322 WARMING AND VENTILATION. 



At tlie foot of this chimney, a grate, separated from the walls and 

 placed about 3 feet above the ground, should contain a coal-fire, which 

 will give to the draught the necessary strength. Experiments show 

 that with proportions about equal to those that have been mentioned) 

 140,000 to 1GO,000 cubic feet of air an hour can be carried oif from a 

 well-lilled lecture-room to every pound of coal burned. On the preced- 

 ing data, the number of pounds of coal to be burned may be calculated 

 from the number of persons in attendance, allowing to each 1,000 cubic 

 feet of air an hour, and the surface of the grate may be determined on 

 the condition that each square foot is to consume 4 pounds an hour, 

 which corresponds to a slow fire. 



Doors and valves should be placed iu this gallery to check the motion 

 of the air as required. 



If in the lecture-room substances that give off bad smells are produced, 

 ventilating-pipes should be arranged under the furnaces, or under the 

 table, which should be 2^ or 3 square feet in sectional area, and pro- 

 longed, if desired, directly to the chimney instead of terminating in the 

 gallery. The openings of these pipes in the furnace or in the table should 

 be closed whenever it is not necessary to use them. 



121. Admission of fresh air. — Generally it will be well, when the con- 

 struction permits, to make the air flow in through the roof over the lec- 

 ture-room, which should in that case be close and ceiled, or in an inter- 

 joist, whence it will descend into the room through openings uniformly 

 spread over the surface of the ceiling. 



When this arrangement can be adopted, the clear surface of the open- 

 ings should be calculated on the condition that the air should pass 

 through them with a velocity of about 20 inches a second. 



In the main lecture-room of the Conservatory, where the amount of 

 air admitted rarely exceeds 630,000 cubic feet an hour, or 177 cubic feet 

 a second, this condition would require a clear area for the fresh-air 

 openings of 108 square feet. They actually have an area of 129 square 

 feet. 



If it becomes necessary to admit the fresh air through one or more of 

 the walls of the room, opposite walls should be preferred, and the open- 

 ings shoidd be placed as far as possible from the audience, fitting guides 

 to them to force the air to follow the flat or curved surface of the ceiling, 

 so that its entering velocity, which may then be as great as 40 inches a 

 second, may" be gradually reduced before it reaches the audience. The 

 air brought in should have in winter a temperature lower by 4 degrees 

 than that which is to be maintained in the room, which should be about 

 6SO. 



For this purpose, the warm air from the heating-apparatus should be 

 mixed in a separate chamber with the cold air taken from outside 

 through a convenient opening. The action of the draught will serve to 

 draw in this cold air, which should be made to flow into the mixing- 

 chamber above the warm air. 



