264 THE FITNESS OF THE ENVIRONMENT 



being what they are, it is impossible to im- 

 agine the presence of vast amounts of am- 

 monia in an atmosphere, while the loss of 

 the greater part of the energy which can be 

 stored by tearing apart hydrogen and oxygen 

 would be a very serious difficulty ; but the 

 loss of substantially all the incomparable 

 chemical activity of oxygen is to all appear- 

 ances an insurmountable obstacle to the sub- 

 stitution of ammonia for water in biological 

 processes. 



From time to time, loose discussion has 

 arisen among chemists as to the possibility 

 of substituting another element for carbon in 

 the organic cycle. Such speculations have 

 never been serious, but they have at least 



all those properties which give to water its unique position 

 among solvents, such as its abnormally high boiling point, 

 its high specific heat, its high heat of volatilization, its high 

 critical temperature and pressure, its high association con- 

 stant,- its high dielectric constant, and its low boiling-point 

 elevation constant, its power as an electrolytic solvent, and 

 the facility with which it forms compounds with salts, liquid 

 ammonia shows a remarkable similarity to water." 



" While the boiling point of liquid ammonia is 33.46° below 

 zero, it still appears abnormally high when compared with 

 the boiling temperatures of phosphine, arsine, stibine, me- 

 thane, ethylene, hydrogen sulphide, hydrochloric acid, etc. 

 The specific heat of liquid ammonia and the heat of fusion 

 of the solid are greater than the corresponding constants 

 for water or any other known substance, while its heat of 

 volatilization, with the one exception of water, is the highest 



