BAKING -POWDERS. 105 



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 one minute. Finish the titration, 

 using phenolphthalein as indicator and correct the reading by adding 0.2 cc. One 

 cubic centimeter of fifth-normal potassium hydroxid solution is equivalent to 0.026406- 

 gram tartaric anhydrid (C 4 H 4 5 ), 0.03001 gram tartaric acid (H 2 C 4 H 4 O 6 ), and 0.03763 

 gram potassium bitartrate (KHC 4 H 4 O 6 ). 



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

 potassium bitartrate. 



The accuracy of this method is indicated by the agreement of the percentages of 

 potassium bitartrate in cream of tartar powders containing no free tartaric arid, 

 obtained by calculation from the tartaric acid, with those obtained by calculation 

 from the potassium oxide. a 



8. DETERMINATION OF STARCH. 

 (a) DIRECT INVERSION METHOD. 



(For all baking powders and baking chemicals free from lime.) 



Weigh 5 grams of the powder into a graduated 500 cc flask. Convert into dextrose 



by the Sachsse's method and determine the reducing power of the solution by the 



Allihn method, as described under Spices (p. 57). 



(b) INDIRECT METHOD. b 



(For phosphate, alum phosphate, and all other baking powders containing lime.) 

 Mix 5 grams of the powder in a graduated 500-cc flask, with 200 cc of 3 per cent 

 hydrochloric arid, and allow the mixture to stand for one hour, with frequent shak- 

 ing. Filter on a Schleicher and Schuell No. 575 11 cm hardened filter, taking care 

 that a clear filtrate is obtained. Rinse the flask once, without attempting to remove 

 all the starch, and wash the paper twice with cold water. Carefully wash the starch 

 from the paper bark into the flask, with 200 cc of water, using a small wash bottle. 

 Add 20 cc of 25 per cent hydrochloric acid and proceed according to Sachsse's 

 method. Determine reducing power by Allihn's method. 



The treatment with 3 per cent hydrochloric acid, without dissolving the starch, 

 effectually removes the lime, which otherwise would precipitate as tartrate in the 

 alkaline copper solution 



(c) M'GILL METHOD. 



The following modification of McGill's method is valuable for check purposes: 

 Digest one gram of tin- powder with 150 cc of 3 per cent hydrochloric acid for 24 

 hours at the room temperature, with occasional shaking. Filter on aGooch crucible, 

 wash thoroughly with cold water and finally once with alcohol and once with ether. 

 Dry at 110 C. (4 hours is usually sufficient), cool and weigh. Burn off the starch and 

 weigh again. To obtain the weight of starch subtract the weight after burning from 

 the weight after drying at 110 C. 



The results by this method on cream of tartar powders and tartaric acid powders 

 a.nive closely with those obtained by copper reduction. On phosphate, alum, and 

 alum-phosphate powders the results are usually satisfactory, but in some instances 

 they may be over 2 per cent too high. 



9. DETERMINATION OK I'OTASSITM BITARTRATK. 



If, as is usually the case, no other potassium salt but the bitartrate is present, 

 multiply the percentage of total potash determined as directed under 12, d, by 3.MM>. 



Conn. \nr. Kxp. Stn. Krp.. 1900, p. 180. 



>Aftrr Wintoii. Conn. Ajrr. Kxp. Shi. Ui'p.. I'.HKI, p. 171. 



