MILK AND MILK PRODUCTS 41 



manner. To each filtrate is added i c.c. of ferric sulfate and 

 then the thiocyanate until the faint permanent brown is ob- 

 tained. If the thiocyanate is exactly — , the difference in c.c. 

 required for the two filtrates multiplied by 0.006 will give the 

 amount of formaldehyde in the quantity originally taken. If 

 the thiocyanate is not — the result must be reduced to that 

 basis. 



Beta naphthol. — Several allied antiseptics of this type may be 

 detected by the following method: 200 grams of the sample 

 are acidified with sulfuric acid and distilled with open steam 

 until 150 c.c. of distillate are obtained. This liquid is shaken 

 with 20 c.c. of chloroform, the latter withdrawn, rendered 

 alkaline with potassium hydroxid, and heated almost to boiling 

 for a few minutes. Color changes as follows: 



Salol, light red. 



Phenol, light red, to brown, to colorless. 



Beta naphthol, deep blue, to green, to brown. 



A portion of the distillate may also be tested as follows : 25 c.c. 

 are made faintly alkaline with ammonium hydroxid, then faintly 

 acid with nitric acid and then a drop of strong sodium nitrite 

 solution. Beta naphthol develops a rose red, but the reaction 

 is sometimes uncertain and seems to be affected by light. 

 The so-called hydronaphthol gives the same effect. 



Benzoates. — Peter's method: The material is made slightly 

 acid and extracted with chloroform, which is then evaporated 

 spontaneously. The vessel containing the residue is placed 

 in melting ice, 2 c.c. of sulfuric acid added, and stirred until 

 the residue is dissolved. Barium dioxid is dusted into the 

 mass, with constant stirring, until the liquid begins to foam, 

 when 3 c.c. of hydrogen dioxid (3 per cent.) are added drop 

 by drop. The dish is then removed from the cold bath, the 

 contents diluted with water to convenient bulk, and filtered. 

 The acid filtrate is extracted with chloroform. The benzoic 

 s 



