ished 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