14 INJURY BY SMELTER WASTES. 
commonly causing the destruction of forests. These samples of 
foliage were classified by the forester and forwarded to the Bureau 
of Chemistry for analysis. 
For purposes of investigation samples of the dead and injured 
trees surrounding the smelters were examined, as well as of the unin- 
jured trees of the same species beyond the range of apparent injury. 
The sulphur trioxid content of the foliage and ash of the two sets 
ef samples was then compared. The soils beneath the injured trees 
were compared with those from beneath the uninjured trees to de- 
termine whether any increase in the sulphur trioxid content of the 
injured trees might be due to an increased amount of sulphur trioxid 
in the soil. 
If the sulphur trioxid content of the uninjured trees, situated much 
farther away from the smelters, is less than that of the injured trees 
situated near the smelters, and yet the sulphur trioxid content of the 
soils in which the trees grow is the same, or nearly the same, in both 
cases, this increase of sulphur trioxid must have been absorbed from 
the air and must be responsible, wholly or partly, for the death of 
the trees, since it is known that small amounts of sulphur dioxid and 
trioxid, when absorbed by the leaves of trees, do kill them. In the 
absence of insect pests in sufficient numbers to cause great injury, of 
forest fires, or other ordinary causes for the death of trees, it must 
be concluded that it was the sulphur dioxid and trioxid alone that 
caused the damage. 
Attention is again called to the fact that this method of comparing 
injured trees with uninjured trees at a greater distance from the 
smelter is better than the method followed by the writer at Redding, 
Cal.,¢ and should undoubtedly be followed in all cases where such a 
comparison is possible. The country around the Tennessee smelters 
easily lent itself to carrying out the investigation in this way, while 
in the country around Redding, Cal., such a method of working out 
the problem would have been extremely difficult. 
In Table II are given the results obtained by examining the foliage 
of the injured and uninjured trees for sulphur trioxid and ash. Ina 
northerly, easterly, and westerly direction the writer collected and 
examined samples from beyond the range of apparent significant in- 
jury. Ina southerly direction a few such samples were collected, but 
unfortunately they were very wet when gathered and molded during 
transit. However, since the samples collected beyond the apparent 
range of injury in an easterly direction grew in a soil containing 
practically the same amounts of sulphur trioxid as the soils south of 
the smelters, and also since the examined area to the south is near 
the area over which the samples were collected east of the smelters, it 
2@U. 8S. Dept. Agr., Bureau of Chemistry, Bul. 89. 
