TiCHBORNE— Dissociation hy Heat of Compounds. 173 
In the above experiment the only point that was satisfactorily 
established was the fact, that a dehydration really does take place, 
and that the molecule HgO is, to a certain extent, torn from its chemi- 
cal position, even in the presence of an excess of water, and that it is 
not due to any specific insolubility of the hydrate at 100° C. 
Experiments 2, 3, and 4 were to determine the solubility of lime 
at different temperatures. Chemically pure carbonate of calcium was 
prepared by dissolving the precipitated commercial preparation in 
hydrochloric acid, and treating the resulting solution with sulphide of 
hydrogen and filtering. The filterate was then allowed to digest with 
a slight quantity of ammonia, and again filtered after warming. A 
few drops of sulphuric acid were added, and it was allowed to stand 
twenty-four hours before filtering from the precipitated sulphates. 
Prom this solution the carbonate was prepared with the aid of carbo- 
nate of ammonium. The well-washed carbonate was ignited in a pla- 
tinum crucible, until it no longer effervesced on the addition of dilute 
hydrochloric acid. Having procured what might be considered, as 
pure lime, the next point was to determine its solubility at different 
temperatures, in the following manner : — 
Experiment II. — Betermination of the Soluhility at 15-5° C. : — 
After standing upon an excess of lime for some days in a silver 
flask, a lime water was procured by decantation. Eor twelve hours 
before pouring off it was rigorously maintained at a temperature of 
15*5 C. 4000 grain measures were operated upon in each determina- 
tion. In the two last determinations the lime water was filtered in 
an apparatus by which as much as possible of the atmospheric carbo- 
nic anhydride was excluded. I am of opinion that these last determi- 
nations give the results as a little under the mark ; but I am also of 
opinion that decantation probably gives it over ; for these reasons the 
average of the three experiments has been taken. The estimation 
was made with a volumetric solution of sulphuric acid, 100 degrees of 
which would neutralize one equivalent of a monevalent element : — 
1 grain of lime, or its equivalent of hydrate, requires 741 grains of 
water at 15-5° C. 
Experiment III. — Determination of the Sohtlility of Lime at 
100° C.:— 
A small copper boiler was used in this experiment, which was pro- 
vided with a valve to regulate the pressure, and a thermometer to in- 
dicate the temperature in the interior. 
Degree of vol. solution. 
First determination (decanted), 
Second do. (filtered) 
Third do. „ 
20 
19 
18-9 
Therefore, as 19-3 
Ca^ 
"20a 
= 5-404 grains of lime present in 4005, so 
