CHAPTER XVII. 



SOLID SUBSTANCES GIVEN OFF BY CHIMNEYS AND THE 

 DISTILLATES THEY CONTAIN. 



The best survey of the material from the streams of smoke affecting 

 vegetation is found in a table by Wislicenus^ which we may repeat here un- 

 changed because it is so very clear. 



No general decision can be reached as to the substances given in this 

 table. Under certain circumstances they may become injurious and, indeed, 

 very injurious but, in other cases, they do not cause any loss of crops worth 

 mentioning. This depends not only upon the greater or less exposure of 

 the plants but also on locally different, secondary conditions. Aside from the 

 individual sensitiveness of different species of plants, the constitution of the 

 soil and the weather at times become decisive, especially with fine fi3ang 

 ashes. 



It should be mentioned in connection with the injuriousness of tar 

 vapor that tar vapors from lime kilns also cause injuries. In burning lime- 

 stone, when the calcination begins, that is, the breaking down of the carbon- 

 dioxid, the smoke becomes laden with great cjuantities of the distillates given 

 in the table, which produce corrosions similar to those described under 

 asphalt fumes. These vary with the plant. 



The injuriousness of soot was previously universally overestimated 

 and is still, to some extent. The more recent investigations of v. Schmitz- 

 Dumont and Wislicenus^ confirm Stockhardt's older discoveries, that soot 

 is usually non-injurious. More delicate plants may show corrosion because 

 of phenol, etc., carried in the soot. 



The theory of the stoppage of the stomata must be left undiscussed. 

 According to my investigations of plants covered with soot the cases are 

 very rare in which the soot particles have succeeded in getting into the 

 cavities of the stomata, or actually have stopped them up, and even in these 

 rare cases, I have not been able to perceive any change in the surrounding 

 cells. Considerable quantities of extractive substances (sulfates and 

 phenols) must first be leached out from the soot before any injury may be 



1 Wislicenus, H. Zur Bcuiteiluna: und Abvvehr von Rauchschaden, Vortragr 

 in Dresden am 31 Mai 1901. Zeitschr. f. angewandte Chemie 1901, Part 28, Taf. V. 



