COMPOSITION OF CHAMBER DUST. 



715 



in the state of chloro-bromo-iodides and sulphides formed by the action of chloro- 

 bromo-iodide of lead and silver, and of sulphide of lead in presence of carbon, on the 

 non-volatile oxides. The volatile chlorides and sulphides thus forn ed are afterwards 

 decomposed by water, when the steam which accompanies the fumes condenses. These 

 reactions, which might appear doubtful from the examination of the chamber-dust 

 alone, are forcibly demonstrated by the analysis of that portion of the fumes which is 

 not condensed and -which escapes into the atmosphere. (See Analysis XXXVI.) 



Roasted dust At one smelter the flue and chamber dusts are roasted, previous 

 to resmeltiug, in the roasting furnace, which is spoken of in the description of this 

 smelter. This operation is probably carried on with a view to getting rid of the large 

 proportion of arsenic which is erroneously supposed to exist in the dust. Whatever 

 may have been the object of the superintendent of this smelter in performing this 

 costly operation, if the composition of the chamber-dust of this smelter is compara- 

 ble to that of the others, the influence of roasting on chamber-dust can be easily seen 

 by comparing Analysis XXXV of the roasted dust with Analyses XXXIII and 

 XXXIV. 



The sample analyzed in XXXV is chiefly formed of roasted dust, but it contains 

 also a little uuroasted dust, which had been spread over the roasted dust taken out of 

 the roasting furnace. The specimens mixed for analysis were in friable whitish and 

 reddish masses, containing scarcely any charcoal or coke dust. The elementary anal- 

 ysis was made like those of the chamber-dust, and the different portions analyzed are 

 in the following proportions : 



Portion soluble in water 1. 16583 



Portion soluble in acids 85. 48129 



Portion insoluble iu acids 13.29600 



Loss 0.05683 



Total 100.00000 



ANALYSIS XXXV. ROASTED CHAMBER DUST. 

 Elementary. 



