Investigation of Charcoal and Coke Pig Irons by W. E. Jominy presents a detailed study on the properties of cupola-melted gray iron to gauge the effect of varying the percentages of charcoal and coke pig irons. Conducted under the auspices of the Department of Engineering Research at the University of Michigan, this research was made possible by the Cadillac Motor Car Company. The study suggests that charcoal irons, when melted and cast under identical conditions, are generally stronger than coke irons. Covariates such as pig iron, scrap iron, coke, coke ratio, blast pressure, chemical composition, and molding sand were meticulously controlled throughout the testing process. The research showed that increasing the percentage of charcoal pig iron in the cupola burden consistently resulted in stronger iron, with an increase in strength seemingly proportional to the percentage of charcoal iron used and the quality of the coke and charcoal pig irons. Notably, this increase in strength was not accompanied by a corresponding increase in hardness, a favorable attribute for machining. The investigation also found that stronger iron results from smaller graphite flakes, which were more uniformly distributed in irons with higher charcoal content. The research concluded that adding charcoal pig iron benefits the strength of the resulting cast iron without making it harder, offering a practical advantage in industrial casting processes.