BAKING POWDER AND BAKING CHEMICALS. 175 



3. Available Carbon Dioxid. 

 Subtract the residual carbon dioxid from the total. 



4. Acidity. 

 (For cream of tartar and its substitutes.) 



Dissolve 1 grain of the material in hot water and titrate with standard fifth- 

 normal potassium hydroxid solution, using phenolphthalein as indicator. 



5. Detection of Tartaric Acid, Free or Combined " Wolff Method. 

 (Applicable in presence of phosphates.) 



Shake repeatedly about 5 grams of the sample with about 250 cc of cold 

 water in a flask and allow the insoluble portion to subside. Decant the solu- 

 tion through a filter and evaporate the filtrate to dryness. To the dry powdered 

 residue add a few drops of a 1 per cent solution of resorcin and about 3 cc of 

 strong sulphuric acid. Heat slowly. A rose-red color indicates tartaric acid, 

 the color being discharged on dilution with water. 



6. Detection of Free Tartaric Acid. 



Extract 5 grams of the powder with absolute alcohol and evaporate the 

 alcohol from the extract. Dissolve the residue in dilute ammonium hydroxid, 

 transfer to a test tube, add a good-sized crystal of silver nitrate, and heat gently. 

 Tartaric acid is indicated by the formation of a silver mirror. If desired, the 

 absolute alcohol extract may be tested by the Wolff method, as described under 

 paragraph 5. 



7. Total Tartaric Acid Goldenberg--Geromont-Heidenhain Method. 



(Applicable only in the absence of aluminum salts, calcium salts, and 



phosphates. ) 



Into a shallow porcelain dish, 6 inches in diameter, weigh out 2 grams of the 

 material and sufficient potassium carbonate to combine with all tartaric acid 

 not in the form of potassium bitartrate. Mix thoroughly with 15 cc of cold 

 water and add 5 cc of 99 per cent acetic acid. Stir for half a minute with a 

 glass rod bent near the end. Add 100 cc of 95 per cent alcohol, stir violently 

 for 5 minutes, and allow to settle at least 30 minutes. Filter on a gooch crucible 

 with a thin layer of paper pulp, and wash with 95 per cent alcohol until 2 cc 

 of the filtrate do not change the color of litmus tincture diluted with water. 

 Place the precipitate in a small casserole, dissolve in 50 cc of hot water and add 

 standard fifth-normal potassium hydroxid solution, leaving it still strongly 

 acid. Boil for 1 minute. Finish the titration, using phenolphthalein as indi- 

 cator and correct the reading by adding 0.2 cc. One cubic centimeter of 

 fifth-normal potassium hydroxid solution is equivalent to 0.026406 gram of 

 tartaric anhydrid, 0.03001 gram of tartaric acid, or 0.03763 gram of potassium 

 bitartrate. 



The standard of the potassium hydroxid solution should be fixed by pure dry 

 potassium bitartrate. 



Wolff, Ann. chim. anal, appl., 1899, 4: 263. 



