Experiment No. 17
Formaldehyde in Cream or Milk
To 10 cc. of milk in a casserole add 10 cc. of the acid reagent. Heat slowly over the flame nearly to boiling, holding the casserole in the hand and giving it a slight rotary movement while heating. The presence of formaldehyde is indicated by a violet coloration varying in depth with the amount present. In the absence of formaldehyde the solution slowly turns brown.
Acid Reagent.—Commercial hydrochloric acid (sp. gr. 1.2) containing 2 cc. per liter of 10 per cent ferric chlorid.
(Adapted from Leach, "Food Inspection and Analysis.")
1. How may the presence of formaldehyde in milk be detected? 2. Why in this test is it necessary to use acid containing ferric chlorid? 3. Describe the appearance of the two samples of milk after adding the acid reagent and heating. 4. Which sample showed the presence of formaldehyde?