BAKING POWDER AND BAKING CHEMICALS. 



10. Free Tartaric Acid. 



Calculate the percentage of tartaric anhydrid combined with the potash as 

 bitartrate, if any, and subtract this from the percentage of total tartaric 

 anliydrid. The difference is the tartaric anhydrid originally added as the free 

 acid, although if the sample has been kept for a long time or has been improp- 

 erly stored a portion of all of this acid may exist at the time of analysis as 

 the sodium salt resulting from the reaction in the can with the sodium bicar- 

 bonate. Multiply by 1.1365 to obtain the percentage of tartaric acid. 



11. Detection of Alum in Presence of Phosphates. a 



(a) IN BAKING POWDER. 



Burn to an ash about 2 grams of the sample in a platinum dish. Extract 

 with boiling water and filter. Add to the filtrate a few drops of ammonium 

 chlorid solution. A flocculent precipitate indicates alum. 



(b) IN CREAM OF TARTAR. 



Mix about 1 gram of the sample with an equal quantity of sodium carbonate, 

 burn to an ash, and proceed as in (a). 



12. Examination of Ash.& 

 (a) INSOLUBLE ASH AND PREPARATION OF SOLUTION. 



Char 5 grams in a platinum dish at a heat below redness. Boil the car- 

 bonaceous mass with dilute hydrochloric acid, filter into a graduated 500-cc 

 flask, and wash with hot water. Return the residue, together with the paper, 

 jto the platinum dish and burn to a white ash. Boil again with hydrochloric 

 acid, filter, wash, unite the two filtrates, and dilute to 500 cc. 



Incinerate the residue after the last filtration for the determination of ash 

 insoluble in acid. 



(b) IRON AND ALUMINA. 



Draw an aliquot of 100 cc and separate silica, if necessary. Mix the solution 

 with sodium-phosphate solution in excess of what is required to form normal 

 aluminum phosphate. Add ammonium hydroxid until a precipitate remains on 

 stirring, then hydrochloric acid drop by drop until the precipitate dissolves. 

 Heat the solution to about 50 C., mix with a considerable excess of 50 per 

 cent ammonium acetate solution and 4 cc of 80 per cent acetic acid. 



As soon as the precipitate of aluminum phosphate, mixed with iron phosphate, 

 has settled, collect on a filter, wash with hot water, ignite, and weigh. 



Fuse the mixed phosphates with 10 parts of sodium carbonate, dissolve in 

 j dilute sulphuric acid, reduce with zinc, and determine the iron by the volu- 

 metric permanganate method. In the same solution determine the phosphoric 

 acid. To obtain the weight of A1 2 O 3 , subtract the sums of the weights of 

 and P 2 O 5 from the weight of the mixed phosphates. 



Thirty-first Ann Kept. Mass. State Board of Health, 1899, p. 638. 

 6 Conn. Agr. Exper. Stat. Kept., 1900, p. 175. 



