32 SCIENCE PROGRESS 



ions are formed, a suggestion which in itself is by no means 

 improbable ; but, as the authors themselves point out, this is 

 not a complete explanation of the behaviour observed, for on 

 this basis a gradual transition from one curve to the other 

 would be expected. The problem, therefore, of the mechanism 

 of ionisation in this solvent has still to be solved. 



The Polymerisation of Water. — It is now generally recog- 

 nised that water in the liquid state consists of three kinds of 

 molecules, monhydrol (H a O), dihydrol (H a O a ), and trihydrol 

 (H 2 0) 8 , in different proportions in equilibrium with one an- 

 other. The relative amounts of the three kinds vary with 

 the temperature, the monhydrol increasing with rising tem- 

 perature at the expense of the trihydrol. (Ice consists prac- 

 tically entirely of trihydrol ; steam of monhydrol). These 

 conclusions have been reached as a result of the examination 

 of several characteristic properties of water itself and of aqueous 

 solutions and the variation of these properties with tempera- 

 ture. 



The problem has been reinvestigated by T. W. Richards 

 and Palitszch (J. Amer. Chem. Soc. 191 9, 41, 59) from the 

 point of view of the compressibility of aqueous solutions, 

 especially of urethane in water. This substance was chosen 

 because of the fact that it is neither associated nor appreciably 

 dissociated in aqueous solution. It has the property of lower- 

 ing the surface tension of water, a fact of importance in view 

 of the possible interrelation between surface tension and 

 compressibility. The compressibility of the solutions was 

 determined as a function of the concentration, measurements 

 of density, viscosity, and surface tension being carried out 

 at the saeme time. 



Pure water at 20 C. has a compressibility of 43-25 x 10"*. 

 It was found that the compressibility of the solutions at first 

 diminishes, as a result of adding urethane, to a minimum 

 value of about 38-9 x io" 9 , and then rises as the concentration 

 increases. On the other hand, the surface tension and the 

 viscosity show no minimum in their course. There is also no 

 minimum in the curve expressing the solution volume — a 

 quantity which is computed from the difference between the 

 volume of the solution and of the water, reckoned per gram 

 of urethane. 



The first point to be considered is the minimum exhibited 



