CAL

CAL

( 203 )

prodigious of any of the fpontaneous actions ofnatural bodies. If a block of ice fwimming inwater may be ellimated to rife about one-fixthof its bulk above the furface of the water, fiveparts of water by weight would occupy about thefame bulk as fix of ice. The force of expan-fion was long known to be fuch as to burft anyveflel in which water was fet to freeze, if filledfull; and by Major Williams’s experiments atQuebec , this force was found in intenfe cold tobe able to burft very large pieces of ordnance.For the particulars of thefe, fee the articleFreezing.

Some of the metals expand on their con-gelation or fixation. Iron is of this kind, andhence the unmelted metal will fwim on the fur-face of the melted; whereas filver, lead, andmany others, contract on cooling, and thereforefink in a melted mafs of the fame metal. Thechief caufe of this expanfion in water, metal,and in an infinite number of faline and other fo-lutions, when palling from the fluid to the folidjftate, appears without doubt to depend on thenew arrangement of particles produced by thecryjlallization, but the fubject is Hill very obfcure.However it does not in the leaft invalidate thegeneral law of expanfion by heat, fince thefefame fubltances when folid are expanded andcontra&ed as before by gain or lofs of caloric.

Of Combined or Latent Caloric.

In the two preceding feel ions of radiated andconduced caloric, heat has been confideredonly in that ftate of freedom or of loofe com-bination in which it exifts in its paflage throughfolids, fluids, and gaffes. This is properly thecaloric of temperature, or that whereby the equi-librium of temperature is conftantly kept up inall bodies in nature; and, as has been amply(hewn, no fubftance, whatever difficulty caloricfinds in permeating it, can abfolutely detain itor prevent its paflage. Perhaps the term oftenfton of caloric, adopted by Prevoft, Piftet,and fome other writers, will exprefs with moreexactnefs the idea which may be formed of thisftate of caloric. This is meafured by the ther-mometer, that is by a very fmall mafs of matter(generally mercury) extremely permeable byheat, which, when put in contact with the fub-ftance examined, readily acquires the fame ten-fion of heat, without leflening the actual quan-tity in any fenfible proportion by what it abforbs,and furnilhes a comparative fcale of temperatureby the expanfion which it undergoes. That diethermometer does not meafure the a£tual quan-tity of caloric is evident from the circumftancethat it gives the fame indication immerfed in a

large as in a fmall mafs of matter, Thus it isobvious that two pounds of boiling water con-tain twice as much caloric as one pound ofboiling water, but the thermometer in bothHands at the fame degree. Neither does thisinftrument give the comparative quantities ofcaloric in the fame bulk of different fubftances.If feparate veffels containing water, mercury,oil, brine, &c. are all immerfed in water kepta fufficient time at the boiling point, after agreater or lefs time they will all acquire a tem-perature a few degrees below 21 2 °; but thisdoes not in the leaft prove that they containequal quantities of heat, and the circumftanceof the unequal times required in each to arriveat this point is a ftrong argument againft thequantities of caloric being equal.

The analogy given by M. Pictet between hu-medfation and heating, will further illuftrate,as far as it holds, the nature of thermometricalindication. Suppofe at the fame inftant a poundof dried fponge, a pound of blotting paper, anda pound of fome porous wood be plunged into ahafon of water. After a fliort time the fub-ftance that receives water the eafieft (fuppofethe blotting paper) will be thoroughly foaked;in a little longer time the fponge will be in thefame condition, and after a longer time, thewood. When taken out of the water they willall be. thoroughly wet, and if a hygrometer(which is a machine that {hews the degree ofmoifture of the air by expanfion or contra&ionof hair, catgut, or any other hygrometrical fub-ftance) could be applied to them all, it wouldonly fliew in each the fame and the extremedegree of humidity, but would give no indi-cation whatever of the actual quantity of waterwhich each contained. In this therefore itrefembles the thermometer applied to heatedbodies. Let the three fubftances be now tho-roughly dried in a very warm fituation, and thehygrometer would only mark in them the termof extreme drynefs, and not the quantities ofwater which they had refpeclively loft, whichwould be the moft in the fponge, the next inthe paper, and the leaft in the wood. But afterthis thorough exficcation, if the three fubftanceswere ftrongly heated in clofe veffels, they wouldyield a further quantity of water, alfo in unequalproportions, as the wood would now furniihthe greateft; and this may bear an analogy tothe caloric of combination, which is no moreindicated by the thermometer than the combinedwater would be by the hygrometer.

Let a quantity of ice cooled down to 20° beput in a veffel and gently heated by a fmall2 c 2