PROTEINS 145 



what smaller than those of hemoglobin. Unlike ferments, proteins 

 are not strongly adsorbed by filter material. 



All albumins are amphoteric electrolytes, i.e., they yield H and OH 

 ions; otherwise expressed, they have at the same time the character 

 of weak acids and of weak bases, with the acid character more or less 

 in excess. The consequences resulting in the case of albumin have 

 been discussed more extensively on p. 154. 



The isoelectric point is that where the sum of the H and OH ions 

 is least. This point acquired especial significance from the studies 

 of L. MICHAELIS who showed that the isoelectric point was charac- 

 teristic for each albumin. That albumins are most easily precipitated 

 at this point was also demonstrated [by HARDY. Tr. 1 . In this respect 

 they behave like crystalloid electrolytes. Neutral molecules are 

 much more difficult to dissolve than their ions. Acids slightly dis- 

 sociated electrically, e.g., uric acid, salicylic acid, quinine, are much 

 more difficult to dissolve than their strongly dissociated salts. 



Adsorption phenomena are of great importance. Proteins may be 

 strongly adsorbed or, on the other hand, exert a powerful adsorption. 

 The purely physical phenomena are complicated by the intermingling 

 of specific chemical properties and thus very decided differences be- 

 tween the various groups of albumins are brought to light. 



Proteins as Adsorbed Substances. Adsorption has been most 

 carefully studied in the case of albumin. As a result of its faint 

 acidity it is completely adsorbed by ferric oxid hydrogel, but mastic 

 and kaolin suspensions on the contrary adsorb it only in faintly 

 acid solution (L. MICHAELIS and P. RONA*). On this account, any 

 suspension may be employed to remove albumin from acid solutions, 

 e.g., urine, whereas an electropositive adsorbent (e.g., ferric oxid gel) 

 must be chosen in the case of neutral fluids. Although the distri- 

 bution between solvent and adsorbent has the shape of an adsorp- 

 tion curve, it must nevertheless be emphasized that the process 

 (adsorption by iron-oxid, cellulose and kaolin) is only incompletely 

 reversible, thus resembling the phenomena of dyeing (W. Bii/rz* 4 ). 

 The adsorption of euglobulin by kaolin (K. LANDSTEINER and 

 UHLIRZ*) is to be explained in a similar way. 



Proteins as Adsorbents. Proteins are frequently used as adsorb- 

 ent both in a solid and in a denatured condition. They take up 

 acids, alkalis, salts, dyes, etc., from solution, in accordance with the 

 formula of an adsorption curve. In my opinion it is best to regard 

 the compound as an adsorption whenever the chemical constitution of 

 the adsorbed substance is unknown or when it, itself, possesses col- 

 loid properties. To view the facts from the standpoint of chemical 

 constitution (see p. 154), a viewpoint which presupposes a more 



