FRUITS AND FRUIT PRODUCTS. 77 



7. EXAMINATION OF ASH. 

 (a) ALKALINITY OF THE ASH. 



Into the platinum dish containing the ash run an excess of fifth-normal nitric acid 

 and add a few drops of methyl orange. Carefully rub up the ash with a rubber 

 tipped stirring rod and titrate the excess of acid with decinormal potassium hydroxid. 

 Calculate the alkalinity to per cent of potassium carbonate in the original substance. 

 One cubic centimeter of decinormal acid equals 0.00691 gram of potassium carbonate. 



(b) SULPHATES AND CHLORIDS. 



Wash the ash into a 50-cc flask and make up to the mark with water. In 25 cc of 

 this solution determine the sulphates by precipitation with barium chlorid. The 

 weight of barium sulphate times 0.7478 gives the weight of sulphates calculated as 

 potassium sulphate. 



In the other portion of the solution determine the chlorids by the Volhard* 

 method for chlorin. The nitric acid added before making the titration will, if it 

 contain enough nitrous oxid, completely destroy the red color of the methyl orange 

 and leave a clear solution for the titration. Calculate the chlorid as per cent of 

 sodium chlorid. .Pure fruit jellies and jams give practically no chlorids or sulphates 

 in this amount of ash, but glucose goods give appreciable amounts. If it is desired 

 to make a complete ash analysis of juices or fresh fruits much larger amounts will 

 have to be ashed. 



8. DETERMINATION OF TOTAL ACIDITY. 



Take 25 cc of the solution of jelly or diluted sirup [see 2 (a)], 10 grams of juice 

 or fresh fruit, or 50 cc of the washings from the determination of insoluble solids, 

 and dilute with recently boiled distilled water to about 250 cc, or less if the jelly be 

 not highly colored; add phenolphthalein and titrate the acid with decinormal 

 potassium hydroxid. In case of highly colored products litmus paper may be used 

 instead of phenolphthalein. Calculate the results as sulphuric acid. b 



It is very desirable that acidity be so expressed as to allow of comparison. This 

 end is not attained by expressing the acidity in terms of the dominant acid of the 

 various fruits; hence H 2 S0 4 has been suggested, and already a number of laboratories 

 have used this as a basis. 



9. DETERMINATION OF VOLATILE ACIDS. 



The determination of volatile acids in fruit products may be desirable in cases where 

 fermentation or the use of decayed fruit is suspected. Dissolve 25 grams of sub- 

 stance, dilute to 50 ce, and distill in a current of steam until about 200-cc have passed 

 over. Titrate the distillate with decinormal potassium hydroxid and express the 

 results as acetic acid. Each cubic centimeter of decinormal alkali is equivalent to 

 0.006 gram of acetic acid. 



10. DETECTION OF FREE MINERAL ACIDS. 



A. S. Mitchell and A. E. Leach have both called attention to the presence of free 

 sulphuric and phosphoric acid in jellies. For method of detection see Hehner's 

 method, page 64. 



11. DETERMINATION OF NITROGEN. 



Use*grams of jelly or other fruit product or 10 grams of juice or fresh fruit for 

 the determination of nitrogen according to either the Gunning or the Kjeldahl 

 method. Kxpivss results as protein (nitrogen multiplied by 6.25). 



Ann. (1. Chcm. 1877, 190, 1. Sutton, Volumetric Analyses, eighth edition, p. 165. 

 h See Composition of Jellies and Jams. Tolman, Munson, and Bigelow. Jour. Am. Chem. Soc. 

 1901, 23, 348. 



