a

a

 

 

132
259

THS

 

 

| THESIS
UPN ISON INNIS

iD
Clarenee B. Smith.
1895

I i eee

 

 
WAT TAMU

, 31293 01404 9401 -

 

LIBRARY

Michigan State
University

 

 

 
wee OO ere
THESIS.

THE ARSENIC INSECTICIDES.

Prapared for the degree of Master of Science.
By

Clarence B: Smith.

SS ,

1SG 5
~ a esl
THE ARSENIC INSECTICIDES.
~---000----

The Michigan Legislature of- 1895, passed a law which is
of considerable importance to the farmers am fruit growers of
the state. In substance, it is as follows: The fruit grow-

' ers of each townshdp are compelled by law to spray their or-

 

 

 

chards with insecticides of known value when five fruit grow-
ers of the township so petition.

One result of the law is the lar.e increase in the demand
for the arsenic compounds as poisons. Paris Green (Aceto-ar-
semite of copper) and London Purple (Calcium arsenite) have in
the past supplied this demand. But, these preparations have
lately become the subjects of a monopolist’e concern, in conse-
quence of which, the price has been constantly rising. It was
to find sane material vhich has poisoning qualities equal to
that of Paris Green and which costs only a nominal sum for its
manufacture, that the work recorded in the following pages was
performed. Arsenic is taken as the basis for this work, be-
cause, at the present time, arsenic in its compounds, is the
cheapest and most effective of all known insecticides.

Arsenic in form of arsenious acid (As203) can be bought
in the drug stores at from ten to fifteen cents per pound; but
it is impossible to use the arsenic in this form as it not énly
kills all the insects, bWt also entirely destroys the foliage.
And this is true not only of the pure arsenic, but also of all
soluble compounds of arsenic. In fact, it has been conclusive-

| ly pgpoven by the experiment stations in both North Carolina

and Iowa that the amount of injury done to foliage by the use
of arsenite canpounds is exact ratio to the amount of soluble
arsenic found in them. 5o0,in experimenting with arsenical com-
pounds as insecticides, this fact has been kept constantly in
mind. It is also to be remembered in advocating any special
form of insecticides for general use, that the great majority
of those who use them have little knowledge of the chemical

properties of the substances they are using; hehce, the form-
ANDRAS,
 

 

 

 

 

 

 

-2-

ula must be a concise, exact, and never-failing one. In this
connection it may be well to state that as long as the price of
Paris Green remains at twenty cents per pound, it will be ad-
visable for most small fruit growers to use it; first, be-
cause it is always ready for use; second, because it is always
effective; then third, it is small in bulk amd , fourth, it has
been so long in use that every one is acquanted with its prop-
erties. But, when the price rises to thirty or forty cents a
pound, as it has during the past spring and summer, it will
pay in dollars ani cents for th e horticulturist bo use some-
thing cheaper.

White arsenic is a substance exceedingly difficult of sol-
ubility in water, yet in alkaline solutions it is readiy sol-
uble. {it easily forms salts with the metals; and the arsanic
salts with the exception of potasthum and sodium, are mostly

, insoluble in water. This is especially true of the arsenites
| of lead, calcium, and copper; and it is with these metals in
| combination with arsenic thats has made the foundation for my

work during the summer. The ideal worked for in each case was
an insecticide which should be cheap, easily prepared, harmless
to the foliage, and possessing good sticking qualities.

My first work was with the water-aoluble compounds, nitrate
and acetate of lead, as a basis. I didsolved white arsenic in
sodium carbonate and water forming the soluble arsenite of
lime (Na2C03 plus H20 equals 2Na0H plus C02. 4Na0H plus As203

| equals 2 Na2HAs03 plus H20) This added to either the nitrate or

the acetate of lead gives a very fine, white, flocculent preci-

i platate of the arsenite of lead leaving sodium nitrate or ace-

tate in the solution. (Na@HAs03 plus Pb(N03)2 equalsPbHAs03 pus
2NaCH3C02). The supernatant, fluid, however, when the ansenite
of soda is used, contains free arsenic. To get rid of this a
small quantity of lime must be added; and, indeed, it may be

said that with all arsenites, the addition of lime is requi-
| site to insure the complete precipitation in the insoluble form

of the free arsenité. When, however, the commercial arsenate of
-3-

soda is used with either the nitrate or acetate of lead, an in-
soluble precipitate of the arsenate of lead is formed, the sup-
enalent fluid of which is entirely free from uncombined arsenic
as is é@learly proven by Marsh's test for arsenic. But both

: these compounds of lezd are expensive, the nitrate costing 16

and the acetate 18 cents per pound. The commercial arsenate
now in the Jaboratory cost about 15 cents per pound and the
arsenate of soda, made by boiling sal soda and white arsenic,
cost about the same. This would make a total cost of something
like 25 or 30 cents a pound which is altogether too expensive
for practical purposes. Thss being true, a much cheaper sub-
stance than lead must be obtained; this is found in the sulphat
Bf copper (CuS04.5H20). When the arsenite of soda, made by
bpiling NaC08.10aq. and As203 together is added to a solution
of copper sulphate, a precipitate of the arsenite and hy.irate
of copper is formed.(The hydrate is formed because of the sligh
excess of Na2C08 taken to dissolve the arsenic) with reactions
as follows: Na2gHAsO3 plus CuS04 equals C,yHAsO3 plus NaaS04 and
NaOH plus CuS04 equals Na2gS04 plus Cu0H2. If now we add a lit-
tle lime to this, free arsenic in the supernatant fluid will be
found to be entirely absent, making the mixture acceptable as
an insecticide as the copper sulphate costs only four cents

a pound, hence making the total cost of an amount eqhivalent
to a pound of’ Paris Green, twenty cents,---a price very reason-
ale.

During the spring and summer, Dr. Kedzie and Professor
Taft have been working with the arsenite of soda mixed with
lime as a basis,---a much cheaper substance than either lead or
copper. Their methods of preparation differ slightly bt both
are dependent upon the same principle. Dr. Kedzie makes a sol-
ttion of the arsenite of soda by boiling the white arsenie wth
carbonate of soda for half an hour. This solution is then add-
ed as needed to a little lime and boiled in an iron kettle.
This forms the insoluble arsenite of lime. (NagHAs03 plus
Ca(0H)2 equals CaHAsO3 plus 2Na0H). As lime coats practically
 

he

nothing, this makes a very cheap insecticide. Professor Taft
however, boils the arsenic with the lime direct. The alkali-
nity of the lime dissolves the asenic and at the same time it
enters into combination with it forming the insoluble arsenite
of lime. (As02 plus 2Ca(0H)2 equals 2CaHAs03 plus H20). I per-
formed a number of experiments as to the time required for
boiling the arsenic and lime before the whole was converted
into the insoluble salt, and found that to be perfectly sure
the supernatant fluid is devoid of free arsenic requires at
least thirty minutes steady boiling. The disadvantage in this
method is at once apparent. Every time one wishes to use a
solution for spraying, no matter now small the quantity, he
must stop and boil the ingredients for a half an hour. I prefe
a modificathon of Dr. Kedzie’s method. Make a solution of the
arsenite of soda by boiling three par ts of soda anu one of
arsenic. Now I find by repeated experiments that fresh lime,
slaked with this arsenite of soda solution enters at once into
chemical combination with it and that when the lime is after-
waras diluted with water, the supernatent fluid does not give
the slightest deposition oi arsenic with Marsh's test. The
advantage of this method over that of boiling with the lime
direct, is considerable,,because a solution of the arsenite of
soda cay be made at one time sufficient to last during an en-
tire season and kept in jugs or othr vessels. It can then be
used from time to time as occasion demands by simply using the
solution to slake the lime with. The strength of the liquid
being known(Na2As03), about three pounds of fresh lime should
be taken for slaking a solution containing a pound of NagHAs03.
In skilled hands two pounds of lime is an abundance but three
pounds makes its use absolutely safe in the hands of amateurs.
Thé msame thing is true when the arsenate of soda is used. A
Solution used in slaking lime gives the insoluble compound of
the arsenate of ddd lime. Now the arsenate of soda is quoted
in the chemical journals at thirteen cents a pound. The greater
part of it, however, consists of the arsenate of lime and

| other impurities. But should there be a large demand made

 

for the pure arsenite of soda, some enterprising firm would
soon commence its manufacture. In that case we could take at
our convenience, our arsenite of soda, dissolve it ina little
Vide water and slake the lime with it, and thus do away with
the boiling which is certainly an inconvenience of no smal] im-

' portance.

As compared with the preeipitate obtained when the arsenite
of woda and sulphate #6 of copper are used, the arsenite of

' calcium is not as good for spraying purposes. First because

| in the coppere arsenite, CullAsO3, we have not only the poison
of the arsenic but also the poison of the copper, thus making
' the whole a more potent poison: second the hydrate of copper,
' Cu(0H)2, formed, is a good fungicide in itself while calcium is

devoid of such properties; and thatd, the bulk of the depositdd
material is much smiller and more floculent than is that of the

' araenite of lime; thus making it easier to spray and requiring
' less agitatton to keep it thoroughly mixed.

A working formula of the copper sulphate solution, derived
from the molecular weights of the substances and proved by

actual tests is as follows:

Carbonate of soda Na2C08 , 10H20 Sparts.
White arsenic As203 lpart
Sulphate of copper CuS04,5 H20 4 parts.
Lime CaO 2 parts.

Te copper sulphate solution is added to the soda arsenite
solution and then added to the lime. If the above formula is
taken in pounds, the whole, to be made equivalént to Paris
green should be reduced to 600 gallons which makes an actual
cost, estimated with the pride of carbonate of soda at 3 cants
copper sulphate at 4 cents, and white arsenic at le cents, per
pound respectively, at a little less than two cents per barrel.

The sqme formula without the copper sulphate makes & abo.
one and one-half pounds of the arsenite of calcium which cm.
be diluted to about 350 gallons; this makew a cost of a!
-6-

more than 1.5 cents per barrel, so there is not much difference
.& the relative costs of tn> two mixtures.

i" briefly summarizing, I would say: Lead salts are too

: expensive for present use. Copper sulphate with the arsenite

| of soda and with lime is the most general and eféctive in-

| secticide of those worked with.

C&lcium arsenite is the cheapest of all known valuable

! insecticides and can be b:st made by slaking lime with an
/an arsenite of soda so lution.
ROOM USE ON
IV. LIBRARIES

Wn

049401

T

“IIH
3129

TE

al

 
 
 
 
TU iil

A
|
3

MICHI
|

il

31

wilt

49401

 
 
IES

I

MICHIGAN STATE UNIV. LI
|

DALLA

i
|
3129301404940