Me. George Thomson on Blast Furnaces. 



' 3d, Influence of Blast — In cold blast work- Fio. ■*• 



ing, some practical men hold that the density 

 of the blast sliould not exceed 2 lbs. to the 

 inch, while others work it as high as 3 lbs. to 

 the inch, or even more. In re-smelting also 

 in the cupola, many prefer the fanners, which 

 give a mucli softer blast than the old method 

 of the cylinder ; while others, after having tried 

 the fanners, have returned to the original 

 and stronger blast of the cylinder. We cannot 

 suppose that this is altogether fancy or preju- 

 dice ; I have no doubt that the differences of 

 the material subjected to the blast, is the cause, 

 in a great measure, of such opposite results. 



At Lightmoor, the various requirements of 

 blast to make the best yield, with the different 

 coals, were striking ; coal No. 1, (of Table I,) 

 which is the best, required a considerably less 

 dense blast than the inferior. No. 2, (yard 

 coal.) Indeed, blast, either in volume or pres- 

 sure, seemed to bo of little consequence to the 

 working of the clod coal — from 1| lbs. to 21 

 lbs. to the inch, the yield was not affected, 

 the only difference being a slight increase of quantity. Nor did 

 diffusing the blast by a number of tweres seem to make a material 

 difference. It is a fact that, with this coal, and a furnace of ordinary 

 dimensions, 60 tons of iron have been made in a week by one blast 

 pipe onlyy the muzzle only 3 inches diameter, or 9 circular inches of 

 blast. 



On the other hand, the inferior, or as they are called there, the " sul- 

 phury " coals, required a highly compressed blast to bring them to 

 their best yield — one under 2\ lbs. to the inch gave very inferior 

 results ; compare this with Mr. Gibbons' result — his materials seem 

 well adapted for cold blast working — and we find density of blast 

 not a great object to them. 1 lb. 13 oz. only was his density at 

 tweres, and this continued the same although he doubled the capacity 

 of his furnace. 



These general facts seem to contradict the opinion, that the whole 

 rationale of the effect of the hot blast is merely a decrease in the 

 density of the blast, because, with the inferior material, which requires 

 with cold blast the greatest density, the hot blast has the greatest and 

 best effect. 



Those who are acquainted with cold blast working, know that most 

 materials work best with what is technically called a " snuff " at the 

 tweres ; and to form this it is usual to blow a few inches below the 

 surface of the scoria, which floats on the iron in the hearth. The 



