ENERGETICS 



THE most striking characteristic of living organisms is the perpetual state of 

 change which they show, as will have been clear from the previous chapter. It 

 is a matter of general experience that, in order to effect changes, work must be 

 done. This capacity of doing work is due to the possession of something which 

 is called energy, and is frequently defined in these very words. 



LAWS OF ENERGETICS 



There are two great laws dealing with changes of energy, known as the first 

 and second laws of Thermodynamics or Energetics. The reason of the name 

 thermodynamics, used in this connection, is that the laws were first arrived at, 

 in the main, from considerations of heat energy. The first law tells us that, 

 while energy may be of many kinds, kinetic, thermal, chemical, electrical, and so 

 on, which can be converted into one another, there is never any gain or loss. 

 This fact, derived from universal experience, is known as the " conservation of 

 energy." 



It may be noted here that the observation that energy of motion can be transformed into 

 heat suggested the thought that the latter is itself a form of movement, and ultimately that 

 the other forms of energy which can be derived from heat are also kinetic in nature, not 

 excepting chemical energy itself. 



The second law is somewhat more abstruse, and deals with the " quantitative 

 relations which restrict the convertibility of energy,' 1 as Nernst puts it (1911, 

 p. 16). Thus, "while external work and the kinetic energy of moving bodies 

 can be transformed into one another completely and in many ways, and can 

 also be converted into heat, as by applying brakes to a railway train in motion, 

 the reverse change of heat into work is only possible under certain conditions." 

 This is the principle of Carnot and Clausius in one of its forms. 



For example, in the case of a steam engine, the part of the energy given out by the fuel 

 which is available for work is given by the ratio of the difference of temperature between the 

 boiler and condenser to the absolute temperature of the latter ; this means, of course, that only 

 a certain part of the heat energy given out by the burning coal can be utilised even in 

 the most perfect steam engine. 



FREE ENERGY 



The fact just referred to led to the important distinction made by Helmholtz 

 (1882, p. 33) between "free" and "bound" energy. It is plain that, of the 

 energy contained in a system, only that part which can do work is of value. 



As an illustration, imagine a system of two similar copper balls, isolated completely from the 

 surroundings, one of which is initially at a higher temperature than the other. The system 

 as a whole contains a definite quantity of heat energy, given by temperatures and thermal 

 capacities of the constituents of the total mass. If left to itself, a part of this energy will pass 

 from the warmer to the cooler body, until both are at the same temperature. During this 

 process a certain fraction of the energy transferred may be used to perform work. When the 

 two balls have arrived at the same temperature, although no loss of energy has occurred, no 

 more work can be got out of the system in itself, but only when brought into relation with 

 another system at a lower temperature. In this state, so far as the system itself is concerned, 

 its energy content is not free, but bound and useless. 



A further important fact, also arising from experience, is that free energy 

 always decreases, if it possibly can, but never increases. In the above illustra- 



