INTRODUCTION. LITTLE if anything was done towards the application of machinery to the purposes of ventilation until very recent years, although, so early as the year 1657, Agricola, in his interesting work "De re Metallica," gives particulars and a drawing of a mechanical ventilator for mines, driven by water-power, and at the Hartz mines, nearly 200 years ago, another, somewhat similar to the Struve, was in operation. In the year 1849, Mr. Warrington Smyth referred to this in his evidence before the House of Lords' Committee, and at the same time Mr. Struve said his ventilator at the Eaglesbush Colliery, then the only place where it was yet applied, began its work in February 1849. Mr. Brunton also then explained and gave drawings of his centrifugal ventilator. But so late as the year 1852 a Committee of the House of Commons reported : "Your Committee are of opinion "That any system of ventilation depending on complicate machinery is undesirable, since under any disarrangement or fracture of its parts the ventilation is stopped or becomes inefficient. "That the two systems which alone can be considered as rival powers are the furnace and steam jet. "Your Committee are unanimously of opinion that the steam jet is the most powerful and at the same time least expensive method for the ventilation of mines." In 1861 the centrifugal fan at Elsecar was described to the North of England Institute of Mining Engineers by the late Mr. J. J. Atkinson, and to him must be given the credit of having, in several valuable papers on the subject, first shown clearly the superiority of mechanical ventilators over every other system. From that time until now the question as to which fan is the best has been a source of constant contention; every fresh invention being introduced as at least 10 per cent. better than anything which preceded it. Numberless experiments have been made by private individuals and committees to ascertain the truth of these questions. Nearly all the results obtained have varied, and the question to-day still remains unanswered-" Which ventilator is the best; and which, taking all circumstances into account, should I, as a mining engineer, adopt ?" The cause of this unsolved state of the problem is not far to seek. The useful effect of a fan is not the only question involved. We must consider 1. First cost; 2. Durability; 3. Efficiency. The enormous first cost and want of durability of some of our largest ventilators, has overshadowed in a great degree the question of efficiency, especially where, as at many collieries, steam is obtained from the heat of coke-ovens. Some of the results published as to efficiency, are the work of experimenters quite unused to the rigorous accuracy demanded in scientific research, still it is very important, and to appreciate reliable data, such for instance as the recent report of the North of England Institute, there is wanted a general knowledge of the laws governing the variation in results under varying conditions of work. To supply this hitherto un supplied need of the engineer in England, I have been led to translate and publish the very excellent treatise of M. Murgue. Many attempts have been made to follow these laws of ventilators, but nothing approaching the lucidity of his methods has been attained; a little attention and study on the part of those who care thoroughly to understand the various questions involved, will give a perfect mastery over them, and then when seeking to know which is the best ventilator, they will at least be able to make the selection with their eyes open. The leading ideas given by M. Murgue are― First, That every mine may be assimilated to an orifice in a thin plate, which he calls its " Equivalent Orifice." Second, That a ventilator, even whilst exhausting the air from the mine, forms at the same time an obstacle to the passage of this air, causing a sensible loss of duty, so that the depression produced by the ventilator is always higher than what we observe in the galleries of approach, some part of this depression being employed in overcoming the various resistances in the fan; this he treats as the "Orifice of Passage." Third, The theoretical depression or water gauge, due to the speed of the periphery, is in a perfect fan equal to twice the height of column necessary to generate such velocity in a falling body. This meets a difficulty experienced by a writer on the subject, who says "It is especially worthy of notice that the water gauge indicated at the inlet is greater than the theoretical result," the hitherto recognised theory having been u2 where u = speed in feet per second, and g = 32.2. 2 g' Fourth, That there is an initial depression which each fan * See 'Proceedings of Northern Mining Institute,' vol. xiv., p. 80. |