The production method is as follows:

1, go to the supermarket to buy a purple cabbage (purple kale);

2, find a clean bowl at home;

3, tear the purple kale and put it into the bowl;

4, introduce warm water (30-40 degrees) into it;

5, use chopsticks to stir until the water in the cup turns blue (if it is If it is too pale, you can put in the torn kale);

6, use a dropper to extract some drops on the object to be identified (you can also pour a small amount on the object without a dropper).

Purple kale who turns green then that object is alkaline, turn red is acidic.