PREFACE 



THE Proteins, with which, as its title indicates, this work has 

 most particularly to deal, have, ever since the publication of the 

 classic researches of Graham, been generally recognized as typical 

 examples of that class of substances which Graham designated 

 "Colloids." This work, therefore, although primarily concerned 

 with the physical chemistry of a limited section of the class, may 

 also, in some measure, be regarded as contributing to an analysis 

 of the properties and behavior of colloids in general, in so far as 

 these permit of illustration by the properties and behavior of 

 the various members of the protein group. 



The leading problems in every field of chemical investigation are, 

 to a large extent, determined by the salient properties of the sub- 

 stances which form the subject of inquiry, and for this reason a 

 thorough acquaintance with what may be termed the " descriptive 

 chemistry" of any group of substances is prerequisite to a suc- 

 cessful attempt to interpret their behavior. If we were to en- 

 deavor to interpret the behavior of the proteins solely in the light 

 of preconceptions derived from the study of the chemistry of the 

 metals, for example, or the simpler organic compounds, we would 

 find that the behavior of the proteins displays merely a bewilder- 

 ing variety of inconsistencies. Their "amphoteric" character, 

 their multiple basicity and acidity, their instability in aqueous solu- 

 tion and, above all, the enormous mass and catenary configuration 

 of their molecules, confer upon them properties which are com- 

 paratively unfamiliar in other fields of chemistry or else exaggerate 

 properties which are normally displayed by the simpler chemical 

 bodies only to a comparatively negligible degree. 



The proteins in this respect are not exceptional. Thus the mode 

 of investigation and the interpretation of the behavior of the 

 various lipoids must primarily be conditioned by their very general 

 insolubility in water and instability in the presence of oxygen. 

 The behavior of the complex polysaccharides is conditioned by 

 their relative stability and by the extraordinary tendency to op- 



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