate tested varied widely in toxicity.
When lime or Bordeaux mixture was added to arsenicals, the toxici-
ties were reduced. The average toxicity of the three samples of |
Paris green and that of one zinc arsenite tested was slightly more
than that of an acid lead arsenate and a sodium arsenate. Of the
four samples of arsenites, the Paris green samples gave the highest
values, zinc arsenite being much less toxic. Based on equivalent
metallic arsenic percentages, the Paris green samples gave values no
higher than that of the acid lead arsenate tested. Several new arse-
nates tested did not show as high toxicities as did acid lead arsenate.
Of the various bases tested, lead oxid showed some insecticidal value, |
while the oxids of zinc, magnesium, and copper showed little and |
lime no value. Arsenic acid, acid lead arsenate, and one sample of
calcium arsenate gave high and practically equal toxicities. Arse- —
nious oxid (white arsenic) gave lower and variable results. The per-
centages of water-soluble arsenic in the original arsenicals had little
or no influence on the toxicity, except in the case of those arsenicals
which were entirely or largely water soluble. These had high per- |
centages of toxicity.

The determination of reaction in terms of the pH value of water |
extracts from the bodies of various insects fed all of the different |
arsenicals, and also from the bodies of control insects, showed uni-
formly a slight acidity. These results indicate that the arsenic
compounds fed did not affect the pH values as determined on dead |
insects.

The minimum dosage of metallic arsenic required to kill a honeybee
is approximately 0.0005 milligram, while 0.0273 milligram (or 54
times as much) is required to kill a full-grown silkworm. Honey-
bees, confined in cases, void none of the arsenic eaten, whereas sill
worms void 90 per cent of the amount ingested. Thus, in reality |
about 6 times, rather than 54 times, as much arsenic is fatal to a
silkworm as is required to kill a honeybee under the somewhat —
unnatural living conditions.

ARSENICALS. ~ 55

The conclusions that may be drawn from this investigation are
that a chemical analysis of an arsenical does not give sufficient data
to judge satisfactorily its insecticidal properties, and a toxicity study
alone does not show that an arsenical is suitable for general insecti-
cidal purposes, but both a chemical analysis and a thorough toxicity
study are required in order to judge auathes or not an arsenical is
a satisfactory insecticide.

LITERATURE CITED.

(1) ASSOCIATION OF OFFICIAL AGRICULTURAL CHEMISTS.
Official and tentative methods of analysis as compiled by the committee on
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(2) Avery, S., and Brans, H. T.
Soluble arsenious oxide in Paris green. Jn J. Am. Chem. Soc. (1901), 23:
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(3) Beprorp, DUKE or, and Pickering, S. U.
Lead arsenate. Jn 8th Rept., Woburn Exp. Fruit Farm (1908), p. 15-17.
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Poisons: Their effects and detection, 5th ed., p. 745. London (1920).
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and Tartar, H. V.
Further studies of the reactions of lime sulfur solution and alkali waters
on lead arsenates. In J. Ind. Eng. Chem. (1910), 2: 328-329.
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70 p.
(8) CLARK, WM. and Luss, H. A.
The calorimetric determination of hydrogen-ion concentration and its appli-
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(9) Coan, B. R.
Recent experimental work on poisoning cotton boll weevils. U.S. Dept.
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(6)

(10) and Cassipy, T. P.

Cotton boll weevil control by the use of poison. U.S. Dept. Agr. Bul. 875
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11

meme Ne for poisoning the cotton-boll weevil. U.S. Dept. Agr. Circ. 162
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(12) Cook, F. C.
Pickering sprays. U.S. Dept. Agr., Bul. 866 (1920), 47 p.
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Latest developments in arsenical insecticides. Jn Better Fruit (1920), 15: 9.
(14) Cusuny, A. R.
A textbook of pharmacology and therapeutics, 6 ed., 708 p., 70 figs. Phila-
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(15) Fretps, W.S., and Exziort, J. A.
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Paris green spraying experiments. U.S. Dept. Agr., Bur. Chem. Bul. 82
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and Sirsa, C. M.
A method for preparing a commercial grade of calcium arsenate. U.S. Dept.
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Thsecpicide tests with Diabrotica vittata. In J. Econ. Entomol. (1918), 11:
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(18)

56 BULLETIN 1147, U. S. DEPARTMENT OF AGRICULTURE.

(20) Krrxtanp, A. H.
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Digestion in the larve of the gypsy moth. Jn 45th Ann. Rept. Mass. State
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(24)

(25)

Insecticide investigations. Oreg. Agr. Exp. Sta. Bul. 169 (1920), 55 pp.
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ARSENICALS. 57

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ORGANIZATION OF THE
UNITED STATES DEPARTMENT OF AGRICULTURE.

May 1, 1924.
Secretary of Agreculiure:. 2.02. 220924 SR Henry C. WALLACE.
AASSTSLOANG SCETCUUTY & 24 ee he ae Sawa ese Howarp M. Gore.
Director of, Scientifiz (Works sek = 2 woctettee «Len <- E. D. Bat.
Director of Regulatory’ Work .o. /20s25. Vo: WALTER G. CAMPBELL,
Director of Extension Work..............----- C. W. WARBURTON.
SLOT oP ee a aia AO I YN Ree Bae YE etn aoe R. W. WiitraMs.
WV COLR CRAB UP COAL No caste tape Phat ee OEE TEE © Cartes F. Marvin, Chief.
Bureau of Agricultural Economics.......--.-- Henry C. Taytor, Chief.
Bureau af Animal industry 2-220 22 = senna e ee JoHN R. Mouter, Chief.
Bureau Of Plant INGUSAYs Bee woe = es ci ee ee Wri1iam A. Taytor, Chief.
Morest, Sernices sien he eerie BS Seles ae W. B. GREELEY, Chief.
Boreau,of: Chenssiry.) 33 oil Bind es lamer C. A. Browne, Chief.
PUELOM OJ SOUS tee ee outers ole ee EERE ee Mitton Wuirney, Chief.
BUTCON Of PEMMOMOLOG Ys = wes oleta, woe eo sis see L. O. Howarp, Chief.
Bureau of Biological Survey....-.-.....---.-+-- EK. W. Netson, Chief.
Burcauojeb bite Roads. 320 ae See See Tuomas H. MacDonatp, Chief.
IBUreOD Of TOTLe CONGNINES: oe oe ne eee ee Louise STANLEY, Chief.
Office of Experiment Stations.........-...-.-. E. W. ALLEN, Chief.
Fixed Nitrogen Research Laboratory ......--..- F. G. Corrrety, Director.
PAU DEMCALIDNSY NBO ae Societe Migs at ee L. J. Haynes, in Charge.
ER OROTY See oe ee Se IN ees SOR ee rae CLARIBEL R. Barnett, Librarian.
Federal Horticultural Board... 22-000. J2- se << C. L. Maruatr, Chairman.
Insecticide and Fungicide Board ...........--- J. K. Haywoop, Chairman,
Packers and Stockyards Administration .......-- CHESTER MorriL1, Assistant to the
Grain Futures Administration............---- Secretary.

This bulletin is a contribution from

Bureau of Chemistry 2 to) 5 ae soe eee WALTER G. CAMPBELL, Acting Chief.
Miscellaneous Division..............-.-. J. K. Haywoop, in Charge.
Bureau. of Entomology Le eS Sa sea L. O. Howarp, Chief.
runt TRsect vestiggnion 2. oe ae eese ae S A. L. QUAINTANCE, Entomologist, in
Charge.
58

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