22 
ON PYRITE AND MAROASITE. 
[BULL. 186. 
a blotter to remove most of the water and transferred to a vacuum 
desiccator containing sulphuric acid and filled with carbon dioxide, 
which is then exhausted. The 
use of carbon dioxide in this con- 
nection is essential, as even the 
best vacuum attainable by ordi- 
nary means contains enough oxy- 
gen to produce sensible oxida- 
tion. The drying is complete in 
half an hour. 
OXIDATION APPARATUS. 
The decomposition apparatus 
is represented in fig. 2. A flask 
holding about 400 cm. 3 is 
pro- 
vided with a doubly perforated 
rubber stopper which has been 
well boiled out in caustic soda; 
through this pass the inlet tube 
for carbon dioxide and the con- 
denser. The latter consists of 
an elongated calcium chloride 
tube, into which fits loosely a 
test tube through which cold 
water passes. The condenser has 
a hole at a to allow the passage 
of the steam, so that the return 
water drops quietly from the end 
of the tube. It is absolutely es- 
sential to prevent the return 
water from striking the sides of 
the flask or inlet tube, as at such 
points a film of basic sulphate 
invariably forms. 
The flask is placed up to the 
stopper in a cylinder of asbestos 
board provided with windows of 
mica or glass on opposite sides, 
to admit of watching the opera- 
tion. This rests on a plate 1 of 
asbestos contain ing a circular 
hole covered with gauze, and is 
closed at the top by a similar plate. The object of this arrangement 
is to prevent as far as possible the condensation of water on the sides 
1 In the figure the flask is represented as elevated above the plate. During the boiling it must 
rest on it. 
Apparatus for oxidizing sulphides with 
ferric solution. 
