SCHOOL-ROOM VENTILATION, 533 



bonic oxide passes up the chimney along with the other gases of com- 

 bustion. As the products of combustion are much lighter than the 

 surrounding atmosphere volume for volume on account of their 

 much higher temperature, and as the expansibility of gases is very 

 great, they exert a pressure upon the sides of the pipe or flue through 

 which they ascend. This being the case, these gases will escape 

 through chinks, holes, or defective joints, along their course, like steam 

 through a leaky conduit. Downward air-currents in the flue, and lat- 

 eral currents from open windows, etc., occasionally blow large quan- 

 tities of the gases of combustion through the open door of the stove, 

 or through seams or cracks therein ; and in these two ways through 

 stove and flue sulphur, carbonic oxide, and carbonic-acid gas, may find 

 their way into the room. It is claimed by some physicists that carbonic 

 oxide will make its way through heated iron, and thus escape through 

 the sides of the stove, but the quantity given out in this way if, in- 

 deed, any is so given out, of which there is a reasonable doubt must 

 be so small that it is practically of no account, while quantities large 

 enough to be decidedly injurious may issue through the door and other 

 openings. Of course, these remarks apply only to schools heated by 

 stoves ; but it must not be forgotten that in rural districts, and many 

 cities, all the schools are still heated in this wav. 



Carbonic oxide is a deadly poison, fixing itself in the blood -cor- 

 puscles and paralyzing them so that they can not carry on the func- 

 tion of respiration. To the inhalation of this gas is chiefly due the pale 

 color of those who sj^end much time in apartments heated by stoves and 

 poorly ventilated. Its presence can not be recognized by the senses, as 

 it is tasteless, colorless, and inodorous. 



Carbonic acid is produced in two ways, as before explained by 

 combustion and by breathing. The quantity thrown off in breathing 

 is very much increased often nearly doubled during active diges- 

 tion. As the fullest meal is taken at dinner, and digestion is most 

 active soon after, it follows that the exhalation of carbonic-acid gas is 

 greatest during the early part of the afternoon, and therefore during 

 this time ventilation needs more attention. Of all the impurities 

 found in the school-room, this is vastly the largest in amount, and 

 popularly considered the most important. It is once and a half as 

 heavy as air. At first sight, it might be supposed that, being heavier 

 than air, it would sink to the floor and settle there in a layer of uni- 

 form height and density, like so much water. But this is not the case, 

 for it is even more expansible than air. (Coefficient of expansion of 

 air== -00366; of CO, = -00371.) :N"ow, the law which governs the 

 mixtures of gases is this : 



The mixture of gases in free communication, lohatever their den- 

 sity, takes place rapidly, and is homogeneous that is, the mixture 

 contains the gases in the same proportion; so that the percentage of 

 carbonic-acid gas is about the same in all parts of the room. 



