OSMOTIC PRESSURE 339 



medium." These results are obviously in complete agreement 

 with results obtained by Robertson and Burnett, employing the 

 cryoscopic method, which are commented on above. The decrease 

 in pressure observed in very dilute acid may be attributable to the 

 neutralization by the acid of base bound by the protein prepara- 

 tion employed. Lillie draws an analogy between his results and 

 those obtained by Ostwald (78) (79) in investigating the swelling 

 of gelatin plates in dilute acid and bases. Egg-albumin, how- 

 ever, exhibits the opposite behavior, namely, the osmotic pressure 

 which it exerts is slightly diminished by acids and bases. 



The osmotic pressure of gelatin and egg-albumin is unaffected 

 by the addition of non-electrolytes such as cane-sugar, dextrose, 

 glycerol and urea, but is considerably affected by the addition of 

 inorganic salts being (and this is true both for gelatin and egg- 

 albumin) depressed thereby. According to Lillie the depression 

 of the osmotic pressure exerted by this protein is a function of the 

 nature of both the anion and cation of the added salt. It increases 

 in the order alkali metals < alkaline earths < heavy metals (for 

 cations) ; and CNS < I < Br < NO3 < CI < F < plurivalent 

 anions, SO4, tartrate, citrate, phosphate (for anions). This 

 observation is of extraordinary significance when we recollect that 

 this is the order in which, according to Hofmeister and Pauli, the 

 various ions bring about the dehydration and coagulation of the 

 salts which proteins form with bases (Cf. Chap. VI).* 



Very remarkable phenomena are displayed by the solutions of 

 soluble chitin which have been prepared by Alsberg and Hedblom 

 (1) from the chitin of Limulus polyphemus by prolonged treatment 

 with weak hydrochloric acid. The chitin when subjected to this 

 treatment forms at first a gelatinous mass and later a colloidal 

 solution. The analytical figures obtained for this "soluble 

 chitin" and the gelatinized chitin obtained by adding KOH and 

 then reneutralizing with HCl are best explained, according to the 

 authors, by assuming that the chitin, on passing into colloidal 

 solution, unites with water. Soluble chitin depresses the freezing 

 point but slightly, so that its molecular weight is probably very 

 high. It passes through collodion and parchment paper, but has 

 the extraordinary property of carrying the water in which it is 



* Moore and Roaf (72) have sought to explain the coagulation of proteins 

 by salts by the formation of large aggregates, basing their argument upon data 

 similar to these obtained by LiUie. 



