86 PROVISIONAL METHODS FOB ANALYSIS OF FOODS. 



11. DETERMINATION OF GUM AND DEXTRIN. 



Evaporate 100 cc of wine to about 10 cc and add 10 cc of 96 per cent alcohol 

 (sp. gr. 0.81). If gum or dextrin be present (indicated by the formation of a 

 voluminous precipitate) , continue the addition of alcohol slowly and with stirring 

 until 100 cc have been added. Let stand over night, filter, and wash with 80 per 

 cent alcohol by volume (sp. gr. 0.84). The precipitate may then be dried and 

 weighed, or it may be treated according to Sachsse's method for the determination 

 of starch. 



12. DETERMINATION OF TANNIN AND COLORING MATTER. a 



Dealcoholize 100 cc by evaporation and dilute with water to the original volume. 

 Transfer 10 cc to a porcelain dish of about 2 liters capacity; add about a liter of 

 water and exactly 20 cc of indigo 11 solution, measuring the latter by means of a 

 burette. Add decinormal potassium permanganate solution, which has been stand- 

 ardized against decinormal oxalic acid, a cubic centimeter at a time, until the blue 

 color changes to green; then a few drops at a time until the color becomes bright 

 yellow. Designate the number of cubic centimeters of permanganate solution 

 employed by (a). 



Treat 10 cc of the dealcoholized wine, prepared as above, with carefully purified 

 boneblack for fifteen minutes; filter and wash the boneblack thoroughly with 

 water. Add a liter of water and 20 cc of indigo solution and titrate with perman- 

 ganate as above. Designate the number of cubic centimeters of permanganate 

 solution employed by (b). 



Then a b = c = the number of cubic centimeters of permanganate solution 

 required for the oxidation of the tannin and coloring matter in 10 cc of wine. 



Multiply (c) (corrected to cubic centimeters of decinormal solution, if the solution 

 employed is not exactly decinormal) by 0.04157 for tannin and coloring matter, 

 expressed in grams per 100 cc. 



One cubic centimeter of decinormal permanganate solution is equivalent to 

 0.004157 gram tannin. 



13. DETERMINATION OF SODIUM CHLORID. 



Sodium chlorid is obtained by dissolving the ash in water, slightly acidifying with 

 nitric acid, neutralizing with calcium carbonate, and titrating with silver nitrate, 

 using normal potassium chromate as indicator. 



14. DETERMINATION OF POTASSIUM SULPHATE. 



Precipitate sulphuric acid directly in 50 cc of wine by means of barium chlorid, 

 and determine the resulting barium sulphate by the ordinary method. Express the 

 result in grams of potassium sulphate per 100 cc. In all cases this determination 

 should be made in the original wine, as results obtained with the ash are always low. 



15. DETERMINATION OF PHOSPHORIC ACID. 



Determine phosphoric acid in the ash by the official volumetric method. In case 

 the ash has been used for other determinations, and it is necessary to begin with the 

 original wine, evaporate 100 cc of dry wines and ignite directly. With sweet wines, 

 evaporate 100 cc to a sirupy consistency in a flask of about 250-cc capacity, add 25 cc 

 of concentrated sulphuric acid and heat with a low flame till the evolution of g;as 



"Neubauer-Lowenthal method. Annalen der Oenologie, 2, 1. 



b Instead of the indigo-carmin called for by the original method, sodium sulphindigotate maybe 

 employed, as suggested by Schroeder (Ztfcchr. anal. Chem., 1886, 25, 112). To prepare the solution, 

 dissolve 6 grams of sodium stilphindigotate m 500 cc of water with aid of heat; cool; add 50 cc of con- 

 centrated sulphuric acid; dilute to 1 liter and filter. (U. S. Dept. of Agr., Bui. 46 revised, p. 66.) 



