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.