Iron. 



310 



of the coke, with which the ore has been surrounded in 

 the cementing part. The appearance of the metal, when 

 it flows from the furnace, will indicate when the coke 

 has been used in excess. A substance floats upon the 

 surface of the metal, which, when cold, has a shining 

 appearance resembling plumbago, and is known to the 

 workmen by the name of kish. The presence of this 

 substance shows that the metal is saturated with car- 

 bon ; since it is found to consist principally of carbona- 

 ceous matter. If it is produced in any considerable 

 quantity, it gives the iron master a hint to increase the 

 burden of his furnace, by increasing the proportion of 

 ore. 



The appearance of the cinder is, also, a good crite- 

 rion for snowing *he working order of the furnace, as 

 well as the quality of the iron. When the ore is not 

 sufficiently cemented, unchar ; ed oxide, in some cases, 

 and the defect of carbon, allov s a considerable quantity 

 of the oxide of iron to incorporate with the cinder ; by 

 which it assumes a greenish-yellow colour, which is 

 not so favourable an appearance as the blue tint, or 

 when it has the least colour. 



In some instances, when the furnace is in very bad 

 condition, the cinder becomes of so dark a green, as to 

 appear almost black ; this arises from a great excess of 

 oxide of iron, which has escaped reduction iii the fur- 

 nace. This cinder is very fusible, from the presence 

 of the oxide, and is considered a very unfavourable ap- 

 pearance. The cinder which has the least colour, soon 

 becomes solid after it flows from the furnace, from its 

 containing less of the oxide of iron. This shows that 

 the cementing process is carried on to a proper extent, 

 1>y which the oxide has been converted into carburetted 

 iron, in which state it no longer can combine with the 

 earthy matter, and deserts it when the cemented masses 

 arc melted by the action of the blast. The blue tint 

 in the cinder, which, in some instances, is almost as 

 vivid as ultramarine, generally accompanies the more 

 colourless cinder, and owes its colour, in all probability, 

 to an oxide of iron, containing less oxygen than the 

 black oxide. This may throw some light upon the 

 mystery of the black and red oxide of iron being com- 

 bined with quantities of oxygen, which are as 2 to S, 

 indicating the existence of a third oxide, which, in all 

 probability, is that to which the cinder owes its blue 

 colour. This idea is strengthened by the fact, that it is 

 never produced but when there is the least oxide of 

 iron in the rest of the cinder. Much light may be 

 thrown on the subject of iron smelting, by a series 

 of experiments upon the relative probability of diffe- 

 rent proportions of the earths. Previous to such a 

 course of experiments, however, it might be advisable 

 to make a correct analysis of the best cinder, which is 

 that freest from colour, and at the same time fusing 

 with the least heat. 



We have generally stated, that the furnace above de- 

 scribed, is supplied with 25,000 cubic feet of air in one 

 minute. This fact is obtained from the area of the 

 blowing cylinder being 12.56 feet, and the capacity 

 100 cubic feet, which being discharged 25 times in 

 one minute, gives 2500 cubic feet in the same time. 

 The steam cylinder is 32 inches in diameter, and the 

 piston moves through 200 feet in one minute, work- 

 ing, it is stated, with lOlbs. upon an inch. Then 

 by multiplying 10, the pounds upon an inch of the 

 steam cylinder, by 5.585, the area of the same, and 

 dividing the product by 12.56, the area of the blowing 

 cylinder, we get 4.44 Ib. for the force of the blast upon 

 a square inch, which is about the average in practice, 

 as shown by a measured guage attached "to the blowing 



I R O k 



machine. This pressure would give a velocity equal 

 to 635 feet per second. 



It', however, 2500 cubic feet of air he discharged through 

 a circular aperture of 2 J inches in diameter, in one mi- 

 nute, this would give a velocity equal to 1073 feet per 

 second. This indicates a loss of air at the waste valve 

 equal to 23 cubic feet at each stroke of the engine. If 

 no air were forced out by the waste valve, and 2500 

 cubic feet had to be expelled in one minute through the 

 above aperture, the pressure of the blast would require 

 to be equal to 2 1 Ib. upon a square inch, and the area 

 of the steam cylinder more than 17 feet, and its diame- 

 ter about 4 feet 8 inches. If the present nose-pipe be 

 used, and the blowing cylinder discharged 25 times in 

 a minute, the area of the latter, supposing the piston 

 still to move at the same rate, will be 7.25 feet, its dia- 

 meter being a little more than 3 feet. If the steam 

 cylinder, the blo'wing cylinder, and the speed and pres- 

 sure remain the same ; then, to prevent any escape at 

 the waste valve, the diameter of the nose-pipe must be 

 a little less than 3<} inches instead of 2f , its present dia- 

 meter. In order to estimate the quantity of air which 

 is blown into a furnace, it would be incorrect to take 

 that which enters the blowing cylinder, as it will be 

 frequently much less. Hence the quantity should be 

 estimated by the velocity and the area of the nose-pipe, 

 the velocity being first determined by experiment, by 

 observing the pressure upon a column of mercury, 

 since the velocity of air is as the square root of the 

 pressure. 



Let V = the velocity of air into a vacuum, with the 

 pressure P, which may be deemed 1 5 pounds upon 

 a square inch. 



Let p be any additional pressure, and v its velocity. 

 Then, since P-J-/J acts against P when the air is dis- 

 charged into the atmosphere, we shall have p for the 

 moving force. Hence, from the above fact we have 



P+p 



- 

 v " 



Let A r: the area of the steam cylinder. 



S := the pressure of steam upon a square inch. 



a = the area of the blowing cylinder. 



p = the pressure of the air upon a square inch, 



the same as the above. 



b = the space the pistons pass through in 1 second. 

 v =: the velocity of the air's discharge through 



the nose-pipe. 

 n =s the area of the nose- pipe. 



Then an = SA. 

 SA 



Then from the above theorem 



SA _ 







P+/> 



Pa + SA 



P+p 



also when no air escapes at the waste valve. 



The value of v may also be obtained from the follow- 

 ing operation, n v=a I and v , but in this case no 



n 



air must escape at the waste valve, it will then be more 

 safe to get it from the theorem first given, in which p 

 is obtained by experiment, or by the following equa- 



SA 

 tion, p a = SA, and;? = From these two equations 



all theorems may be obtained for calculating the difl'e- 



