'98 
THE PRINCIPAL FLOOR. 
a large portion of lead in a state of comparative purity is 
removed, and the fluid portion which remains at the last is 
exceedingly rich in silver. This enriched lead is subjected to the 
oxidising process, or cwpellation, and the silver separated. 
While the old process was in use, if the lead contained less 
than eight ounces of silver to the ton, it was not found profitable 
to separate it, but by Pattinson’s process it is profitable when it 
does not contain more than three ounces to the ton. Beyond 
this, more 'silver is now obtained from the lead than formerly. 
In many places the Pattinsonisation process has now been 
displaced by a process of “zincing/’ whereby the lead is 
desilverised by means of zinc, as originally suggested by 
Mr. Alexander Parkes, of Birmingham. 
An interesting series of specimens is exhibited to illustrate 
Mr. Baker’s process of softening hard lead, patented in 1860. 
A small group of specimens illustrating one of the processes 
employed for the manufacture of white lead is also here intro- 
duced. Metallic lead, cast into the form of gratings, is exposed 
to the action of the vapour of vinegar in beds of fermenting 
tan. The basic acetate of lead first formed is decomposed by 
the carbonic acid present, and in this way is obtained a carbonate 
of lead, which, when purified by washing and levjgation is ready 
for use as a pigment. When white lead is roasted it suffers 
decomposition, and the residuum, consisting of oxide of lead 
with a little carbonate, is employed under the name of orange 
lead. Litharge is obtained by oxidising lead in a reverbera- 
tory furnace, and the product when further roasted forms the 
higher oxide known as red lead. 
Amalgamation of Silver Ores. 
Table Case 17. — : The process of the amalgamation of silver ores 
as formerly practised at Halsbriicke, near Freiberg in Saxony, 
is illustrated by a complete series of specimens. The process 
consisted essentially in roasting the ore with common salt ; the 
main result being the conversion of the sulphide of silver into 
chloride of silver. This was mixed with mercury and frag- 
ments of wrought iron, and placed in revolving casks, the 
mass being kept in motion for about 20 hours, when the 
amalgamation was complete. 
Mercury. 
Xl ■ 
Table Case 17. — Some mercurial ores from Idria in Austria, 
and from Hungary, are here associated vntln the metallic 
mercury and the vermilion prepared from them,. The ore from 
Idria is principally bituminous cinnabar associated , with native 
mercury. On submitting the ore to distillation, the , sulphur is 
expelled, whilst the mercury, or quicksilver, is. volatilised and 
collected in a series of condensing chambers. 
iWhen mercury is rubbed with sulphur in amortar the black 
sulphide, Ethiops mineral, is produced. If .this powder be 
