1844.] 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL 



235 



But tthen li^liletl and put into oxygen it falls in a stieam of liquid fire. 

 These are all cases of communication j the taper is lighted from the candle, 

 and then can communicate to any number of combustibles. All combus- 

 tions are similar ; they are all successive; no such thing as instantaneous 

 combustion is known. In a mass of gunpowder, which seems to give but one 

 flash, the combustion travels from particle to particle, noonepiirticle becom- 

 ing ignited but by the flame of its neighbour ; even in each grain the combus- 

 tion is progressive, travelling from the outside to the inside. In a mixture of 

 two gases, where the particles must be in intimate contact, there is the nearest 

 approach to instantaneousness. Still, here, there is progression of flame. If 

 a mixture of hydrogen and oxygen be fired, the explosion sounds instanta- 

 neous. .So also does it if they be divided into bubbles by being made to pass 

 through a solution of soap, though here it is evident the flame from one 

 bubble must light the other. In a long narrow tube full of the same gases, 

 the flame is seen to run from end to end, and scarcely any noise is produced. 

 Still, in all this variety of circumstance, tlie amount of heat produced by the 

 same amount of combustible is always the same. The ignition of the mixture 

 of some other gases takes place more slowly ; with defiant gas and chlorine, 

 the flame is seen to travel slowly along, marking its progress by a dense de- 

 posit of soot. 



Many other substances are known, besides those commonly used, which 

 burn in the air. A certain preparation of lead, for instance, becomes red-hot 

 on exposure to air, and is called a pyrophorus. But a comparison of this 

 with a piece of charcoal will show the beautiful fitness of common fuel for the 

 purpose of heating. The charcoal continues to glow as long as it has air, 

 and at length leaves nothing but a very little light ash ; a mass of the pyro- 

 phorus, on the contrary, requires constant stirring to expose it to the air. 

 and more ash remains than fuel used. This would be a serious inconve- 

 nience, for before the pot could boil, the grate would be full of ashes, pre- 

 venting entirely the use of such powerful machines as steam engines. 



But there are other .sources of heat besides the chemical one of combustion, 

 and none more astonishing th.an the heat caused by friction ; there is nothing 

 more puzzling to the philosopher, and he is obliged to acknowledge that it is 

 entirely beyond his power of explanation. In other cases there is a limit to 

 its extent, a cause for its production ; but the heat from Iriction seems inex- 

 haustible, its origin inexplicable. Here there is no case of allinity, nothing 

 consumed. The Indian takes advantage of this source of heat, for he obtains 

 a light to kindle his fire, by means of rubbing together two pieces of dry 

 wood ; and the school boy burns his fellow's hand by a button which he has 

 rubbed on the f)rm on which they sit. In nature, the chafing together of 

 two branches of a tree frequently sets fire to a forest. Count Rumford kept 

 water boiling for hours together by the heat arising from friction. The lec- 

 turer saw an ingenious carpenter melt a small portion of glue by placing it in 

 the lioUow of a gouge and rubbing it a few times backwards and forwards. 

 The same may be done with a piece of jelly in a silver spoon. The fire from 

 a flint and steel is a case of both friction and combustion ; for the friction of 

 the blow of the flint causes a piece of iron to fly ofl' at such a heat that it 

 burns in the air ; ami although the hand can bear it with impunity, it has 

 heat enough to fire gunpowder, as is seen in the flint-lock of a gun. The 

 miner, frequently surrounded by an atmosphere of gaseous gunpowder ready to 

 blow him to pieces, cannot use a common fl ime ; and before Davy's invention 

 of the safety -lamp, a shower of sparks Irom a steel- mill, turned by a boy, was 

 the only light by which he ilare work. A dexterous smith avails himself of 

 the heat of friction to light a match, fur by a few blows of his hammer on a 

 uail, turning it at the same time on the anvil, he will make the point of it 

 red hot. This heat arises from the friction of the particles of iron against 

 each other, and has nothing to do with any alteration of its capacity for heat. 

 Lead becomes heated in the same manner. 



From heat electricity can be obtained, and from electricity heat; and 

 llie heat from the latter source can be considered as heat from friction, for 

 bodies evolve heat by the passage of electricity, just in proportion as they 

 resist 1 !s progress, or are bad conductors. A powerful current of electricity 

 from a galvanic battery may be made to develope great heat and light, by 

 sending it through various substances. Between charcoal points they are 

 most intense. Passed through wires the phenomena are different, accord- 

 ingly as they are good or bad conductors. In a chain, the links of which are 

 alternately silver and platinum, the platinum becomes red hot, whilst the 

 silver is not so ; and here, as in other cases of friction, there is no consump- 

 tion of any thing to produce this heat, neither the electricity is lost nor the 

 platinum consumed. 



Evolution of heat takes place in animals to a very great extent. They are 

 always giving heat ofl' to the air from their bodies, losing it by evaporation 

 of moisture from their surface, and giving it off by their breath, ami yet, in 

 the most frigid climate, the same temperature is maintained in their bodies, 

 which in most animals is far above that of the air. And what, it may be 

 asked, is the source of this heat. The answer is, combustion ; fur the burning 

 of charcoal in the animal Irame is supposed to be continually going on, giving 

 out, in this case also, as much heat, though difTused over a longer time, as 

 when it is burning more rapidly in a grate. No less than eight ounces of 



carbon, taken into the system in the food, is supposed to be consumed daily 

 by a man, for the purpose of maintaining a proper temperature in his body, 

 by being brought into contact with the oxygen of the air he breathes. He 

 ought, consequently, to proiluce carbonic acid largely in his system, and he 

 does so, throwing it off by breathing. 



The Professor then brouglit forward two pieces of apparatus, to compare 

 the efl^ect produced on the air by breathing with that produced by burning 

 charcoal ; by means of one of which he passed the air from his lungs through 

 lime water, and by the other the air wliich had passed over a piece of burn- 

 ing charcoal, in both cases the lime water was rendered turbid by a formation 

 of carbonate of lime, proving in both a like formation of carbonic acid gas. 



Lecture II. 

 The power of beat to expand bodies, to make tliem occupy a larger space 

 than they did when cold, is most enormous, in solids, indeed, is almost ir- 

 resistible. But it varies in degrees according to the substance. If two pieces 

 of ditl'eient metals be soldered together and heated, they will curve into a 

 bow, that metal which expands the most forming the outer or convex side. 

 Bad conducting substances act in a similar manner, and are frequently broken 

 by heat. A thick piece of glass, as the bottom of a test glass, if heated sud- 

 denly, is broken, owing to unequal expansion in its various parts, as occurs, 

 also, when boiling water is poured into a tumbler, especially in cold weather. 

 Hence great care is requisite in the laboratory when applying heat to glass 

 vessels. Owing to this it is that a thick glass rod which will bear hundreds of 

 pounds weight of even pressure, is easily broken by beat. A piece of sulphur 

 w hich is strong enough to bear a great deal of even pressure, flies asunder by 

 the heat of the hand. By alternate expansions and contractions rocks are 

 broken up, so as to form the soil for the plant to grow in. Solid metal in- 

 serted into pillars, frequently becomes the means of weakening instead of 

 strengthening buildings, as may be seen at the Bank, .Somerset House, the 

 Custom House, and other public buildings. The linear expansion of some of 

 the metals from the freezing to the boiling point of water, is given in the 

 following table : — 



Linear expansion of metals from 32° to 212°. 



In fluid bodies the expansion is greater than in solid, as may be seen by 

 healing water in a tube having a piston touching its surface. The rise of the 

 piston shows the difi'erence between the expansion of the glass and the water. 

 When a solid is heated irregularly, it breaks, but not so with a liquid, be- 

 cause its particles are free to move. But other effects take place, such as the 

 formation of a series of beautiful currents cireulating through the mass of 

 the fluid. These currents can be easily tr.nced by placing at the bottom of 

 the water some light particles of a coloured substance, which on the applica- 

 tion of the heat from a lamp under the flask, are instantly set in motion, 

 rising in the hottest part and descending in the coolest. The particles, be- 

 coming hot, increase in size ; because they are large they are light, and 

 because they are light they rise to the top, till, becoming cool again, they fall 

 to the bottom. If hot water be carefully poured on to the top of a similar 

 arrangement, so that the two liquids do not mix, it forms a strata into which 

 the heated particles cannot rise until they have received the same tempera- 

 ture, and the lamp may be kept underneath for a considerable time, the two 

 fluids remaining quite separate, the hotter colourless liquid floating on the 

 top of the colder blue liquid. This shows the reason why it is not proper to 

 heat liquids at the top. An arrangement such as the following shows the 

 current in a very striking manner. Place a glass vessel full of water up high, 

 and into the top and bottom of it fasten the ends of a long metallic pipe, in 

 the upper part of which is a small chamber filled with a coloured fluid ; heat 

 the lower part of that side of the pipe where the small chamber is, and as 

 soon as the water becomes a little warm, a current is established, which pas- 

 sing through the coloured fluid carries it with it, and pours into the water of 

 the glass vessel a beautiful stream of coloured water. This arrangement will 

 serve to illustrate one of the latest methods of warming buildings, by means 

 of one long length of iron pipe filled with water carried through the various 

 rooms of a building, the bottom part of the pipe being made to lie in a coil in 

 a furnace. Thermometers, also, owe their utility to this property ol expan- 

 sion, the Iieat they indicate being calculated by the height to which the fluid 

 in the tube has risen. All liquids expand by heat and contract on its with- 

 drawal ; but for a wise purpose water has been made to depart, in one portion 

 of its course, from this general rule. When water cools down it contracts 

 until it has arrived at a temperature of 40°, but on continuing to cool, it 

 begins to expand till it arrives at a temperature of 32°, when it is solidified or 

 freezes. BeginniDg at the temperature of 40°, therefore, water is expanded 



