POPULAR MINING GEOLOGY.

Otago Witness, Issue 1950, 4 April 1889, Page 12

POPULAR MINING GEOLOGY.

Bt J. A. Miller.

VI.-SOME CHEMICAL FACTORS. The properties by which bodies^are distinguisbed are either physical or chemical. To the physical properties belong those peculiarities which are perceptible to the senses, such as colour, smell, taste ; while the chemical properties cannot be determined in this manner, because the body in order to ba investigated must undergo a change. When it is said of sulphur that it is yellow, crystallises in rhombic octahedrons, and melts at 112deg, the physical properties of sulphur are described ; but when it is added that sulphur burns with a blue flame and- gives out a peculiar snad^ its chemical properties are referred to, .because ittey denote, a change the body is undergoing as it enters into new combinations during tjhe axjfe of burning, ■

, Ifc'is necessary to observe- this distinction when dealing with' chemical factors. Amongst the chemical factors which work the most rapid and most momentous changes in the air, in the water, in the solid crust of, the earth, in the plants and in the animals upon- its surface, heat, electricity, magnetism, crystallisation, pressure ; acids, salts, alkalis, bases ; and air and water are the most important ones. ! Heat has been defined as " the great worker of the universe," and it may with equal fitness be called the mother of the earth, for our globe, born of fire, is maintained by heat. Applied to matter of any kind, heat works changes in and upon them which are as wonderful as they are ' endless. It is as mysterious in its genial influence of light and warmth as when it bursts forth in its overwhelming terrors of the volcano. , Every act of chemical union generates heat. The combination of burning fuel and the oxygen ef the air causes the heat of our domestic fires, and gives the cheerful light in our habitations. When a crystal deposits and separates from a liquid a certain amount of heat is given off. Heat manifests itself as— ~(1) '• Expansion "—that is, bodies brought under its influence increase in bulk. (2) " Specific Heat," which is a fixed quantity of beat necessary to produce a defined change of temperature. (3) "Melting Point" is that degree of heat required for the liquefaotion or fusion of substances. (4) "Boiling Point" is that degree of heat necessary for converting substances into vapours, and for giving to gases and vapours a certain degree of elasticity. (5) "Latent Heat of liquids and gases is that degree of heat required to produce a given change of aggregation. (6) "Conduction and Radiation, of Heat" is the manner and rapidity of being susceptible to and of conducting and communicating heat. Electricity.— This astounding factor— the combination, it would appear, of two opposing forces equally powerful in their negative as in their positive functions — has so far baffled analysis, and therefore description. Electricity possesses analytical as well as synthetical powers. An electric current passed through water divides it into its component gases, oxygen and hydrogen, while the fluid disappears. These two gases, though in contact in the exact proportions required to form water, cannot unite again except on the application of a light or an electric spark, when the. two gases uniting again form water ; so that it may be said that electricity can make . and unmake, separate and combine, at the will of the operator. Crtstallisation.— When a liquid has taken up as much of a solid as it can contain, and further additions of the solid sink to the bottom in an unaltered state the liquid, h said to be " saturated." But a liquid, holding a solid in solution may be made to give up its prey by charging it with another body for which it has a greater affinity. Thus, if to a solution of nitre in water spirits of wine be added, the water combines with the spirits of wine, and drops the nitre to the bottom of the vessel. Cohesion alone may, and in most cases does, bring about a separation between solids and fluids by its own inherent force. In such cases one particle of a solid body separating from a liquid joins another par- | tide of the same kind, and in obedience of ! certain laws, as yet little understood, arrange themselves in regular and uniform bodies which resemble each other as if they all had been cast in one and the same mould. These bodies are called " crystals," and the process by which they are formed is " crystallisation." Bodies may also be crystallised by sublimation and evaporation, and it is also the case with some substances that they can be crystallised by more than one of the processes mentioned. However, fche same substance crystallised by different processes adopts forms which vary with the process, and also with the degree of temperature at which they were formed. Pressure. — By pressure is understood the effect of weight at rest. Thus the pressure of the atmosphere is said to be equal to 151b per square inch; the pressure of water is so great that at a pressure equal to a depth of 10,000 ft water may be heated to a white heat before it boils ; the pressure of the rocks is accepted to generate so great a heat as to melt at a depth of a few miles the most refractory rock. Pressure, therefore, is an important factor in the air, the water, and the earth, explaining many phenomena in Nature, working changes by chemical as well as mechanical means. Pressure acts only in vertically parallel directions with the weight, and not as in fluids and gases, where there is a lateral as well as a vertical pressure. ..Acids. — Acids are the] opposites to alkalis, and, as the word implies, have generally s sour taste. They colour litmus paper and vegetable blue red. With bases the acids form salts. No acid is a simple body, and nearly all acids are formed by the combiuation of oxygen with one of the demerits, in the proportion of two or more equivalents of oxygen to one of the element. Salts. — When an acid combines with a base a salt is formed. The principal salt makers Arc fluorine, chlorine, bromine, and iodine. They' ere all present in sea water, which is the great magazine whence three of them— chlorine, bromine, and iodjae-^ore obtained. Alkalis. — The alkalis neutralise the acids, and restore the blue colours turned into red by the acids. To the alkalis belong opium, morphium, narcotine, strychnine, atropine, coffeine, pepperine, and a host of other vegetable poisons. Combined with acids the alkalis form salts. Basks. — Bases originate in a combination of oxygen in fixed quantities with different metals, and have the property of neutralising the acids. The organic bases are most frequently met with in plants, they play an important part in medicine, and are known for their powerful effects upon animal organisms. All bases contain nitrogeu. A base is generally the ogide of a metal. Air.— Air performs most important functions in geology. Its chief component gases — oxygen, nitrogen, and carbon — act upon the hardest rooks, and when agitated by wind it is also a most powerful factor in abrading the most refractory substances. Water. — A factor that is so übiquitous, that is present in soch quantities, that acts both chemically and mechanically, that is as active upon the surface of the earth as in the inner* most recesses of the rooks, that is ever ready to' combine with other agents the most dissimilar imaginable to aid in the work of pulling down and building up, must play a part in the mutations of the globe and the life upon it that is second to none. Water is chiefly composed of hydrogen and oxygen, in proportions of one part of hydrogen and eight parts of oxygen in weight ; or in bulk, of two volnmes of hydrogen and one of oxygen. It absorbs and unites with solids and gases, and mixes readily with fluids. All the above factors act and re-act, solve and re-solve, pull down and build up. Here solid bodies disappear into gases, there gases form solid bodies ; fluids consume and carry away rocks in atoms, which are built up again in another, place. There is a constant exchange going on between the solids, fluids, and gases, transforming the whole creation. The green glow of spring, the gorgeous colours of the summer flowers', the fading shades', of autumn;,the ioe and. snow of winter— all, are the result of chemical aoHpn. The impulsive ardour of jouth, the strong self-reliant vigour of manhood, the ripe wisdom of age, tfcj very weakness and dewy

known to man as death, in their due and inviolable succession, express the temporary chemioal conditions of man. Nay, even the noblest thoughts, the most generous acts, the highest aspirations depend for their inception upon certain chemico- physical conformations, without which they would be impossible. A few additional chemical processes which will make the workings of Nature still more clear to the reader may follow. When nitric acid, which is of a yellow colour, is poured upon copper, it produces a green liquid which is neither acid nor metallic, and from which rises a gas, at first colourless, but after mixing with the equally colourless air, becomes a deep redbrown, the gas arising being neither liquid nor metallic. Zinc and copper plates placed in sulphuric acid baths, and connected by a silver wire, will emit sparks, accompanied with heat, light, and detonations, when the wire is broken in two. If to some liquid muriatic acid a mixture of lime and alumina be added, the lime will all be absorbed by the acid before a particle of the alumina will be taken up. If a thin piece of iron is put into nitric acid dens« brown fumes arise from the acid, the vapours being deadly poisonous. The acid is soon in a state of boil- j ing or fierce effervescence, though no fire be applied, which continues until the iron has disappeared, the atoms of the iron being taken up by the remaining liquid which has not been given off during the state of effervescence. A piece of iron and another of copper put into muriatic avid at the same time, the acid will at once attack the iron, and not until it has consumed the iron will it attack the copper. Such illustrations of the actions of substances one upon another might be given almost without end ; suffice it, however, to add one more, which must have been observed by most persons at some time or another in their lives. When a man sustains a wound from any cause and the pain subsides, it will be noted that from the lacerated flesh a yellow fluid, called " pus," is poured into the wound. This pus is described by a medical authority as follows : — " This remarkable morbid secretion has generally a specific gravity of 103 (only very little heavier than water). It consists of a clear liquid, in which float a great number of yellow globules of various sizes, the largest of which are about twice the size of the globules of the blood. Pus loses by drying 86*1 of water in 100 parts, and hence contains 13 9 of solid matter, from which alcohol takes 5*9 of fatty and extractive matters, and leaves 74 per cent, of a residue, which consists of coagulated albumen, the solid globules, and a substance peculiar to pus." And this is about ail that is known about pus, and yet out of it are built up the lymphatics, nerves, connecting tissue, blood vessels, skin, and even the very bone itself, though there is not a trace of any of these in the pus. If the pus is removed from the wound, as it forms the healing will be much delayed, it will be imperfectly done, leaving a hole or depression and an ugly scar. It may be assumed, therefore, that " the substance peculiar to pus" — to revert to the above quotation—does the work of healing and replacing the wanting tissues, and if so the process can be no other than a chemico-physiological one.

The illustration of the wound and its pus has been admitted here because of the strong analogy it bears to another process in Nature closely connected with "Mining Geology"; for the metalliferous lodes are, after all, nothing else but healed-up wounds in the crust of the earth inflicted by earthquakes or torn by some other convulsion, the lodes themselves representing the scars. As in the case of the wound, water in the place of pus, charged with the materials to build up- the lode, percolates into the fracture, bringing with it minute atoms of metal to be safely enclosed as a solatium, until the whole is filled up, the torn rent firmly cemented, and the fractured world made whole again.