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.