182 KANSAS CITY REVIEW OF SCIENCE. 



created a widespread interest in the subject, were extended by other observers 

 in all parts of the world. These observers, prominent among whom were Pro- 

 fessors Fleck and Fodor in Germany, Drs. Lewis and Cunningham in India, 

 Prof. Wm. Ripley Nichols in Boston, and Surgeons J. H. Kidder and S. H. 

 Griffith, of the U. S. Navy, in Washington, demonstrated that the increase of 

 carbonic acid in the ground air is due to increased vegetable decomposition and 

 to lessened permeability of the soil. A permeable, that is to say, a sandy or 

 gravelly soil, is likely to contain less carbonic acid in its atmosphere than a dense, 

 less permeable clay, although the amount of decomposition going on, and the 

 production of carbonic acid in the former, may considerably exceed the latter. 

 In the loose sandy soil the circulation of the air is less obstructed, and the car- 

 bonic acid may easily escape and be diffused in the superincumbent air, while 

 the close-pored clay imprisons the carbonic acid and prevents or retards its escape 

 into the air above. 



The disappearance of oxygen from the ground atmosphere is coincident 

 with the production of an equivalent amount of carbonic acid. It appears from 

 this that in the soil an oxidation of carbonaceous substance takes place, the pro- 

 duct of which is the excess of carbonic acid in the ground air. 



Prof. Nichols has found the proportion of carbonic acid in the air taken 

 from a depth of ten feet below the surface in the " made land" of Boston, amount 

 to 2 1 "2 1 per thousand, the observation being made in August. In December, at 

 a depth of six feet, the proportion was 3*23 per thousand. Fodor, in Buda-Pesth, 

 found the proportion of carbonic acid to be 107*5 P^^ thousand (over 10 per 

 cent), the air being taken from a depth of thirteen feet. 



Movements of the ground atmosphere are principally due to differences of 

 pressure and temperature in the air above ground. Owing to such differences 

 the air from the soil frequently permeates houses, entering from cellars or base- 

 ments. In winter, when the air of houses is very much more heated (and con- 

 sequently less dense) than the air out of doors, the difference of pressure, thus 

 caused, draws the ground air up through the house, while the cold external 

 atmosphere penetrates the soil and occupies the place of the displaced ground 

 air. 2 A similar effect occurs in consequence of heavy rains. The water fills up 

 interstices of the soil near the surface, and forces the ground air out at points 

 where the pores remain open. These places are the dry ground under buildings, 

 where the air escapes and passes through floor and ceilings into the house above. 

 Heavy rains may thus be the cause of pollution of the air in houses. The greater 

 the porosity of the soil, the more likely is this to happen. This pollution of the 

 house air may be prevented by having impervious floors and walls to cellars and 

 basements, or by interposing a layer or charcoal between the ground and the 

 floor of the house. 



In the spring and early summer the ground being colder than the air above 



2 It is, of course, not strictly correct to say that the air is drawn up tlirough the house by 

 the dimiuution ol pressure; it being rather /o;-ced out of the soil by the colder and denser outside 

 air; but the phrase is sufficiently exact and will be readily understood. 



