32 



b. CARAMEL TEST" (MODIFICATION BY BLYTH OF LEACH'S TEST&). 



Use a milk known to be free from caramel as a control. Take 50 cc of the sus- 

 pected milk and the same quantity of the control, coagulate each by the addition of 

 acetic acid, strain off the whey from the curd by means of a piece of fine muslin. 

 Carefully compare the colors of the whey from both samples. Place the curds in 

 two white porcelain basins and just cover them with strong hydrochloric acid. 

 Compare the colors after they have stood several hours. Caramel will be indicated 

 by a brownish- violet color; but the pure curd will also develop a similar color after 

 standing for a long time, so that great care must be exercised in coming to a conclu- 

 sion. The use of the control milk greatly increases the delicacy of the test. 



E. MILK (SOUR), BLYTH' S METHODS 



The color of the milk should be carefully noted, as some dyes, such as anilin yel- 

 low and acid yellow, impart a faint pink color to the curd of sour milk. Butter yel- 

 low, on the other hand, rises with the fat, which it at first colors yellow, but 

 afterwards becomes colorless. Annatto imparts a characteristic color to the curd 

 and, like saffron and turmeric, does not become colorless in decomposed milk. Car- 

 amel colors both the curd and the whey. If it be desired to make a comparison 

 between the milk when fresh and after partial decomposition, two portions should 

 be incubated, one containing sufficient formalin to prevent any decomposition. 



The following general method will be found most convenient: Take 50 cc or more 

 of the milk and render it just alkaline to delicate litmus paper, evaporate to a paste, 

 and thoroughly extract the fat with ether. Although turmeric, annatto, and such 

 dyes as anilin yellow are all somewhat soluble in ether from an alkaline solution, 

 yet in the presence of casein such small quantities are dissolved that they may be dis- 

 regarded. (Phosphin is much more soluble in ether and should be looked for both 

 in the ether and alcohol extract. ) 



Evaporate the ethereal solution to dryness, shake up the fat with a small quantity 

 of hot distilled water in a small separating funnel, separate the water from the fat, 

 and evaporate to dryness on the water bath in a small flat porcelain dish; carefully 

 note the color of the residue. (See following table. ) Pure milk will give no colored 

 residue. Next thoroughly exhaust the fat-free milk residue with absolute alcohol, 

 pass the extract through a small filter, and evaporate to dryness in three or four 

 small flat porcelain dishes; if unreduced artificial coloring matter be present the 

 residue will be colored orange, yellow, or brown. Wash one of the residues into a 

 test tube with a small quantity of water made acid with sulphuric acid. The sul- 

 phonated azo dyes will be at once indicated by the color of the solution. Shake the 

 solution with ether. This will divide the coloring matters into two groups as in the 

 table; the natural coloring matters and the non sulphonated acid coal-tar dyes i. e., 

 the dyes precipitated by Weingartner' s tannin reagent being soluble in ether, while 

 the basic dyes and the sulphonated dyes are insoluble in ether. The ordinary tests 

 may then be applied to the remaining portions of the dyes. 



Analyst, 1902, p. 151. 



& Blyth finds that caramel may be formed from the milk sugar if any evaporation 

 process be used in testing for caramel. 

 c Analyst, 1902, p. 146. 



