326 SCIENCE PROGRESS 



condition has the power of taking up another colloid from its 

 solution with the formation of " adsorption compounds." Biltz 

 replaced the gel which serves to take up the dissolved colloid 

 by animal and vegetable fibres and found that inorganic as well 

 as organic colloids were taken up by the fibres. A coloured 

 colloid was fixed with its characteristic colour. Coloured 

 inorganic substances when converted into the colloidal condition 

 thus acquire the capacity of being "adsorbed." Experiments 

 were made with colloidal solutions of selenium, tellurium, gold, 

 vanadium pentoxide, molybdenum-blue, tungsten-blue, cadmium 

 sulphide, arsenious sulphide, antimony disulphide (SbS 2 ), copper 

 ferrocyanide, mercury, stannous sulphide, cupric hydroxide, and 

 molybdenum tungsten purple. In the case of selenium, tellurium, 

 and gold the fibre is dyed and the solution is more or less com- 

 pletely exhausted. In the other cases also the fibre is dyed, but 

 the colour is not extracted from the solution to so great an 

 extent. A colloidal solution of gold prepared by Zsigmondy's 

 method will not dye silk; a constituent of the latter (called by 

 Biltz a " protective colloid ") passes into solution and prevents 

 the gold from being deposited. The colloidal gold solution after 

 being boiled with silk can no longer be precipitated by electro- 

 lytes. In several cases, too, the dyeing of the fibre by inorganic 

 colloids was found to be favoured by the addition of salt just as 

 ordinary dyeing is. There is no essential difference between 

 the dyeing properties of coloured inorganic colloidal substances 

 and organic dyestuffs, the partition law holding good in both 

 cases. In further experiments the hydrogel of alumina was 

 used in place of the organic fibre, and here again it was found 

 that the substitution of the inorganic colloid for the organic 

 fibre had no effect on the quantitative relations observed in the 

 dyeing process. Again, solutions of such dyestuffs as the 

 Immedial sulphur dyestuffs in alkaline sulphides were submitted 

 to dialysis, clear colloidal solutions being thus obtained free 

 from alkali, and it was found that these were coagulated by 

 electrolytes in a similar manner to other colloidal solutions, e.g. 

 the coagulating power of the electrolytes on the dyestuff solutions 

 increased with the valency of the cation ; and the process was in 

 every way identical with the coagulation of ordinary colloids. 



Finally Biltz turned his attention to another disputed point 

 and tried to show whether the " lakes" which adjective organic 

 dyestuffs form with metallic oxides (mordants) are chemical 



