A

UNI

United States Department of Agriculture,

BUREAU OF CHEMISTRY— Circular No. 10 (Revised).
H. W. WILEY, Chiei ot Bureau.

METHODS OF ANALYSIS OF INSECTICIDES AND FIX.K I DES.

GENKHAL

Samples of paris green, london purple, soft soap, copper carbonate and tobacco

•xtracts are to be thoroughly mixed before analysis, taking care that tin- first

\\.. -amples an- not further pulveri/ed. Samples of lye and potassium cyanid

are to be weighed in large quantities in weighing bottles and aliquot portions

rom a \\ater solution taken for analysis.

PAH is CK'KKN.

Pi;n\ |SK>NAL).l

Pry 1 to •_• • 10 liours at lo:> to IK) (', and calculate the loss as

iK>i -hire.

TOT.M ARSEHIODG <>\n>. Mi:moD I (OFFICIAL).

SOLUTIONS REQUIKl l>.

A Starch -olution is used \\hieh is prepared by boiling L' grams of starch with
200 cc of distilled water for about "> minutes.

A .-tandard iodin solution is prepared in the following manner: Dissolve PJ.7

;rams of p(. \\dered iodin in about !'•")( ) cc of water to which has been added is

•ams of C. P. potassium iodid, and make up the whole to a volume of 2

-landardi/e this solution, weigh out 1 gram of C. P. dry arsenioiis

>xid, tran-fer to a '_'~»o-cc lla.sk by means of about lOOccof a solution containing

mis of sodium hydroxid in each 100 cc, and boil until all arsenious oxid

into solution. Make up to a volume of 250 cc and use^oO cc for analysis.

Thi- ~'«i «•<• portion is concentrated, by boiling in a 250-cc flask to half its volume,

and allowed to cool to about 80° C. An equal volume of concentrated hydro-

id is now added, accompanied by .". grams of potassium iodid, mixed,

and the \\ hole allowed to stand for 10 minutes (to reduce the arsenic oxid formed

by boiling and the alkaline arsenite to arsenious oxid). The brown solution is

then diluted \\jth cold water and an approximately tenth-normal solution of

MM thiosnlphate added drop by drop, until the solution becomes exactly

colorless. iThisend point is easy to read \\ithout the aid of starch.) This solu-

tion is made slightly alkaline with dry sodium carbonate ( using a drop of methyl

BJC to read the change) and then is made slightly acid with hydiochlorie

ne that all lumps of sodium carbonate on the bottom are acted on

by the hydrochloric acid. Sodium bicarbonate is now added in excess and the

'on of iodin run in drop by drop, using starch water to read the end reaction.

.-times the solution gets dark toward the end of the titration. This change

must not be confused with the final dark blue "color given by the iodin and

' i. i

1 TV -ional" and "official" refer to adoption of methods by the Association of

•utural Clu-raists.

Frorn the number of cubic centimeters of iodin solution used and the weight
of arsenious oxid taken, the value of each cubic centimeter of iodin in terms of
arsenious oxid can be determined.

METHOD.

Two grams of paris green are weighed out ancj transferred to a 250-cc flask
and about 100 cc of water and 2 grams of sodium hydroxid added. This mixture
is boiled for 5 to 10 minutes, or until all the green particles have changed to
red cuprous oxid. It is then cooled to room temperature and the volume made
up to 250 cc. The well-shaken liquid is filtered through a dry filter and 50-cc
portions taken for analysis. The analysis is carried out from this point for-
ward the same as when standardizing the iodin solution.

TOTAL ARSENIOUS OXID, METHOD .II (PROVISIONAL).1

SOLUTIONS REQUIRED.

A standard, approximately twentieth-normal, solution of iodin is made as
follows: Dissolve 12.7 grams of powdered iodin in 250 cc of water to which has
been added 25 grams of potassium iodid, and make up to 2,000 cc. To stand-
ardize this solution weigh out 1 gram of dry C. P. arsenious oxid, transfer to
a 250-cc flask, and dissolve by boiling about 20 minutes with 5 grams of
sodium bicarbonate and about 100 cc of water; cool; add hydrochloric acid till
acid, and sodium bicarbonate again until alkaline; make to the mark and take
aliquots of 50 cc for standardizing.

A solution of sodium acetate containing 12.5 grams of the crystallized salt in
each 25 cc.

A solution containing 2 to 3 grams of sodium potassium tartrate dissolved in
each 50 cc.

A starch solution.

METHOD.

A gram of paris green is weighed out and transferred to a 100-cc flask, where
it is boiled for 5 minutes with 25 cc of a solution of sodium acetate containing
12.5 grams of the crystallized salt. It is then made to the mark, shaken, and
passed through a dry asbestos gooch filter. An aliquot portion of this filtrate
is used to determine the soluble arsenious oxid. The residue on the filter is
transferred to a brakcr, and, after being beaten up with a little water, dissolved
in hydrochloric acid by adding the concentrated acid a drop at a time. The
whole is now transferred to the 100-cc flask and aliquot portions of 20 to 40 cc
each taken for analysis. To each of these aliquots is added concentrated sodium
carbonate solution a drop at a time until a slight permanent precipitate is
formed. This precipitate is dissolved by adding 50 cc of a 4 to 6 per cent
solution of sodium potassium tartrate. The sample is now diluted to about 200
cc, solid sodium bicarbonate and starch water added, and the solution titrated
with standard iodin.

TOTAL ARSENIOUS OXID, METHOD III (PROVISIONAL).2

SOLUTIONS REQUIRED.

The same solutions as were required for Method II.

METHOD.

Boil 0.4 gram of the finely ground green with 25 cc of sodium acetate (con-
taining 12.5 grams of the crystallized salt) for 5 to 10 minutes. Add concentrated

!Has been once recommended by a referee as "optional official." This method can also be
used to determine soluble arsenious oxid.
2 Has been recommended once by a referee as an "optional official" method.

hydrochloric acid a drop at a time until solution of the green is effected (about
10 cc of the acid will be necessary). Add concentrated sodium carbonate solu-
tion a drop at a time until a slight precipitate appears, then add 50 cc of a J to
t; per cent sodium potassium tartrate solution, and finally sodium bicarbonate
in excess. Titrate with standard iodin solution in the usual manner.

SonirM-ArKTATK-soi.rm.i-: AKSKNIOTS o.xin (PROVISIONAL).

Snl.lTlONS KKOJ'IKKD.

A solution of sodium acetate containing IL'.-"> grams of the crystallized salt in
each 25 cc ; a solution of starch; and a twentieth-normal solution of iodin pre-
pared as indicated above.

METHOD,

Digest 1 gram of paris green over the flame for about "• minutes, with 25 cc of
the .-odium acetate solution described above, cool the solution, make up to 100
CC, lilter off 50 cc through a dry filter, and titrate with twentieth-normal iodin
solution.

WATER-SOLUBLE ARSENIOUS OXID (PROVISIONAL).

SOLUTIONS REQUIRED.

A -larch solution and a twentieth-normal iodin solution, prepared as described
ibove,

MKTHOD.

One gram of paris green is treated with 1,000 cc of water (previously boiled
to e\pel carl)on dioxid, and again cooled to room temperature) in a large flask.
The Mask is stoppered and shaken eight times each day for 10 days. At tin-
end of this time the solution is filtered off through a dry lilter. Two hundred
cubic centimeters of this filtrate are treated with sodium bicarbonate and titrated
with t \\eiitieth-normal iodin solution.

TOTAL COITKK <>xn>, MKTHOD I (OFFICIAL).
METHOD.

The cuprous o\id obtained in Method I for total arsenious oxid, by boiling
th»- paris green with sodium hydroxid, is poured on the filter and well washed
\\ith hot \\ ater. after an aliquot portion of the filtrate has been taken for the
determination of arsenious oxid. It is then dissolved in hot dilute nitric acid
and made up to a volume of 250 cc. Fifty to 100 cc of this solution is used for
the electrolytic determination of copper, as described on page 7, paragraph 2-b
of Bulletin It. i revised), Bureau of Chemistry, U. S. Department of Agriculture.

TOTAL COPPER OXID, METHOD II (PROVISIONAL). >

SOLUTIONS REQUIRED.

A standard twentieth-normal solution of sodium thiosulphate is prepared by
•Sving 21. s giams of the cr\ st alli/ed salt in 2 liters of water. This solution
is -laiidardi/ed again.-t ('. P. copper foil dissolved in nitric acid by the method
of analysis given in the following paragraph.

METHOD.

An aliquot portion of the nitric acid solution of copper oxid, used in Method I

for total copper oxid, i- made alkaline with sodium carbonate, then made

•/// acid \\ith acetic acid, diluted with water, and a considerable quantity

1 Has been r«-ruimiieini«-.i i.y :i n-feree as an "optional orticial method.

of solid potassium iodid added, about 2 or 3 grams. When it is all dissolved by
shaking, the free iodin is titrated with the twentieth-normal thiosulphate, using
starch as indicator.

TOTAL COPPER OXID, METHOD III (PROVISIONAL).

SOLUTIONS REQUIRED.

A fifth-normal solution of potassium cyanid is prepared, which is standardized
against a known weight of copper dissolved in nitric acid, the method being the
same as that described in the following paragraph.

METHOD.

An aliquot portion of the nitric acid solution used in Method I for total copper
oxid is neutralized with sodium carbonate and a trifling excess of the carbonate
added. One cubic centimeter of 0.960 sp. gr. ammonia is added and the dark
blue solution titrated to the disappearance of the blue color with standard potas-
sium cyanid.

LONDON PURPLE.

MOISTURE (PROVISIONAL).

Dry from 1 to 2 grams of substance for 10 to 12 hours at a temperature of 105°
to 110° C.

TOTAL ARSENIOUS OXID (PROVISIONAL).

SOLUTIONS REQUIRED.

A starch solution and a twentieth-normal iodin solution, prepared by either of
the methods given under " paris green."

METHOD.

Two grams of london purple are dissolved in about 80 cc of water and 20 cc
of hydrochloric acid at a temperature of 60° to 70° C, filtered, and washed to a
volume of 300 cc. One hundred cubic centimeters of this solution are treated
with sodium bicarbonate in excess and made up to the mark in a 500-cc flask,
using a few drops of ether to destroy bubbles. Two hundred and fifty cubic
centimeters are then filtered off through a dry filter, starch water added, and the
solution titrated with standard iodin to the appearance of a blue color. The
result is the arsenious oxid, as such, in 50 cc of the original solution or 0.3333
gram of the original london purple.

TOTAL ARSENIC OXID, METHOD I (PROVISIONAL).

SOLUTIONS REQUIRED.

The same solutions as those described above for total arsenious oxid are used.

METHOD.

Fifty cubic centimeters of the hydrochloric acid solution of london purple,
prepared by the preceding method, is heated to 80° C on the water bath and
then taken off and 50 cc of concentrated hydrochloric acid and 3 grams of potas-
sium iodid added. The mixture is allowed to stand for at least 15 minutes, the
" ic " arsenic thus being reduced to " ous" arsenic and the iodin set free. The
solution is then rinsed out into a large beaker, well diluted, and tenth-normal
sodium thiosulphate added drop by drop, to eliminate the free iodin. The end
point here is rather difficult to read on account of the very dark color of the
solution, but with a little practice the chemist can determine it by proceeding as
follows :

The sodium thiosulphate is run in a little at a time, and occasionally a drop of
tin- solution is withdrawn and added to a drop of starch paste. This will, of
course, give a blue color with the starch, which becomes fainter as the iodin is
used up. Finally, when a drop of the solution gives only the slightest blue color
with the starch, a little starch paste is added directly to the whole solution and
the blue color dissipated with a few drops of thiosulphate. With a little prac-
tice the chemist can in this way get the exact end point. The solution is
immediately made alkaline with solid sodium carbonate. It is again made
slightly acid with hydrochloric acid, taking care that all of the solid particles of
the sodium carbonate <m the bottom are neiitrali/ed by the acid, and finally made
alkaline with sodium bicarbonate. Starcli paste is now added ami t \\entieth-
normal iodin until the blue color appears. This end point is easily read if the
beaker is placed on a white surface between the eye and the light and the iodin
solution run in until a distinct purple color appears. The figure thus obtained
gives the number of cubic centimeters of iodin corresponding to the total amount
of arsenic in the solution as arsenious oxid. Subtracting from this the number
of cubic centimeters of iodin corresponding to the arsenious oxid in the previous

?thod gives the number of cubic centimeters of iodin corresponding to the
ai -'-nic oxid in ' am of the sample.

TOTAL ARSKMC OXID, MKTIIOD II (PROVISIONAL).
1 >r>i^ned to eliminate part of coloring matter.)

SOLUTIONS REQUIRED.

The same as in preceding method.

METHOD.

One hundred cubic centimeters of the hydrochloric acid solution of london
purple prepared under the determination of total arsenious oxid is placed in a
heaki-r and made alkaline with a saturated solution of sodium carbonate. It is
then transferred to a 200 cc flask, filled to the mark, and 100 cc filtered off
thnniL'h a dry filter for analysis. This is evaporated to about 50 cc on a hot
plate, allowed to cool to about 80° C and 50 cc concentrated hydrochloric acid
added, followed by 3 grams of potassium iodid. The mixture is allowed to stand
for 1 "i minutes, the " ic " arsenic being reduced to "ous" arsenic, and the
iodin set free. The solution is then rinsed out into a large beaker and the
iodin exactly used up with tenth-normal sodium thiosulphate. To get the
exact end point it may sometimes be necessary to proceed as in the previous
method, but usually there is no trouble. The solution is immediately made
alkaline with >olid sodium carbonate, again made slightly acid with hydrochloric
acid, taking care that all solid particles of sodium carbonate are acted on, and
finally made alkaline with sodium bicarbonate. Starch paste is now added and
the solution titrated to a blue color. The calculation is the same as that
bed under Method I for total arsenious oxid.

SOLUBLE ARSENIOUS OXID (PROVISIONAL).

SOLUTIONS REQUIRED.

The same as those used in the preceding method.

HOD.

:tract 1 gram of london purple in a stoppered fl as fc with ~>(K)cc of cold carbon-
dioxid-free water for 7 days, shaking eight times each day. Filter off 100 cc of
the solution through a dry filter, add sodium bicarbonate, and titrate with
standard iodin, using starch as indicator.

6

SOLUBLE ARSENIC OXID (PROVISIONAL).

SOLUTIONS REQUIRED.
The same solutions as those used in the preceding method.

METHOD.

To determine the soluble arsenic oxid, an aliquot portion of the water extract !
from the determination of soluble arsenious oxid above (about 200 cc) is 1
transferred to a flask, made slightly alkaline with sodium hydroxid, and
evaporated to about 25 cc on a hot plate. The flask is then removed and ;
allowed to cool to about 80° C and an equal volume of concentrated hydro- j
chloric acid and 3 grams of potassium iodid added. It is allowed to stand 15 }
minutes, the iodin set free is exactly used up with tenth-normal thiosulphate
(using starch if necessary), and the solution neutralized with sodium carbonate.
It is again made slightly acid with hydrochloric acid, taking care that all lumps
of sodium carbonate are acted on, then made alkaline with an excess of sodium
bicarbonate, and titrated with iodin, using starch as indicator. From this
figure is subtracted the figure representing the amount of soluble arsenious
oxid, and the remainder is calculated as arsenic oxid.

•
COPPER CARBONATE.

COPPER OXID.
SOLUTIONS REQUIRED.

The same solutions as those described under the determination of total copper
in paris green are used.

METHODS.

A weighed quantity of the substance is dissolved in nitric acid and the same
method of analysis employed as given under the determination of total copper
in paris green, Method I being official and Methods II and III provisional.

POTASSIUM CYANID.
CYANOGEN (OFFICIAL).

SOLUTION REQUIRED. -

A twentieth-normal solution of silver nitrate.

METHOD.

A large quantity of the sample is weighed out in a weighing bottle, dissolved
in water, and made up to a definite volume. Aliquot portions of this are taken
for analysis. The twentieth-normal silver nitrate solution is added a drop at a
time with constant stirring, until one drop produces a permanent turbidity. In
calculating the results, one equivalent of silver is equal to two equivalents of
cyanogen, according to the following equation:

2 KCN + AgNO:! = KCN.AgCN + KN03.
CYANOGEN AND CHLORIN.

SOLUTIONS REQUIRED.
Same as preceding method.

METHOD.

The cyanogen is determined as in the preceding method. After this is done a
few cubic centimeters of a dilute potassium chromate solution are added and the

titration with twentieth-normal silver nitrate continued to the appearance of the
red-brown color of silver chromate. The first titration with silver nitrate repre-
sents the cyanogen present according to the equation above. The second t it rat i< >n ,
using potassium chromate as indicator, represents the cyanogen according to the

following

KCN.AgCN + AgN():t = KNO3 + 2 AgCN,

plus the chlorin present ; therefore the second minus the first ivading represents
the ehlorin present in terms of silver nitrate.

BOAP.
BBAL STATEMENT,

In mo.-t -oap> u-ed by the entomologist (not considering the resin soaps) it is
necessary to know three constituents in older to judge of the value of the soap
I'or -praying purpo-es, vi/, moisture, total fatty matter, and total soda or pot a.- h.
The moisture an. I alkali an- usually determined and the total fatty matter a p-
proximately estimated hy difference.

Moi.-i i i;i. l'i;u\ I.-IONAL).

The following method is given hy Benedikt and I.ewkowitsch for determining
water in -"ap. Tare accurately a heaker of HIM cc capacity, the bottom of which
.\ered with recently ignite(l, perfectly dry sand about one-half inch deep,
together \\ith a small glass rod.

Weigh off in a beaker about •"> grams of the sample; add 25 cc of alcohol or
more if necessary and dissolve the soap" in the alcohol by constant stirring on the
water bath. Kvaporate the alcohol and finally dry in an oven at 110° C until
the weight is constant. A few precautions should be taken which are not men-
tioned in the above method, vix : If the soap is hard the ."> grams should be cut
off in very thin strips so that it will dissolve more readily in the alcohol ; also no
sample- i.i -nap examined by the writer have ever come to a constant weight on
drying, but finally begin either to gain or to lo>e a little indefinitely. It is, there-
fore, he.-t to heat the soup at HOC until it is nearly dry and weigh, then return
the soap to the oven and dry another half hour, ('ontimie this alternate drying
and weighing until the weight changes only a few milligrams during the course
of a half hour'.-. dr\ ing.

TOTAL ALKALI • l'i;«>\ I-IOXAL).

A \\ei«_rhed (plant ity of the soap is decomposed by hydrochloric acid and the
water is filtered off I'M i m the fat, which is \\ashed. Hot h potassium and sodium
in the filtrate are first determined as mixed chlorids in the ordinary manner and
the potassium is then determined by means of platinum chlorid.

A rapid but only approximate determination of the alkali in soap IK made in
the following manner: Weigh out a small quantity of the soap, treat with con-
centrated sulphuric acid, burn, repeat treatment with sulphuric acid, and burn
again. Add a -mall amount of ammonium carbonate to the disk, cover and
heat. Repeat this a number of times till all bisulphates have changed to sul-
phate-. Te-i the re-idue qualitatively to determine whether it is sodium or
pota--Jim -ulphate, and calculate the residue to soda or potash as the case
may be.

If the determination of other constituents of the soap be desired the methods
given on page H2 of Bulletin 68, Bureau of Chemistry, U. 8. Department of
ilture. have been found fairly satisfactory.

SODA LYE.
CARBONATE AND HYDROXID, METHOD I (PROVISIONAL).

SOLUTIONS REQUIRED.

A half-normal solution of hydrochloric acid; methyl orange and phenol-
phthalein indicators.

METHOD.

A large quantity of the sample is weighed out in a weighing bottle, dissolved
in water— previously boiled to get rid of carbon dioxid— and made up to a
definite volume. Aliquot portions of this are taken for analysis. One portion
is titrated with half-normal acid, using methyl orange as indicator, and the total
alkalinity thus found noted. Another aliquot portion of the same size is trans-
ferred to a measuring flask, and enough barium chlorid added to precipitate
out all carbonate, avoiding any unnecessary excess. The volume is made up to
the mark with carbon-dioxid-free water, stoppered, shaken, and set aside to
allow the precipitate to settle. When the liquid becomes clear one-third of it
is drawn off by means of a pipette and titrated with half-normal hydrochloric
acid, using phenolphthalein as indicator. This number of cubic centimeters of
half-normal acid multiplied by 3 gives the number of cubic centimeters of half-
normal acid corresponding to the original amount taken. The last figure
obtained represents sodium hydroxid, and the difference between the first and
last figures represents the sodium carbonate.

CARBONATE AND HYDROXID, METHOD II (PROVISIONAL).

SOLUTIONS REQUIRED.

A fifth-normal solution of potassium acid sulphate ; methyl orange and phenol-
phthalein indicators.

METHOD.

The lye is weighed out and dissolved to a definite volume in carbon-dioxid-
free water just as described in Method I. An aliquot portion is taken, diluted
with carbon-dioxid-free water and a few drops of phenolphthalein added. A
fifth-normal solution of potassium acid sulphate is added at the rate of about 1
drop per second, with constant stirring, until the pink color fades out and the
solution becomes colorless. The reading thus obtained, which we will call n,
represents the sodium hydroxid and one-half of the sodium carbonate present
since the sodium carbonate is changed to sodium bicarbonate. Methyl orange
is added and the titration continued to the appearance of a pink color. Let
this number of cubic centimeters be represented as m. Since this last
titration represents the sodium bicarbonate present, or one-half the sodium
carbonate, 2m represents all the sodium carbonate present and n — m the sodium
hydroxid.

TOBACCO AND TOBACCO EXTRACTS.
NICOTIN, METHOD I (OFFICIAL).

SOLUTIONS REQUIRED.

An alcoholic soda solution containing 6 grams of sodium hydroxid, 40 cc of
water, and 60 cc of 90 per cent alcohol. A weak sodium hydroxid solution con-
taining 4 grams of sodium hydroxid in l,000cc of water. A standard sulphuric
acid solution.

METHOD.

About ."> t<» i; grams of tobacco extract or 20 grams of finely powdered tobacco,
[which has been previously dried at 60° C so as to allow it to be powdered, is
weighed out into a small beaker. Ten culm- centimeters of the alcoholic- soda
[solution is added, followed, in the case of the tobacco extract , with enough C. P.
powdered calcium carbonate to form a moist but not lumpy mass. The whole
[is well mixed. Tins is transferred to a Soxhlet extractor and exhausted for
about 5 hours with ether. The ether is evaporated off at a lo\\ temperature by
being held over the steam bath, and the residue is taken up with ">() ec of the
weak soda solution mentioned above under "solutions required." This is trans-
fen !••! by means of water to a Kjeldahl flask, capable of holding about .">(M
and distilled in a current of steam, using a condenser through which water is
Mowing rapidly. A three-bend outflow tube i- used, and a feu pieces of pumice
and a .-mall piece of pa ratlin are added to prevent bumping and frothing. The
distillation is continued till all the nicotin has passed over, the distillate usually
varying from KM) to ~.<M) cc. When the distillation is complete only about 15 cc
of the liquid should remain in the distillation Mask. The distillate is titrated
with standard sulphuric acid, using pheiiacetolin or cochineal'a> indicator. ( >ne
molecule of sulphuric acid is equivalent to two molecules of nicotin.

NICOTIN, METHOD II • I'KMVISIONAL).

SOLUTIONS RKljriKKP.

A weak sodium hydroxid solution containing -1 grams to the liter :tnd a standard
fth-normal hydrochloric acid solution.

METHOD.

A solution of ('. P. nicotin of approximately 1 per cent strength is first pro-
pared and an aliquot portion carefully tit rated against fifth-normal hydrochloric
acid, using methyl orange as indicator, so as to definitely establish the exact
percentage <>f nicotin in solution. A separate portion of the same solution is
then placed in a -Ill-cm tube and its rotation in terms of the sugar scale deter-
mined, lly dividing the percentage of nicotin present by the reading on the
-II.MI -cale the value of one degree of the >cale in terms of per cent of nicotin
is established and the figure so obtained can be used as a factor in all determi-
nation- of nicotin made, provided the same polariscope is used.

A \\eighed amount of the sample, about .'! to "> grams, is now rendered alka-
line with •'•<> cc of the weak -oda solution, mentioned under " solutions required,"
and transferred to a round-bottomed flask of about ::m to r»(K) cc capacity with
l.'iOec of distilled water. The whole is nou subjected to distillation in a current
of steam and the distillate made to a volume of fiw cc. A portion of the dis-
tillate is then placed in a Id-cm tube and a polariscope leading taken. Know-
ing the value of each degree of tin- -ii-ar -cale in terms of per cent of nicotin in
the solution, the per cent of nicotin in the sample can be calculated.

FOK.MAUX.

I OBM u.i'i.HYi'i:. Mi riion I.
BOL1 PIOHfl REQ1 U

A normal solution of sulphuric acid, a normal solution of sodium hydi..
and a solution of purified litmu-.

10

METHOD.

Measure out 50 cc of normal sodium hydroxid in a small Erlenmevcr flask (of
500 cc capacity, for example) and add 50 cc of hydrogen dioxid. Now add 3 ccl
of the formaldehyde solution under examination (the specific gravity of which |
has been previously determined), allowing the point of the pipette to almost
reach the liquid in the flask. Place a funnel in the neck of the flask and put on
the steam bath for 5 minutes, shaking occasionally during this time. Remove
from the steam bath, wash the funnel with distilled water, cool the flask down
to about room temperature, and titrate the excess of sodium hydroxid with
normal acid, using litmus as indicator. This cooling of the flask before titration
with acid was found necessary in order to get a sharp end reading with the
litmus. From the volume of formaldehyde used and the specific gravity the per
cent of formaldehyde can be determined.

FORMALDEHYDE, METHOD II (PROVISIONAL).

SOLUTIONS REQUIRED.

A tenth-normal solution of silver nitrate, a tenth-normal solution of ammonium
sulpho-cyanate, a dilute solution of potassium cyanid containing 3.1 grams to 500
cc of water, and a 50 per cent solution of nitric acid.

METHOD.

Fifteen cubic centimeters of tenth-normal silver nitrate are treated with 6 drops
of 50 per cent nitric acid in a 50-cc flask ; 10 cc of a solution of potassium cyanid
(containing 3.1 grams of potassium cyanid in 500 cc of water) are then added
and well shaken. The solution is then made to the mark and an aliquot portion
of the filtrate (say 25 cc) is titrated according to the method of Volhard with a
tenth-normal solution of ammonium sulpho-cyanate for the excess of silver.
Another 15-cc portion of tenth-normal silver nitrate is acidified with (> drops of
50 per cent nitric acid and treated with 10 cc of the potassium cyanid solution
.to which has been added a weighed quantity of the dilute formaldehyde solution.
The whole is made up to 50 cc and a 25-cc filtrate from it is titrated with tenth-
normal ammonium sulpho-cyanate for the excess of silver as before. The differ-
ence between these results multiplied by 2 gives the amount of potassium cyanid
that has been used by the formaldehyde in terms of tenth-normal ammonium
sulpho-cyanate. Each cubic centimeter of this is equivalent to 3 milligrams of
formaldehyde.

LIME-SULPHUR DIPS AND LIME-SULPHUR-SALT MIXTURE (PROVISIONAL).

TOTAL SULPHUR.
SOLUTIONS REQUIRED.

A saturated potassium hydroxid solution or a solution of caustic soda con-
taining 100 grams to 100 cc of water. A 10 per cent barium chlorid solution.
An approximately 3 per cent solution of hydrogen peroxid free from sulphates ;
if it contains sulphates add freshly precipitated barium carbonate and shake
occasionally for several hours, then filter and use the clear solution.

METHOD.

Measure off 10 cc of the clear sample in a 100-cc measuring flask and fill to
the mark. Use aliquot portions of 10 cc of this for analysis. Treat this aliquot

1 Has been recommended once as an official method.

11

with 3 cc of the caustic potash or soda solution, following this by 50 cc of
hydrogen peroxid free of sulphates. Heat on the steam bath for just one-half
hour and then acidify with hydrochloric acid, precipitate with barium chlorid
In the ordinary manner in boiling solution, and finally weigh as barium
sulphate.

BIBLIOGRAPHY.

I ..Mowing is a list of the publications which explain the advantages of the
above methods for examining the several classes of insecticides and fungicides

mentioned :

Tin- Adulteration and Analysis of the Arsenical Insecticides. J. Am. Chem.

1900, 22, [9], •

The Analysis of Arsenical Insecticides. J. Am. Chem. Soc., 1900, 22, [10],
TO").

The Composition and Analysis of London Purple. J. Am. Chem. Soc., 1900,
2i>, [I'-' I- 8

:<on dt' kefeiee on I nsrrt icioles and Fungicides. Proceedings of the Asso-
•iatiou of < Mlicial Agricultural Chemists for 1900, p. 139.

Soluble Arsniiou* o.xid in Paris < liven. .1. Am. Chem. Soc., 1901, 23, [2],
111.

\ 1,'apiil Method for HM- Determination of Arsenious Oxid in Paris (ireen.
I. Am. Chem. Soc., HMH, :>.>, [7], 185.

eport of the Keferee on Insecticides and Fungicides. Proceedings of the

iatii'ii of <Mlicial Agricultural Chemists for 1901, p. 87.

The Chemical Composition of Insecticides and Fungicides. U. S. Dept. Agr.,
Bureau of Chemistry, I5ul. «>S.
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:;iion of < Mlicial Agricultural Chemists for liMrJ, p. 158.

A Modification ()| tm> A very-P.eans Method for Determining Total Arsenious
Kid in Paris Green. .!. Am. Chem. Soc., 1903, 25, [9], 963.
A Comparative Study of Methods of Determining Formaldehyde. .1. Am.
hem. So,-., I'M):;. i'.5, [10], lO'JX.
I;. -port of the Ilefeive on Insecticides and Fungicides. Proceedings of the

ition of (Mlicial Agricultural Chemists for 1903, p. 15»">.

l;.-pi'i-i of the Uefeive on Insecticides and Kungicides. Proceedings of the
iatioii of < Mlicial Agricultural Chemists for I'.'OI, ]>. !».'>.
niation of Nicotin in Presence of Pyridine. J. Am. Chem. Soc., 1904, 26,
\ i::.

Tin- Metermiiiatioii of I.ime and Sulphur in Solutions of Sulphides and Poly-
lphi.k- u-e-1 as liiserticiil«-<. Proceedings of the Association of OHicial Agri-
ltural C|,,.|i.i>ts for I'.xil. p. KM.

!landel>analyse \on l-'nnualdi-liyd. /ts. anal. Chem., I'.tn:,, //, [1], ];{.
\ <iinl\ of the llydrti^en lVn»xid Method of Determining FormaMehyde.
Am. Ch( in. Soc., September, 1905.

J. K. II \Y\VUOD,
c/n>f. Miscellaneous Laboratory.

\pplo\r.l ;

.IAMKS WILSON,

Sect-' i 'in i.

W.\-]IIN«;TOX, D. ('.. I ttgust 21, 1905.

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