180 METHODS OF ANALYSIS [Chap. 



STARCH. 



19 Qualitative Test. — Tentative. 



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

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

 jelly nearly to boiling, add several cc. of dilute sulphuric acid and then potassium 

 permanganate solution 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 amount in the apple, and 

 occasionally in other fruits, and unless it is found in the fruit product in consider- 

 able amount its presence may be due to these natural sources. 



GELATINi. 



20 Qualitative Test. — Tentative. 



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 as directed under 



I, 18, 21 or 23. 



AGAR AGAR. 



QUALITATIVE TESTS. 



21 By Microscopic Examination^. — Tentative. 



Heat the jelly with 5% sulphuric acid, add a crystal of potassium permanganate 

 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. 



22 By Precipitation^. — Tentative. 



Cover 30 grams of the jam or jelly with 270 cc. of hot water, stir until thoroughly 

 disintegrated and boil for 3 minutes. Filter immediately, while still boiling hot, 

 through a filter paper of texture similar to No. 597, S. & S. In the presence of agar 

 agar a precipitate will form upon standing not longer than 24 hours. Filter, 

 wash with cold water and dissolve from the paper by means of a very small amount 

 of boiling water. Upon chilling this hot water solution a firm jelly will be formed 

 that can be examined by the touch. This method will detect 0.2% of agar agar with 

 certainty if the proportions of jam or jelly and water are strictly observed. 



TARTARIC ACID.-TENTATIVE. 



23 PREPARATION OF SOLUTION. 



Filter fruit juices and employ the filtrate directly. In the case of jellies filter 

 the solution, prepared as directed in 1 (b), and employ the filtrate. In the case of 

 sirups or substances containing insoluble matter like ptilped fruit, jams, marmalades, 

 etc., weigh 50-100 grams, the amount selected being dependent upon the content of 

 solids, of the sample, prepared aS directed in 1 (C) or (d), introduce into a 200 cc. 

 graduated flask, make up to the mark with water, allow to stand for an hour, shake at 

 frequent intervals, filter through a dry paper and use the filtrate. 



24 DETERMINATION. 



Determine the tartaric acid in 100 cc. of fruit juice or the same amount of a solu- 

 tion of the sample, prepared as directed in 23, employing the method given under XVI, 

 29, except that 20 cc. of alcohol are used in the precipitation instead of 15 cc. 



