10() PROVISIONAL METHODS FOR ANALYSIS OF FOODS. 



10. DETERMINATION OF FREE TARTARIC ACID. 



Calculate the percentage of tartaric anhydrid combined with the potash as bitar- 

 trate (if any) and subtract this from the percentage of total tartaric anhydrid. 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 improperly stored, a portion or 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 bicarbonate. Multiply by 1.1365 to obtain the 

 percentage of tartaric acid. 



11. DETECTION OF ALUM IN PRESENCE OF PHOSPHATES.* 



(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 chloride 

 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 Asn. 1 ' 



(a) DETERMINATION OF INSOLUBLE ASH AND PREPARATION OF SOLUTIONS: 



Char 5 grams of the material in a platinum dish at a heat below redness. Boil the 

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

 and wash with hot water. Return the residue, together with the paper, to the plati- 

 num 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. c 



Draw an aliquot portion of 100 cc and separate silica, if necessary. Mix the solu- 

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

 aluminum phosphate. Add ammonia 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 solu- 

 tion and 4 cc of 80 per cent acetic acid. 



As soon as the precipitate of aluminum phosphate, mixed with a little iron phos- 

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



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

 sulphuric acid, reduce with hydrogen sulphid and determine the iron by the vol- 

 umetric permanganate method. In the same solution determine the phosphoric 

 acid. To obtain the weight of A1 2 O 3 , subtract the sum of the weights of Fe 2 O 3 and 

 P./.) 5 from the weight of the mixed phosphates. 



(c) LIME. 



Heat the filtrate from the mixed phosphates, which is acid with acetic acid, to 50 C. 

 and precipitate with ammonium oxalate. Filter, wash, ignite over a Bunsen burner, 

 and finally convert into oxid by heating over a blast lamp. 



"Thirty-first An. Rep. Mass. SUito Board of Health, 1899, p. 638. 

 1 c.mn. Agr. Exp. St.. lt.-p. I'.NK), p. ITS. 

 See Appendix, p. Kill. 



