Paragraph 4 Method of carrying out the test

weigh 4 +/-0.1 g. of ammonium sulphate A.R. into a 50m1. conical flask. Measure out 20 +/-0.5 ml. of the milk sample, and pour into the conical flask. Ensure that the ammonium sulphate dissolves by shaking for three minutes. Leave for not less than five minutes and then filter through a folded paper (Whatman 12.5 cm. No. 12) into a test tube. When not less than 5 ml. of a clear filtrate have collected, place the tube in a beaker of water, which is kept boiling, and keep it therein for five minutes. Transfer the test tube to a beaker of cold water;

when the tube is cool, examine the contents for turbidity by moving the tube in front of an electric light shaded from the eyes of the observer, and comparing each tube with a control tube prepared as directed in the next succeeding paragraph.