This example and also the percentage examples can be proved by the following reasonings: 18 fluidounces glycerin sp. gr. 1.25 = 18 X 454.6 X 1.25 25 fluidounces alcohol sp. gr. 0.82 = 25 X 454.6 × 0.82 43 fluidounces of liquid weigh 43 fluidounces of water weigh 43 × 454.6 = = = 10228.5 grains. 19547.8 grains. · 19547.8 grains. Hence the mixture has about the same specific gravity as water, since 43 fluidounces of it weigh the same as 43 fluidounces of water. The same method is used to solve such examples as: What will be the specific gravity of a mixture of 5 fluidounces of solution of tersulphate of iron, specific gravity 1.555, and 3 fluidounces water? The figuring being as follows: Hence the liquid weighs 4898.33636.8 as much as water and has the specific gravity 1.346. While speaking of such examples, reference should be made to the simple example involving percentage solutions, such as: How much cocaine is needed for one fluidounce of a 5 per cent. solution? The absolutely accurate way of solving this is as follows: which represents the number of grains cocaine (hydrochloride presumably) needed to make the solution. In this case, however, in order to obtain accurate results, the 22.73 grains cocaine hydrochloride, must be weighed out, dissolved in water, and finished by bringing the finished solution up to 454.6 grains by weight, which, of course, will measure slightly less than one fluidounce. Another and less accurate method, very largely employed, is by taking 5 per cent. of 480 minims, or 24 grains, dissolving this in water to make a fluidounce. This, while by no means as accurate as the former process, is more convenient, and can be safely employed in preparing solutions in small percentages. A simple modification of alligation is that of percentages outlined in the last pharmacopoeia under alcohol, where a rule of dilution is given. The rule is practically as follows: If we have a 95 per cent. alcohol and want to dilute it to 20 per cent., we must then take 20 fluidounces of the 95 per cent. and add enough water to make 95 fluidounces; when we will have approximately 20 per cent. alcohol. It may also be solved by the regular process of alligation if we recast the problem to the following wording: How much 95 per cent. alcohol and 0° alcohol (water) needed to make 20 per cent. alcohol? Solved by "rule of the balance." This shows that we can reduce 95 per cent. alcohol to 20 per cent. by reversing the fluidounces with the percentages. That is, from 20 fluidounces of 95 per cent. alcohol we can make 95 fluidounces of 20 per cent. But suppose the question is: How much' 20 per cent. alcohol could be made from 5 fluidounces 95 per cent.? It is a case of simple proportion. If 20 fluidounces 95 per cent. give 95 fluidounces 20 per cent., 5 fluidounces 95 per cent. (4 of 20) will give us 4 of 95 fluidounces 20 per cent., or 2334 fluidounces. It is important that this be understood. The rule, by the way, applies exactly only when there is no diminution in volume. BIBLIOGRAPHY Hydrometers.—(History) Dornke and Reimerdes, Handbuch der Aräometrie, 1912; Bourgougnon, Ch. Zt. Rep., 16, 1892, 166; Lippmann, Ch. Zt., 36, 1912, 385 and 629. (General) Schelenz, Ch. Zt., 27, 1903, 88 and 39, 1915, 913. (Baume's) Pilé, A.Ph.A., 18, 1870, 155; Pemberton, A.J.P., 24, 1852, 1. Mohr-Westphal Balance.-Anon, N. R., 6, 1877, 78. Density of Wax.-Hager, Analyst, 4, 1879, 206; Dietrich, Ph. Zt., 32, 1887, 37. CHAPTER IV HEAT is that form of molecular motion which produces the physiologic sensation we call warmth, this molecular motion being produced by friction, electricity, light, or chemical action. In order to obtain a clear understanding of heat, a comprehension of the molecule as explained on p. 345 is essential. Suffice it to say here that molecules are very minute particles of matter, and these molecules, working among themselves, produce friction. That friction is the source of heat is well known, and can be demonstrated by such simple experiments as rubbing one surface on another when both become hot. This is shown by rubbing the finger rapidly on a piece of wood, when the sensation of warmth is transmitted to the body. It is also known that when any metallic body, such as an axle, rubs rapidly on its bearings, if the axle is not well greased to prevent this friction, the heat produced is sufficient to set fire to the surrounding objects, producing the condition called "hot box." Primitive people, such as Indians, becoming adept at the art, were able to kindle fires by rubbing two pieces of wood together. In each case we have a striking illustration of friction as a source of heat. Another source of heat is electricity, and in such cases the friction of the molecules of the non-conductor produces heat. In many cases the resistance causes the substance to glow or become incandescent. Such is the basis of the incandescent electric light in which the electricity is forced through a filament of poorly conducting carbon, the molecules of carbon, in resisting the electric pressure, being heated sufficiently to become incandescent. A discussion of the principles of electricity is beyond the scope of this work, and for details of this force the reader is referred to any standard text-book of physics. Suffice it here to state that electricity is a molecular condition, and that this condition is transmitted from one molecule to another with more or less rapidity, dependent on the character of the substance. influenced. Matter which rapidly transmits the electric condition from one molecule to another is called a conductor of electricity, while matter the molecules of which do not transmit the condition is said to be a nonconductor or a poor conductor. As the question of conduction of electricity is a purely relative matter -all bodies transmitting the condition to an extent more or less great— the terms above mentioned are gradually becoming obsolete, and the words "conductivity" and "resistance" being substituted to cover the respective meanings. When we talk of "the electric current" passing through a wire, we mean that the electric condition affecting the end molecule of the wire is rapidly transmitted to the adjoining molecule, and thence from one molecule to another, the whole length of the wire. This being clearly understood, we can use the simpler term, "passage of the electric current," in the following explanations. Electricity passes rapidly from molecule to molecule through a conductor; but if compelled to run through a non-conducting substance, it requires a current of high potential, of great force, to overcome the resistance of this body. Light also affords a minute amount of heat. Heat, light, and electricity are so-called physical forces affecting molecules, and are, under certain circumstances, convertible one into another. We have just seen that electricity is converted into heat; inversely. heat can be converted into electricity. By applying heat to two metal plates in close contact with each other, an electric current is formed in the apparatus known as the "pyroelectric battery." Hence it is not strange that light can be converted into heat, although the amount produced is very minute and very difficult to measure, inasmuch as almost invariably all sources of light are also sources of heat, and, therefore, it is very difficult to isolate light from its accompanying heat. Chemical action is the chief source of heat. This phenomenon, which is fully described on p. 347 means a breaking up of the molecules of a substance, with the formation of new molecules. This decomposition is accompanied with considerable movement of the molecules and their constituent atoms, thus producing a form of friction and, therefore, producing heat. Combustion. Most chemicals reacting on one another produce heat, although in some cases the reverse is true. As an illustration of heat produced by chemical action, iron combined with iodine in a test-tube in the presence of water will so heat the test-tube as to render it difficult to hold same in the hand. Likewise, sulphuric acid combined with solution. of soda produces great heat, and numberless other illustrations could be given. The production of heat by such chemical action is different from the chemical action in the burning of wood. The invariable accom paniment of the latter being flame, such form of chemical action is called combustion; that is, chemical action accompanied by heat and light. We know that wood is composed of hydrogen, oxygen, and carbon; that the air around us contains oxygen, and that by applying a flame to the wood there is commenced a chemical reaction which results in the formation, from the carbon hydrogen and oxygen that is present, of carbon dioxide (CO2) and of water (H2O). In this chemical reaction, as in the formation of ferrous iodide, heat is produced, and of much greater intensity. So great is the heat that some of the carbon, which in the hurry of the reaction escapes combination with the oxygen, glows with heat, just as does the carbon filament in the incandescent light. To prove the presence of incandescent carbon hold a plate over any luminous flame, when it will become blackened with soot, which is pure carbon. Whenever the combustion-as this reaction, in which the carbon and hydrogen of a substance combine with the oxygen of the air, is called-is accompanied by unchanged carbon glowing with heat, a flame is produced. Any substance with which we can perform a combustion is called fuel. Such matter is very abundant, and is found in all three states of aggregation-solids, liquids, and gases. Solid Fuels. The solid fuels are wood, coal, and charcoal. Wood contains hydrogen and oxygen besides carbon, whereas coal and charcoal consist very largely of carbon. In the case of each fuel the chemical action involved is the combination of the carbon with the oxygen of the air, forming carbon monoxide and carbon dioxide, with more or less particles of unconsumed carbon, called soot. In burning solid fuels the apparatus designed to contain same is called stove or furnace, and consists fundamentally of the fire-box in which the fuel is held, the chimney or flues for removal of the gaseous products of combustion, and damper or vents for the admission of air necessary to produce the action. Provision is made, by means of grating, for the removal and storage of ashes, which constitute the inorganic salts present in wood or coal. In order to produce successful combustion the oxygen of the air is absolutely necessary, hence if a furnace or stove is not supplied with sufficient air, the fire within the box will be "smothered" or " go out." This explains the method of smothering a fire by surrounding the burning substance with blankets, thus preventing access of air. In order to produce good combustion, a comparatively good draft of air must be had, the intensity of the draft being regulated by the opening or closing of the vents or dampers, and in large furnaces by the relative height of the chimney or smoke-stack. For the practical application of combustion of solid fuels the reader is referred to any kitchen-range or house-furnace. The liquids used as fuels are alcohol and petroleum products (gasoline and insurance oil, etc.). In using liquids as fuel there are two methods employed: If the liquid is not very volatile, such as insurance oil, astral oil, etc., the liquid is sucked up through a wick by capillary attraction, and burned as a liquid off the top of the wick. Such a method is also employed in the burning of the volatile liquid alcohol in the ordinary alcohol lamp (Fig. 36). In cases where the liquid is quite volatile (as gasoline), the apparatus used for the purpose is so arranged that the liquid is first converted into vapor and this vapor burned. Such is the principle of the vapor stove (Fig. 37), which possesses a great advantage over the wick stoves by having the vapor burned mixed with air, as in the Bunsen burner, thus preventing a sooty flame. Alcohol is also burned in the form of vapor in the so-called "Russian blast lamp," which produces an intensely hot flame (Fig. 38). Gaseous Fuels.-The gases used to produce heat are coal-gas, acetylene, and natural gas, the first two being manufactured, while the latter is obtained in certain sections of the world by simply sinking iron tubes, through which the gas escapes from pockets under the earth's surface. As to the manufacture of artificial gas, coal-gas is made by the destructive distillation of coal; details of the manufacture can be found in any advanced work on technical chemistry. Acetylene is produced by the action of water on calcium carbide. Chemically, these fuel gases resemble one another, all being combinations of carbon, which furnishes the heat and light when consumed in the presence of air in the operation of combustion in different forms of of burners, according as the intention is to produce a luminous or a nonluminous flame, the latter being used for heating purposes. A luminous flame is produced in the so-called "fish-tail" burner, in which the gas, as it comes in contact with the air, is ignited by a match or other flame, burning to carbon dioxide and water with incomplete combustion; that is, in the reaction all the carbon is not consumed, and the unconsumed carbon, through the influence of the intense heat generated by the chemical reaction, glows with heat, or, technically expressed, becomes "incandescent." Another example of incandescence is the brilliant light produced when metallic magnesium is burned (p. 460). Why can some part of the carbon escape chemical combustion? |