Back Aa

Reason Why

Close

<h2>CHAPTER V.</h2> 71. What is heat? Heat is a principle in nature which, like light and electricity, is best understood by its effects. We popularly call that heat, which raises the temperature of bodies submitted to its influence. 72. What is caloric? Caloric is another term for heat. It is advisable, however, to use the term caloric when speaking of the cause of heat, and of heat as the effect of the presence of caloric. [Pg 40] <hr class="bible-verse" /> "While the earth remaineth, seed-time and harvest, and cold and heat, and summer and winter, and day and night, shall not cease."—Gen. viii. <hr class="bible-verse" /> 73. What is the source of caloric? The sun is its chief source. But caloric, in some degree, exists in every known substance. 74. What are the effects of caloric? Heat which, in proportion to its intensity, acts variously upon all bodies, causing expansion, fusion, evaporation, decomposition, &c. 75. Why is caloric called a repulsive agent? Because its chief effects are to expand, fuse, evaporate, or decompose the substances upon which it acts. 76. What is an attractive agent, in contradistinction to a repulsive agent? Chemical attraction, or affinity, is an attractive agent—as when bodies seek of their own natures to unite and form some new body. 77. When is a body said to be hot? When it holds so much caloric that it diffuses heat to surrounding objects. 78. When is a body said to be cold? When it holds less caloric than surrounding objects, and absorbs heat from them. 79. How may caloric be excited to develop heat? By any means which cause agitation, or produce an active change in the condition of bodies. Thus friction, percussion, sudden condensation or expansion, chemical combination, and electrical discharges, all develope heat. 80. Why do "burning glasses" appear to set fire to combustible substances? Because they gather into one point, or focus, several rays of caloric as they are travelling from the sun, and the accumulation of caloric developes that intensity of heat which constitutes fire. 81. What is a focus? In optics, it is the point or centre at which, or around which, divergent rays are brought into the closest possible union. [Pg 41] <hr class="bible-verse" /> "Yet man is born to trouble, as the sparks fly upward.—I would seek unto God, and unto God would I commit my cause."—Job v. <hr class="bible-verse" /> 82. What is fire? It is a violent chemical action attending the combustion of the ingredients of fuel with the oxygen of the air. 83. What are the properties of fire? It imparts heat, which has the effect of expanding both fluids and solids. It cannot exist without the presence of combustible materials. It has a tendency to diffuse itself in every direction. It cannot exist without oxygen or atmospheric air. 84. What elements take part in the maintenance of a fire? Hydrogen, carbon, and oxygen. Hydrogen and carbon exist in the fuel, and oxygen is supplied by the air. 85. How does the combustion of a fire begin? A match made of phosphorous and sulphur (highly inflammable substances) is drawn over a piece of sand-paper; the friction of the match induces the presence of caloric, which developes heat, and ignites the match, the burning of which is sustained by the oxygen of the air. The flame is then applied to paper or wood, and the heat of the flame is sufficient to drive out hydrogen gas, which unites with the oxygen of the air, and burns, imparting greater heat to the carbon of the coals, which assumes the form of carbonic acid gas by union with oxygen, and in a little while all the conditions of combustion are established. 86. What are the properties of heat? It may exist without fire or light. It is not sensible to vision. It makes an impression upon our feelings. It acts powerfully upon all bodies. It has no weight. It attends, or is connected with, all the operations of nature. It radiates from all bodies in straight lines, and in all directions. It strikes most powerfully in direct lines. Its rays may be collected into a focus, just as the rays of the sun. It may be reflected from a polished surface. It is more easily conducted by some substances than by others. [Pg 42] <hr class="bible-verse" /> "For my days are consumed like smoke, and my bones are burned as an hearth."—Psalm cii. <hr class="bible-verse" /> 87. What is animal heat? Animal heat is derived from the slow combustion of carbon in the blood of animals with the oxygen of the air which the animals breathe. 88. What is latent heat? Latent heat (or more properly latent caloric) is that which exists, in some degree, in all bodies, though it may be imperceptible to the senses. 89. Is there latent caloric in ice, snow, water, marble, &c? Yes; there is some amount of caloric in all substances. A blacksmith may hammer a small piece of iron until it becomes red hot. With this he may light a match, and kindle the fire of his forge. The iron has become more dense by the hammering, and it cannot again be heated to the same degree by similar means, until it has been exposed in fire, to a red heat. Is it not possible that, by hammering, the particles of iron have been driven closer together, and the latent heat driven out? No further hammering will force the atoms nearer, and therefore no further heat can be developed. But when the iron has again absorbed caloric, by being plunged in a fire, it is again charged with latent heat. Indians produce sparks by rubbing together two pieces of wood. Two pieces of ice may be rubbed together until sufficient warmth is developed to melt them both. The axles of railway carriages frequently become red hot from friction. 90. Have vegetables heat? Yes; whenever oxygen combines with carbon to form carbonic acid gas, an extrication of heat takes place, however minute the amount. Such a combination occurs much more extensively during the germination of seeds and the impregnation of flowers, than at any other time. In the germination of barley heaped in rooms, previous to being converted into malt, it is well known that a considerable amount of heat is developed. 91. Has any investigation of this subject ever been carefully made? Yes. Lamarck, Senebier, and De Candolle, found the flowers of the Arum Maculatum, between three and seven o'clock in the afternoon, as much as 7 deg. Reaum. warmer than the external air. Schultz found a difference of 4 deg. to 5 deg. between the heat of the spathe of the Canadian pinnatifolium and the surrounding [Pg 43] air, at six to seven o'clock p.m. Other observations have established differences of as much as 30 deg. between the temperature of the spathe of the Arum cordifolium, and that of the surrounding atmosphere. <hr class="bible-verse" /> "And there are diversities of operations, but it is the same God which worketh in all."—Corinthians xii. <hr class="bible-verse" /> 92. Have plants sometimes a temperature lower than that of the surrounding air? Yes. It has not only been found that under particular circumstances the heat of certain parts of plants is elevated to a very remarkable degree, but that, under nearly all circumstances, they have a temperature different from that of the external air, being warmer in winter, and cooler in summer. <hr class="chap" /> <div style="break-after:column;"></div>

1 of 2

2 of 2