At the top the conditions of abrasion are extreme, as has already been described, while the temperature in good practice in this zone of the furnace is generally below 1000°, so that the necessity of refractory character in the lining of this zone can be to a certain extent neglected, or at least need only receive an insignificant amount of attention as compared with what it demands in the lower zones. For this purpose the bricks are made with a large proportion of plastic clay pressed very hard, and burned to a great density, some of them resembling what is known as vitrified paving brick almost as much as they do firebrick, and for the same purpose, resistance to abrasion.

Where no form of stock-line protection is used such as those described above or an equivalent, the quality of the top brick is fully as important as that of the hearth and the bosh brick, since top bricks which do not resist abrasion permit the stock line to be gouged out by the drop of the stock from the bell, with the result that the correct distribution of the stock is made impossible and becomes largely haphazard, this is necessarily followed by extremely bad operation in the lower portion of the furnace, with the result of poor quality of iron, or high fuel consumption, or both. For this reason the necessity of repairing the stock line has in the past been responsible for an appreciable percentage of all the cases in which it has been necessary to blow out for repairs, though the fact may not have been apparent in all cases, because when a furnace which has been working well gradually begins working worse and worse, it is commonly and in general rightly, assumed that the lining is too far gone to permit it to do further good work, and without any analysis as to the location of the wear which is responsible for the bad work, it is generally attributed to the inwall, although the top may be the part to blame.

It is unfortunate that more exact and accurate knowledge is not at hand on the subject of firebrick and their suitability for lining purposes, but the problem is so complicated that a complete analysis would be possible only after years of experience by an organization which contained both an experienced firebrick maker and experienced furnacemen, a condition which has seldom if ever existed.

The firebrick manufacturer has, therefore, to adapt his product to the conditions described by the furnaceman, and the furnaceman has to use the brick furnished to him by the brick maker in the prayerful hope that they will give the results desired, but in the vast majority of cases without any better foundation for this hope than his confidence in a given brand of brick, and perhaps his belief that a certain brick maker understands the conditions well enough to provide him with a suitable lining.

It is greatly to be desired that the furnaceman and brick manufacturer should meet directly rather than through their respective selling and purchasing agents. By discussing frankly and without prejudice their respective objects and difficulties progress would be made in real knowledge of this subject with resultant benefit to both.

I have already described the enormous change in the furnace conditions which began in the middle nineties. The greatly increased outputs and the vast increase in percentage of fine ore used in the burden, in combination with the introduction of mechanical charging brought about conditions under which the lining problem seemed to be almost insoluble. I know on the best authority that one of the largest brick makers was desperate at one time over the situation and would have been glad, had he felt that he could afford to do so, to surrender the furnace-lining portion of his business.

It seems extremely likely from the information which has been developed within recent years concerning methods of charging, that these have been more responsible for unsatisfactory life of linings than was the poor quality of the linings, in many cases in which the firebrick manufacturer had to take the blame.

It has long been known that bad filling would rapidly destroy a lining by channeling, but certain types of mechanical charging which are theoretically correct produce conditions in practice under which it would be impossible for any lining to survive for any considerable length of time.

This matter really belongs under the subject of stock distribution and will be treated at greater length in an article on that subject.