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the blast furnaces; in like manner as carburetted hydrogen gas was

purified。  The ironmaster supposed that it was the presence of sulphur

in the air that caused blast…furnaces to work irregularly; and to

make bad iron in the summer months。  Mr。 Neilson was of opinion that

this was not the true cause; and he was rather disposed to think it

attributable to the want of a due proportion of oxygen in summer;

when the air was more rarefied; besides containing more aqueous

vapour than in winter。  He therefore thought the true remedy was in

some way or other to throw in a greater proportion of oxygen; and he

suggested that; in order to dry the air; it should be passed; on its

way to the furnace; through two long tunnels containing calcined

lime。  But further inquiry served to correct his views; and eventually

led him to the true theory of blasting。



Shortly after; his attention was directed by Mr。 James Ewing to a

defect in one of the Muirkirk blast…furnaces; situated about half a

mile distant from the blowing…engine; which was found not to work so

well as others which were situated close to it。  The circumstances of

the case led Mr。 Neilson to form the opinion that; as air increases

in volume according to temperature; if he were to heat it by passing

it through a red…hot vessel; its volume would be increased; according

to the well…known law; and the blast might thus be enabled to do more

duty in the distant furnace。  He proceeded to make a series of

experiments at the Gas…works; trying the effect of heated air on the

illuminating power of gas; by bringing up a stream of it in a tube so

as to surround the gas…burner。  He found that by this means the

combustion of the gas was rendered more intense; and its illuminating

power greatly increased。  He proceeded to try a similar experiment on

a common smith's fire; by blowing the fire with heated air; and the

effect was the same; the fire was much more brilliant; and

accompanied by an unusually intense degree of heat。



Having obtained such marked results by these small experiments; it

naturally occurred to him that a similar increase in intensity of

combustion and temperature would attend the application of the

process to the blast…furnace on a large scale; but being only a

gas…maker; he had the greatest difficulty in persuading any

ironmaster to permit him to make the necessary experiment's with

blast…furnaces actually at work。  Besides; his theory was altogether

at variance with the established practice; which was to supply air as

cold as possible; the prevailing idea being that the coldness of the

air in winter was the cause of the best iron being then produced。

Acting on these views; the efforts of the ironmasters had always been

directed to the cooling of the blast; and various expedients were

devised for the purpose。  Thus the regulator was painted white; as

being the coolest colour; the air was passed over cold water; and in

some cases the air pipes were even surrounded by ice; all with the

object of keeping the blast cold。  When; therefore; Mr。 Neilson

proposed entirely to reverse the process; and to employ hot instead

of cold blast; the incredulity of the ironmasters may well be

imagined。  What!  Neilson; a mere maker of gas; undertake to instruct

practical men in the manufacture of iron!  And to suppose that heated

air can be used for the purpose!  It was presumption in the extreme;

or at best the mere visionary idea of a person altogether

unacquainted with the subject!



At length; however; Mr。 Neilson succeeded in inducing Mr。 Charles

Macintosh of Crossbasket; and Mr。 Colin Dunlop of the Clyde Iron

Works; to allow him to make a trial of the hot air process。  In the

first imperfect attempts the air was heated to little more than 80

degrees Fahrenheit; yet the results were satisfactory; and the

scoriae from the furnace evidently contained less iron。  He was

therefore desirous of trying his plan upon a more extensive scale;

with the object; if possible; of thoroughly establishing the

soundness of his principle。  In this he was a good deal hampered even

by those ironmasters who were his friends; and had promised him the

requisite opportunities for making a fair trial of the new process。

They strongly objected to his making the necessary alterations in the

furnaces; and he seemed to be as far from a satisfactory experiment

as ever。  In one instance; where he had so far succeeded as to be

allowed to heat the blast…main; he asked permission to introduce

deflecting plates in the main or to put a bend in the pipe; so as to

bring the blast more closely against the heated sides of the pipe;

and also increase the area of heating surface; in order to raise the

temperature to a higher point; but this was refused; and it was said

that if even a bend were put in the pipe the furnace would stop

working。  These prejudices proved a serious difficulty in the way of

our inventor; and several more years passed before he was allowed to

put a bend in the blast…main。  After many years of perseverance; he

was; however; at length enabled to work out his plan into a definite

shape at the Clyde Iron Works; and its practical value was at once

admitted。  At the meeting of the Mechanical Engineers' Society held in

May; 1859; Mr。 Neilson explained that his invention consisted solely

in the principle of heating the blast between the engine and the

furnace; and was not associated with any particular construction of

the intermediate heating apparatus。  This; he said; was the cause of

its success; and in some respects it resembled the invention of his

countryman; James Watt; who; in connection with the steam…engine;

invented the plan of condensing the steam in a separate vessel; and

was successful in maintaining his invention by not limiting it to any

particular construction of the condenser。  On the same occasion he

took the opportunity of acknowledging the firmness with which the

English ironmasters had stood by him when attempts were made to

deprive him of the benefits of his invention; and to them he

acknowledged he was mainly indebted for the successful issue of the

severe contests he had to undergo。  For there were; of course; certain

of the ironmasters; both English and Scotch; supporters of the cause

of free trade in others' inventions; who sought to resist the patent;

after it had come into general use; and had been recognised as one of

the most valuable improvements of modem times。*

 'footnote。。。

Mr。 Mushet described it as 〃a wonderful discovery;〃 and one of the

〃most novel and beautiful improvements in his time。〃  Professor

Gregory of Aberdeen characterized it as 〃the greatest improvement

with which he was acquainted。〃  Mr。 Jessop; an extensive English iron

manufacturer; declared it to be 〃of as great advantage in the iron

trade as Arkwright's machinery was in the cotton…spinning trade; and

Mr。 Fairbairn; in his contribution on 〃Iron〃 in the Encyclopaedia

Britannica; says that it 〃has effected an entire revolution in the

iron industry of Great Britain; and forms the last era in the history

of this material。〃

 。。。'



The patent was secured in 1828 for a term of fourteen years; but; as

Mr。 Neilson did not himself possess the requisite capital to enable

him to perfect the invention; or to defend it if attacked; he found

it necessary to invite other gentlemen; able to support him in these

respects; to share its profits; retaining for himself only

three…tenths of the whole。  His partners were Mr。 Charles Macintosh;

Mr。 Colin Dunlop; and Mr。John Wilson of Dundyvan。  The charge made by

them was only a shilling a ton for all iron produced by the new

process; this low rate being fixed in order to ensure the

introduction of the patent into general use; as well as to reduce to

a minimum the temptations of the ironmasters to infringe it。



The first trials of the process were made at the blast…furnaces of

Clyde and Calder; from whence the use of the hot blast gradually

extended to the other iron…mining districts。  In the course of a few

years every furnace in Scotland; with one exception (that at Carron);

had adopted the improvement; while it was also employed in half the

furnaces of England and Wales; and in many of the furnaces on the

Continent and in America。  In course of time; and with increasing

experience; various improvements were introduced in the process; more

particularly in the shape of the air…heating vessels; the last form

adopted being that of a congeries of tubes; similar to the tubular

arrangement in the boiler of the locomotive; by which the greatest

extent of heating surface was provided for the thorough heating of

the air。  By these modifications the temperature of the air introduced

into the furnace has been raised from 240 degrees to 600 degrees; or

the temperature of melting lead。  To protect the nozzle of the

air…pipe as it entered the furnace against the action of the intense

heat to which

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