66 ORGANIC FUNCTIONING 



(a) Thus a falling weight is made to rotate paddle-wheels in 

 a calorimeter (see Section 38). In falling the potential energy 

 of the weight transforms into the kinetic energy of the rotating 

 paddle-w^heel and this latter energy transforms, by friction, into 

 heat so that the water of the calorimeter rises in temperature. 

 We cannot trace any other change than this and we say that all 

 the available energy of the falling weight transforms into heat 

 energy. This is the first law of thermo-dynamics, or the law of 

 conservation. When a weight of i kilogram falls freely through 

 a distance of 424 metres its loss of potential energy is equivalent 

 to the quantity of energy that is necessary in order that the 

 temperature of i kilogram of water may be raised by 1° C. But 

 suppose that in falling some of the potential energy of the weight 

 transforms into some other energy-form unrecognized by us 

 but w^hich may be detected in the future : in that case we should 

 simply alter the measure of equivalence and the law of conserva- 

 tion will still hold good. 



(b) In analogous ways other quantities of energy — chemical, 

 electrical, etc., can be made to transform wholly into heat. If 

 M units of mechanical energy, C units of chemical energy, E units 

 of electric energy all transform wholly into O units of heat 

 energy then M, C, and E are equivalent. 



(c) But suppose that M units of mechanical energy are made 

 to transform as completely as possible into electric energy : then 

 we shall not observe the above equivalence, that is, we shall not 

 observe E units of electricity come out of the transformation. 

 If the mechanical energy is made to rotate a dynamo the latter 

 may deliver only (say) 90 per cent, of the E units that we expect 

 from the equation M = E. The remainder can be (partially) 

 traced as heat energy which is due to the friction, etc., of the 

 imperfect mechanism of transformation. 



(d) If we have C units of chemical energy in the form of coal 

 which can unite with the oxygen of the air and burn we can 

 cause all this chemical energy to transform into heat = Q. Now 

 from (h) above this heat, O is equivalent to M units of mechanical 

 energy, but no mechanism enables us to effect this transformation. 

 If we burn the coal in the furnace of a steam boiler and couple 

 this to an engine we do obtain mechanical energy from heat, but 

 we may obtain only about 10 per cent, of M. All the rest of the 

 chemical energy of the coal transforms into heat. 



