Patina

“ Great importance has always been attached by Japanese experts to the patina of metal used for artistic chiselling. It was mainly for the sake of their patina that value attached to the remarkable alloys shakudo (3 parts of gold to 97 of copper) and shibuichi (1 part of silver to 3 of copper) . Neither Patina. metal, when it emerges from the furnace, has any beauty, shakudo being simply dark-coloured copper and shibuichi pale gun-metal. ”

“ By friction, two pieces of ice may be made to melt each other; and could we, by mechanical pressure, force water into a solid state, an immense quantity of heat would be set free. By the condensation of hydrogen and oxygen gases, pulverulent platinum will become glowing red-hot, and, with certain precautions, even the compact metal, platinum, itself; the heat being derived from the gases, the union of which it has effected. A body passing from the solid to the fluid state absorbs heat from all surrounding substances, and hence a degree of cold is produced. ”

“ The chemist thus interprets the phenomenon:—Water is a compound of oxygen and a highly inflammable gas called hydrogen; when potassium is thrown into Water it combines with a portion of its oxygen to form potash, and the heat which attends their union sets fire to the liberated hydrogen. It is not the metal that burns so furiously, but one of the constituents of water.
Here is a revelation far more wonderful than anything we find in our old story books!
Oxygen gas is the great supporter of combustion; even the metals will burn away in it like tinder. Hydrogen is the lightest gas known ”

“ One of the most remarkable facts in chemistry—a science abounding in wonders—is the circumstance that the mere contact of hydrogen, the lightest body known, with the metal platinum, the heaviest when in a state of minute division called spongy platinum, produces an intense heat sufficient to inflame the hydrogen; of course this experiment must be made in the presence of atmospheric air or oxygen. If a small piece of the metal in the state above named be introduced into a mixture of oxygen and hydrogen, it will cause them to explode. ”

“ Put any measured quantity of the water into a platina, or silver evaporating basin, the weight of which is known, and evaporate the water upon a steam bath, at a temperature of about 180°, nearly to dryness; and, lastly, remove the basin to a sand bath, and let the mass be evaporated to perfect dryness. The weight of the platina basin being already known, we have only to weigh it carefully. When the solid saline contents of the water is attached to it, the increase of weight gives the quantity of solid matter contained in a given quantity of the water. ”

“ With much more reason, as it appears to me, might a person object to the common term metal, as applied to things so very different from one another as gold, quicksilver, and lead.
Besides, acid and alkaline air do not differ from common air (in any respect that can countenance an objection to their having a common appellation) except in such properties as are common to it with fixed air, though in a different degree; viz. that of being imbibed by water. But, indeed, all kinds of air, common air itself not excepted, are capable of being imbibed by water in some degree. ”

“ I would now observe, that no substance possesses absolutely any one of those conditions; that modern chemistry recognises nothing unchangeably solid, liquid, or aeriform: means have been devised for effecting a change of state in almost every known substance. Platinum, alumina, and rock crystal, it is true, cannot be liquified by the most intense heat of our furnaces, but they melt like wax before the flame of the oxy-hydrogen blowpipe. ”

“ It burns with a beautiful violet colour, and [Pg 391] a very pretty experiment may easily be performed by throwing a piece upon a basin of water. The fragment combines with the oxygen of the water, the hydrogen is evolved, and burns, and the potassium vapour gives the gas its purple or violet colour. The metal can be procured by pulverizing carbonate of potassium and charcoal, and heating them in an iron retort. The vapour condenses into globules in the receiver, which is surrounded by ice in a wire basket. ”

“ Our pint of water would then occupy 1800 times its present volume.
Let us now give a striking and beautiful illustration of chemical affinity. We will throw into this tumbler a piece of potassium (symbol K) half as large as a pea. This interesting metal was discovered by Davy in 1807. Its affinity for O is very great. As soon as it falls upon the water it abstracts oxygen and forms potassium oxide (potash) , while the hydrogen and a small amount of volatilized K escape and are burned with a brilliant violet flame, on account of the heat evolved by the energetic chemical action. ”

“ At such temperatures every metal would become fluid, even if it were not transformed into a cloud of vapour. But none of our laboratory experiments can tell us whether, under the pressure of thousands of tons on the square inch, the application of any heat whatever would be adequate to transform solids into liquids. It may indeed be reasonably doubted whether the terms solids and liquids are applicable, in the sense in which we understand them, to the materials forming the interior of the earth. ”

“ Is there any such thing as an igneous fluid? Is there anything that can with propriety be called caloric?
"We have seen that a very considerable quantity of heat may be excited in the friction of two metallic surfaces, and given off in a constant stream or flux in all directions without interruption or intermission, and without any signs of diminution or exhaustion.
"Whence came the heat which was continually given off in this manner in the foregoing experiments? Was it furnished by the small particles of metal, detached from the larger solid masses, on their being rubbed together? ”

“ The metal tin actually changes into powder below a certain temperature, and in so doing evolves a measurable quantity of heat. A mixture of the gases oxygen and hydrogen, in the proportions in which they combine to form water, evolves when burnt sufficient heat to raise more than thirty times its weight of water from the freezing to the boiling point ”

“ Heat a piece of the metal potassium in a metal spoon (platinum is best) , and if introduced in a state of ignition into the gas, it will continue burning brilliantly, producing a quantity of dense smoke, which is the carbon from the carbonic acid, the potassium having seized the oxygen, and being converted by it into potash. ”

“ Thus, when a gas is absorbed by water, much heat is evolved, and we may suppose the result to be due in part to chemical combination, and in part to the condensation of the gas into a liquid, by which means its latent heat is rendered sensible. On the other hand, when a liquid unites with a solid, or when two solids unite with one another, and the product is a liquid, we have very often the absorption of heat, the heat rendered latent by the dissolution of the solid being more than that generated by combination. ”

“ When water is heated to 212° it is converted completely into a gas, which gas returns to the fluid state without any loss on cooling below 212°. In like manner if we raise an essential-oil, such as turpentine, to 320°, or oil of peppermint to 340°, or orange-peel oil to 345°, or patchouli to 489°, and other such oils to various other temperatures, they pass into a state of vapor, and these vapors, when cooled, recondense into their original form of liquid oil without alteration. ”

“ It will be remembered that the amount of gas obtained by distillation, from the very best coal, ranged between 10,000 and 16,000 cubic feet. Water-gas contains as a rule 40 to 50 per cent, of hydrogen, 30 to 40 per cent, of carbonic oxide, 10 per cent, of naphtha or petroleum gas, and a few per cent, of carbonic acid. The large proportion of heavy petroleum-gas (sp. gr. 0.600 to 0.700) and carbonic oxide (sp. gr. 0.967) makes its specific gravity much heavier than that of coal gas ”

“ Metals are conductors of the caloric. The heat accumulated in the still, rises to the cap, from whence it runs into the urns: with this difference—that the pewter, of which the cap and pipes are made, transmits less [Pg 31] caloric than copper, because it is less dense: and that bodies are only heated in reason of their density.
However, a great deal of heat is still communicated to the worm, and heats the water in which it is immersed. I diminish this inconvenience by putting a wooden pipe between the worm and the pipe of the third urn. ”

“ Liquefaction and Solidification of Gases.—Water boils at 100 degrees, under standard pressure, though evaporating at all temperatures; it vaporizes at a lower point if the pressure be less, as on a mountain, and at a higher temperature if the pressure be greater, as at points below the sea level. Alcohol boils at 78 degrees, standard pressure, and every liquid has a point of temperature and pressure above which it must pass into the gaseous state. Likewise every gas has a critical temperature above which it cannot be liquefied at any pressure. ”

“ If we add to hard water a quantity of sodium or potassium, the carbonate of lime is precipitated as a white or yellowish powder, according to the quantity of iron contained in the water, and a soft water remains.
The sun produces on a great scale in nature, what the chemist achieves on a smaller scale by evaporation or precipitation and cooling of steam, a water free of all mineral salts, which we call distilled water. ”

“ Water, flowing over a bed of this mineral, liberates the gas in the form of an almost invisible vapor. It is swept forward in a cloud by the wind, some of it is carried along above the course of the underground stream, and as soon as it reaches an opening in the earth, like a fissure crack in the rock or ground, the gas rises and whoever breathes it dies or is rendered unconscious for a time, according to the strength of the vapor. ”

“ Gas, therefore, in our nomenclature, becomes a generic term, expressing the fullest degree of saturation in any body with caloric; being, in [Pg 51] fact, a term expressive of a mode of existence. To distinguish each species of gas, we employ a second term from the name of the base, which, saturated with caloric, forms each particular gas. Thus, we name water combined to saturation with caloric, so as to form an elastic fluid, aqueous gas; ether, combined in the same manner, etherial gas; the combination of alkohol with caloric, becomes alkoholic gas ”

“ No, my dear; vapour is, indeed, an elastic fluid, and bears a strong resemblance to a gas; there are, however, several points in which they essentially differ, and by which you may always distinguish them. Steam, or vapour, owes its elasticity merely to a high temperature, which is equal to that of boiling water. And it differs from boiling water only by being united with more caloric, which, as we before explained, is in a latent state. When 183 steam is cooled, it instantly returns to the form of water; but air, or gas, has never yet been rendered liquid or solid by any degree of cold. ”

“ This button, treated by sulphuric acid, will suffer a loss of weight equal to the amount of silver present. The residuum, by quartation with silver and boiling with nitric acid, will part with its platinum, and the gold will remain pure. For more detailed explanations, see Platinum.
ATOMIC WEIGHTS or ATOMS, are the primal quantities in which the different objects of chemistry, simple or compound, combine with each other, referred to a common body, taken as unity. Oxygen is assumed by some philosophers, and hydrogen by others, as the standard of comparison. ”

“ By the aid of pressure and of low temperatures, the force of cohesion may be so far increased in many gases that they are readily converted into liquids, and we know now that with sufficient pressure and cold they may all be liquified. On the other hand, heat, which increases the vis viva of the molecules, converts liquids, such as water, alcohol and ether or gas into the aëriform state in which they obey all the laws of gases. The aëriform state of liquids is known by the name of vapor, while gases are bodies which, under ordinary temperature and pressure, remain in the aëriform state. ”

“ Perfectly pure water is without taste: even the pleasant character of freshly-drawn spring-water is due to the admixture of atmospheric air and carbonic acid. The manner in which water absorbs air is evidently due to a peculiar physical attractive force, the value of which we do not at present clearly perceive or correctly estimate. It is chemically composed of two volumes of hydrogen gas—the lightest body known, and at the same time a highly inflammable one—united with one volume of oxygen, which excites combustion, and continues that action,—producing heat and light,—with great energy. ”

“ Such gas likewise tarnishes all metallic bodies—it discolours the paintings effected with metallic oxids, and always produces a suffocating odour very noxious to health. It is freed from the sulphuretted hydrogen and may be rendered fit for illumination by passing it repeatedly through very dilute solutions of sub-acetate of lead, green sulphate of iron, quicklime and water, or hyper-oxymuriate of lime. ”

“ Gases in many cases undergo a remarkable condensation when chemically combined. In slaking lime, the water becomes solid in the molecules of the hydrate of lime formed, and the intense heat produced arises from the liberation of that caloric which had been employed to keep the water liquid. When a solid passes into the liquid state, cold is produced by the abstraction from surrounding objects of the heat required to effect fluidity. An alteration of temperature occurs whenever chemical change takes place, as we have already shown, with a few trivial and uncertain exceptions. ”