LUEDEKING THE HYDRATION OF COLLOIDS. 



379 



with lop. ct. ZnSo ^ -\- yH .jO , there were mixed 3co g. of gelatine 

 with i6o g. of water and 40 g. of ZnSo4 + 7H20 added when 

 the solution had taken place. Finally, the entire mass was made 

 to weigh 400 g. by adding water. 



The galvanic conductivity of each of the six solutions was com- 

 pared with that of an aqueous solution of the same concentration, 

 which was maintained at a constant temperature. The measure- 

 ments were made between about 5° and 90° C. A Kohlrausch 

 universal rheometer and a Wiedemann galvanometer were used 

 for this purpose. The current was closed only for a very short 

 time and often reversed in direction. The solutions were con- 

 tained in vessels of construction given in figure, which is a slight 



modification of Kohlrausch, and permits of determining the tem- 

 perature of the substance under examination by means of the ther- 

 mometer /. This is very desirable in case of such tenacious 

 liquids as solutions of gelatine are, as the temperature does not 

 become equalized in them by convection currents. The appara- 

 tus was clamped and held in position in the water-bath by the 

 thermomet&r. 



The following tables contain the results obtained. The figures 

 express the relations of the conductivities of the solutions exam- 

 ined to that of an equally concentrated aqueous solution of 20° C. 

 As electrodes, amalgamated zinc plates were used. 



The plates appended to this paper give a graphical representa" 

 tion of the variation of electrical conductivity with temperature. 



2 p. Ct. Zn. Yitriol in (l) Water; (2) in 25 p. ct Gelatin soi.; (3) 50 p. ct. in Gel. Sol. 



