| OCR Text |
Show 196 COMBUSTION. of the current, except the artificial cov~ring that • may be on them; but there is self-protectiOn ~n the face. The breath which is expired is heated ~n the lungs, and also charged with moisture. As m ~he operation of breathing, carbon or c~arcoal, wl~Ich previously existed in ~rob?-bly 3: sohd st_ate? umtes with the oxygen of the mspued air, and with It forms carbonic acid gas, it might be supposed that cold would be the result, as is the case when most ~ubstances pass from any more condensed state mto the state of gas. Such, however, is not the fa~t; otherwise a common fire would cool the room mstead of heating it, and furnaces wot;~ld harden met~ls instead of melting them ; . for the ch~ef process wh~ch goes forward in the burmng of fuel Is the conversiOn of the oxygen of the air and the c?rbon of the fuel into carbonic acid gas. There are, mdeed, gener3;lly other matters in the fuel-such as. hydrogen, whiCh passes off, mixing with oxygen~ m flame, 3:nd the result is water, which goes up m vapour ~Ith the smoke · and various other substances whiCh form solid p:oducts with oxygen. In these t~e ~hole of the heat which held the oxygen of the au m a state of gas becomes free and Rf~paren~ tG the senses ; and as the carbon which combmes with the ox~gen does not increase the volume, while it very much mcreas~s the density, the oxygen which _forms. the carboniC acid gas gives out a great quantity of Its .heat ; and yet the gas which is formed may have a lngher temperature than the oxygen. Here we may see, by-theway why fires burn briuhtest in cold weather; and why' the sunbeams, or any other light, put o~t t_he ~r~, or make it burn feebly. The colder the au IS, It IS the more condensed, and of cot~rse has the more oxygen in an equal bulk. Thus It moves faster to the fire, and carries more of the ~lP-ment that !eeds the firP.. The light expands the au, and that causes it to c~me more slowly, and also to hav~ less supply of oxygen in the same bulk ; and the duect rays of HEAT IN BREATHING. 197 the sun so expand the air that the current to the fire is greatly diminished, and stops altogether. 'Ve hence see ~ow very unskilfully many persons blow the fire w1th bellows. They put the nose of the b~llows close to the fire, and thus drive the expanded a1r upo_n all parts of the fire, except the little space on which_ the bla~t a_cts; and the consequence is, that that little portwn Is very rapidly and unprofitably consumed, and the rest of the fire is not at all improved; whereas, if the bellows were kept farther off t~ey w_ould blow a much more effective current of air agamst the whole fire. The position of the bellows s~o~lld be sloping upward to the fire, because then the au Is of the proper quality; whereas, if the n?~,e of th~ bellows slope downward, the "burnt mr -the ~utrogen and the products of the fire are blown agamst the fire, and tend to weaken it. The heat produced in breathing does not appro::tch near~y to that of fla~e .or combustion, but still it is constde~·able, though It IS not easy to distinguish between _It and the heat produced by circulation. There IS no r~ason to dou~t that heat might be produced _by resistance to ctrculatwn, and to that of b~eathmg, among other circulations, sufficient to kmdle an~ consume the body; for though all the reco_rded mstances of spontaneous or inward combustiOn a~e not probably true, yet so many of them are me!ltwned that they must have at least some foundatiOn. We know that when either the breathmg o: the pulse _of the blood is quickened, either by e.xer:wn or by d1~ease, the heat increases in proportiOn, so that ~htle the temperature of health varies f~om about nmety-five to one hundred degrees, a d1~eased heat may be as great as one hundred and thirty or one hu':ldred and forty degrees. So also w~en the breathmg or. the circu~ation is very Iangm~ the t~mperature smks; and m those faintings, duri':lg whiCh hardly any pulse or breathing is per cephble, the body becomes exceedingly cold. R2 |
