Undoubtedly; when oxygen loses its gaseous form, in order to combine with a solid body, it becomes condensed, and the caloric evolved produces the elevation of temperature. The specific gravity of bodies is at the same time altered by chemical combination; for in consequence of a change of capacity for heat, a change of density must be produced. CAROLINE. That was the case with the sulphuric acid and water, which, by being mixed together, gave out a great deal of heat, and increased in density. MRS. B. The 5th law of chemical attraction is, that _the properties which characterise bodies, when separate, are altered or destroyed by their combination_. CAROLINE. Certainly; what, for instance, can be so different from water as the hydrogen and oxygen gases? EMILY. Or what more unlike sulphat of iron than iron or sulphuric acid? MRS. B. Every chemical combination is an illustration of this rule. But let us proceed-- The 6th law is, that _the force of chemical affinity between the constituents of a body is estimated by that which is required for their separation_. This force is not always proportional to the facility with which bodies unite; for manganese, for instance, which, you know, is so much disposed to unite with oxygen that it is never found in a metallic state, yields it more easily than any other metal. EMILY. But, Mrs. B., you speak of estimating the force of attraction between bodies, by the force required to separate them; how can you measure these forces? MRS. B. They cannot be precisely measured, but they are comparatively ascertained by experiment, and can be represented by numbers which express the relative degrees of attraction. The 7th law is, that _bodies have amongst themselves different degrees of attraction_. Upon this law, (which you may have discovered yourselves long since,) the whole science of chemistry depends; for it is by means of the various degrees of affinity which bodies have for each other, that all the chemical compositions and decompositions are effected. Every chemical fact or experiment is an instance of the same kind; and whenever the decomposition of a body is performed by the addition of any single new substance, it is said to be effected by _simple elective attractions_. But it often happens that no simple substance will decompose a body, and that, in order to effect this, you must offer to the compound a body which is itself composed of two, or sometimes three principles, which would not, each separately, perform the decomposition. In this case there are two new compounds formed in consequence of a reciprocal decomposition and recomposition. All instances of this kind are called _double elective attractions_. CAROLINE. I confess I do not understand this clearly. MRS. B. You will easily comprehend it by the assistance of this diagram, in which the reciprocal forces of attraction are represented by numbers: _Original Compound_ Sulphat of Soda.