IRON 971 



being tho same through the whole horizontal sectional area at that height, and conse- 

 quently arriving at the zone of fusion in an equally prepared state. If the mouth of 

 the furnace be too wide, the heated gases have a greater tendency to pass up the sides 

 than through tho centre, thus destroying the horizontality of the lines of equal tem- 

 perature, and giving thorn a curved form with the convex side downwards ; hence ores, 

 at different temperatures, and of various stages of preparation, will occupy any given 

 horizontal sectional area of the furnace ; these descending together and mixing in the 

 zone of fusion will produce evils in proportion to the extent of the deflection of the 

 curves from a horizontal line. On the contrary, if the mouth of the furnace be too 

 narrow in proportion to the other parts, we may expect an undue portion of the gases 

 to pass up the centre, leaving the minerals around the sides comparatively unacted 

 upon. It is easy to see that evils of the same kind as before must exist here, the 

 isothermal lines becoming now concave downwards, instead of convex, giving as before, 

 through any horizontal section of the furnace, ores at various temperatures, and at 

 different degrees of deoxidation or carburation, according to the depth which they may 

 have attained in the furnace. There are several instances of furnaces originally built 

 with too narrow tops, being greatly improved by widening them ; this may conve- 

 niently be done by feeding them through a conical charger, which, by lowering the 

 surface of the minerals, virtually increases the width of the mouth : on the other 

 hand, furnaces having the opposite defect of being too wide at the top, may be 

 benefited to some extent, provided the walls are nearly perpendicular, or do not widen 

 too rapidly downwards, by employing as large a cone as it is possible to work in the 

 throat ; for, by the use of this feeder, the minerals must fall close to the sides, and 

 the larger lumps roll to the axis of the furnace, and so facilitate the passage of the 

 gases in that direction, besides giving to the surface a concave or cup form, and 

 consequently a diminished height and resistance to the upward current in the middle. 

 This principle of improving the charging of such defective furnaces is even carried 

 out to some extent in feeding open-top furnaces where the gases are wasted. The 

 charging-plate is so placed as to prevent the nose of the barrow from projecting any 

 distance into the furnace ; the minerals, being thus discharged close to the edge, the 

 larger lumps have a tendency to roll over towards the centre, leaving the smaller at 

 the ring-walls, to check the upward current in that direction. 



The above considerations will materially assist in furnishing an answer to the oft- 

 repeated and very important question, ' What form and proportions should a blast- 

 furnace have to produce the best results in quality of iron, and in economy of fuel, 

 whether worked on the open-top principle, or enclosed for the purpose of utilising 

 the waste gases ? ' Experience has proved that when the mouth of the furnace is 

 one-half the diameter of the widest part, good work is obtained, and that any de- 

 viation from that proportion, if in excess, has been productive of great derangement 

 in its action. The height of the furnace should also bear a certain proportion to 

 the greatest diameter, in order to secure an uniform flow of the ascending current 

 through all its parts ; for if the widest part bear too great a relation to the height, 

 the boshes must necessarily be of a low angle, and consequently the minerals 

 -1044 around the sides near their top be at too great a distance 



out of the direct line of passage of the ascending current, 

 and consequently remain only partially prepared for fusion. 



The proportions recommended by Mr. Parry, and which 

 have been practically tested most satisfactorily in several 

 instances, are as shown in fig. 1244. The mouth b' b' one- 

 half the diameter of the widest part c c, and this should not 

 be at a less depth than its own diameter. The sides of 

 the furnace to this depth should be formed slightly dome- 

 fashioned, for the purpose of giving to that region a larger 

 capacity than would be obtained by a conical form. The 

 radius of the curve should be at right angles to the axis of 

 the furnace, and formed by a prolongation of the line repre- 

 senting the greatest diameter. When the radius is set at a 

 great angle with this line, which is t>ften done to give greater 

 capacity to the domed part, the distortion produced by the 

 sharpness of the curve may leave a segment of the minerals 

 unacted upon by the gases in their passage to the mouth, and 

 entail greater evils than would be compensated for by in- 

 creased capacity. The curve is continued below the widest 

 part of the furnace till it meets the top of the boshes d d, 

 the angle of which should not be less than 70, and start from the point of the 

 tuyeres //. The depth also from the widest part to the tuyeres should not be less 

 than its own diameter plus half the diameter of the tuyeres. These proportions 



