55 



Chemical Notes on Ventilation. 



By Percy Norton Evans. 



What is the direct cause of the enervating and injurious effect of 

 poor ventilation on the human system is still uncertain. The old theory 

 that it is due to increased carbon dioxide and decreased oxygen in re- 

 spired air seems quite inadequate in view of the smallness of the actual 

 difference between ordinary poor air and fresh air ; to be sure the carbon 

 dioxide may be increased many times, but it is not poisonous, and experi- 

 ments have shown that equal quantities added to air by purely chemical 

 means have no such marked physiological effects ; and the concentration 

 of oxygen is altered to a scarcely appreciable extent in any case of ordi- 

 nary poor ventilation. 



It is held by some that definite toxic substances ax"e exhaled in respi- 

 ration, and that these, rather than the alteration in the proportions of 

 inorganic constituents of the air, are responsible for the undesirable effects. 

 Exhalations from the skin have also been considered of importance, and 

 this liypothesis receives some measure of confirmation from the veiT notice- 

 able difference in the intensity of the effect of a well-washed and a not- 

 well-washed crowd in a poorly ventilated assembly ronm, the respiration 

 products being tlie same in both cases presumably. Again, some claim 

 that the excessive moisture is an important factor, but this seems an in 

 sufficient explanation, for the air of badly ventilated buildings in cold 

 weatlier contains nothing like the amount of moisture present in fresh air 

 in warm, damp weather. 



Whatever the cause or causes — and they may be many — of the evil 

 effects of poor ventilation, it is surely true that anything that tends to 

 cany away the air that has been exhaled or in contact with the person 

 and replace it by fresh air, must be beneficial. 



Elaborate provision is often made to insure by mechanical means this 

 movement of air. As will be shown, something can also be done by auto- 

 matic physical means to bring about tjie same result, and where mechan- 

 ical means are employed they should for economy and efficiency operate in 

 such a direction as to assist rather than oppose the natural automatic 

 movement. 



