Even with the best possible practice several tons of fireclay are used in laying the lining of a furnace, and this being mixed with something like an equal weight of water there is a great quantity of water in the lining when the brick laying is finished. This is capable of doing great damage and should therefore be removed by thoroughly drying the lining before the furnace is put into operation.

Various methods are in use for this but usually a temporary brick oven is built immediately in front of the tapping hole, and communicating with the furnace through it. The bell is closed and draft produced either by opening the bleeder or allowing the main draft stack to draw on the furnace through a stove. A fire is built in the temporary oven and the gas from this passes into the furnace and warms it up, drawing out the moisture from the face of the brickwork first, and gradually as the heat works through drying out the whole mass quite completely.

The hot gas also acts as a carrier for the steam formed from the moisture and takes it out of the furnace. This drying-out process lasts anywhere from one to three weeks according to the judgment of the furnace manager and the state of the iron market.

There is no doubt that the operation is much better carried on slowly than rapidly, but a very moderate rate of firing will bring the warmth through a wall of 2 ft. or 3 ft. thickness in the course of three or four days, and a week of this treatment is in general sufficient to dry out the clay about as thoroughly as it can be done by this method. Of course, if the furnace is ready for operating before the rest of the plant, it is well worth while to continue the fire for drying out for two or three weeks or even longer if convenient. But in my judgment three-fourths of all the benefits to be obtained by drying will be obtained in the first week of moderate but steady firing, day and night.

The removal of this moisture not only prevents the possibility that the rapid heating which would come from the actual operation of the furnace on a green lining would convert the moisture of the fireclay into steam so fast as to drive the clay out of the joints, and perhaps blow objectionable holes through the packing at the back, but it also eliminates the very objectionable effect of moisture on the operation of the furnace while blowing in, when it is already very cold by reason of the fact that its initial charge is not preheated in its descent, but necessarily cold clear to the bottom.

I have never had any experience with blowing in on a green lining, but I should expect that much more fuel would be required for the first two or three days of such blow-in than would be required on a furnace with a thoroughly dried and warmed lining, and that the difficulty and delay in getting the furnace into normal operation would be much greater.