1038 Dynamic Theory. 



closer to each other, and thus within reach of each other's attractive 

 influence. Thus hydrogen and oxygen may be mingled together with- 

 out being chemically combined, but if platinum be then introduced 

 they combine in the formation of water. Now if the molecules of the 

 gases are held apart by their activity, or the force of their velocities, it 

 must be that the platinum in some way reduces this activity. A ready 

 explanation is that the fundamental pitch of the ether of the platinum 

 is such as to interfere with the vibrations of that of the gases, b} T 

 which they are checked, and the molecules thus allowed to fall closer 

 together. After thus getting within reach of each other's attraction, 

 they fall the rest of the way and the energy of their vibrations is 

 turned into heat, a large quantity of which is evolved when water is 

 formed. 



There are some reactions in which a third party is employed, in which 

 it is shown to have taken an active part, and yet come out just as it 

 went in, without having, on the whole, either gained or lost. The 

 third body in such cases is called a carrier. It was pointed out on page 

 178 that the red blood corpuscles are carriers of oxygen from the lungs 

 to the interior tissues of the body. There are numerous other carriers 

 of oxygen; nitric oxide NO is a carrier in supplying oxygen to the sul- 

 phurous oxide S0 2 in the manufacture of sulphuric oxide S0 3 . The 

 NO takes oxygen from the air, becoming nitric peroxide N0 2 ; then it 

 is exposed to the action of S0 2 , which gets away the acquired oxygen, 

 reducing N0 3 back to NO, and becoming itself S0 3 . The addition of 

 water H 2 to this makes H 2 S0 4 , sulphuric acid. Sulphates and other 

 compounds of iron, copper, manganese, and other metals likewise take 

 up oxygen from the air but give it up to solutions of sulphurous oxide, 

 and may be made to repeat the operation indefinitely. There are bodies 

 too that carry chlorine in the same way, by taking it from one and giv- 

 ing it to another. The probable action of the carrier in such cases is 

 much the same as in catalysis. The carrier first reduces the velocities 

 of the body to be carried, which reduction brings it within reach of the 

 attraction of the third body. Thus sulphurous oxide is unable to take 

 free oxygen from the air, but can take it after nitric oxide has taken it 

 and altered its rate. 



Chemical action is accompanied by either a development or disap- 

 pearance of heat; and in many cases a change in temperature enables 

 a combination to take place which would not be possible otherwise. 

 Some examples are given in chapter 37. As in gravitation the produc- 

 tion of heat results from the collision of bodies, so without doubt the 

 falling together of molecules in chemical combinations is one cause of 

 heat. But this heat is also mixed up with heat from another source; 

 namely, that resulting from the reduction of the velocities of the mole- 



