What is ATTRACTION ?
What is the cause of attraction ?
How will you prove the existence of Attraction ?
How does the spherical form of the drops of a fluid prove the
existence of attraction ?
What is attraction of Gravitation ?
What is Cohesive Affinity ?
Does this kind of affinity operate on the particles, or masses of matter ?
What is Chemical Affinity?
What is the difference between cohesive attraction and chemical affinity ? How is this difference illustrated ? How is chemical affinity divided ? What is Elective Affinity? What is Complex affinity ?
What is the difference between these two kinds of affinitu ? In what class of bodies is cohesive affinity most strongly exerted?
How may tlie cohesion of bodies be overcome ? Why are substances more easily soluble in the state of powder lhan in the mass.
To what is heat the antagonistforce ? How does Heat overcome the Power of Cohesion ? On what does the cohesive attraction depend ? Id what manner does the Heat destroy the Cohesion of particles ?
What is Solution ? or how is this term applied ? How does a fluid overcome the cohesive force of the particles of a solid ?
What is CRYSTALIZATION ?
What connection has been observed between the chemical Composition, and external Forms of crystals ?
How are the Invariable Forms of Crystals accounted for?
Do substances of Different chemical compositions ever crystalize under the same forms ?
What is the Distance at which Chemical Affinity is effective ?
Does chemical affinity bring particles of Different kinds to unite, or those of the Same kind ?
What effect does chemical union have on the cotrosive qualities of the acids and alkalies?
When is an acid said to be Saturated ?
Does saturation destroy the active principles of an acid, or only restrain its action ?
What is the General Effect which chemical combination has on the Properties of bodies ?
One some illustrations of this effect.
What is the difference between mixture and combination ?
W hat are four of the most Obvious Changes which result from chemical combinations ?
Give an example of the change of colour.
Give an example of the change of specific gravity.
In what cases does change of temperature take place ?
Give some examples of the changes o/'form.
Give an illustration of Elf.cttve Affinity?
What will be the chemical effect of adding sulphuric acid to a solution of muriate ot lime ?
Draw a diagram to illustrate elective a ffinity.
Con struct a short table slurwing the relative forces of affinity between several subHames.
What are the uses of tables, showing the relative forces of affinity?
From what circumstunce is it inferred that the force of chemical affinity is great?
Under what circumstances does Complex Affinity take place ?
Describe the changes of composition which take place, when muriate of lime (tnd sulphate of soda, are mixed together.
What is the cause of the turbidness which attends this mixture ?
OF THE GASES.
It frequently happens that the conpound of two principles cannot be destroyed either by a third or fourth separately applied; but if the third and fourth be combined, and placed in contact with the former compound, a decomposition, or a change of principles will ensue. Thus when lime is added to a solution of sulphate of soda, no decomposition happens, because the sulphuric acid attracts the soda more strongly than it attracts lime. If muriatic acid be applied to the same compound, still its principles remain undisturbed, because the sulphuric acid attracts soda more strongly than the muriatic acid does. But if the lime and muriatic acid previously combined be mixed with the sulphate of soda a double decomposition is effected. The lime leaving the muriatic acid, unites with the sulphuric acid ; and the soda, being separated from the sulphuric acid combines with the muriatic. These decompositions are rendered more intelligible by the following diagram.
Muriate of Soda.
Sulphate
of
Soda.
Soda. Muriatic acid.
Sulphuric acid. Lime.
Muriate
of Lime.
Sulphate of Lime. On the outside of the vertical brackets are placed the original compounds, sulphate of soda and muriate of lime; and above and below the diagram, the new compounds. The upper line being strait, indicates that the muriate of soda remains involution, and the middle of the lower line being directed downwards, shows that the sulphate of lime is precipitated.
OA*. The turbid, or milky appearance which is seen on adding the clear solutions of muriate of lime and sulphate of soda together, is owing to the fact that one of the newly formed salts, sulphate of lime, is insoluble in water, and consequently is precipitated, or falls to the bottom of the vessel occasioning in its descent the turbidness. The same appearance is seen in every case where an insoluble precipitate is formed by chemical decomposition.
81. Experiments illustrating chemical affinity.
Exp. Mix together some olive oil and water in a vial. The oil will rise to the top of the water, and cannot be made to unite with it, there being no affinity between them. But if some pieces of potash be added, and the vial shaken, there takes place a chemical union between the three substances.
Oba. The potash having an affinity both for the oil and the water, it attracts each with a force sufficient to effect their union. In this manner soap is formed.
83. Bodies do not act on each othw unless either one I or both are in a state of solution, or at least contain water.
Illus. Spread thinly on a piece of tinfoil three or four inches square, some dry nitrate of copper and wrap it up. No effect will be produced. Unfold the tinfoil and having sprinkled the nitrate of copper with the smallest possible quantity of water, wrap the tinfoil up again as quickly as possible, pressing down the edges closely. Considerable heat attended with copious red fumes, will now be excited; and if the experiment has been dexterously made, sparks of fire or even name will be emitted.
Olts. This shows that nitrate of copper has no action on tin, except it is in a state of solution.
84. Experiments illustrating single elective affinity. Exji. 1. Add to a solution of soap in water a few drops of
sulphuric, or any other acid. The acid will combine with the A potash ; the oil will be set free, and will rise to the top. * Obs. The same effect is produced by those waters which naturally contain a small quantity of any acid, as the carbonic. These waters are called hard and will not wash, because the acid which they contain decomposes the soap.
2. To a solution of camphor in spirits or alcohol, add a quantity of water. The mixture will instantly become white and turbid, and the camphor will rise to the top in flakes.
Obs. The alcohol has a stronger attraction for the water than it has for the camphor, it therefore leaves the latter and unites to the former, while the camphor being insoluble in water takes the solid form, and rises to the top because it is of less specific gravity than the fluid.
85. The properties characterizing bodies when separate, are destroyed by chemical combination, and new properties appear in the compound.
Ilhis. Thus, muriate acid and lime, which in a separate state have a most corrosive taste, lose this entirely when mutually saturated ; the compound is extremely soluble, though lime itself is very difficult of solution: the acid no longer reddens syrup of violet, nor does the lime change it as before to green. The resulting compound, muriate of lime also exhibits new properties. It has an intensely bitter taste; is susceptible of crystalization, and the crystals when mixed with snow or ice, generate a degree of cold sufficient to freeze mercury.
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.