2iO Dr> Betice Jones on Ventilatiwis [April 18, 



Moreover, we have no accurate experiments to show the smallest 

 quantity of carbonic acid that is injurious in tlie longest time. Is 

 one per cent, of carbonic acid in air breathed for 12 hours injurious? 

 Is half a per cent, injurious in 24 hours ? Is a quarter per cent, 

 hurtful if breathed for 48 hours or longer ? Assuming that about 

 one cubic foot of fresh air per minute gives to a man about one per 

 cent, of carbonic acid in air he breathes — 



2 cubic feet would give ^ per cent. 



(2i „ minimum, according to Vierort) . 



3 to 4 „ Dr. Arnott considers insufficient , ^ to i „ 

 10 „ Dr. Reed advises ^ „ 



20 „ Dr. Arnott advises 



2 » 



Is then one part of carbonic acid in 2000 parts of air injurious 

 when continually breathed? The atmosphere contains 3 parts 

 carbonic acid in 10,000 parts of air when most pure, that is 1 part 

 carbonic acid in 3333 parts of air. 



Hence Drs. Arnott and Reed have given the highest limit, 

 whilst the lowest healthy limit is what we require to enable us to 

 decide when we have got as much air as we want. 



From the best experiments, namely, those of M. Leblanc, I 

 shall assume that air containing one per cent, of carbonic acid 

 indicates such an impure state of atmosphere, that if breathed for 

 12 hours there will be an injurious action on the system; and that 

 air containing half a per cent, of carbonic acid breathed continuously 

 for 24 hours or more will probably prove hurtful. Whether at- 

 mospheres having this amount of impurity are more injurious to 

 women and children, though probable, is also unproved. Whether 

 this amount of impurity, acting day after day, becomes more tolerated 

 by the system is very doubtful. On all these questions much 

 might be said, and much has yet to be done. But the question at 

 present to be answered is. How are we to know when the air is 

 thus far impure ? What means do we possess of determining the 

 amount of ventilation in this or any other room ? 



There are three methods of obtaining this knowledge. The 

 physiological method ; the physical method ; and the chemical 

 method. 



1. The physiological method consists in the determination of 

 the action of the air of any room on its inmates, when well or 

 when ill. The offensiveness of a room to a person just entering it, 

 that is the action of the air on the sense of smell, is liable to great 

 variations, depending on the observer himself. The nerves do not 

 measure actual amounts of impression, but only variations arising 

 from different degrees of impression ; and the action on the nervous 

 system of one person is not a measure of the impression on the 

 nerves of another person. Moreover, it is far from proved that 

 the offensive smelling substances are poisonous. They may be more 



