50 



All the remaining plants were healthy and new leaves were 

 shooting. 



No further ob?;ervations were made on these plants as they all 

 made a normal recovery. 



Further Experiments. 



Subsequently three condensing chambers, built of bricks, were 

 erected ; these consisted of brick boxes connected to each other by 

 iron pipes, the last box being connected to the stack. 



In this way it was anticipated that most, if not all, of the arsenic 

 in the fumes might be condensed and observations made to prove 

 what was believed to be the chief cause of the injurious effects of the 

 fumes, viz., the effect of the sulphurous oxide. 



The condensing chambers unfortunately interfered seriously with 

 the draught, and before suitable alterations could be effected, further 

 experiments had to be abandoned owing to lack of time. 



The necessity for further experiments has now ceased as the 

 Chinese roasting furnaces have since been stopped by order and a 

 large plant has been erected by the Straits Trading Company for the 

 special treatment of these low grade arsenical ores — in order to retain 

 both the sulphur and arsenic. 



These observations are published in this incomplete form as it is 

 unlikely that the investigation will be continued. 



Conclusions. 



1. The results of this experiment prove conclusively the harmful 

 effect of these fumes, particularly on the Para rubber tree and the 

 Rambong tree, although it does not prove whether these effects are 

 due entirely to one or the other or to both of the principal constituents 

 of the fumes, viz., arsenious acid or sulphur dioxide. 



2. In the writer's opinion the sulphur dioxide is the more harm- 

 ful to vegetation — especially at long distances from the furnace^ as 

 the sulphur fumes would be carried considerable distances by the 

 prevailing winds whereas the arsenic would be condensed in the 

 immediate vicinity of the furnaces. 



A large amount of the arsenic undoubtedly condenses in the 

 stack itself as mentioned before. 



3. The first noticeable effect is a spotting of the leaves, yellowish 

 white spots being found on the surface, which gradually spread over 

 the whole surface of the leaves, the latter eventually dropping off. 

 The plants thus become quite defoliated. The leaves naturally grow 

 again if the fumes are stopped, but if the fumes from the furnaces are 

 continuous, as is the case in practice, then complete defoliation would 

 occur, and the plant would subsequently die. 



