151 



In making the solutions a quantity of zinc chloride was weighed ont and 

 dissolved in such an amount of water as to niake a solution somewhat 

 stronger than 3%. Some precipitate was formed and this was filtered out. 

 the remaining clear solution heing then standardized and diluted to the 

 required strength. Colloidal membranes were prepared by coating vege- 

 table parchment, of as miiform thickness as possible, with collodion. These 

 were fastened on the ends of tubes having a diameter of about five centi- 

 meters, the tubes being of equal cross-section. Of the respective solutions 

 50 CO. were placed in separate tubes and the latter were innnersed in sepa- 

 rate beakers of distilled water, adjustment being made so that the water 

 outside was at the same level as the solutions inside. No attempt was 

 made to keep the temperature constant but changes in temperature affected 

 the tubes alike. After certain periods of time, as stated in the tables 

 below, the beakers containing the water and the diffused zinc salt were 

 removed and substituted by beakers containing fresh water. The zinc 

 which had diffused through the membranes was determined by titration 

 with standard solution of potassium ferrocyanide, uranium nitrate beiu'j; 

 used as indicator. The amount of ^^■ater placed outside the membranes was. 

 in every case, 100 cc. The standard solution of potassium ferrocyanide was 

 of such concentration that 1 cc. was equi^'alent to 0.00455 gram of zinc. 



In order to correct for any pos.sible difference in thickness or perme- 

 ability of the two membranes the solutions were interchanged after 2.'U 

 hours, each solution thereafter diffusing through the membrane that had 

 previously held the other. 



In the tables the symbols have the following significance: 



B. M. = solution of zinc chloride o9r and aluminum sulpli;ite 1.5%, 



B. P. = solution of zinc chloride 39r , 



t = hours for each period <if dilTusion, 



T =: total hours before reversal of membranes. 



Tr — total hours after reversal of membranes, 



m = milligrams zinc chhu-ide diffused each period. I*. M., 



M = total milligrams zinc chloride difl'u.sed, B. M., 



Mr = total milligrams diffused after reversal, B. M., 



p = milligrams zinc chloride, diffused each period, B. I'.. 



P = total milligrams diffused, B. P., 



Pr = total milligrams diffused after reversal, B. P., 



Cm = milligrams zinc cliloiide left in B. M. = 1.500 — M, 



Cp = milligrams zinc chloride left in B. P. = 15011 — P. 



