258 PRINCIPLES AND PRACTICE OF MILK HYGIENE 



phuric acid to make a paste is added to the ash and 3 

 c.c. of methyl alcohol is mixed with it. The vapor which 

 is then given off is ignited. If boric acid or borax is 

 present, even in very small quantity, the flame will be 

 green. 



Turmeric Test. Add 6 or 7 drops of hydrochloric 

 acid to 10 c.c. of milk and, after coagulation has occurred, 

 filter. Dip a piece of turmeric paper into the filtrate and 

 allow it to dry. If boric acid is present in the proportion 

 of 0.02 per cent, or borax in the proportion of 0.03 per 

 cent., the paper will be colored cherry-red (Kiihl) ; this 

 color will be changed to bluish-black by ammonia water. 



Another method of applying the turmeric test is de- 

 scribed by Farrington and Woll as follows : " One hun- 

 dred cubic centimetres of milk are made alkaline with 

 a soda or potash solution and then evaporated to dryness 

 and incinerated. The ash is dissolved in water, to which 

 a little hydrochloric acid has been added, and the solu- 

 tion filtered. A strip of turmeric paper moistened with 

 the filtrate will be colored reddish-brown when dried at 

 100 C. on a watch glass if boric acid is present." 



Formaldehyde. Formaldehyde, the favorite preserva- 

 tive for milk, is used in the form of formaldehyde solution, 

 formalin, formol, etc. A very small quantity (0.008 per 

 cent, of formaldehyde, 0.02 per cent, of formalin) will 

 prevent curdling for four days. The following tests may 

 be used for detecting the presence of formaldehyde : 



Richmond's Test. Place a small quantity of milk 

 in a test tube, add an equal quantity of water and then 

 pour a little commercial sulphuric acid slowly down the 

 side of the tube so that it will form a layer at the bottom. 

 A bluish or violet ring at the point where the acid and 

 milk come in contact indicates the presence of formalde- 

 hyde. If no formaldehyde is present a faint, greenish 



