40 MOLECULAR MOTION AND ITS ENERGY 21 



able again to escape from the liquid. Therefore the higher 

 the temperature the less gas will be absorbed, as observation 

 has taught. 



Molecules of a gas can also be held fast by a solid body 

 just as by a liquid, porous bodies especially being able to 

 condense considerable masses of gas. In other cases the 

 mass condensed increases with the extent of surface of the 

 body, and we must therefore assume that only the surface 

 layers are active in causing condensation by the attractive 

 forces they exert. On this account it has been thought 

 necessary to introduce a new name and designate the 

 phenomenon as Adsorption when the condensation is caused 

 by a solid body. It differs, however, in nothing else from 

 absorption in liquids ; on the contrary, everything that has 

 been stated about absorption can be ascribed to adsorption 

 without further remark. One such fact is that by adsorp- 

 tion also can considerable heat be developed, as, for instance, 

 in Dobereiner's lamp, on the condensation of hydrogen 

 by spongy platinum. 



