114 PROVISIONAI METHODS FOR ANALYSIS OF FOODS. 



Extraction of fruit colors ivith amyl-alcohol and with ether. 



It will be seen from these two tables that amyl-alcohol, as a rule, extracts fruit 

 coloring matter from acid solution, while ether does not. Neither amyl-alcohol nor 

 ether extracted any color from alkaline solution of the fruit juices. 



5. DETERMINATION OF ACID MAGENTA GIRARD'S METHOD.* 



Add to 100 cc of the solution to be tested 2 cc of potassium hydroxid (5 to 100). 

 If this does not neutralize the acid, add enough to do it. Then add 4 cc of mercuric 

 acetate (10 to 100), agitate and filter. The filtrate should be colorless and slightly 

 alkaline. Acidify with a slight excess of dilute sulphuric acid, and if the solution 

 remains uncolored there is no acid magenta present. If it becomes a light violet-red 

 and there has been no other dye shown by the amyl-alcohol extracts, the presence 

 of acid magenta is shown. 



Acid magenta in acid solution dyes wool a magenta red. Wool dyed with it is 

 turned yellow by strong hydrochloric acid, decolorized by ammonium hydroxid, 

 and regains its color when washed with water. 



6. TEST FOR MARTIUS YELLOW OR NAPHTHALENE YELLOW. 



Extract with 95 per cent alcohol from an acidulated sample. Evaporate the 

 alcoholic solution to dryness with a piece of wool, which will be dyed a bright 

 yellow, and test the dyed wool. Both sulphuric and hydrochloric acids completely 

 decolorize it. 



7. ROTA'S METHOD OF IDENTIFICATION OF ORGANIC COLORING MATTER. b 



The coloring matters are divided into four groups by the use of stannous chlorid 

 and hydrochloric acid and of caustic potash. 



The reagents are a 10 per cent solution of stannous chlorid and a 20 per cent solu- 

 tion of caustic potash. 



Dilute the aqueous or alcoholic solution of coloring matter to about 1 to 10,000. 

 This strength is not of vital importance, but the color must not be too deep, as it 

 will mask the reduction in some cases, such as the safranins, where it is slow and not 

 complete. Add to the solution a few drops of stannous chlorid and a few drops of 

 hydrochloric acid; shake, and heat to boiling. Care must be taken to carry along for 

 comparison a solution of the coloring matter acidified with hydrochloric acid, in 

 order not to mistake the action of the acid alone for reduction. Some of the colors 

 for instance, safranins and indulins are slow to be reduced and must be allowed to 

 stand for some time. For the stannous chlorid and hydrochloric acid can be substi- 

 tuted a solution of tin in strong hydrochloric acid. 



Girard & Dupre, Analyse des Matieres, Alimentaires, etc., p. 169; Winton, Conn. Expt. Sta. Rept., 

 1899, Pt. II, 132. 

 i>Chem. Ztg., 1898, 22, 437-442; Analyst, 1899, 24, 41. 



