On and after the first day of August, Anno Domini one thousand nine hundred and one, each and every keg of black blasting powder used, manufactured or sold in and around the coal mines of this Commonwealth, shall contain twenty-five pounds of said black blasting powder, standard weight; every one-half keg shall contain twelve and a half pounds of said black blasting powder, standard weight, and every quarter keg shall contain six and one-quarter pounds of said black blasting powder, standard weight; each of said kegs to be plainly stamped with the name of the person, firm or corporation manufacturing said powder, and also the number of pounds of powder contained in said keg.