The next step is to add a strong

The next step is to add a strong

The next step is to add a strong

The next step is to add a strong, biting acid known as sulphuric acid to the test-bottle into which you have just put the milk. A glass marked to show just how much acid to use also comes with the machine. Fill this glass measure to the mark. Then pour the acid carefully into the test-bottle. Be sure not to drop any of the acid on your hands or your clothes. As the acid is heavier than the milk, it will sink to the bottom of the bottle. With a gentle whirling motion, shake the bottle until the two fluids are thoroughly mixed. The mixture will turn a dark brown and become very warm.