TiCHBORNE— Dissociation hy Heat of Compounds, 181 
testing with ferricyanide of potassium all trace of the magnetic salt 
had nearly disappeared. This product was then diluted with fifty times 
its weight of water — such a solution is perfectly clear, and will remain 
so for some little time ; but ultimately it decomposes spontaneously 
at ordinary temperatures, the time being determined by the amount 
of dilution and temperature. "When diluted so as to represent '5 per 
cent., a given volume a of this liquid gave on precipitation with 
ammonia, and on ignition, 1'557 gramme of ferric oxide. In a second 
determination, the solution was brought to 100° C. and maintained 
at that temperature for some time ; the precipitate that fell was 
separated from the liquid by filtrations, washed with a small quantity 
of water, and dissolved in hydrochloric acid, and the oxide estimated 
in this solution with ammonia, as in the first instance — -559 gramme 
was procured, which is over the amount of base really in excess of the 
acid present -= "519 gramme. The filterate again on dilution, and 
o 
boiling gave a precipitate representing "049 gramme of oxide. The 
filtrate again on dilution and boiling became opaque, but it was not 
necessary to follow out this experiment further — it being evident that 
there was no actual limit. It is probable that many of the ores, such 
as hsematite, brown iron ore, bog iron ore, ochres, &c. are formed in 
somewhat a similar manner to that detailed, and it is curious to ob- 
serve that sulphuric acid is seldom absent from such as are hydrated, 
and frequently in much larger quantities than the published analyses 
would lead one to suppose. Vide analyses, p. 190. 
We have now to consider the action of heat upon such fluids under 
pressure. 
Experiment XIY. : — ' 
A solution of ferric sulphate ivas placed in a tube of hard german 
glass, and hermetically sealed. This tube was then placed in 
a gun metal apparatus capable of bearing a considerable pressure. 
A little water being placed in the apparatus to equalize the pressure 
outside the glass tube, the heat was gradually raised until a 
thermometer, the bulb of which was placed in a cavity outside the 
apparatus, marked 177° C. The whole apparatus was maintained at 
this temperature for two hours ; on cooling and taking out the tube, 
it was seen that a similar decomposition had taken place as that 
obtained under ordinary atmospheric pressure, only in a more marked 
manner ; at the bottom of the tube there was a considerable precipitate 
of an ochrey nature, consisting of basic sulphate, but at the surface of 
the fluid there was an incrustation, composed of red oxide of iron, 
adhering to the side of the tube in the form of a ring. 
JExperiment XV. : — 
"Was a modification of the previous one ; but in this case 
* It is necessary in these experiments to have a good glass, as some specimens 
of lead glass seem to be rapidly acted upon at high temperature by many of the 
solutions used. 
