254 Transactions of the American Institute. 



Examinino; into the origin of carbonic acid, we find that it is one 

 of tlie products of the combustion of all vegetable and animal struc- 

 tures, as is easily shown b}^ burning these substances or a portion of 

 charcoal in oxygen and then submitting the products of combustion 

 to the lime-water test. Processes of respiration also produce a simi- 

 lar result, there is then a double reason for the accumulation of this 

 in the air of public buildings. 



It is interesting to note that though carbonic acid is heavier than 

 air, it is not found in the greatest proportion near the floor, nor is it 

 distributed equally throughout the air of an apartment. Eoscoe, for 

 example, discovered that in a theatre there were twenty-seven parts 

 of carbonic acid in 10,000 of air, at a distance of (four feet above 

 the stage, while the proportion arose to thirty-four parts at a 

 height of thirty-four feet. In a library near the table the proportion 

 was twelve, and near the ceiling sixteen. This ascent of the carbonic 

 acid, produced by combustion and respiration is owing to the expan- 

 sion of the gas by the heat developed in both of these processes, and, 

 as in the combustion of* sulphur in oxygen, it was evident that the 

 proper method for allowing the products of the action to escape was 

 by making an opening in the top of the jar ; so in the case of rooms, 

 if we would ventilate them we must make the opening of exit for the 

 foul gases near to the ceiling. 



The second of the variable ingredients is carbonic oxyd. It is 

 also formed by the union of charcoal with oxygen, and is produced 

 whenever the supply of air is insufficient. Evolving it, as in the 

 experiment before you, it is found to be a colorless combustible gas, 

 burning with a pale blue flame, that we have all seen playing over 

 the surface of an anthracite fire that has been recently replenished. 

 Like carbonic acid, carbonic oxyd is a noxious gas, but far more 

 energetic and destructive, since it acts upon the blood discs, turning 

 them permanently red, and unfitting them to serve as the carriers of 

 oxygen to the tissues. It is therefore cumulative in its action, and a 

 very small proportion is capable of producing profound physiological 

 results if the air, thus contaminated, is breathed for a considerable 

 period of time. 



It is a very common opinion that carbonic acid is the most serious 

 vitiator of the air, but if we investigate the relation of carbonic ox3'd 

 to iron, we find that, in rooms warmed by stoves and furnaces, the 

 latter gas is probably in a majority of instances the chief culprit ; for 

 though metallic iron is almost impervious to this gas at ordinary tern- 



