SCIENTIFIC.

Otago Witness, Issue 1951, 11 April 1889, Page 35

SCIENTIFIC.

The. combustion of' coal ds nothing morenofless than its combination with oxygen gas. JVb^n; a ,iuel< .of any kind combines with oxygen, heat is produced.' Why fuel should combine witti oxygen no onecanijell. It is onc^.of NatureV'secrets." The ctiemisfe tells us that the oxygen and the fuel have an ' affinity for each other. But when this statement;, h^beeri : made we are no nearer to understanding why combination takes place than'weiwere before. > In text-books nothing Wjll be;fo'nnd as to tvhjr is produced by tble C9n>^inatiion. ' On ,^tii§ point an all but universal silence prevails. W&are told, however, by a few writers'of ithe ; bld schobl3hat j heat energytras stored up in the coal million's J of r y ( ears T agp^by the ' sun^a'rld ' that this heat energy is liberated when< the. coal.comlbines ! with oxygen?- This is absurd. . rltr It will not be I put of rjlace^.^o/giv^here' ail' 'explanation j whicn is cdhsistentwith faqt^ and therefore j appears trabeisatisfaotory. ( , ' All .bodies, substances," gasfes^ahd ; liquors are,,supposo^ io be domposed of paultitudes bf particles or molecules of almost inconceivable >smalln€ss. and 'these arb supposed to be in mcitipn, ! ainorig' 'liitemselyed/,' This motion is heat];,, that is to say, heat: i& neither more npr less than a kind of motion, and this internal "vibration, can be transmuted into a.perceptible mechanical movement or, on the bther . hand,' mechanical movement can be converted into the invisible motion called heat. How the dh'ange takes place no' one knows, but the • change is /none the. less a fact. '. Now,ib.e ■ difference between a solid- and a gas is'that the motion of the particles of the molecules of r tne gas i^ niu!ch greater in extent tban is the .motion of the particles of the solid. Also, some : gases: have.' a greater, range of •motion. than* other gases.,, It by any means we can take the "motion out of gas, say by -compressing it into a~ : yessel, the sides and; Wds of which' reduce the range of movement, 'feh'en, "as 1 nothing is lost in Nature^ the invisible and s ifasensibldj motion of tW,gas, which it has lost, reappears., as heat 'in a sensible 1 form, and we find .that sides of the vessel' become hot. Now, the" oxygen which nas combined with coal has a very considerable range of internal motion, but when the oxygen has combined with' the coal another gas, known as carbonic acid gas, is produced, as will be explained further on ; and the particles of this gas having a much smaller range of motion tban the particles of the oxygen have, the difference appears* in the form of heat. It is* not necessary to tell readers that coal is not always the same. It is composed of various substances and gases. The principal are carbon, hydrogen, oxygen, and certain impurities which make the> ash with which we are so familiar. The carbon,- 'hydrogen, and oxygen are elements ; that is to say, they are not composed of separate, substances combined together. They 'cannot be split, up into anything else. In 10001b of anthracite coal there are' about 9151b of carbon, 351b of hydrogen, and 261b of oxygen. In a good bituminous or North Country coal there will be 8001b of carbpn, 541b pf hydrogen, and 161b of oxygen ■ • • The difference between the sum of these quantities and 10001b is matter entirely non-combustible,-which^.-appears as ash. Of .course tjhere /are? an infinite . number of Variations in- 'the! proportion!, wjach' the. constrtuentsiof coal' bear to^eacn other, but the figures we have given fairly represent good WeliH'Mdirfdrth 'Gbuntry i cbalJS respectively;. The air we breathe is composed of two gases-f-oxygen > and- nibrpgen. , The latter 'appears 1 have no "^ effect whatever on humtoflife and-co'mbastion ; ..'.*'lfr^erves to dilute the oxygen. The two gases are mixed, they are not in chemidal combina^tiojp t JBy u weight (approximately), 361b of air contain 281b of nitrogen and 81b, oxygen. In bulk they are mixed in the proportion of, roughly, four'td orfe-^-4ft (cubic) of nitrogen and -one of oxygen making sft (cubic) of air. — Mechanical Engineer. - • Iron Fibre— Bending and Breaking. When we wish to break a bar of iron we usually cut a channel with a cold chisel around the entire bar at the point where the break 4s desired. This having been done, we place the bar on an anvil with the channel slightly 'over its edge. A smart blow on the outlying portion will cause a fracture, which, at first sight, has all the appearance of crystallisation.- Now, if we take this-same bar and cut .a channel on one side, and subject it to the same treatment with the channelled face up, the crystalline, appearance will show slightly in close proximity to the bottom pf the channel, but the main body of the bar will be bent and partly broken, displaying a fibre with a long, silky appearance. Again, if we take this bar with no previous preparation and subject it to the same treatment, we shall find that, instead of breaking, it will simply bend, showing no fracture whatever. The question arises why,' with the same blow, do these different specimens of iron show such widely diflprent results,? It has been -said that the blow on the cold chisel disturbed the' fibre of the iron, weakening it and putting it in condition to fracture at the point cut. Being 4 ' desirous of demonstrating this matter, and for reasons given below; we obtained a bar' bf iron l^in wide and fin thick. Instead of using a cold chisel, we made use of a file, and put a channel around the entire bar. We then placed the bar on an anvil, with the channel -slightly over the edge, struck the outlying portion a smart blow, and it flew from the bar like cast iron. The fracture presented a crystalline appearance. This experiment satisfied us that something other than the disturbance of the ! fibre by the cold chisel was the cause of this sudden disruption and consequent crystal;, line appearance. Some have argued that when the original skin bf the iron wa3 broken or cut the ; strength was greatly reduced, and that frac; ture in bending was well-nigh certain. To settle this theory, we cut again a channel around the bar, and put it upon -a planer and planed away the surface for some distance each side of the channel, until the channel was entirely " planed out." The bar was reduced in thickness nearly one-third, but the " original skin "of the iron was gone; We next subjected this to the same treatment as described above, and it bent beautifully, witH

no indication of fracture. This demonstrated to our satisfaction that the " original skin" of the iron.was^ot^.in this kind otsjrain, what savecV iron ' from "fracture*. v ' "(BT should be stated ; here, that .iron pf good quality^bas been broken with an' apparent* crystalline fracture, where ,na channeJUing; o^preyious preparatidn' has ' been.^inadeT^see , Kirk^dy's e^erjimen^s; % oh wrought iron an'4-gfee>-rbut oircumstances were ,Sifferent:lmmijthose under ; discussion- here.) r When we; bend a bar of ironslowly, the fibres on v the -convex of outer surface, of '.{theubend are "disturbed very greatly,' comparativelyf andHhisdistfention or elongation of fibre decreaieaf as approach is made td the other sicld of tibe bar, where a' crumbling of 'the'"surface" r fi J bre rt 4?ili take-plade. l: " "2 ," Jib-*'* ■ From a careful examination , of ' v the r bent portion, .tb!^ t d^rei?t.^ay«;S{pf,f fibr§s A sp* to "speak", 'sfippecji^ or'i jfiil jdne ' oVefthe "other, .tp^anj^tent depending. upon stb.3 degree v 'p^ . strains bsaught td^ bear jupon 'each.* ..Scions ..cut fromcthe f bent,sportion, when examined with aHmicroscope, show .more or . less distinctly that I;b:e % laminse'tfnd iron (threads haVe " b'dcome 'aisftafi'bed' r^nd loosened in •' their cinder ISivelßiJes, "particularly on'the outer <r 6ide bffie" bj&d. <r l£ •the biding "is fep^ld'.taM'^dV^ith ; Be^6mltinißß,'ttilopse^g'iip M .the'ifibj^ is [ distinctly seen^^ouij^tne^aid pi, %^ss/tHaying, brieifly;, cpn^erect^be apiion of iron, fibre in tW.prqcess pf;,vbejiding,',wei return to the.cjue^ion.of i fracturen> does ( she bar break suddenly and^with :'« Qrystalline appearanpe under a smart'blow/at the point marked !or channelled wifch^aX'file ? , When aj-bar:of irofr'is: bent, the'&th;er < 'fiirre3 receive thesifcrain 'fir>'fc7'brekkihg l its l iffißLtiy as it is transmitted to tnoM|u^erl^Ef£^^he disturbitig : fbr^' < is~dis^patex|.L BMeeif tne' en> tire portion 6f the, elongated fibre, ja^uaishiog ! each 1 way jfrpm " the' '.pb^.j.pffr greyest strain. , No^it^wiy^bq^ejx^tblaibyj.c^ng a' chanripl,, v thro,ugh{ihepjutfis of) fibre, the strain .is* confined ito theipoint I wherefthe chanhelis cut. >, The fibres on -seithbr'sideto the depth of the channel' is riot'^adted upon at all, and exerts no .influence 1 as, -tf tion tothe underlying layers 6f fiW6 ' j'fience, > when - the blow "is receieved," the is^onfined to the channel, £he fibre having^little bf*tfo ; 6pp^Hunit3r\W' : pr^^(^t^ l j^4, it; breaks 'Shorb off. ajjCh'afln.eLwas. put in tne bar on qoth' ' sides, and^then planed out, the "bar, wasjyirtually^restoiedjJiO'Jits normal.condition, and its behaviour; .was the same as when in its original Condition. -< Had we space, allusion inigbfci be made to inferior qualities of- iron where, in pilingi the centre portions'-are 1 very' poor'iri^llefl/vfhile the outside bars are of unexceptionalljf good quality. -This kind' : of s iron pfesentsf^aigood i surface, fcut'in lending and"^f^^gj^s |n- ' feriorquality is readily discb^e|ed^^ot, the expenmenfe.whitli. we made.' we^w^^gobd bar ifbn'.^-FronV a'Sibley College Lecturs by J. M. Allen.