Many attempts had been made to use the skip for filling purposes as well as many other mechanical appliances, which would at least permit the elimination of men to dump the barrows at the top, since these men were usually the hardest worked, and always the ones with the greatest capacity for doing harm, by improper dumping. But the results of all these early attempts had been excessively unsatisfactory because the work of the furnace was so much poorer that increased fuel consumption, diminished output, lowered quality of product, and reduced life of lining amounted to very many times more on the debit side of the ledger than the slight saving of labor on the credit side.

In that early day it is well to note that the barrows were generally filled by hand shoveling, furnace operators having been exceedingly slow in realizing the value of bins. The impression that the greater portion of the work of the bottom fillers could not be reduced explains why the early attempts at mechanical filling were directed mainly at eliminating the top fillers. This made the saving relatively small, while the loss due to bad distribution may easily be, in fact generally is, of enormous proportions, and may quickly convert a profitable into a bankrupt concern.

With the rapid increase in output which took place in the early nineties and culminated in the Duquesne revolution, the difficulties of filling the furnace became more and more serious. In addition to the vast difficulty of training and keeping crews of the size necessary to do this work by hand, and of supervising their performance of it to secure good furnace operation, it became almost a physical impossibility to handle the number of barrows required, and get them on and off of the hoist platform at the top and bottom of its travel, even though the operation was kept up at the highest possible pressure for twenty-four hours a day and practically without intermission. If any interruption occurred it became more and more difficult to "catch" the furnace after the stock line had gone down below the proper level; the fillers were kept almost up to their maximum speed to keep even with it under normal conditions and obviously had to make a stern chase in order to overcome any lead that it might get by an interruption in the charging.

The great expense of this method also became more and more obvious as the number of men required increased, and looking at the matter from the financial point of view it was well worth while to make an investment which would eliminate the labor of sixty men, while the same investment to eliminate the labor of only twenty might be a very poor one. In other words the annual cost was high enough to pay fixed charges on a heavy plant investment if a suitable means could be found for filling the furnace mechanically.

The necessities of the case were so great that renewed and more extensive efforts were made to solve the problem of stock distribution mechanically, and in the middle nineties a number of designs were brought out by various engineers for the accomplishment of this purpose.

There are two broad classes of mechanical filling as already described in Chapter II (Filling The Blast-Furnace) which may be broadly called "bucket filling" and "skip filling." There are several varieties of each, though the variations are much more matters of detail than of principle. It will be easier to discuss the points of the bucket system after considering the different types of skip filling, and we will therefore consider the latter first.