TiCHBORNE — On Dissociation by Heat of Compounds. 187 
oxides hold as regards dissociation ; also, the laws that govern their 
dissociation in the presence of other salts. Thus, the alums of the 
ferric oxide, which have been chosen to determine this point, are seen 
to obey the chemical laws of affinity. As regards the disturbing mo- 
lecule introduced, its power of substitution determines the lowering 
of the thermanalytic point ; also, the basylous power of this atom de- 
termines the amount of decomposition. AVhere the trioxides alone 
replace the hydrogen in the acid, the molecules are held together with 
a force in ratio to the relative affinities ; but when a second molecule 
comes into play, a power of determining or lowering the thermana- 
lytic point is found in the disturbing basylous element introduced. 
Thus, we find in the alkali group, potash acts more forcibly than am- 
monia ; in fact, they act in this respect according to their power of 
substitution. 
As before stated, the ferric salts have been experimented upon by 
M. Debray.*' That experimenter says — Je ne suppose pas que le 
chlorure de fer se dedouble en acide chlorhydrique et en chlorure ba- 
sique, parce que 1' existence de ces composes basique soluble, en tant 
que composes definis, me parait pen conciliable avec le fait de leur de- 
composition par le filter dans I'appareil dialyseur, ou par le sel marin 
qui en precipite de I'oxyde de fer pur. II me parait plus naturel de 
considerer ces composes comme des dissolution de I'oxyde colloidal de 
fer dans I'acide chlorhydrique outout au moins dans le sesquichlorure 
de fer ordinaire." 
'Eow, although M. Debray's views are in the main correct, we 
cannot conceive that the action of the dialyzer can have anything to 
say to the actual condition of the solution before dialysis. Immediately 
that we bring a septum into play, we introduce another decomposing 
influence to bear, and entirely modify the balance of the forces at 
work. I hope shortly to be able to demonstrate — that not only the 
oxides of the group we have been considering, are capable of existing 
in either the colloidal or crystalloidal condition — the modifying 
agent appearing to be in some instances the combined water. There 
can be little doubt that at elevated temperatures we get a partition of 
the acid, so arranged as to give an acid salt and a basic salt ; and that 
the amount of basicity is dependent not upon temperature, which only 
determines a constant decomposition for each degree, but upon a relative 
volume of water, and when we come to extraordinary pressure, rela- 
tive volatility of the basylous molecules in the presence of steam. M. 
Debray again says, Le chlorure de fer se dedouble done a une 
temperature de 70 degrees en acide chlorohydrique et en sesquioxide 
de fer soluble dans I'eau," &c. All through his paper he speaks of this 
thermanalytic point, as I will call it, as a constant quantity for the 
same salt, under all conditions. ITow this involves a principle, and I 
* Note sur la decomposition des sels de sesquioxide de fer, par M. Debray. — 
Comptes Rendus ; et Journal de Pharin. et de Chim., Septembre, 1869. 
