INSECTICIDES AXD Fr.WIClDES

? longer and if iodine color carefully mid more

tion. Immediately add, as rapidly as can f* done wit I.
-~vescence? 15 gm of sodium bicarbonate, free from luia
3nce with standard Iodine solution, deferring the additu
il near the end point. Calculate the per cent of arsen

-rsenous oxide, In the Paris green.

he residue of cuprous oxide is treated on the with 5

1, specific gravity 1.2, the solution in it 250-i.-

^a-sh. the paper well with hot water and as direct«ni Sx the

adardization of sodium thiosulphate copper.

;inning with i4Boi! until red fumes have . . .'*

per cent of copper in the Paris green. The also be ..

cupric oxide? if desired.

distinction between Arsenates and Arsenites.-—it is frequently

sirable to distinguish qualitatively

senites in spray mixtures. Probably the

: an arsenate depends upon the of a of

ignesium ammonium arsenate a salt is

. to the basic solution:

2XH4CL

uU* ar J
i r % asi»
a , f the
arsen;?

3NH4OH -+ (NH4)3AsO4 -
3As04 + MgCla -» MgNHiAsO i
-Dissolve about 0.5 gm of sodium arseniteandsod'un
>-cc portions of water. Add 3 cc of nnxturt t*/ eot'ls t
ir. It will be noted that no precipitate will be pro«iui*od ir th« f rr
it a white crystalline one forms in the ad! to the Kdt
:ssel. Repeat, using the filtered spray solution instead of known
Its.
Silver nitrate is a reagent which is useful for the of
rsenites. In a neutral solution of an this a
reclpitate of silver arsenite while with an
rsenate is produced.
Water-soluble Arsenous Oxide. — It has
aat water-soluble arsenic (of free arsenous or
ie) is very injurious to young foliage. The Federal insecticide
ct of 1910 specifies a maximum of 3.5 per cent of
rsenous oxide in Paris green and not more 0.75 per in
3ad arsenate paste.
It is very important that the directions as to be
observed closely because the amount of soluble varies
.onsiderably with small deviations in temperature.