46 Mr. W. E. Bousfield and Dr. T. M. Lowry. [June 19, 



and the conductivity between the two layers of mercury was deter- 

 mined by a potentiometer method ; the conductivities are expressed in 

 arbitrary units. Above 200° the curvature is very slight and the curve 

 is similar to that of an aqueous electrolyte above 0°. Extrapolation 

 from this part of the curve would indicate the existence of a " conduc- 

 tivity zero" at about 185° C, but as this temperature is approached 

 the decrease of conductivity becomes much less rapid, the " critical 

 temperature " is passed without any abrupt change in the curve, and 

 even below 100° the conductivity is still measurable. 



Further evidence of a similar character is supplied by the tempera- 

 ture-viscosity curves. The formula given by Kohlrausch leads to a 

 limit of fluidity at - 38 c, 5, but no statement is made as to the experi- 

 mental data on which it is based. Thorpe and Rodger* give two 

 formulae for the viscosity of water. The first, 



-q = 5-9849(43-252 + /)- 15 ^ 3 , 



expresses the experimental data from 3 to 100 3 , and would lead to a 

 limit of fluidity at -43' -2, a temperature within 5° of Kohlrausch's 

 critical temperature. But the second formula, 



-q = 58-7375(58-112 + 0~ r9W4 , 



which expresses with accuracy the viscosity of water between 0° and 

 8 C , would lead to a limit of fluidity at - 58 3- l, that is, 20° below 

 Kohlrausch's " critical temperature."! In this case, therefore, a change 

 in the law governing the relationship between viscosity and tempe- 

 rature is already noticeable above the freezing point of water, and is 

 of such a character as to lead to a " fluidity zero " considerably 

 below the " conductivity zero " deduced from measurements between 

 2 = and 34° C. 



"We conclude therefore that, whilst the conductivity zero at - 39° C. 

 is an important physical constant of water, it is a measure of the 

 properties of water between 2° and 34° only (the temperature limits 

 of Deguisne's conductivity measurements), and not an actual critical 

 temperature comparable with the freezing point. In accordance with 

 this view we have, in summarising the influence of temperature on 

 conductivity (fig. 3), represented the conductivity as persisting at a 

 temperature T x considerably below the conductivity zero at T 2 . 



To express the relationship between conductivity and temperature, 

 Deguisne and Kohlrausch employ the formula 



* ' Phil. Trans.,' A, 1894, vol. 1S5, pp. 397—710. 



f A still more striking illustration of the influence of the experimental tempera- 

 tures on the fluidity-limit is afforded by the case of active amyl alcohol (Thorpe 

 and Rodger, loc. cit., p. 542). The viscosity of this is represented by three 

 different formulae, which hold good from : to 35 : , 35 ; — 73°, and 73° — 124°, and 

 would lead to zero values for the fluidity at —101°, —65°, and —8° respectively. 



