28 FRUITS AND FRUIT PRODUCTS. 



DETECTION OF ACID MAGENTA.^ 



Add to 100 cc of the solution to be tested 2 ec of potassium M^droxid 

 (5 to 100); if this does not neutralize the acid, add enough to do it. 

 Then add 1 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 dyes wool a magenta red from acid solution. 



AVool dyed with it is turned yellow by strong h3^drochloric acid, 

 decolorized b}^ ammonium hydroxid, and regains its color when washed 

 with water, 



DETECTION OF COCHINEAL. 



Cochineal is used to a certain extent as a coloring matter in foods, and 

 a very satisfactory test for it is that given in Girard and Dupre.^ Dis- 

 solve the food product in water, filtering if necessary. Acidulate 

 with hydrochloric acid and extract with amyl alcohol, which becomes 

 colored more or less yellow or orange, depending on the quantity of 

 cochineal present. Separate the amyl alcohol and wash with water 

 until neutral. Then separate into two portions; to the first add drop 

 by drop a very dilute solution of uranium acetate, shaking thoroughly 

 after each addition. In the presence of cochineal a characteristic 

 emerald-green color is produced. 



To the second portion add a drop or so of ammonia, and in presence 

 of cochineal a violet coloration results. This, however, is not so sen- 

 sitive to very small amounts as the first test, and many fruit colors 

 give tests hardly to be distinguished. 



Cochineal carmin is liable to contain tin, as it is often a tin lake, 

 although alum is also used. It is also liable to adulteration with lead 

 compounds. 



DETECTION OF CAKAMEL. 



Amthor test.'' — Place 10 cc of the solution to be tested into a high, 

 narrow glass with perpendicular sides, as, for example, a small bottle; 

 add from 30 to 50 cc of paraldehyde, depending on the intensity of the 

 coloring, and enough absolute alcohol to make the solutions mix. In 

 the presence of caramel a brownish- yellow to dark-brown precipitate 

 will collect in the bottom of the glass. Decant the liquor, wash once 

 with absolute alcohol, dissolve in a small amount of hot water, and 

 filter. The color of this will give some idea as to the amount of caramel 

 present. 



"^Girard and Dupre, Analyse des Matieres AHmentaires, etc., p. 169; Winton, Conn. 

 Expt. Sta. Kept. 1899, Pt. II, 132. 

 ^ Analyse des Matieres AHmentaires, etc. , p. 580. 

 •^Ztschr. anal. Chem. 1885, 24, 30; Borgmann Anal, des Weines., p. 98. 



