Preface to the New Edition ix 



bilities, viscosities of solution, and mechanical properties of con- 

 tinuous solid forms prepared from solutions. 



In accordance with this general and, at the same time, 

 limited plan of the original, we have produced volumes of 

 1 Researches ' intended as supplements, in which the growth 

 of the subject-matter is recorded in the form of abstracts of 

 original memoirs. To these we have added critical notes 

 intended as adumbrations of extensions of general theory, 

 towards which all workers may be presumed to be striving, 

 whether of set purpose or less consciously. 



In the twenty years' period under consideration a con- 

 spicuous advance has followed the systematic investigation of 

 typical colloids, towards a general theory of the colloidal state. 



Cellulose 'is the prototype of colloidal matter, and the 

 exhaustive study of celluloses and derivatives in their infinitely 

 varied forms, natural and artificial, promises to be the most 

 important source of material for generalisations as to the 

 condition of matter in colloids. At present there are none 

 which command acceptance, and it is outside the scope of a 

 text-book to discuss hypotheses and tentative theory. 



It is particularly in view of the somewhat nebulous aspect 

 of this region of potentially exact science that we abstain from 

 any present attempt to recast our original volume. 



It will be implied from this confession that we have little 

 to note of really novel and fundamental importance that is, as 

 contributing to a positive solution of problems of constitution 

 or of the more immediate problem of the reacting unit of 

 the typical cellulose. But there have been notable additions 

 of experimental method, of new groups of derivatives, and 

 evident progress in the critical appreciation of the subject. 



' Normal Cellulose.' Many bleached cottons, even those 

 produced by carefully regulated ' standard ' processes, are 



A 2 



