182 
ProceeduKjfi of the Royal Iri^h Acadoiii/. 
a, more volatile styloiis element was chosen, and although it was 
placed in a tube as in the previous experiment the orifice was 
left unsealed. "We were, therefore, on placing it in the apparatus 
described above, submitting the fluid to the action of a considerable 
volume of steam at a pressure of nine atmospheres. After two and a 
half hours' digestion the contents of the tube presented a remarkable 
appearance. The greater part of the iron lay at the bottom of the tube, 
not in the form of a basic precipitate, but as a dark and heavy oxide 
of iron. Thin layers of this oxide adhered to the tube at the surface 
of the fluid, which when examined by the microscope were seen to be 
transparent and brilliantly red ; by reflected light they possessed a 
blackish metallic lustre. The tube still contained an acid salt of iron, 
which however no longer acted upon the enclosed oxide ; the latter 
seemed anhydrous. 
In the first experiment (Exp. XIY.), there can be no doubt that a 
similar change had partially taken place ; but only to a slight extent ; 
it was the limited volume of steam generated in the tube reacting 
upon the surface of the fluid that formed the ring of ferric oxide. 
Certain specimens of specular ore (analysis 4) are formed in this 
manner ; they are simply pseudomorphs of the sublimed and anhydrous 
ferric chloride produced by volcanic agency, and ultimately submitted 
to the action of high pressure steam. ^' 
Experiment XYI. : — 
The basic precipitate procured upon boiling a solution of ferric 
sulphate at ordinary temperature was next placed in a tube 
with a little water, and submitted to the action of steam for 
two and a half hours at a temperature of 177° C. The result was the 
gradual conversion of the precipitate, which lay at the bottom of the 
tube to the extent of about fifteen millimetres, into a bright red and 
dense precipitate, which, however, gradually assimilated its original 
appearance until, at the depth of six millimetres, it appeared to have 
retained its primitive composition and ochrey appearance. Some con- 
siderable proportion of this precipitate seemed to have been carried 
up the side of the tube ; at the line of juncture of steam and fluid this 
precipitate was converted into anhydrous oxide of iron — above this 
the basic salt was intact, except that it seemed to be perfectly dehy- 
drated and white, and it was not until it had been in contact with the 
fluid contained in the tube, that it seemed to regain its original appear- 
ance. It is evident, therefore, that as regards the more fixed and 
non- volatile acids no dissociation is eff'ected at the temperature tried, 
except in the presence of condensed water, but that the steam is 
capable of removing water of hydration under such conditions. 
* In speaking upon this subject, in his Lectures on Chemical Geology, Dr. 
Percy says, — " Supposing we have the vapour of sesqui-chloiide of iron, there is no 
difficulty in accounting for the formation of this sesqui-oxide in volcanic regions. 
If that vapour be brought in contact with the vapour of water, we get a deposit of 
crystallized sesqui-oxide of iron, with the formation of hydrochloric acid. 
