. Transfer the precipitate and filter to the beaker, or
precipitating vessel, dissolve the precipitate in a small excess of the
standard alkali, add a few drops of phenolphthalein solution, and
titrate with the standard acid.

12. _Insoluble Phosphoric Acid in the Ash--Official_

Determine phosphoric acid (P_2_O_5) in the Insoluble ash by the
foregoing method.

13. _Chlorides--Official_

Moisten 5 grams of the substance in a platinum dish with 20 cc. of a
5-percent solution of sodium carbonate, evaporate to dryness and ignite
as thoroughly as possible at a temperature not exceeding dull redness.
Extract with hot water, filter and wash. Return the residue to the
platinum dish and ignite to an ash; dissolve in nitric acid, and add
this solution to the water extract. Add a known volume of N/10 silver
nitrate in slight excess to the combined solutions. Stir well, filter
and wash the silver chloride precipitate thoroughly. To the filtrate and
washings add 5 cc. of a saturated solution of ferric alum and a few cc.
of nitric acid. Titrate the excess silver with N/10 ammonium or
potassium thiocyanate until a permanent light brown color appears.
Calculate the amount of chlorin.

14. _Caffein--The Fendler and Stueber Method--Tentative_

Pulverize the coffee to pass without residue through a sieve having
circular openings 1 mm. in diameter. Treat a 10-gram sample with 10
grams of 10-percent ammonium hydroxid and 200 grams of chloroform in a
glass-stoppered bottle and shake continuously by machine or hand for
one-half hour. Pour the entire contents of the bottle on a 12.5-cm.
folded filter, covering with a watch glass. Weigh 150 grams of the
filtrate into a 250-cc. flask and evaporate on the steam bath, removing
the last chloroform with a blast of air. Digest the residue with 80 cc.
of hot water for ten minutes on a steam bath with frequent shaking, and
let cool. Treat the solution with 20 cc. (for roasted coffee) or 10 cc.
(for unroasted coffee) of 1-percent potassium permanganate and let stand
for 15 minutes at room temperature. Add 2 cc. of 3-percent hydrogen
peroxid (containing 1 cc. of glacial acetic acid in 100 cc.). If the
liquid is still red or reddish, add hydrogen peroxid, 1 cc. at a time,
until the excess of potassium permanganate is destroyed. Place the flask
on the steam bath for 15 minutes, adding hydrogen peroxid in 0.5-cc.
portions until the liquid becomes no lighter in color. Cool and filter
into a separator