FOREST PROTECTION 143 



Since a large number of calories of heat are set free by the union 

 of S and 0, in forming the S0 2 , the anhydrid is a constant 

 combination. 



SO 2 is readily reduced, by H 2 S, into water and sulphur. 



In watery solutions as well as in gaseous form SO 2 readily oxidises 

 into SO s, when exposed to the influence of the atmosphere, 

 32 calories of heat being liberated by such oxidation. 



On the other hand, S0 3 at red heat dissolves into oxygen and S0 2 . 

 It stands to reason that with increasing distance from the 

 smoke-stack the contents of the smoke are more S0 3 than S0 2 . 



After von Schroeder, the gases of S0 3 are, without a doubt, less 

 damaging to vegetation inhaling them than the gases of S0 2 . 



Within the leaves S0 2 is very quickly converted, by oxidation, 

 into SO 3 . 



A few hours after gas-poisoning, only S0 3 (not S0 2 ) can be proven 

 to be present within the leaves. 



Chemical analysis of leaves can only fix the territory infested in 

 a random way. It can never be used as a measure of damage 

 locally found. The damage can be assessed only according 

 to the effects discernible with the naked eye. So-called "in- 

 visible damages" have never been allowed by the Courts. 



The chemical analysis of leaves suspected to be poisoned deals 

 only with an abnormal (unnatural) surplus of S0 3 . 



All leaves contain, in nature, certain amounts of S0 3 , the amounts 

 depending on the composition of the soil and on the species. 



Hence a comparative analysis of the leaves is absolutely necessary 

 where it is intended to establish the influence of sulphurfumes 

 on vegetation. This analysis must allow for the difference 

 in the soil and the difference in the distance from the smelters. 

 At the same time, the leaves examined must be taken from 

 the same part of the tree and from the same side of the tree; 

 further, the leaves must be in the same stage of development. 



After recent experiments the sulphuric contents in the leaves within 

 the lower part of the crown are much higher than the sulphuric 

 contents in the upper part of the crown. 



The ashes obtained from trees growing in low lands are relatively 

 poorer in SO 3 than the ashes from trees growing on mountains. 

 Weak limbs show more S0 3 than strong limbs. 



C The Merits op the Chemical Analysis. 



Science has not established any absolutely reliable means to 

 connect death or injury of trees with a poisoning effect of 

 SO a or SO 3 suspended in the air surrounding such trees. 



