180 
Proceedings of the Royal Irish Acadenuj. 
of sulphuric acid. The gradual increase of temperature brought 
about all the reactions and phenomena observed in the above experi- 
ments, only in a much more marked and decided manner ; whilst 
again this lowering of the thermanalytic point was even more evident 
with the potash alum. 
It is unnecessary to detail the experiments performed with the 
solutions of ferric chloride, because the results were almost the same« 
I would wish, however, to observe that, even on prolonged boiling, there 
seems to be little or no loss of HCl, at ordinary atmospheric pressure. 
It having been determined that the first results of a continuous 
boiling of a neutral ferric salt is the precipitation of a basic salt, con- 
taining but a small part of the stylous element, further experiments 
were performed to determine how far these acid molecules were re- 
movable at ordinary atmospheric pressure, by the combined and con- 
tinuous action of water and heat. 
Experiment XII. : — 
A large quantity of a diluted solution of ferric sulphate was submit- 
ted to continuous boiling until a considerable precipitate was ob- 
tained. This precipitate was collected upon a filter, washed once, 
and dried at 100° C. '219 gramme, gave '141 of ferric oxide when dis- 
solved in HCl, precipitated with ammonia, and weighed after igni- 
tion. This corresponds to 64 '4 per cent, of ferric oxide. A portion 
of this precipitate, before drying, was placed in a considerable body 
of water, and again submitted to a temperature of 100° C. for two 
hours. After this treatment the appearance was much changed. The 
colour, which was originally of a light ochrey-yellow, had been 
changed to a reddish-brown, whilst the precipitate became much 
denser; -338 gramme now gave "32, on precipitation, as in the 
previous estimation, and, therefore, corresponds to 82*5 per cent. ; it 
however, still contained a trace of the basic salt. The further action 
of heat upon these basic salts will be found described in Experiment 
XIY. 
It must be borne in mind that all the above experiments had been 
performed with Avhat we might call chemically neutral salts, but it 
is probable that from a geological point of view there would be 
2 a" 
formed Pca"' — - or a deficiency of one-third of the acid, e. g. from the 
o 
oxidation, for instance, of iron pyrites. In such a case we would 
have to start with a basic solution, the first result of the oxidation 
of the pyrites being a ferrous salt, which ultimately becomes oxidized 
into the ferric. Vide remarks, p. 181. 
Experiment XIII. : — 
To a weighed quantity of pure crystallized ferrous sulphate 
a quantity of pure nitric acid was added, sufiicient to exactly 
oxidize the ferrous salts to its higher term. The acid was allowed 
to remain in contact with the powdered salt without the addi- 
tion of water, until on dissolving a portion, and after warming and 
