White vinegar is acidic, baking soda solution is alkaline, and water is neutral. Therefore, dripping purple cabbage juice into baking soda solution turns blue, adding it into white vinegar turns blue, and dripping it into water turns purple.
Precautions:
Because the cold tolerance of cabbage is stronger than that of Chinese cabbage, the time of entering the cellar can be slightly later than that of Chinese cabbage, and it can be stored in the cellar by stacking, shelf storage and basket storage. Stacking can be made into triangular stacks and rectangular stacks, and it is best to store them on shelves, and 2 ~ 3 floors can be placed on each shelf, which is conducive to ventilation and heat dissipation. Stacking in baskets is also beneficial to ventilation and the effect is good.
2 ~ 4 layers of cabbage can be piled in the ditch. For those cabbages that are not yet firm, cover them with straw, and then gradually cover them with soil according to the change of external temperature to prevent freezing injury. You can also uproot the leaves, keep the outer leaves, and compact them with the roots down. When the heel in is in the ditch, you can also water it less when the soil is dry, and cover it properly to prevent freezing.