LEAVENING MATERIALS
BAKING POWDERS
Baking powders consist of bicarbonate of soda and an acidifying agent as
acid potassium tartrate, acid calcium phosphate, tartaric acid or alum.
Some powders contain both acid calcium phosphate and alum. The kind of
powder is determined by testing for these. Gypsum has been added to
baking powders to increase the weight.
TARTARIC ACID
FREE OR COMBINED
_Wolff’s Method._--If no starch is present, mix a little of the powder
with some dry resorcin. Add a few drops of sulfuric acid and heat
gently. A rose-red color forms if tartaric acid or tartrates are
present. The color should disappear when diluted with water. When starch
is present, mix well by shaking about 5 grams of the powder with 250 cc.
of cold water. Let the insoluble matter settle and pour the liquid upon
a filter. Evaporate the filtrate to dryness, treat the powdered residue
with a few drops of a 1 per cent solution of resorcin. Add 3 cc. of
strong sulfuric acid, heat slowly. A rose-red color forms if tartaric
acid is present. The color should be destroyed on the addition of
water. This test is applicable in the presence of phosphates and the
acid may be free or combined.
TARTARIC ACID
FREE
Make an absolute alcoholic extract of 5 grams of the powder and
evaporate the alcohol. Add sufficient dilute ammonia to dissolve the
residue, place in a test tube and drop in a crystal or two of silver
nitrate. Heat gently, and a silver mirror will form if tartaric acid is
present.
SULFATES
CALCIUM, ETC.
Boil a portion of the sample gently with strong hydrochloric acid, add
barium chlorid. A white precipitate of barium sulfate will form if
sulfuric acid is present.
GYPSUM
CALCIUM SULFATE
Ash a portion of the sample and make the usual qualitative tests for
calcium sulfate.
AMMONIUM SALTS
Extract a few grams of the sample with cold water, boil the extract with
sodium hydroxid and place a piece of moist red litmus paper in the
steam. It will be colored blue if ammonia is present.
ALUM
Reduce to an ash about 2 grams of the powder in a platinum dish. Extract
with boiling water, add ammonium chlorid solution to the filtrate until
a distinct odor of ammonia is given off.
If a flocculent precipitate forms it indicates the presence of alum.
This test for alum is applicable in the presence of phosphates.
_Mrs. Richards._--Cover some logwood chips (they must be pure) with
water and bring to a boil. Repeat this four times, saving only the last
decoction. Shake some of the sample (a couple of teaspoonfuls) in a
beaker half full of water. When it ceases effervescing, strongly acidify
with acetic acid. Add a few drops of the logwood extract, and if alum is
present a bluish-red color will appear.
CREAM OF TARTAR
Cream of tartar is bitartrate of potassium and is obtained from the lees
deposited in wine casks. If gypsum has been used to clarify the wine, it
will be present in the cream of tartar as calcium tartrate.
Other adulterants of cream of tartar are acid calcium phosphate, starch,
gypsum, and alum.
TARTARIC ACID
FREE OR COMBINED
If the sample is known to be free from starch the following test may be
made:
Mix a bit of the powder with a small quantity of dry resorcin and add a
few drops of concentrated sulfuric acid. Heat slowly, and if a rose-red
color forms, which disappears when diluted with water, there is present
either tartaric acid or a tartrate.
When the sample contains starch, shake about 4 or 5 grams of it a number
of times with 250 cc. of cold water in a large flask. Pour on a filter
after the insoluble material has settled and evaporate the filtrate to
dryness. The residue is to be tested for tartaric acid and tartrates,
the same as when starch was absent.
ALUMINIUM SALTS
Mix equal quantities (about 1 gram) of the sample and sodium carbonate
and burn to an ash. Extract with boiling water and filter. Add to this
filtrate enough ammonium chlorid solution to cause a distinct evolution
of ammonia. The formation of a flocculent precipitate shows the presence
of aluminium. This test may be used when phosphates are present.
AMMONIA
PRESENT IN THE FORM OF AMMONIA ALUM OR AMMONIUM CARBONATE
Make a cold water extract of the powder and boil it with sodium
hydroxid. Test the steam with moist red litmus paper.
EARTHY MATERIALS
Treat the sample with warm potassium hydroxid. A residue indicates some
earthy material.