568 Hie Architectural Review and American Builders' Journal. [Mar., of 10°, in a shaft fifty feet high, would produce a current of eight feet per second, (less the friction,) it would re- quire a temperature of 200°, to produce a motion of thirty-six feet per second, or it would take twenty times the coal to produce between four and five times the effect. To work economically, therefore, the flues should be large enough, to produce the desired results, with a very moderate velocity. Another fatal error, now detri- mental to many of our large public buildings, is to place the coils of steam- pipe, or other arrangements for heating, at the top, instead of the bottom, with the expectation, that the cold air will be so accommodating, as to flow up there itself, to get warmed, before being turned out of doors. Instead of which, the air from above falls in on one side, is heated, and is thus driven out on the other. I have noticed, in many large public buildings lately erected, that attempts have been made to draw down the air, from the third and fourth stories of several detached buildings, and, from thence to conduct it, by one under- ground duct, to the engine chimney, at a great distance. Such complicated and bungling ar- rangements, will, of course, prove fail- ures : Because, when the wind blows hard, on one exposed building, it presses down the duct with great force, entirety overcoming the draught from portions of the building less exposed ; and the foul air, from the windward side of the house and the main duct, is often pressed up into the rooms on the lee- ward side. Another very common error, is to have a flue very large, in some places, but greatly throttled in others, as in the House of Refuge, in Philadelphia, where an immense ventilator was put on the roof, equal, probably, to thirty or forty feet area ; and, emptying into this, were four long, horizontal shafts, made of rough boards, only one foot square each, giving an aggregate of four square feet ; but on the top of the roof, for the public to look at, was the ventilator aforesaid. I have been informed, that this was about the manner of executing the ven- tilation (so called) in the new School- Houses, in Philadelphia, where they at- tempted to use the heated flue, and kept up a fire to create a draught. The chimney was all right, what there was of it ; but, in making the connec- tion with the chimney between the floors, there was only the width of a single brick left out, or probably, not a tenth part of the space there should be. Of course, all such arrangements as these, besides being a disgrace to the profession, and a great injury to the cause of ventilation, are stumbling- blocks in the way of the casual and superficial inquirer for the best system. There are so many causes rendering one flue liable to interfere with another, unless carried the entire distance by a separate tube, that it is undesirable to extend the system of flues to a very great distance, especially in a horizontal direction ; and, in practice, I seldom find any occasion for doing so. It is nearly always possible to find some cor- ner, or space of little value, that can be spared for the purpose, at frequent in- tervals, throughout the building. It is a very good plan, to place the ventilating shaft in the immediate vi- cinity of the water-closets. All the pipes for hot and cold water majr be carried up therein, as well as the soil-pipes and, perhaps, rain-water pipes also. They are thus very convenient for attachment and repairs, and always kept from freezing, while the building is occupied. By reference to the accom- panying plans and sections, it will be seen, that it is proposed to take some of the flues from the floor of the first and second stories down to the cellar, and let them enter the heated shaft at that point. These will drawoff the coldest air of the rooms; and it can, consequently, be drawn down, with the least force. The flues from the top of the rooms, which are liable to be heated excessively
