nilka23

Elective Affinity. An important law of affinity, which is the basis of almost all chemical theory, is, that one substance has not the same force of affinity towards a number of others, but attracts them unequally. Thus A will combine with B in preference to C, even when these two are presented to A under equally favorable circumstances. Or when A is united to C, the application of B will detach A from C, and we shall have a new compound of A and B, C being set at liberty. Such cases are examples of single decomposition.
Illus. Into a solution of muriate of lime, let fall a few drops of sulphuric acid. The muriate will be decomposed, a sulphate of lime will be formed, and the muriatic acid will be set free.
Now if we call the muriatic acid A, and the lime B, we shall have A and B combined, forming muriate of lime. On adding the sulphuric acid C this first combination is destroyed, because B has a stronger affinity for C than it has for A, consequently B and C unite, while A remains alone in the solution.
79. The force of affinity which one body has for another, is so different and obvious, as to admit of the construction of tables, showing at a single view, what substance will decompose a primary compound, and what again will decompose this, and so on.
Obs. Thus, taking muriatic acid as a substance for which several of the alkalies and earths have affinities, the relative forces of attraction will be thus ; placing that which attracts it most strongly althe top, and that for which it has the weakest affinity at the bottom.
MURIATIC ACID.
Barytes.
Potash.
Soda.
Lime.
Ammonia.
Magnesia, &c.
Tables of this kind, on an extensive scale are of great use to the practical chemist, as they show at once what substances will decompose any given compound, as well as what are incompatible with each other on this account.
Id the present example, magnesia, being placed lowest in the scale, shows that when this is united to muriatic acid, the salt, muriate of magnesia, would be decomposed by ammonia, because of the two, ammonia has the strongest affinity for the acid. By adding ammonia therefore to muriate of magnesia, the magnesia would be precipitated and muriate of ammonia would be formed. By adding lime to a solution of muriate of ammonia, the ammonia would be precipitated and a muriate of lime would be formed, and so of the others.
Ofts. No chemical facts can appear on first view, more simple, or intelligible, than those which are explained by the operation of single elective affinity. It will be found however, on a more minute examination, that this force abstractly considered, is only one of several causes which are concerned in chemical decompositions, and that its action is modified, and sometimes even subverted by counteracting forces.
80. Although it is ascertained that the affinities of one body for a number of others are not all of the same degree of force ; we are yet ignorant how much the affinity of one body for another is superior to that of a third. The determination of the precise forces of affinity would be an important step in chemical philosophy, for its phenomena would then be reduced to calculation, and we should be enabled to anticipate the results of experiment.
Ofo. That the force of chemical affinity must be prodigiously great, is evident from its effect in preserving the combination of water with some bodies, as the alkalies, when exposed to a violent heat.
lllus. Notwiihstanding the great expansive force of heat and the ease with which uncombined water is turned into steam and driven off by it, it appears that in some instances the force of attraction is still greater, for, on submitting potash, or soda to the most violent heat of a furnace, they still retain a quantity of water, though water is not essential to the constitution of these bodies.
81. Complex Affinity, or double elective affinity, is exerted whenever two compound bodies mutually decompose each other, and by a double interchange of ingredients form two new compounds.

Gucci Casual Shoes,Gucci Shoulder Bags