90 Mr. George Thomson <m Blast Furnaces. 



"snuff" is a kind of arched tube formed by the cinder at the end 

 of twcro iu the inside of furnace, and through which the blast passes. 

 Now it appears to me that this natural muzzle of cinder has a great 

 deal to do in diffusing the blast in contact with the material ; and, 

 mark that those materials which, from inferiority, required blast of 

 the greatest density, gave the greatest trouble at the tweres, and 

 presented practical difficulties in the " snuffing," which required 

 a great pressure mechanically to overcome, and clear away for the 

 passage of the blast upwards ; for such materials (from what cause I 

 know not) always work with great uncertainty at the tweres — sometimes 

 having a tendency to stop up entirely, at others not snuffing at all. 



If tliis practical difficulty could be avoided, perhaps the bad material 

 might give a better result with a soft blast than we found it to do. 



As regards the blast's density, when used hot, it must of necessity 

 be mucli less than cold ; for the quantity of air injected from the 

 blowing apparatus is, generally speaking, no more with hot blast than 

 with cold, while the area of the nose-pipes, taken together, is doubled 

 or trebled. The diffusion of the blast by increasing the number of 

 nose-pipes, and disposing them around the hearth, has produced great 

 increase in make ; and in some cases by this, together with increased 

 shape, coals have been brought to work raw, which, with the first hot 

 blast trials, could only be used when coked. 



It seems agreed on all hands, the greater the number of the tweres 

 around the hearth the better : and as I am aware that practical diffi- 

 culties occur in doing so by the furnace " blowing forward," I will state 

 a simple plan by which we overcame the difficulty. In building our 

 furnace we had a round base, as is now common, but instead of the 

 usual four openings, we made five — one for the opening of the hearth, 

 and four for tweres. By this method the blast from one twere does 

 not blow against the other, and neither of them blow directly to the 

 fore part ; thus eight tweres may be used — two at each twere side. 



More pressure is required even with hot blast to work some ma- 

 terials than others. For instance, we required but 2\ lbs. per inch 

 in North Staffordshire when working coke, but with coal, 3 lbs. per 

 inch, with much greater heating surface, was required. The quantity 

 of blast required here was very great. Blowing at four sides, we 

 injected into a furnace fully 3000 cubic feet of air per minute, and 

 heated to a high temperature. If this pressure happened at any time 

 to be reduced, the effect was immediately perceptible, or if one of 

 the tweres was taken off, a falling off in quantity and yield was the 

 immediate consequence. The materials were, as I have before noticed, 

 the worst I ever saw ; both coals and ironstone being sulphury. 



I will give only one other fact, a very extraordinary one, showing a 

 most peculiar effect produced by a simple increase of temperature^ at a 

 work near Tipton, where the materials are of fair quality. The furnace 

 upon which the experiment was made is only 11^ feet at "bosh," and 



