CAL
CAL
C 2
may readily be condenfed into the liquid ftateby union with water, and home by union witheach other even pafs into folids. In both thefecafes fenfible heat fhould be given out to thefurrounding bodies, as in the condenfation offteam, and this actually happens, though by nomeans in fuch quantity. Thus when fulphuricacid is added to common fait, muriatic acid gasis given out in great abundance, and in clofedry vellels it fcarcely exceeds the temperatureof the air at the time, or if furrounded with icemay readily be cooled to 32 0 . But if a largeftream of this gas be palled into water, it isimmediately condenfed, uniting with this fluidinto liquid muriatic acid, and during the procefsfo much heat is given out as to raife the liquideven as high as 160°; fo that in preparing it,it is necefi'ary to keep the veflel artificially coolby wet cloths or ice. The caloric given out isthat which was latent in the gas during itsaeriform ftate. Alfo if muriatic gas and ammo-niacal gas, both of the common temperature,be mixed together, they inftantly unite, form-ing white clouds of folid muriated ammonia,and by lofing their gafeous form fo much heatis given out as to make the veflel very fenfiblywarm to the hand. It mull be mentioned how-ever that the quantity of caloric given out bythe permanent gaffes during their union withfolids or liquids, is in no degree proportionedto the eafe with which they are condenfed, andis in many cafes fo fmall as to be fcarcely if atall perceptible by the thermometer.
Of Specif c and Abfolute Caloric.
When equal quantities of the fame fubftance,but of different temperatures, are mixed to-gether, the temperature after mixture is veryexactly the arithmetical mean, or the middlepoint between the higheft and loweft. Thuswhen a pound of water at 50° is mixed with apound of water at 90°, the mixture will be70° (allowing for the effect of the veflel itfelfin which they are contained, and taking pre-cautions to avoid any fenfible error from thetemperature of the furrounding air.) Now,though the abfolute quantity of heat containedin each pound of water is unknown, it is obviousthat the water at 90° contains as much heat asthe water at 50°; and in addition, as much asis requifite to raife it 40 degrees of a certainthermometrical feale. After mixture the twopounds therefore contain twice as much heat asw ftl raife one pound of water to 50°, and befides,T) ™u°h as will raife one pound 4° degrees,lhe firft portion, being permanent, may be put
1 Experiment! on An
I )
out of the queftion, and therefore, only con-fidering that which forms the excefs betweenthe two, it appears that as much caloric as willraife one pound of water 40 degrees will raiietwo pounds 20 .degrees. Now all the experi-ments on the diftribution of caloric iliew thattwo bodies unequally heated when mixed to-gether will fooner or later acquire an equaltemperature, the cooler body gaining precifelywhat the hotter body lofes ; and as in the aboveexample the temperature of 70° is the middlepoint between 15o° and 90°, the hotter and the.cooler, it appears that equal quantities of heatare required to raife equal weights of water thefame number of degrees of temperature, what-ever be the a£tual temperature before the caloricis added. This inference is confirmed by ex-periments made at various parts of the rangefrom 3 2° to 212°.
But if equal weights of heterogeneous fub-ftances are employed, the refult is widely dif-ferent, the temperature after mixture beingnever the mean of the thermometrical difference,but fometimes above, fometimes below it. Thusif a pound of water at 4© 0 be mixed with apound of mercury at 69°, the temperature ofthe mixture will not be 74.5°, the arithmeticalmean, but only 41 0 . Confequently the mer-cury has loft 28 degrees of heat, all of whichhas been abforbed by the water, and has onlyraifed it 1 degree, and therefore it may be ftatedthat it requires twenty-eight times as muchcaloric to raife water to a given temperature asto raife an equal weight of mercury to the famepoint. This power of retaining caloric or pro-portion between the quantity of heat receivedand the confequent rife of temperature, wasfirft termed by Dr. Black, Capacity for Heat tan expreflion which is fufficiently intelligiblethough not perfe&ly accurate. It has beenadopted by Dr. Irvine and Dr. Crawford, 1 whowere among the firft to elucidate this moft im-portant fubject, and to bring to regular demon-ftration what was only fuggefted by Black. Thusin the inftance above mentioned, water is faidto have twenty-eight times the capacity forcaloric that mercury has, becaufe it will hold,or requires, twenty-eight times as much heat,to produce an equal change of temperature.The term Specif c Caloric is better devifed toexprefs the fame thing, that is to fay, the pro-portional quantities of caloric requifite to raifeequal weights of matter the feme number ofdegrees of thermometrical temperature. Thisis exactly the fame as the refpective capacities
25 1