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Show If ELEMENTARY HEAT. No·n VIL I·_y b ~ence a com 1·1 1a11•011 of 1nctals with acids, of e!fential oils and ac•i ds, of alco· hol a• n1d water, o f ac1· d san d w.a ter ' g1'vc out heat·' whil!l: · a 1f'o !ution o.f fnow 1.1 1 water or l1l ac· H s,f and of neutral faits in water, attraCt heat from the furround111g ~od1es. So the acHl o m·t rc m1·x .c d w1· th 0 1·1 of cloves unites with it and produces a mofl: vwlent flame; the fam1e aCI· d o f n1· 1r e poure d on fnow infb• ntly di!folves it and produces the g. reatefl: degree of cod yet k· nown, by which 'a t Peteifbur~e h qlllckfilver was firfl: f.r oz. en Ill 1760. fil'dfl Water may be cooled below :-p0 without being frozen, If It bcpla_ced on_a o 1 oor and fecured from agitation, but when thus cooled below the freezing pomt the !call: agitation turn part of it fuddenly into icc, and wh_en ~hi_s fudd:n freezmg_takes pla~c a thtrmometer pbced in it infl:antly riles as fome heat IS g1ven out 111 the act of congela:10n, and the icc is thus left with the fame jeJ!fibli! degree of cold as the water had po!lt:!fd before it was agitated, but is neverthelefs now combined v~ith lcfs lattJnt heat.' . A cubic inch of water thus cooled down to 32° mixed w1th an equal q11anuty of boiling water at 21 2Q will cool it to the midcllc number betwe;:en thc_fe two, or to 122._ Bllt a cubic inch of ice \\ hofe fcnfible cold alfo is bm 32, mixed With an equal quant1ty of boiling water, will cool it fix times as much as the cubic inch of ~ol~ water ab~vementioned, as the icc not only gains its flure of the fenfible or grav1tatmg heat ot the boiling water but attratl:s to itfelf alfo and combines with the quantity of latent heat which it luJ loft at the time of its congd::ttion. So boiling water will acquire but ZI2Q of heat under the common preflure of the atmofphere, but the !l:eam railed from it by its cxp:lll!ion or by its folurion in the annofphere combines with and carries away a prodigious quantity of heat which it again. parts with on its condenfation: as is feen in common di!l:ilbtion where the large quantity of water in the worm tub is fo foon heated. Hence the evaporation of ether on a thermometer foon finks the mercury below freezing, and hence a warmth of the air in winter frequently fuccceds a lh-ower. When the matter of heat or calorique is fet at liberty from its combinations, as by inflammation, it pa!fes into the furroundi11g bodies, which poiTcfs different capacities of acquiring their fhare of the loofe or fenfible heat; thus a pint meafure of cold water at 4.8~ mixed with a pint of boiling water at 21 2~ will cool it to the degree between thefe two numbers, or to 154 °, but it requires two pint meafures of quick!llver at 48° of heat to cool one pint of water as above. Thcfe and other curious experiments are adduced by Dr. Black to evince the exifl:ence of combined or latent heat in bodies, as has been explained by fome of his pupil , and well illu!l:rated by Dr. Crawford. The world has long been in expetl:ation of an account of his difcoveries on this fubjetl:: by the celebrated author himfclf. As this doB.rine of elementary heat in its fluid and combined !l::ate is not yet univerfally received, I fhall here add two arguments in fupport of it drawn from different fources, viz. from the heat given out or abforbed by the mechanical condenfation or ex pan !ion of the air, and perhaps of other bodies, and from the analogy of the various phenomena of hci!.t with thofe of elecrricity. NoTE VII. ELEMENTARY HEAT. I. If a thermometer be placed in the receiver of an air-pnmp, and the air haflily exhauflcd, the thermometer will ftnk fome degrees, and the glafs become fleamy; the fame occurs in hallily admitting a part of the air again. This I fuppofe to be produced by the cxpanfion of part of the air, both during the exhauflion and re-admilTion of it; and that the air fo expanded becomes capable of attracting from the bodies in its vicinity a part of their heat, hence the vapours contained in it and the glafs receiver are for a time colder and the !l:e:1m is precipitated. That the air thus parts with its moiflure from the cold occa!ioned by its rarebcrion and not !imply by the rarefacrion itfclf is evident, becaufe in a minute or two the fame rarefied air will again take up the dew depofitcd on the receiver; and becaufe water will evaporate fooner 1n rare than in dcnfe air. There is a curious phenomenon fimilar to this obf'ervcd in the fountain of Hiero confl: rucrcd on a large fcalc ::tt the Chemniccnfian mines in Hungary. In this machine the air in a large ve!fel is comprcffed by a column of water 26o feet high, a fl:op-cock is then opened, and as the air ilTues out with great vehemence, aiLd thus becomes immediately greatly expanded, fo much cold is produced that the moifl:ure from this fhcam of air is precipitated in the form of fnow, and ice is formed adhering to the nofel of the cock. This remarbble circumfhncc is defcribed at large with a plate of the machine in Philof. Tranf. Vol. LII. for q6r. The following experiment is related by Dr. Darwin in the Philof. Tr:1nf. Vol. LXXVIII. Having charged an air-gun as forcibly as he weii could the air-cell and fyringe became exceedingly hot, much more fo than could be afcribed to the friction in working it; it was then left about half an hour to cool down the temperature of the air, and a thermometer having been prcvioufl y fixed againfl: a wall, the air was difchargcd in a continual fl:ream on its bulb, and it funk many degrees. From thefe three experiments of the fl:eam in the cxhaullcd receiver being depofitco and re-abforbed, when a part of the air is cxhau!1ed or re-admitted, and the fnow produced by the fountain of Hicro, anJ the extraordinary heat given out in charging, and the cold produced in difcharging an air-gun, there is reafon to concl11de that when air is mechanically comprcffed the elementary fluid heat is ptciTed out of it, and that when it is mechanically expanded the fame fluid heat is re-abforbc-d from the common mafs. It is probable all other bodies zts well as air attnct heat from their neighbours when they :Jrc mechanically cxp:mded, and give it out when they arc mechauic:llly condcnfcd. Thus when a vibration of the particles of h:ud bodies is excited by friClion or by percuffion, thcfc particles mutually recede from and approach e:1ch othtr reciprocally; at the times of their rccelTion from each other, the body becomes enlarged in bulk, and is then in a condition to attracr heat from thofe in its vicinity with great and fud.Jcn power; at the times of their approach to each other this heat is again g1vcn out, but the bodies in contact having in the mean while received the heat they had thus lol!, from other bodies behind them, do not fo fuddenly or fo forcibly re-abfo1 b the: htat aciain from the body in vibration; hence it remains on its furface like the elect fie Jlu,J on ..1 rubbedglafs globe, and for the fame reafon, becaufe there is no good crmductor tv tak:e it up again. Hence at every vibration more and more hrat is acquired and ttan !s loo e upon the fmface ; as in filing metals or rubbing glafs tubes ; anJ thus a fmith with a few !l:rokes on |