146 
Iron, 
The various shapes may, in point of the principle of 
their construction, be reduced to three. (See Plate, Fig* 
1 , 2 , 3 .) 
To understand properly the objectionable parts of the 
construction of nose-pipes, it must be recollected, that 
much has been said to depend upon the blast reaching 
the opposite extremity of the furnace, as little impaired 
of the compactness and velocity of its original discharge 
as possible. When it is otherwise, the results in the in- 
ternal operations of the furnace must be consequently al- 
tered. If the compression is diminished 1-2 or 2-3ds 
when it reaches the opposite wall, decomposition in that 
portion must be effected before the air has attained its 
elevated situation in the furnace. It is even possible to 
disperse the whole column of air in such a manner that 
the ignited materials of the opposite side may receive little 
of its effects to promote combustion® 
The discharging-pipe Fig. 1. is frequently used : its 
length is 12 inches or more ; the discharging aperture 
3 inches, the other end 5 inches ; but this is arbitrary, 
depending upon the size of the adjoining pipe. From a 
pipe thus constructed, the air disperses or diverges too 
suddenly ; and at a small distance from the orifice, a con- 
siderable portion of it answers but imperfectly the pur- 
poses of combustion. Part of it is speedily decomposed 
and the oxygen brought into immediate contact with the 
iron. The quantity of metal is reduced by the former, 
and the quality injured by the latter. Though long 
custom, by a continued use of such shaped pipes, has 
prevented their pernicious effects from being observed, 
yet they must prove, in many cases, detrimental to the 
^economical distribution of air, and the manufacture of 
iron ; # * 1 
Fig. 2. represents a nose-pipe, of another construction^ 
.even more exceptionable : because the air dispersing still 
