DETAILS OF THE METHOD. 
21 
with ether, two or three times with 20 per cent hydrochloric acid 
(1 part concentrated and 1 
part water), and heated with 
the latter for a quarter of 
an hour or more, to remove 
basic sails, oxides of iron, 
and any contaminating sul- 
phides or soluble silicates 
which may thus be extracted. 
It should be remarked that 
under these conditions pure 
pyrite evolves no percepti- 
ble hydrogen sulphide 1 if 
tested a few moments with 
lead paper, while marcasite 
continues to give off minute 
amounts however long it may 
be heated with the acid. The 
evolution of hydrogen sul- 
phide from pyrite indicates 
the presence of other sul- 
phides. The material is then 
collected on a Gooch crucible 
fitted with a disk of Schlei- 
cher & Schull hardened filter 
paper and washed with dilute 
hydrochloric acid, and then 
with water which has been 
boiled and cooled in carbon 
dioxide. The washing iscon- 
ducted in an atmosphere of 
carbon dioxide, and for 1 his 
purpose I use the apparatus 
shown in tig. 1, in which the 
wash water is delivered from 
the dropping funnel, and 
the carbon dioxide, supplied 
from an ordinary automatic 
generator, 2 itself affords the 
pressure necessary to drive 
the liquid through the filter. 
The crucible is then sucked 
out by attaching a pump to the outlet tube, placed for a moment on 
Fig. 1. 
Apparatus for washing sulphides in an atmo- 
sphere of carbon dioxide. 
1 One-half gram pure powdered pyrite, boiled in the decomposing apparatus for one hour with 
7 per cent sulphuric acid, in a slow current of carbon dioxide, caused a slight blackening of lead 
paper placed in the top of the condenser. 
2 Liquefied carbon dioxide contains air and should not be employed. 
