DAMAGE BY SMOKE, ASII. AND FUMES 371 



all sorts of objects growing in the soil or resting thereon. The flue 

 dust, taken from brass mills shows on analysis a large percentage of the 

 insoluble zinc oxide. It also shows a high percentage of the radical SO3 

 as illustrated in the following representative analysis : Copper oxide, 

 4.26 per cent : zinc oxide, 20. 43 per cent ; lead. .018 per cent ; total SO,, 

 8.98 per cent. 



The relatively high percentage of zinc oxide and SO,.; clearly indicate 

 that the two substances are the chief .sources of injury to the vegetation 

 in that the sulphur compound acting on the insoluble zinc oxide makes 

 it soluble in the form of zinc sulphate. 



Analyses of the surface soil taken from representative areas where 

 marked damage to surface-rooted vegetation had occurred showed 

 the presence of zinc in soluble form. It is evident that the conversion 

 of the zinc ash into the soluble zinc sulphate is constantly going on 

 after the ash comes to rest on the soil so long as the radical SO^ is 

 present and is as constantly being absorbed by the vegetation. 



Vast quantities of ash escape from the brass mills into the valley 

 and come to rest not only on the soil but on trees, the roofs of houses, 

 and other objects. The finer particles are carried a mile or more before 

 coming to rest. Other things being eciual, however, the amount of ash 

 which reaches the soil is directly proportional to the distance from its 

 source and the direction of the prevailing wind. 



When the ash with its contained radical SO., comes to rest on the 

 foliage of trees and other vegetation, if moisture is present part is con- 

 verted into zinc sulphate. Some of this may be directly absorbed by 

 the foliage but as little moisture passes directly from the surface of 

 leaves to their interior the amount of zinc sulphate which enters the 

 leaves by absorption is practically negligible. On the other hand, when 

 the ash which falls directly on the soil or is washed from trees and 

 other vegetation and from the roofs of buildings into the soil the soluble 

 cine is absorbed through the roots. 



Its presence in the soil is quickly detected by its efitect on the vege- 

 tation. Deep-rooted plants like trees sufifer little damage because the 

 roots are out of reach of the greatest concentration of zinc sulphate 

 but surface-rooted plants suffer great injury and are frequently killed 

 because the roots are in the top layers of the soil where the greatest 

 concentration of the soluble zinc occurs. 



Visible damage to grass and other surfaee-rooted plants takes place 

 zchen the accumulation of flue dust (sine ash) on the surface soil 



