This is the Austin Magic Pistol

From the look of the box, I would guess this toy was produced sometime between 1945 and 1960.

The instructions refer to "Magic Crystals" and water, but we know it is really calcium carbide.

The plastic (cellulose?) ball is just a bit deformed with age.
Many thanks to fellow collector Ron Weingarten, who brought the Austin Magic Pistol to my attention and helped me get the one you see here.