THE MANUFACTURE AND PROPERTIES OF COKE. 17
for obtaining the best " selected " coke is that of cooling off the coke inside the ovens and in picking out the black ends and fine as well as poorly burned coke. There are times when coke is burned from ninety-six to one hundred and twenty hours, and then again only coked twenty-four hours in bee-hive ovens; but this latter product is generally not suited for making or melting iron. It is said that if coke makers take the precaution, they can make 24-hour coke nearly as good as the 48-hour article, with the exception of its not being quite as long in its body.
Gas house coke is obtained from the retorts used in gas works to produce illuminating gas, or from the retorts used in manufacturing coal-tar or other byproducts. Some kinds of coal will produce gas coke by the use of which iron can be melted. Coal of the quality found in the Connellsville region is suitable for making this coke. When gas, or soft coke, is used for melting it is often necessary to iise double the quantity or number of bushels than of hard oven coke, and at its best it is an undesirable 'fuel for this purpose. It will often give good satisfaction in drying cores or moulds, and work even better than hard coke, but much more of it must generally be used than of the oven, or hard coke.
Comparison of Connellsville coke with others has shown that the opinion held by many that Connellsville coke could not be equalled, was an error. The localities shown in Table 5, by Mr. John"R. Proctor, published in the Kentucky Geological Survey Report, are furnishing considerable good coke to furnacemen and founders,and hence the former will give a greater yield from the same amount of coal. The method usedt has proved an excellent fuel for this and kindred uses.''