Affinity - (Webster's 1828 Dictionary)
AFFIN'ITY, n. [L. affinitas, from affinis, adjacent, related by marriage; ad and finis, end.]
1. The relation contracted by marriage, between a husband and his wife's kindred, and between a wife and her husband's kindred; in contradistinction from consanguinity or relation by blood.
Solomon made affinity with Pharaoh. 1 Ki 3.
2. Agreement; relation; conformity; resemblance; connection; as, the affinity of sounds, of colors, or of languages.
3. In chimistry, attraction; elective attraction, or that tendency which different species of matter have to unite, and combine with certain other bodies, and the power that disposes them to continue in combination There are two kinds of affinity.
1. Affinity of aggregation, which is the power that causes two homogeneous bodies to tend towards each other, unite and cohere, as two drops of water, which unite in one.
2. Affinity of composition, which is the tendency of bodies of different kinds to unite and form new combinations of bodies with different properties. Such is the affinity which unites acids and alkalies, the results of which combination are neutral salts.
The operations of this principle are various. When heterogeneous bodies have mutually an equal attraction, it is called compound affinity. When one substance decomposes a combination of others, unites with one of them and precipitates the other, the power is called the affinity of decomposition. When bodies will not unite, but by means of a third, which enables them to combine, this is affinity by means of a medium.
Double affinity is when by means of four bodies, two decompositions and two new combinations are effected.