The Boy's Playbook of Science Part 8

When the crystallization is accomplished, the whole ma.s.s is usually so completely solidified, that on inverting the vessel, not a drop of liquid falls out.

[Ill.u.s.tration: Fig. 89. A. Gas-jar, with stopper open at first, to be shut when the lamp is withdrawn. B. Wooden stand, with hole to carry the cup C, containing the benzoic acid, heated below by the spirit-lamp, S.

F. Flowers or sprigs arranged on pieces of rock or mineral.]

[Page 79]

It may be observed that the same ma.s.s of salt will answer any number of times the same purpose. All that is necessary to be done, is to place the vial or flask, in a saucepan of warm water, and gradually raise it to the boiling point till the salt is completely liquefied, when the vessel must be corked and secured from the air as before. When the solidification is produced much heat is generated, which is rendered apparent by means of a thermometer, or by the insertion of a copper wire into the pasty ma.s.s of crystal in the flask, and then touching an extremely thin shaving or cutting of phosphorus, dried and placed on cotton wool. Solidification in all cases produces heat. Liquefaction produces cold.

In Masters's freezing apparatus certain measured quant.i.ties of crystallized sal-ammoniac, nitre, and nitrate of ammonia, are placed in a metallic cylinder, surrounded with a small quant.i.ty of spring water contained in an outer vessel. Directly the crystals are liquefied by the addition of water, intense cold is produced, which freezes the water and forms an exact cast of the inner cylinder in ice, and this may afterwards be removed, by pouring away the liquefied salts, and filling the inner cylinder, with water of the same temperature as the air, which rapidly thaws the surrounding ice, and allows it to slip off into any convenient vessel ready to receive it. (Fig. 90.)

[Ill.u.s.tration: Fig. 90. A. The inner cylinder which contains the freezing mixture. B B. The outer one containing spring water. C C. The ice slipping away from the inner cylinder.]

For an ingenious method of obtaining large and perfect crystals of almost any size, experimentalists are indebted to Le Blanc. His method consists in first procuring small and perfect crystals--say, octohedra of alum--and then placing them in a broad flat-bottomed pan, he pours over the crystals a quant.i.ty of saturated solution of alum, obtained by evaporating a solution of alum until a drop taken out crystallizes on cooling. The positions of the crystals are altered at least once a day with a gla.s.s rod, so that all the faces may be alternately exposed to the action of the solution, for the side on which the crystal rests, or is in contact with the vessel, never receives any increment. The crystals will thus gradually grow or increase in size, and when they have done so for some time, the best and most symmetrical, may be removed and placed separately, in vessels containing some of the same saturated [Page 80] solution of alum, and being constantly turned they may be obtained of almost any size desired.

Unless the crystals are removed to fresh solutions, a reaction takes place, in consequence of the exhaustion of the alum from the water, and the crystal is attacked and dissolved. This action is first perceptible on the edges and angles of the crystal; they become blunted and gradually lose their shape altogether. By this method crystals may be made to grow in length or breadth--the former when they are placed upon their sides, the latter if they be made to stand upon their bases.

On Le Blanc's principle, beautiful crystal baskets are made with alum, sulphate of copper, and bichromate of potash. The baskets are usually made of covered copper wire, and when the salts crystallize on them as a nucleus or centre, they are constantly removed to fresh solutions, so that the whole is completely covered, and red, white, and blue sparkling crystal baskets formed. They will retain their brilliancy for any time, by placing them under a gla.s.s shade, with a cup containing a little water.

The sketch below affords an excellent ill.u.s.tration of some of Nature's remarkable concretions in the peculiar columnar structure of basalt.

[Ill.u.s.tration: Fig. 91. The Giant's Causeway.]

[Page 81]

CHAPTER X.

CHEMISTRY.

[Ill.u.s.tration: Fig. 92. Alchemists at work.]

There is hardly any kind of knowledge which has been so slowly acquired as that of chemistry, and perhaps no other science has offered such fascinating rewards to the labour of its votaries as the _philosopher's stone_, which was to produce an unfailing supply of gold; or _the elixir of life_, that was to give the discoverer of the gold-making art the time, the prolonged life, in which he might spend and enjoy it.

Hundreds of years ago Egypt was the great depository of all learning, art, and science, and it was to this ancient country that the most celebrated sages of antiquity travelled.

Hermes, or Mercurius Trismegistus, the favourite minister of the Egyptian king Osiris, has been celebrated as the inventor of the art of alchemy, and the first treatise upon it has been attributed to Zosymus, of Chemnis or Panopolis. The Moors who conquered Spain were remarkable [Page 82] for their learning, and the taste and elegance with which they designed and carried out a new style of architecture, with its lovely Arabesque ornamentation. They were likewise great followers of the art of alchemy, when they ceased to be conquerors, and became more reconciled to the arts of peace. Strange that such a people, thirsting as they did in after years for all kinds of knowledge, should have destroyed, in the persons of their ancestors, the most numerous collection of books that the world had ever seen: the magnificent library of Alexandria, collected by the Ptolemies with great diligence and at an enormous expense, was burned by the orders of Caliph Omar; whilst it is stated that the alchemical works had been previously destroyed by Diocletian in the fourth century, lest the Egyptians should acquire by such means sufficient wealth to withstand the Roman power, for gold was then, as it is now, "the sinews of war."

Eastern historians relate the trouble and expense incurred by the succeeding Caliphs, who, resigning the Saracenic barbarism of their ancestors, were glad to collect from all parts the books which were to furnish forth a princely library at Bagdad. How the learned scholar sighs when he reads of seven hundred thousand books being consigned to the ignominious office of heating forty thousand baths in the capital of Egypt, and of the magnificent Alexandrian Library, a mental fuel for the lamp of learning in all ages, consumed in bath furnaces, and affording six months' fuel for that purpose. The Arabians, however, made amends for these barbarous deeds in succeeding centuries, and when all Europe was laid waste under the iron rule of the Goths, they became the protectors of philosophy and the promoters of its pursuits; and thus we come to the seventh century, in which Geber, an Arabian prince lived, and is stated to be the earliest of the true alchemists whose name has reached posterity.

Without attempting to fill up the alchemical history of the intervening centuries, we leap forward six hundred years, and now find ourselves in imagination in England, with the learned friar, Roger Bacon, a native of Somersetshire, who lived about the middle of the thirteenth century; and although the continual study of alchemy had not yet produced the "stone," it bore fruit in other discoveries, and Roger Bacon is said, with great appearance of truth, to have discovered gunpowder, for he says in one of his works:--"From saltpetre and _other_ ingredients we are able to form a fire which will burn to any distance;" and again alluding to its effects, "a small portion of matter, about the size of the thumb, _properly disposed_, will make a tremendous sound and coruscation, by which cities and armies might be destroyed." The exaggerated style seems to have been a favourite one with all philosophers, from the time of Roger Bacon to that of Muschenbroek of the University of Leyden, who accidentally discovered the Leyden jar in the year 1746, and receiving the first shock, from a vial containing a little water, into which a cork and nail had been fitted, states that "he felt himself struck in his arms, shoulders, and breast, so that he lost his breath, and was _two days_ before he recovered from the effects of the blow and the terror;" [Page 83] adding, that "he would not take a _second_ shock for the kingdom of France." Disregarding the numerous alchemical events occurring from the time of Roger Bacon, we again advance four hundred years--viz., to the year 1662, when, on the 15th of July, King Charles II. granted a royal charter to the Philosophical Society of Oxford, who had removed to London, under the name of the Royal Society of London for Promoting Natural Knowledge, and in the year 1665 was published the first number of the _Philosophical Transactions_; this work contains the successive discoveries of Mayow, Hales, Black, Leslie, Cavendish, Lavoisier, Priestley, Davy, Faraday; and since the year 1762 has been regularly published at the rate of one volume per annum. With this preface proceed we now to discuss some of the varied phenomena of chemical attraction, or what is more correctly termed

CHEMICAL AFFINITY.

The above t.i.tle 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 cla.s.sification 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 pa.s.s 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 a.n.a.lysed, 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 [Page 84] 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 ([Greek: _dis_] twice, and [Greek: _morphe_] a form), and, Proteus-like, can a.s.sume two forms.

Take another ladle, and melt some nitre in it at a dull red heat, then add a small quant.i.ty 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 pota.s.sium, 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 pa.s.sed 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 pota.s.sium 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 pota.s.sium, 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 pota.s.sium under such circ.u.mstances is another striking proof of the opposite qualities of the three elements--sulphur, oxygen, and pota.s.sium--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 [Page 85] 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 pa.s.sing 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 const.i.tuents, 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.

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CLa.s.sIFICATION 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.

7. Fluorine F = 18.9 8. Carbon C = 6 9. Boron B = 10.9 10. Sulphur S = 16 11. Phosphorus P = 32 12. Silicon Si = 21.3 13. _Selenium_ Se = 39.5

51 _Metals._

1. Aluminum Al = 13.7 2. Antimony Sb = 129 3. a.r.s.enic As = 75 4. Barium Ba = 68.5 5. Bis.m.u.th 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. Pota.s.sium 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. _t.i.tanium_ 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.)

[Footnote 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. [Page 87] 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 repet.i.tion of long words, just as the signs + plus, and - minus, are used in algebraic formulae. For instance--the constant recurrence of water in chemical combinations must be named, and would involve the most tedious repet.i.tion; 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 C_{4}H_{4}O_{2}, 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 C_{30}H_{12}.

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 quant.i.ties 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 a.n.a.lysis 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 quant.i.ty 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

CHEMICAL EXPERIMENTS.

As the permanent gases head the list, they will first engage our attention, beginning with the element oxygen--Symbol O, combining proportion 8. There is nothing can give a better idea of the enormous quant.i.ty of oxygen present in the animal, vegetable, and mineral kingdoms, than the statement that it represents _one-third_ of the weight of the whole crust of the globe. Silica, or flint, contains about half its weight of oxygen; lime contains forty per cent.; alumina about thirty-three per cent. In these substances the element oxygen remains inactive and powerless, chained by the strong fetters of chemical affinity to [Page 88] the silicium of the flint, the calcium of the lime, and the aluminum of the alumina. If these substances are heated by themselves they will not yield up the large quant.i.ty of oxygen they contain.

Nature, however, is prodigal in her creation, and hence we have but to pursue our search diligently to find a substance or mineral containing an abundance of oxygen, and part of which it will relinquish by what used to be called by the "old alchemists" the _torture_ of heat. Such a mineral is the black oxide of manganese, or more correctly the binoxide of manganese, which consists of one combining proportion of the metal manganese--viz., 27.6, and two of oxygen--viz., 8 2 = 16. If three proportions of the binoxide of manganese are heated to redness in an iron retort, they yield one proportion (equal to 8) of oxygen, and all that has just been explained by so many words is comprehended in the symbols and figures below:--

3 MnO_{2} = Mn_{3}O_{4} + _O_.

Thus the 3 MnO_{2} represent the three proportions of the binoxide of manganese before heat is applied, whilst the sign =, the sign of equation (equal to), is intended to show that the elements or compounds placed _before_ it produce those which _follow_ it; hence the sequel Mn_{3}O_{4} + _O_ shows that another compound of the metal and oxygen is produced, whilst the + _O_ indicates the liberated oxygen gas. The iron retort employed to hold the mineral should be made of cast iron in preference to wrought iron, as the latter is very soon worn out by contact with oxygen at a red heat. A gun-barrel will answer the purpose for an experiment on the small scale, to which must be adapted a c.o.c.k and piece of pewter tubing. Such a make-shift arrangement may do very well when nothing better offers; but as a question of expense, it is probably cheaper in the end to order of Messrs. Simpson and Maule, or of Messrs. Griffin, or of Messrs. Bolton, a cast-iron bottle, or cast-iron retort, as it is termed, of a size sufficient to prepare two gallons of oxygen from the binoxide of manganese, which, with four feet of iron conducting-pipe, and connected to the bottle with a screw, does not [Page 89] cost more than six shillings--an enormous dip, perhaps, in the juvenile pocket, and therefore we shall indicate presently a still cheaper apparatus for the same purpose. (Fig. 93.)

[Ill.u.s.tration: Fig. 93. A. The iron bottle, containing the black oxide of manganese, with pipe pa.s.sing to the pneumatic trough, B B, in which is fixed a shelf, C, perforated with a hole, under which the end of the pipe is adjusted, and the gas pa.s.ses into the gas-jar, D.]