90

QUANTITATIVE AGRICULTURAL ANALYf.

concentrated nitric acid (specific gravity 1.42) and 1150 cc of '
to stand at a temperature of 30 to 40° for several days, the
preserve in glass-stoppered bottles.

The phosphate sample should be finely ground and well m
about 2.5 gm, accurately to milligrams, and brush into £t
Add 30 cc of concentrated nitric acid and 5 cc of concentrate c:
acid and warm until solution is complete, or until only inso
matter remains. Cool, rinse into a 250-cc volumetric flask,
mark and mix well. Pour the solution into a dry filter. DIfc
10 to 25 cc of filtrate, and receive the remainder in a dry flask.

Pipette 25-cc portions of the clear solution into 250-ec
flasks. Add ammonium hydroxide until a slight precipitate *
of iron, aluminium or other earth metals persists. Clear with a
nitric acid, dilute to about 100 cc and heat to 60 to 65°. Imir:
in water which is at this temperature, a thermometer being; ;
flask. Add 75 cc of molybdate solution, mix and maintain at
ture noted above for 1 hour. Filter and wash well witlx,
ammonium nitrate solution. The precipitate that adheres
need not be removed but it must be well washed. Test the filtri
more molybdate and returning to the water bath. If mor"<
forms it must be added to the main body.

Place the flask 'n which precipitation was made under tin
drop over the paper enough concentrated ammonium hydroxicl
the precipitate, avoiding unnecessary excess. Wash this sohar
flask below with hot water and, if necessary, add more ammonita
to dissolve all of the precipitate in the flask. Wash the paper,
with hot water, then rinse the entire solution into a 200-cc befi
to room, temperature. Nearly neutralize with hydrochloric acic]
solution slightly basic. The formation of yellow precipitate
sequent resolution by ammonia is sufficient indication.

Cool if necessary and add, very slowly arid with vigorous »t
of magnesia mixture. After 15 minutes add concentrated
hydroxide as directed for analysis of soluble phosphates, page ;
ceed from this point as there directed. Calculate in the same w

Volumetric, by Titration of Ammonium Phosphomo

It has been shown that the precipitation of ammon
phomolybdate from acid solutions of phosphates j
means for separation from metals that would form,
phosphates in basic solutions. This precipitation also t
basis for an indirect determination of phosphorus. Tt:
already given for the double compound shows that it I*
as a compound of ammonium phosphate and mo
trioxide, the latter being the anhydride of molybdic a,<
therefore capable of neutralizing a base, as was shov

i t