226 MILK 



2. Leach's Hydrochloric Acid Test. " Commercial hydrochloric 

 acid (spec. grav. 1.2) containing 2 c.c. of 10 per cent, ferric chlorid 

 per liter is used as reagent. Add 10 c.c. of the acid reagent to an 

 equal volume of milk in a porcelain casserole, and heat slowly 

 over a free flame nearly to boiling, holding the casserole by the 

 handle and giving it a rotary motion while heating to break the 

 curd. The presence of formaldehyd is indicated by a violet* col- 

 oration, varying in depth with the amount present. In the ab- 

 sence of formaldehyd the solution slowly turns brown. By this 

 test 1 part of formaldehyd in 250,000 parts of milk is readily de- 

 tected before the milk sours. After souring the limit of delicacy 

 proves to be about 1 part in 50,000." 



3. Confirmatory Tests with Distilled Milk (Leach). Distil 100 

 to 200 c.c. of the milk and use the first 20 c.c. of the distillate for 

 testing. The following tests can be applied : 



(a) To a few drops of the distillate in a test-tube add 1 drop of 

 SchhTs reagent. A pink coloration appears in the presence of an 

 aldehyd. 



Preparation of SchifFs reagent : One gram of f uchsin is dissolved 

 in water and a mixture of 20 c.c. of a saturated solution of sodium 

 bisulphate and 10 c.c. of pure hydrochloric added, and the volume 

 made up to 1000 c.c. 



(6) Add to 5 c.c. of the milk distillate a few drops of a 1 per 

 cent, aqueous solution of resorcin or phenol, mix, and pour down 

 the side of a tube containing sulphuric acid. A rose-red zone is 

 formed at the junction of the liquids. Formaldehyd can be de- 

 tected 1 part to 200,000. If present in larger- quantity than 1 

 part to 100,000 a white turbidity or precipitate is formed above 

 the colored zone. 



(c) Use 1 or 2 c.c. of the milk distillate in a test-tube. Add to 

 this 2 to 4 drops of the following reagent: One gram of phenyl- 

 hydrazin hydrochlorid and 1.5 grams sodium acetate dissolved in 

 1-0 c.c. of water. A green coloration appears when formaldehyd is 

 present. 



(d) To a distillate from milk which has been acidified before 

 distillation to bind ammonia a few drops of Nessler's reagent are 

 added. A yellow color appears in presence of formaldehyd. If 

 much formaldehyd is present the color is dark and a grayish 

 precipitate may form upon standing. 



The following methods for detecting formadehyd in milk are 

 given by the Association of Official Agricultural Chemists: 



1. To 3 to 5 c.c. of milk add a lump of phenylhydrazin hydro- 

 chlorid about the size of a pea, from 2 to 4 drops (not more) of 

 a 5 to 10 per cent, solution of potassium ferrocyanid, and from 8 

 to 12 drops of an approximately 12 per cent, solution of sodium 



