Drops of Kovac substances into tubes keep the solution over a period of 20 minutes notice colors above substance. If it does not produce the yellow, but if it is a dedicated manufacturing Indonesia will be purple.
Kovac drops of solution into the tube. Leave on for 20 minutes observing the color of the top. If not produce indole is yellow. If the product indole is purple.
Dropping into the tube Kovac solution for 20 minutes notice the color on the top of, if do not produce indole is yellow. But if produce indole is purple.