320 PROCEEDINGS OF SECTION B. 
The composition of the Rivertree ore after chloridising was :— 
SiO las es ae aes ee a ee 
BASIE OF ce: mS a i coo E20 
CaO e.. ee -e Ae Pp eR 
MigOr a a at 128 ‘68 
Pb oe ae er oe =f 3°43 
Cu boy: we nets ae ae 28 
Fe ae oe nae ee sco 12239 
Zn me ae on sue ee 86 
As Doe see ae ae ae Seta: 
{ Sol. in water ote a Ast 1:61 
\ Insol. in water... <. Been JSS 
Percentage soluble in water, 12°17. 
Lead compounds are always somewhat easily volatilised ; but, 
apparently, in the presence of salt, losses from this cause are con- 
siderably increased by the formation of the readily volatile chloride. 
Lead sulphate and oxide are soluble in hyposulphite solutions, at 
the expense of the latter’s strength, and where it is not economical 
to recover the lead from the liquors by precipitation with sodium 
carbonate, this increased loss is a material advantage for this 
cause, and because of the resulting improvement in the grade of 
the precipitates. 
Although a large excess of salt is used in the roasting, much of 
which exists undecomposed in the ore after it leaves the roasting 
furnace, a considerable amount of the silver may be left unchlori- 
dised, as may be shown by its insolubility in sodium hyposulphite. 
This is probably due to mechanical rather than chemical causes, 
the centre portions of the grains of silver sulphide being protected 
from oxidation by the film of chloride found on their surface and 
by enveloping fragments of quartz, etc. 
In chloridising this ore at Rivertree in a Howell-White furnace, 
firm concretions were found to form on the sides of the furnace, 
and to increase so rapidly in the centre half of it as to reduce its 
internal sectional area by nearly one-half in a few weeks. Partial 
analysis of two samples of these concretions from different parts 
of the furnace, which are given below, show that they contained 
a large proportion of soluble salts, and were probably composed of 
partially roasted ore fritted together with sodium sulphate and a 
little chloride. 
Analyses of Concretions. 
(c) (d) 
Si0, sg iat By any Ocal! 40°73 
Al,O, 2B ra tet teat WOROe 8-88 
CaO. 3 1:15 lS 
