CHEMICAL AFFINITY.
The above title refers to an endless series of changes brought about by chemical combinations, all of which can be reduced to certain fixed laws, and admit of a simple classification and arrangement. A mechanical aggregation, however well arranged, can be always distinguished from a chemical one. Thus, a grain of gunpowder consists of nitre, which can be washed away with boiling water, of sulphur, which can be sublimed and made to pass away as vapour, of charcoal, which remains behind after the previous processes are complete; this mixture has been perfected by a careful proportion of the respective ingredients, it has been wetted, and ground, and pressed, granulated, and finally dried; all these mechanical processes have been so well carried out that each grain, if analysed, would be similar to the other; and yet it is, after all, only a mechanical aggregation, because the sulphur, the charcoal, and the nitre are unchanged. A grain of gunpowder moistened, crushed, and examined by a high microscopic power, would indicate the yellow particles of sulphur, the black parts of charcoal, whilst the water filtered from the grain of powder and dried, would show the nitre by the form of the crystal. On the other hand, if some nitre is fused at a dull red heat in a little crucible, and two or three grains of sulphur are added, they are rapidly oxidized, and combine with the potash, forming sulphate of potash; and after this change a few grains of charcoal may be added in a similar manner, when they burn brightly, and are oxidized and converted into carbonic acid, which also unites in like manner with the potash, forming carbonate of potash; so that when the fused nitre is cooled and a few particles examined by the microscope, the charcoal and sulphur are no longer distinguishable, they have undergone a chemical combination with portions of the nitre, and have produced two new salts, perfectly different in taste, gravity, and appearance from the original substances employed to produce them. Hence chemical combination is defined to be "that property which is possessed by one or more substances, of uniting together and producing a third or other body perfectly different in its nature from either of the two or more generating the new compound."
To return to our first experiment with the gunpowder: take sulphur, place some in an iron ladle, heat it over a gas flame till it catches fire, then ascend a ladder, and pour it gently, from the greatest height you can reach, into a pail of warm water: if this experiment is performed in a darkened room a magnificent and continuous stream of fire is obtained, of a blue colour, without a single break in its whole length, provided the ladle is gradually inclined and emptied. The substance that drops into the warm water is no longer yellow and hard, but is red, soft, and plastic; it is still sulphur, though it has taken a new form, because that element is dimorphous (δις twice, and μορφη a form), and, Proteus-like, can assume two forms. Take another ladle, and melt some nitre in it at a dull red heat, then add a small quantity of sulphur, which will burn as before; and now, after waiting a few minutes, repeat the same experiment by pouring the liquid from the steps through the air into water; observe it no longer flames, and the substance received into the water is not red and soft and plastic, but is white, or nearly so, and rapidly dissolves away in the water. The sulphur has united with the oxygen of the nitre and formed sulphuric acid, which combines with the potash and forms sulphate of potash; here, then, oxygen, sulphur, and potassium, have united and formed a salt in which the separate properties of the three bodies have completely disappeared; to prove this, it is only necessary to dissolve the sulphate of potash in water, and after filtering the solution, or allowing it to settle, till it becomes quite clear and bright, some solution of baryta may now be added, when a white precipitate is thrown down, consisting of sulphate of baryta, which is insoluble in nitric or other strong acids. The behaviour of a solution of sulphate of potash with a nitrate of baryta may now be contrasted with that of the elements it contains; on the addition of sulphur to a solution of nitrate of baryta no change whatever takes place, because the sulphur is perfectly insoluble. If a stream of oxygen gas is passed from a bladder and jet through the same test, no effect is produced; the nitrate of baryta has already acquired its full proportion of oxygen, and no further addition has any power to change its nature; finally, if a bit of the metal potassium is placed in the solution of nitrate of baryta it does not sink, being lighter than water, and it takes fire; but this is not in any way connected with the presence of the test, as the same thing will happen if another bit of the metal is placed in water—it is the oxygen of the latter which unites rapidly with the potassium, and causes it to become so hot that the hydrogen, escaping around the little red-hot globules, takes fire; moreover, the fact of the combustion of the potassium under such circumstances is another striking proof of the opposite qualities of the three elements—sulphur, oxygen, and potassium—as compared with the three chemically combined and forming sulphate of potash. The same kind of experiment may be repeated with charcoal; if some powdered charcoal is made red-hot, and then puffed into the air with a blowing machine, numbers of sparks are produced, and the charcoal burns away and forms carbonic acid gas, a little ash being left behind; but if some more nitre be heated in a ladle, and charcoal added, a brilliant deflagration (deflagro, to burn) occurs, and the charcoal, instead of passing away in the air as carbonic acid, is now retained in the same shape, but firmly and chemically united with the potash of the nitre, forming carbonate of potash, or pearl-ash, which is not black and insoluble in water and acids like charcoal, but is white, and not only soluble in water, but is most rapidly attacked by acids with effervescence, and the carbon escapes in the form of carbonic acid gas. Thus we have traced out the distinction between mechanical aggregation and chemical affinity, taking for an example the difference between gunpowder as a whole (in which the ingredients are so nicely balanced that it is almost a chemical combination), and its constituents, sulphur, charcoal, and nitre, when they are chemically combined; or, in briefer language, we have noticed the difference between the mechanical mixture, and some of the chemical combinations, of three important elements. Our very slight and partial examination of three simple bodies does not, however, afford us any deep insight into the principles of chemistry; we have, as it were, only mastered the signification of a few words in a language; we might know that chien was the French for dog, or cheval horse, or homme man; but that knowledge would not be the acquisition of the French language, because we must first know the alphabet, and then the combination of these letters into words; we must also acquire a knowledge of the proper arrangement of these words into sentences, or grammar, both syntax and prosody, before we can claim to be a French scholar: so it is with chemistry—any number of isolated experiments with various chemical substances would be comparatively useless, and therefore the "alphabet of chemistry," or "table of simple elements," must first be acquired. These bodies are understood to be solids, fluids, and gases, which have hitherto defied the most elaborate means employed to reduce them into more than one kind of matter. Even pure light is separable into seven parts—viz., red, orange, yellow, green, blue, indigo, and violet; but the elements we shall now enumerate are not of a compound, but, so far as we know, of an absolutely simple or single nature; they represent the boundaries, not the finality, of the knowledge that may be acquired respecting them.
The elements are sixty-four in number, of which about forty are tolerably plentiful, and therefore common; whilst the remainder, twenty-four, are rare, and for that reason of a lesser utility: whenever Nature employs an element on a grand scale it may certainly be called common, but it generally works for the common good of all, and fulfils the most important offices.
CLASSIFICATION OF THE ALPHABET OF CHEMISTRY.
13 Non-Metallic Bodies.
| Name. | Symbol. | Combining proportion or atomic weight. | |
| 1. | Oxygen | O = | 8 |
| 2. | Hydrogen | H = | 1 |
| 3. | Nitrogen | N = | 14 |
| 4. | Chlorine | Cl = | 35.5 |
| 5. | Iodine | I = | 127.1 |
| 6. | Bromine | Br = | 80.0 |
| 7. | Fluorine | F = | 18.9 |
| 8. | Carbon | C = | 6 |
| 9. | Boron | B = | 10.9 |
| 10. | Sulphur | Sv = | 16 |
| 11. | Phosphorus | P = | 32 |
| 12. | Silicon | Si = | 21.3 |
| 13. | Selenium | Se = | 39.5 |
| 1. Aluminium | Al = 13.7 |
| 2. Antimony | Sb = 129 |
| 3. Arsenic | As = 75 |
| 4. Barium | Ba = 68.5 |
| 5. Bismuth | Bi = 213 |
| 6. Cadmium | Cd = 56 |
| 7. Calcium | Ca = 20 |
| 8. Cerium | Ce = 47 |
| 9. Chromium | Cr = 26.7 |
| 10. Cobalt | Co = 29.5 |
| 11. Copper | Cu = 31.7 |
| 12. Donarium | |
| 13. Didymium | D |
| 14. Erbium | E |
| 15. Gold | Au = 197 |
| 16. Glucinum | Gl |
| 17. Iron | Fe = 28 |
| 18. Ilmenium | Il |
| 19. Iridium | Ir = 99 |
| 20. Lead | Pb = 103.7 |
| 21. Lanthanium | La |
| 22. Lithium | Li = 6.5 |
| 23. Magnesium | Mg = 12.2 |
| 24. Manganese | Mn = 27.6 |
| 25. Mercury | Hg = 100 |
| 26. Molybdenum | Mo = 46 |
| 27. Nickel | Ni = 29.6 |
| 28. Norium | |
| 29. Niobium | Nb |
| 30. Osmium | Os = 99.6 |
| 31. Platinum | Pt = 98.7 |
| 32. Potassium | K = 39.2 |
| 33. Palladium | Pd = 53.3 |
| 34. Pelopium | Pe |
| 35. Rhodium | R = 52.2 |
| 36. Rhuthenium | Ru = 52.2 |
| 37. Silver | Ag = 108.1 |
| 38. Sodium | Na = 23 |
| 39. Strontium | Sr = 43.8 |
| 40. Tin | Sn = 59 |
| 41. Tantalum | Ta = 184 |
| 42. Tellurium | Te = 64.2 |
| 43. Terbium | Tb |
| 44. Thorium | Th = 59.6 |
| 45. Titanium | Ti = 25 |
| 46. Tungsten | W[A]= 95 |
| 47. Uranium | U = 60 |
| 48. Vanadium | V = 68.6 |
| 49. Yttrium | Y |
| 50. Zinc | Zn = 32.6 |
| 51. Zirconium | Zr = 22.4 |
(N.B. The elements printed in italics are at present unimportant.)
[A] From the mineral Wolfram, and now exceedingly valuable, as when alloyed with iron it is harder than, and will bore through steel.
A few words will suffice to explain the meaning of the terms which head the names, letters, and numbers of the Table of Elements. The names of the elements have very interesting derivations, which it is not the object of this work to go into; the symbols are abbreviations, ciphers of the simplest kind, to save time and trouble in the frequent repetition of long words, just as the signs + plus, and - minus, are used in algebraic formulæ. For instance—the constant recurrence of water in chemical combinations must be named, and would involve the most tedious repetition; water consists of oxygen and hydrogen, and by taking the first letter of each word we have an instructive symbol, which not only gives us an abbreviated term for water, but also imparts at once a knowledge of its composition by the use of the letters, HO.
Again, to take a more complex example, such as would occur in the study of organic chemistry—a sentence such as the hydrated oxide of acetule, is written at once by C4H4O2, the figures referring to the number of equivalents of each element—viz., 4 equivalents of C, the symbol for carbon, 4 of H (hydrogen), and 2 of O (oxygen).
The long word paranaphthaline, a substance contained in coal tar, is disposed of at once with the symbols and figures C30H12.
The figures in the third column are, however, the most interesting to the precise and mathematically exact chemist. They represent the united labours of the most painstaking and learned chemists, and are the exact quantities in which the various elements unite. To quote one example: if 8 parts by weight of oxygen—viz., the combining proportions of that element—are united with 1 part by weight of hydrogen, also its combining number, the result will be 9 parts by weight of water; but if 8 parts of oxygen and 2 parts of hydrogen were used, one only of the latter could unite with the former, and the result would be the formation again of 9 parts of water, with an overplus of 1 equivalent of hydrogen.
It is useless to multiply examples, and it is sufficient to know that with this table of numbers the figures of analysis are obtained. Supposing a substance contained 27 parts of water, and the oxygen in this had to be determined, the rule of proportion would give it at once, 9: 27:: 8: 24. 9 parts of water are to 27 parts as 8 of oxygen (the quantity contained in 9 parts of water) are to the answer required—viz., 24 of oxygen. The names, symbols, and combining proportions being understood, we may now proceed with the performance of many interesting