METHODS OF COLLOID RESEARCH 



99 



PRIBRAM and KIRSCHBAUM is the application of compressed air for 

 stirring; the gas which supplies the pressure enters the bottom of the 

 vessel through a perforated spiral and thus agitates the fluid. I 

 have had no occasion to determine whether this has any advantages 

 over the mechanical stirrer. 



The Gauging of Ultrafilters. It is important in many cases to 

 have a measure for the limits of effectiveness of ultrafilters, as in 

 this way we may obtain information concerning the size of the par- 

 ticles of the colloid under investigation. The following methods 

 given by BECHHOLD are suitable for the purpose: 



1. Hemoglobin Method: A 1 per cent solution of hemoglobin 

 (hemoglobin scales, Merck) is prepared and the filter is tested to 

 see if it permits the hemoglobin to pass through. If the hemoglobin 

 is retained, the filter is impermeable to most inorganic colloids 

 (with the exception of freshly prepared silicic acid). The degree of 

 permeability of the filter for hemoglobin may be recognized by the 

 intensity of the red color in the filtrate. 



H. BECHHOLD has prepared the following table of permeability 

 for ultrafilters, which is arranged in the order of the diminishing 

 size of the particles of the colloids in solution, and was obtained by 

 using ultrafilters having different degrees of porosity. 



Suspensions. 



Prussian blue. 



Platinum-sol, BREDIG. 



Ferric oxid hydrosol. 



Casein, in milk. 



Arsenic sulphid hydrosol. 



Gold solution, ZSIGMONDY, 



No. 4, c. 40 IJLIJL. 

 Bismon, colloidal bismuth oxid, 



PAAL. 



Lysargin, colloidal silver, PAAL. 

 Collargol, silver, v. HEYDEN, 



20 MM- 

 Gold, solution, ZSIGMONDY, 



No. 0, c. 1-4 ju/z. 

 1 per cent gelatin solution. 



1 per cent hemoglobin solution, 

 molecular weight c. 16,000. 



Serum, albumin, molecular 

 weight 5000 to 15,000. 



Diphtheria toxin. 



Protalbumoses. 



Colloidal silicic acid. 



Lysalbinic acid. 



Deutero albumoses A. 



Deutero albumoses B, mol. wt. 

 c. 2400. 



Deutero albumoses C. 



Litmus. 



Dextrin, mol. wt. c. 965. 



Crystalloids. 



2. Air Transpiration Method. 1 This method affords approxi- 

 mately absolute values for the largest pores of an ultrafilter. It is 

 based on the following principle. In order to force air through a 



1 Before actually undertaking methods 2 and 3 the original paper should be 

 consulted (Bechhold* 6 ), as the details cannot be abstracted. 



