132 SCIENCE PROGRESS 



phase and dispersion medium ; only a small quantity of electrolyte is required for 

 coagulating, and this coagulation, as a rule, is irreversible. Emulsoids, on the 

 other hand, have great internal friction and the property of foam formation ; 

 considerable quantities of electrolytes are required for coagulation, which, as a 

 rule, is reversible. 



The new method in colloid chemistry which is indicated by Sorensen's 

 researches is the close study of a single substance from colloid-chemical, physical- 

 chemical, and also from purely chemical standpoint. Although Sorensen's work 

 in some respects is a continuation of Pauli's, and often runs parallel with some 

 of his researches on proteins, he has obtained his important results by confining 

 himself to the detailed study of one substance, namely, egg-albumen, while Pauli 

 worked with a large number of substances. 



Sorensen expresses his disagreement with Wo. Ostwald, who, in the second 

 edition of Grundriss der Kolloidchemie, issues a warning against drawing parallels 

 between the conditions in true and in colloidal solutions. It is absolutely essential 

 for the understanding of the character of emulsoid systems to compare the pro- 

 perties of true and colloidal solutions, and Sorensen emphasises that the study of 

 true solutions may benefit from investigations on a well-defined protein solution, 

 because methods may be used in the latter case, e.g. the employment of semi- 

 permeable membranes, which can only be used in exceptional cases in investiga- 

 tions on true solutions. The proof of the applicability of Gibbs' phase-rule to the 

 equilibrium condition between crystalline egg-albumen and its mother liquid, and 

 the elaboration of Donnan's formulas in respect to the osmotic pressure of egg- 

 albumen solutions containing salt, more than justifies the claim made by Sorensen. 



In this review it is impossible to go into all the details of the research dealt 

 with in Sorensen's work. His book is divided into five chapters. Chapter I. 

 describes the methods for preparing the material and tests for its purity. 

 Chapter II. deals with acid and base binding power of egg-albumen, particularly 

 the binding power with regard to sulphuric acid at various ammonium-sulphate 

 concentrations. Chapter III. deals with the crystallising out of egg-albumen by 

 addition of ammonium sulphate. Chapter IV. treats of the equilibrium condition 

 between the crystallised egg-albumen and the surrounding mother liquid. 

 Chapter V. discusses the question of the osmotic pressure of egg-albumen 

 solutions, and its relation to the composition of the solution. 



The success of Sorensen's researches is due in the first instance to his using a 

 well-defined material, which allows the reproduction of the same conditions in all 

 series of experiments. Lack of realisation of this important point has been the 

 cause of many uncertain and contradictory results obtained in earlier investiga- 

 tions. The egg-albumen which has been used in many researches has not been 

 purified to any great extent, and consequently the results obtained are of little 

 value. Even if the egg-albumen has been purified by recrystallisation and sub- 

 sequent dialysis the material is still undefined, because the dialysis is never 

 complete, and the quantity of electrolytes which remain behind to a great extent 

 determines the properties of the egg-albumen, and their amount must therefore be 

 determined quantitatively. 



The method used for crystallisation is essentially the same as that used by 

 F. G. Hopkins and S. N. Pinkus (Journ. of Physiol, vol. 23, p. 130, 1898). By 

 crystallisation and washing are removed in the first case ash compounds and 

 "mucoids" (nitrogen substances which are not coagulable) and "conalbumen" 

 (coagulable but non-crystallisable nitrogen-containing substances). The trace of 

 ash which pure egg-albumen leaves on incineration is not due to impurities but to 



