82 METHODS OF ANALYSIS. 



20. Detection of Starch. Provisional. 



First destroy the color of the jelly by treatment with sulphuric acid and 

 potassium permanganate and then test with iodin. Bring the solution of jelly 

 nearly to the point of boiling, add several cubic centimeters of dilute sulphuric 

 acid and then potassium permanganate until all color is destroyed. The starch 

 remains unaffected by this treatment. The presence of starch is not 'necessarily 

 an indication of its addition as an adulterant. It is usually present in small 

 amounts in the apple, and occasionally in other fruits, and unless it is found 

 in the fruit product in considerable amounts its presence may be due to these 

 natural sources. 



21. Detection of Gelatin. a Provisional. 



The presence of gelatin in jellies and jams is shown by the increased content 

 of nitrogen. Precipitate a concentrated solution of jelly or jam with 10 volumes 

 of absolute alcohol and determine nitrogen in the dried precipitate by the 

 Kjeldahl or Gunning method. ("I. Fertilizers," p. 5.) 



22. Detection of Agar Agar.& Provisional. 



Heat the jelly with 5 per cent sulphuric acid, add a crystal of potassium per- 

 manganate, and allow to settle. If agar agar is present the sediment will be 

 rich in diatoms, which can be detected by the use of the microscope. 



23. Heavy Metals. Provisional. 

 Proceed as directed under " IX. Canned Vegetables," page 61. 



A. Boemer, Chem. Ztg., 1895, 19: 552. 



*K Marpmann, Zts. angew. Mikrosk., 189G, 2: 260. 



