<3I6 



BLOWING. 



Blowing, ty into a furnace, for the purpose of increasing its 

 '" t ""-' combustion. 



When large bellows are employed for this purpose, 

 or when the air is pumped from a cylinder directly 

 into the furnace, it is introduced in irregular puffs, 

 which are completely insufficient for the intended 

 purpose. In order to equalise and continue the blast, 

 three different contrivances have been adopted. The 

 Regulating first method is by a regulating cylinder, which is fit- 

 cylinder, ted with a piston heavily loaded, having at least three 

 pounds on the square inch. The air which is pump- 

 ed from the blowing cylinder, passes into the regu- 

 lating cylinder, and as this cannot escape, it will, of 

 course, raise the loaded piston. The twere, or pipe, 

 which conveys the air out of this cylinder into the 

 furnace, is connected with this cylinder, so that when 

 the mouth of the twere is open, the air will rush from 

 the regulating cylinder into the furnace, and the 

 weight of the loaded piston will force the air through 

 the twere with a constant blast during the intervals 

 between each stroke of the piston of the blowing cy- 

 linder. This method was originally adopted in blast 

 furnaces ; but though the quality of the air is subject 

 to little alteration from any change in the atmo- 

 sphere, yet the regulating cylinder has several disad- 

 vantages. Owing to the small capacity of this cy- 

 linder, the blast is not altogether free from irregula- 

 rities. A considerable quantity of dense air, likewise, 

 escapes by the sides of the piston ; and if this is re- 

 medied by fitting the piston closer to the cylinder, 

 the friction is so much increased, that the piston does 

 not follow the air fast enough down, and the blast 

 weakens a little at the end of every stroke ; while at 

 the beginning of the succeeding stroke, the air must 

 overcome this friction before the piston will rise, and 

 hence another puff accompanies the commencement of 

 each stroke. 

 Air vault. The second method of equalizing the blast, is by 

 discharging the air from the blowing cylinder into an 

 -airJtight apartment, or air vault, the air being pre- 

 vented from returning into the cylinder by a valve. 

 Let us suppose that the air vault is of such a size as 

 to contain 100 fulls of the blowing cylinder, and that 

 the nose pipe, which discharges the air into the fur- 

 nace, is stopped. After the engine has made 25 

 strokes, and forced into the air vault 25 cylinders of 

 air, the air vault will then contain 125 cylinders of 

 air in a state of condensation, and having a force of 

 three pounds upon the square inch. Let the nose 

 pipe be now opened, and let it be of such a size as to 

 discharge one full of the blowing cylinder during one 

 stroke of the engine. The blowing cylinder will 

 then supply the air vault as fast as the air is carried 

 off by the twere, and the blast will be very equal ; 

 the end of each blast being only about two parts 

 weaker than the beginning of the blast. It is ob- 

 vious, that the elasticity of the condensed air will 

 keep up the regularity of the blast during the inter- 

 vals between each stroke of the engine. The air 

 vault. at the Devon iron works is excavated out of 

 the solid rock. It is 72 feet long, 14 feet wide, and 

 13 feet high, and contains about 13,000 cubic feet of 

 air. Mr Mushet is of opinion, that the air from the 

 air vault is of a very bad quality for the purpose for 

 which it is required. " This immense magazine of 

 compressed air," he observes, " generates a consider- 



able portion of heat, which greedily seizes the damps 15 

 which are unavoidable in under ground excavations, '- - 

 and conveys them to the furnace. In the summer 

 months, the air becomes so debased, as to affect the 

 quality of the iron, and change it from grey to white. 

 Every change in the temperature of the atmosphere, 

 during this period, is indicated by various changes in 

 the furnace." 



The third method of equalizing the blast is, by the W.iter 

 water vault, or water regulator, which is described in regulator, 

 the following article, and represented in Plate LXIII. Plate 

 The water regulator has the advantage of a steady LXIII. 

 and cold blast. No air is lost, as in the case of the 

 regulating cylinder, and no irregularity arises from 

 friction. The air, however, always contains a con- 

 siderable portion of moisture from its being in con- 

 tact with water; and the blast is so cold, that the 

 temperature of the discharged air seldom exceeds 

 38, when the temperature of the atmosphere is 60 

 65 and 70. 



The effect of the blowing engine depends, in a 

 considerable degree, on the density of the air, and 

 the velocity with which it enters the furnace. Mr 

 Mushet is of opinion, that the area of the discharging 

 pipe, and the compression of the blast, depend on the 

 qualities of the coals employed. " A soft or mixed 

 qualify of coal," he observes, " is more susceptible 

 of combustion than either the splint or clod coal ; the 

 consequences of which is, that unless the necessary 

 compression of air is used, decomposition is too early 

 accomplished, and the cokes become oxygenated by 

 combustion in a greater ratio than is^prope'r for the 

 carbonation of the metal. To avoid this, the column 

 of air ought to be discharged, in the case of soft 

 coals, under such a degree of compression as to resist 

 entire decomposition in the ignited passage." From 

 this cause, the density of the blast should vary from 

 2 to 34- pounds in the square inch. Mr Roebuck 

 supposes, that, " with the given power, it is rather 

 by a great quantity of air thrown into the furnace 

 with a moderate velocity, than by a less quantity 

 thrown in with a greater velocity, that the greatest 

 benefit is derived in the smelting of iron stones in 

 order to produce pig iron." " Chemically speaking,'? 

 says Dr Robison, " it seems to be the quantity, not 

 the density of the air, which renders it effective in 

 the iron furnace. Yet I can conceive a great quan- 

 tity of air sent through a furnace without effect, be- 

 cause, being spread through much of the materials, 

 it consumes the fuel too slowly in the different parts 

 of the furnace for raising the smelting heat, whereas 

 the same quantity made more dense, by crowding it 

 into one part of the fuel, will rapidly consume it, and 

 give out all its heat in a very narrow space, and thus 

 produces effects which cannot be produced in any 

 other way." For some of the preceding observations, 

 we have been indebted to a manuscript paper of the 

 late Professor John Robison, which, we believe, was 

 the last production of that distinguished philosopher. 

 It is an answer to several queries of Mr Grieve re- 

 specting blowing engines ; and we hope to have it in 

 our power to present it to our readers in a future 

 part of our work. For farther information on the 

 subject of this article, see Smeaton's Reports; Roe- 

 buck, Phil. Trans. Edin. vol. v. p. 31.; and Mushet, 

 Fhil Mag. vol. vi. p. 60, 113, 362. (*) 



