Science Lecture.

Wairarapa Standard, Volume XIX, Issue 1842, 9 June 1886, Page 3

Science Lecture.

Tkc following lecture is in continuation of Uw court* oi lectures to teachers, foar of which lecture! were delivered in Grey to wo School during last November, and appeared in the columns of the Waiiarafa Stanpabd : Ltct cre V—Heat. By Alex. Pordie, M.A. We are very familiar with the terms hot and cold, yet in using them we must remember that in ordinary use they denote simply relations between ourselves and the bodies spoken ef, and that onr impressions often mislead ns as to the actual temperature of bodies we touch. Take for instance a piece of metal and a piece of wood nnder exactly the same conditions and probably of nearly the same temperature. Touch them ; the metal we say is colder than the wood, bat the real atotamest of ths ease is that the heat of oar hand runs away more quickly along the metal than along the wood, not that the one object is actually warmer or colder than the other. To give another example, take three dishcc, fill this first with water as hot as the hand can bear, tbs second with lukewarm water, and the third with cold water. Place the right hand in the very hot water, and the left hand in the cold water. In a little while put both hands into the other dish containing the Inkewarm water, and note tbe imprmsinos yon receive. To the right band the water will seem cold, while to tbe left it •eems warm. This shows ns then how liable wo may be to make mistakes in trusting to each impressions about the temperature of bodice about us.

From the syllabus yon will see that the subject of beat is by no means fully gone into, but that only the simpler parts of the ■nbjeet an taken np. it being thought that to introduce at present such branches as specific beat, latent heat, and radiant heat, woo Id be laying too great burdens npon yon. Batoning then to the syllabus, you see that Lecture Y begins with the sources of heat. Tbe first scares of beat, of which we shall tnat. is tbe snn, mid that heat proceeds from tbe son scarcely seems to call for demonstration, yet as it is customary, and also well to introduce experiments and actual observation at all poosible points we may take tbe old-fashionad experiment with a burning glass or tons. Every schoolboy is supposed to know that by thus causing tha rays of the son to eon verge to a point, intense heat is obtained at that point I'he action of the lena is to bring to a point or foens all the raya ol beat striking on its surface. Exp 1. By bolding a match or other inflammable matter at that point flame may be obtained. Sometimes fires are supposed to have been kindled m this way through tbe little bubbles, to often seen in bad window glass, acting as lenses, and converging the son’s rays on tome inflammable matter inside the boose. The beat of tbe sun is very great, and it has been estimated that tbe amount of beat received by the earth from tbe son in one year would melt a layer of ice 100 ft thick all over the earth. The genial warmth of tbe son is indispensable for the well-being of most plant and animal life. Tbe internal heat of the earth itself is considerable, for it bas been found in trying the temperature at different levels in mines, that the increase in heat in tbe earth’s crust is about 10 degrees for every 60 feet of descent If this rule holds good to the centre of tbe earth, then at no great distance from the surface, the earth’s temperature would be so great that even tbe most refractory sabetances known would be in a molten state. In this island, as in many parts o( the world, we have proofs of subterranean hea in tbe existence of hot springs and volcanoes not altogether slumbering even yet. Bat leaving now tbe natural production of bent and coming to that which can be more easily dealt with experimentally, tbe artificial production of beat, we find that heat can be produced in various ways. For instance, heat sen be produced by friction, compression or permission of many bodies. Exp. 2. The eboolboy’s trick of tubbing a brass headed nail on the deck, and then applying ite head to a neighbour’s hand will serve to illustrate the production of beat by {notion. Itssama almost superfluous to give directions thto experiment. Fix a brass MMad teak in a eork, and rub tha bend of task briskly on a hard aurfaea. and tbs head *** !”»"■■ *oo hot to bs touched with ■Mf_~P~ *• siapU presses of striking a auothm iSartratiuii. Tha match “JJf * l,l ****"— ealtod phosphorus, »uds acquaintance in tbs **>• ««m. This substance ****”» •£. little beat, so that the • match head briskly on a my sswlses to to kindle the phosphorus, which ta turn ktadlss tbs sulphur and chlorate of umtakkMd. Wbas of savages obtain *** *7. kriak twirling ol a pouted fj"*** ttofc m —ethic piece of sttok, and ■7 ■"■»»«ta|«tar’atauat with a wooden frr. 1 ? **W that eonsidsrahto h**r*tf**f*9Uitim ft m jhf

of wood on another piece. After boring for some time into a piece of bard wood you will find that a small piece of phospi otu. Top] , i into the bole would be HiHined. ii.v more perfect mechanical arrangements it is possible to produce smoke during the luring, but with this simple apparatus the best produced is not so great as to kindle tbe wood. Chemical action is very frequently accompanied with the production of heat, and to shew this we may use an experiment, with which you are already familiar. Exp. 5. Cut a small piece of potassium, and throw it on water. Tbe metal decomposes tbe water, freeing hydrogen gas, and the heal produced is so great that the gas kindles and burns away as produced, Exp. 6. Or take a small piece of phosphorus. and Iffy npon it a few grains of iodiue, the ensuing chemical action produces beat enough to set fire to tbe phosphorus. A popular experiment often seen at conversaziones and such like entertainments, is to sprinkle in a mortar a few grains of sulphur with a few grains of chlorate of potash. Exp. 7. Put in a very little of each or tbe action will be inconveniently violent. Grind the two together strongly with the pestle, and the heat of friction starts tbe decomposition of tbe chlorate of potash, which parts with its oxygen to the sulphur. Tbe sulphur burns away, as yea find by tbe flashes of light and the fumes cl burning snlpbor. Chemical action with the production of light and heat goes on daily in our dwellings in the burning of wood, coal, candles, kerosene, or gas, bat we are so familiar with these things that we perhaps but seldom think of what is tbe scientific explanation of what is going on. The substances mentioned consist in great part of carbon and hydrogen, and their horning is simply the combination of their constituents with the oxygen of tbe sir. The hydrogen burns away to form water, see Exp. 7 in Lecture 11, while tbe carbon mostly produces carbonic acid, see Exp. 5 and 6 iu Lecture IV. This chemical action or combination is attended with the production of light and beat so valuable to ns. We ourselves in our own bodies carry on a more or less rapid combustion, our carbon and hydrogen just like those of tbe candle, combining with oxygen, producing in tbe one care water, and in the other carbonic acid gas. These products we get rid of by breathing and by perspiration, and just as we can eanse a fire to burn more rapidly, so we can increase tbe raw of combustion in our bodies. Take violent exercise, and you know well that tbe breathing will quicken, and perspiration ensue, thus ridding ns of the extra quantities of carbonic acid gas and water produced. In life our bodies are warm, but when oar fires are pot out by death the body becomes cold. Electricity is an agent in producing heat. Lightning is tbe passage of ao e ectric current from one olond to another, or from a eloud to tbe earth, aud it is supposed that tbe intense beating of the air daring the passage of the current causes the flash we call lightning. By the use of a simple form of electrical apparatus called an electrophorus,' we can produce an electric spark on a small scale. There are many other facts that might be shewn, and teacher* will of course, decide for themselves about introducing other experiments. For instance, it might be mentioned that the . axles of wheels of machinery, steam engines, dec., require constant oiling to reduce friction and production of heat, Those that journey often over tbe Bimutaka Railway Line must ! have noticed frequently on dark nights the sparks flying from the brakes. In tbe case of heat from chemical action, many instances , might be given in addition to those above. For instance, quicklime with water produces great heat, so also does the mixture cl sul- j phutio acid and water, and so on through • many examples. (To be Continued).