SECT. 4. No person shall sell to any child under the age of sixteen years without the written consent of a parent or guardian of such child, any cartridge or fixed ammunition of which any fulminate is a component part, or any gun, pistol, or other mechanical contrivance arranged for the explosion of such cartridge, or of any fulminate. But the provisions of this section shall not apply to paper caps of which the only component parts are chlorate of potash and sulphide of antimony, nor to any appliance for exploding the same. The provisions of this section shall be inserted in every license granted for the sale of gunpowder.