50 
All the remaining plants were healthy and new leaves were 
shooting. ' • . : . 
No further observations 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 he 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., arseaious 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 
. contiauous, as .is the .case in practice, then complete defoliation would 
occur, and the plant would subsequently die. 
