INSECTICIDES AND FUNGICIDES	309
Determination of Copper.—Prepare solutions as directed for the determi-
nation of copper in cuprous oxide, page 162 (feeds). Weigh about 2 gm of
the sample, dissolve in about 50 cc of 10-per cent nitric acid and add ammo-
nium hydroxide solution in slight excess. Then without removing the
precipitate which has formed, add acetic acid to clear and 5 to 10 cc in
excess. Cool, add 10 cc of 30-per cent potassium iodide solution and titrate
with thiosulphate as directed on page 162. Calculate the per cent of
copper present in the sample (dried, partly dried or paste) and in the
sample as received.
SOAP SPRAYS AND EMULSIONS
Soaps are used to a considerable extent for making oil emul-
sions and they are often added to other sprays to cause the latter
to spread uniformly and to adhere more closely to the foliage.
The soap-kerosene emulsions are used somewhat for the soft-
bodied sucking insects, such as aphides, but they are being
replaced, by solutions of nicotine sulphate. Soap-oil emulsions
are used for scale insects.
Determination of Moisture in Soap.—Weigh rapidly about 5 gm of the
carefully selected sample into a weighed 50-cc beaker in which has been
placed a one-half inch layer of recently ignited dry sand and a small glass
rod. If the soap is hard, cut it up into very thin strips. Add 25 cc of
alcohol (more if necessary) and dissolve the soap by warming on a steam
bath, stirring constantly. Evaporate the alcohol, heat in an oven at 110°,
stirring occasionally, until the soap is nearly dry, then weigh; dry again for
30 minutes and weigh. Continue this process until the weight changes only
a few milligrams during 30 minutes of drying.
CHLORPICRIN
Chlorpicrin is trichlornitromethane, CC1_3N02. It is rated
as 283 times as toxic as carbon disulphide, compared on a basis
of molecular weights. It is not as inflammable as is carbon
disulphide, and its vapor is about twice as heavy, which feature
makes it quite desirable for grain fumigation. Chlorpicrin
vapor is so very poisonous^1 and active that not more than one-
half pound is needed for the fumigation of 1000 cu. ft. of space.
Ten times this amount of carbon disulphide would be required.
Much work is being done upon the adaptation of other poison
gases to insecticidal and fungicidal uses. No doubt this field
will be developed very rapidly during the next few years and the
agricultural analyst will have many new problems presented
for his solution, as a result.
iJ.Econ. Ent., 11,4 (1918).