282 MR. W. R. BOUSF1ELD AND DR. T. M. LOWRY ON THE ELECTRICAL 



accurate estimate of the limiting value of the solution volume ; the limiting value 

 previously given was 0'145 ('Dictionary of Chemistry,' vol. TV., p. 491). By the 

 same process of extrapolation it can be deduced that the molecular volume does not 

 become constant until a dilution of about 100 litres is reached. The molecular 

 conductivity reaches a maximum value at about 1000 litres, and it is therefore clear 

 that the decrease of molecular volume proceeds side by side with the process of 

 ionisation, and does not cease until the latter is almost complete. 



A study of the influence of temperature on the solution volume of sodium hydroxide 

 gave somewhat remarkable results. Instead of increasing steadily from C. to 

 100 C., as was expected, the solution volume at all percentages was found to reach a 

 maximum value at 60 C. to 70 C., and then to decrease between 70 C. and 100 C. 



There is thus a close resemblance between the solution volume at 90 C. and that 

 at 30 C. The extent of the variation produced by alterations of temperature 

 decreases with increasing concentration, and at 50 per cent. NaOH amounts only to 

 7 per cent. The data for the solution volume are given in Table XI. and are 

 represented graphically in diagrams V. and VI. 



In discussing the significance of the variations of solution volume it may be 

 regarded as certain that the great variation in the case of dilute, as compared with 

 concentrated, solutions must be attributed to the complex character of liquid water 

 and not to any complexity introduced by the addition of soda. It appears, in fact, 

 that the maximum of simplicity is reached in a 50-per cent, solution at 100 C., and 

 that the most complex solution with which we have to deal is water. 



The complex character of the water molecule was demonstrated by RAOULT (' Ann. 

 Chim. Phys.,' 1884, (6), vol. 2, p. 66), and was made use of by RONTGEN (' Wied. 

 Ann.,' 1891, vol. 45, p. 91), who attributed the increase of density between C. 

 and 4 C. to the dissociation of " ice molecules " having a greater molecular volume 

 than the water molecules. This view was elaborated by SUTHERLAND ('Phil. Mag.,' 

 1900, vol. 50, p. 460), who suggested that RONTGEN'S ice molecules had the formula 

 H fl O 3 and might be called trihydrol, whilst the water molecules consisted of dihydrol, 

 H,,O 2 . A further discussion is given by STRADLING ('Jour. Frank. Inst.,' 1901, 

 vol. 152, pp. 257-268) with reference especially to the compressibility of water. It 

 is probable that the simplification in the density-temperature curves of the preceding 

 Part III. of the paper, which results from the addition of soda or from an increase 

 of temperature, is due primarily to the destruction of the ice molecules to which 

 water owes most of its abnormal properties. A similar explanation may be given of 

 the large negative solution volume of sodium hydroxide, which is most pronounced at 

 those low temperatures at which the water contains a large proportion of the bulky 

 ice molecules. This explanation does not, however, in any way account for the fact 

 that the molecular volume of sodium hydroxide decreases from 70 C. to 100 C. The 

 only explanation that we can offer to account for this unexpected behaviour is 

 that over this range of temperature the water contains a large proportion of steam 



