This so-called hardness of water can be very easily got rid of by a simple though interesting chemical process. Thus it requires two equivalents of carbonic aeid to render lime soluble in water ...

Although aqueous solutions of 'slaked' lime are alkaline, its solubility in water is so low that the solution would not be a caustic hazard (causing chemical burns) used in a hand warmer.

which was used at his chemical works, and through which a current of carbonic acid gas passed from a neighboring lime-kiln. This current of gas should have been shut off while the men were at work ...