OXIDA TIONS IN THE PRESENCE OF MOISTURE. 101 



ence of moisture. The rusting of iron, for example, is 

 an oxidation or burning of the metal, and takes place 

 faster in damp air than in dry; during the slow rusting in 

 moisture just as much heat is set free as if the same com- 

 pound of iron and oxygen were prepared in a more rapid 

 way. Such experiments throw great light on the oxida- 

 tions which take place in our own bodies. All of them 

 are slow oxidations, which never at any one moment give 

 off a great amount of heat, and all occur in the damp 

 tissues. 



Summary. (1) Energy can be turned from one form in- 

 to another ; as from heat into mechanical work by a steam- 

 engine. (2) Our bodies are constantly losing energy, partly 

 in muscular work, and partly as heat lost to surrounding 

 objects. (3) Energy cannot be created ; all that can be 

 done is to turn one kind of it into another kind: heat can 

 be turned into mechanical work (as in a locomotive) ; or 

 mechanical work into heat (as by friction) ; or heat into 

 electricity (as in a thermo-electric machine) ; and so forth. 

 (4) Since our bodies spend energy all our life long they 

 must be supplied with it from outside : they can turn into 

 other forms the energy which they receive, but they cannot 

 make it from nothing. (5) The chief forms of energy which 

 our bodies expend are muscular (i. e. mechanical) work, 

 and heat. (6) In ordinary machines, as a locomotive, the 



Give an instance. Does the rate of oxidation or the presence 

 of moisture affect the amount of heat liberated ? 



Of what kind are the oxidations which occur in our bodies ? 



Give a summary of the contents of this chapter with reference to 

 the following points: (1) The transformation of energy; (2) The loss 

 of energy from the body ; (3) The fact that man cannot create ener- 

 gy but can transmute it ; (4) The fact that our bodies must be con- 

 stantly supplied with energy from outside ; (5) The chief forms of 

 energy spent by the body ; (6) The. source of the energy spent by a 

 working steam-eugiue. 



