Cars of coke, limestone, fluorspar, etc., are inspected, analyzed and treated in the same way, so that nothing is left to guess work. The compositions as determined by the laboratory serve not only as the basis for acceptance or rejection, but the analyses of accepted materials are forwarded at once to the metallurgists, who from them figure the mixtures to be used in the cupolas. Having great stocks of analyzed raw materials in the labeled bins in the receiver building, the metallurgists who supervise the mixing and melting of the iron determine by mathematical calculation just what irons and how much of each must be taken to give molten iron of the best composition and properties for the castings. [Illustration: TITRATING THE SULPHUR Sulphur is evolved from the drillings as a gas (hydrogen sulphide). This is absorbed in a solution of chloride of zinc. The amount of sulphur is measured by slowly running in from a burette a solution of iodine of very accurately known strength. The iodine unites with the sulphur compound as long as any of the latter remains, but the first drop added thereafter turns blue the whole solution because of the reaction of the excess of iodine with starch paste that has been added previously as an indicator. Accuracy is about .005 per cent of sulphur. ] The total iron materials charged must have a definite amount of silicon, of manganese, of phosphorus and of carbon. For a 4,000–pound charge for soft cast iron, for instance, the total silicon in the materials which make up the charge must be somewhere near 118 pounds, the manganese and the phosphorus about 30 pounds each. The usual losses of these materials through oxidation are known, of course, and sufficient excess has been allowed that the desired final composition will result. [Illustration: TITRATING PHOSPHORUS A yellow precipitate containing the phosphorus is filtered out on filter paper. It is redissolved in alkali and titrated with a standard solution of nitric acid, similarly to the sulphur. The solution in the flask turns pink with the first drop added after the phosphorus has been measured. ] On several scales which are regularly inspected and kept carefully adjusted, the weighers weigh out the prescribed quantities of the raw materials. “Buggies” holding nearly one ton each are loaded in turn with coke, with proper amounts of pig iron, cast iron scrap, sprues from the foundry castings of the preceding day, and a proper weight of limestone flux. Each charge of two tons of iron requires four buggies for its transportation from the raw-material bins and scales to the cupolas.