(or H_{4}SO_{5}), appear as true definite chemical compounds. If, then, we imagine such a definite compound in a liquid state, and admit that it partially decomposes in this state, separating water--not as ice or vapour (for then the system would be heterogeneous, including substances in different physical states), but in a liquid form, when the system will be homogeneous--we shall form an idea of a solution as an unstable, dissociating fluid state of equilibrium between water and the substance dissolved. Moreover, it should be remarked that, judging by experiment, many substances give with water not one but _diverse_ compounds,[67] which is seen in the capacity of one substance to form with water many various _crystallo-hydrates_, or compounds with water of crystallisation, showing diverse and independent properties. From these considerations, _solutions[68] may be regarded as fluid, unstable, definite chemical compounds in a state of dissociation_.[69] [66] Such a phenomenon frequently presents itself in purely chemical action. For instance, let a liquid substance _A_ give, with another liquid substance _B_, under the conditions of an experiment, a mere minute quantity of a solid or gaseous substance _C_. This small quantity will separate out (pass away from the sphere of action, as Berthollet expressed it), and the remaining masses of _A_ and _B_ will again give _C_; consequently, under these conditions action will go on to the end. Such, it seems to me, is the action in solutions when they yield ice or vapour indicating the presence of water.