58 
Proceedings of Royal Society of Edinburgh. [sess. 
larger decrease in the last case than that actually found if there 
had been any acidic character at all about urea. Further, the 
form of the curve obtained here (figure 4) resembles very closely 
that obtained for the case of urea and potassium chloride. We 
conclude, then, that there is no measurable acid function in the 
amides. As the basic character is itself only a slight one, 
we should expect that aqueous urea solutions would conduct 
the electric current feebly. The ions here in the case of 
urea are CO(NH 2 ) 2 H' and - OH', and the dissociation constant 
K = — has been calculated from the amount 
of salt formation between urea and hydrochloric acid* to be 
1 *5 x 1 0~ 14 (25° C.). The value of the dissociation constant for water 
is *8 x 10 -14 . Such water has a specific conductivity of *05 x 10 -6 , 
but it is impossible, under ordinary conditions, to prepare water any- 
thing like this. With water purified by ordinary methods we should 
be able to prepare a solution of urea having almost identically the 
same conductivity as the water used. Using water of spec. 
conductivity 1*5 x 10 -6 , 1 have prepared urea solutions Q? j having 
a conductivity indistinguishable from that of the water. The purest 
specimen of urea obtained by recrystallisation from alcohol gave 
a molecular solution (60 grams per litre) of spec, conductivity 
2’8x 10 -6 . There is little doubt that this small amount of con- 
ductivity, in excess of that of the pure water, is due to impurity in 
the urea, but the determination is of interest in so far as it shows 
how pure such substances may be obtained by the ordinary process 
of recrystallisation. In preparing other amides in a pure state I 
have found the determination of electrical conductivity a very 
useful means of following the purification. 
The Viscosity of some of the above-mentioned Solutions. 
I next give some measurements of the viscosity of solutions 
containing (a) potassium chloride and urea, (b) hydrochloric acid 
and urea ; and in making these determinations I have had the 
valuable assistance of Mr Clerk Ranken, B.Sc., to whom I wish 
* Wood, Journ. Chem. Soc., 83, 484 (1903). 
