47 



in roasting a batch of ore depends on the amount of pyrites present. 

 The charge is rabbled over periodically to allow all the ore to under- 

 go thorough oxidation. 



In this way much of the arsenic is carried off as arsenious acid 

 or oxide commonly known as white arsenic, while the sulphur is 

 carried off as sulphur dioxide in the fumes. Some of the arsenic and 

 sulphur is left behind in combination with the iron as sulphate and 

 arsenate and can be removed by lixiviation with water. A portion of 

 the arsenic and sulphur is probably also carried off in the fumes as 

 arsenic sulphide. As might be expected much of the white arsenic 

 is deposited in the stacks and has to be removed at intervals to avoid 

 choking up the stack. In several instances this material (in a very 

 pure state) has been found near the roadside in the vicinity of the 

 furnaces, remaining a source of danger to cattle grazing near. 



Experimental. 



To investigate the influence of the fumes on Hevea Brasiliensis 

 and Ficus Elastica in particular^ a small furnace was erected in the 

 grounds of the Institute for Medical Research — the furnace being one- 

 quarter of the size of the ordinary furnace used by the Chinese ore 

 roasters. 



A long attap roof shed was erected on long poles, one end being 

 adjacent to the furnace stack, the floor being on a level with the top 

 of the stack. 



In this shed was placed a number of ordinary unglazed earthen- 

 ware pots containing young plants of the Para and Rambong rubber 

 trees and of the Rain tree (Pithecolobium Saman) ; the latter plant 

 was added as it was known to be particularly sensitive to the fumes. 

 The plants were placed in the pots some time previous to the experi- 

 ment, and were also placed in the shed some days before the first 

 batch of ore was roasted, being watered regularly. All the plants 

 were strong and in vigorous growth prior to the experiment. 



A count of the leaves and observations on their general appear- 

 ance was also carried out. 



Method of Roasting. 



In the experiment a charge of 80 lbs. of a low grade arsenical — 

 pyritical tin ore — was placed in the furnace, forming a layer about 

 2 inches deep on the furnace bed. The fuel used was wood. The 

 roasting was commenced at 7 a.m., and by 9 a.m. the whole mass of 

 ore had become a cherry red colour. The roasting was continued for 

 twelve hours, the ore being ]ioriodically " rabbled " over to expose 

 fresh surfaces to oxidation. 



