PRINCIPLES OF THE MECHANICAL THEORY OF HEAT. 259 



In a second experiment tlie external work done amounted in an hour to 

 20750 metre-kilograms, while 112.2 grams of oxygen were consmned, and 255.6 

 units of heat produced. These 112.2 grams of oxygen would, in a state of 

 rest, have atlorded 5S5.7 units of heat; thus 585.7 — 255.6 = 330.1, and, conse- 

 quently, 330.1 units of heat more than the experiment shows. 'J'hese 330.1 units 

 of heat have been hence expended in mechanical work; but the cpiantities of heat 

 consumed in both experiments for mechanical work, 436.68 and 330.1 stand, in 

 fact, in relation to the external work done ; for, from the proportion 



330.1 : 436.68=20750 : x 

 results .T=27450, which coincides (piite nearly with the observed number 27448. 



A strong horse, when he remains standing at rest in a stal)le, is amply nourished 

 with 7.5 kilograms of hay, and 2.5 kilograms of oats, which, together, contain 

 4 kilograms of carbon. But as soon as tlie horse is put to work this aniovmt of 

 nourishment does not suffice; it is necessary, if he is to be kept in good condition, 

 to add 5.i> kilograms of oats, which contain 2.2 kilograms of carbon. On a day 

 of work, therefore, 6.2 kilograms of carbon are supplied to this animal's body. 



As the power of one horse executes, in a second, a work of 75 inetre-kilograms, 

 the work done in 8 hours equals 75 • 60 • 60 • 8, or 2,160,000 metre-kilograms, 

 According to the experiments (tf Favre and Silbermann, by the oxidation of one 

 kilogram of carbon 8080 units of heat are developed, which corresponds to a 

 mecluinical work of 8080 • 424, or 3,425,920 metre-kilograms. Hence the day's 

 work jierformed by a horse, 2,100,000 metre-kilograms, corresponds to a consump- 

 tion of 



2160000 nroi-1 f 1 



= 0.03 kuoOTam of carbon. 



3425920 ^ 



Of the nutriment, therefore, supplied to the horse's body for a day's work, namely, 

 6.2 kilograms of carbon, only 0.63, l)eing about Jg-, is expended for the perform- 

 ance of mechanical labor, the rest being partly used for the sustentation of animal 

 life, for the production of heat, and in part passing unoxidized through the body. 

 According to Bonssingault only 65 per cent, of the carbon introduced into the 

 body is oxidized, while 35 per cent, is given off unconsumed. Of the four 

 pounds of carbon, therefore, which the horse at rest takes for his daily nourish- 

 ment, only 2.6 pounds, and of the additional 2.2 kilograms of carbon alhitted for 

 days of labor only 1.4 kilogram arrive at oxidation in the body of the animal. 

 Hence in a day of rest there are produced in the horse's body 8080 • 2.6 = 21008 

 units of heat. C)f the 1.4 kilogram of carbon, further oxidized on days of labor, 

 0.63 are consumed in mechanical work, while the remaining 0.77 kilogram 

 (1.4 — 0.63) go to sujiply the increase<l heat production of 8080-0.77 = 6221 units. 

 Thus on a day of work the heat developed in the horse's body ascends to 27229 

 units, while only 8080 • 0.63 = 5090 units of heat are converted into work. 



VI. ELEMENTS OF THE MECHAXICAL THEORY OF HEAT. 



If we conceive heat to be a molecular movement, the temperature of a body 

 is to be taken as proportional to the vis-viva inherent in the material atoms 

 which move in some way, perhaps viliratc around their position of eipiilibrium. 

 An increase of temperature consists, therefore, in an augmentation of this vis-viva, 

 and hence in an enhanced velocity of tlie molecular movement. 



Not all the heat, however, added to a body contributes to tlie raising of its 

 temperature; and hence not all the heat added to it is employed in the augmenta- 

 tion of the active vis-viva of its molecular vibrations, for a ])art of the heat may, 

 under conditions, be consumed in order to overcome the molecular forces which 

 exert an action between the several atoms of the body and present an imjiedi- 

 nient to their free movement. This last heat, which Clausius denotes as that 

 consumed in internal work, is usually called latent heat. 



