TiCHBORNE — On Dissociation hij Heat of Compounds. 179 
dissociation of crystalloidal water, and then tlie splitting up of the 
structure into a basic salt, and free hydrochloric acid ; and that the 
dissociation may be carried ultimately so far as to result in the total 
splitting up of the structure. These results do not, however, agree 
with M. Debray's conclusions. Presuming that there is no other dis- 
turbing cause, the molecules regain their original arrangement of 
structure on cooling ; but time becomes an important element here — 
the time required being in ratio to the extent of dissociation. The 
preparation of the ferric salts used was effected in the following man- 
ner : — A neutral persulphate was formed in the moist way, preference 
being given to this method to that first adopted — namely, that of mak- 
ing the chloride obtained by sublimation, the starting point. 
To a weighed quantity of ferrous sulphate dissolved in water, the 
requisite proportions of nitric and sulphuric acids were added by the 
aid of volumetric solutions carefully adjusted. The salt was evapo- 
rated to dryness, at about 80° C, and, after powdering, was kept for 
some days at a temperature of about 75° C. This powder, when 
thrown into water, slowly dissolved in the cold, giving a slightly 
tinged and basic solution, which required the cautious addition of 
weak sulphuric acid. The addition of chloride of barium to this salt, 
in equivalent proportions, gave also a neutral solution of ferric chlo- 
ride, &c. 
Experiment YIII. : — 
A concentrated solution of ferric sulphate was submitted to a tem- 
perature of 100° C, the solution gradually became darker during the 
increment of heat ; but there was no evidence of precipitatioD . 
Experiment IX. : — 
The above solution was rather copiously diluted, and on being re- 
heated, it gave a basic precipitate of a yellow character, which con- 
tained sulphuric acid. Placed under the microscope it was seen to 
consist of semitransparent and crystalline masses. By long and con- 
tinued boiling a precipitate was procured in a concentrated solution. 
Experiment^.: — 
The basic precipitate procured in the above experiment was sealed 
up in the liquid in which it was found, and occasionally agitated. 
After the lapse of some considerable time it re-disolved, with the for- 
mation of the original salt. To ensure success it is necessary that the 
boiling in the first instance should not be carried too far, and that the 
fluid be not too much diluted. A similar tube, tied upon the beam of 
a steam engine, to ensure constant and energetic agitation, gave the 
same results in two days. 
Experiment XL : — 
The addition of alkaline salts to the ferric compounds determines 
more easily the precipitation, or dissociation. Therefore, the iron 
alums, either with ammonia, or potash, exhibit this phenomenon in 
a marked degree. These alums, which show a beautiful but very 
faint amethyst tint, gave, on solution in the cold, a slightly- 
coloured liquid, made paler on the addition of a very dilute solution 
